Inbreeding and selection on sex ratio in the bark beetle Xylosandrus germanus
1 Department of Ecology and Evolution, University of Lausanne, Biophore, CH 1015 Lausanne, Switzerland
2 Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, CH- 3032 Hinterkappelen, Switzerland
3 Trinserstrasse 31, A-6150 Steinach, Austria
4 School of Biology, Harold Mitchell Building, University of St Andrews, St Andrews, KY16 9TH, UK
BMC Evolutionary Biology 2011, 11:359 doi:10.1186/1471-2148-11-359Published: 13 December 2011
Local Mate Competition (LMC) theory predicts a female should produce a more female-biased sex ratio if her sons compete with each other for mates. Because it provides quantitative predictions that can be experimentally tested, LMC is a textbook example of the predictive power of evolutionary theory. A limitation of many earlier studies in the field is that the population structure and mating system of the studied species are often estimated only indirectly. Here we use microsatellites to characterize the levels of inbreeding of the bark beetle Xylosandrus germanus, a species where the level of LMC is expected to be high.
For three populations studied, genetic variation for our genetic markers was very low, indicative of an extremely high level of inbreeding (FIS = 0.88). There was also strong linkage disequilibrium between microsatellite loci and a very strong genetic differentiation between populations. The data suggest that matings among non-siblings are very rare (3%), although sex ratios from X. germanus in both the field and the laboratory have suggested more matings between non-sibs, and so less intense LMC.
Our results confirm that caution is needed when inferring mating systems from sex ratio data, especially when a lack of biological detail means the use of overly simple forms of the model of interest.