Spatial and Seasonal Plasticity in Digestive Morphology of Cavies (Microcavia australis) Inhabiting Habitats with Different Plant Qualities

Geographic Variation in Organ Size in a Toad (Duttaphrynus melanostictus)

Adaptive evolution is the process by which organisms change their morphological, physiological and biochemical characteristics to adapt to different environments during long-term natural selection. Especially, researching variation in organ size can provide important insights into morphological adaptation in amphibians. In this study, we comparatively studied differences in organ sizes (heart, lungs, liver, gallbladder, kidneys, spleen, digestive tract, testes and brain) among five geographical populations of the Asian common toad Duttaphrynus melanostictus. Our results revealed significant variations in the size of these nine specific organs among the populations. Notably, we observed a significant positive correlation between the relative size of the testes and latitude and/or altitude. However, no correlation was found between the relative size of the heart and the length of the digestive tract with altitude across populations, respectively, contradicting Hesse's rule and the digestion theory. These findings suggest that our study does not provide substantial theoretical support for the adaptive evolution of organ size in this particular toad species, but rather contributes to the understanding of the evolution and adaptations of species' different environmental conditions. Further research is warranted to delve deeper into the factors influencing organ size in amphibian populations.

Evolutionary and plastic variation in larval growth and digestion reveal the complex underpinnings of size and age at maturation in dung beetles

Age and size at maturity are key life-history components, yet the proximate underpinnings that mediate intra- and interspecific variation in life history remain poorly understood. We studied the proximate underpinnings of species differences and nutritionally plastic variation in adult size and development time in four species of dung beetles. Specifically, we investigated how variation in insect growth mediates adult size variation, tested whether fast juvenile growth trades-off with developmental stability in adult morphology and quantified plastic responses of digestive systems to variation in food quality. Contrary to the common size-development time trade-off, the largest species exhibited by far the shortest development time. Correspondingly, species diverged strongly in the shape of growth trajectories. Nutritionally plastic adjustments to growth were qualitatively similar between species but differed in magnitude. Although we expected rapid growth to induce developmental costs, neither instantaneous growth rates nor the duration of larval growth were related to developmental stability in the adult. This renders the putative costs of rapid growth enigmatic. We further found that larvae that encounter a challenging diet develop a larger midgut and digest more slowly than animals reared on a more nutritious diet. These data are consistent with the hypothesis that larvae invest into a more effective digestive system when exposed to low-quality nutrition, but suggest that species may diverge readily in their reliance on these mechanisms. More generally, our data highlight the complex, and often hidden, relationships between immature growth and age and size at maturation even in ecologically similar species.

Comparative Features of the Upper Alimentary Tract in the Domestic Fowl (Gallus gallus domesticus) and Kestrel (Falco tinnunculus): A Morphological, Histochemical, and Scanning Electron Microscopic Study

The avian alimentary tract has evolved into different histologic structures to accommodate the physical and chemical features of several food types and flight requirements. We compared the esophagus, proventriculus, and gizzard of the domestic fowl, Gallus gallus domesticus (GGD) and kestrels, Falco tinnunculus (FT) using immunohistochemistry and scanning electron microscopy with various stains and lectins [Dolichos biflorus agglutinin (DBA) and Ricinus communis agglutinin I (RCA120)], and α-smooth muscle actin (α-SMA). The esophagus of GGD demonstrated thickened epithelium, muscularis mucosae, and inner circular longitudinal tunica muscularis layers; moderate outer longitudinal tunica muscularis layers; and a true crop. In contrast, the esophagus of FT showed a thin epithelium, no muscularis mucosae, moderate inner longitudinal and thick outer circular tunica muscularis layers, and no true crop. In the proventriculus, the nature of the secretion in GGD was neutral, but that of FT was acidic and neutral. In the gizzard, the muscle coat of GGD by α-SMA had no muscularis mucosae, unlike FT, which had muscularis mucosae. In summary, there are many histologic differences between GGD and FT to meet their different physiologic needs, such as feeding.

Anatomical, histological and biochemical studies of desert rodent Gerbillus tarabuli (Thomas, 1902) kidney

The present work aimed to study the anatomy, histology, cytology and some biochemical parameters (urea, osmolality, haematocrit, serum natrium, serum kalium) of the kidney of Gerbillus tarabuli. The investigated animals (n = 16) were collected from the desert, weighed and transferred alive to the laboratory in separate cages. A blood sample was taken by puncture at the retro-orbital sinus of each animal using a Pasteur-type capillary pipette capillary. They were anaesthetized with urethane injection (25%), after which they were carefully dissected; their organs were taken out and prepared for the histological and cytological studies. Pasteur pipette capillary type the kidney of the Gerbillus tarabuli is subdivided into three regions: Cortex (1193.625±60μm), Outer Medulla (1316.72±73μm), Inner Medulla (2525.08±85 μm). Pasteur pipette capillary type the kidney of the Gerbillus tarabuli is subdivided into three regions: Cortex (1193.625±60μm), Outer Medulla (1316.72±73μm), Inner Medulla (2525.08±85 μm). The concentration of the biochemical parameters of urea (0.41 ± 0.02 g/L), osmolality (300.75 ± 3.33 mOs/kg), haematocrit (34.18 ± 1.3%), serum natrium (141.37 ± 2.31 mmol/L) and serum kalium (7.69 ± 0.39 mmol/L) is in the interval of the norm compared with several studies on desert and semi-desert rodents and also on the Wistar rat. These findings revealed the adaptive morphology and physiological function in the kidney of G. tarabuli to the desert environment.

Integration and diversity of the caviomorph mandible (Rodentia: Hystricomorpha): assessing the evolutionary history through fossils and ancestral shape reconstructions

Caviomorph rodents constitute a highly diverse clade of Neotropical mammals. They are recorded since at least the late Middle Eocene and have a long and complex evolutionary history. Using geometric morphometric data, we analysed the variation in mandibular shape of this clade through integration analyses, allometry and shape optimizations onto a phylogenetic tree of 104 extant and extinct species. The analyses of shape variation revealed a strong influence of phylogenetic structure and life habits. A remarkable allometric effect was observed for specific mandibular traits. Morphological changes occurring in the alveolar and muscular functional units were moderately associated. Interestingly, the coordinated evolution of these two functional units was decoupled in the clade of extant abrocomids. A sequential and nearly synchronic acquisition of convergent traits has occurred in chinchillids and derived cavioids since at least the early Middle Oligocene, probably derived from grass-feeding habits or similar adaptations to other abrasive items. Convergences between fossorial taxa evolved in two main events through the Oligocene and middle Late Miocene. Morphological analysis of the fossil representatives allowed a better understanding of the timing of trait acquisitions during the evolutionary history of caviomorphs and its relationship with global and regional palaeoenvironmental changes.

Dialium seed coprophagy in wild western gorillas: Multiple nutritional benefits and toxicity reduction hypotheses

Unraveling the relationship between the unusual feeding behaviors and the nutritional intake of endangered species may provide crucial information for understanding species response to habitat unpredictable changes. Primates occasionally re-ingest fruit seeds alongside ingestion of feces, a behavior called coprophagy. The nutritional benefit is one of the several non-mutual exclusive hypotheses proposed to explain this behavior. We investigated the ecological correlates of coprophagy in wild western gorillas. We tested whether coprophagy occurred during periods of lower fruit availability and whether it led to higher nutrient intake in comparison to the other food. Data integrated phenological, fecal and nutritional analyses of gorilla food with behavioral observations collected at two sites in Central Africa (Mbeli Bai: ad libitum observations on 15 groups/solitary males, October 2002-November 2005; Bai Hokou: 5-min scan on a habituated group, December 2004-December 2005). Coprophagy occurred at the end of the high-fruiting season in association of two Dialium species. Coprophagy correlated positively with the occurrence of Dialium spp. fruit in gorilla feces and in the feeding scans, and showed a positive trend with Dialium availability but not with total fruit availability. Nutritional comparison of Dialium seeds with other important gorilla food showed higher fat and mineral content, particularly of Mg, but also of phenols and tannins in Dialium seeds. We discuss how the effect of gut processing and gut heat via coprophagy may act as cooking-like effect: increasing the ability to maximize nutrient intake by concurrently softening fibers and decreasing the toxic effect of antifeedants, like in human traditional cooking. Our results support both the multiple nutritional benefit hypothesis and the toxicity reduction hypothesis. Since Dialium is precious timber, the importance of this tree for the critically endangered western gorillas should be taken with high consideration when planning controlled logging of degraded forests or in face of habitat changes.

Developmental plasticity: re-conceiving the genotype

In recent decades, the phenotype of an organism (i.e. its traits and behaviour) has been studied as the outcome of a developmental 'programme' coded in its genotype. This deterministic view is implicit in the Modern Synthesis approach to adaptive evolution as a sorting process among genetic variants. Studies of developmental pathways have revealed that genotypes are in fact differently expressed depending on environmental conditions. Accordingly, the genotype can be understood as a repertoire of potential developmental outcomes or norm of reaction. Reconceiving the genotype as an environmental response repertoire rather than a fixed developmental programme leads to three critical evolutionary insights. First, plastic responses to specific conditions often comprise functionally appropriate trait adjustments, resulting in an individual-level, developmental mode of adaptive variation. Second, because genotypes are differently expressed depending on the environment, the genetic diversity available to natural selection is itself environmentally contingent. Finally, environmental influences on development can extend across multiple generations via cytoplasmic and epigenetic factors transmitted to progeny individuals, altering their responses to their own, immediate environmental conditions and, in some cases, leading to inherited but non-genetic adaptations. Together, these insights suggest a more nuanced understanding of the genotype and its evolutionary role, as well as a shift in research focus to investigating the complex developmental interactions among genotypes, environments and previous environments.

The role of dietary fiber content on energy metabolism, thermogenesis, and leptin in Chevrier’s field mouse (Apodemus chevrieri)

Food quality and availability are important factors influencing the survival and reproduction of animals. The aim of the present study was to examine the effect of dietary fiber content high-fiber (HF) diet treatment or low-fiber (LF) diet treatment) on energy metabolism, thermogenesis, and leptin concentrations in Chevrier’s field mouse (Apodemus chevrieri (Milne-Edwards, 1868)) (Mammalia: Rodentia: Muridae). Mice on the HF treatment showed a lower body mass compared with LF treatment from day 27 to day 37, and a lower but insignificant body mass to day 71. Dry matter intake (DMI) and gross energy intake (GEI) were greater in HF compared with LF, whereas the digestible energy intake (DEI) was similar for both treatments. Nonshivering thermogenesis (NST) decreased in HF mice, whereas LF mice remained stable; no significant differences were detected in the basal metabolic rate (BMR), uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT), or the levels of serum tri-iodothyronine (T3) and thyroxine (T4) between HF and LF mice. Although there were no differences in body fat content and serum leptin concentrations between HF and LF mice, serum leptin levels were positively correlated with body fat mass. These results support the hypothesis that A. chevrieri can compensate the poor-quality diet physiologically by way of increasing food intake and decreasing thermogenesis.

Characterization and selection of microhabitat of Microcavia australis (Rodentia: Caviidae): first data in a rocky habitat in the hyperarid Monte Desert of Argentina

A rocky habitat, in its broadest sense, may be described as any locality that contains boulders, rocks, scree, pebbles, outcrops, cliffs, or caves. In these habitats, mammals find shelter sites that they use as nesting sites or dens to raise their young in a stable microclimate that is relatively secure from predators. The aim of this study was to characterize and evaluate the microhabitat selection by the southern mountain cavy (

Renal intraspecific variation along an aridity gradient detected by new renal indices in a desert herbivorous rodent

Mammals that live in arid and semi-arid environments in South America present physiological mechanisms that enable them to conserve water. Body water is lost through the kidneys, lungs, skin, and intestines. Regarding renal adaptation for water conservation, several indices have been used to estimate the capacity of the kidneys to produce a maximum urine concentration. Most studies were conducted at an inter-specific level, with only few performed at the intraspecific level. In this work, we compare renal function and morphology among five populations of Southern mountain cavy, Microcavia australis, present along an aridity gradient. We hypothesized that individuals from drier zones would present morphological and functional renal modifications that imply a greater capability to conserve body water. These features were studied considering the classical indices (RMT, PMT, PMA, and RMA) and three new indices that consider area measurements; the latter showed to be more adequate to reflect intraspecific differences. Our results suggest that the morphological modifications of kidneys, that is, the greater areas of renal inner medulla, would be related to the aridity gradient where populations of Southern mountain cavy occur.

Contrasting patterns of morphological variation with dietary preferences in Micropogonias furnieri: insights from stable-isotope and digestive-trait analyses

The dietary preferences of populations of whitemouth croaker Micropogonias furnieri, which commonly inhabit estuarine and oceanic environments of the south-western Atlantic Ocean, were investigated using stable-isotope analysis and digestive traits, and compared with previous genetic and morphometric surveys of this species. Isotopic and C:N-derived data suggested that individuals from coastal lagoons are the most differentiated from the remaining localities surveyed. In contrast, the analysis of the digestive traits did not show the same differentiation pattern. The overall correlation between isotopic, molecular and morphological variations suggests that genetic and phenotypic differences among populations are accompanied by differential resource use, supporting the idea that selective forces could be playing an important role in population differentiation.

Influence of photoperiod on hormones, behavior, and immune function

Photoperiodism is the ability of plants and animals to measure environmental day length to ascertain time of year. Central to the evolution of photoperiodism in animals is the adaptive distribution of energetically challenging activities across the year to optimize reproductive fitness while balancing the energetic tradeoffs necessary for seasonally-appropriate survival strategies. The ability to accurately predict future events requires endogenous mechanisms to permit physiological anticipation of annual conditions. Day length provides a virtually noise free environmental signal to monitor and accurately predict time of the year. In mammals, melatonin provides the hormonal signal transducing day length. Duration of pineal melatonin is inversely related to day length and its secretion drives enduring changes in many physiological systems, including the HPA, HPG, and brain-gut axes, the autonomic nervous system, and the immune system. Thus, melatonin is the fulcrum mediating redistribution of energetic investment among physiological processes to maximize fitness and survival.

Membrane-bound intestinal enzymes of passerine birds: dietary and phylogenetic correlates

Bird species exhibit great diversity in digestive tract morphology and enzymatic activity that is partly correlated with the chemical composition of their natural diets. However, no studies have assessed whether the activities of digestive enzymes of the enterocytes correlate with dietary chemical composition data analyzed as a continuous variable at an evolutionary scale. We used a phylogenetically explicit approach to examine the effect of diet on the hydrolytic activity of three digestive enzymes (maltase, sucrase, and aminopeptidase-N) in 16 species of songbirds (Order Passeriformes) from Central Chile. The total activities (μmol/min) of these enzymes were positively associated with body mass using both conventional least squares regressions and phylogenetically independent contrasts. After removing mass effects, we found a significant negative correlation between the ratio of aminopeptidase-N and maltase to the proportion of seeds found in the gizzard, but this relationship was no longer significant after controlling for phylogeny. When we analyzed the specific nutritional content of the diet, we found that the percentage of nitrogen in diet was negatively correlated with residual maltase activity and positively correlated with the ratio aminopeptidase-N/maltase. Given the large interspecific differences in biochemical capacity, we conclude that these differences reflect genetically determined evolutionary changes associated with the nutrient contents of each species' natural diet.

Between-population differences in digestive flexibility in the olivaceous field mouse

The flexibility of digestive traits characterizes a standard model of physiological flexibility, demonstrating that animals adjust their digestive attributes in order to maximize overall energy return. Using an intraspecific experimental study, we evaluated the amount of flexibility in digestive tract mass and length in individuals from field mouse populations inhabiting semi-arid and temperate rain forest habitats and acclimated for six months to diets of different qualities. In accordance with the predictions of the theory of digestion, we observed a highly significant relationship between dietary variability and digestive flexibility in both specific digestive chambers and in the total digestive tract mass and length. Specifically, we found higher digestive plasticity in response to diet quality in rodents inhabiting southern temperate ecosystems with higher dietary variability in comparison to individuals from northern semi-arid habitats.

Photoperiod modulates gut bacteria composition in male Siberian hamsters (Phodopus sungorus)

Seasonal changes in day length (i.e., photoperiod) provide animals with a reliable environmental cue to determine time of year, and many physiological changes occur in laboratory animals simply by extending or shortening day length. Male Siberian hamsters (Phodopus sungorus) housed in long summer-like day lengths have significantly elevated body and fat masses compared to short-day hamsters. Because others have demonstrated that the intestinal microbiota of humans and rodents promotes host adiposity, we hypothesized that photoperiod-induced changes in body and fat masses could be associated with changes in the microbial composition in the intestines. We used bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP) to assess microbial diversity in the cecal contents of hamsters; long days significantly increased the relative abundance of bacteria in the phylum Proteobacteria. This effect was primarily due to a significant increase in the abundance of the genus Citrobacter, with both the abundance of Proteobacteria and Citrobacter spp. significantly correlated with body mass and with inguinal fat mass. In general, the abundance of the Firmicutes phylum was inversely associated with body mass. These data indicate that the intestinal microbiota are responsive to changes in photoperiod and suggest that these changes may in part influence photoperiodic changes in body and fat masses.

Behavior, nutrition, and veterinary care of patagonian cavies (Dolichotis patagonum)

Patagonian cavies (Dolichotis patagonum) are large South American rodents well adapted for cursorial life (well adapted for running). They are monogamous but can live in groups of up to 70 individuals who maintain communal burrows. They are primarily herbivorous and may be maintained on commercially produced rodent or primate diets. Their long, thin legs and skittish nature make them difficult to restrain. Common medical problems include malocclusion of cheek teeth, gastrointestinal parasites, hypertrophic cardiomyopathy, and traumatic leg fractures.

Do changes in dietary chemistry during ontogeny affect digestive performance in adults of the herbivorous rodent Octodon degus?

We characterize the flexibility in digestive performance in degus (Octodon degus) an herbivorous rodent. We tested the hypothesis that dietary and physiological-digestive flexibility are correlated. Degus were fed with artificial diets of different chemical composition from weaning to adulthood and their digestive performance was measured through records of apparent digestibility. The starch content of the acclimation diet was not correlated with protein digestibility nor was it correlated with starch digestibility. In addition, digestive tract morphology was not affected by dietary treatments. Hence, an absence of morphological and physiological flexibility related to digestive traits was observed in degus. The lower flexibility in digestive performance given by our dietary experimental treatments of degus, may be an evolutionary constraint related to their specialized herbivorous food habits.