Is increased chromosomal diversity in house mice from Lombardy (Italy) congruent with genic divergence?

Abstract

Recent studies in metacentric (MC) populations of the house mouse, Mus musculus domesticus, singled out underdominance more so than recombination suppression as the foremost barrier to gene flow. Here, MC populations from Lombardy (Italy) were sampled to identify the nature and strength of the barriers to gene flow. The chromosomal analysis recovered the three major MC populations (abbreviated to IBIN, IGAL, both with 2n = 24 and ICRE, 2n = 22), but revealed the existence of a new one (IONE, 2n = 24) which likely derived from IGAL through a single WART (Whole-Arm Reciprocal Translocation). This, once again, highlights the paramount role of WARTs in the chromosomal diversification of this subspecies. Contacts between MC and standard populations coincided with rivers confirming these hybrid zones as tension zones. Divergence between populations was estimated using available allozyme data. Although the overall low genetic structure globally agreed with the chromosome structure, a large variation in divergence levels was retrieved that only partially matched the underdominance degree. This disparity from expectations highlighted the additional contribution of physical barriers and geographic isolation to the differential rate of evolution of the MC populations of the house mouse.

Tracking Chromosomal Origins in the Northern Italy System of Metacentric Races of the House Mouse

“…Of these systems, the NIS was the earliest discovered and, consequently, has been one of the best studied [e.g., Giménez et al, 2017]. A range of parsimony tree-building approaches has been used to infer the relationships between metacentric races based on their karyotype [Hauffe and Piálek, 1997;Britton-Davidian et al, 2005;Piálek et al, 2005;White et al, 2010;Castiglia et al, 2015;Montgelard et al, 2016], but these phylogenetic hypotheses need to be tested, and centromeric molecular markers from variable metacentrics have proven efficient in such studies [Giménez et al, 2016]. Here, we have tested predictions regarding the evolutionary relationships among several metacentric races in the NIS system by examining centromeric loci of 4 chromosomes -1, 3, 4, and 6 -that were crucial for the phylogenetic reconstructions of these 5 races (Fig.…”

“…Attempts to infer the evolutionary relationships among chromosomal races within metacentric systems of house mice have applied phylogenetic reconstructions based on karyotypes, including evolutionary phylogenetic networks [White et al, 2010]. Consideration of Rb fusions, WARTs, and the role of hybridisation in the generation of new races ("zonal raciation") in such reconstructions can yield parsimonious phylogenies that require significantly fewer mutational steps than when these processes are excluded [Britton-Davidian et al, 2005;Piálek et al, 2005;White et al, 2010;Castiglia et al, 2015;Montgelard et al, 2016]. Molecular markers provide the opportunity to test the validity of these inferred karyotypic phylogenies, particularly those loci closely linked to the centromeres of variable metacentrics.…”

“…Most recently, Franchini et al [2020] used centromeric loci from whole-genome sequencing to show further instances of metacentrics with the same arm combination being independently derived, even though they are in the same metacentric system in the Aeolian archipelago off southern Italy. DOI: 10.1159/000527106 Some of the best studied metacentric races in the house mouse are in the Northern Italy System (NIS) [Hauffe and Piálek, 1997;Piálek et al, 2001Piálek et al, , 2005Montgelard et al, 2016;Giménez et al, 2017] (Fig. 1).…”