A hybrid zone of the genus Ctenomys: a case study in southern Brazil

Abstract

We describe variation at microsatellite loci and the chromosomal polymorphisms of a hybrid population, and hybridizing populations of Ctenomys minutus (the minor tuco-tuco) from the coastal plain of Rio Grande do Sul, southern Brazil. Cytogenetic analysis and a survey of six microsatellite loci included 101 specimens of C. minutus from the parental populations (2n/AN = 42/74 and 48a/76) and their contact zone. Cytogenetic analysis recorded 26 different karyotypes exhibited by 50 individuals from the hybrid population. Of the 26 karyotypes, only 14% presented a parental-like configuration, and none had the combinations of 2n and AN expected for an F1 hybrid. The remaining karyotypes were alternative hybrid forms, with 2n varying from 42 to 46 and AN from 68 to 80. These results suggest chromosomal rearrangements are only of minor significance in the establishment of reproductive barriers for this species.

The role of chromosomal rearrangements and geographical barriers in the divergence of lineages in a South American subterranean rodent (Rodentia: Ctenomyidae: Ctenomys minutus)

“…The cytogenetic data available for C. minutus reveal a total of 45 distinct karyotypes (Freitas, 1997;Freitas, 2002, 2003;Freygang et al, 2004;Castilho et al, 2012;this study), and most of this polymorphism was retrieved in the intraspecific karyotypic hybrid zones.…”

“…Most of the specimens were collected and karyotyped previously in studies by Freitas (1997), Freitas (2002, 2003), Freygang et al (2004) and Castilho et al (2012) (Table 1). The tissue samples were preserved in 95% ethanol and stored at À20 1C in the collection of the Laborató rio de Citogenética e Evoluc¸ão of the Departamento de Genética of the Universidade Federal do Rio Grande do Sul, Brazil.…”

“…To search for positive correlations between genetic and geographical distances, a simple Mantel test was implemented, Freitas (1997), Freitas (2002, 2003), Freygang et al (2004) and Castilho et al (2012). c Statistical significance (Po0.05).…”

“…BAR, Barco Beach; BJ1, Bujuru 1; BJ2, Bujuru 2; EBL, East Barros Lake; FOR, Fortaleza Lake; FSM, Farol de Santa Marta; GAI, Gaivota Beach; GUA, Guarita Beach; ILH, Ilhas; JG, Jaguaruna; MC, Morro dos Conventos; MOS, Mostardas; PAL, Palmares do Sul; PAS, Passinhos; PIT, Pitangueira; PST, Passo de Torres; OSO,Osório;35,road km 35;53,road km 53;64,road km 64;96,road (iv) 42  46b ¼ 43, 44, 45; (v) 46b  48b ¼ 47b; and (vi) 48b  50 b ¼ 49b. The intraspecific hybrid zones were determined based on diploid numbers and chromosomal rearrangements observed through G-band patterns compared with the adjacent parental karyotypes (Freitas, 1997;Freitas, 2002, 2003;Freygang et al, 2004;Castilho et al, 2012;this study). The distribution of these karyotypes shows 2n ¼ 50 at both ends of the geographical range, whereas toward the middle of the distribution, it is progressively reduced to 2n ¼ 42 through Robertsonian rearrangements, tandem fusions/fissions and a pericentric inversion, which originated the distinct karyotypic systems 'a/c' and 'b'; see Figures 1 and 2 (Freitas, 1997;Freygang et al, 2004).…”

Chromosomes and speciation in tuco-tuco (Ctenomys, Hystricognathi, Rodentia)

“…Диплоидное число варьирует в диапазоне от 42 до 50, а число плеч аутосом -от 68 до 80. Внутри вида выделя-ется восемь парапатрически распределенных хромосом-ных рас, которые образуют шесть гибридных зон, в них и наблюдается самое высокое разнообразие кариотипов (Freitas, 1997;Gava, Freitas, 2002Freygang et al, 2004;Castilho et al, 2012). При этом 2n = 50 находится на северном и южном концах ареала, постепенно уменьшаясь к середине распределения до 2n = 42 за счет робертсонов-ских и тандемных слияний / разделений и одной перицен-трической инверсии.…”