A recent study published (subscription only) in PNAS by two scientists in WA (Australia) and the US has found that:

beetles with the biggest horns have the smallest testes, showing that in evolutionary terms you cannot have it all. [ABC Online]

Apparently according to earlier research by the scientists, the smaller horned (and sometimes hornless) males have much more powerful sperm and are much sneakier!

Instead, small, hornless males seem to invest their limited resources in longer sperm and disproportionately larger testes, compensating for their inability to guard a female by ejaculating more seminal fluid per copulation. In this way, small males may increase the odds of fertilizing an egg each time they manage to sneak past their larger competitors who mate more often but possibly with less efficiency. When unable to scuttle past their larger opponents, sneaker males may even dig side tunnels into a female’s chamber, where they are often detected by the resident guard and booted out. In the midst of all this rivalry, the female seems equally willing to mate with any male who manages to reach her, and it is likely that the competition continues within her, between the sperm of rival males. Thus the tradeoffs associated with horns may explain why males have evolved the two alternate mating strategies of guarding and sneaking. [Innovation - Princeton Journal of Science and Technology]

For plenty more information on weird beetle facts, check out Professor Douglas Emlen’s homepage.

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