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Evolutionary Studies of the New Zealand Coastal Mosquito Opifex Fuscus (Hutton) I

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Evolutionary Studies of the New Zealand Coastal Mosquito Opifex Fuscus (Hutton) I EVOLUTIONARY STUDIES OF THE NEW ZEALAND COASTAL MOSQUITO OPIFEX FUSCUS (HUTTON) I. MATING BEHAVIOUR by ELISABETH SLOOTEN and DAVID M. LAMBERT1)2) (Marine Research Laboratory, R.D. Leigh, and Department of Zoology, University of Auckland, Private Bag, Auckland, New Zealand) (With2 Figures) (Acc.1-XI-1982) Introduction An understanding of the selective pressures that produced the diversity of animal reproductive behaviour is one of the major goals of evolutionary biology. Clearly, deviations from random mating caused by differences in reproductive behaviour can have a profound effect on the genetic com- position of populations. Insects exhibit a remarkable diversity of sophisticated and complex forms of mating behaviour, and are particularly suitable for studies of this kind due to the rapid turnover rate of most insect populations. The swarming and mating flight of Diptera, typical of most mosquito species, has been reviewed by DowNES (1969). There has been some controversy over the function of swarming in mosquitoes (e.g. BATES, 1949; NIELSEN & HAEGER, 1960; HADDOW & CORBET, 1961; DOWNES, 1969). On the one hand it has been claimed that it has an epigamic function and is associated with mating, on the other that its original function has been lost or is unknown. Certainly in many Anophelines, swarming appears to be associated with mating, defining a time and place in which males and virgin females of the same species are brought into close proximity (e.g. CHARLWOOD & JONES, 1980). The mating behaviour of Opifex fuscus described here is an unusual and interesting variation on the typical mosquito mating system outlined 1) Thanks are due to Brian MCARDLEand Steve DAWSONwho read and criticized the manuscript, and to Heather SILYN-ROBERTSwho took the Scanning Electron Micrographs. The research was partly funded by the Auckland University Research Committee Grant number 114Z129. 2) For reprint requests please write to D.M.L. 158 above. Mating aggregations occur, not in flight, but on the water surface of the pools from which the adults emerge. Opifex fuscus is an endemic New Zealand mosquito which inhabits ex- posed rocky coasts on both the North and South Islands. The coastal en- vironment is an uncommon habitat for mosquitoes. Less than 5% of all described mosquito species regularly breed in brackish water (O'MEARA, 1979). Females lay their eggs in pools above high-tide level, the salinity of which ranges from about twice as saline as seawater to almost fresh, depending on weather conditions and height on the shore. Larvae and pupae are free swimming in these pools and come to the surface to breathe at regular intervals. Opifex fuscus (Hutton) is considered by BELKIN (1968) to be descended from the same stock as Aedes (Nothoskusea) chathamicus (Dumbleton) and Aedes (Halaedes) australis (Erichson). He argues that many of the features of Opifex represent the most primitive condition found in the tribe Aedini and are annectent with the other tribes. Because the more striking primitive and derived features are found in fuscus, it is retained in a separate monotypic genus. The species has a most unusual mating system. Both sexes mate ex- tremely early in adult life. Male mosquitoes are capable of sexual activity as soon as the terminal segments of the abdomen have rotated a minimum of 135 degrees (PROVOST et al., 1961), although they do not necessarily use this capability immediately. In Op£ex fuscus rotation takes 5 to 6 hours, one of the fastest rates of terminalia rotation recorded (PROVOST et al., 1961; HAEGER & PROVOST, 1965; O'MEARA, 1979), and start searching for mates 6 to 24 hours after emergence (PROVOST & HAEGER, 1967). The males of a few other species are known to rotate their terminalia at similar rates, for example Deinocerites cancer and Culiseta inornata (PROVOST et al., 1961), but these are certainly exceptions to the rule. Early mating is taken to an even greater extreme in Opifex females which mate at the time of emergence. Males spend most of their adult life on the water surface of rock pools searching for and attempting to grasp pupae which are close to emergence. The only other mosquito species in which males have been described to grasp and guard pupae in a similar way is Deinocerites cancer (PROVOST & HAEGER, 1967). This species does not appear to be par- ticularly closely related to Op£ex fuscus. Deinocerites cancer is classified in the tribe Culicini. A small number of brief descriptions of the mating behaviour of Opifex fuscus have appeared over 60 years (KIRK, 1923; MARKS, 1958; .
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