Heterozygote deficiency in the mussel Mytilus edulis species complex revisited

Abstract

In order to understand the phenomenon of heterozygote deficiency (F,,) in m a n n e molluscs, all the relevant literature concerning this phenomenon in the Mytilus edulis species complex was reviewed. Due to large heterogeneity in methods of data analysis, in particular for the choice of the estimator measuring heterozygote dcficiency and for the choice of the testing procedure, no clear overview was possible. To overcome this problem, similar est~mators and tests were used to analyze or re-anallze some additional large data sets from the Baltic [M. trossulus), France (M. galloprovincialis), England [ M edulis), Atlantic USA (M. edulis) and Pacific US-A (M. trossulus). La.rge and significant heterozygote deficiencies exist in these data sets. Estimated F,, (Fls) values are generally h!gher for Lap than for other loci, consistent with a n effect of selection. No other significant variation of F,, values across loci within each data set or across data sets for each locus was detected, however no specific test has been designed for this null hypothesis. The possible contribution of a Wahlund effect to explain the heterozygote deficiency is discussed. It is likely that there is no unique explanation of heterozygote defic~ency (such as a M'ahlund effect or selection) in M. edulis or in other organisms, and that speciesspecific, locus-specific or populat~on-specific explanat~ons are to be sought

No evidence for genetic differentiation of the mussel Mytilus galloprovincialis between lagoons and the seaside

“…Nevertheless, comparison between studies is difficult as calculations and tests differ. To overcome this problem Raymond et al (1997) re-analysed large data sets of mussels from the Mytilus edulis complex. They found that in the existing literature heterozygote deficiencies were rather underestimated.…”

“…It is possible that artificial migrations caused by man partly explain our results (Wahlund effects and lack of coherent differentiation). However, the large variances observed from one site to another, and from one locus to another, remain difficult to interpret and it is probable that, as suggested by Raymond et al (1997), numerous different factors have to be considered, many of which have not yet been identified and, thus, are difficult to take into account.…”

Spawning, copulation and inbreeding coefficients in marine invertebrates

“…F IS values reflect deviation from Hardy-Weinberg equilibrium (HWE) genotype frequencies and (indirectly) reflect relative population heterozygosity. High positive F IS values (and heterozygosities significantly less than those predicted at HWE) may be caused by laboratory artefacts, unobserved null alleles, natural selection acting on the genetic markers, mating among relatives, or unrecognized spatial or temporal structure within samples known as the Wahlund effect (Zouros & Foltz 1984;David et al 1997;Raymond et al 1997;Whitaker 2003). Here we report the results of a literature survey that reveals a taxonomically broad association between one life history trait (spawned planktonic sperm versus copulation) and F IS variation.…”

Spatial and temporal population genetics at deep-sea hydrothermal vents along the East Pacific Rise and Galapagos Rift

“…Elevated F IS values were unlikely the result of initial Wahlund effects that may be created by rapid colonization from several divergent source populations, as those effects would be eliminated at individual loci after one generation of random mating . It is possible that differential selection for homozygotes in resident or colonist cohorts could be the cause of heterozygote deficiencies (Zouros & Foltz 1984, Raymond et al 1997. Though not all elevated F IS values were statistically significant, four of the five subpopulations with heterozygote deficiencies were resident cohorts, potentially suggesting that homozygous residents confer elevated fitness over more heterozygous colonists.…”