Life histories of some Australian Siphlonurid and Oligoneuriid mayflies (Insecta : Ephemeroptera)

Abstract

The life histories of nine populations of mayflies were investigated through monthly field collections over a 3-year period. Seven species were studied, one each from the genera Tasmanophlebia, Ameletoides and Mirawara (Siphlonuridae) and four from Coloburiscoides (Oligoneuriidae). Nymphs were sorted and measured and life histories inferred from size frequency diagrams, and cohorts were separated using a technique for distinguishing multiple overlapping normal distributions. The life histories were all relatively poorly synchronized with adult emergence extended over 5 months or more in every case. A wide size range of nymphs was present in most populations for most of the year and these often formed multiple overlapping cohorts. The time required for development by different cohorts of a single population was quite varied. Marked differences in the length and timing of the adult emergence period, and of the importance of particular cohorts, were apparent in different years. It was concluded that more than a single year's data from one site was necessary to interpret the life histories of Australian mayflies adequately. The four Coloburiscoides species investigated displayed a wide range of development times and patterns, the shortest being displayed by C. haleuticus. This species had some cohorts that seemed to complete their development in about 6 months, whereas C. giganteus had some cohorts that required up to 3 years and also appeared to have a nymphal or early-instar diapause of between 9 and 11 months. The life-history patterns found in this study did not readily fit into the classification schemes proposed by Northern Hemisphere workers. The general asynchrony found in this and previous Australian studies makes it doubtful that a useful classificatory system for Australian mayfly life histories can be developed.