We usually think about male and female mates getting along pretty well (that’s ‘mate’ in the biological sense, not your friendly British/ Australian friend). Often after mating, male and females have to work together to ensure that the female gets the nutrition she needs while incubating eggs or rearing offspring. Even after this, many animals stay together as a partnership to raise their offspring or even beyond this. My favourite example of this is the sleepy lizard. Male sleepy lizards will court a female for two months, following her around, gently nudging and licking her. They then stay together through her six-month pregnancy and reunite annually as monogamous pairs.
However, nature is rarely as nice as it seems at first glance, and in most animals there is some kind of conflict going on between the sexes. Sexual conflict isn’t the day-to-day disagreements between males and females of a species (although it can often manifest itself this way), but instead it is conflict on an evolutionary timescale.
What does this mean? Well, without you even realising it, there may be things in your environment that favour you as a member of a particular sex (say, female) that are disadvantageous to the opposite sex. As natural selection acts to favour traits that keep animals alive and reproducing, if this particular trait is good for one sex but bad for the other, this leads to conflict.
In some animals males and females will eat each other either during or after copulation. I don’t think I’ll be making an overstatement if I say that this is perhaps the most dramatic form of sexual conflict. In thinking about sexual cannibalism, the first example that might spring to mind is the black widow spider. However, other animals eat their mates too, including scorpions and praying mantids.
From a female mantid’s point of view, eating her male is a good move. It not only gives her a great meal, it also means she can have more offspring and they will be more likely to survive. However, from the male’s point of view, he won’t be able to have more offspring in the future if he is, well, eaten. However, as contradictory (and macabre) as this might seem, it could actually benefit a male to be eaten (in the evolutionary sense, we have no idea about his emotional feelings on the topic) if it means that he is more likely to reproduce successfully. This could happen, for example, if he manages to transfer more sperm to a female if she’s busy eating him during mating.
In praying mantids, females eat their male mates around 30% of the time. I think if I were a male mantid, I wouldn’t like those odds. However, a recent study from the University of Buenos Aires has found that while males tend to prefer to mate with less-aggressive females, they don’t do this as much as you might expect.
Scientists placed a male between two females – one that was seen to be attacking another male and one that was not. As a side note, it wasn’t hard to get females to be seen to be attacking another male- as soon as the male was presented to them, all females attacked. The male watching this take place would then generally slowly sidle towards the female that seemed less aggressive. And when I say slowly, I mean slowly – this took over an hour. While males preferred to hang out on the side with the female they hadn’t just seen munching on another male, they were only slightly more likely to want to mate with this female. However, this could be that because it took males so long to approach females they wanted to mate with; the scientists only actually got to see a third of all their male subjects actually mating with females.
Male praying mantids, then, are particularly attentive insects. They closely watch the females around them, judging which are least likely to result in their demise after mating.
A pair of sleepy lizards: Kieran Palmer
Mantis female eating male: wikipedia
Male P. tessellata: Romina Scardamaglia
Mantis face: Benjamin Balázs
Scardamaglia, R.C. et al. (2015) Sexual conflict in a sexually cannibalistic praying mantid: males prefer low-risk over high-risk females. Animal Behaviour, 99: 9-14. (main reference)
Polis, G. A. (1981). The evolution and dynamics of intraspecific predation. Annual Review of Ecology and Systematics, 225-251.