A Male-Biased Natal Sex-Ratio in Inbred Collared Lemmings, Dicrostonyx Groenlandicus

Abstract

A captive colony of collared lemmings (Dicrostonyx groenlandicus) from northern Alaska produced a male-biased sex ratio of 67% males for about three generations. These lemmings have a pair of autosomes fused to the sex chromosomes. Thus, males have two copies of some (formerly autosomal) sex-linked genes: One set is X-linked; the other can be described as Y-linked. Given such a karyotype, deleterious recessive alleles on the autosomal portion of the X chromosome are more resistant to selection than truly autosomal loci because they can be eliminated by homozygosity only in females. The male-bias could have resulted from one or more lethals carried on the formerly autosomal arm of the X chromosome. As inbreeding coefficients approached 0.3, the lethal was apparently homozygous in half of the homogametic (female) zygotes. This phenomenon may explain the excess of males and XY females attributed to meiotic drive in Dicrostonyx torquatus from Siberia. If under the natural mating system, inbreeding depression limits fitness, then fusion of autosomal chromatin to the sex chromosomes could be an adaptation to reduce inbreeding depression in heterogametic individuals.

Sex ratios observed in 80 species of parrots

“…By their nature, the effective population sizes of captive‐bred stocks are already reduced, and will be limited by the rarer sex. Small population size is linked to inbreeding depression, and sex ratio bias can result from this (Jarrell, 1995; Werren & Hatcher, 2000). A further factor that is known to influence sex ratio bias of parrots is laying date within the breeding season (Krebs et al , 2002).…”

“…Potential bias in sex ratio is of concern in the management of vulnerable and endangered species, and the majority of parrots fall into this category (Snyder et al , 1999). Inbreeding and small effective population size have both been implicated in sex ratio bias (Senner, 1980; Jarrell, 1995; Werren & Hatcher, 2000), and these are likely to be important factors in parrot biology. Habitat loss or fragmentation, and the removal of birds from the wild for trade, are both having a major impact on this family of birds, reducing overall and effective population sizes (Snyder et al , 1999).…”

Inbreeding and Sex Ratio in two Captive Colonies of Dicrostonyx Torquatus Pall., 1779: A Reply to G. H. Jarrell

“…But in D . groenlandicus they are euchromatic (JARRELL 1995), and most likely synapse at meiosis, though it cannot be ruled out that a small segment where the lethals are located is excluded from crossing over. In general, cytogenetic evidence is not very favourable to Jarrell's interpretation, although not conclusive.…”

Evaluating the Evidence for Transmission Distortion in Human Pedigrees

“…Moreover, because systems of distortion loci and their responders coevolve rapidly and can generate Dobzhansky–Muller incompatibilities, they may play an important role in the evolution of reproductive isolation ( Frank 1991 ; Hurst and Pomiankowski 1991 ). On the X chromosome, segregation distortion loci can influence sex ratios and even lead to novel sex-determining mechanisms ( Jarrell 1995 ; Gileva 1998 ; Hurst and Werren 2001 ). Thus, understanding the prevalence of TD is important for many aspects of evolutionary genetics.…”