Darwin’s breeding puzzle explained by fish

A study by Swansea University scientists may explain why some plant and animal species alternate their mating strategy between self-fertilization to bi-parental breeding.

Mangrove Killifish hermaphrodite

The study published in Proceedings of the Royal Society B was led by Dr Sonia Consuegra at the College of Science in collaboration with researchers at Cardiff, Adelaide, Aberystwyth and Oviedo Universities.  The research focused on the mangrove killifish (Kryptoblebias marmoratus) which is a unique vertebrate than can self-fertilise and whose populations are mainly formed by self-fertilising hermaphrodites and a low proportion of males (1-20%).

The research team looked at epigenetic changes in the species, which can be explained as the way in which environmental factors cause changes in gene expression rather than the genetic code itself. They found that temperature-induced epigenetic changes could explain the long standing breeding puzzle of how some self-fertilising species alternate between uni- and bi-parental breeding.

The research team incubated eggs from single selfing hermaphrodites of the mangrove killifish at different temperatures and analysed the proportion of males in the offspring as well as the epigenetic profiles and expression of sex-related genes in the brain of both sexes.

The researchers found:-

  • The percentage of males increased from 1% to up to 80% at the lowest temperature extreme.
  • This variation in temperature-related sex-ratios was closely associated with epigenetic changes and gene expression of genes related to sex differentiation that were less expressed in males in response to epigenetic changes.
  • This indicates that environmental change may influence self-fertilisation in hermaphrodites.

Mangrove Killifish male

Dr Consuegra said: “Self-fertilisation or selfing ensures reproduction even in the absence of available mates, but also results in inbred offspring with low genetic diversity. In contrast, bi-parental breeding or outcrossing can be more difficult but maintains genetic diversity and produces more adaptable offspring.

“Some plants and animals have the best of both worlds by alternating between both modes of reproduction but the mechanism of this mixed mating strategy has been an evolutionary puzzle ever since Darwin. Our new study revealed for the first time that epigenetic changes regulated by environmental conditions by controlling sex ratios, explains the regulation of selfing through mate availability.  This is a concerning finding when considering the potential consequences of climate change for the population dynamics of species with environmental sex determination.”

The study is available here.

Ellison, A., Rodriguez Lopez, C., Moran, P., Breen, J., Swain, M., Megias, M., Hegarty, M., Wilkinson, M., Pawluk, R.  & Consuegra, S.  (2015). Epigenetic regulation of sex-ratios may explain natural variation in self-fertilisation rates. Proceedings of the Royal Society B
Pictures courtesy of Amy Ellison: Picture 1: Mangrove killifish hermaphrodite Picture 2: Mangrove killifish male