The Devils Hole pupfish, Cyprinodon diabolis, is restricted to a small habitat in southwestern Nevada. In 1972 the species was federally listed as an endangered species. Management efforts to mitigate extinction risks have been plagued by the inability to propagate the species in aquaria-anomalous for the genus-and repeated failure of propagation attempts in large, outdoor, artificial pools designed to mimic natural conditions in Devils Hole. These difficulties indicate that the species either has niche requirements that are not adequately recreated under artificial conditions or that it harbors a relatively large genetic load of deleterious mutations that compromises propagation. We used variation at 12 microsatellite loci to evaluate the results of natural, uncontrolled hybridization involving a population of C. diabolis inhabiting an artificial pool and invaders from a nearby population of the closely related C. nevadensis. The results suggest that following invasion of the pool by three C. nevadensis individuals, the gene pool underwent a rapid shift from pure C. diabolis to one comprised mostly of C. nevadensis alleles. Alleles diagnostic for C. nevadensis increased from about 0.03 to an average of 0.76 across four diagnostic loci over the course of 8 years or less. Although we cannot exclude explanations based on adaptation to Devils Hole, genetic drift, or demographic variability, these results and various other aspects of the biology of C. diabolis are best explained by the genetic load hypothesis. The work suggest avenues for future experimental work to evaluate these possibilities directly and provide an explanation for why some previous propagation efforts designed to mitigate extinction risk have failed.
The Hawaiian monk seal ( Monachus schauinslandi) is a critically endangered species that has failed to recover from human exploitation despite decades of protection and ongoing management efforts designed to increase population growth. The seals breed at five principal locations in the northwestern Hawaiian islands, and inter‐island migration is limited. Genetic variation in this species is expected to be low due to a recent population bottleneck and probable inbreeding within small subpopulations. To test the hypothesis that small population size and strong site fidelity has led to low within‐island genetic variability and significant between‐island differentiation, we used two independent approaches to quantify genetic variation both within and among the principal subpopulations. Mitochondrial control region and tRNA gene sequences (359 base pairs) were obtained from 50 seals and revealed very low genetic diversity (0.6% variable sites), with no evidence of subpopulation differentiation. Multilocus DNA fingerprints from 22 individuals also indicated low genetic variation in at least some subpopulations (band‐sharing values for “unrelated” seals from the same island ranged from 49 to 73%). This method also provided preliminary evidence of population subdivision ( F′st estimates of 0.20 and 0.13 for two adjacent island pairs). Translocations of seals among islands may therefore have the potential to relieve local inbreeding and possibly to reduce the total amount of variation preserved in the population. Genetic variation is only one of many factors that determine the ability of an endangered species to recover. Maintenance of existing genetic diversity, however, remains an important priority for conservation programs because of the possibility of increased disease resistance in more variable populations and the chance that inbreeding depression may only be manifest under adverse environmental conditions.
It is thought that genetic variation can affect the persistence of a population through its influence on disease susceptibility. We assessed genome-wide genetic variation, variation at a locus involved in the immune system, and acceptance or rejection of skin grafts in three natural populations of the pocket gopher (Thomomys bottae). Multilocus DNA fingerprints confirmed previous allozyme data, revealing high levels of variation among Hastings Reserve pocket gophers and almost complete within-population identity for individuals from the two Patricks Point populations (Patricks J and Patricks F), although Patrtcks J animals were dissimilar to animals from Patricks F despite their proximity. Individuals from the high-variation population consistently rejected u~qthin-population reciprocal skin grafts, whereas Patricks J and Patricks F individuals accepted within-population grafts. Patricks J and Patricks F individuals were found to be immunocompetent, however, as revealed by the ability of all individuals to reject between-population grafts, including those that previously accepted within-population grafts. A DNA heteroduplex analysis was then used to directly characterize variability at DQog a locus of the immune system's major histocompatability complex. Both populations low in genetic variation were fixed for unique DQ~ alleles, whereas observed heterozygosity in the Hastings population was 0. 43, ascribable to at least three unique alleles. These data are in accord with previous cheetah skin-graft results and confirm that skin grafts can be used to assess genetic similarity. We suggest that although many animal populations can persist with extremely low levels of genetic variation in the wild, such populations may be at a greater risk of extinction front particular pathogens because of their genetic uniformity. Variaci6n Genetica y Respuesta Inmune en Poblaciones Naturales de ToposResumen: Se piensa que la variaci6n gendtica puede afectar la persistencia de una poblaci6n por su influencia en la susceptibilldad a enfermedades. Esto punto de vista ha sido presentado en forma prominente a travds de varios estudios interesantes, aunque controvertidos y la aceptaci6n o rechazo de injertos de piel en tres poblaciones del topo Tomomys bottae. Huellas digitales del ADN multllocus revelaron un alto nivel de variaci6n entre los topos de la Reserva Hastings, e identidad intrapoblacional cam completa para los individuos de dos poblaciones de Patricks Point (Patricks J y Patricks F) confirmando prevlos datos de alozimas, aunque, a pesar de su proximidad los animales Patricks J eran diferentes a los Patricks F. Individuos de las poblaciones con alta variaci6n rechazaron en forma consistente injertos de piel recfprocos dentro de la po-blaci6n mientras que individuos Patricks J y Patricks F aceptaron injertos dentro de la poblaci6n, se encontr6 que individuos Patricks J y Patricks F eran inmunocompetentes, a pesar de lo revelado por la habilldad de todos los individuos para rechazar injertos entre poblaciones, incluso aquellos...
We describe the genomes of two mycobacteriophages, MosMoris and Gattaca, newly isolated on Mycobacterium smegmatis. The two phages are very similar to each other, differing in 61 single nucleotide polymorphisms and six small insertion/deletions. Both have extensive nucleotide sequence similarity to mycobacteriophage Marvin and together form cluster S.
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