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

Abstract

The reproductive features of wild all-acrocentric and 2n 22Robertsonian (Rb) house mice (M. m. domesticus) from Tunisia were studied. The aim was to examine the possibility of a reproductive selective advantage associated with chromosomal change as well as to measure the effect of heterozygosity for a large number of Rb fusions on the fertility of hybrids. Results showed that litter sizes were significantly smaller in Rb than in all-acrocentric mice. This difference, which may represent a favourable demographic strategy related to the habitat segregation observed in the Tunisian mice, needs to be studied further. The F1 hybrids between the two chromosomal races showed a significantly reduced reproductive success and litter size (respectively, 53 per cent and 60 per cent less than either parental race). Analysis of the testicular histology of F1 and backcross males showed in some cases a breakdown of spermatogenesis. The degree of this disturbance was not related to the level of chromosomal heterozygosity suggesting that genetic incompatibilities between the two genomes might be involved. The strong reduction in fertility measured in these hybrids represents a reproductive isolating mechanism effectively reducing gene flow between the all-acrocentric and 22Rb mice populations of Tunisia.

Nonrandom segregation in multiple Robertsonian heterozygotes in the house mouse (Mus musculus domesticus): Analysis of metaphases of spermatocytes II of mice from a hybrid zone between a Robertsonian population and a population with the standard karyotype

“…Segregation analysis on multiple heterozygous house mice for centric fusions are not frequent; however, data based on the karyotypical analysis of embryos derived from backcrossing of triple heterozygous males (White et al, 1978), although they are compatible with random segregation (as stated by the authors), fit better with a probability value of preferential segregation of 0.66 (95% confidence limits: 0.5-0.75); also the results of the karyotypical analysis of backcross progeny of heterozygotes for nine centric fusions (Said et al, 1993) are indicative, following our statistical analysis, of a preferential segregation (0.66 with 95% confidence limits: 0.56-0.71).…”

Spermatogenesis in house mouse in a Robertsonian polymorphism zone

“…Therefore, these results indicate lower spermatogenic activity in Rb mice (heterozygotes and homozygotes) than in 40ST ones. Previous studies also reported a reduction in the tubular diameter in simple Rb heterozygote mice carrying nine fusions and in backcrosses of these hybrids with the parental races (Said et al 1993, Chatti et al 2005.…”

Origin of the chromosomal radiation of Madeiran house mice: a microsatellite analysis of metacentric chromosomes

“…It has been demonstrated that house mice heterozygous for metacentrics have impaired reproductive fitness (for example, Wallace et al, 1992Wallace et al, , 2002Saïd et al, 1993;Hauffe and Searle, 1998), and that there are recombination effects in the vicinity of the centromere in such heterozygotes (for example, Davisson and Akeson, 1993;Bidau et al, 2001;Merico et al, 2003). Thus, one or both of these processes could affect gene flow in the centromeric region of the metacentric chromosomes investigated by us.…”