Stalk-eyed fly

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Stalk-eyed flies
Temporal range: Eocene–Recent
Diopsis stuckenbergi
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
(unranked): Cyclorrhapha
Section: Schizophora
Superfamily: Diopsoidea
Family: Diopsidae
Billberg, 1820
Subfamilies
Synonyms
  • Centrioncidae[1]

Stalk-eyed flies are insects of the

sexually dimorphic, with eyestalks present but shorter in females.[3]

The stalk-eyed flies are up to a centimeter long, and they feed on both decaying plants and animals. Their unique morphology has inspired research into how the attribute may have arisen through forces of sexual selection and natural selection. Studies of the behavior of the Diopsidae have yielded important insights into the development of sexual ornamentation, the genetic factors that maintain such a morphological feature, sexual selection, and the handicap principle.

Distribution and habitat

A diopsid from Cameroon

More than 100 species in the Diopsidae are known, with the greatest diversity found in the Old World tropics.[4] They are distributed throughout the region, with the best-known species being from Southeast Asia and Southern Africa. Also, two species in North America have been described and a European species has recently been found in Hungary.[5]

Adult diopsids are typically found on low-lying vegetation in humid areas, often near streams and rivers, where they feed on fungi and bacteria, which they scavenge from decaying vegetation. The larvae are

phytophagous, eating decaying and fresh plant matter. Diopsis macrophthalma Dalman, 1817, is a pest of rice and sorghum
in tropical Africa.

The peculiar morphology of stalk-eyed flies makes it easy to identify their fossils (e.g. in amber); one fossil genus is Prosphyracephala, known from Eocene aged Baltic amber.[6] This genus has stalked eyes and is the earliest diverging member of the Diopsinae.[3]

Morphology

The Diopsidae are small to medium-sized flies, ranging from about 4.0 to about 12.0 mm in length. Their heads are subtriangular, with transverse eye stalks in all genera except the African genus

vibrissae (whiskers) absent.[7]

The posterior portion of the fly's

ventral band.[7]

Stalk-eyed flies, as the name implies, typically possess eyestalks (in all but the two genera listed above). Their eyes are mounted on projections from the sides of the head, and the antennae are located on the eyestalks, unlike stalk-eyed flies from other families. Though both males and females of most species have eyestalks, they are much longer in males, a sexual dimorphism thought to be due to sexual selection.[8] A rather remarkable feature of stalk-eyed flies is their ability, shortly after they emerge from their pupae, to ingest air through their oral cavity and pump it through ducts in the head to the tips of the eye stalks, thereby elongating them while they are still soft and transparent.[9]

Taxonomy

True stalk-eyed flies are members of the family Diopsidae, first described by

Diptera and suborder Cyclorrhapha;[12]
it is divided into two subfamilies:

Centrioncinae

  1. Centrioncus Speiser, 1910
  2. Teloglabrus Feijen, 1983

The African genus Centrioncus (once placed in Sepsidae, but then moved to Diopsidae) was once recommended to be treated as a separate family, Centrioncidae, a sister group of the diopsids,[13] but since then this lineage has usually been treated as a subfamily.[14]

Main article: List of stalk-eyed flies

Diopsinae

Stalk-eyed fly (Diasemopsis)
Male Teleopsis dalmanni

The Global Biodiversity Information Facility includes:[15]

  1. Cladodiopsis Séguy, 1949
  2. Cobiopsis Feijen, 1989
  3. Cyrtodiopsis Frey, 1928
  4. Diasemopsis Rondani, 1875
  5. Diopsina Curran, 1928
  6. Diopsis Linnaeus, 1775
  7. Eosiopsis Feijen, 2008
  8. Eurydiopsis Frey, 1928
  9. Madagopsina Feijen, Feijen & Feijen, 2017
  10. Megalabops Frey, 1928
  11. Pseudodiopsis Hendel, 1917
  12. Sinodiopsis Feijen, 1989
  13. Sphyracephala Say, 1828
  14. Teleopsis Rondani, 1875

Vision

Despite the unusual morphology of the eye, each

Conspecifics are most likely to elicit a threat or flight reaction when they are at a distance of about 50 mm, and reactions to model flies and reflections in a mirror also occur at about this distance.[16]

Mating

Stalk-eyed flies roost at night on root hairs hanging by streams. Mating usually takes place in the early morning in the vicinity of their roosts. Females show a strong preference for roosting and mating with males with longer eyestalks, and males compete with each other to control

lekking aggregations through ritualized contest. This contest involves males facing one another and comparing their relative eye spans, often with the front legs spread apart, possibly to emphasize their eye-stalk lengths.[18] Male stalk-eyed flies with long eyestalks gain mating advantages both because of female choice and because they are better able to compete with rival males.[4][19]

Sexual selection

Though the evolution of exaggerated male traits as a result of female

alleles, with the magnitude of resulting genetic correlations influencing evolutionary outcomes. If the genetic correlation is high relative to the heritability of the male ornament, then a runaway process can occur leading to extreme sexually selected traits, such as the incredible eye spans observed in male stalk-eyed flies. Otherwise, the trait and preference for the trait increase until natural selection against further trait elaboration balances sexual selection.[22]

Close-up of a male Teleopsis dalmanni

The extreme morphology exhibited by stalk-eyed flies (especially males) has been studied in an effort to support the hypothesis that exaggerated male traits could evolve through female mate choice and that the selection on male ornaments should cause a correlated response in female preferences. Researchers noted that the flies roosted along stream banks in peninsular Malaysia and that the males with the largest eye spans were accompanied by more females than males with shorter eye spans. From January to October, the researchers counted males and females on 40 root hairs along a single 200-m stretch of stream bank to confirm this observation.[24]

Sexual selection experiments

Researchers collected stalk-eyed flies and observed their behavior under laboratory conditions. In the lab, each individual was scored for eye spans, body length, age, and

female choice in the presence and absence of male competition and in the presence of males with abnormally long and abnormally short eye spans.[24]

Males dispersed themselves, while females clustered in certain areas of the cage. As observed prior to the study, researchers found that the average number of females per male increased with male eye span in field collected aggregations of stalk-eyed flies. Under laboratory conditions, researchers found that female preferences for male characteristics changed as the males sexual characteristics changed. After 13 generations of artificial selection, they found that long eye-span male line females (i.e. females whose fathers had long eye spans) preferred long eye spans in both the selected males and in males that were not bred through artificial selection, while short eye-span male line females (i.e. females whose fathers had short eye spans) found short eye spans to be the most attractive, even over males with long eye spans. Because researchers kept the females separate from males prior to mate selection, the finding supported the hypothesis that the change in female mate choice was genetically based and not learned. Thus, stalk-eyed flies have been able to evolve a sexual trait in males that corresponds directly to traits that affect mating choices made by females.[24]

Handicap selection

However, the evolution of extreme morphology in male flies and the corresponding evolution of female preference for these characteristics as an effect of sexual selection is only half the picture.[26] Handicap models of sexual selection predict that male sexual ornaments have strong condition-dependent expression, and this allows females to evaluate male genetic quality.[27][28][29][30][31]

Genetic variation underlies the response to environmental stress, such as variable food quality, of male sexual ornaments, such as the increased eye span, in the stalk-eyed fly.[26] Some male genotypes develop large eye spans under all conditions, whereas other genotypes progressively reduce eye spans as environmental conditions deteriorate. Several nonsexual traits, including female eye span and male and female wing length, also show condition-dependent expression, but their genetic response is entirely explained by scaling with body size. Unlike these characteristics, male eye span still reveals genetic variation in response to environmental stress after accounting for differences in body size. Thus, it could be inferred that these results strongly support the conclusion that female mate choice yields genetic benefits for offspring as eye span acts as a truthful indicator of male fitness. Eye span is, therefore, selected not only on the basis of attractiveness, but also because it demonstrates good genes in mates.[26]

Furthermore, some populations of stalk-eyed fly females carry a meiotic drive gene on their X chromosomes that causes female-biased sex ratios.[32] In these populations, males which carry a gene to suppress X-chromosome meiotic drive have longer eyestalks. Thus, females that mate with these males gain a direct genetic benefit by producing male offspring in a female-biased population. In other words, the gene for long eye-stalks is linked to a gene that makes males sire more male offspring.[33] Alternatively, long stalks may signal fertility, perhaps by encouraging females to use the sperm of a long-stalked male so as to produce more fertile sons.[33]

References

  1. ^ Feijen, Hans R. (1983). "Systematics and phylogeny of Centrioncidae, a new afromontane family of Diptera (Schizophora)". Zoologische Verhandelingen. 202: 1–137. Retrieved 30 October 2016.
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  5. ^ L. Papp, M. Földvári & P. Paulovics (1997). "Sphyracephala europaea sp. n. (Diptera: Diopsidae) from Hungary represents a family new to Europe" (PDF). Folia Entomologica Hungarica. 58: 137–146.
  6. doi:10.1002/mmnd.19940410111
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  7. ^ a b Peterson, B. V. (1987). "Diopsidae." In McAlpine, J. F., B. V. Peterson, G. E. Sherwell, H. J. Tekey, J. R. Vockerorth, and D. M. Wood, (cords.). Manual of Nearctic Diptera. Vol. 2: 785–789.
  8. ^ a b Davies N, Krebs J, and West S. (2012). An Introduction to Behavioral Ecology, 4th Ed. Wiley-Blackwell; Oxford: pp. 196-198.
  9. ^ Buschbeck, E. K., Roosevelt, J. L. and Hoy, R. R. (2001). Eye stalks or no eye stalks: A structural comparison of pupal development in the stalk-eyed fly Cyrtodiopsis and in Drosophila. J. Comp. Neurol., 433: 486–498.
  10. ^ Shillito, J. (1976). Fothergill and Linnaeus: The background of De Bigis Insectorum, 1775. Biol. J. Linn. Soc., 8; 75-86.
  11. ^ Shillito, J. (1976). Bibliography of the Diopsidae-II. Journal of the Society for the Bibliography of Natural History. Volume 8, Page 65-73.
  12. ^ Allaby, M. (1999). "Diopsidae." A Dictionary of Zoology. Encyclopedia.com. (December 15, 2012). http://www.encyclopedia.com/doc/1O8-Diopsidae.html
  13. ^ Feijen, H.R. (1983). "Systematics and phylogeny of Centrioncidae, a new afromontane family of Diptera (Schizophora)". 202 (1): 1–137. {{cite journal}}: Cite journal requires |journal= (help)
  14. doi:10.1046/j.1439-0469.2000.381128.x
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  15. ^ Global Biodiversity Information Facility: Family Diopsidae (retrieved 19 March 2024)
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  18. ^ Wilkinson, G. (2001). Model Syestems in Behavioral Ecology: Integrating Conceptual, Theoretical, and Empirical Approaches. Ed. Lee Alan Dugatkin. Princeton University Press; Princeton: pp. 84-91.
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  20. ^ Kirkpatrick, M and M.J. Ryan. (1991). “The evolution of mating preferences and the paradox of the lek.” Nature, Lond. 350: 33-38.
  21. ^ Maynard Smith, J. (1991). “Theories of sexual selection.” Trends Ecol. Evol. 6: 146-151.
  22. ^ a b Lande, R. (1981). “Models of speciation by sexual selection on polygenic traits.” Proc. Natn. Acad. Sci. U.S.A. 78: 3721-3725.
  23. ^ Kirkpatrick, M. (1982). “Sexual selection and the evolution of female choice.” Evolution 36: 1-12.
  24. ^ a b c Wilkinson, G. and P. Reillo. (1994). “Female choice response to artificial selection on an exaggerated male trait in a stalk-eyed fly.” Proc. R. Soc. Lond. B. 255: 1-6.
  25. ^ Wilkinson, G. (1993). “Artificial sexual selection alters allometry in the stalk-eyed fly Cyrtodiopsis dalmanni.” Genet. Res. 62: 212-222.
  26. ^
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  27. ^ Andersson, M. (1986). “Evolution of condition-dependent sex ornaments and mating preferences: sexual selection based on viability differences.” Evolution 40: 804–816.
  28. ^ Pomiankowski, A. (1987). “Sexual selection: the handicap principle does work—sometimes.” Proc. R. Soc. Lond. B 231: 123–145.
  29. ^ Grafen, A. (1990). “Biological signals as handicaps.” J. Theor. Biol. 144: 517–546.
  30. ^ Iwasa, Y. and A. Pomiankowski. (1994). “The evolution of mate preferences for multiple handicaps.” Evolution 48: 853 –867.
  31. ^ Rowe, L. and D. Houle. (1996). “The lek paradox and the capture of genetic variance by condition dependent traits.” Proc. R. Soc. Lond. B 263: 1415–1421.
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External links

Wikispecies has information related to Diopsidae.
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