Chromosomal Polymorphism and Speciation: The Case of the Genus Mazama (Cetartiodactyla; Cervidae).

David Javier Galindo,José Maurício Barbanti Duarte,Miluse Vozdova,Agda Maria Bernegossi,Jiri Rubes,Halina Cernohorska,Dita Kadlcikova,Gabriela Siqueira Martins,Svatava Kubickova

doi:10.3390/genes12020165

Abstract

Chromosomal polymorphism plays a major role in speciation processes in mammals with high rates of karyotypic evolution, as observed in the family Cervidae. One remarkable example is the genus Mazama that comprises wide inter- and intra-specific chromosomal variability. To evaluate the impact of chromosomal polymorphisms as reproductive barriers within the genus Mazama, inter-specific hybrids between Mazama gouazoubira and Mazama nemorivaga (MGO × MNE) and intra-specific hybrids between cytotypes of Mazama americana (MAM) differing by a tandem (TF) or centric fusion (Robertsonian translocations—RT) were evaluated. MGO × MNE hybrid fertility was evaluated by the seminal quality and testicular histology. MAM hybrids estimation of the meiotic segregation products was performed by sperm-FISH analysis. MGO × MNE hybrids analyses showed different degrees of fertility reduction, from severe subfertility to complete sterility. Regarding MAM, RT, and TF carriers showed a mean value for alternate segregation rate of 97.74%, and 67.23%, and adjacent segregation rate of 1.80%, and 29.07%, respectively. Our results suggested an efficient post-zygotic barrier represented by severe fertility reduction for MGO × MNE and MAM with heterozygous TF. Nevertheless, RT did not show a severe effect on the reproductive fitness in MAM. Our data support the validity of MGO and MNE as different species and reveals cryptic species within MAM.

Highlights

Chromosomal polymorphisms have played a meaningful role in speciation [1], by leading to the formation of efficient barriers to gene flow and subsequent differentiation process [2,3]
The family Cervidae stands out as one of the families with the highest presence of chromosomal polymorphisms, which is demonstrated in genera such as Muntiacus, whose diploid number ranges from 2n = 6/7 (Muntiacus muntjak) to 2n = 46 (Muntiacus reevesi) [4,5], and Mazama, whose diploid number ranges from 2n = 32– 34 + Bs (Mazama bororo—MBO) to 2n = 70 + Bs (MGO) [6,7,8]
Using FISH with bovine WCP probes, we identified homologies between bovine chromosomes and the translocated chromosomes in the analyzed brocket deer hybrids

Summary

Introduction

Chromosomal polymorphisms have played a meaningful role in speciation [1], by leading to the formation of efficient barriers to gene flow and subsequent differentiation process [2,3]. Both of them standing in independent clades and distant from other Mazama, sharing the gray clade with other genera such as Blastocerus, Ozotoceros, and Hippocamelus [16,17]. In the meantime, this group is characterized by low levels of inter-specific chromosome difference and karyotypes with a high diploid number [11,16,17]. Due to their parapatric distribution [18] and morphological similarity, the differentiation between these two species has been the subject of extensive debate over the years, being demonstrated only recently through morphological [19,20], cytogenetic [11,20,21], and phylogenetic [20,22] analyzes

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