The Homozygosity of Clones of the Self-Fertilizing Hermaphroditic Fish Rivulus marmoratus Poey (Cyprinodontidae, Atheriniformes)

Gonadal morphology in the self-fertilizing mangrove killifish, Kryptolebias marmoratus

“…Genetic studies have also confirmed that all reproduction of hermaphrodites in this species is by internal self-fertilization (Harrington and Kallman, 1968). A previous histological study (Soto et al, 1992) revealed that the gonad of K. marmoratus is a bilobed structure with the posterior tips of the lobes fused and a genital duct.…”

Differences in life-history traits in two clonal strains of the self-fertilizing fish, Rivulus marmoratus

“…Since the two strains come from different geographic locations (DAN from Belize and PAN-RS from Panama), the observed difference in sex ratio may be a unique feature of the groups in question. Since all the fish in the laboratory were maintained at 25 ± 1°C, the observed difference in the number of primary males may not be due to the artificial environment of the laboratory, as male induction has previously been reported to occur when embryos are incubated between 18 and 20°C, (Harrington 1967, Harrington & Kallman 1968. Additional field and laboratory studies are necessary to determine the influence of environmental conditions on male occurrence and to clarify its role in a population dominated by hermaphrodites.…”

“…It inhabits mangrove areas, which are exposed to alternate flooding and desiccation; thus, it is necessarily tolerant of a wide range of environmental conditions (Taylor 2000). There are three recognized sexual types: hermaphrodites, which have a marbled brownish color pattern usually including a caudal ocellus, and are capable of internal synchronous self-fertilization, and thus are capable of producing clonal lineages (Kallman & Harrington 1964, Harrington & Kallman 1968; primary males, which have an orange body coloration usually without caudal ocellus and remain male throughout their lives; and secondary males, which arise from hermaphrodites following the loss of female function (Harrington 1975). Based on these biological features, this species has been found suitable for studies on life-history traits, since hermaphrodites are able to produce clones.…”

Allard's argument versus Baker's contention for the adaptive significance of selfing in a hermaphroditic fish

“…The Mangrove Rivulus belongs to a small killifish clade that includes several closely related taxa with proclivities for hermaphroditism and in some cases self-fertilization (27,28). Selfing by Kmar was discovered in the early 1960s (29), and in nature it yields highly homozygous lines composed of individuals so genetically uniform as to be, in effect, clonally identical to one another (30). Thus, Kmar became a model for studying the evolutionary ramifications of self-fertilization and clonality in a vertebrate species (reviewed in ref.…”

“…This seems unlikely however because selfing rates have been estimated both from direct genetic assays of progeny in the laboratory (40) and indirect genetic evidence from natural populations (27,43). Furthermore, males (who presumably mediate the outcross events) are documented to be rare in Florida in field surveys that now span nearly half a century (30,45).…”