Coexistence of clones in a heterogeneous environment.

Two genetically distinct clones of the asexual triploid fish Poeciliopsis 2 monacha-lucida inhabit the Rio del Fuerte of northwestern Mexico. Their coexistence apparently depends on feeding specializations that result in partitioning of the limited food resources in the desert streams. The findings suggest that these asexual organisms have sufficient clonal diversity to occupy a broad, heterogeneous, adaptive zone.

Fitness differences among remnant populations of the endangered sonoran topminnow.

Four correlates of fitness were measured in three stocks of the endangered Sonoran topminnow, Poeciliopsis occidentalis, from Arizona. Survival, growth, early fecundity, and developmental stability were greatest in laboratory-reared fish from the most heterozygous natural population studied. Conversely, all four traits were poorest in fish from a population with no electrophoretically detectable genetic variation. These results emphasize the need for genetic as well as demographic information for the development of comprehensive species recovery programs.

Conservation genetics of endangered fish populations in Arizona.

Genetic diversity in remnant populations of the Sonoran topminnow Poeciliopsis occidentalis (Pisces: Poeciliidae) from Arizona, where the species is endangered, is compared with that in populations from Sonora, Mexico, where the fish is widespread and abundant. Geographically peripheral Arizona populations contain substantially lower levels of genetic variation than do Mexican populations near the center of the species' range. Allelic differences among three genetically and geographically distinct groups are responsible for 53 percent of the total genetic diversity in this species, 26 percent is due to differences among local populations within the groups, and 21 percent is due to heterozygosity within local populations. Recommendations for conservation and restocking efforts in Arizona are based on these genetic findings.

Biogeography and ecological setting of Indian Ocean hydrothermal vents.

Within the endemic invertebrate faunas of hydrothermal vents, five biogeographic provinces are recognized. Invertebrates at two Indian Ocean vent fields (Kairei and Edmond) belong to a sixth province, despite ecological settings and invertebrate-bacterial symbioses similar to those of both western Pacific and Atlantic vents. Most organisms found at these Indian Ocean vent fields have evolutionary affinities with western Pacific vent faunas, but a shrimp that ecologically dominates Indian Ocean vents closely resembles its Mid-Atlantic counterpart. These findings contribute to a global assessment of the biogeography of chemosynthetic faunas and indicate that the Indian Ocean vent community follows asymmetric assembly rules biased toward Pacific evolutionary alliances.

Bone-eating Osedax females and their 'harems' of dwarf males are recruited from a common larval pool.

Extreme male dwarfism occurs in Osedax (Annelida: Siboglinidae), marine worms with sessile females that bore into submerged bones. Osedax are hypothesized to use environmental sex determination, in which undifferentiated larvae that settle on bones develop as females, and subsequent larvae that settle on females transform into dwarf males. This study addresses several hypotheses regarding possible recruitment sources for the males: (i) common larval pool--males and females are sampled from a common pool of larvae; (ii) neighbourhood--males are supplied by a limited number of neighbouring females; and (iii) arrhenotoky--males are primarily the sons of host females. Osedax rubiplumus were sampled from submerged whalebones located at 1820-m and 2893-m depths in Monterey Bay, California. Immature females typically did not host males, but mature females maintained male 'harems' that grew exponentially in the number of males as female size increased. Allozyme analysis of the females revealed binomial proportions of nuclear genotypes, an indication of random sexual mating. Analysis of mitochondrial DNA sequences from the male harems and their host females allowed us to reject the arrhenotoky and neighbourhood hypotheses for male recruitment. No significant partitioning of mitochondrial diversity existed between the male and female sexes, or between subsamples of worms collected at different depths or during different years (2002-2007). Mitochondrial sequence diversity was very high in these worms, suggesting that as many as 10(6) females contributed to a common larval pool from which the two sexes were randomly drawn.

Directional dispersal between mid-ocean ridges: deep-ocean circulation and gene flow in Ridgeia piscesae.

This study examined relationships between bathymetrically induced deep-ocean currents and the dispersal of the hydrothermal vent tubeworm Ridgeia piscesae along the northeast Pacific ridge system. A robust diagnostic model of deep-ocean circulation in this region predicted strong southeasterly currents following contours of the Blanco Transform Fault, a 450-km lateral offset that separates the Gorda and Juan de Fuca ridge systems. Such currents should facilitate the southward dispersal of R. piscesae larvae. Immigration rates for populations north and south of the Blanco Transform Fault were estimated from molecular population genetic data. Mitochondrial DNA evidence revealed population subdivision across the Blanco Transform Fault, and a strong directional bias in gene flow that was consistent with predictions of the circulation model. The distribution of mitochondrial diversity between the northern and southern populations of R. piscesae suggests that the Gorda Ridge tubeworms have maintained larger effective population sizes than the northern populations, a pattern that also exists in co-occurring limpets. Together, these data suggest that the northern vent fields may experience a higher frequency of habitat turnover and consequently more rapid losses of genetic diversity.

Acquisition of dwarf male "harems" by recently settled females of Osedax roseus n. sp. (Siboglinidae; Annelida).

After the deployment of several whale carcasses in Monterey Bay, California, a time-series analysis revealed the presence of a new species of Osedax, a genus of bone-eating siboglinid annelids. That species is described here as Osedax roseus n. sp. It is the fifth species described since the erection of this genus and, like its congeners, uses a ramifying network of "roots" to house symbiotic bacteria. In less than 2 months, Osedax roseus n. sp. colonized the exposed bones of a whale carcass deposited at 1018-m depth, and many of the females were fecund in about 3 months post-deployment. As with other Osedax spp., the females have dwarf males in their tube lumens. The males accrue over time until the sex ratio is markedly male-biased. This pattern of initial female settlement followed by gradual male accumulation is consistent with the hypothesis that male sex may be environmentally determined in Osedax. Of the previously described species in this genus, Osedax roseus n. sp. is most similar to O. rubiplumus, but it has several anatomical differences, as well as much smaller females, dwarf males, and eggs. Osedax roseus n. sp. is markedly divergent (minimally 16.6%) for mitochondrial cytochrome oxidase subunit I (mtCOI) sequences from any other Osedax species.

Genetic dissection of clonally inherited genomes of poeciliopsis. I. Linkage analysis and preliminary assessment of deleterious gene loads.

Theoretical considerations suggest that a high load of deleterious mutations should accumulate in asexual genomes. An ideal system for testing this hypothesis occurs in the hybrid all-female fish Poeciliopsis monacha-lucida. The hybrid genotype is retained between generations by an oogenetic process that transmits only a nonrecombinant haploid monacha genome to their ova. The hybrid genotype is re-established in nature by fertilization of these monacha eggs with sperm from a sexual species, P. lucida. The unique reproductive mechanism of these hybrids allows the genetic dissection of the clonal monacha genome by forced matings with males of P. monacha. The resultant F(1) hybrids and their backcross progeny were examined to determine the amount and kinds of genetic changes that might have occurred in two clonal monacha genomes.-Using six allozyme markers, four similar linkage groups were identified in each clonal genome. Segregation and assortment at these loci revealed no apparent differences between monacha genomes from sexually and clonally reproducing species. Mortality of F(1) and backcross progeny revealed differences between the two clonal genomes, suggesting that deleterious genes may accumulate in genomes sheltered from recombination.

Genetic dissection of clonally inherited genomes of Poeciliopsis: II. Investigation of a silent carboxylesterase allele.

According to the ratchet mechanism hypothesis, deleterious mutations should accumulate in clonal genomes of unisexual fish of the genus Poeciliopsis. This study defines one such mutant, a silent carboxylesterase allele (ES-5 degrees) which is found in the heterozygous condition in a particular population of P. monacha-occidentalis. An antiserum to purified Poeciliopsis carboxylesterase cross-reacts with the gene product of the Es-5 degrees allele upon immunoelectrophoresis. This finding of cross-reacting material associated with the Es-5 degrees allele provides a useful marker for the breeding of a carboxylesterase deficient strain.

Molecular evidence for multiple origins of hybridogenetic fish clones (Poeciliidae:Poeciliopsis).

Hybrid matings between the sexual species Poeciliopsis monacha and Poeciliopsis lucida produced a series of diploid all-female lineages of P. monacha-lucida that inhabit the Río Fuerte of northwestern Mexico. Restriction site analyses of mitochondrial DNA (mtDNA) clearly revealed that P. monacha was the maternal ancestor of these hybrids. The high level of mtDNA diversity in P. monacha was mirrored by similarly high levels in P. monacha-lucida; thus hybridizations giving rise to unisexual lineages have occurred many times. However, mtDNA variability among P. monacha-lucida lineages revealed a geographical component. Apparently the opportunity for the establishment of unisexual lineages varies among tributaries of the Río Fuerte. We hypothesize that a dynamic complex of sexual and clonal fishes appear to participate in a feedback process that maintains genetic diversity in both the sexual and asexual components.

Mode of origin and sources of genotypic diversity in triploid gynogenetic fish clones (Poeciliopsis: Poeciliidae).

Most tributaries of the Río Fuerte in northwestern Mexico contain one or more clones of allotriploid fish of the genus Poeciliopsis. We used multilocus allozyme genotypes and mitochondrial DNA (mtDNA) haplotypes to examine several potential modes of origin of these gynogenetic all-female fish. The allozyme studies corroborated earlier morphological work revealing the hybrid constitution of two triploid biotypes, Poeciliopsis 2 monacha-lucida and Poeciliopsis monacha-2 lucida. Each biotype carries one or two whole genomes from the each of the sexual species P. monacha and P. lucida. Restriction site analysis of mtDNA revealed that P. monacha was the maternal ancestor of five electrophoretically distinguishable triploid clones. Four of five clones were marked by closely related, composite, allozyme/mtDNA genotypes, suggesting they had common origins from an allodiploid clone of the P. monacha-lucida biotype. Genotypic analysis revealed that all five clones arose via the "genome addition" pathway. Fertilization of unreduced ova in P. monacha-lucida females by sperm from P. monacha and P. lucida males, respectively, gave rise to both biotypes.

Hybridogenetic reproduction and maternal ancestry of polyploid Iberian fish: the Tropidophoxinellus alburnoides complex.

Iberian minnows collectively known as the Tropidophoxinellus alburnoides Steindachner complex comprise diploid and polyploid forms with highly female biased sex ratios. Previous investigators suggested that all-female clonal reproduction and interspecific hybridization may occur in this complex. We examined nuclear (allozymes) and cytoplasmic genes (mtDNA) to assess the evolutionary origins, relationships, and reproductive modes of T. alburnoides from western Spain. The multi-locus allozyme data clearly revealed the hybrid nature of all polyploid forms of this fish and some diploid forms as well. Diagnostic markers identified fish from the genus Leuciscus as the paternal ancestor of hybrids in the Duero and Guadiana River Basins. Additionally, analysis of nuclear markers revealed that hybridogenetic reproduction occurs in the diploid and triploid hybrids. The hybrids fully express the paternal Leuciscus genome and then discard it during oogenesis. Hybridogenetic ova contain only maternal nuclear genes and mtDNA from a non-hybrid T. alburnoides ancestor. Apparently diploid and triploid hybrids of T. alburnoides persist as sperm parasites on males of a sexually reproducing Leuciscus host species.

Population structure in Biomphalaria glabrata: examination of an hypothesis for the patchy distribution of susceptibility to schistosomes.

It has been suggested that the patchy distribution of snail susceptibility to schistosomes might be due to genetic drift. Since direct estimation of genes for susceptibility is not feasible in population studies, electrophoretic techniques were used to examine this hypothesis for populations of Biomphalaria glabrata from Puerto Rico. These populations were characterized by relative genetic homogeneity within populations and differentiation among local populations. The data presented are consistent with the hypothesis that random genetic drift and low rates of migration might be responsible for the patchy distribution of small susceptibility to schistosomes.

Molecular evidence that Sclerolinum brattstromi is closely related to vestimentiferans, not to frenulate pogonophorans (Siboglinidae, Annelida).

Siboglinids, previously referred to as pogonophorans, have typically been divided into two groups, frenulates and vestimentiferans. Adults of these marine protostome worms lack a functional gut and harbor endosymbiotic bacteria. Frenulates usually live in deep, sedimented reducing environments, and vestimentiferans inhabit hydrothermal vents and sulfide-rich hydrocarbon seeps. Taxonomic literature has often treated frenulates and vestimentiferans as sister taxa. Sclerolinum has traditionally been thought to be a basal siboglinid that was originally regarded as a frenulate and later as a third lineage of siboglinids, Monilifera. Evidence from the 18S nuclear rDNA gene and the 16S mitochondrial rDNA gene presented here shows that Sclerolinum is the sister clade to vestimentiferans although it lacks the characteristic morphology (i.e., a vestimentum). The rDNA data confirm the contention that Sclerolinum is different from frenulates, and further supports the idea that siboglinid evolution has been driven by a trend toward increased habitat specialization. The evidence now available indicates that vestimentiferans lack the molecular diversity expected of a group that has been argued to have Silurian or possibly Cambrian origins.

Genetic and morphometric characterization of mussels (Bivalvia: Mytilidae) from mid-atlantic hydrothermal vents.

Mussels were collected from deep-sea hydrothermal vents along the Mid-Atlantic Ridge. Specimens from the Snake Pit site were previously identified genetically and anatomically as Bathymodiolus puteoserpentis, but the relationships of mussels from other sites (Logatchev and Lucky Strike) were unclear. Molecular genetic and morphological techniques were used to assess differences among these mussel populations. The results indicate that the range for B. puteoserpentis extends from Snake Pit to Logatchev, and that an unnamed second species, B. n. sp., occurs at Lucky Strike. Analysis of mitochondrial NADH dehydrogenase subunit 4 (ND4) revealed 13% sequence divergence between the two species. Nei's genetic distance (D) based on 14 allozyme loci was 0.112. A multivariate morphometric analysis yielded a canonical discriminant function that correctly identified individuals from these sites to species 95% of the time.

Vestimentiferan on a whale fall.

Discovery of chemosynthetic communities associated with whale bones led to the hypothesis that whale falls may serve as stepping-stones for faunal dispersal between disjunct hydrothermal vents and cold seeps on the ocean floor (1). The initial observation was followed by a faunal inventory that revealed a diverse assemblage of microbes and invertebrates, supported by chemoautotrophic production, living in close proximity to whale remains (2, 3). To date, the conspicuous absence from whale falls of vestimentiferan tubeworms (a predominant constituent of eastern Pacific vent and seep habitats) has been a major objection to the stepping-stone hypothesis (4-5). We report the first evidence of a vestimentiferan tubeworm associated with a whale fall (Fig. 1). The tubeworm, Escarpia spicata, was identified by morphological criteria and DNA sequence data from a portion of the mitochondrial cytochrome oxidase C subunit I (COI) gene. Additionally, the bacterial endosymbiont in the tubeworm possessed a 16S rRNA gene that was similar to that of endosymbionts from vestimentiferans in sedimented cold-seep environments.

Enzyme polymorphism in Ascaris suum (Nematoda).

The potential of multilocus electrophoretic studies for providing insight into the population biology of parasitic organisms was studied using the swine parasite Ascaris suum suum. Thirty-eight loci encoding enzymatic or nonenzymatic proteins have been resolved in extracts of adult worms by starch-gel electrophoresis. A preliminary study of variation in Ascaris from eastern Iowa revealed an average heterozygosity of 6.6%. Allele frequencies at six polymorphic loci were similar in males and females and genotypic frequencies were in accord with those expected in a single, randomly mating population; however, the significant linkage disequilibrium between Pep-2 and Es-3 suggested that there may be some genetic substructuring within Ascaris from Iowa. Genetic comparisons of Ascaris from Iowa with Ascaris from New Jersey and Maryland indicated slight differences between eastern and midwestern populations, as well as between the east coast localities. Larger samples from more locations are needed before any statistical significance can be attached to these differences; however, qualitative comparisons suggest that the differentiation is a biological reality. Knowledge of the population biology of this and other parasites may contribute to planning effective control programs.

Three nuclear genes for phylogenetic, SNP and population genetic studies of molluscs and other invertebrates.

The study reports new primers capable of amplifying fragments from three nuclear protein-coding genes in a variety of deep-sea molluscs and annelids - adenine nucleotide translocase (Ant), calmodulin (Cal) and cyclophilin A (CycA). The Ant primers appear to be restricted to bivalve molluscs, whereas the Cal and CycA primers also amplified appropriate gene fragments from Lepetodrilus gastropod molluscs and Osedax polychaete worms. The amplified fragment of Cal contains an intron in the molluscs, but no intron was detected in the Ant and CycA fragments from any of the tested animals. DNA sequences generated by the three primer sets exhibited one to 15 single nucleotide polymorphism sites in deep-sea vesicomyid clams and Osedax boneworms. The observed levels of polymorphism indicate that the genes are likely to be useful in both population genetic and phylogenetic analyses of different invertebrate taxa.

Rubyspira, new genus and two new species of bone-eating deep-sea snails with ancient habits.

Rubyspira, a new genus of deep-sea snails (Gastropoda: Abyssochrysoidea) with two living species, derives its nutrition from decomposing whalebones. Molecular phylogenetic and morphological evidence places the new genus in an exclusively deep-sea assemblage that includes several close relatives previously known as fossils associated with Cretaceous cold seeps, plesiosaur bones, and Eocene whalebones. The ability to exploit a variety of marine reducing environments may have contributed to the evolutionary longevity of this gastropod lineage.