Back from the brink: potential for genetic rescue in a critically endangered tree

Abstract

Rare plant species are vulnerable to genetic erosion and inbreeding associated with small population size and isolation due to increasing habitat fragmentation. The degree to which these problems undermine population viability remains debated. We explore genetic and reproductive processes in the critically endangered long-lived tropical tree Medusagyne oppositifolia, an endemic to the Seychelles with a naturally patchy distribution. This species is failing to recruit in three of its four populations. We evaluate whether recruitment failure is linked to genetic problems associated with fragmentation, and if genetic rescue can mitigate such problems. Medusagyne oppositifolia comprises 90 extant trees in four populations, with only the largest (78 trees) having successful recruitment. Using 10 microsatellite loci, we demonstrated that genetic diversity is high (H(E) : 0.48-0.63; H(O) : 0.56-0.78) in three populations, with only the smallest population having relatively low diversity (H(E) : 0.26 and H(O) : 0.30). All populations have unique alleles, high genetic differentiation, and significant within population structure. Pollen and seed dispersal distances were mostly less than 100 m. Individuals in small populations were more related than individuals in the large population, thus inbreeding might explain recruitment failure in small populations. Indeed, inter-population pollination crosses from the large donor population to a small recipient population resulted in higher reproductive success relative to within-population crosses. Our study highlights the importance of maintaining gene flow between populations even in species that have naturally patchy distributions. We demonstrate the potential for genetic and ecological rescue to support conservation of plant species with limited gene flow.

Contemporary pollen-mediated gene immigration reflects the historical isolation of a rare, animal-pollinated shrub in a fragmented landscape

“…teretifolius populations that were previously separated by woodland habitat that acted as a barrier to pollen migration between populations are now separated by cleared agricultural land that acts as a contemporary barrier. Reported estimates of pollen immigration into populations of species with rare or naturally patchy populations range from low (4.3-16.5%; Bittencourt and Sebbenn, 2007;Muller et al, 2009;Finger et al, 2011;Llorens et al, 2012) to high (43-77%;OddouMuratorio and Klein, 2008;Lander et al, 2010). Reported changes in immigration levels in recently fragmented species include both increases Bacles and Jump, 2011) and decreases (Robledo-Arnuncio and Gill, 2005;Sebbenn et al, 2011).…”

“…Conservation strategies for some rare species have included genetic rescue through artificial crosses in species with low gene flow (Finger et al, 2011) but in others, genetic connectivity may not be a high conservation priority (Lander et al, 2010).…”

Long-term experimental hybrid swarms between nearly incompatible Tigriopus californicus populations: persistent fitness problems and assimilation by the superior population

“…While some intentional hybridizations appear to have been successful (e.g. Pimm et al 2006;Finger et al 2011), they run the risk of producing offspring that are intrinsically unfit or poorly adapted to local conditions (Hatfield and Schluter 1999;Huff et al 2011). Accidental mixing of populations or species can also occur through the spread of invasive species (Bleeker et al 2007;Gilchrist and Lee 2007), potentially threatening the biodiversity of native species (Barilani et al 2005;Halis and Morley 2005;Muhlfeld et al 2009).…”

Cryptic genetic subdivision in the San Benito evening primrose (Camissonia benitensis)

“…Gene flow between C. benitensis populations is not enough to reduce inter-population differentiation as most genetic variation occurred among populations. The observed low gene flow could be due to short seed dispersal distances (Colling et al 2010;England et al 2002;Finger et al 2011;Furches et al 2009;Schaal 1980). Seed dispersal is most likely the primary gene flow mechanism in self-pollinated plants where pollen flow is rare.…”