Reproductive isolation due to the genetic incompatibilities betweenThrichomys pachyurusand two subspecies ofThrichomys apereoides(Rodentia, Echimyidae)

Abstract

We tested intrinsic reproductive isolation between 3 taxa of the South American caviomorph rodent Thrichomys (Rodentia, Echimyidae): T. pachyurus, T. apereoides subsp. apereoides and T. apereoides subsp. laurentius. They were mated in captivity and produced viable progeny. Some F1 hybrid females were fertile, whereas all F1 males were sterile. Histological examination revealed meiotic arrest at the primary spermatocyte stage. No sperm was detected in testes or epididymes. Electron microscopic analysis of surface spread synaptonemal complexes revealed a complete failure of chromosome pairing in F1 hybrids of T. pachyurus with T. apereoides subsp. laurentius and T. apereoides subsp. apereoides. In the male hybrids between T. apereoides subsp. apereoides and T. apereoides subsp. laurentius, meiosis did not proceed beyond diplotene, although all of the chromosomes, including heteromorphic ones, paired in an orderly fashion. Backcross males with homomorphic karyotypes showed segregation in meiosis progression. This indicates that male hybrid sterility is due to genetic, but not chromosomal, incompatibility of the parental taxa.

Mechanistic basis of infertility of mouse intersubspecific hybrids

“…In sterile F1 hybrids of Mus spretus and Mus m. domesticus, Eicher and coworkers (58) observed autosomal univalency in 70% of pachytene nuclei. Crosses of three taxa of caviomorph rodents (Trichomys) resulted in male sterility in all three F1 hybrid combinations, two of them showing extensive failure of chromosome pairing at pachytene stage (59). Massive asynapsis also was observed in sterile males of a hybrid stock arising from two taxa of the house musk shrew (Suncus murinus).…”

The pachytene checkpoint and its relationship to evolutionary patterns of polyploidization and hybrid sterility

“…Hybrid sterility in mammals has been well-studied in rodents (Forejt, 1996;Borodin et al, 1998Borodin et al, , 2006, where it shows a clear pattern of pachytene checkpoint effects. Female hybrids are mostly fertile, whereas male hybrids are sterile with meiotic arrest around pachytene (Forejt and Ivanyi, 1974;Yoshiki et al, 1993).…”

“…laurentius, but no spermatocytes beyond diplotene were detected, suggesting that the pachytene checkpoint is activated. This meiotic disruption phenotype segregates during backcrossing in males with homomorphic karyotypes, again suggesting a genic rather than chromosomal basis for sterility (Borodin et al, 2006). Thus far, five hybrid sterility (Hst) loci have been identified in the mouse genome (Forejt, 1996), but the genes have not been identified.…”

Reproductive Isolation in Hybrid Mice Due to Spermatogenesis Defects at Three Meiotic Stages

“…These animals include Drosophila (Joly et al 1997), stickleback fish Pungitius (Takahashi et al 2005), caviomorph rodent Thrichomys (Borodin et al 2006), house musk shrew Suncus (Borodin et al 1998), wallaby Petrogale (Close et al 1996), and genus Mus (Forejt and Iványi 1974;Matsuda et al 1992;Hale et al 1993;Yoshiki et al 1993;Kaku et al 1995;Gregorová and Forejt 2000;Elliott et al 2001Elliott et al , 2004Good et al 2008). Although reproductive isolation by spermatogenic impairment is a well-known phenomenon, its underlying genetic mechanism and molecular basis have remained elusive.…”