Abstract
Genetic diversity is a critical resource for species’ survival during times of environmental change. Conserving and sustainably managing genetic diversity requires understanding the distribution and amount of genetic diversity (in situ and ex situ) across multiple species. This paper focuses on three emblematic and IUCN Red List threatened oaks (Quercus, Fagaceae), a highly speciose tree genus that contains numerous rare species and poses challenges for ex situ conservation. We compare the genetic diversity of three rare oak species—Quercus georgiana, Q. oglethorpensis, and Q. boyntonii—to common oaks; investigate the correlation of range size, population size, and the abiotic environment with genetic diversity within and among populations in situ; and test how well genetic diversity preserved in botanic gardens correlates with geographic range size. Our main findings are: (1) these three rare species generally have lower genetic diversity than more abundant oaks; (2) in some cases, small population size and geographic range correlate with genetic diversity and differentiation; and (3) genetic diversity currently protected in botanic gardens is inadequately predicted by geographic range size and number of samples preserved, suggesting non-random sampling of populations for conservation collections. Our results highlight that most populations of these three rare oaks have managed to avoid severe genetic erosion, but their small size will likely necessitate genetic management going forward.
Highlights
Genetic diversity is a critical resource for species to adapt to future challenges including pests and diseases, climate change, and other environmental changes
We compare the genetic diversity of three rare oak species—Quercus georgiana, Q. oglethorpensis, and Q. boyntonii—to common oaks; investigate the correlation of range size, population size, and the abiotic environment with genetic diversity within and among populations in situ; and test how well genetic diversity preserved in botanic gardens correlates with geographic range size
We found that genetic diversity and differentiation were influenced by both population size and range size, but that patterns did not perfectly accord to predictions
Summary
Genetic diversity is a critical resource for species to adapt to future challenges including pests and diseases, climate change, and other environmental changes. While genetic diversity has been assessed in hundreds of rare species globally, there are few comparative, multispecies studies of the influence of range size, environmental, and demographic variables on genetic diversity in rare species. Previous studies have shown that, on average, species with larger range sizes (and more populations, larger populations, and lower genetic drift) have higher genetic diversity [4,5,6]. Environmental factors may influence genetic diversity at certain loci through selection by climate or habitat [8,9], or may influence genetic diversity genome-wide through drift as population sizes are reduced or fluctuate in size [10]
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