No abstract

Apparently between 1980 and 1984, Cyprinodon variegatus was introduced into an area of the Pecos River in Texas, where it hybridized with an endemic species, C. pecosensis. Protein electrophoresis indicated that, by 1985, panmictic admixtures of these two pupfishes occupied approximately 430 river-kilometers of the Pecos River, roughly one-half of the historic range of the endemic species. The average frequency of introduced alleles at four diagnostic loci ranged from 0.18 to 0.84 at the 15 sites sampled from the Pecos River in Texas. Clinal patterns in allele frequencies suggest that C. variegatus was introduced into a mid-reach of the river and that this was followed by both upstream and downstream dispersal of the introduced alleles. All pairwise combinations of loci showed significant linkage disequilibrium. The level of disequilibrium indicates chromosomal linkage for one gene-pair, Gpi-A and Est-1. The change in pupfish allele frequencies in the Pecos River represents an extreme example of rapid natural selection in a seminatural situation.

Analysis of mtDNA sequence variation (2,548 bp from ND2, cytb, and part of the control region) indicates that the genus Cyprinodon began diverging in the Late Miocene from a common ancestor with Megupsilon, a monotypic genus on the Mesa del Norte of Mexico. The geographic pattern of mtDNA variation, with estimates of divergence time, suggests that by the end of the Miocene Cyprinodon occurred from the Atlantic Coast and West Indies to near the western margin of North America via ancestral Rio Grande and Colorado River systems. Phylogeographic structure within the major mtDNA complexes supports a variety of hypotheses from geology and previous phylogenetic analyses for Late Neogene connections among basins in southwestern North America now separated by formidable barriers to dispersal. Comparison of the mtDNA tree with previous phylogenetic inferences from allozymes indicates that reticulate evolution involving divergent lineages probably was important in the history of Cyprinodon.El análisis de variació n de secuencias de ADNmt (ND2, cytb, y parte de la región reguladora; 2,548 pb) indica que el género Cyprinodon empezó a divergir en el mioceno tardío de un antepasado comú n con Megupsilon, un género monotípico de la Mesa del Norte de México. El patró n geográfico de la variació n de ADNmt, con estimadas de los tiempos divergencias, sugiere que al llegar al fin del mioceno Cyprinodon ocurrió desde la costa Atlántica y las Antillas hasta casi el margen oeste de Norteamérica por los sistemas pluviales antiguos del río Bravo y del río Colorado. La estructura filogeográfica entre los grupos principales de ADNmt apoya a una variedad de hipó tesis de la geología y de los análisis filogenéticos anteriores para conexiones del neogeno tardío entre cuencas del suroeste de Norteamérica que ahora están separadas por barreras imponentes contra la dispersió n. La comparació n del árbol de ADNmt con deducciones filogenéticos anteriores de alozimas indica que la evolució n reticulada que incluye líneas divergentes probablemente fue importante en la historia del Cyprinodon.

No abstract

Anthropogenic changes to the Great Plains rivers of North America have had a large, negative effect on a reproductive guild of pelagic‐broadcast spawning (PBS) cyprinid fishes. The group is phylogenetically diverse, with multiple origins of the PBS mode. However, because of incomplete life‐history information, PBS designation often relies only on habitat and egg characteristics. We identified 17 known or candidate PBS fishes and systematically synthesized the literature on their biology and ecology in relation to major threats to persistence. Research output on an individual species was unrelated to conservation status, but positively correlated with breadth of distribution. The PBS species have opportunistic life‐history strategies and are typically short‐lived (generally 1–3 years) fishes. Many PBS species have truncated ranges showing declines in both distribution and abundance, especially those endemic to the Rio Grande catchment. Fundamental habitat associations are unknown for many species, particularly regarding seasonal shifts and early life stages. Critical thermal tolerances have been quantified for five PBS species and are generally >35°C. Turbidity and salinity changes are linked to responses at multiple life stages, but information is lacking on interactions between water quality and quantity. Hydrologic alteration appears to be a primary threat to PBS species, through complex interactions with landscape fragmentation, and habitat change. We highlight areas where scientific and management communities are lacking information and underline areas of potential conservation gain.

No abstract

A comparison of allozyme and mtDNA frequencies was used for insight into a situation in the Pecos River, Texas where contact between the endemic pupfish (Cyprinodon pecosensis) and an introduced congener (C. variegatus) has resulted in rapid, geographically extensive genetic introgression. Temporal changes in mean frequencies of diagnostic allozyme markers indicate that the clinal pattern of introduced genetic material (Echelle and Connor 1989) is slowly decreasing in amplitude. Significant rank concordance in diagnostic allele frequencies among sites and across sampling years indicates directional influences upon temporal allele frequency change. These observations are consistent with the theory of gene flow in neutral clines. Levels of introgression indicated by each of four allozyme loci and mtDNA were roughly equivalent. The early history of the hybrid swarm is explained by genetic swamping, possibly mediated by selection for C. variegatus or C. variegatus × C. pecosensis, at a time when the normally abundant endemic species had been catastrophically depleted. High frequencies of an introduced GPI-A allele in all samples of intergrades suggests that the introduced genome originated with a single founding event.

We conducted an allozyme survey of genetic variation at 33 gene loci in smallmouth bass Micropterus dolomieu from 57 localities encompassing most of the range of the species, but with an emphasis (51 samples) on the Interior Highlands (Ozark and Ouachita uplands). Samples exhibited a moderate amount of total genic diversity (H T ϭ 0.068), but high genetic heterogenity (F ST ϭ 0.383). Phylogenetic analyses supported recognition of three clades from the Interior Highlands: (1) the previously recognized Neosho smallmouth bass in Ozark tributaries of the middle Arkansas River; (2) the Ouachita smallmouth bass in the Little and Ouachita river drainages of the Ouachita Highlands; and (3) a clade that included populations from the White, Black, Missouri, and other streams in the northern and eastern Ozarks. This third clade was very similar to populations from the Ohio and upper Mississippi river basins, and, on the basis of allele frequency parsimony, more closely related to them than to the Neosho and Ouachita smallmouth basses. To preserve genetic diversity and the options that divergent native stocks represent for future management, stock transfers of smallmouth bass should take into account potential effects on native forms of the species.