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Abstract Detail

Reasons for Rarity? Exploring Acclimatory and Adaptive Constraints to Commonness

Lindsey, Annie [1], Baskauf, Carol [2].

Comparing the population genetics of two eastern Boechera (Brassicaceae): the widespread B. laevigata and its rare congener, B. perstellata.

Congeneric comparisons of genetic diversity can provide phylogenetic context and more nuanced understandings of evolutionary and environmental forces shaping species' population genetic structure. As the most widespread Boechera in eastern North America,  B. laevigata's geographic range contrasts with the extremely narrow range of the rare B. perstellata. To contextualize the low diversity reported for B. perstellata, we conducted a population genetics study of 15 B. laevigata populations across 11 states. Sixteen polymorphic microsatellites were resolved with population-level polymorphism ranging from 6.3 to 93.8%. Alleles per locus ranged from 2 to 28 for the species, with a population average of 1.8 alleles per locus. Excess heterozygosity exhibited in three populations was attributed to apomictic reproduction. While the remaining populations likely reproduce sexually with extensive inbreeding, the possibility of some degree of apomixis cannot be excluded; thus, all analyses were conducted on a full data set as well as a data set consisting of only unique multilocus genotypes (MLGs). From a sample of 304 individuals, 155 unique MLGs were identified, with no shared MLGs across populations. Only one "sexual" population had significant linkage disequilibrium (LD) at most loci, but three had LD at a few loci. Across all populations, there was no significant LD among locus pairs. Genotype frequencies departed from Hardy-Weinberg expectations at most polymorphic loci in each population. For "sexual" populations, observed heterozygosity was less than expected, resulting in high FIS ­ estimates and suggesting substantial inbreeding. The three "apomictic" populations had high levels of fixed heterozygosity. For "sexual" populations, 69% of genetic variation was due to population differentiation. For "apomictic" populations, only 24% of genetic variation was due to differences among populations, with most variation occurring within individuals. Comparing "sexual" populations of B. laevigata with B. perstellata at 11 loci assayed for both species, B. laevigata populations averaged more polymorphic loci, more alleles per polymorphic locus, and higher observed and expected heterozygosity than populations of the rare B. perstellata. Although both exhibited a high degree of population differentiation and potential inbreeding, as indicated by high FST and FIS estimates, these values were greater in B. perstellata than in B. laevigata. Such patterns are consistent with many studies that have found widespread species to have higher levels of genetic diversity than their rare relatives. Our results indicate that examination of reproductive modes in B. laevigata populations is warranted and would contribute to understanding the complexities of the North American Boechera species.

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1 - Austin Peay State University, Biology, 681 Summer St, Clarksville, TN, 37040, USA
2 - Biology, 681 Summer St., Clarksville, TN, 37040, United States

Population Genetics
Boechera laevigata
Boechera perstellata
Congeneric comparison.

Presentation Type: Colloquium Presentations
Session: C06, Reasons for Rarity? Exploring Acclimatory and Adaptive Constraints to Commonness
Location: /
Date: Wednesday, July 21st, 2021
Time: 5:00 PM(EDT)
Number: C06007
Abstract ID:597
Candidate for Awards:None

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