â€" The Gunnison Sage-Grouse ( Centrocercus minimus ) is described as a new species from southwestern Colorado and contrasted with the Sage-Grouse (Centrocercus urophasianus ) from northern Colorado and western North America. Gunnison Sage-Grouse differ from all other described sage-grouse (C. u. urophasianus , C. u. phaios) in morphological measurements, plumage, courtship display, and genetics. The species currently is limited to 8 isolated populations in southwestern Colorado and adjacent San Juan County, Utah. Total estimated spring breeding population is fewer than 5000 individuals with the largest population (<3000) in the Gunnison Basin (Gunnison and Saguache counties), Colorado.

Population divergence can occur due to mechanisms associated with geographic isolation and/or due to selection associated with different ecological niches. Much of the evidence for selection‐driven speciation has come from studies of specialist insect herbivores that use different host plant species; however, the influence of host plant use on population divergence of generalist herbivores remains poorly understood. We tested how diet breadth, host plant species and geographic distance influence population divergence of the fall webworm (Hyphantria cunea; FW). FW is a broadly distributed, extreme generalist herbivore consisting of two morphotypes that have been argued to represent two different species: black‐headed and red‐headed. We characterized the differentiation of FW populations at two geographic scales. We first analysed the influence of host plant and geographic distance on genetic divergence across a broad continental scale for both colour types. We further analysed the influence of host plant, diet breadth and geographic distance on divergence at a finer geographic scale focusing on red‐headed FW in Colorado. We found clear genetic and morphological distinction between red‐ and black‐headed FW, and Colorado FW formed a genetic cluster distinct from other locations. Although both geographic distance and host plant use were correlated with genetic distance, geographic distance accounted for up to 3× more variation in genetic distance than did host plant use. As a rare study investigating the genetic structure of a widespread generalist herbivore over a broad geographic range (up to 3,000 km), our study supports a strong role for geographic isolation in divergence in this system.

Because avian females are heterogametic, the reverse of mammals, avian sex chromosomes undergo significantly different patterns and numbers of DNA replications than do those in mammals. This makes the W (female-specific) and the Z chromosomes an excellent model system for the study of the replicative division hypothesis, which purports that DNA substitution rate is determined by the number of germline replications. The sex-specific chromosome in birds (the W) is predicted to change at the slowest rate of all avian chromosomes because it undergoes the fewest rounds of replication per unit of evolutionary time. Using published data on gametogenesis from a variety of sources, we estimated the ratio of male-to-female germline replications (c) in galliforms and anseriforms to be approximately 4.4. The value of c should predict the value of the ratio of male-to-female mutation rates (alpha(m)) if the replicative division hypothesis is true. Homologous DNA sequences including an intron and parts of two exons of the CHD gene were obtained from the W and the Z chromosomes in ostrich, sage grouse, canvasback duck, tundra swan, and snow goose. The exons show significantly different nucleotide composition from the introns, and the W-linked exons show evidence of relaxed constraint. The Z-linked intron is diverging approximately 3.1 times faster than the W-linked intron. From this, alpha(m) was calculated to be approximately 4.1, with a confidence interval of 3.1 to 5.1. The data support the idea that the number of replicative divisions is a major determinant of substitution rate in the Eoavian genome.

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Mountain Plover (Charadrius montanus) distribution and abundance have been reduced drastically in the past 30 years and the conversion of shortgrass prairie to agriculture has caused breeding populations to become geographically isolated. This, coupled with the fact that Mountain Plovers are thought to show fidelity to breeding grounds, leads to the prediction that the isolated breeding populations would be genetically distinct. This pattern, if observed, would have important management implications for a species at risk of extinction. Our study examined genetic variation at two mitochondrial regions for 20–30 individuals from each of four breeding sites. We found no evidence of significant population differentiation in the data from the control region or the ATPase 6/8 region. Nested-clade analysis revealed no relationship between haplotype phylogeny, and geography among the 47 control region haplotypes. In the ATPase 6/8 region, however, one of the two clades provided information suggesting that, historically, there has been continuous range expansion. Analysis of mismatch distributions and Tajima's D suggest that the Mountain Plover underwent a population expansion, following the Pleistocene glacial period. To explain the lack of detectable genetic differentiation among populations, despite their geographic isolation and fidelity to breeding locations, we speculate that there is sufficient female-mediated gene flow to homogenize gene pools among populations. Such gene flow might ensue if pair bonds are formed in mixed flocks on wintering grounds rather than on the summer breeding grounds. Análisis Genéticos de Poblaciones de Charadrius montanus Usando Secuencias de ADN Mitocondrial Resumen. La distribución y la abundancia de Charadrius montanus se han reducido drásticamente desde hace 30 años y las poblaciones han quedado más aisladas geográficamente debido a la transformación de las praderas de pastos cortos a tierras agrícolas. Estos cambios, combinados con el hecho de que se cree que C. montanus presenta fidelidad a sus áreas de nidificación, sugieren que las poblaciones reproductivas aisladas podrían ser distintas genéticamente. De observarse este patrón, tendría consecuencias importantes para el manejo de esta especie en peligro de extinción. En nuestro estudio, investigamos el patrón de variación genética en dos regiones mitocondriales en 20–30 individuos de C. montanus provenientes de cuatro sitios de nidificación. No encontramos evidencia de diferencias poblacionales significativas en los datos de la región de control, ni en la región de ATPasa 6/ 8. Un análisis de clados anidados reveló que no hay ninguna relación entre haplotipos filogenia y geografía entre los 47 haplotipos de la región de control. Sin embargo, en la región ATPasa 6/8, uno de los dos clados proveyó información que sugiere que la especie ha aumentado históricamente su rango de distribución. Análisis de distribuciones “mismatch” y de la D de Tajima sugieren que la población se expandió después del período glacial del Pleistoceno. Para explicar la falta de diferenciación genética entre las poblaciones, a pesar de su aislamiento geográfico y de la fidelidad a sus sitios de nidificación, especulamos que el flujo de genes es controlado por las hembras de la población de tal modo que los acervos génicos son bastante homogéneos entre las poblaciones. Dicho flujo de genes podría ocurrir si se formaran las parejas en las bandadas mixtas en el invierno, no en el verano cuando están en sus áreas de nidificación.