Effects of population disjunction on isozyme variation in the widespread Pilgerodendron uviferum

Abstract

Geographical range is considered a good predictor of the levels of isozyme variation in plants. Widespread species, often consisting of historically larger and more continuous populations, maintain higher polymorphism and are less aected by drift, which tends to erode genetic variation in more geographically restricted species. However, widespread species occurring in small and disjunct populations may not ®t this pattern. In this study we examined genetic variation in Pilgerodendron uviferum, a conifer endemic to temperate forests of southern South America, and is such a widespread and habitat-restricted species. Twenty populations along the whole range of Pilgerodendron were analysed by isozyme electrophoresis to resolve 14 putative genetic loci. Eleven were polymorphic in at least one population although only six of them were polymorphic in more than one population. We found reduced within-population levels of isozyme variation, with only 11% polymorphic loci (0.95 criterion), 1.2 mean number of alleles per locus, and mean observed and expected heterozygosities of 0.024 and 0.033, respectively. Most genetic diversity was found within populations (H T 0.039, H S 0.033, F ST 15%). Greater polymorphism and lower divergence was estimated in the more geographically restricted and closely related Fitzroya. Thus, total range, in combination with information on the degree of among-population isolation, may be a better predictor of the levels of polymorphism than range size alone.

Can the reproductive system of a rare and narrowly endemic plant species explain its high genetic diversity?

“…While these attributes generally suggest a depletion of genetic diversity (Ellstrand & Elam 1993), they are not reliable predictors of genetic dynamics (Premoli et al 2001), as is demonstrated by our findings in P. secreta. The rate of seed germinability in endogamous treatments was at least equivalent to that obtained from outcrossing (Fig.…”

Genetic differentiation and diversity analysis of medicinal tree Syzygium cumini (Myrtaceae) from ecologically different regions of India

“…Further, Salvador et al (2000) showed that a range in genetic variation of forest tree from low to very high depending upon specific population. Broader area of sampling from geographically distinct populations is the possible cause of high gene diversity in present study (Premoli et al, 2001). …”

Genetic structure of Tunisian natural carob tree (Ceratonia siliqua L.) populations inferred from RAPD markers

“…The genetic structure of plant populations reflects the interactions among different factors, including the long-term evolutionary history of the species, genetic drift, mating system, gene flow and selection (Burgarella et al, 2007;Schaal et al, 1998). Geographically disjunct populations showed higher genetic structure than populations with more continuous distributions (Hamrick and Godt 1996;Premoli et al, 2001). The fragmentation of carob populations associated probably to a limited movement of pollinators and seed dispersal are the main factors affecting gene flow and differentiation among population.…”