Poecilia Mexicana Research Articles

INTERSPECIFIC HYBRIDIZATION AND THE EVOLUTIONARY ORIGIN OF A GYNOGENETIC FISH, POECILIA FORMOSA.

In recent years, largely through the application of allozyme techniques, several unisexual (thelytokous) vertebrates have been shown to be genetically equivalent to F1 hybrids of certain related bisexual species. The causal relationship, however, between interspecific hybridization and the origin of unisexuality has not been elucidated, and the role of hybridization per se is controversial (Cuellar, 1974, 1977, 1978; Cole, 1978; Wright, 1978). The amazon molly, Poeciliaformosa (Girard), an ovoviviparous gynogentic teleost (family Poeciliidae) was the first known unisexual vertebrate (Hubbs and Hubbs, 1932). The discoverers of its unisexuality recognized early that it was probably of hybrid origin, as it was an almost exact morphological intermediate between the sailfin molly (Poecilia latipinna) and the shortfin mollies (which were then regarded as a single species, P. sphenops). Laboratory hybridization of the presumptive parental species, however, produced only bisexual progeny, including fertile males (Hubbs, 1933, 1955, 1961; Meyer, 1938; Hubbs and Hubbs, 1946a, 1946b). Subsequent to those early hybridization experiments, P. sphenops, as it was then recognized, has been shown to be an assemblage of morphologically similar but genetically quite distinct species (Hubbs, 1961; Schultz and Miller, 1971; Miller, 1975; Brett et al., unpubl.). A variety of zoogeographic, morphological (Darnell and Abramoff, 1968), chromosomal (Prehn and Rasch, 1969), and biochemical genetic (Abramoff et al., 1968; Turner et al., 1980) data suggest that the shortfin species involved in the ancestry of P. formosa was P. mexicana, a species restricted to the

PROBLEMS WITH THE CULTURE OF TOPMINNOWS (FAMILY POECILIIDAE) AND THEIR USE AS LIVE BAITFISHES1

ABSTRACTThe intensive culture and live bait potential of a topminnow (Poecilia vittata) and shortfin molly (P. mexicana) was investigated in Hawaii, American Samoa, and Palau. Although these baitfishes are unusually hardy, problems were encountered during their culture, handling, shipboard confinement, and use as live bait for skipjack tuna (Katsuwonus pelamis). Principal problems included predation, fouling and nuisance organisms, disease and parasites, cannibalism, slow growth rates, poor water quality, and difficulties during handling and transportation.

Cytological evidence for temporal differences during the asynchronous ovarian maturation of bisexual and unisexual fishes of the genus Poecilia

Comparisons based upon morphological features and cytochemical staining properties of chromatin, nucleoli, and the ooplasm were used in the present analysis of ovarian maturation in wild‐caught Poecilia mexicana and its related gynogenetic diploid and triploid' species'. Using an empirically derived ovarian maturation index, seasonal and collection site differences were found between the unisexual and bisexual forms. These fish seem equally suited to their environments. However, our data indicate that differences in microhabitat can have a profound influence on oocyte development. Although females of Poecilia spp. have asynchronous cycles of ovarian maturation, we could not detect any peculiar cytological events associated with the gynogenetic mode of reproduction. Sperm were found in ovaries of both unisexual and bisexual forms indicating that the unisexuals can compete effectively with females of P. mexicana for matings with males of this species. The methods employed in this study provide a sensitive measure of reproductive potentials in sympatric species.

Ecological Distribution of Fishes of Moapa (Muddy) River in Clark County, Nevada

Abstract Fish collections were made at nine stations along the Moapa River of southern Nevada. Four native species are ecologically separated into headwater and middle-stream types. The headwater fishes are ecologically segregated into one pond species (Crenichthys baileyi) and one stream species (Moapa coriacea). The apparent temperature preference for both species is near 29.5 C. Temperature range for Crenichthys is 27–32 C and for Moapa 19.5–32 C. Both Gila robusta and Rhinichthys osculus are most abundant in the turbid middle portion of the stream in undisturbed, deep riffle habitats. A fifth native species, Plagopterus argentissimus, is extremely rare or of accidental occurrence. The unsaturated Moapa River environment has been easily colonized by exotic or non-native species, most recently and most successfully by Poecilia mexicana. An additional species, Gambusia affinis, is widespread and abundant throughout much of the stream. Cyprinus carpio, Notropis lutrensis, Pimephales promelas, Ictalurus me...