lessness is known from more than 20 families of Diptera (review, Hackman 1964), and can be broadly categorized as responses to three general types of selective pressure: a) climactic, especially to cold or overcast habitats, in alpine areas, high latitudes, and islands. b) adaptation to parasitism, either as inquilines in the nests of social insects, or on vertebrate hosts, and c) life in cryptic habitats, where wings would have little function or be easily damaged. There are various categories of wing reduction: shortened or reduced in length (brachyptery), narrowed or reduced in width, but often with a distinct radial vein (stenoptery), reduced to a tiny appendage (microptery), or totally absent (aptery). Flightlessness can have strong synergistic effects on other structures, such as the reduction or loss of halters, loss of flight muscle and associated thoracic shrinkage, and modification of the legs for cursorial life. Flies of the family Dolichopodidae are free living and all known instances of wing reduction appear to be adaptations to climatic conditions. Evenhuis (1997) reviewed flightlessness in the family and recorded 15 species with varying degree of wing reduction, with the majority of cases on islands. Eight stenopterous or micropterous species are known from the tropical Hawaiian Islands, almost all from elevations above 1500 m. Three micropterous or apterous species are known from the cold and windy Campbell and Macquarie islands above 50°S latitude south of New Zealand, and an undescribed stenopterous species from Stewart Island, New Zealand. Two brachypterous species are known from North America, one being a variant of a fully winged species associated with coastal dunes in California, and the other is known from bogs in eastern Canada. Finally, the brachypterous Hydrophorus celestialis Takagi is found from 3,500-4,000 m on snow and rocky alpine herb fields in Nepal (Takagi 1972). Flightlessness in most Dolichopodidae appears to have developed where cold and/ or overcast conditions make thermoregulation of thoracic flight muscles difficult. This is the case in the subantarctic islands, wet montane tropics and alpine habitats. As well, strong winds would select against flight on small islands. However, ground predation, particularly from ants, appears to be a major factor limiting wider development of flightlessness in Diptera. Ants are not present on subantarctic islands or in high alpine conditions. And although tropical, the eight flightless Hawaiian
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Oct 17, 2023
Siyu Pang + 2
Open Access