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Extensive geographical variation in testes size and ejaculate traits in a terrestrial-breeding frog
Tabitha S Rudin-Bitterli1, Nicola J Mitchell1, Jonathan P Evans1
1School of Biological Sciences, University of Western Australia, Crawley, WA 6009, Australia.
Biology Letters
|September 29, 2020
Summary
Male frogs (Pseudophryne guentheri) in drier regions have smaller testes and lower quality sperm. This suggests sperm traits adapt to local rainfall patterns and sperm competition levels.
Area of Science:
- Evolutionary biology
- Reproductive biology
- Amphibian ecology
Background:
- Ejaculate traits show extensive variation within and among species.
- Intraspecific variation in male reproductive investment is less understood.
- Geographic variation in precipitation can influence breeding seasons and sperm competition.
Purpose of the Study:
- Investigate intraspecific variation in male reproductive investment in Pseudophryne guentheri.
- Examine local adaptation in sperm traits related to phenological differences among populations.
- Determine if rainfall patterns drive divergence in testes and ejaculate traits.
Main Methods:
- Analyzed testes and ejaculate traits from six natural populations of Pseudophryne guentheri.
- Correlated trait variation with annual rainfall and rainfall seasonality across a geographic gradient.
- Compared sperm count, size, and motility between populations.
Main Results:
- Significant divergence in testes and ejaculate traits was observed across populations.
- Males from drier, northern regions had smaller testes with fewer, smaller, and less motile sperm.
- Populations from mesic central areas exhibited larger testes and higher quality sperm.
Conclusions:
- Sperm traits in Pseudophryne guentheri show local adaptation to rainfall patterns.
- Divergence in ejaculate traits likely reflects spatial variation in postcopulatory sexual selection.
- Precipitation seasonality and amount are key drivers of reproductive trait evolution in this species.
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