When Giant Beetle Horns Fail

Rhinoceros beetle, Trypoxylus dichotomus

Rhinoceros beetle, Trypoxylus dichotomus

Last year, I reported on new insights into the evolution of animal weaponry that University of Montana evolutionary biologist Erin McCullough found in her studies of rhinoceros beetle horns’ mechanical limits. Theory that explained why animal weapons (such as deer antlers or beetle horns) evolve said that such traits will become more and more exaggerated until the costs to survival outweigh the benefits to breeding success. McCullough’s research shows that sometimes it’s the costs to breeding success that outweigh the benefits to breeding success, at least for rhinoceros beetles, because sometimes the damn things become so unwieldy that they break easily. Mechanical limits, rather than mortality, regulates beetle horn size. No other possible limitation to survival or fitness explained these beetles’ horn size.

McCullough’s research has now withstood some scientific limits: Her results were published recently in the Proceedings of the Royal Society B. The research already withstood the trials and tribulations of the field, no small feat when studying nocturnal beetles in Taiwan. You can hear about those feats in my post about some of McCullough’s field stories.


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