Problems and paradigms: Altering sex ratios: The games microbes play
✍ Scribed by Gregory D. D. Hurst; Laurence D. Hurst; Michael E. N. Majerus
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 398 KB
- Volume
- 15
- Category
- Article
- ISSN
- 0265-9247
No coin nor oath required. For personal study only.
✦ Synopsis
The male gametes of most organisms lack cytoplasm. Consequently, most cytoplasmic genetic elements are maternally inherited: they cannot be transmitted patrilinnearly. The evolutionary interests of cytoplasmic elements therefore lie in transmission through the female. These elements may thus be in evolutionary conflict with nuclear genes which are transmitted by both sexes. This conflict is manifested in observations of cytoplasmically induced biased sex-ratios. Some cytoplasmic genes avoid this fate by biasing the primary sex ratio towards females, or by inducing parthenogenesis. Others kill male hosts, and either achieve transmission via dispersal, or benefit their clonal relatives in the dead male's female siblings. Still others cause the failure of zygotes resulting from pairings between males carrying specific microbes and females lacking them, causing an increase in the microbes through the sterilisation of non-bearing females. Many, but not all, of these 'ultra-selfish' microbes are closely related. Investigations of the significance of their phylogenetic affinities, or lack of them, their adaptability in terms of the methods by which they avoid, or ameliorate, the adverse effects of being in male hosts, and their importance as selective agents in the evolution of invertebrate sex determination systems, provide fertile spheres for future research.
Female Armudillium vulgure, an isopod crustacean, vary in the number of male and female progeny they produce. Some females produce an equal number of inalc and female progeny as expected of organisms with XY sex determination.