Module 6.2: Inbreeding

   From my research, I might have gathered that inbreeding interrupts the evolution of assortative mating. There are several models of assortative mating that show increase of homozygosity in each population, and the theory and empirical data showing benefits of inbreeding is abundant, however studies showing the relationship of the two seem to be basically absent. A study conducted by some graduate students at Uppsala University in 2009 aims at studying the interaction between assortative mating and inbreeding by using the population Cowpea weevil, Callosobruchus maculatus. After six generations of inbreeding, the results show that female fertility was indeed affected by inbreeding depression; females laid fewer eggs after mating with males that were closely related. Both the number of eggs laid, and individuals hatched were significantly reduced over generations, which highlights that inbreeding reduces female fecundity and reproductive rate. The study also indicates that sources of food affected the female fecundity significantly. Offspring from females that fed on black-eyed beans always had larger body size than those from mung beans. This project concludes that the effect of mating patterns on female fecundity during lifetime was significant. The extent of inbreeding depression is larger at smaller population sizes, which means inbreeding happened more frequently in smaller population size. The results show deviations from Hardy-Weinberg equilibrium, which means assortative mating was avoided mostly. One of the most conceivable reasons could be inbreeding depression. This concludes that inbreeding is a factor that disturbs the effects of assortative mating on sympatric speciation. The populations that can mate assortatively and at the same time avoid inbreeding are the ones that survive and may evolve into new species. Inbreeding is disadvantageous to fitness for organisms. Inbred offspring mature slower than outbred offspring and inbred adult females have lower reproductive output. This negative impact is expected to drive sexual selection for mating preference with unrelated partners. Organisms differentiate between kin and non-kin partners in mate choice, as a mechanism to avoid inbreeding. Organisms have shown to exhibit mate choice to increase fitness, but the question remains whether it can also distinguish between relatives and non-relatives and whether it can select a mate to avoid inbreeding.

Sources

Tien, N.S.H., Massourakis, G., Sabelis, M.W. et al. (2011). Mate choice promotes inbreeding avoidance in the two-spotted spider mite. Exp Appl Acarol 54, 119–124. https://doi.org/10.1007/s10493-011-9431-y

Doebeli, M. 2005. Adaptive speciation when assortative mating is based on female preference for male marker traits. Journal of Evolutionary Biology 18:1587-1600.