The impact of Pleistocene glaciation across the range of a widespread European coastal species

There is a growing consensus that much of the contemporary phylogeography of northern hemisphere coastal taxa reflects the impact of Pleistocene glaciation, when glaciers covered much of the coastline at higher latitudes and sea levels dropped by as much as 150 m. The genetic signature of postglacial recolonization has been detected in many marine species, but the effects of coastal glaciation are not ubiquitous, leading to suggestions that species may intrinsically differ in their ability to respond to the environmental change associated with glacial cycles. Such variation may indeed have a biological basis, but apparent differences in population structure among taxa may also stem from our heavy reliance on individual mitochondrial loci, which are strongly influenced by stochasticity during coalescence. We investigated the contemporary population genetics of Syngnathus typhle, one of the most widespread European coastal fish species, using a multilocus data set to investigate the influence of Pleistocene glaciation and reduced sea levels on its phylogeography. A strong signal of postglacial recolonization was detected at both the northern and eastern ends of the species’ distribution, while southern populations appear to have been relatively unaffected by the last glacial cycle. Patterns of population variation and differentiation at nuclear and mitochondrial loci differ significantly, but simulations indicate that these differences can be explained by the stochastic nature of the coalescent process. These results demonstrate the strength of a multilocus approach to phylogeography and suggest that an overdependence on mitochondrial loci may provide a misleading picture of population‐level processes.     

Functional performance of turtle humerus shape across an ecological adaptive landscape

The concept of the adaptive landscape has been invaluable to evolutionary biologists for visualizing the dynamics of selection and adaptation, and is increasingly being used to study morpho‐functional data. Here, we construct adaptive landscapes to explore functional trade‐offs associated with variation in humerus morphology among turtles adapted to three different locomotor environments: marine, semiaquatic, and terrestrial. Humerus shape from 40 species of cryptodire turtles was quantified using a pseudolandmark approach. Hypothetical shapes were extracted in a grid across morphospace and four functional traits (strength, stride length, mechanical advantage, and hydrodynamics) measured on those shapes. Quantitative trait modeling was used to construct adaptive landscapes that optimize the functional traits for each of the three locomotor ecologies. Our data show that turtles living in different environments have statistically different humeral shapes. The optimum adaptive landscape for each ecology is defined by a different combination of performance trade‐offs, with turtle species clustering around their respective adaptive peak. Further, species adhere to pareto fronts between marine–semiaquatic and semiaquatic–terrestrial optima, but not between marine–terrestrial. Our study demonstrates the utility of adaptive landscapes in informing the link between form, function, and ecological adaptation, and establishes a framework for reconstructing turtle ecological evolution using isolated humeri from the fossil record.     

Increased competition as a cost of specialization during the evolution of resource polymorphism

Identifying the factors that promote or preclude the evolution of resource polymorphism is essential for understanding the origins of diversity. Although such polymorphisms have long been viewed as an adaptive response to intraspecific competition, they are by no means ubiquitous, even in populations experiencing strong competition. In the present study, we examined a potentially important cost of resource polymorphism. Specifically, resource polymorphism typically entails the evolution of one or more resource‐use specialists, and these specialists may suffer more from competition with other specialists than generalists would with other generalists. Using spadefoot toad tadpoles as a model system, we combined stable isotope analyses with an experiment aiming to characterize dietary differences between alternative carnivore and omnivore morphs and to assess the potential ecological consequences of any such differences. We found that carnivores and omnivores represent alternative trophic specialists and generalists, respectively. We also established that the specialist morph (carnivores) experienced greater intramorph competition than the generalist morph (omnivores). We hypothesize that the greater intramorph competition faced by specialists stems ultimately from functional limitations associated with trophic specialization, which prevent specialists from switching to alternative resources when their resource is depleted. These costs may even preclude the evolution of distinct resource‐use specialists, and hence resource polymorphism, in certain populations. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Predicting ecological and phenotypic differentiation in the wild: a case of piscivorous fish in a fishless environment

Environmental variation drives ecological and phenotypic change. How predictable is differentiation in response to environmental change? Answering this question requires the development and testing of multifarious a priori predictions in natural systems. We employ this approach using Gobiomorus dormitor populations that have colonized inland blue holes differing in the availability of fish prey. We evaluated predictions of differences in demographics, habitat use, diet, locomotor and trophic morphology, and feeding kinematics and performance between G. dormitor populations inhabiting blue holes with and without fish prey. Populations of G. dormitor independently diverged between prey regimes, with broad agreement between observed differences and a priori predictions. For example, in populations lacking fish prey, we observed male‐biased sex ratios, a greater use of shallow‐water habitat, and larger population diet breadths as a result of greater individual diet specialization. Furthermore, we found predictable differences in body shape, mouth morphology, suction generation capacity, strike kinematics, and feeding performance on different prey types, consistent with the adaptation of G. dormitor to piscivory when coexisting with fish prey and to feeding on small invertebrates in their absence. The results of the present study suggest great potential in our ability to predict population responses to changing environments, which is an increasingly important capability in a human‐dominated, ever‐changing world. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 588–607.     

A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters

Mammalian molluscivores feed mainly by shell-crushing or suction-feeding. The extinct marine arctoid, Kolponomos, has been interpreted as an otter-like shell-crusher based on similar dentitions. However, neither the masticatory biomechanics of the shell-crushing adaptation nor the way Kolponomos may have captured hard-shelled prey have been tested. Based on mandibular symphyseal morphology shared by Kolponomos and sabre-toothed carnivores, we hypothesize a sabretooth-like mechanism for Kolponomos prey-capture, whereby the mandible functioned as an anchor. Torque generated from jaw closure and head flexion was used to dislodge prey by prying, with prey then crushed using cheek teeth. We test this hypothesized feeding sequence using phylogenetically informed biomechanical simulations and shape analyses, and find a strongly supported, shared high mandibular stiffness in simulated prey-capture bites and mandibular shape in Kolponomos and the sabre-toothed cat Smilodon. These two distantly related taxa converged on using mandibles to anchor cranial torqueing forces when prying substrate-bound prey in the former and sabre-driving forces during prey-killing in the latter. Simulated prey-crushing bites indicate that Kolponomos and sea otters exhibit alternative structural stiffness-bite efficiency combinations in mandibular biomechanical adaptation for shell-crushing. This unique feeding system of Kolponomos exemplifies a mosaic of form-function convergence relative to other Carnivora.     

The impact of digging on the evolution of the rodent mandible

There are two main (but not mutually exclusive) methods by which subterranean rodents construct burrows: chisel-tooth digging, where large incisors are used to dig through soil; and scratch digging, where forelimbs and claws are used to dig instead of incisors. A previous study by the authors showed that upper incisors of chisel-tooth diggers were better adapted to dig but the overall cranial morphology within the rodent sample was not significantly different. This study analyzed the lower incisors and mandibles of the specimens used in the previous study to show the impact of chisel-tooth digging on the rodent mandible. We compared lower incisors and mandibular shape of chisel-tooth digging rodents with nonchisel-tooth digging rodents to see if there were morphological differences between the two groups. The shape of incisors was quantified using incisor radius of curvature and second moment of area (SMA). Mandibular shape was quantified using landmark based geometric morphometrics. We found that lower incisor shape was strongly influenced by digging group using a Generalized Phylogenetic ancova (analysis of covariance). A phylogenetic Procrustes anova (analysis of variance) showed that mandibular shape of chisel-tooth digging rodents was also significantly different from nonchisel-tooth digging rodents. The phylogenetic signal of incisor radius of curvature was weak, whereas that of incisor SMA and mandibular shape was significant. This is despite the analyses revealing significant differences in the shape of both mandibles and incisors between digging groups. In conclusion, we showed that although the mandible and incisor of rodents are influenced by function, there is also a degree of phylogenetic affinity that shapes the rodent mandibular apparatus.     

The evolution of species interactions across natural landscapes

Given the potential for rapid and microgeographical adaptation, ecologists increasingly are exploring evolutionary explanations for community patterns. Biotic selection can generate local adaptations that alter species interactions. Although some gene flow might be necessary to fuel local adaptation, higher gene flow can homogenise traits across regions and generate local maladaptation. Herein, I estimate the contributions of local biotic selection, gene flow and spatially autocorrelated biotic selection to among-population divergence in traits involved in species interactions across 75 studies. Local biotic selection explained 6.9% of inter-population trait divergence, an indirect estimate of restricted gene flow explained 0.1%, and spatially autocorrelated selection explained 9.3%. Together, biotic selection explained 16% of the variance in population trait means. Most biotic selection regimes were spatially autocorrelated. Hence, most populations receive gene flow from populations facing similar selection, which could allow for local adaptation despite moderate gene flow. Gene flow constrained adaptation in studies conducted at finer spatial scales as expected, but this effect was often confounded with spatially autocorrelated selection. Results indicate that traits involved in species interactions might often evolve across landscapes, especially when biotic selection is spatially autocorrelated. The frequent evolution of species interactions suggests that evolutionary processes might often influence community ecology.     

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.     

Shape changes and growth trajectories in the early stages of three species of the genus Diplodus (Perciformes, Sparidae)

The larvae of three species of the genus Diplodus (Diplodus vulgaris, D. sargus, and D. puntazzo) colonize shallow waters along the Mediterranean coasts and, after a short period spent in the water column, they settle. For all three species this habitat transition is characterized by important shape changes mostly related to swimming capacity and feeding behavior. In this study, geometric morphometrics are used to characterize shape changes during the early juvenile life of specimens collected in a single locality in order to compare growth curves and allometric relationships. Size-related shape changes proved to be similar for all three species and are consistent with the ecological transition. A nonparametric smoothing technique (Loess) was used to fit the scatter of shape on size. The graphical representation (of most size-related shape variability) of this fitting technique shows how major shape changes are rapid for small sizes and slow down successively. The approach allows for the visualization of allometry and the fitting technique might help in defining the allometric growth pattern, thus contributing to the study of the autoecology of the species and in establishing terms for comparison with other ecologically or phylogenetically related species.     

Variation in the digging apparatus of the subterranean silvery mole-rat, Heliophobius argenteocinereus (Rodentia, Bathyergidae): the role of ecology and geography

The skull of most subterranean tooth-digging rodents is markedly affected by their digging mode. In the present study, we investigated the cranial variation in a strictly subterranean, highly specialized Afrotropical tooth-digger, Heliophobius argenteocinereus (Bathyergidae, Rodentia), using a geometric morphometric approach and evaluated the effect of different factors on size and shape differences among four populations. No evidence for sexual dimorphism was found in skull size or shape. The cranial shape variation was large and influenced mainly by the type of habitat (miombo woodland versus farmland and grassland) and the latitudinal gradient. The dorsal side of the skull appears to be more plastic and adaptable to local environments, as well as more independent of size, than the ventral side. Only the shortening of the rostrum is presumably an adaptive process independent of size that leads to an increase of efficacy of the tooth-digging apparatus in Heliophobius , whereas the increase in the in-force and the more procumbent incisors both comprise size-related changes caused by ontogenetic allometric growth.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 822–831.     

Dental topographic and three-dimensional geometric morphometric analysis of carnassialization in different clades of carnivorous mammals (Dasyuromorphia,Carnivora, Hyaenodonta)

The evolution of carnassial teeth in mammals, especially in the Carnivora, has been subject of many morphometric and some dental topographic studies. Here, we use a combination of dental topographic analysis (Dirichlet normal energy) and 3D geometric morphometrics of less and high carnassialized lower teeth of carnivoran, dasyuromorph and hyaenodont taxa. Carnassial crown curvature, as indicated by Dirichlet normal energy, is high in lesser carnassialized teeth and low in higher carnassialized teeth, where it is influenced by the reduction of crown features such as cusps and crests. PC1 of the geometric morphometric analysis is linked to enlargement of the carnassial blade, reduction of the talonid crushing basin and an increasingly asymmetric cervix line with an enlarged mesial flexure in more carnassialized teeth. Distribution of PC1 values further indicates that along the tooth row of dasyuromorphs (m2–m4) and hyaenodonts (m1–m3) the most distal carnassial is the most carnassialized (principal carnassial), and in most taxa with overall higher carnassialized teeth, carnassialization successively increases from the anterior to the posterior tooth position along the tooth row. PC2 indicates that a longitudinal elongated carnassial is present in caniforms and in unspecialized feliforms, which separates these taxa in morphospace from all dasyuromorphs, hyaenodonts and specialized feliforms. An ancestral state reconstruction shows that this longitudinal elongation may be a plesiomorphic ancestral state for the Carnivora, which is different from the Dasyuromorphia and the Hyaenodonta. This elongation, enabling the presence of a longitudinally aligned carnassial blade as well as a complete talonid basin, might have provided the Carnivora with an advantage in terms of adaptive versatility.     

What is bred in the bone: Ecomorphological associations of pelvic girdle form in greater Antillean Anolis lizards

Ecological niche partitioning of Anolis lizards of the Greater Antillean islands has been the focus of many comparative studies, and much is known about external morphological convergence that characterizes anole ecomorphs. Their internal anatomy, however, has rarely been explored in an ecomorphological context, and it remains unknown to what degree skeletal morphology tracks the diversity and ecological adaptation of these lizards. Herein, we employ CT scanning techniques to visualise the skeleton of the pelvic girdle in situ, and 3D geometric morphometrics to compare the form of the ilium, ischium, and pubis within and between ecomorphs. We examine 26 species of anoles representing four ecomorphs (trunk‐ground, trunk‐crown, crown‐giant, twig) from three islands (Jamaica, Hispaniola, and Puerto Rico). The subtle variations in pelvic girdle morphology discovered are directly associable with all three parameters that we set out to focus on: phylogenetic relationship, specimen size, and assigned ecomorph category. Morphometric variation that correlates with size and/or phylogenetic signal varies between species and cannot be eliminated from the data set without markedly reducing its overall variability. The discovered patterns of skeletal variation are consistent with the demands of locomotor mechanics pertinent to the structural configuration of the microhabitat of three of the four ecomorphs, with the fourth having no discernible distinctive features. This manifests itself chiefly in the relative anteroposterior extent and anteroventral inclination of the ilium and pubis, which differ between ecomorphs and are postulated to reflect optimization of the direction of muscle vectors of the femoral protractors and retractors. Our investigation of the form of the pelvic girdle of anoles allows us to generalize our findings to entire ecomorph categories within a broad phylogenetic and biogeographic context. Differences in the form and configuration of the postcranial skeleton are directly related to ecological patterns.     

Systematics of the Platyrrhinus helleri species complex (Chiroptera: Phyllostomidae), with descriptions of two new species

Platyrrhinus is a diverse genus of small to large phyllostomid bats characterized by a comparatively narrow uropatagium thickly fringed with hair, a white dorsal stripe, comparatively large inner upper incisors that are convergent at the tips, and three upper and three lower molars. Eighteen species are currently recognized, the majority occurring in the Andes. Molecular, morphological, and morphometric analyses of specimens formerly identified as Platyrrhinus helleri support recognition of Platyrrhinus incarum as a separate species and reveal the presence of two species from western and northern South America that we describe herein as new ( Platyrrhinus angustirostris sp. nov. from eastern Colombia and Ecuador, north‐eastern Peru, and Venezuela and Platyrrhinus fusciventris sp. nov. from Guyana, Suriname, French Guiana, Trinidad and Tobago, northern Brazil, eastern Ecuador, and southern Venezuela). These two new species are sister taxa and, in turn, sister to Platyrrhinus incarum. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 785–812.     

The impact of diet,habitat use,and behaviour on head shape evolution in homalopsid snakes

An organism's morphology is driven by selection on function while being constrained by phylogenetic and developmental factors as well as functional trade‐offs. If selection on function is strong and solutions limited, then convergence is expected. In this paper we quantify head shape in a group of ecologically diverse snakes (homalopsid snakes) differing in habitat use and diet using three‐dimensional geometric morphometric approaches. Using data on head shape we explore whether snakes eating different prey show different morphologies. Moreover, we test whether head shape is constrained by other factors such as habitat use, burrow use, or activity pattern. Our results demonstrate similar head shapes in species consuming similar prey. Snakes that capture elusive prey under water differ from those that capture and swallow prey like frogs or crustaceans. Moreover, habitat use, the use of burrows, and activity pattern also significantly impact head shape in this group of snakes. However, this signal appears to be partly confounded by the diet signal. For axes discriminating specifically between habitat use groups or animals that use burrows vs. those that do not shapes were in accordance with our predictions. Our results suggests an adaptive signal in the evolution of head shape in homalopsid snakes with diet, habitat use and the use of burrows all influencing the evolution of head shape in the group.     

Morphofunctional analysis of Svobodaina species (Brachiopoda,Heterorthidae) from south‐western Europe

Geometric morphometric methods applied to the ventral muscle field outline of the various species of Svobodaina from south‐western Europe identify criteria for discriminating among this key cluster of brachiopod species. These data indicate the close relationship between the patterns of the ventral muscle field in the Svobodaina species and the environmental conditions where each inhabited; the fields are better developed in species related to high‐energy environments. For example, S. armoricana, with the smallest diductor scars, would have inhabited the quiet marine environments of the lower offshore or within protected lagoonal settings. S. feisti would have inhabited the upper offshore, a more energetic environment than S. armoricana. Finally, S. havliceki, with the largest diductor scars, would have thrived in the most energetic environments among all the south‐western European Svobodaina species, living just above the fair‐weather wave base in the lower shoreface. The palaeoecological results suggest a distribution of Svobodaina species during the Late Ordovician along an onshore–offshore transect across the shallow marine platforms of the Mediterranean margin of Gondwana. On the other hand, the occurrence in some localities of several species with overlapping ranges or within the same assemblage indicates that the biostratigraphical efficacy of the genus is restricted. Thus, the previously defined taxon‐range biozones characterized by Svobodaina species of the north Gondwanan margin are in need of reassessment. The morphology of Svobodaina may be a considerable aid to environmental analyses rather than to precise biostratigraphical correlations.     

Latitudinal variation in ecological opportunity and intraspecific competition indicates differences in niche variability and diet specialization of Arctic marine predators

Individual specialization (IS), where individuals within populations irrespective of age, sex, and body size are either specialized or generalized in terms of resource use, has implications on ecological niches and food web structure. Niche size and degree of IS of near‐top trophic‐level marine predators have been little studied in polar regions or with latitude. We quantified the large‐scale latitudinal variation of population‐ and individual‐level niche size and IS in ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) using stable carbon and nitrogen isotope analysis on 379 paired ringed seal liver and muscle samples and 124 paired beluga skin and muscle samples from eight locations ranging from the low to high Arctic. We characterized both within‐ and between‐individual variation in predator niche size at each location as well as accounting for spatial differences in the isotopic ranges of potential prey. Total isotopic niche width (TINW) for populations of ringed seals and beluga decreased with increasing latitude. Higher TINW values were associated with greater ecological opportunity (i.e., prey diversity) in the prey fish community which mainly consists of Capelin (Mallotus villosus) and Sand lance (Ammodytes sp.) at lower latitudes and Arctic cod (Boreogadus saida) at high latitudes. In beluga, their dietary consistency between tissues also known as the within‐individual component (WIC) increased in a near 1:1 ratio with TINW (slope = 0.84), suggesting dietary generalization, whereas the slope (0.18) of WIC relative to TINW in ringed seals indicated a high degree of individual specialization in ringed seal populations with higher TINWs. Our findings highlight the differences in TINW and level of IS for ringed seals and beluga relative to latitude as a likely response to large‐scale spatial variation in ecological opportunity, suggesting species‐specific variation in dietary plasticity to spatial differences in prey resources and environmental conditions in a rapidly changing ecosystem.     

Convergence and remarkably consistent constraint in the evolution of carnivore skull shape

Phenotypic similarities between distantly related marsupials and placentals are commonly presented as examples of convergence and support for the role of adaptive evolution in shaping morphological and ecological diversity. Here we compare skull shape in a wide range of carnivoran placentals (Carnivora) and nonherbivorous marsupials using a three-dimensional (3-D) geometric morphometric approach. Morphological and ecological diversity among extant carnivorans is considerably greater than is evident in the marsupial order Dasyuromorphia with which they have most commonly been compared. To examine convergence across a wider, but broadly comparable range of feeding ecologies, a dataset inclusive of nondasyuromorphian marsupials and extinct taxa representing morphotypes no longer present was assembled. We found support for the adaptive paradigm, with correlations between morphology, feeding behavior, and bite force, although skull shape better predicted feeding ecology in the phylogenetically diverse marsupial sample than in carnivorans. However, we also show that remarkably consistent but differing constraints have influenced the evolution of cranial shape in both groups. These differences between carnivorans and marsupials, which correlate with brain size and bite force, are maintained across the full gamut of morphologies and feeding categories, from small insectivores and omnivores to large meat-specialists.     

Chewing on the trees: Constraints and adaptation in the evolution of the primate mandible

Chewing on different food types is a demanding biological function. The classic assumption in studying the shape of feeding apparatuses is that animals are what they eat, meaning that adaptation to different food items accounts for most of their interspecific variation. Yet, a growing body of evidence points against this concept. We use the primate mandible as a model structure to investigate the complex interplay among shape, size, diet, and phylogeny. We find a weak but significant impact of diet on mandible shape variation in primates as a whole but not in anthropoids and catarrhines as tested in isolation. These clades mainly exhibit allometric shape changes, which are unrelated to diet. Diet is an important factor in the diversification of strepsirrhines and platyrrhines and a phylogenetic signal is detected in all primate clades. Peaks in morphological disparity occur during the Oligocene (between 37 and 25 Ma) supporting the notion that an adaptive radiation characterized the evolution of South American monkeys. In all primate clades, the evolution of mandible size is faster than its shape pointing to a strong effect of allometry on ecomorphological diversification in this group.     

Subtle,pervasive genetic correlation between the sexes in the evolution of dimorphic hummingbird tail ornaments*

Male hummingbirds have repeatedly evolved sexually dimorphic tails that they use as ornaments during courtship. We examine how male ornament evolution is reflected in female morphology. Lande's two-step model of the evolution of dimorphism predicts that γ (the genetic correlation between the sexes) causes trait elaboration to first evolve quickly in both sexes, then dimorphism evolves more slowly. On the hummingbird phylogeny, tail length does not fit this two-step model; although hummingbirds repeatedly evolved ornamental, elongated tails, dimorphism evolves on the same phylogenetic branch as elongation, implying that γ quickly evolves to be low over phylogenetic timescales. Male “bee” hummingbirds have evolved diverse rectrix shapes that they use to produce sound. Female morphologies exhibit subtle, pervasive correlations with male morphology. No female-adaptive hypotheses explain these correlations, since females do not also make sounds with their tail. Subtle shape similarity has arisen through the genetic correlation with males, and is subject to intralocus sexual conflict. Intralocus sexual conflict may produce increased phenotypic variation of female ornaments. Other evolutionary constraints on tail morphology include a developmental correlation between neighboring tail-feathers, biasing tail elaboration to occur most often at the ends of the feather tract (rectrix 5 or 1) and not the middle.