Genital Papilla Morphogenesis in Gravid Female Blue-Banded Gobies, Lythrypnus dalli
Additional Funding Sources
The project described was supported by a student grant from the UI Office of Undergraduate Research.
Presentation Date
7-2022
Abstract
Female genitalia have been largely neglected in studies of genital evolution, perhaps due to the long‐standing assumption that they are relatively invariable and therefore taxonomically and evolutionarily uninformative in comparison with male genitalia. Here, we investigated this idea in Lythrypnus dalli, a bi-directionally hermaphroditic fish, that exhibits complex and sexually dimorphic reproductive behaviors. The external genital papilla (GP) undergoes dramatic morphogenesis concurrent with physiological changes associated with sex change. Males have a longer, tapered GP with length:width ratio (L:W) >1.6, female to male transitioning fish have a conical GP with L:W 1.4-1.6, and females have a L:W <1.4. In this study, we hypothesized that the variation in female GP shape is associated with the gravidity state of females. We investigated the GP L:W of sexually mature female L. dalli of variable sizes (N=190). The data supported the hypothesis that the standard length of the fish was not related to gravidity; thus, smaller fish were capable of having similar gravidity ratios as larger fish. There was an inverse relationship between GP L:W and gravidity ratio, such that a wider GP was associated with more gravid females. We split up the range of GP ratios into two categories: those that ranged from 0.85-1.2 were in the “rounded” category (corners to the opening were curved) and those < 0.85 were in the “flattened” category (corners to the opening were at right angles). We hypothesize that the wider opening of the GP morphology allows for a more efficient release of mature vitellogenic eggs in gravid females. More gravid females have higher levels of estradiol and it is possible that differences in estradiol sensitivity via estradiol receptor expression might underlie morphological changes in GP in gravid females.
Genital Papilla Morphogenesis in Gravid Female Blue-Banded Gobies, Lythrypnus dalli
Female genitalia have been largely neglected in studies of genital evolution, perhaps due to the long‐standing assumption that they are relatively invariable and therefore taxonomically and evolutionarily uninformative in comparison with male genitalia. Here, we investigated this idea in Lythrypnus dalli, a bi-directionally hermaphroditic fish, that exhibits complex and sexually dimorphic reproductive behaviors. The external genital papilla (GP) undergoes dramatic morphogenesis concurrent with physiological changes associated with sex change. Males have a longer, tapered GP with length:width ratio (L:W) >1.6, female to male transitioning fish have a conical GP with L:W 1.4-1.6, and females have a L:W <1.4. In this study, we hypothesized that the variation in female GP shape is associated with the gravidity state of females. We investigated the GP L:W of sexually mature female L. dalli of variable sizes (N=190). The data supported the hypothesis that the standard length of the fish was not related to gravidity; thus, smaller fish were capable of having similar gravidity ratios as larger fish. There was an inverse relationship between GP L:W and gravidity ratio, such that a wider GP was associated with more gravid females. We split up the range of GP ratios into two categories: those that ranged from 0.85-1.2 were in the “rounded” category (corners to the opening were curved) and those < 0.85 were in the “flattened” category (corners to the opening were at right angles). We hypothesize that the wider opening of the GP morphology allows for a more efficient release of mature vitellogenic eggs in gravid females. More gravid females have higher levels of estradiol and it is possible that differences in estradiol sensitivity via estradiol receptor expression might underlie morphological changes in GP in gravid females.