Allometry and size in ontogeny and phylogeny

Postmetamorphic ontogenetic allometry and the evolution of skull shape in Nest-building frogs Leptodactylus (Anura: Leptodactylidae)

Allometry constitutes an important source of morphological variation. However, its influence in head development in anurans has been poorly explored. By using geometric morphometrics followed by statistical and comparative methods we analyzed patterns of allometric change during cranial postmetamorphic ontogeny in species of Nest-building frogs Leptodactylus (Leptodactylidae). We found that the anuran skull is not a static structure, and allometry plays an important role in defining its shape in this group. Similar to other groups with biphasic life-cycle, and following a general trend in vertebrates, ontogenetic changes mostly involve rearrangement in rostral, otoccipital, and suspensorium regions. Ontogenetic transformations are paralleled by shape changes associated with evolutionary change in size, such that the skulls of species of different intrageneric groups are scaled to each other, and small and large species show patterns of paedomorphic/peramorphic features, respectively. Allometric trajectories producing those phenotypes are highly evolvable though, with shape change direction and magnitude varying widely among clades, and irrespective of changes in absolute body size. These results reinforce the importance of large-scale comparisons of growth patterns to understand the plasticity, evolution, and polarity of morphological changes in different clades.

Evolution of Ovipositor Length in Drosophila suzukii Is Driven by Enhanced Cell Size Expansion and Anisotropic Tissue Reorganization

Morphological diversity is dominated by variation in body proportion [1], which can be described with scaling relationships and mathematical equations, following the pioneering work of D’Arcy Thompson [2] and Julian Huxley [3]. Yet, the cellular processes underlying divergence in size and shape of morphological traits between species remain largely unknown [4, 5, 6, 7, 8]. Here, we compare the ovipositors of two related species, Drosophila melanogaster and D. suzukii. D. suzukii has switched its egg-laying niche from rotting to ripe fruit [9]. Along with this shift, the D. suzukii ovipositor has undergone a significant change in size and shape [10]. Using an allometric approach, we find that, while adult ovipositor width has hardly changed between the species, D. suzukii ovipositor length is almost double that of D. melanogaster. We show that this difference mostly arises in a 6-h time window during pupal development. We observe that the developing ovipositors of the two species comprise an almost identical number of cells, with a similar profile of cell shapes and orientations. After cell division stops, we find that the ovipositor area continues to grow in both species through the isotropic expansion of cell apical area and the anisotropic cellular reorganization of the tissue. Remarkably, we find that the lengthening of the D. suzukii ovipositor compared to that of D. melanogaster results from the combination of the accelerated expansion of apical cell size and the enhanced anisotropic rearrangement of cells in the tissue. Therefore, the quantitative fine-tuning of morphogenetic processes can drive evolutionary changes in organ size and shape.

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D. suzukii has evolved a bigger egg-laying organ compared to D. melanogaster

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The inter-species size difference arises during a short development time window

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The fine-tuning of shared cellular processes drives this difference in morphogenesis

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The rate of cell apical area expansion and the tissue shape anisotropy have evolved

The fallacy of biphasic growth allometry for the vertebrate brain

The concept of biphasic, loglinear growth of the vertebrate brain is based on graphical displays of logarithmic transformations of the original measurements. Such displays commonly give the appearance of two distinct mathematical distributions – one set of observations following a steep trajectory at the low end of the size range and another set following a shallow trajectory at the high end. However, the appearance of two distributions is an artefact resulting from the logarithmic transformations. Observations of brain mass vs. body mass in each of the eight vertebrate species examined in the current investigation conform to a single mathematical distribution that is well described by a single equation fitted to the original, untransformed data by non-linear regression. Data for carp, chickens, kangaroos and rabbits are described by three-parameter power equations whereas those for dolphins and primates are described by exponential functions that rise rapidly to a maximum. The brain continues to grow throughout life in carp, chickens, kangaroos and rabbits but not in dolphins and primates. Future investigations of relative growth of the brain should be based on graphical and analytical study of observations expressed on the native mathematical scale.

Sexual dimorphism of the cuticle and body-wall muscle in free-living mycophagous nematodes

Sexual dimorphism in motility-related traits is widespread among animals, including several species of Nematoda. However, no study has examined motility-related structural components and compared them between sexes. We examined the motility-related components in four species: Bursaphelenchus conicaudatus Kanzaki, Tsuda and Futai, 2000; Bursaphelenchus rainulfi Braasch and Burgermeister, 2002; Bursaphelenchus doui Braasch, Gu, Burgermeister and Zhang, 2005; Parasitaphelenchus costati Kanzaki, Ekino, Ide, Masuya and Degawa, 2018. We measured the structure and amount of cuticle and body-wall muscles and estimated their relationship to body diameter or total cross-sectional area. Although no structural differences were observed in muscle, the relevant muscle area of B. doui and P. costati was significantly smaller in females than in males. This difference was greatest in P. costati. In all but B. doui, the relative cuticle thickness was significantly smaller in females than in males. Furthermore, only P. costati females had no striated basal zones in their cuticles; these are thought to be cross-linked proteins that provide strength to nematode cuticle during body movement. These results indicate that sexual dimorphism in motility-related structural components is present in P. costati and that females invest less energy in the components than do males.

Genome-wide association analysis uncovers variants for reproductive variation across dog breeds and links to domestication

BACKGROUND AND OBJECTIVES

The diversity of eutherian reproductive strategies has led to variation in many traits, such as number of offspring, age of reproductive maturity and gestation length. While reproductive trait variation has been extensively investigated and is well established in mammals, the genetic loci contributing to this variation remain largely unknown. The domestic dog, Canis lupus familiaris is a powerful model for studies of the genetics of inherited disease due to its unique history of domestication. To gain insight into the genetic basis of reproductive traits across domestic dog breeds, we collected phenotypic data for four traits, cesarean section rate, litter size, stillbirth rate and gestation length, from primary literature and breeders' handbooks.

METHODOLOGY

By matching our phenotypic data to genomic data from the Cornell Veterinary Biobank, we performed genome-wide association analyses for these four reproductive traits, using body mass and kinship among breeds as covariates.

RESULTS

We identified 12 genome-wide significant associations between these traits and genetic loci, including variants near CACNA2D3 with gestation length, MSRB3 and MSANTD1 with litter size, SMOC2 with cesarean section rate and UFM1 with stillbirth rate. A few of these loci, such as CACNA2D3 and MSRB3, have been previously implicated in human reproductive pathologies, whereas others have been associated with domestication-related traits, including brachycephaly (SMOC2) and coat curl (KRT71).

CONCLUSIONS AND IMPLICATIONS

We hypothesize that the artificial selection that gave rise to dog breeds also influenced the observed variation in their reproductive traits. Overall, our work establishes the domestic dog as a system for studying the genetics of reproductive biology and disease.

LAY SUMMARY

The genetic contributors to variation in mammalian reproductive traits remain largely unknown. We took advantage of the domestic dog, a powerful model system, to test for associations between genome-wide variants and four reproductive traits (cesarean section rate, litter size, stillbirth rate and gestation length) that vary extensively across breeds. We identified associations at a dozen loci, including ones previously associated with domestication-related traits, suggesting that selection on dog breeds also influenced their reproductive traits.

Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes

Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here we use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes.

The androgenic gland in male morphotypes of the Amazon River prawn Macrobrachium amazonicum (Heller, 1862)

Sexual differentiation and primary and secondary sexual characteristics in male crustaceans are modulated by hormones produced in the androgenic gland (AG). The AG is also responsible for the determination of morphotypes in caridean shrimps, such as Macrobrachium amazonicum that shows four morphotypes: translucent claw (TC), cinnamon claw (CC), green claw 1 (GC1) and green claw 2 (GC2). Here, we verified the anatomical, histological and ultrastructural characteristics of the AG in different morphotypes of this species with both amphidromous and hololimnetic life cycles. In submissive morphotypes (TC and CC), the AGs are reduced and concentrated in the terminal expansion of the distal portion of vasa deferentia (DVD), the ejaculatory ducts (ED). In dominant morphotypes (GC1 and GC2) these glands lie along the DVD and ED. Two morphological stages (I and II) were recorded for AG cells. In submissive morphotypes stage I cells predominated in the AGs, while in dominant morphotypes stage II cells were more common. AG cells in both stages were positive for proteins, confirming the protein nature of the secreted hormone. Stage I cells have abundant rough endoplasmic reticulum (RER) with numerous parallel cisternae, whereas in stage II cells, the cisternae of RER are highly dilated. Stage II cells do not produce secretory granules, but they undergo hypertrophy and the hormone release to hemolymph probably occurs by holocrine secretion. The AGs in TC, GC1 and GC2 morphotypes increase as the animals grow and are larger in GC1 males. On the other hand, AGs decrease in the CC morphotype as the animal grows. These differences are related to the type of reproductive strategy adopted by each morphotype. In M. amazonicum, the AGs show the same morphological, histochemical and ultrastructural patterns between the different life history populations.

Morphometric and meristic study of four freshwater fish species of river Ganga

The present study was carried out in Ganga River from Devprayag to Haridwar district of Uttarakhand to analyse morphometric measurement and meristic count of some selected fish species during April 2017 to March 2018. Specimens (20) of each fish species were collected from different zones of river Ganga and 24 morphometric measurements and eight meristic count parameters were studied for each fish species. The total length and weight of Cyprnius carpio ranged from 14–18 cm and 60–78 g; Mahseer fish species 21–28 cm and 120–185 g; 20–26 cm and 100–160 g (Labeo rohita) and 17–25 cm and 20–34 g (Xenentodon cancila) respectively were recorded during the study period. The regression coefficient ‘b’ shows higher growth rate with respect to Total length. It was maximum in case of standard length (b= 1.115) and lowest in pelvic fin length (b=0.146) for Cyprnius carpio, maximum in case of standard length (b=1.132) and lowest in pectoral fin length (b=0.126) for Mahseer, maximum in case of Fork and standard length (b=0.995) and lowest in length of caudal peduncle (b=0.135) for Labeo rohita and maximum in case of standard length (b=1.020) and lowest in case of pelvic fin length (b=0.018) for Xenentodon cancila respectively.

Sexual size and shape dimorphism in two ground beetle taxa, Carabus (Procrustes) coriaceus cerisyi and C. (Morphocarabus) kollari praecellens (Coleoptera: Carabidae) - A geometric morphometric approach

We investigated morphometric variation in size and shape of the head, pronotum, and abdomen between the taxa and sexes of two ground beetles, Carabus coriaceus cerisyi Dejean, 1826 and C. kollari praecellens Palliardi, 1825. These two taxa differ in overall size, and both of them are characterized by significant sexual size dimorphism. In many taxa, allometry, the relationship between changes in shape and changes in size, can be a major component of intra- and interspecific variation in body shape. In the present study, we applied landmark-based geometric morphometrics to explore allometric and non-allometric components of shape variation between the taxa and more importantly between sexes within the taxa. We were able to show that the differences of shape between the taxa cannot be explained by allometric changes, as allometry explains only a small amount of total shape variation between the taxa, which was expected due to the fact that the taxa belong to separate subgenera. Between the sexes, on the other hand, allometry contributes largely to the variation, particularly in abdomen shape. However, the differences of head and pronotum shape between the sexes cannot be entirely explained in terms of allometric scaling. Our results indicate that allometry contributes largely to differences of body shape between the sexes, while differences between the taxa are influenced by other factors and processes.

Pollinator size and its consequences: Robust estimates of body size in pollinating insects

Body size is an integral functional trait that underlies pollination-related ecological processes, yet it is often impractical to measure directly. Allometric scaling laws have been used to overcome this problem. However, most existing models rely upon small sample sizes, geographically restricted sampling and have limited applicability for non-bee taxa. Allometric models that consider biogeography, phylogenetic relatedness, and intraspecific variation are urgently required to ensure greater accuracy. We measured body size as dry weight and intertegular distance (ITD) of 391 bee species (4,035 specimens) and 103 hoverfly species (399 specimens) across four biogeographic regions: Australia, Europe, North America, and South America. We updated existing models within a Bayesian mixed-model framework to test the power of ITD to predict interspecific variation in pollinator dry weight in interaction with different co-variates: phylogeny or taxonomy, sexual dimorphism, and biogeographic region. In addition, we used ordinary least squares regression to assess intraspecific dry weight ~ ITD relationships for ten bees and five hoverfly species. Including co-variates led to more robust interspecific body size predictions for both bees and hoverflies relative to models with the ITD alone. In contrast, at the intraspecific level, our results demonstrate that the ITD is an inconsistent predictor of body size for bees and hoverflies. The use of allometric scaling laws to estimate body size is more suitable for interspecific comparative analyses than assessing intraspecific variation. Collectively, these models form the basis of the dynamic R package, "pollimetry," which provides a comprehensive resource for allometric pollination research worldwide.

Changes in ontogenetic patterns facilitate diversification in skull shape of Australian agamid lizards

BACKGROUND

Morphological diversity among closely related animals can be the result of differing growth patterns. The Australian radiation of agamid lizards (Amphibolurinae) exhibits great ecological and morphological diversity, which they have achieved on a continent-wide scale, in a relatively short period of time (30 million years). Amphibolurines therefore make an ideal study group for examining ontogenetic allometry. We used two-dimensional landmark-based geometric morphometric methods to characterise the postnatal growth patterns in cranial shape of 18 species of amphibolurine lizards and investigate the associations between cranial morphology, and life habit and phylogeny.

RESULTS

For most amphibolurine species, juveniles share a similar cranial phenotype, but by adulthood crania are more disparate in shape and occupy different sub-spaces of the total shape space. To achieve this disparity, crania do not follow a common post-natal growth pattern; there are differences among species in both the direction and magnitude of change in morphospace. We found that these growth patterns among the amphibolurines are significantly associated with ecological life habits. The clade Ctenophorus includes species that undergo small magnitudes of shape change during growth. They have dorsoventrally deep, blunt-snouted skulls (associated with terrestrial lifestyles), and also dorsoventrally shallow skulls (associated with saxicolous lifestyles). The sister clade to Ctenophorus, which includes the bearded dragon (Pogona), frill-neck lizard (Chlamydosaurus), and long-nosed dragon (Gowidon), exhibit broad and robust post-orbital regions and differing snout lengths (mainly associated with scansorial lifestyles).

CONCLUSIONS

Australian agamids show great variability in the timing of development and divergence of growth trajectories which results in a diversity of adult cranial shapes. Phylogenetic signal in cranial morphology appears to be largely overwritten by signals that reflect life habit. This knowledge about growth patterns and skull shape diversity in agamid lizards will be valuable for placing phylogenetic, functional and ecological studies in a morphological context.

Genetic and environmental effects on the scaling of metabolic rate with body size

Metabolic rate (MR) often scales with body mass (BM) following a power function of the form MR=aBMb, where b is the allometric exponent (i.e. slope on a log-log scale). The variational properties of b have been debated, but very few studies have tested for genetic variance in b, and none have tested for a genotype-by-environment (G×E) interaction in b. Consequently, the short-term evolutionary potentials of both b and its phenotypic plasticity remain unknown. Using 10 clones of a population of Daphnia magna, we estimated the genetic variance in b and assessed whether a G×E interaction affected b. We measured metabolic rate on juveniles of different sizes reared and measured at three temperatures (17, 22 and 28°C). Overall, b decreased with increasing temperature. We found no evidence of genetic variance in b at any temperature, and thus no G×E interaction in b. However, we found a significant G×E interaction in size-specific metabolic rate. Using simulations, we show how this G×E interaction can generate genetic variation in the ontogenetic allometric slope of animals experiencing directional changes in temperature during growth. This suggests that b can evolve despite having limited genetic variation at constant temperatures.

Reproduction and growth in a Neotropical arboreal mouse: Oecomys rutilus (Sigmodontinae: Cricetidae) in French Guiana

Abstract: Postnatal growth and development of the small Neotropical mouse Oecomys rutilus (Sigmodontinae: Cricetidae) were investigated from birth to day 143, in the laboratory. Morphometric measurements at age of 3 days, of both sexes combined, revealed body weight to be 3.4 ± 0.3 g, mean tail length as 27.4 ± 1.1 mm, and mean hind foot length as 9.3 ± 0.7 mm. Body weight was found to increase steadily until at least 69 days, whereas the instantaneous growth rates of other measurements declined earlier: the daily growth of hind foot length declined to a minimum at age of 24 days, and the growth of tail and of ear declined by the age of 33 days. Average litter size for 12 captive births was 2.5, ranging from 2 to 3. The preserved eye crystalline lens was weighted in 23 captive-born animals of known age, allowing a rough estimate of the age of reproduction in wild-caught animals. Based on the inferred relation between eye-lens weight and age, the youngest reproductive (pregnant) wild-caught females had an estimated age of 90 and 95 days.

Covariation of the endocranium and splanchnocranium during great ape ontogeny

That great ape endocranial shape development persists into adolescence indicates that the splanchnocranium succeeds brain growth in driving endocranial development. However, the extent of this splanchnocranial influence is unknown. We applied two-block partial least squares analyses of Procrustes shape variables on an ontogenetic series of great ape crania to explore the covariation of the endocranium (the internal braincase) and splanchnocranium (face, or viscerocranium). We hypothesized that a transition between brain growth and splanchnocranial development in the establishment of final endocranial form would be manifest as a change in the pattern of shape covariation between early and adolescent ontogeny. Our results revealed a strong pattern of covariation between endocranium and splanchnocranium, indicating that chimpanzees, gorillas, and orangutans share a common tempo and mode of morphological integration from the eruption of the deciduous dentition onwards to adulthood: a reflection of elongating endocranial shape and continuing splanchnocranial prognathism. Within this overarching pattern, we noted that species variation exists in magnitude and direction, and that the covariation between the splanchnocranium and endocranium is somewhat weaker in early infancy compared to successive age groups. When correcting our covariation analyses for allometry, we found that an ontogenetic signal remains, signifying that allometric variation alone is insufficient to account for all endocranial-splanchnocranial developmental integration. Finally, we assessed the influence of the cranial base, which acts as the interface between the face and endocranium, on the shape of the vault using thin-plate spline warping. We found that not all splanchnocranial shape changes during development are tightly integrated with endocranial shape. This suggests that while the developmental expansion of the brain is the main driver of endocranial shape during early ontogeny, endocranial development from infancy onwards is moulded by the splanchnocranium in conjunction with the neurocranium.

BmHpo mutation induces smaller body size and late stage larval lethality in the silkworm, Bombyx mori

As a core member of the Hippo signaling pathway, Hpo plays a critical role in regulating growth and development. Previous studies reported that loss of function of Hpo results in increased proliferation, reduced apoptosis and induction of tissue overgrowth in Drosophila. In this study, we used CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) to study Hpo gene (BmHpo) function in the lepidopteran insect Bombyx mori, known commonly as the silkworm. Sequence analysis of BmHpo revealed an array of deletions in mutants. We found that BmHpo knockout resulted in defects in body size regulation, in developmental defects and pigment accumulation and early death. Our data show that BmHpo is essential for regulation of insect growth and development and that CRISPR/Cas9 technology can serve as a basis for functional analysis of target genes in lepidopteran insects.

Why the long face? Static allometry in the sexually dimorphic phenotypes of Neotropical electric fishes

The evolution of sexually dimorphic traits is thought to have marked effects on underlying patterns of static allometry. These traits can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male–male interactions. We also estimate jaw-closing performance between the sexes of both species to track changes in kinematic transmission associated with the development of sexual weaponry. We find significantly different patterns of static allometry between the sexes of both species, with males exhibiting more positive allometric slopes relative to females. We also find a negative relationship between skull shape and mandibular kinematic transmission in C. samueli, suggesting a trade-off where males with longer faces exhibit lower mechanical advantages, suggesting weaker jaw leverage. In contrast, males and females of A. rostratus exhibit no difference between sexes in mechanical advantage associated with facial elongation.

Ecological and evolutionary implications of allometric growth in stomach size of brachyuran crabs

Individual characteristics often scale allometrically with organismal body size and the form of this scaling can be influenced by ecological and evolutionary factors. Examining the specific form of this scaling can therefore yield important insights into organismal ecology and evolution and the ability of organisms to respond to future environmental changes. We examine the intraspecific allometric scaling of stomach volume with body mass for 17 species of brachyuran crabs. We also examine how this scaling is influenced by dietary strategy, maximum body size, and activity level, all while controlling for phylogenetic relationships between the species. We show that the slope and intercept of the allometric scaling relationships vary across species and are influenced by all three ecological factors examined here, as well as by evolutionary relationships. These results highlight potential divergent strategies in stomach growth taken by different groups of crabs and highlight potential limitations that may be imposed on the ability of this group of organisms to respond to warming trends expected with climate change.

Clade-specific evolutionary diversification along ontogenetic major axes in avian limb skeleton

The evolutionary diversification of birds has been facilitated by specializations for various locomotor modes, with which the proportion of the limb skeleton is closely associated. However, recent studies have identified phylogenetic signals in this system, suggesting the presence of historical factors that have affected its evolutionary variability. In this study, to explore potential roles of ontogenetic integration in biasing the evolution in the avian limb skeleton, evolutionary diversification patterns in six avian families (Anatidae, Procellariidae, Ardeidae, Phalacrocoracidae, Laridae, and Alcidae) were examined and compared to the postnatal ontogenetic trajectories in those taxa, based on measurement of 2641 specimens and recently collected ontogenetic series, supplemented by published data. Morphometric analyses of lengths of six limb bones (humerus, ulna, carpometacarpus, femur, tibiotarsus, and tarsometatarsus) demonstrated that: (1) ontogenetic trajectories are diverse among families; (2) evolutionary diversification is significantly anisotropic; and, most importantly, (3) major axes of evolutionary diversification are correlated with clade-specific ontogenetic major axes in the shape space. These results imply that the evolutionary variability of the avian limbs has been biased along the clade-specific ontogenetic trajectories. It may explain peculiar diversification patterns characteristic to some avian groups, including the long-leggedness in Ardeidae and tendency for flightlessness in Anatidae.

A sustained change in the supply of parental care causes adaptive evolution of offspring morphology

Although cooperative social interactions within species are considered an important driver of evolutionary change, few studies have experimentally demonstrated that they cause adaptive evolution. Here we address this problem by studying the burying beetle Nicrophorus vespilloides. In this species, parents and larvae work together to obtain nourishment for larvae from the carrion breeding resource: parents feed larvae and larvae also self-feed. We established experimentally evolving populations in which we varied the assistance that parents provided for their offspring and investigated how offspring evolved in response. We show that in populations where parents predictably supplied more care, larval mandibles evolved to be smaller in relation to larval mass, and larvae were correspondingly less self-sufficient. Previous work has shown that antagonistic social interactions can generate escalating evolutionary arms races. Our study shows that cooperative interactions can yield the opposite evolutionary outcome: when one party invests more, the other evolves to invest less.

The amount and predictability of parental care may influence the evolution of offspring traits. Here, the authors experimentally evolve burying beetles at different levels of parental care and find smaller mandibles and lower self-sufficiency in populations with more care.

The ontogenetic scaling of form and function in the spotted ratfish, Hydrolagus colliei (Chondrichthyes: Chimaeriformes): Fins, muscles, and locomotion

The alteration of form and function through the life of a fish can have profound impacts on the ability to move through water. Although several studies have examined morphology and function in relation to body size, there is a paucity of data for chondrichthyans, an ancient group of fishes. Ratfishes are interesting in that they utilize flapping pectoral fins to drive movement, and they diverged from elasmobranchs early in the gnathostome phylogeny. Using the spotted ratfish, Hydrolagus colliei, we quantified the scaling of traits relevant for locomotion, including median and paired fin external anatomy, the musculature of the pectoral and pelvic fins, and the kinematics of the pectoral fins. Whereas pelvic fins scaled with either positive allometry (fin span and area) or isometry (fin chord length at the base of the fin), pectoral fin measurements either scaled with negative allometry (fin span and aspect ratio) or isometry (fin area and chord length). Correspondingly, all pelvic fin muscles exhibited positive allometry, whereas pectoral muscles exhibited a mix of isometric and positively allometric growth. Caudal fin area and body frontal area both scaled with positive allometry, whereas dorsal fin area and span scale with isometry. Pectoral fin amplitude during swimming exhibited isometry, and fin beat frequency decreased with body size. Our results highlight the complex changes in form and function throughout ontogeny. Finally, we highlight that hierarchical differentiation in morphology can occur during growth, potentially leading to complex changes in performance of a functional system.

Geometric morphometric analyses of sexual dimorphism and allometry in two sympatric snakes: Natrix helvetica (Natricidae) and Vipera berus (Viperidae)

The non-venomous grass snake (Natrix helvetica) and the venomous adder (Vipera berus) are two native species that are often found in sympatry in Great Britain and Europe. They occupy partially overlapping ecological niches and prey on small vertebrates, but use different feeding strategies. Here, we investigated the morphologies of grass snakes and adders from Dorset (UK) using two-dimensional geometric morphometrics to assess the degree of sexual dimorphism in size and shape together with the relative impact of allometry and general body dimensions on head shape. Both species showed significant sexual dimorphism in head size, but not in head shape. We found a clear allometric pattern in N. helvetica, whereas allometry in V. berus was generally less pronounced. Body dimensions were strongly correlated with head shape in the grass snake, but not in the adder. The fact that V. berus is venomous appears to explain the lack of allometric patterns and the lack of an association between body dimensions and head shape. The high degree of size dimorphism identified in both species could originate from the advantages of reduced intraspecific competition that are conveyed by a partial differentiation in feeding morphology.

The Fate of the Method of 'Paradigms' in Paleobiology

An earlier article described the mid-twentieth century origins of the method of "paradigms" in paleobiology, as a way of making testable hypotheses about the functional morphology of extinct organisms. The present article describes the use of "paradigms" through the 1970s and, briefly, to the end of the century. After I had proposed the paradigm method to help interpret the ecological history of brachiopods, my students developed it in relation to that and other invertebrate phyla, notably in Euan Clarkson's analysis of vision in trilobites. David Raup's computer-aided "theoretical morphology" was then combined with my functional or adaptive emphasis, in Adolf Seilacher's tripartite "constructional morphology." Stephen Jay Gould, who had strongly endorsed the method, later switched to criticizing the "adaptationist program" he claimed it embodied. Although the explicit use of paradigms in paleobiology had declined by the end of the century, the method was tacitly subsumed into functional morphology as "biomechanics."

Female status, food security, and stature sexual dimorphism: Testing mate choice as a mechanism in human self-domestication

OBJECTIVES

Humans exhibit multiple anatomical and behavioral signatures of domestication syndrome, leading evolutionary-minded scholars to suggest Homo sapiens is a "self-domesticated" species. We examined one of three mechanisms proposed to explain human self-domestication-that is, intersexual selection against reactive aggression. We hypothesized that this process has been, at least in part, caused by context-dependent female preferences for less-aggressive males. We predicted that societies where women have higher social status will show relatively elevated signs of self-domestication-as indicated by lower stature sexual dimorphism (SSD)-and that this relationship should be mediated by food security.

MATERIALS AND METHODS

To test our prediction, we used male and female stature data for 28 societies from the Standard Cross-Cultural Sample. We applied multivariate regression to examine our hypothesis while controlling for theoretically important confounders.

RESULTS

We found convincing support for the prediction that the relationship between SSD and female status is mediated by food security. As predicted, higher female status was associated with less sexual dimorphism and the effect is stronger when food resources are secure.

DISCUSSION

Context-dependent female mate choices significantly contribute to lower SSD, suggesting female mate choice is likely to have played an influential role in human self-domestication. Future research on this theme will benefit by including more of the expected symptoms of human self-domestication and examining other potential drivers of this process.

Where does diversity come from? Linking geographical patterns of morphological, genetic, and environmental variation in wall lizards

BACKGROUND

Understanding how phenotypic variation scales from individuals, through populations, up to species, and how it relates to genetic and environmental factors, is essential for deciphering the evolutionary mechanisms that drive biodiversity. We used two species of Podarcis wall lizards to test whether phenotypic diversity within and divergence across populations follow concordant patterns, and to examine how phenotypic variation responds to genetic and environmental variability across different hierarchical levels of biological organization, in an explicit geographic framework.

RESULTS

We found a general concordance of phenotypic variation across hierarchical levels (i.e. individuals and populations). However, we also found that within-population diversity does not exhibit a coherent geographic structure for most traits, while among-population divergence does, suggesting that different mechanisms may underlie the generation of diversity at these two levels. Furthermore, the association of phenotypic variation with genetic and environmental factors varied extensively between hierarchical levels and across traits, hampering the identification of simple rules to explain what yields diversity.

CONCLUSIONS

Our results in some cases comply with general ecological and evolutionary predictions, but in others they are difficult to explain in the geographic framework used, suggesting that habitat characteristics and other regulatory mechanisms may have a more substantial contribution in shaping phenotypic diversity.

Misconceptions and issues regarding allometric scaling during the drug development process

INTRODUCTION

Allometry is the study of size and its consequences. The simple hypothesis of allometric scaling is that all physiological parameters are proportional to body size or body mass. This review examines the development of theory-based allometry or fixed exponents (0.75 and 1.0 for basal metabolic rate and volume, respectively) and the evidence for or against the theory. The main focus of this report is to show the readers that there is enough evidence from experimental data that negate the concept of theory-based allometry in biology, physiology, and pharmacokinetics. Areas covered: In this review, the history of the development of theoretical allometry and the strong evidence against theory-based allometry demonstrated by experimental data is provided. During drug development, allometry is applied to both inter-species (from animals to humans) and intra-species (adults to children) scaling. These two forms of allometric scaling in the context of theory-based allometry are discussed and provide insight on scientific progress that refute theory-based allometry. Expert opinion: Theory-based allometry is a mere theory and experimental data and real-life observations strongly negate the existence of such a theory. Pharmacostatistical and physiological models based on theory-based allometry can be misleading and incorrect because the theory-based allometric exponent 0.75 is not universal. The exponents of allometry are data dependent and are not fixed in the universe.

Bioelectric-calcineurin signaling module regulates allometric growth and size of the zebrafish fin

The establishment of relative size of organs and structures is paramount for attaining final form and function of an organism. Importantly, variation in the proportions of structures frequently underlies adaptive change in morphology in evolution and maybe a common mechanism underlying selection. However, the mechanism by which growth is integrated within tissues during development to achieve proper proportionality is poorly understood. We have shown that signaling by potassium channels mediates coordinated size regulation in zebrafish fins. Recently, calcineurin inhibitors were shown to elicit changes in zebrafish fin allometry as well. Here, we identify the potassium channel kcnk5b as a key player in integrating calcineurin’s growth effects, in part through regulation of the cytoplasmic C-terminus of the channel. We propose that the interaction between Kcnk5b and calcineurin acts as a signaling node to regulate allometric growth. Importantly, we find that this regulation is epistatic to inherent mechanisms instructing overall size as inhibition of calcineurin is able to bypass genetic instruction of size as seen in sof and wild-type fins, however, it is not sufficient to re-specify positional memory of size of the fin. These findings integrate classic signaling mediators such as calcineurin with ion channel function in the regulation of size and proportion during growth.

Arabidopsis phenotyping through geometric morphometrics

Background

Recently, great technical progress has been achieved in the field of plant phenotyping. High-throughput platforms and the development of improved algorithms for rosette image segmentation make it possible to extract shape and size parameters for genetic, physiological, and environmental studies on a large scale. The development of low-cost phenotyping platforms and freeware resources make it possible to widely expand phenotypic analysis tools for Arabidopsis. However, objective descriptors of shape parameters that could be used independently of the platform and segmentation software used are still lacking, and shape descriptions still rely on ad hoc or even contradictory descriptors, which could make comparisons difficult and perhaps inaccurate. Modern geometric morphometrics is a family of methods in quantitative biology proposed to be the main source of data and analytical tools in the emerging field of phenomics studies. Based on the location of landmarks (corresponding points) over imaged specimens and by combining geometry, multivariate analysis, and powerful statistical techniques, these tools offer the possibility to reproducibly and accurately account for shape variations among groups and measure them in shape distance units.

Results

Here, a particular scheme of landmark placement on Arabidopsis rosette images is proposed to study shape variation in viral infection processes. Shape differences between controls and infected plants are quantified throughout the infectious process and visualized. Quantitative comparisons between two unrelated ssRNA+ viruses are shown, and reproducibility issues are assessed.

Conclusions

Combined with the newest automated platforms and plant segmentation procedures, geometric morphometric tools could boost phenotypic features extraction and processing in an objective, reproducible manner.

Allometric shell growth in infaunal burrowing bivalves: examples of the archiheterodonts Claibornicardia paleopatagonica (Ihering, 1903) and Crassatella kokeni Ihering, 1899

We present two cases of study of ontogenetic allometry in outlines of bivalves using longitudinal data, a rarity among fossils, based on the preserved post-larval record of shells. The examples are two infaunal burrowing bivalves of the southern South America, Claibornicardia paleopatagonica (Archiheterodonta: Carditidae) (early Paleocene) and Crassatella kokeni (Archiheterodonta: Crassatellidae) (late Oligocene-late Miocene). Outline analyses were conducted using a geometric morphometric approach (Elliptic Fourier Analysis), obtaining successive outlines from shells' growth lines, which were used to reconstruct ontogenetic trajectories. In both taxa, ontogenetic changes are characterized by the presence of positive allometry in the extension of posterior end, resulting in elongated adult shells. This particular allometric growth is known in others infaunal burrowing bivalves (Claibornicardia alticostata and some Spissatella species) and the resulting adult morphology is present in representatives of several groups (e.g., Carditidae, Crassatellidae, Veneridae, Trigoniidae). Taxonomic, ecological and evolutionary implications of this allometric growth pattern are discussed.

Size Exponents for Scaling Maximal Oxygen Uptake in Over 6500 Humans: A Systematic Review and Meta-Analysis

BACKGROUND

Maximal oxygen uptake ([Formula: see text] _2max) is conventionally normalized to body size as a simple ratio or using an allometric exponent < 1. Nevertheless, the most appropriate body size variable to use for scaling and the value of the exponent are still enigmatic. Studies tend to be based on small samples and can, therefore, lack precision.

OBJECTIVE

The objective of this systematic review was to provide a quantitative synthesis of reported static allometric exponents used for scaling [Formula: see text] _2max to whole body mass and fat-free mass.

METHODS

Eight electronic databases (CINAHL, Cochrane Central Register of Controlled Trials, EMBASE, MEDLINE, PubMed, Scopus, SPORTDiscus and Web of Science) were searched for relevant studies published up to January 2016. Search terms included 'oxygen uptake', 'cardiorespiratory fitness', '[Formula: see text] _2max', '[Formula: see text] _2peak', 'scaling' and all interchangeable terms. Inclusion criteria included human cardiorespiratory fitness data; cross-sectional study designs; an empirical derivation of the exponent; reported precision statistics; and reported information regarding participant sex, age and sports background, [Formula: see text] _2max protocol, whole body composition protocol and line-fitting methods. A random-effects model was used to quantify weighted pooled exponents and 95% confidence limits (Cls). Heterogeneity was quantified with the tau-statistic (τ). Meta-regression was used to quantify the impact of selected moderator variables on the exponent effect size. A 95% prediction interval was calculated to quantify the likely range of true fat-free mass exponents in similar future studies, with this distribution used to estimate the probability that an exponent would be above theorised universal values of [Formula: see text].

RESULTS

Thirty-six studies, involving 6514 participants, met the eligibility criteria. Whole body mass and fat-free mass were used as the scaling denominator in 27 and 15 studies, respectively. The pooled allometric exponent (95% Cls) was found to be 0.70 (0.64 to 0.76) for whole body mass and 0.90 (0.83 to 0.96) for fat-free mass. The between-study heterogeneity was greater for whole body mass (τ = ±0.15) than for fat-free mass (τ = ±0.11). Participant sex explained 30% of the between-study variability in the whole body mass exponent, but the influence on the fat-free mass exponent was trivial. The whole body mass exponent of 0.52 (0.40 to 0.64) for females was substantially lower than the 0.76 (0.70 to 0.83) for males, whereas the fat-free mass exponent was similar for both sexes. The effects of all other moderators were trivial. The 95% PI for fat-free mass ranged from 0.68 to 1.12. The estimated probability of a true fat-free mass exponent in a future study being greater than [Formula: see text] power scaling is 0.98 (very likely) and 0.92 (likely), respectively.

CONCLUSIONS

In this quantitative synthesis of published studies involving over 6500 humans, the whole body mass exponent was found to be spuriously low and prone to substantial heterogeneity. We conclude that the scaling of [Formula: see text] _2max in humans is consistent with the allometric cascade model with an estimated prediction interval for the fat-free mass exponent not likely to be consistent with the [Formula: see text] power laws.

Neural crest and the origin of species-specific pattern

For well over half of the 150 years since the discovery of the neural crest, the special ability of these cells to function as a source of species-specific pattern has been clearly recognized. Initially, this observation arose in association with chimeric transplant experiments among differentially pigmented amphibians, where the neural crest origin for melanocytes had been duly noted. Shortly thereafter, the role of cranial neural crest cells in transmitting species-specific information on size and shape to the pharyngeal arch skeleton as well as in regulating the timing of its differentiation became readily apparent. Since then, what has emerged is a deeper understanding of how the neural crest accomplishes such a presumably difficult mission, and this includes a more complete picture of the molecular and cellular programs whereby neural crest shapes the face of each species. This review covers studies on a broad range of vertebrates and describes neural-crest-mediated mechanisms that endow the craniofacial complex with species-specific pattern. A major focus is on experiments in quail and duck embryos that reveal a hierarchy of cell-autonomous and non-autonomous signaling interactions through which neural crest generates species-specific pattern in the craniofacial integument, skeleton, and musculature. By controlling size and shape throughout the development of these systems, the neural crest underlies the structural and functional integration of the craniofacial complex during evolution.

Physical Growth, Body Scale, and Perceptual-Motor Development

In this chapter we consider from the theoretical framework of the ecological approach to perception and action, the relations between physical growth and body scale in the context of children's perceptual-motor development. Body scale and the timescale of its change through growth are shown to relate to the emergence and dissolution of the fundamental skills in infancy, the perception of what an environment affords functionally for action, together with the emergent pattern of movement coordination. A central issue in typical and atypical motor development is the mapping of the timescale of adaptive change in the acquisition of perceptual-motor skill to the accompanying timescale of change in physical growth.

Internal head morphology of minor workers and soldiers in the hyperdiverse ant genus Pheidole

In the hyperdiverse ant genus Pheidole Westwood, 1839, the worker caste evolved into two morphologically distinct subcastes: minor workers and soldiers. The evolution of soldiers, which are larger in size than minor workers and have disproportionately larger heads, are thought to be key to Phediole’s success. Although many studies have focused on external anatomy, little is known about their internal anatomy. We therefore used microCT imaging and quantitative three-dimensional image analysis to reconstruct the major glands of the head, the musculature, nervous system, and digestive organ of minor workers and soldiers of four Pheidole species. We expected these tissues to scale isometrically and to be proportionally larger in soldiers relative to the minor workers. Surprisingly, we found that the nervous system, cephalic gland, and digestive organ volume are absolutely and relatively smaller in soldiers, whereas muscle volume is absolutely and relatively larger, than in minor workers. This may reflect individual-level trade-offs, where muscles grow at the expense of all other cephalic organs. Alternatively, this relationship may reflect the specialization of internal anatomy in each subcaste to enhance division of labour at the colony level. Future studies should test these alternative hypotheses across a larger number of Pheidole species.