Contrasting microsatellite variation between subalpine and western larch, two closely related species with different distribution patterns

Abstract

Subalpine larch (Larix lyallii Parl.) and western larch (Larix occidentalis Nutt.) represent two closely related species with contrasting abundance and distribution patterns in Western North America. Genetic diversity at seven informative microsatellite loci was determined for 19 populations of subalpine larch and nine populations of western larch. Contrasting genetic diversity and patterns of population differentiation were observed between the two species. The overall within-population genetic diversity parameters were lower in subalpine larch (A = 3.2; A(P) = 3.6; H(E) = 0.418) than in western larch (A(P) = 5.51; H(E) = 0.580), a pattern that is likely related to historical or demographic factors. No evidence of interspecific hybridization was observed. Significantly more population differentiation (theta = 0.15; R(ST) = 0.07), consistent with more restricted gene flow, was observed for subalpine larch as compared to western larch (theta = 0.05; R(ST) = 0.04). Under the assumption of an infinite allele mutation model, 12 of the 19 subalpine larch populations showed signs of deviation from the mutation-drift equilibrium, which suggests Holocene population bottlenecks and fluctuations in effective population size for this species. None of the western larch populations deviated significantly from the mutation-drift equilibrium. For both species, Mantel's test revealed a significant positive relationship between geographical and genetic distances indicative of isolation by distance. A similar geographical structure was detected in both species, suggesting at least two genetically distinct glacial populations in each species. The various implications for gene conservation are discussed.

Estimation of population structure in coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] using allozyme and microsatellite markers

“…The mean number of alleles, observed and expected heterozygosities for SSR loci (A=11-36; H o =0.549-0.718; H e =0.877-0.944; see Electronic supplementary materials, Appendix 1) were also relatively higher than those estimated with the same type and number of markers in conifers with wide geographical distributions, such as Larix occidentalis (A=5.5, H o =0.521, H e =0.580; Khasa et al 2006), Pinus strobus (A=9.6, H o =0.522, H e =0.607; Rajora et al 2000;Marquardt and Epperson 2004), Pinus contorta (A=21.0, H e =0.425; Thomas et al 1999), Picea glauca (A=16.4, H o =0.649, H e =0.851; Rajora et al 2005), and also P. menziesii (A=7.5, H e =0.673; Amarasinghe and Carlson 2002) studied earlier. The difference can be explained by the fact that the SSR loci in our study were preselected as the most polymorphic.…”

The effect of long-term historical habitat fragmentation on genetic diversity of the relictual conifer Calocedrus macrolepis (Cupressaceae) in China

“…(H E = 0.58) (Khasa et al 2006) Fitzroya cupressoides I. M. Johnst. (H E = 0.55) (Allnutt et al 1999) and long-lived perennial species (H E = 0.68) (Nybom 2004) (Craft et al 2002).…”

“…The level of gene flow for C. macrolepis (Nm = 1.562) suggests that the genetic diversity in C. macrolepis is low, and the probability of population differentiation has increased due to the fragmentation of habitat. Similar results were found for populations with narrow and fragmented distributions (Larix lyallii Parl., Nm = 1.4, (Khasa et al 2006) and P. pinceana, Nm = 1.39, (Ledig et al 2001). C. macrolepis is wind-pollinated, monoecious, and long-lived, and its small, lightweight seeds have two sub-apical, unequal wings (Wang et al 2004).…”

Genetic differentiation of European larch along an altitudinal gradient in the French Alps

“…It is consistent with the observation made by Pluess (2011) for the same species in the Swiss Alps (H e =0.75, for the five common out of eight microsatellite markers). For other Larix species, genetic diversity may be either similar as in the case of Larix kaempferi in Japan (H e =0.73, for 4 out of 11 common microsatellite markers) (Nishimura and Setoguchi 2010) or lower as observed by Khasa et al (2006) in Larix lyallii and Larix occidentalis (H e =0.42 and 0.58, respectively) in Canada. In this study, the value of the genetic diversity is within the upper range usually detected in trees (on average, H e equals to 0.68; Nybom (2004)).…”