Muscle protein phenotypes and the probable evolutionary origin of a unisexual fish, Poecilia formosa, and its triploid derivatives

Abstract

Several species-specific proteins have been identified by polyacrylamide gel electrophoresis (PAGE) of skeletal muscle extracts from the diploid gynogen, Poecilia formosa, its related triploid unisexuals, and their sympatric, bisexual species, P. mexicana and P: latipinna. These water-soluble, low molecular weight proteins (7,000-13,000) comigrate with a fraction of purified rabbit parvalbumin on nondenaturing gels and show staining properties similar to rabbit parvalbumins. The electrophoretic patterns of these muscle proteins provide a set of distinctive phenotypic markers for each of the host species involved in naturally occurring breeding complexes with P: formosa. The muscle protein phenotypes for wild fishes and F, hybrids of I? mexicana X P latipinna show no evidence of sexual dimorphisms. Furthermore, the hybrid phenotypes are those that would be predicted from appropriate combinations of parental alleles at three gene loci. The patterns found by PAGE for several generations of pedigreed stocks of E? formosa show strictly matroclinous inheritance of a characteristic muscle protein phenotype and coupled with the electrophoretic patterns of several enzymic proteins reflect the probable hybrid origin of this diploid unisexual. Finally, paternal contributions by P: mexicana to the hybrid genome of triploid unisexuals are clearly demonstrated by comparative analyses of muscle protein phenotypes for P: formosa and its contemporary host species. Our identification of distinctive phenotypic markers in the muscle proteins of several poeciliid species involved in unisexual-bisexual breeding complexes provides an important new tool for further studies on the adaptive significance of unisexuality, hybridization, and fixed heterozygosity in the evolutionary biology of these fishes.

Clonal Diversity and Evolutionary Dynamics in a Diploid-Triploid Breeding Complex of Unisexual Fishes (Poecilia)

“…Parvalbumin phenotypes ( Fig. 1; see also Monaco et al, 1982) and recent allozyme surveys (Turner and Brett, unpubl. ) strongly suggest that these genotypes occur within the P. mexicana populations in the Rios Tuxpan and San Rafael and the coastal lagoons between them.…”

Quantifying the threat of extinction from Muller's ratchet in the diploid Amazon molly (Poecilia formosa)

“…Paternal leakage has been demonstrated to lead to the expression of paternal genes [13,50], suggesting a compensatory role in the Amazon molly [13]. There are two mechanistic scenarios that may facilitate this.…”

Cytogenetics of bisexual/unisexual species of <i>Poecilia</i>

“…and the muscle protein pheno type of P. m. mexicana (Monaco et al, 1982). While it is tempt ing to speculate on connections between interspecific hybridiza tion and polyploidy in unisexual-bisexual breeding complexes and that a triploid sexual form might be an intermediate toward a tetraploid poeciliid (Schultz, 1979), it has to be pointed out that unisexual Poecilia individuals are not found in the area where progenitors of the specimen in question were collected.…”

“…There is still some question as to the role of these subspecies in the origin of P. formosa (Abramoff el al.. 1968;Simanek. 1978: Monaco et al, 1982. Identification of appropriate chromosomal markers in these fishes might also allow us to determine whether chro mosomal introgression exists among unisexual and bisexual species of Poecilia and whether triploids can serve as a genetic bridge to introduce variability to a group of individuals that otherwise might have closed gene pools, as proposed by Rasch et al (1970).…”