Teleopsis dalmanni

Cyrtodiopsis dalmanni, also known as the Malaysian stalk-eyed fly, is a species of fly in the family Diopsidae. C. dalmanni possess lateral elongations of their headcapsule called eye-stalks. This physical characteristic of the fly has been the subject of several studies on sexual selection, natural selection, and mating behavior.

Crytodiopsis dalmanni
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Suborder:	Cyclorrhapha
Infraorder:	Muscomorpha
Section:	Schizophora
Subsection:	Acalyptratae
Superfamily:	Diopsoidea
Family:	Diopsidae
Genus:	Crytodiopsis
Species:	C.dalmanni
Binomial name
Crytodiopsis dalmanni Mikan, 1796

Distribution

C. dalmanni is found in Malaysia as well as other parts of Southeast Asia. Flies used in studies are usually collected in Malaysia.

Habitat

C. dalmanni are predominantly found at the edge of forest streams, as they carry out their mating rituals in this habitat. They have been observed resting on dried leaves or undergrowth at the water’s edge or even, at times, on the sand.

Life history

As with other Dipterans, C. dalmanni flies undergo a larval phase before transitioning into adults. There is little information available on the systematics and behavior of the larval stage in C. dalmanni. As holometabolous insects, the flies have dividing cells restricted to the gut and gonads. As a result, the adult size is fixed by the nutrition received in the larval phase. Past the larval stage, further nutrition is required for the development of internal reproductive structures to obtain sexual maturity.

Breeding experiments typically assign three to six weeks for these flies to reach sexual maturity, but a value for wild fly populations has not been determined with confidence. Sexual maturity can be indicated by accessory gland growth, maturing of sperm bundles, and sperm motility. Accessory gland growth was found to have the largest effect on sexual maturity, but not the sole effect.

Food resources

Adult flies exhibit solitary foraging behavior, feeding on rotting vegetative matter in the daytime.

Mating

Female C. dalmanni roost on root threads overhanging streams at dusk. Males compete to gain control of these root hairs. Upon gaining control of a root hair they form harems, and females decide which male’s harem to join. Studies have shown that females prefer to roost with males with large eye-spans. Mating occurs at dawn, and usually multiple mating events take place. Research shows that increased mating frequency correlates with a higher proportion of fertile eggs. This is supported by the idea that matings do not reduce the receptivity of the female fly to copulation, regardless of the characteristics of the mating male. Copulation specifics are not entirely understood, but some copulation events are rapid and last less than 60 seconds.

Male flies produce gourd-shaped spermatophores that occupy only a part of the vaginal capacity, as compared to the spermatophores of certain other diopsid flies that occupy the entire vaginal cavity. Accessory glands are responsible for forming the spermatophore that transports sperm during mating.

Morphology

Eyestalks

The eye-stalks of C. dalmanni, as well as other Diopsidae flies, are frequently used to study the fields of sexual selection and mating preference. Eye-stalks have been known to range from 4 mm in length up to 17 mm. Eye stalks can even be longer than body length.

Hyperencephaly of the type that resembles the eye-stalks in C. dalmanni is seen is other Dipteran organisms, but flies of the family Diopsidae are unique in that both males and females display some degree of eye-stalk elongation. However male C. dalmanni flies have larger eye-spans even relative to body length. These processes play an important role in mating behavior, as studies have shown that females prefer males with larger eye spans relative to body length. Furthermore, eye-span independent of body size or mass has been identified as the key determinant in the outcomes of contests between males.

C. dalmanni is an example of sexual dimorphism that has developed for mating purposes; larger eye-span is selected for. This feature of the fly is subject to studies that investigate the genetic background of sexual selection, female mating preferences and reproductive consequences. Male eye-span is also strongly dependent on conditional factors, comparatively more than other non-sexual traits.

Mate Choice

It was found that female preference for large eye-spans is evident when the difference between eye-spans of available males is large, not moderate. In cases of low and moderate difference, a female with a large eye-span is more likely to pick the male with larger eye-span. There are multiple theories posited to explain this, including the idea that female preference for male eye-span may have a ceiling, or that female choice is linked genetically to female eye-span.

Handicap hypothesis

It was found that male eye-span is highly dependent on the conditions of the fly, and that eye-span became variable under conditions of increased stress. Similar patterns were not seen in comparable nonsexual traits, and were more closely correlated with body size. The hypothesis drawn from these results were that eye-span provides information about the condition beyond that provided by body size. Hence eye-span could be an alternative indication of greater ability to survive. This relates to the handicap theory of evolution of ornamental male traits.

Eyes

C. dalmanni has been used as a study subject in experimental subject in studies on data processing in insect optic centers as it is easy to record impulse activity in the eye-stalk