Evol Ecol Res 4: 1229-1240 (2002)     Full PDF if your library subscribes.

Protandry in the butterfly Bicyclus anynana

Wilte G. Zijlstra,* Fanja Kesbeke, Bas J. Zwaan and Paul M. Brakefield

Section of Evolutionary Biology, Institute for Evolutionary and Ecological Sciences, University of Leiden, PO Box 9516, 2300 RA Leiden, The Netherlands

Author to whom all correspondence should be addressed.
e-mail: zijlstra@rulsfb.leidenuniv.nl


Protandry is the earlier adult emergence of males than females. This is predicted from sexual selection theory because, under certain circumstances, earlier emergence of males will maximize their mating opportunities. The tropical butterfly, Bicyclus anynana, is adapted to highly seasonal environments and selection pressures for protandry may vary across seasons. To examine such effects, we compared protandry across a wide range of rearing temperatures in the laboratory which match those that occur in the different seasons. The absolute amount of protandry (in days) remained constant at intermediate and high temperatures (wet season), but increased with temperature at lower temperatures (dry season). Nevertheless, average male development time as a percentage of female development time remained constant. We also compared lines established by artificial selection on development time and pupal weight across temperatures to assess the impact of different selection pressures on protandry. Data for the pupal weight selected lines were inconclusive. The male to female development time ratio did not change across temperatures for the development time selected lines. However, females were relatively slower than males in the slow selected lines (lower male : female development time ratio) than in either the fast lines or the stock. This indicates that sex-specific components to development time are present in B. anynana and that there is scope for a response of protandry to selection.

Keywords: Bicyclus anynana, life history, protandry, seasonality, selection, sexual differences.

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