Synaptonemal complex analysis of interracial hybrids between the Moscow and Neroosa chromosomal races of the common shrew Sorex araneus showing regular formation of a complex meiotic configuration (ring-of-four).

O Kolomiets,Svetlana Pavlova,Maret Acaeva,Sergey Matveevsky

doi:10.3897/compcytogen.v6i3.3701

Abstract

Immunocytochemical and electron microscopic analysis of synaptonemal complexes (SCs) was carried out for the first time in homozygotes and complex Robertsonian heterozygotes (hybrids) of the common shrew, Sorex araneus Linnaeus, 1758, from a newly discovered hybrid zone between the Moscow and the Neroosa chromosomal races. These races differ in four monobrachial homologous metacentrics, and closed SC tetravalent is expected to be formed in meiosis of a hybrid. Indeed, such a multivalent was found at meiotic prophase I in hybrids. Interactions between multivalent and both autosomes and/or the sex chromosomes were observed. For the first time we have used immunocytochemical techniques to analyse asynapsis in Sorex araneus and show that the multivalent pairs in an orderly fashion with complete synapsis. Despite some signs of spermatocytes arrested in the meiotic prophase I, hybrids had large number of active sperm. Thus, Moscow – Neroosa hybrid males that form a ring-of-four meiotic configuration are most likely not sterile. Our results support previous demonstrations that monobrachial homology of metacentrics of the common shrew does not lead to complete reproductive isolation between parapatric chromosomal races of the species.

Highlights

The concept of chromosomal speciation implies occurrence of reproductive isolation as a result of chromosomal rearrangements (Vorontsov 1960, White 1978, 1982, King 1993)
The most common type of chromosome rearrangements in mammalian evolution is represented by the Robertsonian translocations – fusion of two acrocentric chromosomes into a single submeta – or metacentric chromosome
This paper presents a comparative synaptonemal complex (SC) analysis of prophase I of meiosis using electron microscopy and immunofluorescence in homozygotes and complex Robertsonian heterozygotes from this hybrid zone

Summary

Introduction

The concept of chromosomal speciation implies occurrence of reproductive isolation as a result of chromosomal rearrangements (Vorontsov 1960, White 1978, 1982, King 1993). Hybrids between parapatric chromosomal races of the common shrew are often expected to be complex Robertsonian heterozygotes with monobrachial homology, which form chain (C) or ring (R) configurations of three or more elements at prophase I of meiosis. Such complex meiotic configurations are considered to be more susceptible to irregularity. Karyotypes of the races differ in four metacentrics with monobrachial homology so that the complex heterozygotes should form a ring-of-four (RIV) configuration at meiosis I. A combination of both methods together for SC analysis is used for the first time in Sorex araneus

Material and methods

Results

Discussion