Ectothermic Vertebrates Research Articles

Behavioural fever reduces ranaviral infection in toads

1. Host behaviour is known to influence disease dynamics. Additionally, hosts often change their behaviours in response to pathogen detection to resist and avoid disease. The capacity of wildlife populations to respond to pathogens using behavioural plasticity is critical for reducing the impacts of disease outbreaks. However, there is limited information regarding the ability of ectothermic vertebrates to resist diseases via behavioural plasticity. 2. Here, we experimentally examine the effect of host behaviour on ranaviral infections, which affect at least 175 species of ectothermic vertebrates. We placed metamorphic (temporal block 1) or adult (block 2) Southern toads (Anaxyrus terrestris) in thermal gradients, tested their temperature preferences before and after oral inoculation by measuring individual-level body temperature over time, and measured ranaviral loads of viral-exposed individuals. 3. We found significant individual-level variation in temperature preference and evidence for behavioural fever in both metamorph and adult A. terrestris during the first two days after exposure. Additionally, we found that individual-level change in temperature preference was negatively correlated with ranaviral load and a better predictor of load than average temperature preference or maximum temperature reached by an individual. In other words, an increase in baseline temperature preference was more important than simply reaching an absolute temperature. 4. These results suggest that behavioural fever is an effective mechanism for resisting ranaviral infections.

Female-biased gape and body-size dimorphism in the New World watersnakes (tribe: Thamnophiini) oppose predictions from Rensch's rule.

Sexual‐size dimorphism (SSD) is ubiquitous across animals and often biased in the direction of larger females in snakes and other ectothermic organisms. To understand how SSD evolves across species, Rensch's rule predicts that in taxa where males are larger, SSD increases with body size. In contrast, where females are larger, SSD decreases with body size. While this rule holds for many taxa, it may be ambiguous for others, particularly ectothermic vertebrates. Importantly, this rule suggests that the outcomes of SSD over phylogenetic time scales depend on the direction of dimorphism predicated on the difference in reproductive efforts between males and females. Here, we examine SSD in the context of Rensch's rule in Thamnophiini, the gartersnakes and watersnakes, a prominent group that in many areas comprises the majority of the North American snake biota. Using a dated phylogeny, measurements of gape, body, and tail size, we show that these snakes do not follow Rensch's rule, but rather female‐biased SSD increases with body size. We in turn find that this allometry is most pronounced with gape and is correlated with both neonate and litter size, suggesting that acquiring prey of increased size may be directly related to fecundity selection. These changes in SSD are not constrained to any particular clade; we find no evidence of phylogenetic shifts in those traits showing SSD. We suggest several ways forward to better understand the anatomical units of selection for SSD and modularity.Open Research Badges This article has been awarded Open Data and Open Materials Badges. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5061/dryad.3pn57h0.

Life history and age-dependent mortality processes in tropical reptiles

AbstractActuarial senescence appears to be a common process, and senescence patterns are highly variable across the tree of life. To date, studies on animal senescence have largely focused on model species, such as as fruit flies, humans and a few other endotherms. In contrast, our knowledge about ageing remains fragmentary in ectotherm vertebrates, such as reptiles. Here, we examined life history and age-dependent mortality patterns in three tropical tortoises (Kinixys erosa, Kinixys homeana and Kinixys nogueyi) and snakes (Bitis gabonica, Bitis nasicornis and Causus maculatus). Our study revealed that tortoises of the genus Kinixys had a higher survival and a lower recruitment than snakes of the genera Bitis and Causus, indicating a slower life history. Furthermore, we confirmed that survival decreased more slowly with age in tortoises than in snakes. In addition, we highlighted contrasting patterns of age-dependent mortality among the three genera. In Kinixys, the relationship between mortality rate and age was positive and linear, suggesting gradual senescence over tortoise lifetime. In contrast, the relationship between mortality rate and age was negative and sharp in Bitis and Causus, possibly owing to a ‘negative senescence’. Our study is one of the few to have examined and compared the demography and age-dependent mortality patterns of tropical reptiles. Among other things, our results suggest that although negative senescence has never been reported in endotherm vertebrates, it could be a common phenomenon in ectotherms.

Molecular characterization of novel mitochondrial peroxiredoxins from the Antarctic emerald rockcod and their gene expression in response to environmental warming

In the present study we describe the molecular characterization of the two paralogous mitochondrial peroxiredoxins from Trematomus bernacchii, a teleost that plays a pivotal role in the Antarctic food chain. The two putative amino acid sequences were compared with orthologs from other fish, highlighting a high percentage of identity and similarity with the respective variant, in particular for the residues that are essential for the characteristic peroxidase activity of these enzymes. The temporal expression of Prdx3 and Prdx5 mRNAs in response to short-term thermal stress showed a general upregulation of prdx3, suggesting that this isoform is the most affected by temperature increase. These data, together with the peculiar differences between the molecular structures of the two mitochondrial Prdxs in T. bernacchii as well as in the tropical species Stegastes partitus, suggest an adaptation that allowed these poikilothermic aquatic vertebrates to colonize very different environments, characterized by different temperature ranges.

Red carotenoids and associated gene expression explain colour variation in frillneck lizards.

A long-standing hypothesis in evolutionary ecology is that red-orange ornamental colours reliably signal individual quality owing to limited dietary availability of carotenoids and metabolic costs associated with their production, such as the bioconversion of dietary yellow carotenoids to red ketocarotenoids. However, in ectothermic vertebrates, these colours can also be produced by self-synthesized pteridine pigments. As a consequence, the relative ratio of pigment types and their biochemical and genetic basis have implications for the costs and information content of colour signals; yet they remain poorly known in most taxonomic groups. We tested whether red- and yellow-frilled populations of the frillneck lizard, Chlamydosaurus kingii, differ in the ratio of different biochemical classes of carotenoid and pteridine pigments, and examined associated differences in gene expression. We found that, unlike other squamate reptiles, red hues derive from a higher proportion of ketocarotenoids relative to both dietary yellow carotenoids and to pteridines. Whereas red frill skin showed higher expression of several genes associated with carotenoid metabolism, yellow frill skin showed higher expression of genes associated with steroid hormones. Based on the different mechanisms underlying red and yellow signals, we hypothesize that frill colour conveys different information in the two populations. More generally, the data expand our knowledge of the genetic and biochemical basis of colour signals in vertebrates.

In defense of proteins: Chaperones respond to freezing, anoxia, or dehydration stress in tissues of freeze tolerant wood frogs.

Wood frogs (Rana sylvatica LeConte) are the major model for studies of natural freeze tolerance by ectothermic vertebrates. Multiple biochemical adaptations support winter freezing survival but, to date, the protective role of chaperone proteins has received little attention. The present study analyzes responses to freezing, anoxia or dehydration exposures and recovery from these stresses by chaperone proteins in six wood frog organs: Five heat shock proteins (Hsc70, Hsp110, Hsp60, Hsp40, and Hsp10) and two glucose-regulated proteins (Grp78 and Grp94) were assessed. Hsc70 was upregulated in liver, muscle, heart and kidney (1.5-2.0 fold) during freezing and levels of its partner proteins also rose (Hsp110 in three tissues and Hsp40 in four tissues), these responses aligning most closely with comparable responses to anoxia rather than to dehydration. The resident chaperones of the endoplasmic reticulum (Grp78 and Grp94) also rose during freezing in liver and muscle (1.4-1.8 fold) but were suppressed in heart and skin, patterns that generally differed from responses to anoxia or dehydration. Elevated GRPs in liver may support the production and secretion of novel freeze responsive proteins. Increased levels of mitochondrial Hsp60 and Hsp10 (1.5-2.2 fold) occurred in most tissues during freezing and generally mimicked responses to anoxia. Overall, this study indicates that increased levels of chaperone proteins resident in multiple subcellular compartments contribute to stabilizing the cellular proteome during whole body freezing of wood frogs. These responses are probably derived from pre-existing amphibian defenses for stabilizing the proteome under environmental low oxygen or dehydration stresses.

Detection and Characterization of Invertebrate Iridoviruses Found in Reptiles and Prey Insects in Europe over the Past Two Decades.

Invertebrate iridoviruses (IIVs), while mostly described in a wide range of invertebrate hosts, have also been repeatedly detected in diagnostic samples from poikilothermic vertebrates including reptiles and amphibians. Since iridoviruses from invertebrate and vertebrate hosts differ strongly from one another based not only on host range but also on molecular characteristics, a series of molecular studies and bioassays were performed to characterize and compare IIVs from various hosts and evaluate their ability to infect a vertebrate host. Eight IIV isolates from reptilian and orthopteran hosts collected over a period of six years were partially sequenced. Comparison of eight genome portions (total over 14 kbp) showed that these were all very similar to one another and to an earlier described cricket IIV isolate, thus they were given the collective name lizard–cricket IV (Liz–CrIV). One isolate from a chameleon was also subjected to Illumina sequencing and almost the entire genomic sequence was obtained. Comparison of this longer genome sequence showed several differences to the most closely related IIV, Invertebrate iridovirus 6 (IIV6), the type species of the genus Iridovirus, including several deletions and possible recombination sites, as well as insertions of genes of non-iridoviral origin. Three isolates from vertebrate and invertebrate hosts were also used for comparative studies on pathogenicity in crickets (Gryllus bimaculatus) at 20 and 30 °C. Finally, the chameleon isolate used for the genome sequencing studies was also used in a transmission study with bearded dragons. The transmission studies showed large variability in virus replication and pathogenicity of the three tested viruses in crickets at the two temperatures. In the infection study with bearded dragons, lizards inoculated with a Liz–CrIV did not become ill, but the virus was detected in numerous tissues by qPCR and was also isolated in cell culture from several tissues. Highest viral loads were measured in the gastro-intestinal organs and in the skin. These studies demonstrate that Liz–CrIV circulates in the pet trade in Europe. This virus is capable of infecting both invertebrates and poikilothermic vertebrates, although its involvement in disease in the latter has not been proven.

Developmental plasticity of cardiac anoxia-tolerance in juvenile common snapping turtles ( Chelydra serpentina).

For some species of ectothermic vertebrates, early exposure to hypoxia during embryonic development improves hypoxia-tolerance later in life. However, the cellular mechanisms underlying this phenomenon are largely unknown. Given that hypoxic survival is critically dependent on the maintenance of cardiac function, we tested the hypothesis that developmental hypoxia alters cardiomyocyte physiology in a manner that protects the heart from hypoxic stress. To test this hypothesis, we studied the common snapping turtle, which routinely experiences chronic developmental hypoxia and exploits hypoxic environments in adulthood. We isolated cardiomyocytes from juvenile turtles that embryonically developed in either normoxia (21% O2) or hypoxia (10% O2), and subjected them to simulated anoxia and reoxygenation, while simultaneously measuring intracellular Ca2+, pH and reactive oxygen species (ROS) production. Our results suggest developmental hypoxia improves cardiomyocyte anoxia-tolerance of juvenile turtles, which is supported by enhanced myofilament Ca2+-sensitivity and a superior ability to suppress ROS production. Maintenance of low ROS levels during anoxia might limit oxidative damage and a greater sensitivity to Ca2+ could provide a mechanism to maintain contractile force. Our study suggests developmental hypoxia has long-lasting effects on turtle cardiomyocyte function, which might prime their physiology for exploiting hypoxic environments.

Fish, amphibian and reptilian assemblage from the middle Miocene locality Gračanica—Bugojno palaeolake, Bosnia and Herzegovina

This paper presents the first fossil fish, amphibian and reptilian fauna from Bosnia and Herzegovina Dinarides. The fauna of ectothermic vertebrates of the Bugojno palaeolake, dated to 15.2–14.0 Ma, composes of killifishes (Cyprinodontiformes indet.), a barb (Barbini indet. (aff. Barbus), a crocodile newt (Chelotriton sp.), a painted frog (Latonia sp.) and a crocodile (Alligatoroidea indet. [?Diplocynodon]). The crocodile remains are confined to the lower part of the section corresponding to the swamp deposit (unit 1). The remaining fauna, which includes fishes and amphibians, come from the upper lacustrine unit 2. A possible Barbus (Barbini indet. (aff. Barbus)) could represent one of the oldest fossil records of the genus found in Europe, which composes of skeletal elements and pharyngeal teeth. The crocodile newt (Chelotriton sp.) represents the first record of this group from the area. For the first time, fossil tadpoles of the genus Latonia are described in this paper, which, moreover, are the first record of tadpole for both the family Discoglossidae and clade of discoglossoid frogs. The crocodile remains, identified as Alligatoroidea indet., should belong to the genus Diplocynodon, which will be tested later on a better preserved material. The fossils, coming from the lacustrine interval, are referred to the deeper water facies. Taphonomic observations of the fossil remains suggest relatively short phase of decay of the animal bodies and their (probably quick) sedimentation in the deeper parts of the lake, with poor oxygen content.

A SNP in a Steroidogenic Enzyme Is Associated with Phenotypic Sex in Seriola Fishes

Vertebrate sex development consists largely of two processes: "sex determination," the initial bifurcation of sexual identity, and "sex differentiation," which subsequently facilitates maleness or femaleness according to the sex determination signal. Steroid hormones promote multiple types of sexual dimorphism in eutherian mammals and avians [1-3], in which they are indispensable for proper sex differentiation. By contrast, in many poikilothermic vertebrates, steroid hormones have been proposed to be key players in sex determination as well as sex differentiation [4-8]. This hypothesis was introduced more than 50 years ago but has never been rigorously tested due to difficulties in discriminating the roles of steroids in sex determination and differentiation. We found that a missense SNP in the gene encoding the steroidogenic enzyme 17β-hydroxysteroid dehydrogenase 1 (Hsd17b1) was perfectly associated with ZZ/ZW sex determination in Seriola fishes. Biochemical analyses revealed that a glutamate residue present specifically in Z-type HSD17B1 attenuated interconversion between 17-keto and 17β-hydroxy steroids relative to the allelic product from the W chromosome, which harbors glycine at that position, by disrupting the hydrogen bond network between the steroid and the enzyme's catalytic residues. Hsd17b1 mRNA is constitutively expressed in undifferentiated and differentiating gonads of both genotypic sexes, whereas W-type mRNA is expressed only in genotypic females. Meanwhile, Cyp19a1 ispredominantly expressed in differentiating ovary. We conclude that the combination of Hsd17b1 alleles determines sex by modulating endogenous estrogen levels in Seriola species. These findings strongly support the long-standing hypothesis on steroids in sex determination.

Discovery of Wild Amphibians Infected with Ranavirus in Brazil

Ranavirus is a double-stranded DNA virus associated with amphibian, fish and reptile die-offs worldwide. International trade of live animals farmed for human consumption, such as the American bullfrog (Lithobates catesbeianus), plays a key role in spreading the pathogen. In Brazil, ranavirus has only been reported in captive bullfrog farms. We found infected tadpoles of both native species and the American bullfrog in the wild, and a case of mass mortality of amphibians and fish potentially associated with ranavirus. Dead animals presented skin ulcerations, hemorrhages, and edemas. We also found an overall prevalence of 37% of the amphibian chytrid in the area, and two bullfrog tadpoles were co-infected with both pathogens. We suggest that the interaction between the two pathogens should be investigated to improve global conservation of ectothermic vertebrates.

Ectothermic vertebrates are too cool to care: a response to comments on Beekman et al.

Ectothermic vertebrates are too cool to care: a response to comments on Beekman et al.

Inflammatory changes and melanization in the Atlantic salmon (Salmo salar) targeted by In situ hybridization

Abstract Research on the immune system of salmonid fish is attracting increased attention, however, progress within this field has been hampered by the general lack of cell markers targeting different immune molecules. Here, we circumvent these challenges by applying in situ hybridization (ISH) to reveal basic cellular responses in salmon immune reactions. Using RNAscope® (ACD, Newark, CA), we have established ISH targeting immunoglobulin (Ig) M and T RNA. Further, we also target other immune genes where we previously had no markers, and tyrosinase, thought to be important for the function of the melano-macrophages which are special, melanin-producing immune cells found in ectothermic vertebrates. We provided target gene sequences to the manufacturer, which supplied us with probes, and we performed ISH according to the manufacturer’s instructions. Different inflammatory conditions in farmed salmon, including cancerous changes from the gut and muscle tissue with chronic myositis and melanization due to the presence of melano-macrophages, were screened by standard histology and subsequently subjected to ISH. For the IgM results, we compared IHC and ISH results, as we have antisera targeting IgM. The results were highly similar. ISH thus seems as a good method that may be used in salmon when applicable and especially to target transcripts where no antibody recognizing the resulting protein is available. Further, we reveal hitherto non-described cellular compositions of inflammatory changes in salmon using probes detecting several different immune cell transcripts. Our results show that ISH using RNAscope® works in Atlantic salmon and is highly reproducible.

The melanomacrophage center is a potential evolutionary precursor to the mammalian germinal center

Abstract The melanomacrophage center (MMC), aggregates of highly pigmented melanomacrophages found within the lymphoid tissues of ectotherm vertebrates, is thought to be the evolutionary precursor to the mammalian germinal center (GC). Studies of cold-blooded vertebrates suggest that the MMC is the site of the humoral adaptive immune response, where B cells proliferate, generate high affinity antibody, and undergo affinity maturation. MMCs transiently increase in size/number following immunization or bacterial infection, supporting the hypothesis that the MMC response is likely linked to the adaptive immune response. However, while morphological studies and shared expression of a GC specific gene further support the idea that the MMC is a proto-GC, melanomacrophages perform many functions not associated with the humoral adaptive immune response. Therefore, to determine if the MMC is serving in a GC-like capacity or is a more generalist feature of ectotherm biology, we turned to the fish model system, three spine stickleback. Fish MMCs increase in size in response to immunization with NP-CGG in alum, but not control injection with adjuvant alone. Fish MMCs are also found in close proximity to lymphocytes and cells expressing the B/T cell activation marker GL7. These preliminary studies not only give further support to the notion of the MMC as a GC homolog, but also provide important tools to broaden the study of adaptive immunity in other fish, reptilian, and amphibian systems.

Independent influence of thermoregulatory cost on the lower and upper set-points of a heliothermic lizard

Studies on ectothermic vertebrates generally lead to average indicators of thermal preferences measured in the laboratory, which do not say about responses to natural environmental change and may not inform about individual variation and its triggering mechanisms. We studied whether and how changes in costs of thermoregulation influence the preferred temperature (Tp) of individual lizards and their energetic investment in thermoregulation by exposing specimens to three treatments of increasing costs, recording body temperature (Tb) and distance walked (energetic investment). Moderate costs induced an investment trade-off between energy-investment in thermoregulation and Tb, and highlighted individual variation that decreased with higher costs. Lower average Tp’s were observed in the high costs trials as a result of the decreased values of the lower and upper voluntary Tb's. As costs increased, lizards walked a shorter overall distance and accepted lower Tb’s, but lizards still engaged in costly thermoregulation. Individual variation resulted in two main thermoregulatory patterns that in certain ecological contexts may have an important role in decision-making and adjusting to temperatures that are far from optimal temperatures for performance and physiological processes.

Ventricular transcriptomic changes induced by cold‐acclimation in the painted turtle suggests epigenetic‐mediated transcriptional remodeling

Ectothermic vertebrates living at extreme latitudes are often forced to endure extended periods with their body temperatures at or just above the freezing point of water. Cold temperatures impose a number of physiological and biochemical challenges directly related to the thermodynamic effects on biological matter, including metabolic enzyme kinetics and even the physical properties of blood. The painted turtle, Chrysemys picta, is a pond turtle that can experience temperatures just above freezing for 3–5 months as adults and can tolerate freezing or even subzero temperatures as hatchlings. In the present study, we characterized how cold acclimation to 3°C affected the ventricular transcriptome in both adult and hatchling turtles. Because hatchlings must tolerate subzero temperatures when they overwinter in their nest, we sought to determine if they might also exhibit a unique gene expression pattern related to possible cryoprotective mechanisms. Despite differences in life history, adults and hatchlings responded similarly to cold acclimation at the transcriptomic level; out of the 1304 genes that were differentially expressed due to temperature, 1272 showed similar expression patterns in adults and hatchlings, the majority of which were upregulated. In adults and hatchlings combined, 776 genes were upregulated at 3°C, 550 genes were downregulated, of which 22 fell into both categories due to development‐specific expression patterns. Of these upregulated genes, 51 encoded for transcription factors, 27 for histone modification proteins, and 26 for mRNA processing and translational regulation enzymes. These results suggest that the ventricle actively remodels chromatin structure and modulates both gene expression and mRNA processing in response to cold acclimation.Support or Funding InformationThis work was supported by NSF CAREER grant 1253939 awarded to DEWThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Is temperature preference in the laboratory ecologically relevant for the field? The case of Drosophila nigrosparsa

Ectotherms are sensitive to temperature change, and predictions about a species' vulnerability to thermal change require an understanding of its thermal responses. The preferred temperature in laboratory assays is a widely used measure commonly taken as an indicator of the temperature at which ectotherms' physiological functions are optimised. The ecological relevance of laboratory-measured temperature preference has been evaluated for vertebrate ectotherms but to our knowledge not for Drosophila. Here, we assessed the links between laboratory thermal preference and habitat temperature in the alpine fly Drosophila nigrosparsa. We found that (i) in the laboratory, D. nigrosparsa preferred a temperature of about 10 °C. In the field, (ii) macrohabitat temperatures ranged from 17 to 22 °C, and (iii) microhabitat temperatures exceeded those of the macrohabitat with up to 35 °C at full sun exposure. (iv) Isotope-tracked flies were localised, among others, at nearly the maximum temperature conditions measured in the microhabitats. (v) Operative environmental temperature models revealed that air temperature has the highest impact on the flies’ experienced temperature, followed by global solar radiation and wind. These findings highlight that the preferred temperature in the laboratory differed strongly from that in the field and that different approaches lead to different conclusions about the preferred and experienced temperatures.

Thermodynamic constraints and the evolution of parental provisioning in vertebrates

Why is postnatal parental provisioning so rare in ectothermic vertebrates while prolonged parental care is almost ubiquitous in endotherms? We argue that the scarcity of postnatal parental care is a result of ectothermy itself. While almost all endothermic young require prolonged postnatal care due to thermal constraints, ectothermic physiology does not pose the same constraint. Most ectothermic young are thus independent from birth. Ectothermic mothers are better off investing in future reproductive events than to continue investing into independent young, because the cost of feeding young does not outweigh the benefits. Ectothermy further releases the constraint on offspring size resulting in offspring of ectothermic vertebrates often being much smaller than their parents. When parents and offspring differ greatly in size, both tend to specialize on different diets, making the feeding of young by much larger individuals not impossible, but less likely. Additionally, when the size difference between parents and offspring is significant, both are likely to live in different habitats. Such spatial segregation is also less conducive to the evolution of parental care. In those species where parents and offspring are not spatially separated and parental care does occur, it is mainly restricted to the guarding of eggs or juveniles; parents of very few species provide their offspring with food. We conclude that parental care beyond the guarding of eggs or young is much less likely to evolve in ectothermic vertebrates compared with endothermic vertebrates, unless there are exceptional circumstances that strongly select for parents to provide for their offspring.

Ontogenetic shifts in the nesting behaviour of female crocodiles.

Body size and age are crucial factors influencing reproductive capacity and success. As females grow, their reproductive investment and success often increase due to improved overall physiological condition and experience gained through successive reproductive events. While much of this work has been conducted on birds and mammals, surprisingly little is known on how body size affects nesting decisions in other long-lived vertebrates. We monitored the movements and nesting behaviour of 57 wild female estuarine crocodiles Crocodylus porosus over a 10-year period (and across consecutive nesting seasons) using externally mounted satellite tags, implanted acoustic transmitters and a network of submerged acoustic receivers. Applying Hidden Markov models to the telemetry-derived location data revealed that female nesting behaviours could be split into three distinct states: (i) ranging movements within home ranges and at nesting sites; (ii) migrations to and from nesting sites; (iii) and nesting/nest guarding. We found that during migration events, larger females migrated further and remained away from dry season territories for longer periods than smaller individuals. Furthermore, not only were migratory movements stimulated by increases in rainfall, larger females migrated to nest sites at lower rainfall thresholds than smaller females. We provide some of the first evidence of body size influencing nesting decisions in an ectothermic vertebrate, with shifts likely resulting from an increased willingness to invest in nest protection among larger and more experienced females.

Shared extremes by ectotherms and endotherms: Body elongation in mustelids is associated with small size and reduced limbs.

An elongate body with reduced or absent limbs has evolved independently in many ectothermic vertebrate lineages. While much effort has been spent examining the morphological pathways to elongation in these clades, quantitative investigations into the evolution of elongation in endothermic clades are lacking. We quantified body shape in 61 musteloid mammals (red panda, skunks, raccoons, and weasels) using the head-body elongation ratio. We also examined the morphological changes that may underlie the evolution toward more extreme body plans. We found that a mustelid clade comprised of the subfamilies Helictidinae, Guloninae, Ictonychinae, Mustelinae, and Lutrinae exhibited an evolutionary transition toward more elongate bodies. Furthermore, we discovered that elongation of the body is associated with the evolution of other key traits such as a reduction in body size and a reduction in forelimb length but not hindlimb length. This relationship between body elongation and forelimb length has not previously been quantitatively established for mammals but is consistent with trends exhibited by ectothermic vertebrates and suggests a common pattern of trait covariance associated with body shape evolution. This study provides the framework for documenting body shapes across a wider range of mammalian clades to better understand the morphological changes influencing shape disparity across all vertebrates.