Robert C. Vrijenhoek

Animal Clones and Diversity

ral clones are particularly relevant as an era begins in which the artificial cloning of mammals, and potentially humans, is no longer a fantasy. To an evolutionary biologist, sex is meiotic recombination and outcrossing, which together create genetically diverse offspring that interact uniquely with the environment in each new generation. Meiotic sex originated in our single-celled protist ancestors, and except for the evolution of distinct male and female gametes (i.e., small motile sperm Studies of animal clones

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.

Deep-sea hydrothermal vent communities of the Logatchev area (14°45′N, Mid-Atlantic Ridge): diverse biotopes and high biomass

Results from recent biological studies (including three Alvin dives in July 1997) of the southernmost deep-sea hydrothermal area known on the Mid-Atlantic Ridge (MAR), the Logatchev hydrothermal area, are described. The Logatchev area includes three vent fields, each with a different geological setting corresponding to: (1) a large sulphide mound with ‘smoking craters’; (2) an active chimney complex (known as ‘Irina-2’); and (3) a diffuse flow through soft sediment (‘Anyas Garden’). Hydrothermal communities found at these fields differ considerably: Anyas Garden is dominated by vesicomyid clams, Ectenagena sp. aff. kaikoi , Irina-2 by mytilid mussels, Bathymodiolus sp. aff. puteoserpentis , with swarms of shrimps and other rich associated fauna, whereas on the main mound the fauna as a whole is less abundant and less diverse. This is the first record of a living clam population on the MAR. Other bivalves found on the clam field included thyasirids, Thyasira ( Parathyasira ) spp., not reported previously from deep-sea hot vent communities. The biomass on the mussel bed at Irina-2 exceeds 70 kg m −2 (wet weight with shells) and is the highest known on the MAR. The large shrimp population at Irina-2 includes swarms of Rimicaris exoculata . A diverse shrimp fauna (including a new species Alvinocaris sp. aff. muricola ) on the mussel bed is dominated by Mirocaris keldyshi . Overall the Logatchev area is dominated by mussels which may be attributable to the presence of both methane-oxidizing (dominant type) and sulphur-oxidizing bacterial symbionts in their gills. The diversity of vent organisms and biotopes at Logatchev appears to be the highest on the MAR.

Variation and Clonal Structure in a Unisexual Fish

A genetic analysis of population structure in the unisexual fish, Poeciliopsis monacha-lucida, was conducted using protein phenotypes encoded by 22 loci. The all-female populations arose by hybridization between P. monacha and P. lucida in narrow zones where their ranges overlap. The unisexual hybrids are sustained by mating with males of P. lucida and are phenotypically intermediate, expressing both maternal and paternal traits. However, only the maternal (P. monacha) set of chromosomes is transmitted through oogenesis in these hybrids; recombination does not occur. By mating laboratory strains of P. monacha-lucida, derived independently from 37 wild females, with males of P. lucida of known genotype, the haploid genotype (haplotype) of the clonally inherited monacha genome was determined. Eight distinct haplotypes were identified among the clonally inherited genomes of the 37 strains. This variation indicates that a minimum of eight clonally inherited genomes (hemiclones) occur naturally, although each of these eight haplotypes may include additional variation at other loci that we failed to observe. Two of the eight haplotypes were found at three distant localities in the Rio Fuerte and may represent well-adapted, generalized clones that have spread to inhabit both stable and diverse habitats as well as fluctuating and depauperate habitats in this river. Additional, unique haplotypes were found only at localities where hybrid syntheses could occur. These haplotypes may represent newly arisen hemiclones that have not yet dispersed. When compared with sexual species, the unisexual fish maintain significantly higher levels of heterozygosity ranging from a low of 36.3% to a high of 50.0% of the tested gene loci in an individual. The high levels of heterozygosity, attributable to their hybrid origin, along with their reproductive potential and vigor apparently explain the success of these unisexual forms.

DIFFERENTIAL SURVIVAL OF SEXUAL AND ASEXUAL POECILIOPSIS DURING ENVIRONMENTAL STRESS

According to the Frozen Niche‐Variation model, coexisting clones of an asexual species can freeze and faithfully replicate ecologically relevant genetic variability that segregates in the sexual ancestors. The present experiments with fish of the genus Poeciliopsis provide further evidence in support of this model. Sexual and clonal forms of Poeciliopsis live in the desert streams of Sonora, Mexico, and are exposed to environmental extremes ranging from flash floods to hot, desiccating, residual pools. We examined coexisting members of the monacha complex to see whether the fish types differed with respect to survival during stress and swimming endurance in an artificial flume. The two coexisting clones of the triploid gynogenetic fish P. 2 monacha–lucida differed dramatically: clone MML/II had the best survival during heat and cold stress and the worst survival during hypoxic stress, whereas clone MML/I had the best survival during hypoxic stress and the worst during heat stress. Poeciliopsis monacha, the sexual species with which these clones coexist, had intermediate survival during heat and hypoxic stress and very poor swimming endurance in the flume. The physiological differences seen in this study are consistent with the Frozen Niche‐Variation model and provide some insights into environmental factors that affect the distribution and abundance of these fish.

Genetic differentiation between spatially-disjunct populations of the deep-sea, hydrothermal vent-endemic amphipod Ventiella sulfuris

AbstractSpecies endemic to deep-sea hydrothermal vent ecosystems have disjunct distributions imposed by the island-like arrangement of their specialized habitats. Using allozyme electrophoresis, we examined genetic population structure of the hydrothermal vent amphipod Ventiella sulfuris Barnard and Ingram, 1990. Samples from five sites along the East Pacific Rise (EPR) and two along the Galapagos Rift were collected in 1990 and 1988, respectively. Variability, based on 12 enzyme loci, was relatively high

Cryptic species of deep-sea clams (Mollusca: Bivalvia: Vesicomyidae) from hydrothermal vent and cold-water seep environments

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Genetic variation among laboratory strains of the planorbid snail Biomphalaria glabrata

(proportion of polymorphic loci whose most common allele not greater than 0.95 in frequency) =41.6%;