Exploring Variation of Female Genital Morphology in Hydrolagus colliei (Spotted Ratfish)


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Female genitalia are found to be more diverse than previously thought, yet they have been historically understudied in the scientific world. Hydrolagus colliei is a particularly interesting model for studying female genital morphology. Female ratfish have paired vaginal openings, as well as a paired vagina and oviducts. We investigated how female ratfish genital morphology varies through body size and ontogeny, and how the female ratfish genitalia may have coevolved with male ratfish genitalia by examining the histology of the vagina in females of different sizes. We also examined the anatomy of the anal pad, a fleshy structure present only in females on the ventral side of the tail. I found that the relationship between vaginal shape and body size is significant, vaginal thickness increases with size of the female ratfish, and that vaginal density does not appear to vary significantly. I also found that the anal pad has a thick layer of collagen that increases in thickness with body size. This study shows that vagina shape changes with body size in females, and that male and female genitalia are coevolving in ratfish. It also provides evidence that females evolve other specializations that differ from males, likely in a reproductive context.



Biological Sciences, Genital Morphology, Ratfish, Evolution, Geometric Morphometrics, Histology, Chimera, Vagina, Anal Pad, Hydrolagus colliei, Sex