Robertsonian chromosomal rearrangements in the short-tailed shrew, <i>Blarina carolinensi</i><i>s</i>, in western Tennessee

Abstract

We report significant heterozygosity for numerous Robertsonian translocations in the southern short-tailed shrew (Blarina carolinensis) in western Tennessee. Eight Robertsonian rearrangements were documented using G-banding techniques that explain the variability in diploid numbers from 46 throughout most of the range of the species to 34–40 in western Tennessee. These fusions resulted in the loss of telomere sequences and were not associated with nucleolar organizer regions. When heterozygocity is considered, the lowest diploid number possibly present would be 30. Four localities with distances of over 180 km apart were sampled, and 80–90% of the collected animals were heterozygous for at least one rearrangement. No putative parental type was found in western Tennessee. Heterozygosity for the same rearrangements was found in these different localities, and no monobrachial fusions were noted. Thus, this is a very wide hybrid zone with rare or absent parental types in the areas sampled or is an evolutionary stage preceding establishment of Robertsonian races. Selective forces, if any, were minimal, as evidenced by the wide area of polymorphism, significant heterozygosity, and the fact that the Robertsonian translocations were in Hardy-Weinberg equilibrium. The origin of such extensive polymorphism in western Tennessee is discussed, especially in light of putative effects of the New Madrid seismic activity. Similarities and differences are noted between the Blαrinα model and the well-documented variation in the European common shrew (Sorex αrαneus) and Mus musculus groups.

Mapping the distribution of the telomeric sequence (T₂AG₃)_n in rock wallabies, <i>Petrogale</i> (Marsupialia: Macropodidae), by fluorescence in situ hybridization

“…This study, and that of Metcalfe et al (1997), has confirmed that telomeric sequences are consistently retained during centric fusion events in taxa of the lateralis/penicillata group, in contrast to similar fusions in mice (Garagna et al, 1995;Nanda et al, 1995) and shrews (Qumsiyeh et al, 1997). It therefore appears that different fusion mechanisms consistently operate within different groups of organisms.…”

Robertsonian metacentrics of the house musk shrew (Suncus murinus, Insectivora, Soricidae) lose the telomeric sequences in the centromeric area.

“…They were also found to be lost at the centromere regions of Rb metacentrics in some polymorphic species, in which rearrangements have occurred recently, for example, in the house mouse (Garagna et al, 1995;Nanda et al, 1995) and short-tailed shrew (Qumsiyeh et al, 1997). Also Meyne et al (1995) did not detected interstitial sites of either vertebrate or putative insect telomeric sequences in the chromosomes of several species of ants from the genus Myrmecia.…”

“…So far only a few species polymorphic for Rb fusions have been studied: Okapia johnstoni (Vermeesch et al, 1996), Akodon cursor (Fagundes et al, 1997); Blarina carolinensis (Qumsiyeh et al, 1997) and Mus musculus (Garagna et al, 1995;Nanda et al, 1995).…”

A potential model for early stages of chromosomal evolution via concentric Robertsonian fans: a large area of polymorphism in southern short-tailed shrews <i>(Blarina carolinensis)</i>

“…A reduction in fertility is also seen in populations of wild mice carrying ROBs in Europe and North Africa (Capanna, 1982;Hauffe and Searle, 1993;Said et al, 1993). By contrast, shrews (Sorex araneus complex in Europe and Blarina carolinensis in Western Tennessee) show little reduction in fertility with simple ROBs (Garagna et al, 1989;Qumsiyeh et al, 1997;Searle, 1986b;Searle, 1990). While variations in Sorex have evolved to fixation of chromosomal races, data on Blarina suggest an earlier stage of this evolutionary process (Qumsiyeh et al, 1997, and data presented here).…”