Quantitative Genetics and Evolution of Head Shape in <Emphasis Type="Italic">Plethodon</Emphasis> Salamanders

The evolution of morphological diversity via selection requires that morphological traits display significant heritable genetic variation. In Plethodon salamanders, considerable evidence suggests that head shape evolves in response to selection from interspecific competition, yet the genetic underpinnings of head shape have not been quantitatively examined. Here I used geometric morphometrics and quantitative genetics to assess heritable patterns of head shape variation from hatchling salamanders in two Plethodon species (P. cinereus and P. nettingi). Head shape differed significantly between species and among clutches within species, suggesting that a sizeable proportion of head shape variation was the result of clutch effects. Further, using a full-sib animal model and restricted maximum likelihood (REML), I identified large values of maximal additive heritability for all study localities ($ h_{\max }^{2} > 0.65 $ h_{\max }^{2} > 0.65 ), revealing that Plethodon exhibit considerable heritable genetic variation for head shape. Comparisons of the components of heritable shape variation showed that the magnitude of shape heritability (h_max² h_{\max }^{2} ) did not differ among localities or species. Therefore, the potential microevolutionary shape change displayed by the two species would be similar if they were exposed to comparable selective forces. However, the direction of maximal shape heritability in morphospace differed between P. cinereus and P. nettingi, indicating that potential evolutionary shape change along these heritability trajectories would diverge between the two species. This finding implies that distinct head shapes could evolve in the two species, even if subjected to the same selection pressure. When combined with previous knowledge of patterns of head shape variation among species and ecological selection on head shape, these findings suggest that microevolutionary and macroevolutionary trends of morphological diversification in Plethodon may be explained as a result of the interaction between ecological selection and underlying patterns of genetic covariance for this multi-dimensional trait.     

Sexual differences in head form and diet in a population of Mexican lance‐headed rattlesnakes,Crotalus polystictus

Sexual dimorphism of phenotypic traits associated with resource use is common in animals, and may result from niche divergence between sexes. Snakes have become widely used in studies of the ecological basis of sexual dimorphism because they are gape‐limited predators and their head morphology is likely to be a direct indicator of the size and shape of prey consumed. We examined sexual dimorphism of body size and head morphology, as well as sexual differences in diet, in a population of Mexican lance‐headed rattlesnakes, Crotalus polystictus, from the State of México, Mexico. The maximum snout–vent length of males was greater than that of females by 21%. Males had relatively larger heads, and differed from females in head shape after removing the effects of head size. In addition, male rattlesnakes showed positive allometry in head shape: head width was amplified, whereas snout length was truncated with increased head size. By contrast, our data did not provide clear evidence of allometry in head shape of females. Adults of both males and females ate predominately mice and voles; however, males also consumed a greater proportion of larger mammalian species, and fewer small prey species. The differences in diet correspond with dimorphism in head morphology, and provide evidence of intersexual niche divergence in the study population. However, because the sexes overlapped greatly in diet, we hypothesize that diet and head dimorphisms in C. polystictus are likely related to different selection pressures in each sex arising from pre‐existing body size differences rather than from character displacement for reducing intersexual competition. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 633–640.     

Landmark-based morphometric analysis of the body shape of two sympatric species, <Emphasis Type="Italic">Ctenopharynx pictus</Emphasis> and <Emphasis Type="Italic">Otopharynx </Emphasis>sp. “heterodon nankhumba” (Teleostei: Cichlidae), from Lake Malawi

 Morphological differences in body shape of two sympatric benthophagous cichlid species from Lake Malawi, Ctenopharynx pictus and an undescribed species, Otopharynx sp. “heterodon nankhumba,” were investigated using geometric morphometric methods. From digitized data of landmark points on lateral profiles of fishes, the shape of each species was compared by the thin-plate spline method. Statistical analyses revealed significant variation in both uniform and nonuniform components of shape between the two species. From the splines generated, it was revealed that most of the significant variation between the two species occurs in the head region. Specifically, C. pictus has a longer and deeper head than Otopharynx sp. In addition, the mouth of C. pictus is larger than that of Otopharynx sp. In the trunk region, C. pictus has a shorter abdominal cavity, which may indicate possession of shorter intestines than Otopharynx sp. The variation in gross head morphology and intestinal length may reflect interspecific differences in trophic ecology, possibly facilitating the coexistence of the two species through resource partitioning.     

Sexual dimorphism of head morphology in three‐spined stickleback Gasterosteus aculeatus

This study examined sexual dimorphism of head morphology in the ecologically diverse three‐spined stickleback Gasterosteus aculeatus. Male G. aculeatus had longer heads than female G. aculeatus in all 10 anadromous, stream and lake populations examined, and head length growth rates were significantly higher in males in half of the populations sampled, indicating that differences in head size increased with body size in many populations. Despite consistently larger heads in males, there was significant variation in size‐adjusted head length among populations, suggesting that the relationship between head length and body length was flexible. Inter‐population differences in head length were correlated between sexes, thus population‐level factors influenced head length in both sexes despite the sexual dimorphism present. Head shape variation between lake and anadromous populations was greater than that between sexes. The common divergence in head shape between sexes across populations was about twice as important as the sexual dimorphism unique to each population. Finally, much of the sexual dimorphism in head length was due to divergence in the anterior region of the head, where the primary trophic structures were found. It is unclear whether the sexual dimorphism was due to natural selection for niche divergence between sexes or sexual selection. This study improves knowledge of the magnitude, growth rate divergence, inter‐population variation and location of sexual dimorphism in G. aculeatus head morphology.     

<Emphasis Type="Italic">Paraliparis adustus</Emphasis> and <Emphasis Type="Italic">Paraliparis bullacephalus</Emphasis>: two new snailfish species (Teleostei: Liparidae) from Alaska

Paraliparis adustus sp. nov., a snailfish species from the Bering Sea near the Aleutian Island Archipelago, Alaska, is described based on a single mesopelagic specimen. This new species is clearly distinguished by a combination of several morphological features and meristic counts, including long pointed gill rakers with 0–3 spinules at or near the tip, anus positioned forward near the pectoral symphysis, and color uniform brown. Paraliparis bullacephalus sp. nov. from Shelikof Strait, Gulf of Alaska, is also described. This new species is very similar in meristic characters and general body shape and size to P. holomelas Gilbert, but differs primarily in morphological features of the head, particularly in the shape of the dorsal contour of the head, snout, and opercular flap, mouth size, and eye position.     

A non‐invasive geometric morphometrics method for exploring variation in dorsal head shape in urodeles: sexual dimorphism and geographic variation in Salamandra salamandra

The study of morphological variation among and within taxa can shed light on the evolution of phenotypic diversification. In the case of urodeles, the dorso‐ventral view of the head captures most of the ontogenetic and evolutionary variation of the entire head, which is a structure with a high potential for being a target of selection due to its relevance in ecological and social functions. Here, we describe a non‐invasive procedure of geometric morphometrics for exploring morphological variation in the external dorso‐ventral view of urodeles' head. To explore the accuracy of the method and its potential for describing morphological patterns we applied it to two populations of Salamandra salamandra gallaica from NW Iberia. Using landmark‐based geometric morphometrics, we detected differences in head shape between populations and sexes, and an allometric relationship between shape and size. We also determined that not all differences in head shape are due to size variation, suggesting intrinsic shape differences across sexes and populations. These morphological patterns had not been previously explored in S. salamandra , despite the high levels of intraspecific diversity within this species. The methodological procedure presented here allows to detect shape variation at a very fine scale, and solves the drawbacks of using cranial samples, thus increasing the possibilities of using collection specimens and alive animals for exploring dorsal head shape variation and its evolutionary and ecological implications in urodeles. J. Morphol. 278:475–485, 2017. © 2017 Wiley Periodicals, Inc.     

Variation in Body Shape across Species and Populations in a Radiation of Diaptomid Copepods

Inter and intra-population variation in morphological traits, such as body size and shape, provides important insights into the ecological importance of individual natural populations. The radiation of Diaptomid species (~400 species) has apparently produced little morphological differentiation other than those in secondary sexual characteristics, suggesting sexual, rather than ecological, selection has driven speciation. This evolutionary history suggests that species, and conspecific populations, would be ecologically redundant but recent work found contrasting ecosystem effects among both species and populations. This study provides the first quantification of shape variation among species, populations, and/or sexes (beyond taxonomic illustrations and body size measurements) to gain insight into the ecological differentiation of Diaptomids. Here we quantify the shape of five Diaptomid species (family Diaptomidae) from four populations each, using morphometric landmarks on the prosome, urosome, and antennae. We partition morphological variation among species, populations, and sexes, and test for phenotype-by-environment correlations to reveal possible functional consequences of shape variation. We found that intraspecific variation was 18-35% as large as interspecific variation across all measured traits. Interspecific variation in body size and relative antennae length, the two traits showing significant sexual dimorphism, were correlated with lake size and geographic location suggesting some niche differentiation between species. Observed relationships between intraspecific morphological variation and the environment suggest that divergent selection in contrasting lakes might contribute to shape differences among local populations, but confirming this requires further analyses. Our results show that although Diaptomid species differ in their reproductive traits, they also differ in other morphological traits that might indicate ecological differences among species and populations.     

Patterns of DNA sequence variation at candidate gene loci in black poplar (<Emphasis Type="Italic">Populus nigra</Emphasis> L.) as revealed by single nucleotide polymorphisms

Black poplar (Populus nigra L.) is an economically and ecologically important tree species and an ideal organism for studies of genetic variation. In the present work, we use a candidate gene approach to infer the patterns of DNA variation in natural populations of this species. A total of 312 single nucleotide polymorphisms (SNPs) are found among 8,056 bp sequenced from nine drought-adaptation and photosynthesis-related gene loci. The median SNP frequency is one site per 26 bp. The average nucleotide diversity is calculated to be θ_W = 0.01074 and π_T = 0.00702, higher values than those observed in P. tremula, P. trichocarpa and most conifer species. Tests of neutrality for each gene reveal a general excess of low-frequency mutations, a greater number of haplotypes than expected and an excess of high-frequency derived variants in P. nigra, which is consistent with previous findings that genetic hitchhiking has occurred in this species. Linkage disequilibrium is low, decaying rapidly from 0.45 to 0.20 or less within a distance of 300 bp, although the declines of r ² are variable among different loci. This is similar to the rate of decay reported in most other tree species. Our dataset is expected to enhance understanding of how evolutionary forces shape genetic variation, and it will contribute to molecular breeding in black poplar.     

Relationships between head morphology, bite performance and ecology in two species of Podarcis wall lizards

Understanding the relationship between form and function is central to our comprehension of how phenotypic diversity evolves. Traits involved in multiple activities, such as social interactions and ecological resource use, are under the influence of different evolutionary forces potentially acting in opposite directions. Such systems provide the opportunity of understanding how potential constraints on morphological variation may influence whole-organism performance. In this study we examined morphology and bite performance in two closely related species of Podarcis wall lizards with divergent microhabitat preferences, to investigate how natural and sexual selection interact to shape the evolution of head traits. Our results show that although head morphology is markedly different between species and sexes, only sexes differ in bite force, indicating that the ecological differentiation between species is reflected in their morphology but does not constrain performance. Rather, the modification of the relative size of head components between species and a shift in the form-function relationship provide a potential explanation of how equal performance is attained by different morphological configurations. Geometric morphometrics provide a clear, biomechanically meaningful image of how this is achieved and show a bisexual pattern of head shape-bite force association in both species. This, together with a strong allometry of head size on body size and head shape on head size, provides indirect morphological evidence for the importance of sexual selection in shaping morphological and functional patterns. Finally, our findings suggest that the differences observed between species and sexes in head traits and bite performance are not reflected in their dietary ecology, implying that if trophic niche segregation between groups occurs, the reasons behind it are not primarily related to head morphology and functional variation.     

A phylogenetic analysis of sex-specific evolution of ecological morphology in <Emphasis Type="Italic">Liolaemus</Emphasis> lizards

Adaptive radiation theory predicts that phenotypic traits involved in ecological performance evolve in different directions in populations subjected to divergent natural selection, resulting in the evolution of ecological diversity. This idea has largely been supported through comparative studies exploring relationships between ecological preferences and quantitative traits among different species. However, intersexual perspectives are often ignored. Indeed, although it is well established that intersexual competition and sex-specific parental and reproductive roles may often subject sex-linked phenotypes to antagonistic selection effects, most ecomorphological research has explored adaptive evolution on a single sex, or on means obtained from both sexes together. The few studies taking sexual differences into account reveal the occurrence of sex-specific ecomorphs in some clades of lizards, and conclude that the independent contribution of the sexes to the morphological diversity produced by adaptive radiation can be substantial. Here, we investigate whether microhabitat use results in the evolution of sex-specific ecomorphs across 44 Liolaemus lizard species. We found that microhabitat structure does not predict variation in body size and shape in either of the sexes. Yet, we found that males and females tend to occupy significantly different positions in multivariate morphological spaces, indicating that treating males and females as ecologically and phenotypically equivalent units may lead to incomplete or mistaken estimations of the diversity produced by adaptive evolution.     

Sex,androgens, and whole‐organism performance in an Australian lizard

Understanding underlying physiological differences between the sexes in circulating androgens and how hormonal variation affects morphology–performance relationships may help clarify the evolution of sexual dimorphism in diverse taxa. Using a widely distributed Australian lizard (Eulamprus quoyii) with weak sexual dimorphism and no dichromatism, we tested whether circulating androgens differed between the sexes and whether they covaried with morphological and performance traits (bite force, sprint speed, endurance). Males had larger head dimensions, stronger bite force, faster sprint speed, and longer endurance compared to females. We found that the sexes did not differ in androgen concentrations and that androgens were weakly associated with both morphological and performance traits. Interestingly, high circulating androgens showed a nonlinear relationship with bite force in males and not females, with this relationship possibly being related to alternative male reproductive tactics. Our results suggest that androgens are not strongly correlated with most performance and morphological traits, although they may play an important organizational role during the development of morphological traits, which could explain the differences in morphology and thus performance between the sexes. Differences in performance between the sexes suggest differential selection on these functional traits between males and females. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 834–849.     

“Reverse” sexual dichromatism in a Neotropical frog

Sexual dichromatism is widespread among animals, but examples of “reverse” sexual dichromatism, in which females are more brightly colored than males, are extremely rare. We discovered a unique case of reverse sexual dichromatism in the golden rocket frog (Anomaloglossus beebei), a diurnal Neotropical frog. Females are bright “golden” in color, and males are drab tan with brown pigmentation that darkens when they are calling. Here, we document this color variation with calibrated digital photography and further show that there is no evidence for sex‐specific habitat matching; both sexes live in the same well‐lit habitat on green bromeliad leaves. Our results suggest that color variation in this species is an intraspecific signal and provide an important exception to the general expectation that males are more visually conspicuous in species with conventional sex roles.     

Comparative Morphometrics and Associated Growth Trends of Two Benthophagous Cichlid Species from Lake Malawi (Pisces, Perciformes)

Body shape differences between two benthophagous, sympatric cichlid species, Ctenopharynx pictus and Otopharynx sp. “heterodon nankhumba” were examined for 14 morphometric characters using measurements obtained from 11 morphological landmarks and additional 6 characters from the head region using principal component and regression analyses. The two species, though not closely related, superficially resemble each other and, being benthic feeders, directly compete for food resources unless morphological differences lead to trophic specialization. Hence, the present study explores the presence of such morphological variations. Principal component analysis (PCA), revealed that only four characters loaded highly on PC II and, therefore, account for most of the variations in the external morphology between the two species. C. pictus has longer lower jaws reflecting longer gape, and a shorter abdominal cavity than O. sp. “heterodon nakhumba”. The regression analyses showed significant differences in the allometric coefficients of the lower jaw and abdominal cavity, which might have contributed to differences in overall shape detected between the two species. The difference in gape size between the two species may be related to different feeding habits employed by each species, and such specializations are suggested to reduce interspecific competition for food resources. We suggest that the ensuing ecological separation promotes sympatry of these two species.     

A NEW BLACKFLY SPECIES OF SIMULIUM (DIPTERA: SIMULIIDAE) FROM GUIZHOU PROVINCE,CHINA*

Abstract The present paper deals with a new species of Simulium (Simulium) from Leigongshan, Guizhou province, S. (S.) qianense sp. nov. The specific name was given in the place of production. On the basis of the morphological characters, the new species (S.) qianense sp. nov evidently falls into S. variegatum species‐group, is most similar to S. (S.) taiwanicum, 1979, but can be distinguished from the latter by the characteristic pattern of scutum and legs color in the both sexes, the shape of male geritalia and several characters in the larva. The type specimens are kept in the Department of Biology of the Guiyang Medical College.     

Multivariate and geometric morphometrics in the analysis of sexual dimorphism variation in Podarcis lizards

Podarcis bocagei and P. carbonelli are two closely related lacertid species, very similar morphologically and ecologically. We investigated sexual dimorphism patterns presented by both species in allopatry and in sympatry. Sexual size and shape dimorphism patterns were analyzed using both multivariate and geometric morphometric techniques. Multivariate morphometrics revealed a marked sexual dimorphism in both species--males being larger with more robust habitus and females presenting a longer trunk. General patterns of sexual size dimorphism are not modified in sympatry, although there is evidence for some morphological change in male head size. The application of geometric morphometrics offered a more detailed image of head shape and revealed that males present a more developed tympanic area than do females, while females have a more rounded head. Differences in the degree of sexual shape dimorphism were detected in sympatry, but no consistent patterns were observed. From the results of the study, and based on previous knowledge on the populations studied, we conclude that the morphological differences observed are probably not caused by exploitative competition between the species, but rather appear attributable to the modification of the relative influence of sexual and natural selection on both sexes.     

Geometric morphometric and phylogenetic analyses of Arizona Sky Island populations of Scaphinotus petersi Roeschke (Coleoptera: Carabidae)

Scaphinotus petersi Roeschke, 1907 (Carabidae) is a ground beetle endemic to Sky Islands in south‐eastern Arizona. Previous taxonomic studies described several subspecies with morphological differences inhabiting geographically isolated mountain ranges. We combined molecular sequence data and morphometric data, especially head and pronotum shape analyses, to examine the variation and divergence in subspecies and isolated montane populations. In this study, we employ a combination of distance morphometrics as well as geometric morphometrics to quantify the level of morphological variation, and to test the hypothesis that geographically distinct populations of S. petersi are phenotypically distinct. Results suggest that these isolated populations have diverged morphologically and genetically. Phylogenetic analyses identified two monophyletic lineages within the species that correspond generally to pronotum shape. We observed significant morphological variation among most montane populations in of S. petersi, with the pronotum shape as the clearest delimiting trait. © 2015 The Linnean Society of London     

Sex‐specific evolution of bite performance in Liolaemus lizards (Iguania: Liolaemidae): the battle of the sexes

Although differential selective pressures on males and females of the same species may result in sex‐specific evolutionary trajectories, comparative studies of adaptive radiations have largely neglected within‐species variation. In this study, we explore the potential effects of natural selection, sexual selection, or a combination of both, on bite performance in males and females of 19 species of Liolaemus lizards. More specifically, we study the evolution of bite performance, and compare evolutionary relationships between the variation in head morphology, bite performance, ecological variation and sexual dimorphism between males and females. Our results suggest that in male Liolaemus, the variation in bite force is at least partly explained by the variation in the degree of sexual dimorphism in head width (i.e. our estimate of the intensity of sexual selection), and neither bite force nor the morphological variables were correlated with diet (i.e. our proxy for natural selection). On the contrary, in females, the variation in bite force and head size can, to a certain extent, be explained by variation in diet. These results suggest that whereas in males, sexual selection seems to be operating on bite performance, in the case of females, natural selection seems to be the most likely and most important selective pressure driving the variation in head size. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 461–475.