Welcome Trust Blog: Monogamy Is Easy
by Fiona Lethbridge
It’s hard enough having to spread yourself thinly during your normal daily activities – work, sustenance, childcare, rest, the list goes on. Luckily for us monogamous types, our efforts in the bedroom are most often directed towards one individual. Imagine, though, the dilemma of having to divide your reproductive resources between many partners. If you were a male seed beetle (Callosobruchus maculatus), you might face this very problem. You would have a limited supply of ejaculate, numerous females of differing ages and reproductive states, lots of rival males, and about a week to live. To fulfil your evolutionary potential and achieve reproductive success you need to prioritise your sexual encounters – do you allocate a little of your seed to several different females, which may offer fairly decent returns, or do you use up all your sperm on one ripe, virgin female in the hope of fertilising each one of her hundreds of eggs?
Sperm is not a limitless resource. Males often have to use it economically to maximise their lifetime reproductive success. In many insects the situation is complex because females store sperm internally from several different mates, much of which is surplus to requirement, so not all males that achieve copulation can be guaranteed paternity. However, males can sometimes bolster their chances, by adopting certain strategies to overcome this sperm competition.
As a promiscuous insect it is essential to assess your surroundings. For example, if you were a male cricket (Gryllus veletis) you might want to allocate lots of sperm when copulating if there is another male waiting his turn with the female, in attempt to father a greater share of the resultant clutch than he does. If there are ten rival males around, you’d probably be better holding onto your ejaculate for now and saving your sperm for other, less competitive situations…
(read more: Welcome Trust Blog)
(image: male Spring Field Cricket, Gryllus veletis, by Kurt Andreas)