Effects of spontaneous mutation accumulation on sex ratio traits in a parasitoid wasp.
Sex allocation theory has proved extremely successful at predicting when individuals should adjust the sex of their offspring in response to environmental conditions. However, we know rather little about the underlying genetics of sex ratio or how genetic architecture might constrain adaptive sex-ratio behavior. We examined how mutation influenced genetic variation in the sex ratios produced by the parasitoid wasp Nasonia vitripennis. In a mutation accumulation experiment, we determined the mutability of sex ratio, and compared this with the amount of genetic variation observed in natural populations. We found that the mutability (h(2)(m)) ranges from 0.001 to 0.002, similar to estimates for life-history traits in other organisms. These estimates suggest one mutation every 5-60 generations, which shift the sex ratio by approximately 0.01 (proportion males). In this and other studies, the genetic variation in N. vitripennis sex ratio ranged from 0.02 to 0.17 (broad-sense heritability, H(2)). If sex ratio is maintained by mutation-selection balance, a higher genetic variance would be expected given our mutational parameters. Instead, the observed genetic variance perhaps suggests additional selection against sex-ratio mutations with deleterious effects on other fitness traits as well as sex ratio (i.e., pleiotropy), as has been argued to be the case more generally.
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3JT, United Kingdom. Bart.Pannebakker@ed.ac.uk
Bart A
BA
Pannebakker
Daniel L
DL
Halligan
K Tracy
KT
Reynolds
Gavin A
GA
Ballantyne
David M
DM
Shuker
Nick H
NH
Barton
Stuart A
SA
West
D000818:Animals; D003433:Crosses, Genetic; D019143:Evolution, Molecular; D005260:Female; D014644:Genetic Variation; D005828:Genetics, Population; D008297:Male; D008957:Models, Genetic; D015233:Models, Statistical; D009154:Mutation; D012641:Selection, Genetic; D012737:Sex Factors; D012744:Sex Ratio; D013045:Species Specificity; D014863:Wasps / Q000235:genetics* / Q000502:physiology*