rhamphotheca:

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)

Wasp & Prey (cricket) by Mojtaba Zeinalzadegan

restless bush cricket (Hapithus agitator)

 In peninsular Florida and eastern Texas, males of the restless bush cricket produce a loud distinctive song. Elsewhere they are not known to call. Little is known of how sexual pairs are formed in populations of non-calling crickets. Since non-calling restless bush crickets live in compact colonies, the males may simply roam about until they contact a female or are alerted to her presence by chemical cues. Once a female is located the male stays with her, sometimes producing soft courtship sounds with his forewings. If the female accepts a spermatophore from him, he puts his forewings to unique use by allowing the female to feed on them while the externally attached spermatophore is emptying into the female’s sperm-storage sac. During one copulation a male may sacrifice a quarter of his forewings, and males are found that have nothing but stubs remaining. Copulating females of many other crickets feed on products of the male-for example, secretions from dorsal thoracic glands in tree crickets and blood from bleeding spines on the hindtibiae in ground crickets. Only in non-calling populations of restless bush crickets is the sexually successful male prominently mutilated. The nutritive value of the male’s forewings and the consequences of a non-calling male averting mutilation are uninvestigated. The reproductive results of a male allowing a female to eat his forewings surely depend in part on whether the forewings can be used to call additional mating partners. Similarly the reproductive consequences for a female inseminated by a male that allows her to eat his forewings depend in part on whether her sons behave like their father.