Fine structure of the compound eye of the black fly Simulium vittatum (Diptera: Simuliidae)

Abstract

1987. Fine structure of the compound eye of the black fly Simulium vittatum (Diptera: Simuliidae) . Can. J. Zool. 65: 1454-1469.The fine structure of the ommatidia in light-and dark-adapted eyes of male and female Simulium vittatum Zetterstedt was investigated using scanning and transmission electron microscopy. The male eye is divided into distinct dorsal and ventral regions. The facets in the dorsal region are approximately two times larger than those in the ventral one, which are similar in size to the ones in the female eye. All ommatidia of S. vittatum examined consist of two general regions: a distal dioptric apparatus with bordering primary and accessory pigment and Semper cells, and a sensory receptor layer. Each ommatidium in the female eye and ventral eye of the male has eight retinular cells (R cells): six peripheral (Rl-6) and two central (R7, R8). R7 occurs distally and R8 basally. Strikingly, the ommatidia in the dorsal eye of the male lack the R7 cell. In all ommatidia, rhabdomeres on the inner surface of the peripheral R cells are separate throughout their length, creating an open rhabdom. A greater diameter of corneal facets, elongated peripheral R cells, and perhaps the lack of the R7 cell are specializations of the dorsal region of the eye that help the male to detect small, rapidly moving females against the skylight as they fly above the swarm of males. Differences observed between light-and dark-adapted eyes of male and female S. vittatum were the same and were associated with the internal components of the peripheral R cells.

The rhabdom structure in the ommatidia of the Heteroptera (Insecta), and its phylogenetic significance

“…It has long been known that, in insects, there are four higher groups that differ from this plesiomorphic pattern in having open rhabdoms. These are the Diptera (see, for example, Dietrich 1909;Tuurala 1963;Eckert 1968;Brammer 1970;Williams 1980;O'Grady and McIver 1987;Melzer and Paulus 1991), the Cucujiformia (Coleoptera) (see, for example, Kirchhoffer 1908;Wachmann 1977Wachmann , 1979Schmitt et al 1982;Wachmann et al 1983;Caveney 1986), the Dermaptera (see, for example , Jörschke 1914;Eckert 1968;McLean and Horridge 1977;Lootz 1982), and the Heteroptera (see Table 1). Although the evolution of open rhabdoms in these groups must be regarded as convergent, the structure of these open rhabdoms is remarkably similar: usually there are six retinula cells (abbreviated R1-R6) forming a more or less ring-like peripheral system, while the two remaining retinula cells (R7 and R8) are fused and form a rod-like central system.…”

Did neural pooling for night vision lead to the evolution of neural superposition eyes?

“…One of the fundamental prerequisites for neural superposition is an open rhabdom, and this is a feature shared by nearly all Diptera (Tuurala 1963;Eckert 1968;Brammer 1970;Meyer-Rochow and Waldvogel 1979;Williams 1980;O'Grady and McIver 1987;Seifert and Wunderer 1989;Melzer and Paulus 1991). Open rhabdoms are also characteristic of heteropteran Hemiptera (Bedau 1911;Kuhn 1926;Eckert 1968;Burton and Stockhammer 1969;Schneider and Langer 1969;Mtiller 1979;Walcott 1971 cucujiform beetles (Eckert 1968;Chu et al 1975;Wachmann 1977Wachmann , 1979Gokan and Hosobuchi 1979a,b;Meyer-Rochow and Gokan 1988;Schmitt et al 1982;Lin 1993) and Dermaptera (Eckert 1968;McLean and Horridge 1977).…”

A Morphological, Functional, and Genetic Investigation of the Male Compound Eye Phenotype of Chrysomya megacephala (Diptera: Calliphoridae))

“…While D. melanogaster provides a basic blueprint for dipteran eye structure and development because of the wealth of morphological and genetic data available, there are dipterans that deviate from this basic plan. A driver of some of these deviations is sexually dimorphic behaviors such as searching for mates (Hardie et al 1981, O'Grady andMcIver 1987). Males of the house fly Musca domestica, for example, have a region in the dorsal portion of their eye containing enlarged facets referred to as the "love spot" .…”

“…Whereas the two central photoreceptors within each ommatidium typically express genes used in color discrimination, the distal most central photoreceptor in this region, R7, instead expresses a gene known to play a role in motion detection , leading to speculation that the function of this area is to track potential mates. A different example of how motion detection can be increased for a male dipteran is present in the black fly Simulium vittatum (O'Grady and McIver 1987). Males of this species have a dorsal area that is characterized by facets nearly twice as large as the ventral facets, but these ommatidia lack the R7 photoreceptor used to help color discrimination (O'Grady and McIver 1987).…”

“…A different example of how motion detection can be increased for a male dipteran is present in the black fly Simulium vittatum (O'Grady and McIver 1987). Males of this species have a dorsal area that is characterized by facets nearly twice as large as the ventral facets, but these ommatidia lack the R7 photoreceptor used to help color discrimination (O'Grady and McIver 1987). This indicates that color detection is less important in this region believed to be specialized for mate tracking (O'Grady and McIver 1987).…”