Steep genetic clines resulting from recent secondary contact between previously isolated taxa can either gradually erode over time or be stabilized by factors such as ecological selection or selection against hybrids. We used patterns of variation in 30 nuclear and two mitochondrial
After decades of discussion, there is little consensus on the extent to which hybrids between endangered and nonendangered species should be protected by
- NSF-PAR ID:
- 10246026
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Molecular Ecology
- Volume:
- 25
- Issue:
- 11
- ISSN:
- 0962-1083
- Page Range / eLocation ID:
- p. 2680-2689
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract SNP s to examine the factors that could be involved in stabilizing clines across a hybrid zone between two subspecies of the Atlantic killifish,Fundulus heteroclitus . Increased heterozygote deficit and cytonuclear disequilibrium in populations near the center of the mtDNA cline suggest that some form of reproductive isolation such as assortative mating or selection against hybrids may be acting in this hybrid zone. However, only a small number of loci exhibited these signatures, suggesting locus‐specific, rather than genomewide, factors. Fourteen of the 32 loci surveyed had cline widths inconsistent with neutral expectations, with twoSNP s in the mitochondrial genome exhibiting the steepest clines. Seven of the 12 putatively non‐neutral nuclear clines were forSNP s in genes related to oxidative metabolism. Among these putatively non‐neutral nuclear clines,SNP s in two nuclear‐encoded mitochondrial genes (SLC 25A3 andHDDC 2), as well asSNP s in the myoglobin, 40S ribosomal protein S17, and actin‐bindingLIM protein genes, had clines that were coincident and concordant with the mitochondrial clines. When hybrid index was calculated using this subset of loci, the frequency distribution of hybrid indices for a population located at the mtDNA cline center was non‐unimodal, suggesting selection against advanced‐generation hybrids, possibly due to effects on processes involved in oxidative metabolism. -
Abstract Questions What are the primary biotic and abiotic factors driving composition and abundance of naturally regenerated tree seedlings across forest landscapes of Maine? Do seedling species richness (
SR ) and density (SD ) decrease with improved growing conditions (climate and soil), but increase with increased diversity of overstorey composition and structure? Does partial harvesting disproportionately favour relative dominance of shade‐intolerant hardwoods (PIHD ) over shade‐tolerant softwoods (PTSD )?Location Forest landscapes across the diverse eco‐regions and forest types of Maine,
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USA and Canada. Despite limitations associated with relatively small plot size, large seedling size class and lack of direct measurements of light, water and nutrients, this study documents the influence of these factors amid high variability associated with patterns of natural regeneration. The curvilinear relationship between mean annual temperature withSR andSD supports the argument that species richness and abundance usually have unimodal relationships with productivity indicators, whereas the curvilinear relationship between overstorey tree size diversity andSR andSD suggest that moderate overstorey diversity incorporates multiple species as well as higher seedling individuals. -
Abstract The arrival to the
U nitedS tates of theA fricanized honey bee, a hybrid betweenE uropean subspecies and theA frican subspecies , is a remarkable model for the study of biological invasions. This immigration has created an opportunity to study the dynamics of secondary contact of honey bee subspecies fromA pis mellifera scutellataA frican andE uropean lineages in a feral population inS outhT exas. An 11‐year survey of this population (1991–2001) showed that mitochondrial haplotype frequencies changed drastically over time from a resident population of eastern and western European maternal ancestry, to a population dominated by theA frican haplotype. A subsequent study of the nuclear genome showed that theA fricanization process included bidirectional gene flow between European and Africanized honey bees, giving rise to a new panmictic mixture of and European‐derived genes. In this study, we examined gene flow patterns in the same population 23 years after the first hybridization event occurred. We found 28 active colonies inhabiting 92 tree cavities surveyed in a 5.14 km2area, resulting in a colony density of 5.4 colonies/km2. Of these 28 colonies, 25 were ofA . m. scutellata‐A. m. scutellata maternal ancestry, and three were of western European maternal ancestry. No colonies of eastern European maternal ancestry were detected, although they were present in the earlier samples. NuclearDNA revealed little change in the introgression of ‐derived genes into the population compared to previous surveys. Our results suggest this feral population remains an admixed swarm with continued low levels of European ancestry and a greater presence of African‐derived mitochondrial genetic composition.A . m. scutellata -
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Abstract Heterospecific mating frequency is critical to hybrid zone dynamics and can directly impact the strength of reproductive barriers and patterns of introgression. The effectiveness of post‐mating prezygotic (
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