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Morphological and genetic analyses of a hybrid zone between short-tailed shrews (Blarina) in Nebraska
Abstract
The parapatric boundary separating Blarina brevicauda and B. hylophaga in Nebraska was trapped to describe boundary characteristics and quantify hybridization. Over 1300 shrews were captured during 23,000 trap nights at six sites. The zone of sympatry between these animals averaged 1.48 km wide; only two individuals were captured greater than two km inside the range of the other species. The boundary has not changed substantially in position in three decades, but is capable of movement, having shifted south 2.4 km in 22 months. The boundary does not follow ecotones but roughly parallels changes in temperature variables, which may determine its location. The boundary is irregularly shaped and often located near roads or creeks. Multivariate analyses of morphological data from 715 shrews from the boundary and 86 reference animals found the two species to be distinct; 49 animals, however, were morphologically intermediate and couldn't be identified to species. These individuals were captured near the boundary, suggesting they are hybrids. Hybrids of trappable age do not appear to suffer reduced survival but may be reproductively less fit than non-hybrids. The similarity of clines for different characters within transects suggests genetic exchange between the species is limited. Genetic analyses were conducted on 190 shrews from the boundary and 60 reference animals. Restriction site analysis of the mitochondrial Cytochrome B gene revealed diagnostic patterns for the reference samples. From the boundary, 17 hybrids were found, recognizable by conflicting morphological and mitochondrial characteristics. These individuals were not morphologically intermediate and probably represent second generation or back-cross hybrids, indicating F1 hybrids are partially fertile. Data also indicate that interspecific mating involves females of both species. While this parapatric boundary might be maintained by selection against hybrids, the impact of interspecific competition or other factors cannot be ruled out. Given the number of parapatric boundaries present in Blarina, the fossil-based evolutionary history proposed, and the morphological difference of extant species, this group might represent a model system for hybrid zone research.
Subject Area
Zoology|Ecology|Genetics
Recommended Citation
Benedict, Russell Adam, "Morphological and genetic analyses of a hybrid zone between short-tailed shrews (Blarina) in Nebraska" (1997). ETD collection for University of Nebraska-Lincoln. AAI9725109.
https://digitalcommons.unl.edu/dissertations/AAI9725109