, Volume 146, Issue 1, pp 3-31

Population dynamics of Ischnura E. elegans (Vander Linden) (Insecta: Odonata) with special reference to morphological colour changes, female polymorphism, multiannual cycles and their influence on behaviour

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Abstract

Laboratory and field experiments on adult I. elegans provide correction techniques for the estimation of population parameters based only on capture-recapture data. Thus it is demonstrated that male and female longevities are identical and that their sex ratio is 0.5 (= Male fraction).

Longevity, measured at the water, erroneously appears to differ between sexes, and sex ratio is also biased. This bias is a function of population density, which causes a different distribution of males and females, matures and immatures, andro- and heteromorphic females, and is regulated by aggressive, territorial and mating behaviour of individuals. The female maturation period exceeds that of the male. Female polymorphism is an adaptation to population density, high density favouring andromorphs. This polymorphism is determined by single allelic autosomal inheritance with a sex-linked expression.

In crowded populations, visual interactions between individuals cause their juvenile hormone titer to rise. This shortens maturation time, the period of morphological colour changes, and life span. This mechanism counteracts crowding, and synchronises maturation and development of sexual behaviour.

In the course of their life, individuals undergo a number of colour changes. The development of the colours after eclosion coincides with spermato- and oogenesis. The morphological colour change at sexual maturity is due to neutralisation of waste products of the protein metabolism. The colour changes at old age are partly due to dehydration.