Abstract
Examining the factors that influence contemporary genetic patterns is important given the alarming rate at which natural environments are changing. In particular habitat fragmentation and climate change are expected to influence the distribution and diversity of natural populations. In this study we used both mitochondrial control region (mtDNA) and microsatellite data to answer the following questions about genetic diversity and divergence in mountain chickadees (Poecile gambeli) a resident bird species in western North America: (1) Do populations exhibit similar levels of genetic diversity across the range? (2) What is the genetic affinity of western populations in Oregon and Washington? (3) Do genetic patterns exhibit isolation by distance, or are genetic patterns more heavily influenced by habitat discontinuity? We tested the effects of isolation by distance and habitat distribution on genetic structure by analyzing 266 samples from 17 sites across western Canada and the United States. We found a near significant relationship between genetic diversity and latitude, however, our results indicate that overall, latitude is not a strong predictor of genetic diversity. Our analyses of populations in Oregon and Washington revealed a mismatch between patterns detected with mtDNA and microsatellite data. In particular, Washington clustered with the Coast Range/Cascades/Rocky Mountain mtDNA group, but with populations in southern Oregon/California based on microsatellite data. These results suggest the presence of a contact zone in Washington between the two mtDNA clades Coast Range/Cascades/Rocky Mountain and southern Oregon/California clades. Finally, our study revealed a greater effect of isolation by distance than isolation by habitat for both mtDNA and microsatellite data. Overall the isolation by distance signal was greater for mtDNA than microsatellite patterns. The greater signal of isolation by distance on mtDNA patterns likely reflects the strong effects of Pleistocene glaciations in shaping genetic patterns in western North America.
Highlights
Examining the factors that influence contemporary genetic patterns is important given the alarming rate at which natural environments are changing
In addition to exploring genetic structure, we sought to answer the following questions: (1) Do populations exhibit similar levels of genetic diversity across the range? Given that their range includes areas that were glaciated during the last glacial maximum (LGM), it allows us to test if younger populations exhibit similar levels of genetic diversity as older populations; (2) What is the genetic affinity of western populations in Oregon and Washington? Previous research found eastern and western clades, but did not sample the area separating these two groups
In this study we sought to answer the following questions: (1) Do populations exhibit similar levels of genetic diversity across the range? (2) What is the genetic affinity of western populations in Oregon and Washington? (3) Do genetic patterns exhibit isolation by distance, or are genetic patterns more heavily influenced by breaks in habitat? Across the range, we found a near-significant positive correlation between latitude and mitochondrial DNA (mtDNA) genetic diversity using both a linear model and RDA approach, and microsatellite genetic diversity using an RDA approach only
Summary
Examining the factors that influence contemporary genetic patterns is important given the alarming rate at which natural environments are changing. The greater signal of isolation by distance on mtDNA patterns likely reflects the strong effects of Pleistocene glaciations in shaping genetic patterns in western North America. In the Pacific Northwest, the legacy of the last glacial maximum (LGM) combined with contemporary landscape features on population genetic structure is especially evident. Within this region, many subalpine species exhibit concordant genetic breaks associated with habitat fragmentation and isolation across arid, low elevation barriers, emphasizing the role of habitat discontinuity on genetic diversity and population differentiation[9,10,11,12,13,14]. Mountain ranges, and habitat discontinuities have all been shown to limit dispersal and promote genetic differentiation between populations[21,22,23]
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