Allometry and size in ontogeny and phylogeny

Scaling at different ontogenetic stages: Gastrointestinal tract contents of a marsupial foregut fermenter, the western grey kangaroo Macropus fuliginosus melanops

Prominent ontogenetic changes of the gastrointestinal tract (GIT) should occur in mammals whose neonatal diet of milk differs from that of adults, and especially in herbivores (as vegetation is particularly distinct from milk), and even more so in foregut fermenters, whose forestomach only becomes functionally relevant with vegetation intake. Due to the protracted lactation in marsupials, ontogenetic differences can be particularly well investigated in this group. Here, we report body mass (BM) scaling relationships of wet GIT content mass in 28 in-pouch young (50 g to 3 kg) and 15 adult (16-70 kg) western grey kangaroos Macropus fuliginosus melanops. Apart from the small intestinal contents, in-pouch young and adults did not differ in the scaling exponents ('slope' in log-log plots) but did differ in the scaling factor ('intercept'), with an implied substantial increase in wet GIT content mass during the out-of-pouch juvenile period. In contrast to forestomach contents, caecum contents were elevated in juveniles still in the pouch, suggestive of fermentative digestion of milk and intestinal secretion residues, particularly in the caecum. The substantial increase in GIT contents (from less than 1 to 10-20% of BM) was associated mainly with the increase in forestomach contents (from 25 to 80% of total GIT contents) and a concomitant decrease in small intestine contents (from 50 to 8%), emphasizing the shifting relevance of auto-enzymatic and allo-enzymatic (microbial) digestion. There was a concomitant increase in the contents-to-tissue ratio of the fermentation chambers (forestomach and caecum), but this ratio generally did not change for the small intestine. Our study not only documents significant ontogenetic changes in digestive morpho-physiology, but also exemplifies the usefulness of intraspecific allometric analyses for quantifying these changes.

Comparative anatomy of the carotid canal in the Miocene small-bodied catarrhine Pliobates cataloniae

The small-bodied Miocene catarrhine Pliobates cataloniae (11.6 Ma, Spain) displays a mosaic of catarrhine symplesiomorphies and hominoid synapomorphies that hinders deciphering its phylogenetic relationships. Based on cladistic analyses, it has been interpreted as a stem hominoid or as a pliopithecoid. Intriguingly, the carotid canal orientation of Pliobates was originally described as hylobatid-like. The variation in carotid canal morphology among anthropoid clades shown in previous studies suggests that this structure might be phylogenetically informative. However, its potential for phylogenetic reconstruction among extinct catarrhines remains largely unexplored. Here we quantify the orientation, proportions, and course of the carotid canal in Pliobates, extant anthropoids and other Miocene catarrhines (Epipliopithecus, Victoriapithecus, and Ekembo) using three-dimensional morphometric techniques. We also compute phylogenetic signal and reconstruct the ancestral carotid canal course for main anthropoid clades. Our results reveal that carotid canal morphology embeds strong phylogenetic signal but mostly discriminates between platyrrhines and catarrhines, with an extensive overlap among extant catarrhine families. The analyzed extinct taxa display a quite similar carotid canal morphology more closely resembling that of extant catarrhines. Nevertheless, our results for Pliobates highlight some differences compared with the pliopithecid Epipliopithecus, which displays a somewhat more platyrrhine-like morphology. In contrast, Pliobates appears as derived toward the modern catarrhine condition as the stem cercopithecid Victoriapithecus and the stem hominoid Ekembo, which more closely resemble one another. Moreover, Pliobates appears somewhat derived toward the reconstructed ancestral hominoid morphotype, being more similar than other Miocene catarrhines to the condition of great apes and the hylobatid Symphalangus. Overall, our results rule out previously noted similarities in carotid canal morphology between Pliobates and hylobatids, but do not show particular similarities with pliopithecoids either-as opposed to extant and other extinct catarrhines. Additional analyses will be required to clarify the phylogenetic relationships of Pliobates, particularly given its dental similarities with dendropithecids.

Anthroengineering: an independent interdisciplinary field

In recent decades, funding agencies, institutes and professional bodies have recognized the profound benefits of transdisciplinarity in tackling targeted research questions. However, once questions are answered, the previously abundant support often dissolves. As such, the long-term benefits of these transdisciplinary approaches are never fully achieved. Over the last several decades, the integration of anthropology and engineering through inter- and multidisciplinary work has led to advances in fields such as design, human evolution and medical technologies. The lack of formal recognition, however, of this transdisciplinary approach as a unique entity rather than a useful tool or a subfield makes it difficult for researchers to establish laboratories, secure permanent jobs, fund long-term research programmes and train students in this approach. To facilitate the growth and development and witness the long-term benefits of this approach, we propose the integration of anthropology and engineering be recognized as a new, independent field known as anthroengineering. We present a working definition for anthroengineering and examples of how anthroengineering has been used. We discuss the necessity of recognizing anthroengineering as a unique field and explore potential novel applications. Finally, we discuss the future of anthroengineering, highlighting avenues for moving the field forward.

Genetic and ecomorphological divergence between sympatric Astyanax morphs from Central America

Intraspecific ecological and morphological polymorphism can promote ecological speciation and the build-up of reproductive isolation. Here, we evaluate correlations among morphology, trophic ecology and genetic differentiation between two divergent morphs (elongate and deep-body) of the fish genus Astyanax in the San Juan River basin in Central America, to infer the putative evolutionary mechanism shaping this system. We collected the two morphs from three water bodies and analysed: (1) the correlation between body shape and the shape of the premaxilla, a relevant trophic morphological structure, (2) the trophic level and niche width of each morph, (3) the correspondence between trophic level and body and premaxillary shape, and (4) the genetic differentiation between morphs using mitochondrial and nuclear markers. We found a strong correlation between the body and premaxillary shape of the morphs. The elongate-body morph had a streamlined body, a premaxilla with acuter angles and a narrower ascending process, and a higher trophic level, characteristic of species with predatorial habits. By contrast, the deep-body morph had a higher body depth, a premaxilla with less acute angles and a broader trophic niche, suggesting generalist habits. Despite the strong correlation between morphological and ecological divergence, the morphs showed limited genetic differentiation, supporting the idea that morphs may be undergoing incipient ecological speciation, although alternative scenarios such as stable polymorphism or plasticity should also be considered. This study provides support for the role of ecological factors promoting diversification in both lake and stream-dwelling freshwater fish.

Postnatal ontogeny of the femur in fossorial and semiaquatic water voles in the 3D-shape space

Water voles of the genus Arvicola constitute an excellent subject to investigate to which extent function affects postnatal developmental growth of limb structures in phylogenetically close species. We performed a comparative analysis of postweaning femur form changes between Arvicola sapidus (semiaquatic) and Arvicola scherman (fossorial) using three-dimensional landmark-based geometric morphometrics. In both species, we observed greater femur robustness in juvenile individuals than in adult ones, probably due to the accommodation of high loads on the bone during initial locomotor efforts. Significant interspecific differences were also found in the femur size and shape of adult specimens, as well as in the postnatal allometric and phenotypic trajectories. In terms of phenotypic variation, fossorial water voles show relatively wider third and lesser trochanters, and greater femur robustness than A. sapidus, characters associated to the digging activity. In contrast, A. sapidus displays a slight increase of the greater trochanter in comparison with A. scherman, which is seemingly an adaptive response for enhancing propulsion through the water. Results evidence that certain morphological traits and differences between A. sapidus and A. scherman in the allometric and phenotypic trajectories of the femur are associated with their different locomotor mode.

3D reappraisal of trepanations at St. Cosme priory between the 12th and the 15th centuries, France

OBJECTIVE

This study aims to place trepanation in a medieval therapeutic context by addressing its medical use in neurological disorders and by testing the existence of particular dietary care for the sick.

MATERIALS

Six cases of trepanation found at the St. Cosme priory (La Riche, France) dated from the 12th-15th centuries.

METHODS

Neurological health was explored by geometric morphometrics by comparing the six cases to 68 skulls and 67 endocraniums belonging to individuals from the same period and geographical area. Trepanned diet was investigated by carbon and nitrogen isotopes and compared to 49 individuals from the same site.

RESULTS

The study of shapes suggests a possible pathological state for four subjects. The diet of the trepanned is not different from the rest of the population.

CONCLUSIONS

The treatment of neurological disorders emerges as the main therapeutic motivation in the corpus, contrary to the reports from the ancient surgical treatises. A specific diet for the sick is not highlighted.

SIGNIFICANCE

Geometric morphometrics is rarely used in paleopathology and the results suggest a potential of this type of analysis in the identification of pathological cases. The results on therapeutic motivations and diet do not fit the descriptions from ancient medical sources.

LIMITATIONS

The study of forms did not lead to definitive diagnosis. The isotopic study does not allow us to appreciate all the aspects of the diet.

SUGGESTIONS FOR FURTHER RESEARCH

A geometric morphometric study of the skulls and endocraniums of individuals with a known neurological condition would allow a better appreciation of the link between shapes and pathologies.

Sex-Biased Gene Expression of Mesobuthus martensii Collected from Gansu Province, China, Reveals Their Different Therapeutic Potentials

The scorpions, named Mesobuthus martensii, commonly called Quanxie (全蝎) in Chinese, have been widely used as one of the animal medicines for more than 1,000 years because of the strong toxicity of their venoms. Meanwhile, scorpions are sexually dimorphic in appearance, and many exhibit traits associated with sex-biased gene expression, including maternal care, mating competition, female mating choices, ecology, and even venom composition and lethality. This study aims to explore the differences in composition of the venom of scorpions of different sex using the method of transcriptomics. Whole de novo transcriptomes were performed on the samples of M. martensii captured from Gansu Province to identify their sex-biased gene expression. The conserved CO-1 sequences of the captured samples matched that of M. martensii. A total of 8,444 (35.15%), 7,636 (31.78%), 8,510 (35.42%), 7,840 (32.63%), 9,980 (41.54%), and 11,829 (49.23%) unigenes were annotated with GO, KEGG, Pfam, Swissprot, eggNOG, and NR databases. Moreover, a total of 43 metalloproteases, 40 potassium channel toxins, 24 phospholipases, 12 defensins, 10 peroxiredoxins, 9 cysteine proteinase inhibitors, 7 serine protease inhibitors, 6 sodium channel toxins, 2 NDBPs, 1 calcium channel toxin, 1 waprin-like peptide, 1 antibacterial peptide, 1 antimicrobial peptide, and 1 anticoagulant peptide were screened out. With the fold change of 2 and 0.5, p value < 0.01, and q value < 0.05 as thresholds, a total of 41 out of 157 (26.11%) toxin-related unigenes had significant differential expression, and this ratio was much higher than the ratio of differentially expressed unigenes out of all annotated ones (8.84%). Of these differentially expressed toxins, 28 were upregulated and occupied the majority, up to 68.30%. The female scorpions showed more upregulated unigenes that annotated with toxins and had the potential to be used as more effective therapeutic drugs. In addition, this method of omics can be further used as a useful way to identify the difference between female and male toxic animals.

Mammalian body size is determined by interactions between climate, urbanization, and ecological traits

Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. Less understood are effects of other human-caused disturbances on body size, such as urbanization. We compiled 140,499 body size records of over 100 North American mammals to test how climate and human population density, a proxy for urbanization, and their interactions with species traits, impact body size. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Our results demonstrate that both urbanization and temperature influence mammalian body size variation, most often leading to larger individuals, thus supporting the resource availability hypothesis. In addition, life history and other ecological factors play a critical role in mediating the effects of climate and urbanization on body size. Larger mammals and species that utilize thermal buffering are more sensitive to warmer temperatures, while flexibility in activity time appears to be advantageous in urbanized areas. This work highlights the value of using digitized, natural history data to track how human disturbance drives morphological variation.

Anthropogenically-driven climate change is responsible for body size decreases in mammals. Using an important dataset of historically-collected data and data from continental-scale survey efforts from the National Ecological Observatory Network, Hantak et al. show that urbanization plays an important role in mediating this dynamic.

Exceptional Changes in Skeletal Anatomy under Domestication: The Case of Brachycephaly

"Brachycephaly" is generally considered a phenotype in which the facial part of the head is pronouncedly shortened. While brachycephaly is characteristic for some domestic varieties and breeds (e.g., Bulldog, Persian cat, Niata cattle, Anglo-Nubian goat, Middle White pig), this phenotype can also be considered pathological. Despite the superficially similar appearance of "brachycephaly" in such varieties and breeds, closer examination reveals that "brachycephaly" includes a variety of different cranial modifications with likely different genetic and developmental underpinnings and related with specific breed histories. We review the various definitions and characteristics associated with brachycephaly in different domesticated species. We discern different types of brachycephaly ("bulldog-type," "katantognathic," and "allometric" brachycephaly) and discuss morphological conditions related to brachycephaly, including diseases (e.g., brachycephalic airway obstructive syndrome). Further, we examine the complex underlying genetic and developmental processes and the culturally and developmentally related reasons why brachycephalic varieties may or may not be prevalent in certain domesticated species. Knowledge on patterns and mechanisms associated with brachycephaly is relevant for domestication research, veterinary and human medicine, as well as evolutionary biology, and highlights the profound influence of artificial selection by humans on animal morphology, evolution, and welfare.

Ontogeny, phylogeny and mechanisms of adaptive changes in evaporative water loss in geckos

Body size dependence of metabolic rate, body surface and scale morphology complicate disentangling the contribution of these characteristics to adaptive changes in total evaporative water loss (TEWL) of reptiles. To separate adaptive changes from size-related dependence, we compared intra- and interspecific scaling of several candidate traits in eyelid geckos (Eublepharidae), a group exhibiting large variation in body size and TEWL. The intraspecific allometry of TEWL of a eublepharid species fits the geometric surface-mass relationship. However, evolutionary shifts to both higher and lower evaporation were strongly correlated with habitat aridity and cannot be explained by shifts in body size alone. The intraspecific allometry of standard metabolic rate is nearly the same as the interspecific allometry. Unlike for mammals and birds, this pattern rules out respiratory water loss as a driver of the adaptive changes in TEWL among eublepharids. Scale morphology was independent of TEWL variation as well, but the correlation between cutaneous water loss and TEWL suggests a crucial role of skin permeability in adaptation to habitat aridity. Our analyses demonstrate how powerful a comparison between intra- and interspecific allometries can be for detecting body size-dependent mechanisms of adaptive changes in ecophysiological traits correlated with body size.

What constrains adaptive radiation? Documentation and explanation of under-evolved morphologies in Anolis lizards

Adaptive radiations fill ecological and morphological space during evolutionary diversification. Why do some trait combinations evolve during such radiations, whereas others do not? 'Required' constraints of pleiotropy and developmental interaction frequently are implicated in explanations for such patterns, but selective forces also may discourage particular trait combinations. Here, we use a dataset of 351 species to demonstrate the dearth of some theoretically plausible trait combinations of limb, toe and tail length in Anolis lizards. For example, disproportionately few Anolis species display long limbs and short toes. We evaluate recovered patterns within three species of Anolis, and find that cladewide patterns are not evident at intraspecific levels. For example, within species, the combination of long limbs and short toes is not significantly rarer than long limbs and long toes. Differences in scale complicate inter- and intraspecific comparisons and disallow concrete conclusions of cause. However, the absence of the interspecific pattern at the intraspecific level is more compatible with selection favouring particular trait combinations than with 'required' forces dictating which trait combinations are available for selection. We also demonstrate the isometry of toe, tail and hindlimb length relative to body length between species but allometry in four of nine trait-body comparisons within species.

Spreadsheet-Based Minimal Physiological Models for the Prediction of Clearance of Therapeutic Proteins in Pediatric Patients

There is a growing interest in the use of physiologically based pharmacokinetic (PBPK) models as clinical pharmacology drug development tools. In PBPK modeling, not every organ or physiological parameter is required, leading to the development of a minimal PBPK (mPBPK) model, which is simple and efficient. The objective of this study was to streamline mPBPK modeling approaches and enable straightforward prediction of clearance of protein-based products in children. Four mPBPK models for scaling clearance from adult to children were developed and evaluated on Excel spreadsheets using (1) liver and kidneys; (2) liver, kidneys, and skin; (3) liver, kidneys, skin, and lymph; and (4) interstitial, lymph, and plasma volume. There were 35 therapeutic proteins with a total of 113 observations across different age groups (premature neonates to adolescents). For monoclonal and polyclonal antibodies, more than 90% of observations were within a 0.5- to 2-fold prediction error for all 4 methods. For nonantibodies, 79% to 100% of observations were within the 0.5- to 2-fold prediction error for the 4 different methods. Methods 1 and 4 provided the best results, >90% of the total observations were within the 0.5- to 2-fold prediction error for all 3 classes of protein-based products across a wide age range. The precision of clearance prediction was comparatively lower in children ≤2 years of age vs older children (>2 years of age) with methods 1 and 4 predicting 80% to 100% and 75% to 90% of observations within the 0.5- to 2-fold prediction error, respectively. The results of the study indicated that mPBPK models can be developed on spreadsheets, with acceptable performance for prediction of clearance.

Ontogenetic shape trajectory of Trichomycterus areolatus varies in response to water velocity environment

Body and head shape among fishes both vary between environments influenced by water velocity and across ontogeny. Although the shape changes associated with variation in average water velocity and ontogeny are well documented, few studies have tested for the interaction between these two variables (i.e., does ontogenetic shape variation differ between velocity environments). We use geometric morphometrics to characterize shape differences in Trichomycterus areolatus, a freshwater catfish found in high and low-velocity environments in Chile. We identify a significant interaction between velocity environment and body size (i.e., ontogeny). Ontogenetic patterns of shape change are consistent with other studies, but velocity environment differentially affects the ontogenetic trajectory of shape development in T. areolatus. Shape change over ontogeny appears more constrained in high-velocity environments compared to low-velocity environments.

Two species? - Limits of the species concepts in the pygmy grasshoppers of the Tetrix bipunctata complex (Orthoptera, Tetrigidae)

Today, integrative taxonomy is often considered the gold standard when it comes to species recognition and delimitation. Using the Tetrix bipunctata complex, we here present a case where even integrative taxonomy may reach its limits. The Tetrix bipunctata complex consists of two morphs, bipunctata and kraussi, which are easily distinguished by a single character, the length of the hind wing. Both morphs are widely distributed in Europe and reported to occur over a large area in sympatry, where they occasionally may live also in syntopy. The pattern has led to disparate classifications, as on the one extreme, the morphs were treated merely as forms or subspecies of a single species, on the other, as separate species. For this paper, we re-visited the morphology by using multivariate ratio analysis (MRA) of 17 distance measurements, checked the distributional data based on verified specimens and examined micro-habitat use. We were able to confirm that hind wing length is, indeed, the only morphological difference between bipunctata and kraussi. We were also able to exclude a mere allometric scaling. The morphs are, furthermore, largely sympatrically distributed, with syntopy occurring regularly. However, a microhabitat niche difference can be observed. Ecological measurements in a shared habitat confirm that kraussi prefers a drier and hotter microhabitat, which possibly also explains the generally lower altitudinal distribution. Based on these results, we can exclude classification as subspecies, but the taxonomic classification as species remains unclear. Even with different approaches to classify the Tetrix bipunctata complex, this case is, therefore, not settled. We recommend continuing to record kraussi and bipunctata separately.

Weight/carapace length relationship and condition factor of the roughneck shrimp, Rimapenaeus constrictus (Stimpson, 1874), on the southeastern Brazilian coast

Rimapenaeus constrictus is a penaeid shrimp widely distributed in the Western Atlantic, frequently captured as bycatch in trawling activities. Here we describe the weight vs. carapace length relationship and the condition factor of the species. Shrimps were sampled in the Ubatuba region, northern littoral of São Paulo State, monthly. We analyzed 4,952 individuals (1,371 males and 3,581 females). We measured the individuals' weight and carapace length, and the condition factor (CF) was calculated for both sexes. Females had a heavier body when compared to males, probably due to their greater maximum body size achieved. Both sexes presented a negative allometric growth in weight, probably due to their reproductive pattern and activities. We found similar mean CF values for males and females. From temporal analysis, the highest CF values for females were observed during the seasons with lower water temperatures. Such a situation may happen because females' CF tend to be influenced by a greater food availability in the environment, induced by the intrusion of the South Atlantic Central Water during the spring and early summer in the Ubatuba. The information presented here could be used as subside in protection actions and management of bycatch species.

The prognostic value of stroke work/end-diastolic volume ratio during stress echocardiography

BACKGROUND

The ventricular stroke work (SW) refers to the work done by the left ventricle to eject the volume of blood during one cardiac cycle. The cath-lab relationship between SW and end-diastolic volume (EDV) is the preload-recruitable SW (PRSW). Recently a non-invasive single-beat PRSW (SBPRSW) has been proposed. However, the single beat formula needs mathematical skillness, and extra software. Aim of this study was to compare the non-invasive SBPRSW with the simpler non-invasive SW/EDVratio in the stress-echo lab.

METHODS

We studied 692 patients, age 62 ± 12 years, ejection fraction 50 ± 17%, with negative stress echo (SE)(exercise, n = 130, dobutamine, n = 124, dipyridamole, n = 438) and follow-up data. The PRSW was estimated at rest and at peak stress by the SBPRSW technique and compared with the SW/EDV. All patients were followed-up. Event rates were estimated with Kaplan-Meier curves.

RESULTS

SBPRSW and SW/EDV were linearly correlated at rest (r = 0.842, p < .001) and at peak stress (r = 0.860, p < .001). During a median follow-up of 20 months (first quartile 8, third quartile 40 months), 132 major events were registered: at receiver operating characteristic (ROC) analysis rest SBPRSW vs. SW/EDV (AUC 0.691 vs. 0.722) and peak stress (AUC 0.744 vs. 0.800) demonstrated both a significant prognostic power (all p < .001) with non-inferior survival prediction of the simpler SW/EDV ratio at Kaplan-Meier curves (Chi-square rest = 38, peak = 56) vs. SBPRSW (Chi-square rest = 14, peak = 42).

CONCLUSIONS

The data obtained with the non-invasive SBPRSW and by the simpler SW/EDV are highly comparable. PRSW with either SB or SW/EDV approach is effective in predicting follow-up events.

Including Distorted Specimens in Allometric Studies: Linear Mixed Models Account for Deformation

Allometry—patterns of relative change in body parts—is a staple for examining how clades exhibit scaling patterns representative of evolutionary constraint on phenotype, or quantifying patterns of ontogenetic growth within a species. Reconstructing allometries from ontogenetic series is one of the few methods available to reconstruct growth in fossil specimens. However, many fossil specimens are deformed (twisted, flattened, and displaced bones) during fossilization, changing their original morphology in unpredictable and sometimes undecipherable ways. To mitigate against post burial changes, paleontologists typically remove clearly distorted measurements from analyses. However, this can potentially remove evidence of individual variation and limits the number of samples amenable to study, which can negatively impact allometric reconstructions. Ordinary least squares (OLS) regression and major axis regression are common methods for estimating allometry, but they assume constant levels of residual variation across specimens, which is unlikely to be true when including both distorted and undistorted specimens. Alternatively, a generalized linear mixed model (GLMM) can attribute additional variation in a model (e.g., fixed or random effects). We performed a simulation study based on an empirical analysis of the extinct cynodont, Exaeretodon argentinus, to test the efficacy of a GLMM on allometric data. We found that GLMMs estimate the allometry using a full dataset better than simply using only non-distorted data. We apply our approach on two empirical datasets, cranial measurements of actual specimens of E. argentinus (n = 16) and femoral measurements of the dinosaur Tawa hallae (n = 26). Taken together, our study suggests that a GLMM is better able to reconstruct patterns of allometry over an OLS in datasets comprised of extinct forms and should be standard protocol for anyone using distorted specimens.

Allometric scaling and growth: Evaluation and applications in subadult body mass estimation

OBJECTIVES

Previously developed methods in subadult body mass estimation have not been tested in populations other than European-American or African-American. This study uses a contemporary Taiwanese sample to test these methods. Through evaluating their accuracy and bias, we addressed whether the allometric relationships between body mass and skeletal traits commonly used in subadult body mass estimation are conserved among different populations.

MATERIALS AND METHODS

Computed tomography scans of lower limbs from individuals aged 0-17 years old of both sexes were collected from National Taiwan University Hospital along with documented body weight. Polar second moment of area, distal femoral metaphyseal breadth, and maximum superior/inferior femoral head diameter were collected either directly from the scans or from reconstructed 3D models. Estimated body mass was compared with documented body mass to assess the performance of the equations.

RESULTS

Current methods provided good body mass estimates in Taiwanese individuals, with accuracy and bias similar to those reported in other validation studies. A tendency for increasing error with increasing age was observed for all methods. Reduced major axis regression showed the allometric relationships between different skeletal traits and body mass across different age categories can all be summarized using a common fitted line. A revised, maximum likelihood-based approach was proposed for all skeletal traits.

DISCUSSION

The results suggested that the allometric relationships between body mass and different skeletal traits are largely conserved among populations. The revised method provided improved applicability with strong underlying theoretical justifications, and potential for future improvements.

Phylogenetic history influences convergence for a specialized ecology: comparative skull morphology of African burrowing skinks (Squamata; Scincidae)

Background

Skulls serve many functions and as a result, are subject to many different evolutionary pressures. In squamates, many fossorial species occupy a unique region of skull morphospace, showing convergence across families, due to modifications related to head-first burrowing. As different substrates have variable physical properties, particular skull shapes may offer selective advantages in certain substrates. Despite this, studies of variation within burrowers have been limited and are typically focused on a single origin of fossoriality. We focused on seven skink genera (Acontias, Typhlosaurus, Scelotes, Sepsina, Feylinia, Typhlacontias, and Mochlus; 39 sp.) from southern Africa, encompassing at least three independent evolutions of semi-fossoriality/fossoriality. We used microCT scans and geometric morphometrics to test how cranial and mandibular shape were influenced by phylogenetic history, size, and ecology. We also qualitatively described the skulls of four species to look at variation across phylogenetic and functional levels, and assess the degree of convergence.

Results

We found a strong effect of phylogenetic history on cranial and mandibular shape, with size and substrate playing secondary roles. There was a clear gradient in morphospace from less specialized to more specialized burrowers and burrowers in sand were significantly different from those in other substrates. We also created an anatomical atlas for four species with each element described in isolation. Every bone showed some variation in shape and relative scaling of features, with the skull roofing bones, septomaxilla, vomer, and palatine showing the most variation. We showed how broad-scale convergence in traits related to fossoriality can be the result of different anatomical changes.

Conclusions

Our study used geometric morphometrics and comparative anatomy to examine how skull morphology changes for a highly specialized and demanding lifestyle. Although there was broad convergence in both shape and qualitative traits, phylogenetic history played a large role and much of this convergence was produced by different anatomical changes, implying different developmental pathways or lineage-specific constraints. Even within a single family, adaptation for a specialized ecology does not follow a singular deterministic path.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01821-w.

Integration drives rapid phenotypic evolution in flatfishes

Evolutionary innovations are scattered throughout the tree of life, and have allowed the organisms that possess them to occupy novel adaptive zones. While the impacts of these innovations are well documented, much less is known about how these innovations arise in the first place. Patterns of covariation among traits across macroevolutionary time can offer insights into the generation of innovation. However, to date, there is no consensus on the role that trait covariation plays in this process. The evolution of cranial asymmetry in flatfishes (Pleuronectiformes) from within Carangaria was a rapid evolutionary innovation that preceded the colonization of benthic aquatic habitats by this clade, and resulted in one of the most bizarre body plans observed among extant vertebrates. Here, we use three-dimensional geometric morphometrics and a phylogenetic comparative toolkit to reconstruct the evolution of skull shape in carangarians, and quantify patterns of integration and modularity across the skull. We find that the evolution of asymmetry in flatfishes was a rapid process, resulting in the colonization of novel trait space, that was aided by strong integration that coordinated shape changes across the skull. Our findings suggest that integration plays a major role in the evolution of innovation by synchronizing responses to selective pressures across the organism.

Feeding design in free-living mesostigmatid chelicerae (Acari: Anactinotrichida)

A model based upon mechanics is used in a re-analysis of historical acarine morphological work augmented by an extra seven zoophagous mesostigmatid species. This review shows that predatory mesostigmatids do have cheliceral designs with clear rational purposes. Almost invariably within an overall body size class, the switch in predatory style from a worm-like prey feeding ('crushing/mashing' kill) functional group to a micro-arthropod feeding ('active prey cutting/slicing/slashing' kill) functional group is matched by: an increased cheliceral reach, a bigger chelal gape, a larger morphologically estimated chelal crunch force, and a drop in the adductive lever arm velocity ratio of the chela. Small size matters. Several uropodines (Eviphis ostrinus, the omnivore Trachytes aegrota, Urodiaspis tecta and, Uropoda orbicularis) have more elongate chelicerae (greater reach) than their chelal gape would suggest, even allowing for allometry across mesostigmatids. They may be: plesiosaur-like high-speed strikers of prey, scavenging carrion feeders (like long-necked vultures), probing/burrowing crevice feeders of cryptic nematodes, or small morsel/fragmentary food feeders. Some uropodoids have chelicerae and chelae which probably work like a construction-site mechanical excavator-digger with its small bucket. Possible hoeing/bulldozing, spore-cracking and tiny sabre-tooth cat-like striking actions are discussed for others. Subtle changes lead small mesostigmatids to be predator-scavengers (mesocarnivores) or to be predator-fungivores (hypocarnivores). Some uropodines (e.g., the worm-like prey feeder Alliphis siculus and, Uropoda orbicularis) show chelae similar in design to astigmatids and cryptostigmatids indicating possible facultative saprophagy. Scale matters-obligate predatory designs (hypercarnivory) start for mesostigmatids with chelal gape > 150 μm and cheliceral reach > 350 μm (i.e., about 500-650 μm in body size). Commonality of trophic design in these larger species with solifugids is indicated. Veigaia species with low chelal velocity ratio and other morphological strengthening specialisms, appear specially adapted in a concerted way for predating active soft and fast moving springtails (Collembola). Veigaia cerva shows a markedly bigger chelal gape than its cheliceral reach would proportionately infer suggesting it is a crocodile-like sit-and-wait or ambush predator par excellence. A small chelal gape, low cheliceral reach, moderate velocity ratio variant of the worm-like feeding habit design is supported for phytoseiid pollenophagy. Evidence for a resource partitioning model in the evolution of gnathosomal development is found. A comparison to crustacean claws and vertebrate mandibles is made. Alliphis siculus and Rhodacarus strenzkei are surprisingly powerful mega-cephalics for their small size. Parasitids show a canid-like trophic design. The chelicera of the nematophagous Alliphis halleri shows felid-like features. Glyphtholaspis confusa has hyaena-like cheliceral dentition. The latter species has a markedly smaller chelal gape than its cheliceral reach would suggest proportionately, which together with a high chelal velocity ratio and a high estimated chelal crunch force matches a power specialism of feeding on immobile tough fly eggs/pupae by crushing (durophagy). A consideration of gnathosomal orientation is made. Predatory specialisms appear to often match genera especially in larger mesostigmatids, which may scale quite differently. Comparison to holothyrids and opilioacarids indicates that the cheliceral chelae of the former are cutting-style and those of the latter are crushing-style. A simple validated easy-to-use '2:1 on' predictive algorithm of feeding habit type is included based on a strength-speed tradeoff in chelal velocity ratio for ecologists to test in the field.

Feet first: Adaptive growth in magellanic penguin chicks

Growing animals should allocate their limited resources in ways that maximize survival. Seabird chicks must balance the growth of features and fat reserves needed to survive on land with those needed to successfully fledge and survive at sea. We used a large, 34-year dataset to examine energy allocation in Magellanic penguin chicks. Based on the temporal trends in the selective pressures that chicks faced, we developed predictions relating to the timing of skeletal feature growth (Prediction 1), variation in skeletal feature size and shape (Prediction 2), and responses to periods of high energetic constraint (Prediction 3). We tested our predictions using descriptive statistics, generalized additive models, and principal component analysis. Nearly all of our predictions were supported. Chicks grew their feet first, then their flippers. They continued to grow their bill after fledging (Prediction 1). Variance in feature size increased in young chicks but declined before fledging; this variance was largely driven by overall size rather than by shape (Prediction 2). Chicks that died grew slower and varied more in feature size than those that fledged (Prediction 2). Skeletal features grew rapidly prior to thermoregulation and feet and flippers were 90% grown prior to juvenile feather growth; both thermoregulation and feather growth are energetically expensive (Prediction 3). To avoid starvation, chicks prioritized storing mass during the first 10 days after hatching; then, the body condition of chicks began to decline (Prediction 3). In contrast to our prediction of mass prioritization in young chicks, chicks that were relatively light for their age had high skeletal size to mass ratios. Chicks did not show evidence of reaching physiological growth limits (Prediction 3). By examining energy allocation patterns at fine temporal scales and in the context of detailed natural history data, we provide insight into the trade-offs faced by growing animals.

Sensory adaptations reshaped intrinsic factors underlying morphological diversification in bats

Background

Morphological evolution may be impacted by both intrinsic (developmental, constructional, physiological) and extrinsic (ecological opportunity and release) factors, but can intrinsic factors be altered by adaptive evolution and, if so, do they constrain or facilitate the subsequent diversification of biological form? Bats underwent deep adaptive divergences in skull shape as they evolved different sensory modes; here we investigate the potential impact of this process on two intrinsic factors that underlie morphological variation across organisms, allometry, and modularity.

Results

We use comparative phylogenetic and morphometric approaches to examine patterns of evolutionary allometry and modularity across a 3D geometric morphometric dataset spanning all major bat clades. We show that allometric relationships diverge between echolocators and visually oriented non-echolocators and that the evolution of nasal echolocation reshaped the modularity of the bat cranium.

Conclusions

Shifts in allometry and modularity may have significant consequences on the diversification of anatomical structures, as observed in the bat skull.

Brain Allometry Across Macroevolutionary Scales in Squamates Suggests a Conserved Pattern in Snakes

Despite historical interest in brain size evolution in vertebrates, few studies have assessed variation in brain size in squamate reptiles such as snakes and lizards. Here, we analyzed the pattern of brain allometry at macroevolutionary scale in snakes and lizards, using body mass and snout vent length as measures of body size. We also assessed potential energetic trade-offs associated with relative brain size changes in Crotalinae vipers. Body mass showed a conserved pattern of brain allometry across taxa of snakes, but not in lizards. Body length favored changes of brain allometry in both snakes and lizards, but less variability was observed in snakes. Moreover, we did not find evidence for trade-offs between brain size and the size of other organs in Crotalinae. Thus, despite the contribution of body elongation to changes in relative brain size in squamate reptiles, snakes present low variation in brain allometry across taxa. Although the mechanisms driving this conserved pattern are unknown, we hypothesize that the snake body plan plays an important role in balancing the energetic demands of brain and body size increase at macroevolutionary scales. We encourage future research on the evolution of brain and body size in snakes to test this hypothesis.

Sexual Dimorphism and Morphological Modularity in Acanthoscelides obtectus (Say, 1831) (Coleoptera: Chrysomelidae): A Geometric Morphometric Approach

Simple Summary

The seed beetle Acanthoscelides obtectus used in this study is a worldwide pest species that inhabits storage facilities and fields of beans. Knowing that sexual dimorphism is very common among insects, we investigated the level of morphological differences between the sexes. Such an approach allowed us to look into the modular organization of this organism. As expected, the females were larger than the males. The observed two modular organization (thorax and abdomen) was sex specific, indicating that reproductive function has the central role in forming the patterns of modularity. It seems that natural selection is driving force for females, while males are influenced more by sexual selection.

Abstract

Sexual dimorphism and specific patterns of development contribute in a great manner to the direction and degree of the sexual differences in body size and shape in many insects. Using a landmark-based geometric morpohometrics approach, we investigated sex-specific morphological size and shape variation in the seed beetle, Acanthoscelides obtectus. We also tested the functional hypothesis of the two morphological modules—thorax and abdomen in both sexes. Female-biased sexual dimorphism in size was shown, while differences in shape were reflected in the wider thorax and abdomen and shorter abdomen in females in comparison to males. The functional hypothesis of a two-module body was confirmed only in females before correction for size, and in both sexes after the allometry correction. Our results indicate that reproductive function has the central role in forming the patterns of modularity. We hypothesize that high morphological integration of the abdomen in females results from intense stabilizing selection, while the more relaxed integration in males is driven by the higher intensity of sexual selection.

Isometric scaling to model water transport in conifer tree rings across time and environments

The hydraulic properties of xylem determine the ability of plants to efficiently and safely provide water to their leaves. These properties are key to understanding plant responses to environmental conditions and evaluating their fate under a rapidly changing climate. However, their assessment is hindered by the challenges of quantifying basic hydraulic components such as bordered pits and tracheids. Here, we use isometric scaling between tracheids and pit morphology to merge partial hydraulic models of the tracheid component and to upscale these properties to the tree-ring level in conifers. Our new model output is first cross-validated with the literature and then applied to cell anatomical measurements from Larix sibirica tree rings formed under harsh conditions in southern Siberia to quantify the intra- and inter-annual variability in hydraulic properties. The model provides a means of assessing how different-sized tracheid components contribute to the hydraulic properties of the ring. Upscaled results indicate that natural inter- and intra-ring anatomical variations have a substantial impact on the tree's hydraulic properties. Our model facilitates the assessment of important xylem functional attributes because it requires only the more accessible measures of cross-sectional tracheid size. This approach, if applied to dated tree rings, provides a novel way to investigate xylem structure-function relationships across time and environmental conditions.

Evaluation of functional muscle anatomy scalability in the canine hind limb

In contrast to other mammals, the large variation in dog sizes is not accompanied by any significant genetic re-organization. In order to study the relationship between body mass, limb length and the functional anatomical muscle parameters of the canine hind limb, a large dataset comprising of muscle masses, optimal muscle fibre lengths and physiological cross-sectional area's (PCSA) were acquired for twenty-five muscles in ten dogs of sizes varying between 20 kg and 52 kg. The potential of body mass and limb length for reliably scaling individual muscle masses, optimal muscle fibre lengths and PCSA's were examined. For the majority of the muscles of the canine hind limb, neither body mass nor limb length were reliable scaling parameter for either muscle masses, PCSA's and optimal fibre length. These results indicate the need of a breed-specific approach to musculoskeletal modelling in future canine musculoskeletal research.

Ontogenetic allometry and scaling in catarrhine crania

In studies of ontogenetic allometry, ontogenetic scaling has often been invoked to explain cranial morphological differences between smaller and larger forms of closely related taxa. These scaled variants in shape have been hypothesized to be the result of the extension or truncation of common growth allometries. In this scenario, change in size is the determining factor, perhaps under direct selection, and changes in cranial shapes are byproducts, not under direct selection themselves. However, many of these conclusions are based on studies that used bivariate generalizations of shape. Even among multivariate analyses of growth allometries, there are discrepancies as to the prevalence of ontogenetic scaling among primates, how shared the trajectories need to be, and which taxa evince properties of scaled variants. In this investigation, we use a large, comparative ontogenetic sample, geometric morphometric methods, and multivariate statistical tests to examine ontogenetic allometry and evaluate if differences in cranial shape among closely related catarrhines of varying sizes are primarily driven by size divergence, that is, ontogenetic scaling. We then evaluate the hypothesis of size as a line of least evolutionary resistance in catarrhine cranial evolution. We found that patterns of ontogenetic allometry vary among taxa, indicating that ontogenetic scaling sensu stricto does not often account for most morphological differences and that large and small taxa within clades are generally not scaled variants. The presence of a variety of ontogenetic pathways for the evolution of cranial shapes provides indirect evidence for selection acting directly on the cranial shape, rather than on size alone.

A shift in ontogenetic timing produced the unique sauropod skull

Sauropod dinosaurs include the largest terrestrial vertebrates that have ever lived. Virtually every part of the sauropod body is heavily modified in association with gigantic size and associated physiological alterations. Sauropod skulls are no exception: they feature elongated, telescoped facial regions connected to tilted neurocrania and reoriented jaw adductor muscles. Several of these cranial features have been suggested to be adaptations for feeding on the one hand and the result of paedomorphic transformation near the base of Sauropoda on the other. However, the scarcity of sauropodomorph ontogenetic series has impeded further investigation of these hypotheses. We re-evaluated the cranial material attributed to the early sauropodomorph Anchisaurus, which our phylogenetic analyses confirm to be closely related to sauropods. Digital assembly of μCT-scanned skulls of the two known specimens, a juvenile and an adult, permitted us to examine the detailed ontogeny of cranial elements. The skull anatomy of Anchisaurus is distinguished by a mosaic of ancestral saurischian and sauropod-like characters. Sauropod-like characters of the braincase and adductor chamber appear late in ontogeny, suggesting that these features first evolved by the developmental mechanism of terminal addition. Shape analyses and investigation of allometric evolution demonstrate that cranial characters that appear late in the ontogeny of sauropodomorphs closely related to sauropods are already present in the embryos and juveniles of sauropods, suggesting a predisplacement-type shift in developmental timing from the ancestral anchisaurian condition. We propose that this developmental shift relaxed prior constraints on skull morphology, allowing sauropods to explore a novel range of phenotypes and enabling specializations of the feeding apparatus. The shift in timing occurred in concert with the evolution of gigantism and physiological and locomotory innovations.

Eye‐body allometry across biphasic ontogeny in anuran amphibians

Animals with biphasic lifecycles often inhabit different visual environments across ontogeny. Many frogs and toads (Amphibia: Anura) have free-living aquatic larvae (tadpoles) that metamorphose into adults that inhabit a range of aquatic and terrestrial environments. Ecological differences influence eye size across species, but these relationships have not yet been explored across life stages in an ontogenetic allometric context. We examined eye-body size scaling in a species with aquatic larvae and terrestrial adults, the common frog Rana temporaria, using a well-sampled developmental series. We found a shift in ontogenetic allometric trajectory near metamorphosis indicating prioritized growth in tadpole eyes. To explore the effects of different tadpole and adult ecologies on eye-body scaling, we expanded our taxonomic sampling to include developmental series of eleven additional anuran species. Intraspecific eye-body scaling was variable among species, with 8/12 species exhibiting a significant change in allometric slope between tadpoles and adults. Traits categorizing both tadpole ecology (microhabitat, eye position, mouth position) and adult ecology (habitat, activity pattern) across species had significant effects on allometric slopes among tadpoles, but only tadpole eye position had a significant effect among adults. Our study suggests that relative eye growth in the preliminary stages of biphasic anuran ontogenies is somewhat decoupled and may be shaped by both immediate ecological need (i.e. tadpole visual requirements) and what will be advantageous during later adult stages.

Segmental series and size: clade-wide investigation of molar proportions reveals a major evolutionary allometry in the dentition of placental mammals

Iterative segments such as teeth or limbs are a widespread characteristic of living organisms. While their proportions may be governed by similar developmental rules in vertebrates, there is no emerging pattern as regards their relation to size. Placental mammals span eight orders of magnitude in body size and show a wide spectrum of dietary habits associated with size and reflected in their dentitions, especially molars. Although variation in size constitutes an important determinant for variation in biological traits, few major allometric trends have been documented on placental molars so far. Molar proportions have been intensively explored in placentals in relation to developmental models, but often at a small phylogenetic scale. Here, we analyzed the diversity of upper molar proportions in relation to absolute size in a large sample of placental species (n = 286) encompassing most of the group's dental diversity. Our phylogenetically informed analyses revealed a twofold pattern of evolutionary integration among upper molars: while molars covary in size with each other, their proportions covary with the absolute size of the entire molar field. With increasing absolute size, posterior molars increase in size relative to anterior ones, meaning that large-sized species have relatively large rear molars while the opposite is true for small-sized species. The directionality of proportional increase in the molar row exhibits a previously unsuspected allometric patterning among placentals, showing how large-scale variations in size may have influenced variation in dental morphology. This finding provides new evidence that processes regulating the size of individual molars are integrated with overall patterns of growth and calls for further testing of allometric variation in the dentition and in other segmental series of the vertebrate body.

Centric Allometry: Studying Growth Using Landmark Data

The geometric morphometric (GMM) construction of Procrustes shape coordinates from a data set of homologous landmark configurations puts exact algebraic constraints on position, orientation, and geometric scale. While position as digitized is not ordinarily a biologically meaningful quantity, and orientation is relevant mainly when some organismal function interacts with a Cartesian positional gradient such as horizontality, size per se is a crucially important biometric concept, especially in contexts like growth, biomechanics, or bioenergetics. “Normalizing” or “standardizing” size (usually by dividing the square root of the summed squared distances from the centroid out of all the Cartesian coordinates specimen by specimen), while associated with the elegant symmetries of the Mardia–Dryden distribution in shape space, nevertheless can substantially impeach the validity of any organismal inferences that ensue. This paper adapts two variants of standard morphometric least-squares, principal components and uniform strains, to circumvent size standardization while still accommodating an analytic toolkit for studies of differential growth that supports landmark-by-landmark graphics and thin-plate splines. Standardization of position and orientation but not size yields the coordinates Franz Boas first discussed in 1905. In studies of growth, a first principal component of these coordinates often appears to involve most landmarks shifting almost directly away from their centroid, hence the proposed model’s name, “centric allometry.” There is also a joint standardization of shear and dilation resulting in a variant of standard GMM’s “nonaffine shape coordinates” where scale information is subsumed in the affine term. Studies of growth allometry should go better in the Boas system than in the Procrustes shape space that is the current conventional workbench for GMM analyses. I demonstrate two examples of this revised approach (one developmental, one phylogenetic) that retrieve all the findings of a conventional shape-space-based approach while focusing much more closely on the phenomenon of allometric growth per se. A three-part Appendix provides an overview of the algebra, highlighting both similarities to the Procrustes approach and contrasts with it.

Effective investments due to seasonal morphological changes? Possible reasons and consequences of allometric growth and reproduction in adult signal crayfish (Pacifastacus leniusculus)

Signal crayfish (Pacifastacus leniusculus (Dana, 1852)) are among the most invasive macroinvertebrates in Europe, representing economic value as well as serious threats to ecosystems. Despite decades of research, uncertainties with respect to its biology remain. The present study describes the observations of adult signal crayfish during a single growing season, with a sex ratio of 1:1, reared under natural ambient conditions, in which moulting events, growth increments, morphological changes, mortality, and reproductive output were monitored. Two moults were observed in the majority of both sexes, with significant differences in moult growth increments of once- and twice-moulted animals. These led to modifications in morphology during the growing season. Females showed isometric growth at the first moult, while, at the second moult, they strengthened the functional state of structures linked to reproduction. In males, the effect was similar, but to a lesser extent, with extensive chelae development at the second moult. There were no differences in relative fecundity of once- and twice-moulted females. However, signal crayfish have different needs during the growing and reproductive seasons. The presented results indicate the ability to use resources according to current needs (development of strategical body parts) via their seasonal morphological plasticity as seen in representatives of the family Cambaridae.

Water constraints drive allometric patterns in the body shape of tree frogs

The origin of morphological diversity is a critical question in evolutionary biology. Interactions between the environment and developmental processes have determining roles in morphological diversity, creating patterns through space and over time. Also, the shape of organisms tends to vary with increasing size as a result of those developmental processes, known as allometry. Several studies have demonstrated that the body sizes of anurans are associated with hydric conditions in their environments and that localities with high water stress tend to select for larger individuals. However, how environmental conditions alter those patterns of covariance between size and shape is still elusive. We used 3D geometric morphometric analyses, associated with phylogenetic comparative methods, to determine if the morphological variations and allometric patterns found in Arboranae (Anura) is linked to water conservation mechanisms. We found effects of the hydric stress on the shape of Arboranae species, favouring globular shapes. Also, the allometric patterns varied in intensity according to the water stress gradient, being particularly relevant for smaller frogs, and more intense in environments with higher water deficits. Our study provides empirical evidence that more spherical body shapes, especially among smaller species, reflect an important adaptation of anurans to water conservation in water-constrained environments.

Testing the Giles hypothesis using geometric morphometrics

OBJECTIVES

The Giles hypothesis posits that differences in the cranial morphology of Pan troglodytes and Gorilla gorilla are largely the result of allometric scaling. However, previous support for the Giles hypothesis was based on bivariate plots of linear measurements. This investigation uses geometric morphometric methods to retest this hypothesis and its prediction that extending the ontogenetic trajectory of a chimpanzee would produce an adult gorilla-like cranial morphology.

MATERIALS AND METHODS

Forty-three 3D cranial landmarks were collected from an ontogenetic series of 76 Pan troglodytes and 58 Gorilla gorilla specimens. Ontogenetic trajectories of cranial shape change were computed via multivariate regression of Procrustes aligned coordinates against LnCS (size vector) and molar eruption stage (developmental vector). These two vectors were then used in developmental simulations to extend the ontogenetic trajectories of adult chimpanzees. Allometric trajectories of chimpanzees and gorillas were also directly compared using Procrustes ANOVA.

RESULTS

Pan and Gorilla significantly differ in their allometric trajectories, and none of the Pan developmental simulations resembled actual adult gorillas. Additionally, the more the Pan developmental vector was extended, the more morphologically distinct the simulations became from actual adult gorillas.

DISCUSSION

Taken together, these results do not support the Giles hypothesis that allometric scaling is primarily responsible for observed morphological differences between chimpanzee and gorilla crania. This investigation demonstrates that neither "growing" a chimpanzee to the size of a gorilla, nor extending a chimpanzee's developmental shape trajectory will result in an adult gorilla-like cranial morphology as they differ in their patterns of allometry.

Effect of Environmental Stress on the Nutrient Stoichiometry of the Clonal Plant Phragmites australis in Inland Riparian Wetlands of Northwest China

Clonal plants play an important role in determining ecosystem properties such as community stability, species diversity and nutrient cycling. However, relatively little information is available about the stoichiometric characteristics of clonal plants and their drivers in inland riparian wetlands under strong environmental stress. In this manuscript, we studied the clonal plant Phragmites australis in an inland riparian wetland of Northwest China and compared its nutrient distribution and stoichiometry trade-offs as well as its responses to soil environmental factors in three different environments, namely, a wetland, a salt marsh, and a desert. We found that (1) P. australis could adapt to heterogeneous environments by changing its nutrient allocation strategies, as evidenced by the significant decrease in N and P concentrations, and significant increase in whole-plant C:P and N:P ratios from the wetland to the desert habitats. (2) P. australis adapted to stressful environments by changing its nutrient allocation patterns among different modules, showing a greater tendency to invest N and P in underground modules (rhizomes and roots) and an increase in the utilization efficiency of N and P in the leaves, and stems as environmental stress increased. (3) The C-N, C-P, and N:P-C in the whole plant and in each module showed significant anisotropic growth relationships in the three habitats (P < 0.05). (4) Soil water, pH and salt were the main factors limiting nutrient stoichiometry. The results of this study clarified the ecological adaptation mechanism of the clonal plant P. australis to heterogeneous environments and provided targeted protection strategies for inland riparian wetlands in Northwest China.

Evolutionary and morphological patterns underlying carnivoran body shape diversity

The diversity of body shapes is one of the most prominent features of phenotypic variation in vertebrates. Biologists, however, still lack a full understanding of the underlying morphological components that contribute to its diversity, particularly in endothermic vertebrates such as mammals. In this study, hypotheses pertaining to the evolution of the cranial and axial components that contribute to the diversity of carnivoran body shapes were tested. Three trends were found in the evolution of carnivoran body shapes: (1) carnivorans exhibit diverse body shapes with intrafamilial variation predicted best by family clade age, (2) body shape is driven by strong allometric effects of body size where species become more elongate with decreasing size, and (3) the thoracic and lumbar regions and rib length contribute the most to body shape variation, albeit pathways differ between different families. These results reveal the morphological patterns that led to increased diversity in carnivoran body shapes and elucidate the similarities and dissimilarities that govern body shape diversity across vertebrates.

Coordinated Development of Innovation System in China’s Yangtze River Economic Belt, a Demand and Supply Perspective

The Development of the Yangtze River Economic Belt (YREB) is not only a major regional coordination development strategy in China but also a core carrier supporting China’s innovation-driven development. Under this background, this paper explored the evolution, spatial difference, and coordination development of the regional innovation system in the period of 2007 to 2017 from the demand and supply perspective. We found that, during the study period, the development level of the innovation demand subsystem (IDS) and innovation supply subsystem (ISS), as well as their coordinated development, all showed an increasing trend. The development gap of IDS and the coordinated development among cities in YREB was quite balanced, while there existed a large gap among cities in YREB in the development of ISS. The development of IDS was better than the development of ISS in most of the cities of YREB, indicating that the innovation development of cities in YREB needs supply-side structural reform urgently. Most cities in YREB were at the moderately or slightly uncoordinated development phase, and Shanghai was the only city with coordinated development between IDS and ISS. This paper enriches the regional innovation system from a new perspective, the demand and supply perspective, as well as providing suggestions for the coordinated development of the regional innovation system in YREB.

Allometric relationships shape foreleg evolution of long-legged oil bees (Melittidae: Rediviva)

Exaggerated traits of pollinators have fascinated biologists for centuries. To understand their evolution, and their role in coevolutionary relationships, an essential first step is to understand how traits scale allometrically with body size, which may reveal underlying developmental constraints. Few pollination studies have examined how traits can adaptively diverge despite allometric constraints. Here, we present a comparative study of narrow-sense static and evolutionary allometry on foreleg length and body size of oil-collecting bees. Concurrently, we assess the relationship between scaling parameters and spur lengths of oil-secreting host flowers. Across species and populations, we found low variation in static slopes (nearly all <1), possibly related to stabilizing selection, but the static intercept varied substantially generating an evolutionary allometry steeper than static allometry. Variation in static intercepts was explained by changes in body size (∼28% species; ∼68% populations) and spur length (remaining variance: ∼36% species; ∼94% populations). The intercept-spur length relationship on the arithmetic scale was positive but forelegs did not track spur length perfectly in a one-to-one relationship. Overall, our study provides new insights on how phenotypic evolution in the forelegs of oil-collecting bees is related to the variability of the allometric intercept and adaptation to host plants.

Static allometry of a small-bodied omnivore: body size and limb scaling of an island fox and inferences for Homo floresiensis

Island dwarfing is a paraphyletic adaptation across numerous mammalian genera. From mammoths to foxes, extreme body size reduction is shared by diverse organisms that migrate to an island environment. Because it largely occurs owing to ecological variables, not phylogenetic ones, skeletal characters in a dwarfed taxon compared with its ancestor may appear abnormal. As a result, allometric patterns between body size and morphological traits may differ for an island dwarf compared with its ancestor. The diminutive Late Pleistocene hominin, Homo floresiensis, displays a unique character suite that is outside of the normal range of variation for any extinct or extant hominin species. To better explain these as ecological traits due to island dwarfing, this research looks at how dwarfing on islands influences limb scaling and proportions in an organism in a similar ecological niche as H. floresiensis. Here, I analyze absolute limb lengths and static allometry of limb lengths regressed on predicted body mass of dwarfed island foxes and their nondwarfed relatives. Dwarfed island foxes have significantly smaller intercepts but steeper slopes of all limb elements regressed on predicted body mass than the mainland gray fox. These allometric alterations produce limbs in the island fox that are significantly shorter than predicted for a nondwarfed gray fox of similar body mass. In addition, the humerofemoral, intermembral, and brachial indices are significantly different. These results provide a novel model for understanding skeletal variation of island endemic forms. Unique body size and proportions of H. floresiensis are plausible as ecological adaptations and likely not examples of symplesiomorphies with Australopithecus sp. Caution should be exerted when comparing an island dwarf with a closely related species as deviations from allometric expectations may be common.

Eye size in North American watersnakes (genus Nerodia) correlates with variation in feeding ecology

Visual acuity and sensitivity positively correlate to eye size in vertebrates, and eye size relates to the ecology of colubrid snakes. We investigated whether eye morphology of North American colubrids of the genus Nerodia correlates with ecology as well. Although all members of the genus utilize aquatic habits, they differ widely in the proportion of anurans they eat. We specifically tested whether eye size and placement is associated with the proportion of frogs in the diet to determine whether these two aspects of eye morphology relate to feeding ecology. Using phylogenetic comparative methods, we found a significantly positive association between eye size and the proportion of anurans eaten by Nerodia species. Although the evidence is equivocal, the anterior placement of relatively small eyes in one species may also enhance anurophagy. Although eye size may improve a snake’s ability to feed on frogs, eye size must compete with other selective forces on head shape in trade-offs that may also influence eye size.

Allometric growth in mass by the brain of mammals

I re-examined published data for ontogenetic change in relative mass of the brain in six species of mammal (i.e., sheep, pig, cow, horse, rat, cat) to illustrate an insidious problem with conventional analyses of brain-body allometry. Graphical displays of logarithmic transformations of the original data for each species give the appearance of two discrete mathematical distributions, but untransformed observations nonetheless conform to a single distribution that is well described by a single, nonlinear equation. The concept of biphasic, allometric growth by the brain consequently is an artifact of transformation. The notion of Rapid and Slow phases in relative growth by the brain also is an artifact, because the notion is based explicitly on the concept of biphasic growth allometry. Relative growth by the brain in sheep, pigs, cows, and horses follows the path of a power curve with an exponent less than 1, so relative growth declines progressively as animals grow to their maximum size, at which point growth effectively ends for both brain and body. Relative growth by the brain in rats and cats follows the path of an exponential curve and consequently is more like relative growth by the brain of odontocoete cetaceans and primates, with the brain growing rapidly relative to the body early in ontogeny and attaining maximum (cats) or near-maximum (rats) mass well before the body reaches its maximum. An exponential pattern of relative growth by the brain appears to have evolved independently in rodents, carnivores, odontocoetes, and primates.

The development of body and organ shape

Background

Organisms show an incredibly diverse array of body and organ shapes that are both unique to their taxon and important for adapting to their environment. Achieving these specific shapes involves coordinating the many processes that transform single cells into complex organs, and regulating their growth so that they can function within a fully-formed body.

Main text

Conceptually, body and organ shape can be separated in two categories, although in practice these categories need not be mutually exclusive. Body shape results from the extent to which organs, or parts of organs, grow relative to each other. The patterns of relative organ size are characterized using allometry. Organ shape, on the other hand, is defined as the geometric features of an organ’s component parts excluding its size. Characterization of organ shape is frequently described by the relative position of homologous features, known as landmarks, distributed throughout the organ. These descriptions fall into the domain of geometric morphometrics.

Conclusion

In this review, we discuss the methods of characterizing body and organ shape, the developmental programs thought to underlie each, highlight when and how the mechanisms regulating body and organ shape might overlap, and provide our perspective on future avenues of research.

Three-dimensional geometric morphometric analysis of the humerus: Comparative postweaning ontogeny between fossorial and semiaquatic water voles (Arvicola)

Different types of locomotion in phylogenetically close rodent species can lead to significantly different growth patterns of certain skeletal structures. In the present study, we compared the allometric and phenotypic trajectories of the humerus in semiaquatic (Arvicola sapidus) and fossorial (Arvicola scherman) water vole taxa, using three-dimensional geometric morphometrics, to investigate the relationships between functional and ontogenetic differences. Results revealed shared humerus traits between A. sapidus and A. scherman, specifically an expansion of the epicondylar and deltopectoral crests along postnatal ontogeny. In both species, the humerus of young specimens is more robust than in adults, possibly as a compensatory response for lower bone stiffness. However, significant interspecific differences were detected in all components of allometric and phenotypic trajectories. Noticeably divergent allometric trajectories were observed, probably as a result of different functional pressures exerted on this bone. Important differences in the form of the adult humerus between taxa were also found, particularly in features located in muscle insertion zones. Furthermore, the allometric regression revealed certain shape variation not associated with size in A. scherman, suggesting mechanical stress produced by the persistent digging activity during adulthood. A. scherman is a chisel-tooth digger that shares several traits in the humerus morphology with scratch-digger rodent species. Nevertheless, these shared characteristics are less pronounced in fossorial water voles, which is congruent with the different implications of the forelimb in the digging activity in these two types of diggers.

The scaling of human basal and resting metabolic rates

PURPOSE

In tachymetabolic species, metabolic rate increases disproportionately with body mass, and that inter-specific relationship is typically modelled allometrically. However, intra-specific analyses are less common, particularly for healthy humans, so the possibility that human metabolism would also scale allometrically was investigated.

METHODS

Basal metabolic rate was determined (respirometry) for 68 males (18-40 years; 56.0-117.1 kg), recruited across five body-mass classes. Data were collected during supine, normothermic rest from well-rested, well-hydrated and post-absorptive participants. Linear and allometric regressions were applied, and three scaling methods were assessed. Data from an historical database were also analysed (2.7-108.9 kg, 4811 males; 2.0-96.4 kg, 2364 females).

RESULTS

Both linear and allometric functions satisfied the statistical requirements, but not the biological pre-requisite of an origin intercept. Mass-independent basal metabolic data beyond the experimental mass range were not achieved using linear regression, which yielded biologically impossible predictions as body mass approached zero. Conversely, allometric regression provided a biologically valid, powerful and statistically significant model: metabolic rate = 0.739 * body mass^0.547 (P < 0.05). Allometric analysis of the historical male data yielded an equivalent, and similarly powerful model: metabolic rate = 0.873 * body mass^0.497 (P < 0.05).

CONCLUSION

It was established that basal and resting metabolic rates scale allometrically with body mass in humans from 10-117 kg, with an exponent of 0.50-0.55. It was also demonstrated that ratiometric scaling yielded invalid metabolic predictions, even within the relatively narrow experimental mass range. Those outcomes have significant physiological implications, with applications to exercising states, modelling, nutrition and metabolism-dependent pharmacological prescriptions.