The gynogenetic reproduction of diploid and triploid hybrid spined loaches (Cobitis: Teleostei), and their ability to establish successful clonal lineages—on the evolution of polyploidy in asexual vertebrates

Abstract

Polyploidisation is assumed to have played a significant role in the evolution of hybrid asexual lineages. The virtual absence of natural asexual systems in which more than a single ploidy level successfully establishes successful independent clonal lineages is generally explained by the strong effects of polyploidisation on fitness. Experimental crosses were made between diploid and triploid asexual Cobitis elongatoides x C. taenia hybrids (female) and both parental spined loach species (male). Genotyping of the progeny using allozymes and multilocus DNA fingerprinting, along with flow cytometric measurement of ploidy level, demonstrated the occurrence of gynogenetic reproduction in both female biotypes. The incorporation of the sperm genome occurred in some progeny, giving rise to a higher ploidy level, but the rate of polyploidisation differed significantly between the diploid and triploid females. These outcomes are consistent with the existence of developmental constraints on tetraploidy, which determine the rarity of tetraploids in natural populations. No cases of ploidy level reduction were observed. Since diploid and triploid hybrid populations occur where the lack of potential progenitor excludes the possibility of de novo origin, it is probable that both diploid and triploid females can establish successful clonal lineages. Spined loaches represent a unique example, among asexual vertebrates, where more than one ploidy level can establish persistent clonal lineages, which are reproductively independent of one another.

Histological evidence that diploid hybrids of Cobitis taenia and C. elongatoides (Teleostei, Cobitidae) develop into fertile females and sterile males

“…Among naturally occurring fish, interspecific or intergeneric hybrids are mostly described in Cyprinidae (Fishelson et al, 1996;Hayden et al, 2010), Acipenseridae (Birstein et al, 2002) and Cobitidae (Janko et al, 2007;Choleva et al, 2012). Sometimes interspecific hybrids appear to be fertile, giving rise to new species.…”

“…Matured Cobitis males exhibit sex dimorphic feature by the presence of a lamina circularis, a bony plate at the base of the pectoral fin ray (Juchno & Boroń, 2006;Juchno et al, 2007). Most of the Cobitis taxa existing in mixed populations are triploid hybrids, resulting in two-step hybridization of C. taenia (2n = 48) with related species such as C. elongatoides (2n = 50) (Vasil'ev et al, 1989;Boroń, 2003;Juchno et al, 2007;Janko et al, 2007Janko et al, , 2012. In the first step, the hybridization of both of these species leads to the formation of diploid hybrids (2n = 49).…”

“…Such hybrid females producing diploid eggs and after fertilization with parental males may produce triploid hybrids, mainly females . These females most often are dominant up to 95% of all Cobitis in mixed populations, whereas diploid hybrids are very rare (Boroń, 2003;Janko et al, 2007).…”

Ploidy manipulation using diploid sperm in the loach,Misgurnus anguillicaudatus: a review

“…Cobitis hybrids (Janko et al, 2003(Janko et al, , 2005(Janko et al, , 2007 and others . These results suggest possible induction of unreduced diploid gametes by artificial hybridization between genetically different populations of the loach.…”

A haploid-diploid-triploid mosaic of the Amazon molly, <i>Poecilia formosa</i>

“…Two alternative pathways most likely lead to mosaic individuals: either some cells or a certain cell lineage gain a chromosome set or individual chromosomes after regular fertilization or some cells lose a chromosome or chromosome set some time during development. For mosaic formation by gaining chromo- Diploid-triploid mosaics, however, are viable and fertile, occur much more frequently in natural populations than haploid-diploid mosaics and seem to be closely associated with gynogenetic reproduction (Bickham et al, 1985;Murayama et al, 1986;Dawley and Goddard, 1988;Lamatsch et al, 2002;Morishima et al, 2004;Janko et al, 2007). Triploid cells in a usually diploid organism can arise from either polyspermy (Morishima et al, 2004) or retention of the polar body (Brems et al, 2003).…”