Males that fight for the right to mate seem to invest less in testis size and more in body size compared with animals that do not fight — highlighting the trade-off that occurs between different strategies for reproductive success.
John Fitzpatrick at the University of Western Australia in Perth and his colleagues collated data on penis length, testis mass and the body mass of males relative to females in sea lions, walruses and seals, such as the Antarctic fur seal (pictured).
In species that compete for a harem, greater body mass — useful in battle — is associated with reduced penis length and testis mass. This indicates that males that invest more in pre-copulatory strategies such as increased body size may do so at the expense of post-copulatory ones such as improving the quality of their ejaculates.
Evolution http://dx.doi.org/10.1111/j.1558-5646.2012.01713.x (2012)
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Fighters invest in body, not testes. Nature 487, 8 (2012). https://doi.org/10.1038/487008a
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DOI: https://doi.org/10.1038/487008a
