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Short-tailed shrews (genus Blarina Gray, 1838) are characterized by divergent karyotypes and are genetically distinct. Blarina species are similar morphologically but, in most cases, can be distinguished morphometrically. Blarina distributions tend to be parapatric along well-defined contact zones; however, it has been suggested that the northern short-tailed shrew (Blarina brevicauda (Say, 1823)) and Elliot's short-tailed shrew (Blarina hylophaga Elliot, 1899) occur sympatrically in Iowa and Missouri. To evaluate this possibility, 179 specimens were collected in southwestern Iowa and northwestern Missouri. Karyotypes and total length were used for field identification, and amplified fragment length polymorphism (AFLP) analysis was used to verify field identifications and to investigate the extent of hybridization. One hundred seventyeight of 179 specimens were identified to species. The one exception had a karyotype of B. brevicauda (2n = 50, FN = 48); however, AFLP analysis indicated that this individual was likely an F1 hybrid. No backcrosses were detected, so it appears that introgression is minimal. The putative hybrid was trapped at a locality with B. brevicauda just north of a locality having only B. hylophaga. No locality contained both species. Therefore, these species are not broadly sympatric as has been suggested, but rather exhibit a distribution similar to the pattern of parapatry seen in most of the contact zones of Blarina.Résumé : Les musaraignes à queue courte (du genre Blarina Gray, 1838) se caractérisent par des caryotypes divergents et sont génétiquement distinctes. Les espèces de Blarina sont semblables morphologiquement, mais dans la plupart des cas, la morphométrie permet de les distinguer. Les répartitions des Blarina ont tendance à être parapatriques le long de zones de contact bien définies; on croit néanmoins que la grande musaraigne à queue courte (Blarina brevicauda (Say, 1823)) et la musaraigne à queue courte d'Elliot (Blarina hylophaga Elliot, 1899) se retrouvent en sympatrie en Iowa et au Missouri. Afin de vérifier cette possibilité, nous avons récolté 179 spécimens dans le sud-ouest de l'Iowa et le nord-ouest du Missouri. Les caryotypes et la longueur totale nous ont servi pour les identifications de terrain et une analyse du polymorphisme des longueurs des segments amplifiés (AFLP) a permis de confirmer les identifications de terrain et de déterminer l'importance de l'hybridation. Des 179 spécimens, 178 ont été identifiés à l'espèce. La seule exception avait un caryotype de B. brevicauda (2n = 50, FN = 48); cependant l'analyse de ALFP indique que cet individu est vraisemblablement un hybride de F1. Comme il n'y a aucune indication de rétrocroisement, l'introgression semble minimale. L'hybride putatif a été piégé dans une localité contenant B. brevicauda située juste au nord d'une localité où vit seulement B. hylophaga. Aucune localité ne contient les deux espèces. Les deux espèces ne possèdent donc pas une importante zone de sympatrie, comme on le croyait; ils ont plu...
Short-tailed shrews (genus Blarina Gray, 1838) are characterized by divergent karyotypes and are genetically distinct. Blarina species are similar morphologically but, in most cases, can be distinguished morphometrically. Blarina distributions tend to be parapatric along well-defined contact zones; however, it has been suggested that the northern short-tailed shrew (Blarina brevicauda (Say, 1823)) and Elliot's short-tailed shrew (Blarina hylophaga Elliot, 1899) occur sympatrically in Iowa and Missouri. To evaluate this possibility, 179 specimens were collected in southwestern Iowa and northwestern Missouri. Karyotypes and total length were used for field identification, and amplified fragment length polymorphism (AFLP) analysis was used to verify field identifications and to investigate the extent of hybridization. One hundred seventyeight of 179 specimens were identified to species. The one exception had a karyotype of B. brevicauda (2n = 50, FN = 48); however, AFLP analysis indicated that this individual was likely an F1 hybrid. No backcrosses were detected, so it appears that introgression is minimal. The putative hybrid was trapped at a locality with B. brevicauda just north of a locality having only B. hylophaga. No locality contained both species. Therefore, these species are not broadly sympatric as has been suggested, but rather exhibit a distribution similar to the pattern of parapatry seen in most of the contact zones of Blarina.Résumé : Les musaraignes à queue courte (du genre Blarina Gray, 1838) se caractérisent par des caryotypes divergents et sont génétiquement distinctes. Les espèces de Blarina sont semblables morphologiquement, mais dans la plupart des cas, la morphométrie permet de les distinguer. Les répartitions des Blarina ont tendance à être parapatriques le long de zones de contact bien définies; on croit néanmoins que la grande musaraigne à queue courte (Blarina brevicauda (Say, 1823)) et la musaraigne à queue courte d'Elliot (Blarina hylophaga Elliot, 1899) se retrouvent en sympatrie en Iowa et au Missouri. Afin de vérifier cette possibilité, nous avons récolté 179 spécimens dans le sud-ouest de l'Iowa et le nord-ouest du Missouri. Les caryotypes et la longueur totale nous ont servi pour les identifications de terrain et une analyse du polymorphisme des longueurs des segments amplifiés (AFLP) a permis de confirmer les identifications de terrain et de déterminer l'importance de l'hybridation. Des 179 spécimens, 178 ont été identifiés à l'espèce. La seule exception avait un caryotype de B. brevicauda (2n = 50, FN = 48); cependant l'analyse de ALFP indique que cet individu est vraisemblablement un hybride de F1. Comme il n'y a aucune indication de rétrocroisement, l'introgression semble minimale. L'hybride putatif a été piégé dans une localité contenant B. brevicauda située juste au nord d'une localité où vit seulement B. hylophaga. Aucune localité ne contient les deux espèces. Les deux espèces ne possèdent donc pas une importante zone de sympatrie, comme on le croyait; ils ont plu...
Blarina brevicauda is distributed across the northeastern region of North America, in areas previously covered by Pleistocene glaciers. Previous molecular systematic study of the species in the genus Blarina suggested the presence of two distinct eastern and western phylogroups within B. brevicauda, in agreement with traditionally recognized semi-species. To expand the previous work, a collection of 76 individuals from 14 localities collected throughout the range of B. brevicauda was used to assess the mitochondrial (mt) cytochrome b genealogy for this species. Minimum evolution, maximum parsimony, analysis of molecular variance and nested clade analysis each supported the same conclusions of two well-differentiated and monophyletic east-west groups, separated by the Mississippi River. Denser sampling in areas immediately East of the Mississippi basin revealed further subdivision within the eastern phylogroup into an East-Central and an Appalachian clade. The western phylogroup differed from the eastern phylogroup by 2.5% mean absolute DNA sequence difference. About 65% of the genetic variance among samples was explained by the east-west subdivision alone. High haplotype diversities, low nucleotide diversities and unimodal mismatch distributions within subclades suggest recent expansion or diversification within each group. No phylogeographic structure was found within the western phylogroup, but genetic structure because of restricted gene flow and isolation by distance was inferred for the eastern group. The present distribution of B. brevicauda is best explained by past fragmentation and range expansion events during and following the Pleistocene glacial cycles.
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