Microsatellite Documentation of Male-Mediated Outcrossing between Inbred Laboratory Strains of the Self-Fertilizing Mangrove Killifish (Kryptolebias Marmoratus)

Abstract

Primers for 36 microsatellite loci were developed and employed to characterize genetic stocks and detect possible outcrossing between highly inbred laboratory strains of the self-fertilizing mangrove killifish, Kryptolebias marmoratus. From attempted crosses involving hermaphrodites from particular geographic strains and gonochoristic males from others, 2 among a total of 32 surveyed progenies (6.2%) displayed multilocus heterozygosity clearly indicative of interstrain gametic syngamy. One of these outcross hybrids was allowed to resume self-fertilization, and microsatellite assays of progeny showed that heterozygosity decreased by approximately 50% after one generation, as expected. Although populations of K. marmoratus consist mostly of synchronous hermaphrodites with efficient mechanisms of internal self-fertilization, these laboratory findings experimentally confirm that conspecific males can mediate occasional outcross events and that this process can release extensive genic heterozygosity.

Long-term retention of self-fertilization in a fish clade

“…18), but our histological appraisal identified putative females as hermaphrodites. The PCR primers for the 33 microsatellite loci that we used were developed for K. marmoratus (9). Our success with these primers varied: 31, 28, and 14 loci from K. marmoratus cross-amplified successfully with K. ocellatus, K. caudomarginatus, and K. brasiliensis, respectively.…”

“…Nevertheless, we present a vertebrate lineage in which simultaneous hermaphroditism has arisen and persisted for at least hundreds of thousands of years. However, self-fertilization is merely a component of a mixed-mating system in Kryptolebias (9)(10)(11)(12), where various populations self-fertilize and outcross at different rates. Although Kryptolebias fishes provide the only known examples of mixed-mating systems in vertebrate animals, such systems are relatively common in many plants and invertebrate taxa (4).…”

“…The PCR amplifications and genotyping of 33 microsatellite loci were carried out as described in ref. 9, except that in the current study we fractioned alleles on a capillary instrument (GA3100) and sized them by using software GeneMapper (both from Applied Biosystems). For the mtDNA analyses, we used samples from our previous studies (10 -12) plus newly collected specimens.…”

“…Simultaneous hermaphroditism and self-fertilization in K. marmoratus were discovered in the 1960s (3). Later, researchers used molecular markers to confirm self-fertilization in this species (8) and to derive the first quantitative estimates of selfing and outcrossing rates (9)(10)(11)(12). The latter vary geographically; outcrossing rates are high (Ϸ50%) in some Belize islands where males are common but low (Ͻ3%) in Florida and the Bahamas where males are rare (11)(12)(13)(14).…”

Evolutionary perspectives on clonal reproduction in vertebrate animals

“…molecular markers (75)(76)(77)(78)(79)(80)(81). Such studies also have disclosed the following further information about K. marmoratus (Kmar): (i) in addition to the self-fertilizing hermaphroditic individuals, pure males exist in some Kmar populations (82), thus making this species androdioecious (83), an extremely rare condition in the organic world (84,85); and (ii) these males sometimes mediate outcross events (86,87), such that the species actually displays a mixed-mating system of predominant selfing with occasional outcrossing (88).…”