Conservation genetics of Magnolia acuminata, an endangered species in Canada: Can genetic diversity be maintained in fragmented, peripheral populations?

Abstract

The genetic diversity of peripheral populations is potentially important to the future adaptive capacity of species, although may be difficult to predict. A large number of species-at-risk in Canada are at the northern edge of their distribution, and many of these live in fragmented habitat. We used nuclear and chloroplast markers to assess patterns of genetic diversity and differentiation within and among populations of Canadian Magnolia acuminata (Cucumber tree), an endangered species in Canada that extends as far north as the fragmented Carolinian forest in southern Ontario. We also compared the genetic composition of Canadian M. acuminata to populations sampled throughout its central distribution in the USA. We found a high proportion of shared microsatellite alleles, plus a single cpDNA haplotype, distributed throughout the entire M. acuminata range. We also found that despite occupying fragmented habitat at their range periphery, Canadian populations showed little reduction in genetic diversity relative to the USA populations, and we attribute this to effective historical dispersal in a longlived, polyploid species. However, a combination of private alleles, genetic substructuring, and lower levels of genetic diversity in seedlings compared to mature trees, suggests that current levels of gene flow are relatively low among Canadian populations. Therefore, despite high levels of genetic diversity in Canadian M. acuminata, managers should be aware that without intervention, populations will likely become increasingly isolated and experience a reduction in genetic diversity which in turn may threaten their long-term survival in Canada.

The genetic structure of Celtis tenuifolia and comparisons to the related species C. occidentalis, and C. laevigata: Implications for the conservation management of threatened populations in Southern Ontario

“…This was verified by another recent study concerning the endangered species Magnolia acuminata (Linnaeus) Linnaeus which showed little reduction in genetic diversity from their fragmented peripheral populations in Canada to the core populations in the U.S. This was attributed to effective pollen dispersal over the long-lived history of the species (Budd, et al 2015).…”

“…This can in turn lead to poor recruitment and reduced fitness. (Young, et al, 1996, Budd et al, 2015.…”

Population Genetic Diversity and Structure of Threatened Magnolia Species in Western Mexico

“…We found levels of genetic diversity comparable to those obtained for M. acuminata, a species distributed in Canada and the United States, and other species distributed in Japan, such as M. stellata and M. kobus. The high levels of genetic diversity found in these species were partly explained by historical dynamics [19,59,61].…”

“…Population genetic studies of Magnolia species have shown different patterns of genetic diversity and gene ow [19,20,22,23], suggesting that the genetic patterns are dependent on the evolutionary history of populations and the strength of stochastic forces that each Magnolia species had experienced. We found levels of genetic diversity comparable to those obtained for M. acuminata, a species distributed in Canada and the United States, and other species distributed in Japan, such as M. stellata and M. kobus.…”

“…Population genetic studies in the Americas showed different levels of genetic diversity and gene ow patterns, suggesting that population parameters are highly dependent on the strength of stochastic forces that each Magnolia species experienced. North American populations of M. acuminata and M. schiedeana have high genetic diversity with moderate to high genetic structure [19,20], and gene ow between populations of M. cubensis could be facilitated because their seeds can be transported among fragmented habitats by birds [21,22]. Even within the same geographic region, different patterns of gene ow were suggested for Magnolia species in southern [23] and western [12] Mexico.…”