Abnormal and variable sex ratios in population samples of ladybirds

Henderson, S.A.; Albrecht, J.S.M.

Abnormal and variable sex ratios in population samples of ladybirds

1988

Henderson, S.A. | Albrecht, J.S.M.

While most ladybird species are believed to show a conventional 1:1 sex ratio, population samples from five different species of ladybird have been found to show significant excesses of females. The species involved are Anatis ocellata, Exochomus quadripustulatus, Chilocorus renipustulatus, C. bipustulatus and C. nigritus. All possess neo-XY sex chromosome systems. It is possible that the excesses of females reflect the recombination of segments present at the ends of the neo-XY sex bivalent. If the products of recombination are more lethal in males than females, differences in sex ratio will result. An alternative hypothesis involves an interaction between Y-linked factors and maternally inherited factors, possibly of a transposable element type. The maintenance of such excesses of females in several species, in different taxonomic groups within the Coccinellidae, and the presence of differences in different populations of one of the species, must reflect a selective advantage for these excesses in natural populations of these species.

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