Evolution

Understanding how anatomical structures evolve requires disentangling the roles of integration and modularity in shaping morphological variation. The vertebral column, a serially repeated and regionally differentiated structure, provides a powerful system for investigating these processes. Here, we examine how vertebral morphology evolves in relation to whole-body elongation across the adaptive radiation of Lake Malawi cichlid fishes. We tested for evolutionary integration between the precaudal and caudal domains, as well as assessed the contributions of vertebral count, centrum shape, and intervertebral spacing on body elongation. We find strong evolutionary integration between precaudal and caudal vertebral shape, with both vertebral shapes varying along shared axes of multivariate shape change. Despite this, precaudal and caudal vertebral counts evolve independently, indicating a decoupling between the evolution of identity and morphology. Whole-body elongation is significantly associated with coordinated changes in vertebral and rib morphology, including proportional increases in centrum size, posterior displacement of neural and haemal spines, and increased rib curvature. In contrast, centrum elongation and intervertebral spacing do not independently explain body elongation beyond vertebral counts. These results demonstrate that body elongation in cichlids necessitates integrated, multivariate changes in axial morphology. Our findings highlight the importance of morphological integration in facilitating coordinated evolutionary responses in anatomical systems.

Mate preferences are often influenced by the magnitude of sexual signals, which are presumed to indicate underlying aspects of signaller quality. Although the perception of these signals depends on sensory processes, the role of perceptual adaptations and constraints in mate assessment is frequently overlooked. Many sensory systems follow Webers law of proportional processing, where discrimination between signals is based upon their proportional, or relative, difference rather than their absolute difference. Because preference strength varies with relative trait magnitude, Webers law could strongly influence sexual selection, changing the coevolution of traits and preferences. Here, we explore the consequences of Webers law for sexual selection using individual-based models, applying Scalar Utility Theory to mate choice. We investigate the coevolution of male ornaments and female preferences under both Fisherian and good genes scenarios, as well as scrutinizing the sexual selection of multiple ornaments and preferences. Including Webers law in these models either reduced ornament exaggeration, or promoted exaggeration and diversification of ornaments and preferences, depending on the costs of choice and how rapidly female survival decreases when preferences evolve away from the naturally selected optimum. These results highlight the importance of perception and cognitive processing in shaping sexual selection and its evolutionary impacts.

Matching habitat choice provides a mechanism for individuals to maximise their expected fitness by selecting an environment that better fits their phenotype. Many animals choose their local environment by evaluating levels of perceived predation risk against possible resource gain. To test if predation risk is a major driver of habitat choice, we quantify scototaxis, or preference for dark versus light backgrounds, in juvenile guppies. As light backgrounds increase visibility to predators, this aspect of habitat choice captures variation in boldness in small fishes. By rearing and testing 586 fish descended from ten natural populations from Trinidad under common garden conditions, we first quantify (broad sense) heritable variation, i.e. evolutionary potential, within populations. Next, we test for evolutionary divergence among populations in mean preference, and if present, whether ancestral predation regime is a mediator of divergence. Finally, we ask whether families and/or populations differ in the amount of behavioural variation they contain. Habitat choice varied among families (12% of total variance), consistent with heritable variation (0.2). We also found mean preference varies among populations (11% of total variance explained). Evolutionary divergence among-populations is partly explained by ancestral predation regime, with populations from low-predation sites showing a stronger average preference for dark backgrounds than high-predation populations from the same river. Additionally, we find that within-population behavioural variation is greater in high-predation populations. We conclude that guppy populations contain heritable variation that could facilitate adaptive evolution if scototaxis is subject to natural selection. Furthermore, while genetic drift may also contribute to evolutionary divergence among-populations, observed patterns are qualitatively consistent with local adaption to predation regime. Our results suggests that high predation sites favour bolder habitat choice on average, but also that local predation regime shape the evolutionary dynamics of variation, perhaps by maintaining shy-bold variation among-individuals or by favouring individuals with less-predicable behaviour.

AO_SCPLOWBSTRACTC_SCPLOWEnvironmental heterogeneity across freshwater systems often promotes phenotypic variation, yet disentangling environmentally induced variation from heritable differentiation remains a central goal in evolutionary ecology. We investigated the geographic distribution and morphological differentiation, and heritability of shell traits among populations of the freshwater lymnaeid snail Pectinidens diaphanus in Patagonia. Extensive field surveys across 196 freshwater sites revealed that the species occupies a broad range of lentic and lotic habitats and constitutes the only lymnaeid inhabiting southern Patagonia. While reproductive anatomical structures were conserved across populations, shell shape differed markedly among populations from contrasting habitat types, with population identity explaining nearly 50% of total shape variation. Populations from hydrologically unstable habitats (ponds and streams) exhibited more elongated shells and relatively smaller apertures, a pattern consistent with functional responses to hydroperiod variability and desiccation risk. To assess the heritability of this differentiation, we conducted a common-garden experiment across two generations. Shell shape differences between permanent- (lagoon) and temporary- (pond) habitat-derived populations persisted into the G2 generation reared under standardized laboratory conditions, indicating that the observed variation is not solely a response to local environmental conditions but includes a heritable component. Together, our findings demonstrate that P. diaphanus constitutes the sole lymnaeid across southern Patagonia, occupying a broader range than previously documented, and that populations show heritable shell differentiation potentially associated with contrasting freshwater habitats. By integrating large-scale biogeographic surveys with morphometric and experimental approaches, this study provides new insight into how habitat variation may contribute to ecological and evolutionary differentiation in freshwater gastropods.

Social interactions are ubiquitous in nature and have the potential to affect trait evolution, particularly in group-living animals such as cooperative breeders. Interactions among conspecific individuals can affect the amount of additive genetic variation for a trait when the phenotype of an individual is also affected by the genotype of its social partner(s) via indirect genetic effects. Thus, quantifying both direct and indirect genetic effects of social partners is critical for understanding and predicting evolutionary trajectories. While much is known about maternal indirect genetic effects, empirical estimates of indirect genetic effects from other social partners remain limited, particularly in wild populations. Here, we use animal models to assess the contribution of indirect genetic effects from all social partners in a family group (mothers, fathers, and helpers) on juvenile morphometric traits across ontogeny in the cooperatively-breeding Florida scrub-jay (Aphelocoma coerulescens). We found indirect genetic effects of helpers and fathers on nestling weight, but no indirect genetic effect of mothers. Across ontogeny, we found increasing additive genetic variation in both weight and tarsus length. Our study provides a comprehensive assessment of within-group indirect genetic effects in a cooperative breeder and highlights the importance of considering indirect genetic effects beyond maternal effects.

Dormancy is a widespread adaptive strategy that allows organisms to survive in temporally varying habitats by suspending development and reproduction. Although environmental variability is expected to shape dormancy strategies, it remains unclear how differences in environmental variability and predictability influence both the production of dormant embryos and the termination of dormancy. We addressed these questions by comparing D. pulex and D. obtusa, two closely related species that inhabit environments differing in variability and predictability. We hypothesized that D. obtusa, which inhabits ephemeral environments, would exhibit a greater propensity for sexual reproduction and dormancy and would require stronger cues to break dormancy than D. pulex, which occurs in more permanent, predictable habitats. Consistent with our hypothesis, D. obtusa lineages produced significantly more males and ephippia than D. pulex when reared under identical laboratory conditions, indicating greater investment in sexual reproduction and dormancy. Contrary to our hypothesis, we found no difference in responsiveness to cues between the two species. Across species, embryos broke dormancy and hatched most readily after experiencing changes in cold and light, even if not experienced at the same time. In contrast, desiccation reduced the propensity to break dormancy. Together, these results indicate that species occupying more ephemeral environments invest more heavily in the production of dormant offspring, but that the environmental cues regulating dormancy termination appear broadly similar between species. This pattern suggests that while investment in dormancy may evolve in response to environmental variability, the mechanisms controlling dormancy termination are more conserved.

In androdioecious species like Caenorhabditis elegans, where the primary mode of reproduction is self-fertilization, the evolutionary role of males has long puzzled biologists. One proposed benefit of males is the potential to escape inbreeding depression. We tested this by enforcing seven generations of inbreeding across nine C. elegans strains differing in baseline male frequency and measuring competitive relative fitness before and after inbreeding. We then relaxed inbreeding for four generations to assess recovery. We predicted that strains with higher male frequency, and greater opportunity for outcrossing, would exhibit faster recovery once inbreeding was relaxed. Strains varied substantially in their responses with most showing significant fitness declines and partial recovery but neither the magnitude of inbreeding depression nor the extent of recovery correlated with male frequency. These results show that male frequency is a poor predictor of inbreeding responses and does not reliably reflect realized outcrossing or its fitness consequences.

Sexual selection is a major evolutionary force, yet its demographic consequences remain unclear. While experimental studies often report positive effects of sexual selection on traits linked to population performance, comparative studies often find null or negative associations with population persistence. One explanation for this discrepancy is that the demographic consequences of sexual selection depend on ecological context, particularly variation in mortality and fecundity. Here, we used six decades of abundance data and test whether sexual selection predicts population trends across 738 bird species from Europe and North America. We quantify sexual selection using complementary proxies capturing different components of sexual selection: mating system, sexual dichromatism, sexual size dimorphism and relative testes mass. We further assess whether the effect of sexual selection in population trends is mediated by mortality and fecundity. Across all proxies, we found no evidence that sexual selection is associated with population trends. This result is consistent across continents and robust to variation in mortality and fecundity. Our findings suggest that, despite its central role in shaping phenotypic evolution, sexual selection does not translate into consistent effects on long-term population trends at macroecological scales. More broadly, these results highlight a potential disconnect between evolutionary processes and population dynamics.

Parasites can alter host populations in fundamentally different ways depending on whether exposure results in infection. Yet, most epidemiological and evolutionary inference focuses on established infections, leaving the fitness consequences of parasite exposure comparatively understudied. This gap is consequential because hosts are frequently exposed to diverse parasite genotypes, and these encounters can impose substantial fitness costs even when infection does not occur. Theory predicts that hosts may mitigate these costs when interacting with commonly encountered parasite genotypes, such that exposure to sympatric parasites incurs lower fitness consequences than exposure to novel, allopatric parasites. Here, we examine the fitness consequences of exposure and infection in the first intermediate host of the trophically transmitted tapeworm Schistocephalus solidus, a cyclopoid copepod that serves as the first host in a three-host life cycle. Using sympatric (Vancouver Island, Canada) and allopatric (Norway) host-parasite combinations, we found a striking reciprocal asymmetry. Sympatric parasites were significantly more infective, yet exposure to sympatric parasites imposed weaker fitness costs when infection did not establish. In contrast, allopatric parasites were less infective, but exposed females produced fewer eggs and had lower hatching success than both controls and females exposed to sympatric parasites, indicating substantial genotype-dependent costs of exposure. Moreover, we found that infection was highly virulent across all genotypes: a single parasite caused near-complete reproductive suppression and reduced host survival across all host-parasite pairings, confirming S. solidus as a castrating parasite in copepods. Together, these results demonstrate that exposure, not just infection, acts as a critical ecological filter with potentially large and underappreciated consequences for host population dynamics and parasite transmission.

In most species, unmated individuals run the risk of dying with zero fitness. This strong selection on virgin females to mate may also explain why females subsequently remate, despite fitness costs; all that is required is a genetic correlation between virgin and non-virgin mating propensity. Despite being the null model for the evolution and maintenance of polyandry, this hypothesis has received no empirical test. We performed separate quantitative genetic and artificial selection experiments to test the presence of this cross-context genetic correlation in the cow-pea weevil, Callosobruchus maculatus. A quantitative genetic experiment did not find evidence of the hypothesised genetic correlation. However, after 13 generations of artificial selection on virgin mating latency, we found strong evidence for evolutionary divergence in remating latency. Females from lines selected for longer virgin mating latency took approximately twice as long to remate and, were less polyandrous if their virgin mating latency was longer. There was no evidence that females could mate indiscriminately and then trade-up, rather, trading up could only occur if virgin discrimination was present. Selection against virgin death will thus constrain both the evolution of non-virgin discrimination and trading up, increasing rates of polyandry. These findings reveal a genetic correlation between virgin and non-virgin latency to mate suggesting that polyandry may be maintained because of the need to breed.

The Red Queen Hypothesis proposes that genetic variation is maintained in populations through antagonistic coevolution of hosts and parasites. A major assumption of the Red Queen Hypothesis is tight genetic specificity for infection. However, it has been argued that this genetic interaction of host and parasite (GHxGP) is sensitive to environmental context (GHxGPxE). Environmental change could accordingly disrupt coevolutionary oscillations on relevant time scales, calling into question antagonistic coevolution as a general and robust explanation for the maintenance of genetic diversity. To evaluate this critique, we used the plant-parasitic nematode Meloidogyne arenaria and its natural bacterial parasite Pasteuria penetrans to determine if specificity is altered by temperature. We exposed six isofemale host lines to five parasite sources at three ecologically relevant temperatures. We found that, at two of three temperatures, susceptibility to infection depended on the specific combination of host line and parasite source (GHxGP). This specificity varied across temperatures, consistent with a GHxGPxE effect. This three-way interaction was driven both by quantitative changes in the strength of specificity across temperatures and shifts in the susceptibility rankings of host-parasite combinations. Our study contributes a rare experimental test of a proposed challenge to the Red Queen Hypothesis and suggests the potential for environmental context to change host-parasite specificity.

The evolution of alternative male reproductive strategies represents an intriguing evolutionary phenomenon. Divergent strategies are persistently at risk of local extinction or invasion, depending on the suites of traits expressed within and between morphs; hence, understanding the correlational selection that aligns reproductive strategies with behaviour, morphology and physiology is key to understanding the origin and maintenance of genetic polymorphisms. In the polychromatic painted dragon, Ctenophorus pictus, yellow, orange and red morphs are well characterised, but the blue morph has been historically absent from studied populations. Here we document the local distribution, morphology and male-contest interactions in a population where blue males are relatively common. We find that blue males express head colouration after a reaching a threshold body size, and that small blue males can reside in close proximity to other males; patterns consistent with a novel size-dependent conditional tactic within the suite of genetic strategies seen in this species. Condition-dependent, positively allometric throat bibs were non-randomly distributed among male morphs, implicating variation in correlational selection and the genetic architecture of the polymorphism. We were unable to definitively assign a morph that was superior in male competition but found that within morphs, male size was the determinant of competitive success, whilst between morphs it was not. Furthermore, contests between morphs were resolved with less aggression than contests within morphs, supporting the idea that badges resolve conflict, and that the invasion of new colour morphs may be facilitated by negative frequency dependent benefits to novel colour variants. These findings highlight the divergent phenotypic, genetic and selective environments that lead to the diversity of colour morphs.

Birds and mammals are shrinking and shapeshifting as global temperatures rise. Ecogeographic rules predict that such changes should ease heat stress by increasing surface-area-to-volume ratios, and thus, the capacity for heat exchange. This has led to the hypothesis that body size reductions are driven by thermoregulatory selection or adaptive plasticity, although recent syntheses point to more complex, multifactorial causes. Crucially, recent theoretical models predict that thermoregulatory benefits of smaller body size only emerge at extreme deviations from average phenotypes. Here, we exploit agricultural selection in Japanese quail to directly test this hypothesis, using three breeds spanning extreme differences in body mass, surface area, and relative appendage lengths. Evaporative cooling capacity and the scope for evaporative water loss broadly followed allometric predictions when contrasting small and larger breeds. As expected, this allowed the smallest breed to tolerate higher air temperatures. However, differences in heat tolerance limits between breeds were consistently much smaller than predicted. Additionally, the breadth of thermoneutral zones overlapped in full, and upper critical temperatures were remarkably similar, between breeds. Together, these results show that heat tolerance is only weakly linked to surface-area-to-volume relationships and cannot be explained by size alone. Thus, although smaller bodies may modestly enhance heat dissipation when size variation in a population is substantial, our findings suggest that recent body size reductions and morphological shifts are unlikely to be driven primarily by thermoregulatory benefits.

Epistasis makes the fitness effect of a mutation depend on the genetic background in which it occurs, thereby shaping the accessibility and reversibility of evolutionary trajectories. Along adaptive walks, this path-dependent epistasis can take distinct forms: contingency, when a mutation requires prior substitutions to be beneficial; entrenchment, when later substitutions make its reversion increasingly deleterious; and diminishing returns, when successive beneficial mutations reduce one anothers effects. Although these regimes have been documented experimentally, the conditions under which each predominates remain poorly understood. Here we use Fishers geometric model to derive a general framework for path-dependent epistasis under stabilizing selection on a multidimensional phenotype. We show that epistasis between substitutions has a simple geometric interpretation: contingency and entrenchment arise when the collateral effects of mutations, orthogonal to the direction of the optimum, are compensated by the preceding or subsequent adaptive path, whereas diminishing returns arise when successive substitutions remain strongly aligned with the same direction of selection. Analytical results and simulations reveal a transition controlled by a single composite parameter combining phenotypic complexity, mutation size, and distance to the optimum. Far from the optimum, adaptive walks are dominated by diminishing returns epistasis. As populations approach the optimum, or as phenotypic complexity increases, antagonistic pleiotropy generates systematic contingency and entrenchment. At mutation-selection-drift equilibrium, these effects become strong, rapidly established, and increase with phenotypic complexity. These results show that contingency and entrenchment do not require specific molecular interactions between residues: they emerge generically from nonspecific epistasis produced by stabilizing selection on pleiotropic traits. Fishers geometric model thus unifies diminishing returns, contingency, and entrenchment as distinct regimes of the same underlying geometry of adaptation.

Conspecific sperm precedence via cryptic female choice is a post-ejaculatory selection process that reduces hybridization, and can be pronounced in sympatric species. In their native Europe, Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) exert conspecific sperm precedence under heterospecific sperm competition, which is at least partially enabled by female reproductive fluid. We examined post-ejaculatory selection of both species in Newfoundland, Canada, where Atlantic salmon evolved in absence of brown trout, but now experience hybridization threats due to anthropogenic introductions. Using split-ejaculate and split-clutch in-vitro fertilizations we evaluated whether allopatric evolution has relaxed this selection in Atlantic salmon, and found that they had no ability to bias paternity towards conspecific males, whereas naturalized brown trout retained a strong ability to do so. Female reproductive fluid influenced this, as when fluid associated with a species eggs was swapped, hybridization increased. In the artificial situation of no female reproductive fluid during sperm competition, paternity changed dramatically, but sperm swimming performance did not predict it. Our findings contribute to understanding the evolution of cryptic female choice and how the mechanisms of reproductive isolation can be reinforced through sympatry, while also highlighting a new potential conservation concern for North American Atlantic salmon.

In many tropical areas, seasonal rainfall leads to distinct dry and wet seasons. Many butterflies developing under wet season conditions develop into adults with large ventral eyespots on the wing margins, whereas those developing under dry season conditions have smaller or no eyespots. In greener, wet season habitats, larger eyespots can divert predator attacks toward the wing margins, while reduced eyespot size improves camouflage in the dry leaf litter-dominated habitat during the dry season. However, the dry season is also characterised by higher desiccation stress than the wet season. We hypothesised that larvae developing under dry season conditions develop into adults with higher desiccation tolerance than those reared under wet season conditions. We tested this by rearing larvae of the butterfly Mycalesis mineus under simulated dry and wet season conditions and assaying the desiccation tolerance of the resulting adults. Butterflies reared in dry conditions survived longer under desiccation stress, lost lesser water during pupal-adult metamorphosis, and were heavier than those reared in wet conditions. We also tested the correlation between eyespot size and desiccation tolerance. A negative correlation between the traits would be expected if similar developmental pathways regulate them. Consistent with this expectation, individuals with smaller eyespots had higher desiccation tolerance. Our results demonstrate plasticity in desiccation tolerance, and suggest that predator avoidance and desiccation tolerance traits may share similar developmental pathways.

Avoiding fertilization with genetically incompatible partners, whether too similar or too divergent, is a central challenge for sexually reproducing organisms. Selection can favor mechanisms acting before and after mating, with postmating processes potentially compensating for constraints on premating choice. In the postmating context, female reproductive fluid (FRF) can modulate sperm performance and bias fertilization outcomes, but its contribution to reproductive isolation remains unclear. We tested whether FRF mediates discrimination against heterospecific and related sperm in two naturally hybridizing sister species of swordtails, Xiphophorus birchmanni and X. malinche, that diverge in premating behavior towards heterospecifics. Effects of FRF differed sharply between species. In X. malinche, FRF enhanced the velocity of conspecific sperm relative to heterospecifics, consistent with postmating discrimination against hybridization. In contrast, FRF in X. birchmanni did not favor conspecific sperm. Evidence for inbreeding avoidance was weaker, and we found no indication of a trade-off between discrimination against genetically similar and dissimilar sperm. These results show that female reproductive fluid can serve as a rapidly evolving axis of reproductive isolation through postmating female choice.

Rapid environmental change is exposing organisms to conditions that do not match those under which they evolved, making it increasingly important to understand how genetic variation shapes phenotypic responses to environmental stress. Since most phenotypic traits arise from interactions between genetic variation and the environments experienced throughout an organisms lifetime, understanding the genetic architecture of these interactions is central to predicting how populations will respond to novel environments. While genotype-by-environment interactions (GxE) are well studied in quantitative genetics, identifying specific loci that contribute to environmentally dependent trait expression remains rare. Salmonids already exhibit a wide portfolio of plastic life-history strategies, reflecting adaptation to highly heterogeneous environments, yet it remains unclear whether known major-effect loci involved in life-history regulation also contribute to variation in plastic responses to environmental change. One such major-effect locus is the transcription factor six6, which has been repeatedly associated with variation in age at maturity across multiple populations of rainbow trout (Oncorhynchus mykiss). Since maturation timing is closely linked to growth trajectories and patterns of energetic allocation during early development, allelic variation at this locus may also influence growth responses to warming conditions. Here, we test this hypothesis using a common-garden experiment in which 6 months old juvenile rainbow trout were reared under current and warming (+2{degrees}C) temperature regimes. By quantifying genotype-specific reaction norms across environments, we show that six6 genotype contributes to environmentally dependent variation in growth and body composition, with individuals heterozygous for the six6 locus showing a distinct and steeper response to warming relative to homozygotes. These findings provide evidence that a major life-history gene shapes plastic responses to thermal stress in juvenile rainbow trout, with novel implications for how standing genetic variation at in large-effect loci may influence population-level responses to climate warming.

Allopatric isolation under contrasting environments can drive rapid phenotypic divergence, even over contemporary timescales. Rapid changes in morphology or physiology can allow organisms to adapt to biotic and abiotic characteristics of their habitats. While studying metabolism, growth and resources needs may allow to understand adaptation to several selective pressures, these traits are rarely jointly considered. We investigated morphological, growth, and metabolic divergence in two allopatric populations of Arctic charr (Salvelinus alpinus) sharing a common evolutionary origin but inhabiting contrasting environments. We combined field observations, common garden and quantitative genetic approaches to disentangle contributions of genetic divergence and plasticity to phenotypic variability. Wild adults differed in body shape and growth trajectories, potentially reflecting plasticity related to resource availability and temperature variations. Under common garden conditions, juveniles displayed inter-population differences in routine metabolic rate, its allometric scaling with body mass. These patterns suggest divergent selection on physiological traits. Despite low neutral genetic differentiation, phenotypic divergence unfolded in fewer than 100 years, suggesting that plasticity and selection can promote rapid multi-trait changes. These findings highlight that considering changes in physiological, growth and morphological traits can reveal the adaptive potential of small, isolated populations facing rapid environmental change.

The diversity of body shapes is one of the most prominent features of phenotypic variation in mammals. Yet, mammalian body shapes are poorly quantified and the underlying components contributing to its diversity as well as its relationship to other components of the skeleton are rarely tested. Here, we use lagomorphs (hares, rabbits and pikas) as a model system to (1) investigate which components of the skeleton contributed the most to body shape diversity, (2) examine the relationships between body shape and relative limb lengths, and (3) test how body size, ecotype, burrowing behavior, and locomotor mode influenced variation in lagomorph body shape and appendicular morphology. We quantified the body shape and functional proxies of the appendicular skeleton in 40 lagomorph species from osteological specimens held at museum collections. Using phylogenetic comparative methods, we found the relative length of the ribs and elongation or shortening of the thoracic and lumbar regions contributed the most to body shape evolution across lagomorphs. Second, we found that only leporids (hares and rabbits) exhibited a significant relationship between limb length and body shape, where more elongate species exhibit relatively shorter forelimbs and hindlimbs. Lastly, we found that models incorporating body size were the best predictors of lagomorph body shape and the majority of the appendicular traits, whereas models incorporating burrowing behavior and locomotor mode were largely poor fits. Broadly, these results indicate that larger lagomorphs tend to exhibit more robust body shapes with longer, more gracile forelimbs, whereas smaller lagomorphs tend to exhibit more elongate body shapes with shorter, more robust forelimbs. Overall, this work contributes to the growing understanding of mammalian body shape evolution and demonstrates the importance of not omitting body size in ecomorphological analyses.