Genetic diversity and the mating system of a rare Mexican piñon, Pinus pinceana, and a comparison with Pinus maximartinezii (Pinaceae)

Abstract

Weeping piñon (Pinus pinceana) has a restricted and fragmented range, trees are widely scattered within populations, and reproduction is limited. Nevertheless, genetic diversity was high; based on 27 isozyme loci in 18 enzyme systems, unbiased expected heterozygosity averaged 0.174. Differentiation also was high (F(ST) = 0.152), reflecting isolation between southern, central, and northern fragments of the range. Among populations in the northern fragment, F(ST) was only 0.056, and the number of migrants per generation (Nm) was 4.21, which should preclude fixation. Nm between central and southern populations or between them and populations in the northern fragment was lower, 0.99-1.66, indicating a degree of genetic isolation. Multilocus outcrossing rates (t(m)) ranged from 0.836 in the south to 0.897 in the north. Therefore, selfing is low but statistically significant. The equilibrium inbreeding coefficient (F(e)) calculated from t(m) was in good agreement with observed inbreeding coefficients, suggesting that weeping piñon may be near equilibrium with respect to inbreeding and selection against selfed trees. Weeping piñon was variable at all loci polymorphic in maxipiñon (Pinus maximartinezii) and, therefore, qualifies as a possible progenitor of maxipiñon. Because of the high level of diversity, reasonable levels of gene flow within the northern fragment of weeping piñon's range, high rates of outcrossing, and, perhaps, only weak selection against inbred trees, protection in reserves would be a viable option for conservation.

No reduction in genetic diversity of Swiss stone pine (Pinus cembra L.) in Tatra Mountains despite high fragmentation and small population size

“…Selection against inbred progeny is considered the main factor responsible for differences in inbreeding levels between adults and early stages in the life cycle. Our results with an average of F IS = 0.063 were close to those reported for isolated populations of English yew (Chybicki et al 2012) but much lower than for Pinus rzedowskii and P. pinceana, endangered pine species in Mexico (Delgado et al 1999, Ledig et al 2001. We found elevated coancestry coefficients in all populations of P. cembra, which can result from limited gene immigration (Reynolds et al 1983).…”

Lack of allozyme and ISSR variation in the Rare endemic tree species, Berchemia berchemiaefolia (Rhamnaceae) in Korea

“…Likewise, Hamrick and Godt [6] reported that, of the four geographic range categories (endemic, narrow, regional, and widespread), endemic species had the lowest levels of genetic variation: endemic species (100 endemic taxa among the 480 species reviewed) had less than 50% of the genetic diversity of widespread species and 70 and 64% of the genetic diversity of narrowly and regionally distributed species. This trend has been confirmed in other studies [16,18,20], although there are exceptions [13,17,19]. On the other hand, only a few studies have reported a complete absence of genetic variability for rare and/or very locally distributed plant species.…”

Comparative genetic structure in pines: evolutionary and conservation consequences

“…= 2, P > 0.10) between genetic differentiation using these markers when nuclear data is used as the independent variable for P. pinaster, P. pinceana, P halepensis and P. heidrechii var. leucodermis (Table 2, Ledig 1998, Ledig et al 2001. They also show that differentiation estimates using allozymes are always lower t h a n t h o s e o b t a i n e d f r o m c h l o r o p l a s t microsatellites as was also found for Picea glauca by Furnier & Stine (1995).…”

“…In general, direct inbreeding estimates coincide with the expected ones based only on the mating system. In some cases like P. sylvestris (Muona & Szmidt 1991) and P. pinceana (Ledig et al 2001) both estimates are clearly different. This is probably produced by natural selection in favor of heterozygotes or overdominance (see Ledig 1998 for a revision in pines).…”

“…Thirdly, genetic drift could also increase the level of homozygosity. The published estimates of inbreeding (F IS ) in pines range from estimates close to zero to 0.14 for P. pinceana (Ledig et al 2001). On the other hand, outcrossing rates estimates range from 0.65 for P. maximinoi (Matheson et al 1989) to values statistically equal to 100 % outcrossing.…”