Effective population size, reproductive success and sperm precedence in: the butterfly, Bicyclus anynana, in captivity

A pedigree approach is used to estimate the effective population size in tw o population cages of the butterfly, Bicyclus anynana. Each cage was founde d with 54 individually marked adults of each sex. Matings were recorded ove r a 3-day period. Eggs were then collected from each female over a similar period before the numbers of hatching larvae were counted to assess progeny number. The males showed a higher variance in reproductive success than th e females. Since about one-quarter of all females mated more than once, we also examined the pattern of sperm precedence using molecular markers or, i n separate crossing experiments, wing pattern mutants. Both instances of co mplete first and last male sperm precedence, as well as of sperm mixing, we re found. In some crosses a 'leakiness' was found in which some of the earl y eggs laid by a female were fertilized by a male partner which was subsequ ently completely unsuccessful. However, the estimates of effective populati on size were largely unaffected by the pattern of sperm precedence. Estimat es for N-e : N in each cage were close to 0.60. The possibility of obtainin g comparable estimates in selected natural populations of butterflies is di scussed.