Having few females turns male tortoises into rapists

by Piter Kehoma Boll

The war between the sexes and the endless conflicts that result from that are a common theme in behavioral and evolutionary research and have been addressed several times here too.

As we know very well, even from examples in our own species, males are usually not very good parents, being more interested in producing as many descendants as possible with little effort. Females, on the other hand, due to their great investment on eggs (and usually other resources for the offspring) are much more selective and will not accept any male to mate with them.

One of the most common solutions for males to resolve this sexual conflict is by forced copulation, or rape as it is called when it happens in our own species. Sometimes this forced copulation is extreme, with males heavily injuring females in order to make them surrender. One of those violent species is the Hermann’s tortoise, Testudo hermanni, a tortoise found around the Mediterranean areas of Europe.


“I’m gonna bang you, bitch!” This photo of a juvenile male trying to mount on an adult female may look funny, but sex is no fun for female tortoises. Photo by Wikimedia user Palauenc05.*

Forced copulation is much more common in species in which males are bigger and stronger than females. This is not the case with tortoises, but male Hermann’s tortoises have found a way to deal with that. They pursue the females, sometimes for hours, pushing them, biting them, sometimes to the point of making them bleed, and eventually the poor females surrender. It is also common for the males to “stimulate” the cloaca of the females with their pointed tail, resulting in a swollen cloaca and sometimes severe injuries that let the females with horrible scars and deformities. Yes, it is not a nice face of nature.


The tail of a male. Photo by Wikimedia user Bizarria.**

A recent study with two populations of the Hermann’s tortoise in Macedonia revealed that male aggressiveness is linked to female availability. The team of researchers studied one population in which the female:male ratio was close to 1:1 and other in which it was extremely male-biased to the point of 1 female to 17.5 males.

The results indicate that in the more balanced population forced copulation was less common and usually only adult females presented injuries caused by males, while in the male-biased population the lack of females made males go mad to the point that they forced copulation even with immature females. The situation as a whole is clearly maladaptive, as females end up injured and males end up exhausted and no offspring is generated.

I can only see two possible outcomes for such a population: either more resistant females will be selected or the population will go extinct after all females die by male violence.

As we see, sexual conflict is one of those deleterious side effects that natural selection created. Afterall, nobody is perfect, not even the fundamental laws of life.

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Male resistance: when females disappear and hermaphrodites don’t like you

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Golubović, A.; Arsovski, D.; Tomović, L.; Bonnet, X. (2018) Is sexual brutality maladaptive under high population density? Biological Journal of the Linnean Society 124(3): 394–402. https://doi.org/10.1093/biolinnean/bly057

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*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

**Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.


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Filed under Behavior, Evolution, Zoology

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