Stalk-eyed fly
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 A Diopsid from Cameroon
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Diasemopsis |
Stalk-eyed flies are insects of the Dipteran family Diopsidae (sometimes called Centrioncidae). The family is distinguished by the possession of eyestalks: projections from the sides of the head with the eyes at the end. Some fly species from other Dipteran families such as the Drosophilidae and Tephritidae carry similar structures but the unique character of the Diopsidae is that the antennae are carried next to the eye at the end of the stalk. There are several hundred species in the family, with the greatest diversity found in the Old World tropics[1] They are distributed throughout the region, with the best known species being from South-East Asia and Southern Africa. There are also two species in North America, both associated with skunk cabbage bogs[citation needed], and a European species has recently been found in Hungary.[2] Adult Diopsids are typically found on low-lying vegetation in humid areas, often near streams and rivers, where they feed on fungi and bacteria on decaying vegetation. The larvae develop in rotting vegetation.
These flies are regarded as classical examples of sexually selected animals. Many species are sexually dimorphic for the length of the eyestalks, with males having much longer eyestalks than females, and this dimorphism is believed to have evolved because of the mating advantages that they bestow on these males. The most widely studied species of diopsid is the Malaysian species Teleopsis dalmanni (until recently called Cyrtodiopsis dalmanni). These insects roost at night on root hairs hanging by streams, and mating usually takes place in the early morning at these sites. Females show a strong preference for roosting and mating with males with longer eyestalks, and males compete with each other to “control” these aggregations by a ritualised contest that involves facing each other and comparing their relative eyespans, often with the front legs spread out to add emphasis. Male T. dalmanni with long eyestalks therefore gain mating advantages both because of female choice and because of they are better able to compete with rival males.[1][3]
[edit] Research on Diopsids
Early research on the Diopsidae concentrated on the visual consequences of the unusual position of the eyes, with emphasis on the flies' field of view and ability to judge distances.[4][5] More recently these flies have become important laboratory models for testing theories about the evolution of secondary sexual characters, with important work being carried out at the University of Maryland in the USA and at University College London, in the UK. Research in these labs has shed light on a number of important questions in evolutionary biology, in particular the question of why female choice for apparently arbitrary male characters should evolve. Diopsid eyestalk length has been shown to be strongly condition dependent in males, meaning that high quality (see also Fitness) males are able to grow large eyestalks even under stressful conditions.[6] Females who mate with these males will therefore benefit by acquiring these good genes for their offspring. Furthermore, in some populations of T. dalmanni female flies carry a meiotic drive gene on their X-Chromosomes that causes female-biased sex ratios. In these populations males that have gene that suppresses meiotic drive have longer eyestalks, meaning that females that prefer to mate with these males will gain a direct genetic benefit by producing male offspring in a female-biased population.[7]
[edit] References
- ^ a b Wilkinson, G.S., and Dodson, G.N. (1997). Function and evolution of antlers and eye stalks in flies. In: The Evolution of Mating Systems in Insects and Arachnids. (J. Choe and B. Crespi, eds.) Cambridge: Cambridge University Press. pp.310–327.
- ^ Papp, L., Földvári, M. and Paulovics, P. (1997) Sphyracephala europaea sp. n. (Diptera: Diopsidae) from Hungary represents a family new to Europe. Folia Entomologica Hungarica 58: 137–146.
- ^ Chapman, T., Pomiankowski, A. and Fowler, K. Quick guide: stalk-eyed flies. Current Biology 15: R533-R535
- ^ Burkhardt, D. and de la Motte, I. (1983) How stalk-eyed flies eye stalk-eyed flies: Observations and measurements of the eyes of Cyrtodiopsis whitei (Diopsidae, Diptera). Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 151: 407-421
- ^ de la Motte, I. and Burkhardt, D. (1983) Portrait of an Asian stalk-eyed fly. Naturwissenschaften 70: 451-461
- ^ David, P., Bjorksten, T., Fowler, K., and Pomiankowski, A. (2000). Condition dependent signalling of genetic variation in stalk-eyed flies. Nature 406: 186–188.
- ^ Wilkinson, G.S., Presgraves, D.C., and Crymes, L.(1998). Male eyespan in stalk-eyed flies indicates genetic quality by meiotic drive suppression. Nature 391: 276–279.
