Is variation in tail vertebral morphology linked to habitat use in chameleons?

Chameleons (Chamaeleonidae) are known for their arboreal lifestyle, in which they make use of their prehensile tail. Yet, some species have a more terrestrial lifestyle, such as Brookesia and Rieppeleon species, as well as some chameleons of the genera Chamaeleo and Bradypodion. The main goal of this study was to identify the key anatomical features of the tail vertebral morphology associated with prehensile capacity. Both interspecific and intra-individual variation in skeletal tail morphology was investigated. For this, a 3D-shape analysis was performed on vertebral morphology using μCT-images of different species of prehensile and nonprehensile tailed chameleons. A difference in overall tail size and caudal vertebral morphology does exist between prehensile and nonprehensile taxa. Nonprehensile tailed species have a shorter tail with fewer vertebrae, a generally shorter neural spine and shorter transverse processes that are positioned more anteriorly (with respect to the vertebral center). The longer tails of prehensile species have more vertebrae as well as an increased length of the processes, likely providing a greater area for muscle attachment. At the intra-individual level, regional variation is observed with more robust proximal tail vertebrae having longer processes. The distal part has relatively longer vertebrae with shorter processes. Although longer, the small size and high number of the distal vertebrae allows the tail to coil around perches.     

Tail growth tracks the ontogeny of prehensile tail use in capuchin monkeys (Cebus albifrons and C. apella)

Physical anthropologists have devoted considerable attention to the structure and function of the primate prehensile tail. Nevertheless, previous morphological studies have concentrated solely on adults, despite behavioral evidence that among many primate taxa, including capuchin monkeys, infants and juveniles use their prehensile tails during a greater number and greater variety of positional behaviors than do adults. In this study, we track caudal vertebral growth in a mixed longitudinal sample of white-fronted and brown capuchin monkeys (Cebus albifrons and Cebus apella). We hypothesized that young capuchins would have relatively robust caudal vertebrae, affording them greater tail strength for more frequent tail-suspension behaviors. Our results supported this hypothesis. Caudal vertebral bending strength (measured as polar section modulus at midshaft) scaled to body mass with negative allometry, while craniocaudal length scaled to body mass with positive allometry, indicating that infant and juvenile capuchin monkeys are characterized by particularly strong caudal vertebrae for their body size. These findings complement previous results showing that long bone strength similarly scales with negative ontogenetic allometry in capuchin monkeys and add to a growing body of literature documenting the synergy between postcranial growth and the changing locomotor demands of maturing animals. Although expanded morphometric data on tail growth and behavioral data on locomotor development are required, the results of this study suggest that the adult capuchin prehensile-tail phenotype may be attributable, at least in part, to selection on juvenile performance, a possibility that deserves further attention.     

Caudal vertebral body articular surface morphology correlates with functional tail use in anthropoid primates

Prehensile tails, capable of suspending the entire body weight of an animal, have evolved in parallel in New World monkeys (Platyrrhini): once in the Atelinae (Alouatta, Ateles, Brachyteles, Lagothrix), and once in the Cebinae (Cebus, Sapajus). Structurally, the prehensile tails of atelines and cebines share morphological features that distinguish them from nonprehensile tails, including longer proximal tail regions, well‐developed hemal processes, robust caudal vertebrae resistant to higher torsional and bending stresses, and caudal musculature capable of producing higher contractile forces. The functional significance of shape variation in the articular surfaces of caudal vertebral bodies, however, is relatively less well understood. Given that tail use differs considerably among prehensile and nonprehensile anthropoids, it is reasonable to predict that caudal vertebral body articular surface area and shape will respond to use‐specific patterns of mechanical loading. We examine the potential for intervertebral articular surface contour curvature and relative surface area to discriminate between prehensile‐tailed and nonprehensile‐tailed platyrrhines and cercopithecoids. The proximal and distal intervertebral articular surfaces of the first (Ca1), transitional and longest caudal vertebrae were examined for individuals representing 10 anthropoid taxa with differential patterns of tail‐use. Study results reveal significant morphological differences consistent with the functional demands of unique patterns of tail use for all vertebral elements sampled. Prehensile‐tailed platyrrhines that more frequently use their tails in suspension (atelines) had significantly larger and more convex intervertebral articular surfaces than all nonprehensile‐tailed anthropoids examined here, although the intervertebral articular surface contour curvatures of large, terrestrial cercopithecoids (i.e., Papio sp.) converge on the ateline condition. Prehensile‐tailed platyrrhines that more often use their tails in tripodal bracing postures (cebines) are morphologically intermediate between atelines and nonprehensile tailed anthropoids. J. Morphol. 275:1300–1311, 2014. © 2014 Wiley Periodicals, Inc.     

Variability of tail length in hybrids of the Japanese macaque (Macaca fuscata) and the Taiwanese macaque (Macaca cyclopis)

In primates, tail length is subject to wide variation, and the tail may even be absent. Tail length varies greatly between each species group of the genus Macaca, which is explained by climatic factors and/or phylogeographic history. Here, tail length variability was studied in hybrids of the Japanese (M. fuscata) and Taiwanese (Macaca cyclopis) macaque, with various degrees of hybridization being evaluated through autosomal allele typing. Relative tail length (percent of crown–rump length) correlated well with the number of caudal vertebrae. Length profiles of caudal vertebrae of hybrids and parent species revealed a common pattern: the length of several proximal-most vertebrae do not differ greatly; then from the third or fourth vertebra, the length rapidly increases and peaks at around the fifth to seventh vertebra; then the length plateaus for several vertebrae and finally shows a gentle decrease. As the number of caudal vertebrae and relative tail length increase, peak vertebral length and lengths of proximal vertebrae also increase, except that of the first vertebra, which only shows a slight increase. Peak vertebral length and the number of caudal vertebrae explained 92?% of the variance in the relative tail length of hybrids. Relative tail length correlated considerably well with the degree of hybridization, with no significant deviation from the regression line being observed. Thus, neither significant heterosis nor hybrid depression occurred.     

Variation of the number of proximal caudal vertebrae with tail reduction in Old World monkeys

Tail length in primates can vary greatly between species or even between local conspecific populations, and the tail is markedly reduced in several lineages. In Old World monkeys, tail length is considered as an important feature reflecting their phylogeny and adaptations. The number of caudal vertebrae is one of the important factors which determine tail length, and it is known that this number varies with tail length. Caudal vertebrae can be divided into two types (proximal and distal), and tail mobility and function are considered to be different in these two regions. Though the number of vertebrae in each region is important for understanding tail length evolution in Old World monkeys, there have been few attempts to investigate this matter. This study focused only on the proximal caudal vertebrae, which are more easily preserved than the distal ones, and tested if there is variation in their number with tail length or phylogenic differences. As a result, two important findings were obtained: (1) the variation of the number of proximal caudal vertebrae was different among the phylogenic groups, and (2) especially in Papionini, there was a great variation in the number of proximal caudal vertebrae, and it correlated strongly with relative tail length [RTL = (tail length/head and body length (sitting height)) × 100 %]. I speculate that these variations in the number of proximal caudal vertebrae were possibly caused by a change of the embryonic developmental mechanism of tail morphogenesis, a common mechanism of morphological evolution. To clarify the mechanisms and evolutionary trends of the variation in the proximal caudal vertebrae, not only morphological approaches but also developmental biological approaches will be necessary in the future.     

Tail development and regeneration throughout the life cycle of the four-toed salamander Hemidactylium scutatum

The salamander tail displays different functions and morphologies in the aquatic and terrestrial stages of species with complex life cycles. During metamorphosis the function of the tail changes; the larval tail functions in aquatic locomotion while the juvenile and adult tail exhibits tail autotomy and fat storage functions. Because tail injury is common in the aquatic environment, we hypothesized that mechanisms have evolved to prevent altered larval tail morphology from affecting normal juvenile tail morphology. The hypothesis that injury to the larval tail would not affect juvenile tail morphology was investigated by comparing tail development and regeneration in Hemidactylium scutatum (Caudata: Plethodontidae). The experimental design included larvae with uninjured tails and with cut tails to simulate natural predation. The morphological variables analyzed to compare normally developing and regenerating tails were 1) tail length, 2) number of caudal vertebrae, and 3) vertebral centrum length. Control and experimental groups do not differ in time to metamorphosis or snout-vent length. Tails of experimental individuals are shorter than controls, yet they display a significantly higher rate of tail growth and less resorption of tail tissue. Anterior to the site of tail injury, caudal vertebrae in juveniles display greater average centrum lengths. Results suggest that regenerative mechanisms are functioning not only to produce structures, but also to influence growth of existing structures. Further investigation of juvenile and adult stages as well as comparative analyses of tail morphology in salamanders with complex life cycles will enhance our understanding of amphibian development and of the evolution of amphibian life cycles. J Morphol 233:15–29, 1997. © 1997 Wiley-Liss, Inc.     

Vertebral numbers in male and female snakes: the roles of natural,sexual and fecundity selection

The relative numbers of trunk (body) and caudal (tail) vertebrae in snakes might be influenced by at least four processes: (1) natural selection for crawling speed, (2) fecundity selection for larger trunk size in females, (3) sexual selection for longer bodies or tails in males and/or (4) developmental constraints (if an increase in the number of body vertebrae requires a decrease in the number of tail vertebrae, or vice versa). These four hypotheses generate different predictions about the relationship between sex differences in the numbers of body vertebrae vs. tail vertebrae. I collated published data to test these predictions, both with raw data and using phylogenetically independent contrasts. Some snake lineages show a negative correlation between the magnitude of sex disparities in trunk vs. caudal vertebrae whereas other lineages show the reverse pattern, or no correlation. Thus, different selective pressures seem to have been important in different lineages. Vertebral numbers in snakes may offer a useful model system in which to explore the conflicts between natural, fecundity and sexual selection.     

Evolving possibilities: postembryonic axial elongation in salamanders with biphasic (Eurcyea cirrigera,Eurycea longicauda,Eurycea quadridigitata) and paedomorphic life cycles (Eurycea nana and Ambystoma mexicanum)

Vaglia, JL., White, K, and Case, A. 2012. Evolving possibilities: postembryonic axial elongation in salamanders with biphasic (Eurcyea cirrigera, Eurycea longicauda, Eurycea quadridigitata) and paedomorphic life cycles (Eurycea nana and Ambystoma mexicanum). —Acta Zoologica (Stockholm) 93 : 2–13. Typically, the number of vertebrae an organism will have postembryonically is determined during embryogenesis via the development of paired somites. Our research investigates the phenomenon of postembryonic vertebral addition in salamander tails. We describe body and tail growth and patterns of postsacral vertebral addition and elongation in context with caudal morphology for four plethodontids (Eurycea) and one ambystomatid. Eurycea nana and Ambystoma mexicanum have paedomorphic life cycles; Eurcyea cirrigera, Eurycea longicauda and Eurycea quadridigitata are biphasic. Specimens were collected, borrowed and/or purchased, and cleared and stained for bone and cartilage. Data collected include snout‐vent length (SVL), tail length (TL), vertebral counts and centrum lengths. Eurycea species with biphasic life cycles had TLs that surpassed SVL following metamorphosis. Tails in paedomorphic species elongated but rarely exceeded body length. Larger TLs were associated with more vertebrae and longer vertebrae in all species. We observed that rates of postsacral vertebral addition varied little amongst species. Regional variation along the tail becomes prominent following metamorphosis in biphasic developers. In all species, vertebrae in the posterior one‐half of the tail taper towards the tip. We suggest that a developmental link might exist between the ability to continually add vertebrae and regeneration in salamanders.     

Effects of size,caudal autotomy,and predator kairomones on the foraging behavior of Allegheny Mountain dusky salamanders (<Emphasis Type="Italic">Desmognathus ochrophaeus</Emphasis>)

Prey must balance the conflicting demands of foraging and defensive behavior. Foraging under the threat of predation may be further complicated among species that engage in caudal autotomy, the loss of a portion of the tail at preformed breakage planes, because the tail may serve as an important energy storage organ and contribute to motility, culminating in a trade-off between foraging and predator avoidance. As a result of the advantages conferred by the presence of a tail, individuals that have recently undergone autotomy may be more motivated to forage despite elevated levels of threat indicated by predator kairomones. We used a full factorial design to evaluate the combined effects of body size, exposure to predator kairomones, and experience with autotomy on the latency to strike at Drosophila prey, number of strikes, and prey captured per strike by Allegheny Mountain dusky salamanders (Desmognathus ochrophaeus). In our study, caudal autotomy was the only significant main effect and influenced both the latency to attack prey and the number of strikes attempted. In terms of latency to attack prey, there was a significant interaction between body size and autotomy such that “small” salamanders (≤3.2 cm SVL) without tails delayed their foraging behavior. In terms of the number of strikes toward prey, there was a significant interaction between autotomy and exposure to predator kairomones such that individuals with intact tails exhibited a greater number of strikes, with the exception of the “large” (>3.2 cm SVL) salamanders, which performed fewer strikes when exposed to the snake kairomones. There was no significant effect on foraging efficiency, although the trend in the data suggests that autotomized individuals forage more efficiently. This study was designed to evaluate the confluence of factors related to size, caudal autotomy, and exposure to stimuli from predators and hints at the magnitude of caudal autotomy on antipredator decision-making. Our data suggest that despite the importance of tail tissue for energy storage, locomotion, and mating, salamanders without tails are cautious when foraging under elevated risk.     

The effects of substrate and vertebral number on locomotion in the garter snake Thamnophis elegans

1. Locomotor performance of limbless vertebrates depends on the substrate through which individuals move and may result in selection on vertebral number in different habitats. To evaluate the effect of push-point density on snake locomotion, the density of vegetation and other potential push-points was quantified at two sites in California (coastal and inland), where conspecific snakes differed greatly in vertebral number (230 and 256 average total vertebrae, respectively; Arnold 1988). The coastal site had significantly higher push-point densities than the inland site.
2. Five experimental push-point densities that fell within the natural range of push-point densities were employed in laboratory trials of juvenile snake locomotion. Density of push-points significantly affected both crawling speed and head-to-tail distance (HTD), an indirect measure of lateral bending. The fastest speed was achieved at an intermediate push-point density. The shortest HTD occurred when snakes moved through the lowest push-point density.
3. Sex, total number of vertebrae and total length significantly affected HTD, regardless of push-point density. Snakes with relatively more vertebrae had a shorter HTD, suggesting they were able to achieve greater lateral bending than snakes with fewer vertebrae. Coastal and inland populations did not differ in HTD during locomotion.
4. Numbers of body and tail vertebrae significantly influenced speed at different push-point densities. In general, snakes with more body vertebrae were slower than those with fewer, while snakes with more tail vertebrae were faster than those with fewer. Snakes of greater total length were faster at all densities. Coastal snakes crawled faster than inland snakes at all push-point densities.     

Evolution of axial patterning in elongate fishes

Within the ray-finned fishes, eel-like (extremely elongate) body forms have evolved multiple times from deeper-bodied forms. Previous studies have shown that elongation of the vertebral column may be associated with an increase in the number of vertebrae, an increase in the length of the vertebral centra, or a combination of both. Because the vertebral column of fishes has at least two anatomically distinct regions (i.e. abdominal and caudal), an increase in the number and relative length of the vertebrae could be region-specific or occur globally across the length of the vertebral column. In the present study, we recorded vertebral counts and measurements of vertebral aspect ratio (vertebral length/width) from museum specimens for 54 species representing seven groups of actinopterygian fishes. We also collected, from published literature, vertebral counts for 813 species from 14 orders of actinopterygian and elasmobranch fishes. We found that the number of vertebrae can increase independently in the abdominal and caudal regions of the vertebral column, but changes in aspect ratio occur similarly in both regions. These findings suggest that abdominal vertebral number, caudal vertebral number, and vertebral aspect ratio are controlled by separate developmental modules. Based on these findings, we suggest some candidate developmental mechanisms that may contribute to vertebral column patterning in fishes. Our study is an example of how comparative anatomical studies of adults can generate testable hypotheses of evolutionary changes in developmental mechanisms.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 97–116.     

Comparative and functional myology of the prehensile tail in new world monkeys

The caudal myology of prehensile-tailed monkeys (Cebus apella, Alouatta palliata, Alouatta seniculus, Lagothrix lagotricha, and Ateles paniscus) and nonprehensile-tailed primates (Eulemur fulvus, Aotus trivirgatus, Callithrix jacchus, Pithecia pithecia, Saimiri sciureus, Macaca fascicularis, and Cercopithecus aethiops) was examined and compared in order to identify muscular differences that correlate with osteological features diagnostic of tail prehensility. In addition, electrophysiological stimulation was carried out on different segments of the intertransversarii caudae muscle of an adult spider monkey (Ateles geoffroyi) to assess their action on the prehensile tail. Several important muscular differences characterize the prehensile tail of New World monkeys compared to the nonprehensile tail of other primates. In atelines and Cebus, the mass of extensor caudae lateralis and flexor caudae longus muscles is more uniform along the tail, and their long tendons cross a small number of vertebrae before insertion. Also, prehensile-tailed monkeys, especially atelines, are characterized by well-developed flexor and intertransversarii caudae muscles compared to nonprehensile-tailed primates. Finally, Ateles possesses a bulkier abductor caudae medialis and a more cranial origin for the first segment of intertransversarii caudae than do other prehensile-tailed platyrrhines. These myological differences between nonprehensile-tailed and prehensile-tailed primates, and among prehensile-tailed monkeys, agree with published osteological and behavioral data. Caudal myological similarities and differences found in Cebus and atelines, combined with tail-use data from the literature, support the hypothesis that prehensile tails evolved in parallel in Cebus and atelines. © 1995 Wiley-Liss, Inc.     

Evolution of Sexual Dimorphism in the Number of Tail Vertebrae in Salamanders: Comparing Multiple Hypotheses

The evolution of sexual dimorphism is an important topic of evolutionary biology, but few studies have investigated the determinants of sexual dimorphism over broad phylogenetic scales. The number of vertebrae is a discrete character influencing multiple traits of individuals, and is particularly suitable to analyze processes determining morphological variation. We evaluated the support of multiple hypotheses concerning evolutionary processes that may cause sexual dimorphism in the number of caudal vertebrae in Urodela (tailed amphibians). We obtained counts of caudal vertebrae from >2,000 individuals representing 27 species of salamanders and newts from Europe and the Near East, and integrated these data with a molecular phylogeny and multiple information on species natural history. Per each species, we estimated sexual dimorphism in caudal vertebrae number. We then used phylogenetic least squares to relate this sexual dimorphism to natural history features (courtship complexity, body size dimorphism, sexual ornamentation, aquatic phenology) representing alternative hypotheses on processes that may explain sexual dimorphism. In 18 % of species, males had significantly more caudal vertebrae than females, while in no species did females have significantly more caudal vertebrae. Dimorphism was highest in species where males have more complex courtship behaviours, while the support of other candidate mechanisms was weak. In many species, males use the tail during courtship displays, and sexual selection probably favours tails with more vertebrae. Dimorphism for the number of tail vertebrae was unrelated to other forms of dimorphism, such as sexual ornamentation or body size differences. Multiple sexually dimorphic features may evolve independently because of the interplay between sexual selection, fecundity and natural selection.     

Heritability and genetic correlation of abdominal and caudal vertebral numbers in latitudinal populations of the medaka <Emphasis Type="Italic">Oryzias latipes</Emphasis>

Body axes of fishes consist of two anatomically distinct types of vertebrae: abdominal and caudal. In the medaka Oryzias latipes, the number of abdominal vertebrae increases with increasing latitudes, whereas caudal vertebrae do not vary systematically across latitudes, suggesting local adaptation in abdominal vertebral numbers. However, because heritable variation in abdominal and caudal vertebral numbers has not been examined within each latitudinal population, it is not clear whether abdominal and caudal vertebrae can evolve independently. Offspring-midparent regression demonstrated substantial heritability of abdominal vertebral numbers in each of two latitudinal populations whereas the heritability of caudal vertebral numbers was not significant. Full-sib analyses revealed that intra-family variation was larger in caudal vertebrae than in abdominal vertebrae, indicating larger non-additive genetic variation and/or larger errors of development in the former. Moreover, the genetic correlation between abdominal and caudal vertebral numbers was very weak. These results suggest that abdominal and caudal vertebrae are controlled by separate developmental modules, which supports their independent evolution with local adaptation of abdominal vertebral numbers in this fish. On the other hand, the weak heritability of caudal vertebrae suggests that the evolution of caudal vertebrae may be restricted, causing unequal evolutionary lability between abdominal and caudal regions.     

On caudal prehensility and phylogenetic constraint in lizards: The influence of ancestral anatomy on function in Corucia and Furcifer

We examined caudal anatomy in two species of prehensile‐tailed lizards, Furcifer pardalis and Corucia zebrata. Although both species use their tails to grasp, each relies on a strikingly different anatomy to do so. The underlying anatomies appear to reflect phylogenetic constraints on the consequent functional mechanisms. Caudal autotomy is presumably the ancestral condition for lizards and is allowed by a complex system of interdigitating muscle segments. The immediate ancestor of chameleons was nonautotomous and did not possess this specialized anatomy; consequently, the derived arrangement in the chameleon tail is unique among lizards. The limb functions as an articulated linkage system with long tendinous bands originating from longitudinal muscles to directly manipulate vertebrae. Corucia is incapable of autotomy, but it is immediately derived from autotomous ancestors. As such, it has evolved a biomechanical system for prehension quite different from that of chameleons. The caudal anatomy in Corucia is very similar to that of lizards with autotomous tails, yet distinct differences in the ancestral pattern and its relationship to the subdermal tunic are derived. Instead of the functional unit being individual autotomy segments, the interdigitating prongs of muscle have become fused with an emphasis on longitudinal stacks of muscular cones. The muscles originate from the vertebral column and a subdermal collagenous tunic and insert within the adjacent cone. However, there is remarkably little direct connection with the bones. The muscles have origins more associated with the tunic and muscular septa. Like the axial musculature of some fish, the tail of Corucia utilizes a design in which these collagenous elements serve as an integral skeletal component. This arrangement provides Corucia with an elegantly designed system capable of a remarkable variety of bending movements not evident in chameleon tails. J. Morphol. 239:143–155, 1999. © 1999 Wiley‐Liss, Inc.     

Caudal vertebral development and morphology in three salamanders with complex life cycles (Ambystoma jeffersonianum, Hemidactylium scutatum, and Desmognathus ocoee)

We describe caudosacral and caudal vertebral morphology across life history stages in three caudate amphibians: Ambystoma jeffersonianum (Ambystomatidae), Desmognathus ocoee (Plethodontidae: Desmognathinae), and Hemidactylium scutatum (Plethodontidae: Plethodontinae). All three species have aquatic larvae, but adults differ in habitat and predator defense strategy. Predator defense includes tail autotomy in D. ocoee and H. scutatum but not A. jeffersonianum. Of the species that autotomize, H. scutatum has a specialized constriction site at the tail base. We investigated whether aquatic larvae exhibit vertebral features similar to those previously described for aquatic adults and examined the effect of metamorphosis, if any, on vertebral morphology and the ontogeny of specialized vertebral features associated with tail autotomy. Interspecific comparisons of cleared-and-stained specimens indicate that vertebral morphology differs dramatically at hatching and that caudosacral and caudal vertebrae undergo continuous ontogenetic change throughout larval, metamorphic, and juvenile periods. Larvae and juveniles of H. scutatum do not exhibit adult vertebral features associated with constricted-base tail autotomy. The pond-type larvae of A. jeffersonianum and H. scutatum have tapering centrum lengths posterior to the sacrum. This pattern is functionally associated with aquatic locomotion. The stream-type larvae of D. ocoee undergo enhanced regional growth in the anterior tail such that the anterior caudal centra become longer than the preceding caudosacral centra. With the exception of the first two caudal vertebrae, a similar growth pattern occurs in H. scutatum adults. We hypothesize that enhanced growth of the anterior caudal segments is associated with tail elongation and autotomy.     

Male pregnancy and the evolution of body segmentation in seahorses and pipefishes

The evolution of complex traits, which are specified by the interplay of multiple genetic loci and environmental effects, is a topic of central importance in evolutionary biology. Here, we show that body and tail vertebral numbers in fishes of the pipefish and seahorse family (Syngnathidae) can serve as a model for studies of quantitative trait evolution. A quantitative genetic analysis of body and tail vertebrae from field-collected families of the Gulf pipefish, Syngnathus scovelli, shows that both traits exhibit significantly positive additive genetic variance, with heritabilities of 0.75 +/- 0.13 (mean +/- standard error) and 0.46 +/- 0.18, respectively. We do not find any evidence for either phenotypic or genetic correlations between the two traits. Pipefish are characterized by male pregnancy, and phylogenetic consideration of body proportions suggests that the position of eggs on the pregnant male's body may have contributed to the evolution of vertebral counts. In terms of numbers of vertebrae, tail-brooding males have longer tails for a given trunk size than do trunk-brooding males. Overall, these results suggest that vertebral counts in pipefish are heritable traits, capable of a response to selection, and they may have experienced an interesting history of selection due to the phenomenon of male pregnancy. Given that these traits vary among populations within species as well as among species, they appear to provide an excellent model for further research on complex trait evolution. Body segmentation may thus afford excellent opportunities for comparative study of homologous complex traits among disparate vertebrate taxa.     

Sexual dimorphism in snake tail length: sexual selection,natural selection,or morphological constraint?

Male snakes typically have longer tails relative to body length than females, but the extent of this dimorphism varies among species. Three hypotheses have been suggested to explain tail dimorphism. The Morphological Constraint Hypothesis proposes that males have relatively longer tails to accommodate hemipenes and retractor muscles. The Female Reproductive Output Hypothesis proposes that females have relatively shorter tails as a secondary result of natural selection for increased reproductive capacity. The Male Mating Ability Hypothesis proposes that sexual selection favours relatively longer tails in males during courtship. These hypotheses make different predictions about the relationships among tail length, body size, male reproductive morphology, female reproductive output, mode of reproduction, and male mating behaviour among and within taxa. Predictions were tested using published data for 56 genera in the family Colubridae and original data for the water snake, Nerodia sipedon. Tail length dimorphism was more male-biased in tam having relatively short tails (r=–0.52, P < 0.001), hemipenes and retractor muscles occupied a greater proportion of the tail in taxa having relatively short tails (r=– 0.71, P < 0.00l and r=– 0.66, P = 0.001, respectively), and tail length dimorphism was more male-biased in taxa in which body size dimorphism was more female-biased (r=– 0.60, P < 0.001). These results support both the Morphological Constraint Hypotheses and the Female Reproductive Output Hypothesis. However, tests of other predictions, including those regarding patterns within N. sipedon , failed to support any of the three hypotheses. Comparisons among taxa suggest several species in which further tests of these hypotheses would be especially appropriate.     

Ecological and phylogenetic variability in the spinalis muscle of snakes

Understanding the origin and maintenance of functionally important subordinate traits is a major goal of evolutionary physiologists and ecomorphologists. Within the confines of a limbless body plan, snakes are diverse in terms of body size and ecology, but we know little about the functional traits that underlie this diversity. We used a phylogenetically diverse group of 131 snake species to examine associations between habitat use, sidewinding locomotion and constriction behaviour with the number of body vertebrae spanned by a single segment of the spinalis muscle, with total numbers of body vertebrae used as a covariate in statistical analyses. We compared models with combinations of these predictors to determine which best fit the data among all species and for the advanced snakes only (N = 114). We used both ordinary least‐squares models and phylogenetic models in which the residuals were modelled as evolving by the Ornstein–Uhlenbeck process. Snakes with greater numbers of vertebrae tended to have spinalis muscles that spanned more vertebrae. Habitat effects dominated models for analyses of all species and advanced snakes only, with the spinalis length spanning more vertebrae in arboreal species and fewer vertebrae in aquatic and burrowing species. Sidewinding specialists had shorter muscle lengths than nonspecialists. The relationship between prey constriction and spinalis length was less clear. Differences among clades were also strong when considering all species, but not for advanced snakes alone. Overall, these results suggest that muscle morphology may have played a key role in the adaptive radiation of snakes.     

Variations in the dietary compositions of morphologically diverse syngnathid fishes

Synopsis We examined the diets of 12 morphologically diverse syngnathid species in shallow seagrass-dominated marine waters of south-western Australia to determine whether they differed among species that varied in body form, size and snout morphology, and in particular whether species with long snouts ingested more mobile prey. Although all species consume mainly small crustaceans, the dietary compositions of these species often vary markedly. We suggest that these differences are related to factors that influence both their foraging capabilities and/or locations. Those species with long snouts (e.g. the common seadragon Phyllopteryx taeniolatus and long-snouted pipefish Vanacampus poecilolaemus) consume far more relatively mobile prey than species with short snouts. Species with short snouts (e.g. the pug-nosed pipefish Pugnaso curtirostris and Macleays crested pipefish Histiogamphelus cristatus) mainly consume slow moving prey. Spotted pipefish, Stigmatopora argus, and wide-bodied pipefish, Stigmatopora nigra, restrict their diets to planktonic copepods, probably because their small gape size limits their ability to feed on alternative larger prey. Both the short-snouted seahorse, Hippocampus breviceps, and West Australian seahorse, Hippocampus subelongatus, ingest mainly slow-moving prey, even though the latter species possesses a moderately long snout. This may reflect the fact that seahorses are weak swimmers that anchor themselves to vegetation or the substrate with a strongly prehensile tail and rarely venture into open water to pursue mobile prey. In contrast, the relatively large P. taeniolatus, which resides above, rather than within, the macrophyte canopy, consumes mysids, which aggregate in open water above the seabed. Those pipefishes with characters that imply relatively enhanced mobility, such as well developed caudal fins and non-prehensile tails, are trophically diverse, suggesting that they are able to feed either on the sediment or phytal surfaces or in the water column.