Re‐evaluation of batoid pectoral morphology reveals novel patterns of diversity among major lineages

Batoids (Chondrichthyes: Batoidea) are a diverse group of cartilaginous fishes which comprise a monophyletic sister lineage to all neoselachians or modern sharks. All species in this group possess anteroposteriorly expanded‐pectoral fins, giving them a unique disc‐like body form. Reliance on pectoral fins for propulsion ranges from minimal (sawfish) to almost complete dependence (skates and rays). A recent study on the diversity of planform pectoral fin shape in batoids compared overall patterns of morphological variation within the group. However, inconsistent pectoral homology prevented the study from accurately representing relationships within and among major batoid taxa. With previous work in mind, we undertook an independent investigation of pectoral form in batoids and evaluated the implications of shape diversity on locomotion and lifestyle, particularly in the skates (Rajoidei) and rays (Myliobatoidei). We used geometric morphometrics with sliding semilandmarks to analyze pectoral fin outlines and also calculate fin aspect ratios (AR), a functional trait linked to locomotion. In agreement with previous work, our results indicated that much of the evolution of batoid pectoral shape has occurred along a morphological axis that is closely related to AR. For species where kinematic data were available, both shape and AR were associated with swimming mode. This work further revealed novel patterns of shape variation among batoids, including strong bimodality of shape in rays, an intermediate location of skate species in the morphospace between benthic/demersal and pelagic rays, and approximately parallel shape trajectories in the benthic/demersal rays and skates. Finally, manipulation of landmarks verified the need for a consistent and accurate definition of homology for the outcome and efficacy of analyses of pectoral form and function in batoids. J. Morphol. 277:482–493, 2016. © 2016 Wiley Periodicals, Inc.     

Comparative analysis of feeding habits and dietary niche breadth in skates: the importance of body size,snout length,and depth

Skates (Elasmobranchii, Rajiformes) are a morphologically conservative group of bentophagous chondrichthyan fishes with a high degree of endemism, that occur on marine soft bottoms. Subtle morphological aspects and bathymetric distribution are traits that vary among skate species that could have implications for their feeding ecology. We test how body size, snout length and bathymetric distribution influence the feeding habits and dietary niche breadth in skates using data on 71 species taken from the literature. We hypothesized that snout length has an effect on diet composition. We also hypothesized that dietary niche breadth increases with increasing depth range and decreases with increasing body size of skate species. Generalized additive models for location scale and shape were fitted with taxonomic level (genera nested within family) included as a random effect term in each model. A model selection approach to test the level of support for alternative models was applied. We found that skate species that forage on large prey have the largest body size and skate species with the smallest body size prey on small and medium-sized invertebrates. The results indicated that body size has an effect on feeding habits of skates, whereas an effect of snout length was not supported. Bathymetric variables have an effect on the diet of skates. Our prediction that dietary niche breadth increases with increasing depth range and decreases with increasing body size of skate species was supported in part: in a first phase the relationship between dietary niche breadth and body size is positive, then in a second phase, including species larger than 1000 mm total length, the relationship become negative.     

The effect of phylogeny on interspecific body shape variation in darters (Pisces: Percidae)

We conducted a geometric morphometric analysis of interspecific body shape variation among representatives of 31 species of darters (Pisces: Percidae) to determine whether there is evidence of a phylogenetic effect in body shape variation. Cartesian transformation grids representing relative shape differences of individual species and subspecies revealed qualitative similarities within most traditionally recognized taxonomic groups (genera and subgenera). Canonical variates analysis and a UPGMA cluster analysis were conducted to explore further the relationships among body shapes of species; both analyses revealed patterns of variation consistent with the interpretation that shape is associated with taxonomic affinities. Normalized Mantel statistics revealed a significant positive association between body shape differences and phylogenetic interrelatedness for each of four recent phylogenetic hypotheses, providing evidence of a phylogenetic effect. This result is somewhat surprising, however, given the largely incompatible nature of these four phylogenies. We provide evidence that this result may be due to (1) the inclusion of multiple sets of closely related species to represent the traditionally recognized genera and subgenera within each phylogeny and/or (2) the inclusion of several species with relatively divergent shapes and their particular positions within the phylogenies relative to one another or to the other species of darters.     

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.     

Character variation in separate body regions of Gerreidae (Osteichthyes: Teleostei) fishes inferred from geometric morphometrics

Body morphology is a valuable feature for distinguishing teleostean fishes. However, the utility of character variation in separate body regions has yet to be tested. The taxonomy of the Gerreidae family is controversial due to character overlapping among its fish species. This work aims to analyze and compare the body shape variation in three regions, cephalic, trunk, and caudal peduncle, using landmark data and geometric morphometric methods in 17 species and five genera of the family Gerreidae. The pattern of shape variation for the cephalic region consisted of well-defined character states exclusive of each species analyzed. Shape variation in the trunk and caudal peduncle regions does not distinguish all species in this study. This study showed that the dorsal cephalic profile is highly variable among the species, therefore, shape variation in this region is useful for distinguishing Gerreidae species. In contrast, some species within the same genus share similar shape states in the trunk and caudal peduncle regions, with the most shape variation in the dorsal profile and anal fin for the trunk and in the middle of the caudal peduncle.     

Seasonal variation of immune response to heterologous erythrocytes in natural populations of red‐backed (Clethrionomys rutilus) and gray‐sided (C. rufocanus) voles in Western Siberia

We studied the seasonal variation of adaptive humoral immunity (AHI) in northern red‐backed vole (Clethrionomys rutilus Pallas, 1779, RBV) and gray‐sided vole (C. rufocanus Sundevall, 1846, GSV) in Tomsk region of Western Siberia. Immunoresponsiveness (IR) to sheep red blood cells was assessed by the number of antibody‐producing cells in the spleen. The use of a generalized linear model to analyze the effects of species, sex, year of research, and season of withdrawal of individuals from nature on IR showed a significant effect of species identity, season of animal capture, and the interaction of species with season. The RBV demonstrated higher immune responses during a year, and both species had higher IR in winter. Suppression of IR in spring was greater, started earlier, and lasted longer (March–May) in GSV. In RBV, immunosuppression was restricted to April. The significant negative within year correlations of IR with body mass and masses of reproductive organs in GSV indicated a trade‐off between AHI and growth and reproduction processes. A probable explanation for the difference between species in the seasonal variation of AHI may be related to the difference in tropho‐energetic requirements of each vole species. GSV is a predominantly herbivorous rodent and its thermoregulation seems less efficient than of RBV. The deeper spring immunosuppression in GSV may explain in part its higher mortality during the season of colds.     

The synarcual cartilage of batoids with emphasis on the synarcual of Rajidae

Comparison of embryonic specimens with juvenile and mature specimens of other skates indicates that the relative developmental sequence of events is maintained among several taxa within larger clades. However, there is a fundamental difference between the pattern of chondrification and the pattern of calcification in skates. Early in ontogeny a short synarcual surrounds the first free vertebral centrum. Additional neural arch segments are incorporated from anterior to posterior and the relative length of the synarcual cartilage to total length of the body normalizes early. A secondary direction of chondrification, from ventral to dorsal, is also present. Juveniles and subadults show that synarcual calcification is relatively late compared to the calcification of other regions of the skeleton and proceeds from lateral to medial. Comparison with extinct taxa also indicates that there is a decrease in vertebral centrum involvement with the synarcual cartilage over the evolutionary history of the clade. Results from exploratory analyses of morphospace and taxonomy reveal that phylogeny explains part, but not all, of the data on the synarcual in Rajidae. There is evidence of individual and ontogenetic variation among all species of skates examined, however, phylogenetically informative variation prevails. Comparison with other batoids demonstrates a trend where the number of vertebral centra flanked by the synarcual cartilage decreases among more derived taxa indicating a high degree of convergent morphology among batoids with potential functional significance. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Getting into Shape: An Empirical Comparison of Traditional Truss-Based Morphometric Methods with a Newer Geometric Method Applied to New World Cichlids

Body shape is a difficult, but important, trait to quantify. Researchers have traditionally used multivariate analysis of several linear measures ('trusses') across the body form to quantify shape. Newer geometric morphometric methods claim to better estimate shape because they analyze the geometry among the locations of all landmarks simultaneously rather than the linear distances between pairs of landmarks. We tested this claim by comparing the results of several traditional morphometric analyses against a newer geometric analysis involving thin-plate splines (TPS), all applied to a common data set of morphologically variable new world cichlids Amphilophus citrinellus and A. zaliosus. The TPS method yielded slightly stronger evidence of morphological differences among forms, although traditional methods also distinguished the two species. Perhaps our most important result was the idiosyncratic interpretation of shape variation among the traditional truss-based methods, whereas the generation of deformation grids using the TPS approach yielded clear and visually interpretable figures. Our results indicate that geometric morphometrics can be a more effective way to analyze and interpret body form, but also that traditional methods can be relied upon to provide statistical evidence of shape differences, although not necessarily accurate information about the nature of variation in shape.     

Morphometric analysis of male reproductive features of octopodids (Mollusca: Cephalopoda)

Taxonomic accounts of octopodids frequently describe the spermatophore, the penis that releases the spermatophore from the internal organs, and the ligula and calamus that transfer it to a female. To explore relationships among these male features and body size, this study applies principal components analysis to data from 43 species of the family Octopodidae, or benthic octopuses. Covariation in penis and mantle length opposed by covariation in ligula and calamus lengths forms primary shape variation. Secondary shape variation is due to opposing variation between ligula and calamus lengths. Primary shape variation is greatest among shallow-water species. The calami and ligulae of diurnal and crepuscular shallow-water species are short compared to those of nocturnal shallow-water species. Because these structures contain heterogeneous collagen arrays and lack camouflaging chromatophore organs, they are white. Diurnal and crepuscular octopus species may minimize their lengths due to selection imposed by visual predators. Secondary shape variation is greater in deep-sea and high-latitude octopuses. Members of Voss's Eledoninae (except Eledone) and Graneledoninae and two species of Benthoctopus have exceptionally long calami and comparatively short ligulae; these lengths vary among members of the Bathypolypodinae. Variation in spermatophore length is independent of the structures considered.     

Morphological and reproductive variation among populations of the Pacific molly Poecilia butleri

In viviparous organisms, pregnant females typically experience an increase in body mass and body volume. In this study, the prediction that variation in reproductive traits among populations of viviparous organisms should be related to variation among populations in body shape was tested in the Pacific molly Poecilia butleri, a viviparous fish that inhabits western Mexico and northern Central America. Variation among 10 populations in four reproductive traits was examined: brood size, individual embryo mass, total reproductive allotment and degree of maternal provisioning of nutrients to developing embryos. Variation among these populations in body shape was also examined. Significant variation among populations was observed in both brood size and reproductive allotment but not in embryo mass or degree of maternal provisioning. Significant variation among populations was also observed in body shape. After correcting for female size, however, reproductive traits and body shape were not associated among populations. This suggests that selective pressures acting on reproduction do not necessarily affect morphology and vice versa. Several factors might contribute to this unexpected lack of association between reproductive traits and morphology.     

Reanalysis of long‐term surveys on the ecology and biology of mud skate (Rhinoraja taranetzi Dolganov, 1985) in the northwestern Pacific (1993–2002)

Based on data sampled in 1992–2002, the occurrence, spatial distribution, bathymetry, bottom temperatures preferences, size composition, feeding, and some features of reproductive biology of mud skate Rhinoraja taranetzi in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka are considered. Throughout the year, the mud skate was most abundant in the central part of the study area, from the coast of Onekotan Island to the southern tip of Kamchatka peninsula. The proportion of this species in bottom trawl catches in different seasons has changed slightly. However, maximum catch occurred in September–December. In April–May mud skates occupied shallower depths (mean 230–270 m), moving deeper in the summer period (mean 340–390 m). In December–March the skate occurred at lower bottom temperatures (mean 0.8–1.6°C) whereas the rest of the year it inhabited warmer waters with mean bottom temperatures of 2.5–3.1°C. Throughout the year decreasing body weight with depth was observed, indicating that adult and juvenile mud skates inhabit different depths. Total length of mud skates in catches ranged from 17 to 70 cm with a mean of 51.71 cm. Relation between total length (TL, cm) and body weight (W, g) was: W = 0.0029TL^3.1614 (r² = 0.978). Males were more abundant among small skates (<30 cm) only, whereas females predominated among larger skates (>30 cm) comprising about 70% in 60–70 cm length class. Female mud skates were longer and heavier than males (mean length 56.9 vs 51.2 cm and mean weight 1206 vs 807 g, respectively). This species is considered to be benthophagous, consuming mostly amphipods (34.9% by weight), polychaete worms (27.6%), decapod crustaceans (12.7%), and fishery discards (13.9%). Small skates (20–40 cm) fed mostly on amphipods (85.4%); medium‐sized (40–60 cm) ate amphipods (40.2%), polychaetes (29.1%) and decapods (19.3%); the largest individuals (>60 cm) consumed fishery offal (27.9%) and less amphipods (26.6%) and polychaetes (27.7%). Preliminary data on the maturation of the species in the western Bering Sea showed that males and females become mature at lengths above 61 cm TL.     

Head shape evolution in monitor lizards (Varanus): interactions between extreme size disparity,phylogeny and ecology

Characterizing patterns of observed current variation, and testing hypotheses concerning the potential drivers of this variation, is fundamental to understanding how morphology evolves. Phylogenetic history, size and ecology are all central components driving the evolution of morphological variation, but only recently have methods become available to tease these aspects apart for particular body structures. Extant monitor lizards (Varanus) have radiated into an incredible range of habitats and display the largest body size range of any terrestrial vertebrate genus. Although their body morphology remains remarkably conservative, they have obvious head shape variation. We use two‐dimensional geometric morphometric techniques to characterize the patterns of dorsal head shape variation in 36 species (375 specimens) of varanid, and test how this variation relates to size, phylogenetic history and ecology as represented by habitat. Interspecific head shape disparity is strongly allometric. Once size effects are removed, principal component analysis shows that most shape variation relates to changes in the snout and head width. Size‐corrected head shape variation has strong phylogenetic signal at a broad level, but habitat use is predictive of shape disparity within phylogenetic lineages. Size often explains shape disparity among organisms; however, the ability to separate size and shape variation using geometric morphometrics has enabled the identification of phylogenetic history and habitat as additional key factors contributing to the evolution of head shape disparity among varanid lizards.     

Inter- and intraspecific variation in grass phytolith shape and size: a geometric morphometrics perspective

Background and AimsThe relative contributions of inter- and intraspecific variation to phytolith shape and size have only been investigated in a limited number of studies. However, a detailed understanding of phytolith variation patterns among populations or even within a single plant specimen is of key importance for the correct taxonomic identification of grass taxa in fossil samples and for the reconstruction of vegetation and environmental conditions in the past. In this study, we used geometric morphometric analysis for the quantification of different sources of phytolith shape and size variation.MethodsWe used landmark-based geometric morphometric methods for the analysis of phytolith shapes in two extant grass species (Brachypodium pinnatum and B. sylvaticum). For each species, 1200 phytoliths were analysed from 12 leaves originating from six plants growing in three populations. Phytolith shape and size data were subjected to multivariate Procrustes analysis of variance (ANOVA), multivariate regression, principal component analysis and linear discriminant analysis.Key ResultsInterspecific variation largely outweighed intraspecific variation with respect to phytolith shape. Individual phytolith shapes were classified with 83 % accuracy into their respective species. Conversely, variation in phytolith shapes within species but among populations, possibly related to environmental heterogeneity, was comparatively low.ConclusionsOur results imply that phytolith shape relatively closely corresponds to the taxonomic identity of closely related grass species. Moreover, our methodological approach, applied here in phytolith analysis for the first time, enabled the quantification and separation of variation that is not related to species discrimination. Our findings strengthen the role of grass phytoliths in the reconstruction of past vegetation dynamics.     

Patterns of morphological variation among populations of the widespread annual killifish Nothobranchius orthonotus are independent of genetic divergence and biogeography

Populations of annual killifish of the genus Nothobranchius occur in patchily distributed temporary pools in the East African savannah. Their fragmented distribution and low dispersal ability result in highly structured genetic clustering of their populations. In this study, we examined body shape variation in a widely distributed species, Nothobranchius orthonotus with known phylogeographic structure. We tested whether genetic divergence of major mitochondrial lineages forming two candidate species is congruent with phenotypic diversification, using linear and geometric morphometry analyses of body shape in 23 wild populations. We also conducted a common‐garden experiment with two wild‐derived populations to control for the effect of local environmental conditions on body shape. We identified different allometric trajectories for different mitochondrial lineages and candidate species in both sexes. However, in a principal components analysis of population‐level body shape, the separation among mitochondrial lineages was incomplete. Higher similarity of mitochondrial lineages belonging to different candidate species than that of same candidate species prevented distinction of the two candidate species on the basis of body shape. Analysis at the individual level demonstrated that N. orthonotus express high intrapopulation variability, with major overlap among individuals from all populations. In conclusion, we suggest that N. orthonotus be considered as a single species with an extensive geographic range, strong population genetic structure and high morphological variability.     

Comparative punting kinematics and pelvic fin musculature of benthic batoids

Although the majority of batoid elasmobranchs, skates and rays, are benthically associated, benthic locomotion has been largely overlooked in this group. Only skates have been previously described to perform a form of benthic locomotion termed “punting.” While keeping the rest of the body motionless, the skate's pelvic fins are planted into the substrate and then retracted caudally, which thrusts the body forward. In this study, we demonstrate that this form of locomotion is not confined to the skates, but is found across a range of phylogenetically and morphologically diverse batoid species. However, only the clearnose skate, Raja eglanteria, and the lesser electric ray, Narcine brasiliensis, performed “true punting,” in which only the pelvic fins were engaged. The yellow stingray, Urobatis jamaicensis, and the Atlantic stingray, Dasyatis sabina, performed “augmented punting,” in which pectoral fin movement was also used to generate thrust. Despite this supplemental use of pectoral fins, the augmented punters failed to exceed the punting capabilities of the true punters. The urobatid and the true punters all punted approximately half their disc length per punt, whereas the dasyatid punted a significantly shorter distance. The skate punted significantly faster than the other species. Examination of the pelvic fin musculature revealed more specialized muscles in the true punters than in the augmented punters. This concordance of musculature with punting ability provides predictive power regarding the punting kinematics of other elasmobranchs based upon gross muscular examinations. In contrast to previous assumptions, our results suggest that benthic locomotion is widespread among batoids. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Convergent evolution of sexual shape dimorphism in Diptera

Several patterns of sexual shape dimorphism, such as male body elongation, eye stalks, or extensions of the exoskeleton, have evolved repeatedly in the true flies (Diptera). Although these dimorphisms may have evolved in response to sexual selection on male body shape, conserved genetic factors may have contributed to this convergent evolution, resulting in stronger phenotypic convergence than might be expected from functional requirements alone. I compared phenotypic variation in body shape in two distantly related species exhibiting sexually dimorphic body elongation: Prochyliza xanthostoma (Piophilidae) and Telostylinus angusticollis (Neriidae). Although sexual selection appears to act differently on male body shape in these species, they exhibited strikingly similar patterns of sexual dimorphism. Likewise, patterns of within-sex shape variation were similar in the two species, particularly in males: relative elongation of the male head capsule, antenna, and legs was associated with reduced head capsule width and wing length, but was nearly independent of variation in thorax length. However, the two species presented contrasting patterns of static allometry: male sexual traits exhibited elevated allometric slopes in T. angusticollis, but not in P. xanthostoma. These results suggest that a shared pattern of covariation among traits may have channeled the evolution of sexually dimorphic body elongation in these species. Nonetheless, static allometries may have been shaped by species-specific selection pressures or genetic architectures.     

Geometric morphometric analysis of Eysarcoris guttiger,E.annamita and E.ventralis (Hemiptera: Pentatomidae)

The genus Eysarcoris can be easily distinguished from other genera through the two spots in the basal angle of the scutellum.Nevertheless,Eysarcoris species show complex variances.Geometric morphometric methods have been increasingly applied to distinguish species and to define the boundary of genera among insects.In the present study,geometric morphometric approach was firstly employed to evaluate the shape variation of three characters (fore wing,hind wing and pygophore) of E.guttiger,E.annamita and E.ventralis using E.aeneus as outgroup to ascertain whether this approach is a reliable method for the taxonomy of Eysarcoris.Analysis was conducted on the landmarks of the three characters of these species.Multivariate regression of procrustes coordinates against centroid size was conducted to test the presence of allometry.Principal component analysis (PCA),canonical variate analysis (CVA)and cluster analysis were utilized to describe variations in shapes among the studied species.For all of the three characters,though PCA analysis showed some overlap among species,p-values for procrustes distance and mahalanobis distance were all less than 0.0001.The distribution of the three studied species corresponds with their species status.This study demonstrates that the geometric morphometrics of both the fore wing and the hind wing might represent a possible tool for the identification of species within this genus.     

A Morphospace for Reef Fishes: Elongation Is the Dominant Axis of Body Shape Evolution

Tropical reef fishes are widely regarded as being perhaps the most morphologically diverse vertebrate assemblage on earth, yet much remains to be discovered about the scope and patterns of this diversity. We created a morphospace of 2,939 species spanning 56 families of tropical Indo-Pacific reef fishes and established the primary axes of body shape variation, the phylogenetic consistency of these patterns, and whether dominant patterns of shape change can be accomplished by diverse underlying changes. Principal component analysis showed a major axis of shape variation that contrasts deep-bodied species with slender, elongate forms. Furthermore, using custom methods to compare the elongation vector (axis that maximizes elongation deformation) and the main vector of shape variation (first principal component) for each family in the morphospace, we showed that two thirds of the families diversify along an axis of body elongation. Finally, a comparative analysis using a principal coordinate analysis based on the angles among first principal component vectors of each family shape showed that families accomplish changes in elongation with a wide range of underlying modifications. Some groups such as Pomacentridae and Lethrinidae undergo decreases in body depth with proportional increases in all body regions, while other families show disproportionate changes in the length of the head (e.g., Labridae), the trunk or caudal region in all combinations (e.g., Pempheridae and Pinguipedidae). In conclusion, we found that evolutionary changes in body shape along an axis of elongation dominates diversification in reef fishes. Changes in shape on this axis are thought to have immediate implications for swimming performance, defense from gape limited predators, suction feeding performance and access to some highly specialized habitats. The morphological modifications that underlie changes in elongation are highly diverse, suggesting a role for a range of developmental processes and functional consequences.     

Prey handling using whole-body fluid dynamics in batoids

Fluid flow generated by body movements is a foraging tactic that has been exploited by many benthic species. In this study, the kinematics and hydrodynamics of prey handling behavior in little skates, Leucoraja erinacea, and round stingrays, Urobatis halleri, are compared using kinematics and particle image velocimetry. Both species use the body to form a tent to constrain the prey with the pectoral fin edges pressed against the substrate. Stingrays then elevate the head, which increases the volume between the body and the substrate to generate suction, while maintaining pectoral fin contact with the substrate. Meanwhile, the tip of the rostrum is curled upwards to create an opening where fluid is drawn under the body, functionally analogous to suction-feeding fishes. Skates also rotate the rostrum upwards although with the open rostral sides and the smaller fin area weaker fluid flow is generated. However, skates also use a rostral strike behavior in which the rostrum is rapidly rotated downwards pushing fluid towards the substrate to potentially stun or uncover prey. Thus, both species use the anterior portion of the body to direct fluid flow to handle prey albeit in different ways, which may be explained by differences in morphology. Rostral stiffness and pectoral fin insertion onto the rostrum differ between skates and rays and this corresponds to behavioral differences in prey handling resulting in distinct fluid flow patterns. The flexible muscular rostrum and greater fin area of stingrays allow more extensive use of suction to handle prey while the stiff cartilaginous rostrum of skates lacking extensive fin insertion is used as a paddle to strike prey as well as to clear away sand cover.