Abstract
Inferences of ancient sex-biased migration patterns using sex-linked genetic markers are usually difficult because of a stochastic process of allele fixation. Nevertheless, incongruent phylogenetic trees between different sex-linked markers and between sex-linked and autosomal markers are frequently interpreted as a signature of sex-biased migration without further statistical evaluation. I investigated the types of incongruent phylogenetic trees from which past sex-biased migration events can be statistically supported under the coalescent model. In the case of mammals, detecting a sex-biased migration pattern is not guaranteed by comparing the phylogenetic pattern of mitochondrial and Y-chromosomal loci. Likewise, evidence of introgression at a mitochondrial locus, but not at autosomal loci, does not support the hypothesis of an ancient female-biased migration pattern with statistical significance. In contrast, evidence of introgression at ≥5 unlinked autosomal loci, but not at a Y-chromosomal locus, would reject the null hypothesis of a sexually equal migration rate with statistical significance. A similar argument can be made to infer a male-biased migration pattern. Furthermore, the investigation of many recombining sex-biased markers such as X-chromosomal loci in mammals has the potential to efficiently detect ancient sex-biased demographic patterns.
Highlights
In sexual organisms, sex-biased migration, in which individuals of one sex are more frequently dispersed than those of the other sex, is widely observed in nature in a wide range of taxa, such as insects, birds, mammals, and plants [1,2]
Gene flow occurred during time T, where time is a unit of 2N generations and migration rate between populations (m) was assumed to be symmetric
It was assumed that the correct genealogies were always inferred from molecular data
Summary
Sex-biased migration, in which individuals of one sex are more frequently dispersed than those of the other sex, is widely observed in nature in a wide range of taxa, such as insects, birds, mammals, and plants [1,2]. Explanation by sex-biased migration is often preferred, partly because socio-sexual structures of species are important subjects in ecology and evolution research, and there are several a priori assumptions about sex-dependent dispersal rates from observations in fields. Roos et al found two types of phylogenetic inconsistencies between sex-linked and autosomal markers in colobine monkeys after excluding confounding factors such as tree inference ambiguity and incomplete lineage sorting: introgression at a mitochondrial locus but not at nuclear loci in African colobines, and introgression at nuclear loci but not at a mitochondrial locus in Asian colobines, which may support female- and male-biased migration in African and Asian colobines, respectively [14]
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