Curtonotidae

Pollock, J. N., 2002, Observations on the biology and anatomy of Curtonotidae (Diptera: Schizophora), Journal of Natural History 36 (14), pp. 1725-1745 : 1742-1743

Evolution within Curtonotidae

Concerning the course of evolution within Curtonotidae, Meier et al. (1997) suggest, very tentatively, that Axinota may be the sister group to the remainder of the family: this was based on characters of the spermathecae.

A feature that might be useful in suggesting the course of evolution within the family is the aedeagus, which is symmetrical and relatively simply constructed in Cyrtona , but more derived and usually (possibly always) asymmetrical in the other genera; more species have to be described and in greater detail before enough data is available in order to make more de nite generalizations. Curtonotum platyphallum appears to have an aedeagal structure somewhat intermediate between that of Cyrtona and those of other curtonotid species; it is unclear whether the structure is symmetrical or asymmetrical, in this species.

Cyrtona males have better conserved tergites 6 and 7 in the male abdomen, than have the males of the other species studied; on these grounds I prefer to see Cyrtona as the sister group of the other two genera combined. This position is also very tentative, as the reduction of the sclerites in question might possibly have occurred independently in the two genera Curtonotum and Axinota ; also more species have to be studied in these respects.

Another important factor is the variation in anatomy of the ejaculatory pump and the duct within Curtonotidae . A small pump attached to the aedeagal apodeme, near to the attachment of the aedeagus, is probably present in Axinota dissimilis (more species need to be studied, especially in the fresh state) and may well be the ground plan condition. The Curtonotum quinquevittatum condition can be envisaged as arising from that original one, by the pump migrating more deeply within the body, with the apodeme ensleeving the duct as the pump migrates. Cyrtona represents a line in which the ejaculatory pump simply became detached from the original site.

Meier et al. (1997) cite the anteroventral pouch as a ground plan feature for Curtonotidae , which is correct. Two views of the signi cance of the pouch in the female reproductive system of Curtonotum and Axinota as reported by Meier et al. appear to be possible. One conceivable view could be that the pouch was used to house eggs before oviposition, but that this function has been lost in the above two genera, with the pouch remaining as a relic structure. Alternatively the pouch could have had a diVerent function, such as the storage of a secretion, but later developed an egg-housing function in Cyrtona . It is perhaps too early to decide which of these views is more likely to be correct.

In respect of the female terminal abdominal segments, Cyrtona (gure 9a) is certainly a more derived type than Curtonotum (gure 9b), re ecting the change to larviparity (or ovoviviparity) from oviparity. In Cyrtona , segments 6 and 7 of the female abdomen do not show the abrupt narrowing to make the telescopic ovipositor, that is so widespread in schizophoran ies. This shows how readily the evolutionary transformation can take place, and is also a model for the change in reproductive strategy that occurred elsewhere, as in the switch from oviparity in gasterophilids to the viviparity of Glossina ( Pollock, 1971, 1973).