The genetic mechanism of sex determination in the conchostracan shrimp Eulimnadia texana.

We report the results of a laboratory pedigree analysis describing the unique sex-determining mechanism of the conchostracan shrimp, Eulimnadia texana. Natural populations of E. texana are mixtures of self-compatible hermaphrodites and males and represent one of the few known cases of androdioecy in animals. Hermaphrodites are of two types: amphigenic (producing both male and hermaphroditic offspring) and monogenic (producing only hermaphroditic offspring). We propose a simple genetic model to explain this polymorphism and show by genetic analysis that males, amphigenics, and monogenics can be interpreted as three alternative phenotypes of a one-locus system of sex determination. We discuss the implications of this novel system of sex determination for understanding the evolution of reproductive systems.

Four independent electrophoretic markers in spadefoot toads.

Four enzyme-encoding genes (Idh-1, Idh-2, Ldh-1, and Mdh-1), with alleles diagnostic for the spadefoot toads Scaphiopus multiplicatus and Scaphiopus bombifrons, were investigated in order to characterize their inheritance and linkage relationships. Electrophoretic phenotypes in the offspring of natural crosses exhibit Mendelian segregation, behaving as genotypes produced by alternative alleles at four independently assorting loci. These phenotypes are useful markers of genetic identity and the degree of genetic admixture in the analyses of hybrid zone dynamics for these two species. Concurrent use of a morphological index verified the diagnostic value of the markers. The morphological index is useful for the identification of parental species and many F1 hybrids, however offspring of backcrosses usually express parental species characteristics. Electrophoretic typing allows the identification of all hybrids and 87 percent of the offspring from backcrosses. It also facilitates the identification of tadpoles, which are extremely difficult to distinguish morphologically. The technique is useful for the assessment of introgression and the evaluation of reproductive interaction in these species, even though it slightly underestimates backcross offspring.

Lactate dehydrogenase: a polymorphism of Anoplarchus purpurescens: geographic variation in central California.

Previous studies on the muscle lactate dehydrogenase polymorphism of the stichaeid fish Anoplarchus purpurescens in Puget Sound have demonstrated the existence of a clinal pattern of allele frequency. The LDH-A' allele was observed to increase toward the south, with several environmental factors showing correlation with this change in allele frequency. Populations from California were sampled in the present study to determine whether or not gene frequencies along an independent transect near the southern end of the species distribution are consistent with the interpretation that the geographic patterns reflect the influence of environmental factors. In California, the LDH-A' allele decreases in frequency to the south. This observation necessitates the reevaluation of possible environmental influences on the LDH polymorphism. Only one of several proposed hypotheses is completely consistent with the geographic patterns observed along both the Washington and California transects. However, the genetic differentiation along the California coast cannot be unequivically ascribed to the influence of environmental factors; current morphological data indicate the possibility of historical influences on the population genetic structure of California A. purpurescens.

Dynamics of a lactate dehydrogenase polymorphism in the wood louse Porcellio scaber latr.: evidence for partial assortative mating and heterosis in natural populations.

Electrophoretic separation of lactate dehydrogenase (LDH) of Porcellio scaber from 14 natural populations in California, and one each in Oregon, Delaware and Massachusetts, indicates a biallelic polymorphism. Phenotypes are recovered from laboratory matings of virgin females in frequencies agreeing with simple Mendelian inheritance, and the frequency distributions of phenotypes in natural populations are typically in agreement with the appropriate Hardy-Weinberg distributions for these same populations. The same allele predominates in all natural populations examined. Temporal stability within populations suggests that the polymorphism is at, or near, equilibrium. The spatial distribution of allele frequencies, however, is apparently mosaic. Abrupt discontinuities in gene frequency over short distances (50 m to 1 km) suggest that interpopulation migration is insufficient to swamp local differences in gene frequency. Analysis of the transmission dynamics of the polymorphism in natural populations using mother-offspring genotype comparisons suggests that the allelic frequencies of transmitted male gametes are not independent of female genotype. Specifically, the observed mating scheme in natural populations appears to be partially assortative. Comparisons of progeny genotype distributions with yearling (or adult) genotype distributions from the same populations indicate a superior post-partum viability of heterozygous individuals relative to homozygotes. The distortion of progeny genotypic distributions created by assortment is thus apparently counteracted by subsequent heterosis.

Glutamate dehydrogenase from coelenterates is NADP specific.

Glutamate dehydrogenases detected in tissue extracts of a broad sample of coelenterate species all require NADP(H) as a co-substrate, rather than being capable of using either NAD(H) or NADP(H). In this respect, the coelenterate phyla appear to be unique in the animal kingdom.

The life cycle of corymorpha (=euphysora) bigelowi (maas, 1905) and its significance in the systematics of corymorphid hydromedusae.

1. Five individuals of the corymorphid jellyfish, Euphysora bigelowi Maas, were collected in 1973 in Monterey Bay, California, for a range extension of more than 8,000 km across the northeastern Pacific Ocean. 2. Larvae released by these medusae were cultured and the resulting polyps, the first known from this medusa genus, are described. 3. The polyps are a Corymorpha, but share some minor characteristics with polyps of the corymorphid genus Euphysa. 4. The polyp and medusa are assigned the name Corymorpha bigelowi (Maas); the systematic implications of this revision are discussed.