Sexual dimorphism in sister species of Leucoraja skate and its relationship to reproductive strategy and life history

Abstract

Instances of sexual dimorphism occur in a great variety of forms and manifestations. Most skates (Batoidea: Rajoidei) display some level of body shape dimorphism in which the pectoral fins of mature males develop to create a distinct bell-shaped body not found in females. This particular form of dimorphism is present in each of the sister species Leucoraja erinacea and Leucoraja ocellata, but differences between sexes are much greater in the former. In order to understand the nature and potential causes of pectoral dimorphism, we used geometric morphometrics to investigate allometry of fin shape in L. erinacea and L. ocellata and its relationship to the development of reproductive organs, based on previous work on the bonnethead shark, Sphyrna tiburo. We found that allometric trajectories of overall pectoral shape were different in both species of skate, but only L. erinacea varied significantly with respect to endoskeleton development. Male maturation was characterized by a number of sex-specific morphological changes, which appeared concurrently in developmental timing with elongation of cartilage-supported claspers. We suggest that external sexual dimorphism of pectoral fins in skates is a byproduct of skeletal growth needed for clasper development. Further, the magnitude of male shape change appears to be linked to the differential life histories of species. This work reports for the first time that pectoral dimorphism is a persistent feature in rajoid fishes, occurring in varying degrees across several genera. Lastly, our results suggest that pectoral morphology may be useful as a relative indicator of reproductive strategy in some species.

First Observations of Long‐Distance Migration in a Large Skate Species, the Winter Skate: Implications for Population Connectivity, Ecosystem Dynamics, and Management

“…The display of long-distance dispersal capabilities in Winter Skate individuals prompts questions regarding the current understanding of their population dynamics, which suggested that individuals do not make long-distance migrations and exhibit high endemicity to specific regions of the continental shelf (Kulka et al 2009). Additionally, while we did not observe compelling evidence of differences in mobility between male and female Winter Skate, the presence of sexually dimorphic pectoral fin shapes in this species (Martinez et al 2016b) suggests that further work is needed to confirm whether more fine-scale or subtle patterns of spatial differentiation exist.…”

“…Additionally, while we did not observe compelling evidence of differences in mobility between male and female Winter Skate, the presence of sexually dimorphic pectoral fin shapes in this species (Martinez et al. ) suggests that further work is needed to confirm whether more fine‐scale or subtle patterns of spatial differentiation exist.…”

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

“…Effort was made to primarily include adult specimens, but in some instances (e.g., very large species) smaller individuals were used. We used both male and female individuals, although sexual dimorphism does occur in some batoid species (e.g., Martinez et al, ). However, inspection of the major axes of variation did not indicate that sex influenced overall interpretations.…”

Reproductive biology of Psammobatis rutrum (Chondrichthyes: Arhynchobatidae) in south Brazil, south‐west Atlantic

“…Sexual dimorphism in W D may occur in species with sexual differences in length‐width relationships (Ebert et al, ) and has been observed in other rajoids (Oddone & Vooren, ; Orlov & Cotton, ). Such dimorphism may be related to the onset of maturity, since it becomes evident in developing and adult individuals (Martinez et al, ).…”