Malekilling Bacteria And Ladybug Sex Ratios

The population sex ratio of the majority of sexually reproducing organisms is close to 1:1; selection will normally promote the production of the rarer sex, so that the stable strategy is for sex ratio equality. Female-biased sex ratios were first recorded in the ladybug A. bipunctata from Russia in the 1940s. Some females were found to produce only female offspring. The trait was inherited maternally. Subsequent research has shown that male embryos die while in the egg as a result of the action of bacteria such as Wolbachia. These male-killing bacteria live in the cytoplasm of cells and are transmitted from infected mothers to their eggs. Although the bacteria in male eggs die when they kill their host, they benefit clonally identical copies of themselves in their host's siblings, which consume the dead male eggs. The additional resources gained by these neonate female larvae increase their fitness and hence that of the bacteria that they carry.

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