Chromosome Synapsis and Recombination in Male Hybrids between Two Chromosome Races of the Common Shrew (Sorex araneus L., Soricidae, Eulipotyphla).

Nadezhda M Belonogova,Anna A Torgasheva,Tatyana V Karamysheva,Andrei V Polyakov,Jeremy B Searle,Pavel M Borodin

doi:10.3390/genes8100282

Nadezhda M Belonogova, Anna A Torgasheva + Show 4 more

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https://doi.org/10.3390/genes8100282

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Abstract

Hybrid zones between chromosome races of the common shrew (Sorex araneus) provide exceptional models to study the potential role of chromosome rearrangements in the initial steps of speciation. The Novosibirsk and Tomsk races differ by a series of Robertsonian fusions with monobrachial homology. They form a narrow hybrid zone and generate hybrids with both simple (chain of three chromosomes) and complex (chain of eight or nine) synaptic configurations. Using immunolocalisation of the meiotic proteins, we examined chromosome pairing and recombination in males from the hybrid zone. Homozygotes and simple heterozygotes for Robertsonian fusions showed a low frequency of synaptic aberrations (<10%). The carriers of complex synaptic configurations showed multiple pairing abnormalities, which might lead to reduced fertility. The recombination frequency in the proximal regions of most chromosomes of all karyotypes was much lower than in the other regions. The strong suppression of recombination in the pericentromeric regions and co-segregation of race specific chromosomes involved in the long chains would be expected to lead to linkage disequilibrium between genes located there. Genic differentiation, together with the high frequency of pairing aberrations in male carriers of the long chains, might contribute to maintenance of the narrow hybrid zone.

Highlights

The role of chromosome rearrangements in speciation is a subject of discussion
In order to determine the role of chromosomal heterozygosity in the restriction of gene flow between the races, we examined chromosome pairing and recombination in shrews of various karyotypes trapped in the hybrid zone between the Tomsk and Novosibirsk chromosome races
High rate of of synaptic aberration in male complex heterozygotes for for chromosome rearrangements with monobrachial homology derived from the hybrid zone chromosome rearrangements with monobrachial homology derived from the hybrid zone between the between theand

Summary

Introduction

The traditional underdominance model suggests that intertaxon hybrids heterozygous for chromosome rearrangements should display various irregularities in meiotic chromosome pairing, recombination and segregation, and become completely or partially sterile, due to meiotic arrest or formation of unbalanced gametes [1]. This model faces serious theoretical difficulties, because rearrangements causing sterility have a very low chance to spread in populations [2]. The common shrew, Sorex araneus, is a model species to examine various scenarios of chromosomal speciation. The hybrids carry only trivalents involving metacentric chromosomes paired with twin acrocentrics, while in the other zones, hybrids carrying chains of up to eleven chromosomes are observed [9]

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