Sex is always a hot topic. Sex in insects is even more intriguing. Most people鈥檚 first reaction when they think of insects, is disgust. After all, insects are (most of them anyway) ugly, strange, and a nuisance when they invade our households. But they are fascinating creatures and easy to study because they are just about anywhere! In fact, there are more insects in the world than any other type of animal, no matter how you measure their numbers, whether in terms of individuals or species. It has been calculated that for every person on earth, there are about 200 million insects alive at any one time.
Although they seem like simple creatures, insects exhibit some remarkably complex behaviour, especially when it comes to sex. The male dance fly, for example, buys love with nuptial gifts, and so does the male firefly, but he is more of a 鈥渉andy-man鈥�. On the other hand, the capricious female danaid butterfly will not accept a groom unless he offers her poisonous perfume. Some males are so devoted to their wives that they sacrifice their own bodies for their love, like the sagebrush cricket, or even 鈥渃ommit suicide鈥�, like some ants. And watch out for the female praying mantis 鈥� if you don鈥檛 stroke her the right way, you are dead meat. Literally.
The dance fly Rhamphomyia sulcata
Nuptial gift giving is part of the male鈥檚 courtship routine in the 鈥渄ance fly鈥� Rhamphomyia sulcata. Gifts frequently consist of food, like nutritious prey items, or dried insect fragments. The female typically eats her gift during copulation and sometimes will terminate copulation when the gifts are distasteful or provide inadequate resources. The larger the gift, the more attractive the male dance fly is to the female, and the longer the female will be willing to copulate, ensuring a better chance for sperm transfer for the male fly. However, females have to watch out for dishonest, sly males, who try to seduce with fake finery such as a silk-wrapped dried insect fragment. Many females have been fooled by such 鈥渟ilk balloons鈥� because of their large size and high visibility. Biologists have noticed females trying to feed from the inedible tokens, turning the silk balls over in their legs and probing them with their proboscis in a manner similar to females eating a genuine nuptial gift.
In order to verify that female dance flies are really attracted by the size of the gift and not just to larger males who can therefore carry larger gifts, two biologists from the University of St. Andrews, LeBas and Hockham, conducted a gift manipulation experiment with the dance fly R. sulcata, in which all males provide a prey item as a nuptial gift, and pairs mate on vegetation where the female eats the gift. Large or small genuine gift, or large or small worthless gift (cotton ball), were the four available offerings, and copulation time was recorded. The biologists found that copulation duration in pairs that were given a large genuine gift was significantly longer than that for pairs given the other types of gifts. Another interesting finding was that worthless tokens were as highly regarded as small valuable gifts, at least from the male perspective. Each of these two types of gifts resulted in the same amount of mating time. Since males take some risk in hunting for a gift (they could be eaten by a bird or become prey themselves), and the time they spend hunting can鈥檛 be spent mating, it may be an advantage to bring an easily obtainable worthless gift and mate more frequently, albeit for a shorter time, as long as the copulation still allows the male to transfer sperm.
Photinus fireflies
While the R. sulcata dance fly hunts for his gift, the Photinus firefly makes his. The nuptial gift of the male firefly is an elegant, spirally-coiled sperm containing package, called the spermatophore. The size of the spermatophore that a male carries is positively correlated with the duration of the bioluminescent flashes, and the longer the duration of the light, the 鈥渨orthier鈥� the male is considered to be by the female. Therefore, it is postulated that females choose males with longer flash signals to increase the chance of reproduction.
During copulation, sperm is released into the female鈥檚 spermatheca for storage, while the remainder of the spermatophore disintegrates in the female鈥檚 spermatophore-digesting gland, a specialized gland located within the reproductive tract. Radio-labelling studies indicate that the proteins derived from the spermatophore are used to help provide for the female鈥檚 developing oocytes. Since most photinus fireflies do not feed as adults, larval energy reserves decline steadily. Nuptial gifts are therefore of particular importance. Unlike the female R. sulcata dance flies that are highly selective, female photinus fireflies need to continue to forage for matings to supplement their diminishing larval reserves. Moreover, male spermatophores provide females with a direct benefit measured in terms of increased fecundity: studies show that females lay many more eggs if they consecutively mate with several males. However, as the mating season progresses, the male exhausts his spermatophore manufacturing ability, which constrains his mating success.
Aren鈥檛 insects fascinating?
Melody Ko is a Critical Care Physician and a 9I制作厂免费 alumnus.
