TY  - JOUR
A1  - Hasselmann, Martin
A1  - Vekemans, Xavier
A1  - Pflugfelder, Jochen
A1  - Koeniger, Nikolaus
A1  - Koeniger, Gudrun
A1  - Tingek, Salim
A1  - Beye, Martin
T1  - Evidence for convergent nucleotide evolution and high allelic turnover rates at the complementary sex determiner (csd) gene of western and Asian honey bees
T2  - Molecular biology and evolution
N2  - Our understanding of the impact of recombination, mutation, genetic drift and selection on the evolution of a single gene is still limited. Here we investigate the impact of all of these evolutionary forces at the complementary sex determiner (csd) gene which evolves under a balancing mode of selection. Females are heterozygous at the csd gene and males are hemizygous; diploid males are lethal and occur when csd is homozygous. Rare alleles thus have a selective advantage, are seldom lost by the effect of genetic drift and are maintained over extended periods of time when compared to neutral polymorphisms. Here, we report on the analysis of 17, 19 and 15 csd alleles of Apis cerana, Apis dorsata and Apis mellifera honey bees respectively. We observed great heterogeneity of synonymous (pi S) and nonsynonymous (pi N) polymorphisms across the gene, with a consistent peak in exon 6 and 7. We propose that exons 6 and 7 encode the potential specifying domain (csd-PSD) which has accumulated elevated nucleotide polymorphisms over time by balancing selection. We observed no direct evidence that balancing selection favors the accumulation of nonsynonymous changes at csd-PSD (pi N/pi S ratios are all < 1, ranging from 0.6 to 0.95). We observed an excess of shared nonsynonymous changes, which suggests that strong evolutionary constraints are operating at csd-PSD resulting in the independent accumulation of the same nonsynonymous changes in different alleles across species (convergent evolution). Analysis of a csd-PSD genealogy revealed relatively short average coalescence times (~6 million years), low average synonymous nucleotide diversity (pi S < 0.09) and a lack of trans-specific alleles which substantially contrasts with previously analyzed loci under strong balancing selection. We excluded the possibility of a burst of diversification after population bottlenecking and intragenic recombination as explanatory factors, leaving high turn-over rates as the explanation for this observation. By comparing observed allele richness and average coalescence times with a simplified model of csd-coalescence, we found that small long term population sizes (i.e. Ne <104), but not high mutation rates, can explain short maintenance times, implicating a strong impact of genetic drift on the molecular evolution of highly social honey bees.
KW  - sex determination
KW  - balancing selection
KW  - genetic drift
KW  - social insects
KW  - convergent adaptive evolution
KW  - molecular evolution
Y1  - 2009
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/6502
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30-65999
SN  - 1537-1719
SN  - 0737-4038
N1  - This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
VL  - 25
IS  - 4
SP  - 696
EP  - 708
PB  - Oxford Univ. Press
CY  - Oxford
ER  -