Male meiosis and gametogenesis in wild house mice (<i>Mus musculus domesticu</i><i>s</i>) from a chromosomal hybrid zone; a comparison between “simple” Robertsonian heterozygotes and homozygotes

Abstract

Wild male house mice Mus musculus domesticus were collected from the hybrid zone between the John o’Groats race (2n = 32) and the standard race (2n = 40) in northern Scotland. Meiosis in both homozygotes (2n = 32, 36, and 40) and single Robertsonian heterozygotes (2n = 33, 35, and 37) was found to be orderly. At prophase/metaphase I in heterozygotes, a trivalent was formed from the metacentric and two homologous acrocentrics. At pachytene, this trivalent usually had a single side arm at the position of the centromeres, as a result of nonhomologous pairing of the acrocentrics. This side arm persisted into diplotene. Generally only a single chiasma was formed between each acrocentric and the metacentric. Ana-phase I nondisjunction frequencies were estimated as 1.5% for the homozygotes and 2.7% for the heterozygotes. The extent of germ cell death between the pachytene and round spermatid stages was 18 % greater in heterozygotes than in homozygotes. Our results concur with previous studies which indicate that single Robertsonian heterozygotes in wild house mice have near-normal fertility.

Reduced recombination patterns in Robertsonian hybrids between chromosomal races of the house mouse: chiasma analyses

“…In house mice, the intensity of the decrease in recombination rates in Rb fusions varied slightly among geographic regions and chromosomal races, irrespective of the method of analysis (chiasma or MLH1; range: 22.16oSto23.0; 20.1oRbo22.28; the present study; Wallace et al, 1992;Bidau et al, 2001;Castiglia and Capanna, 2002;Dumas and Britton-Davidian, 2002;Merico et al, 2013). Exceptionally high levels were observed by Merico et al (2003) in two North Italian races (Rb ¼ 24.58; St ¼ 25.13) that exceeded estimates described so far for the subspecies (Dumont and Payseur, 2011).…”

“…To our knowledge, few analyses on chiasma or MLH1 patterns have compared trivalent-carrying heterozygous wild mice with homozygous standard or Rb individuals, and those that have, involve either few cells (that is, 12 cells; Wallace et al, 1992), few Rb fusions (that is, 4; Bidau et al, 2001) or mostly polymorphic hybrid karyotypes (24o2no39; Castiglia and Capanna, 2002;Capilla et al, 2014). The exception is the study by Merico et al (2003) involving other North Italian races (2n ¼ 24, St mice) and their laboratory-bred F1 hybrids (2n ¼ 32 with eight trivalents).…”

“…Analyses of recombination rates in wild Rb heterozygotes have also been assessed but involve, in most cases, polymorphic individuals, that is, carrying variable numbers of Rb bivalents and trivalents, making it difficult to disentangle the effect of each meiotic type of configuration (Wallace et al, 1992;Bidau et al, 2001;Castiglia and Capanna, 2002;Capilla et al, 2014). In contrast, extensive analyses of recombination patterns in single-Rb heterozygotes have been performed by genetic assays in crosses between different laboratory strains (Davisson and Akeson, 1993).…”

Fertility estimates in the Tunisian all-acrocentric and Robertsonian populations of the house mouse and their chromosomal hybrids

“…Results for wild hybrids indicate that fertility is slightly if at all affected in the case of heterozygotes for one to three fusions (see Viroux & Bauchau, 1992;Wallace et at., 1992). In this study, we attempt to measure hybrid sterility in the progeny of Tunisian Rb mice and neighbouring all-acrocentric wild mice which differ by nine pairs of Rb fusions.…”

“…Among the factors favouring chromosomal change, meiotic drive, genetic drift, inbreeding and the selective advantage of the chromosomally variant individuals or populations have been considered as the most relevant. Although the first three factors have been investigated (see Britton-Davidian et a!., 1989;Viroux & Bauchau, 1992;Wallace et at,, 1992) and do not appear to operate in the Rb differentiation of house mice, the search for a selective advantage has received little attention. In this work, we compare one component of the reproductive fitness by measuring progeny size in wild Rb and all-acrocentric mice.…”