Historic hybridization and persistence of a novel mito-nuclear combination in red-backed voles (genus Myodes)

<p>Abstract</p> <p>Background</p> <p>The role of hybridization in generating diversity in animals is an active area of discovery and debate. We assess hybridization across a contact zone of northern (<it>Myodes rutilus</it>) and southern (<it>M. gapperi</it>) red-backed voles using variation in skeletal features and both mitochondrial and nuclear loci. This transect extends approximately 550 km along the North Pacific Coast of North America and encompasses 26 populations (n = 485). We establish the history, geographic extent and directionality of hybridization, determine whether hybridization is ongoing, and assess the evolutionary stability of novel genomic combinations.</p> <p>Results</p> <p>Identification of <it>M. rutilus </it>and <it>M. gapperi </it>based on the degree of closure of the post-palatal bridge was concordant with the distribution of diagnostic nuclear MYH6 alleles; however, an 80 km zone of introgressed populations was identified. The introgressant form is characterized by having mitochondrial haplotypes closely related to the northern <it>M. rutilus </it>on a nuclear background and morphological characteristics of southern <it>M. gapperi</it>.</p> <p>Conclusion</p> <p>Introgression appears to have been historic as pure populations of <it>M. rutilus </it>are now isolated to the north from introgressants or pure <it>M. gapperi </it>by the LeConte Glacier. As we do not find pure <it>M. rutilus </it>or <it>M. gapperi </it>individuals throughout the distribution of the introgressant form, it appears that the introgressants are a self-sustaining entity not requiring continued hybridization between pure parental forms to generate this novel combination of characters.</p

The Heather Vole, Genus Phenacomys, in Alaska

Four specimens of heather vole (genus Phenacomys) collected in the coastal mountains of Southeast Alaska document the first Recent records of this vole in Alaska. Alternative hypotheses on the relationship of these newly-discovered populations to extant and historical populations are outlined, and additional studies proposed

The complexities of female mate choice and male polymorphisms: Elucidating the role of genetics, age, and mate-choice copying

Genetic, life history, and environmental factors dictate patterns of variation in sexual traits within and across populations, and thus the action and outcome of sexual selection. This study explores patterns of inheritance, diet, age, and mate-choice copying on the expression of male sexual signals and associated female mate choice in a phenotypically diverse group of Schizocosa wolf spiders. Focal spiders exhibit one of two male phenotypes: ‘ornamented’ males possess large black brushes on their forelegs, and ‘non-ornamented’ males possess no brushes. Using a quantitative genetics breeding design in a mixed population of ornamented/non-ornamented males, we found a strong genetic basis to male phenotype and female choice. We also found that some ornamented males produced some sons with large brushes and others with barely visible brushes. Results of diet manipulations and behavioral mating trials showed no influence of diet on male phenotype or female mate choice. Age post maturation, however, influenced mate choice, with younger females being more likely to mate with ornamented males. A mate-choice copying experiment found that, following observations of another female’s mate choice/copulation, virgin mature females tended to match the mate choice (ornamented vs. non-ornamented males) of the females they observed. Finally, analyses of genetic variation across phenotypically pure (only one male phenotype present) vs. mixed (both phenotypes present) populations revealed genetic distinction between phenotypes in phenotypically-pure populations, but no distinction in phenotypically-mixed populations. The difference in patterns of genetic differentiation and mating across geographic locations suggests a complex network of factors contributing to the outcome of sexual selection

The complexities of female mate choice and male polymorphisms: Elucidating the role of genetics, age, and mate-choice copying

Genetic, life history, and environmental factors dictate patterns of variation in sexual traits within and across populations, and thus the action and outcome of sexual selection. This study explores patterns of inheritance, diet, age, and mate-choice copying on the expression of male sexual signals and associated female mate choice in a phenotypically diverse group of Schizocosa wolf spiders. Focal spiders exhibit one of two male phenotypes: ‘ornamented’ males possess large black brushes on their forelegs, and ‘non-ornamented’ males possess no brushes. Using a quantitative genetics breeding design in a mixed population of ornamented/non-ornamented males, we found a strong genetic basis to male phenotype and female choice. We also found that some ornamented males produced some sons with large brushes and others with barely visible brushes. Results of diet manipulations and behavioral mating trials showed no influence of diet on male phenotype or female mate choice. Age post maturation, however, influenced mate choice, with younger females being more likely to mate with ornamented males. A mate-choice copying experiment found that, following observations of another female’s mate choice/copulation, virgin mature females tended to match the mate choice (ornamented vs. non-ornamented males) of the females they observed. Finally, analyses of genetic variation across phenotypically pure (only one male phenotype present) vs. mixed (both phenotypes present) populations revealed genetic distinction between phenotypes in phenotypically-pure populations, but no distinction in phenotypically-mixed populations. The difference in patterns of genetic differentiation and mating across geographic locations suggests a complex network of factors contributing to the outcome of sexual selection

First Records of the Southern Red-backed Vole, Myodes gapperi, in the Yukon

Twenty Southern Red-backed Voles, Myodes gapperi, were collected in July 2004 in the LaBiche River valley of southeastern Yukon. Specimens were identified using morphological characteristics and analysis of cytochrome b gene sequences. These are the first records of this species in the Yukon. No Northern Red-backed Voles, M. rutilus, were collected and it is not known whether the two species are sympatric or parapatric in the Yukon. Further survey work is needed in southeastern Yukon to better delineate the extent of the northwestern range of this species and the extent, if any, of introgression with M. rutilus

Mammal Fleas (Siphonaptera: Ceratophyllidae) New for Alaska and the Southeastern Mainland Collected During Seven Years of a Field Survey of Small Mammals

Ten taxa of mammal fleas were among 124 collection records from 12 host species (one shrew, nine rodents and two carnivores), at 72 localities on the southeastern Alaska mainland in 1989 and during an extensive survey of mammals in 1992-1995 and 1997-1999. Megabothris asio megacolpus (Jordan) ex Microtus pennsylvanicus (Ord), Malaraeus telchinus (Rothschild) ex Peromyscus keeni (Rhoads) and Clethrionomys gapperi (Vigors) are new fleas for Alaska. Orchopeas caedens (Jordan) ex Tamiasciurus hudsonicus (Erxleben) is a new flea for southeastern Alaska. Synaptomys borealis (Richardson) is a new host record for Opisodasys k. keeni (Baker). The other six taxa of fleas collected were Hystrichopsylla dippiei spinata Holland, H. o. occidentalis Holland, Catallagia charlottensis (Baker), Ceratophyllus ciliatus protinus Jordan, Megabothris abantis (Rothschild) and Opisodasys vesperalis (Jordan). Of these, H. o. occidentalis, C. charlottensis and M. abantis have seven new host records for the southeastern Alaska mainland. Distribution patterns of the fleas and their host relationships in North America are discussed

Evolution of Duplicated β-Globin Genes and the Structural Basis of Hemoglobin Isoform Differentiation in \u3ci\u3eMus\u3c/i\u3e

The functional diversification of multigene families may be strongly influenced by mechanisms of concerted evolution such as interparalog gene conversion. The β-globin gene family of house mice (genus Mus) represents an especially promising system for evaluating the effects of gene conversion on the functional divergence of duplicated genes. Whereas the majority of mammalian species possess tandemly duplicated copies of the adult β-globin gene that are identical in sequence, natural populations of house mice are often polymorphic for distinct two-locus haplotypes that differ in levels of functional divergence between duplicated β-globin genes, HBB-T1 and HBB-T2. Here, we use a phylogenetic approach to unravel the complex evolutionary history of the HBB-T1 and HBB-T2 paralogs in a taxonomically diverse set of species in the genus Mus. The main objectives of this study were 1) to reconstruct the evolutionary history of the different HBB haplotypes of house mice, 2) to assess the role of recombinational exchange between HBB-T1 and HBB-T2 in promoting concerted evolution, 3) to assess the role of recombinational exchange between HBB-T1 and HBB-T2 in creating chimeric genes, and 4) to assess the structural basis of hemoglobin isoform differentiation in species that possess distinct HBB paralogs. Results of our phylogenetic survey revealed that the HBB-T1 and HBB-T2 genes in different species of Mus exhibit the full range of evolutionary outcomes with respect to levels of interparalog divergence. At one end of the spectrum, the two identical HBB paralogs on the Hbbs haplotype (shared by Mus domesticus, Mus musculus, and Mus spretus) represent a classic example of concerted evolution. At the other end of the spectrum, the two distinct HBB paralogs on the Hbbd, Hbbp, Hbbw1, and Hbbw2 haplotypes (shared by multiple species in the subgenus Mus) show no trace of gene conversion and are distinguished by a number of functionally important amino acid substitutions. Because the possession of distinct HBB paralogs expands the repertoire of functionally distinct hemoglobin isoforms that can be synthesized during fetal development and postnatal life, variation in the level of functional divergence between HBB-T1 and HBB-T2 may underlie important physiologica