Land barriers and open oceans: effects on gene diversity and population structure in Avicennia germinans L. (Avicenniaceae)

Abstract

Avicennia germinans L. is a widespread mangrove species occupying the west coast of Africa and the Atlantic and Pacific coasts of the Americas from the Bahamas to Brazil and Baja California to Peru. An amplified fragment length polymorphism (AFLP) molecular analysis was carried out to assess genetic architecture within this species and to evaluate the effects of the Atlantic Ocean and the Central American Isthmus (CAI) on population and regional genetic diversity and differentiation. In total, 349 polymorphic AFLP fragments were identified among 144 individuals from 14 populations from the east Atlantic, west Atlantic and east Pacific. Levels of genetic diversity varied considerably among populations, but were generally higher in populations from the east Atlantic. Regional differentiation between the Pacific coast and Atlantic populations was greater than between east and west Atlantic populations, suggesting that the CAI has had an important influence on population genetic structure in this species. The lower level of divergence of east Atlantic from west Atlantic populations suggests some dispersal across the Atlantic Ocean, although migration rates are probably low; Nm from GST equal to 0.41 and accumulation of private and rare alleles in the east Atlantic. Population differentiation did not appear to follow an isolation by distance model and has probably resulted from complex patterns of population bottlenecks, and founder events due to landscape changes during the Pleistocene, particularly in the west Atlantic. The molecular data provide no support for the treatment of east Atlantic populations as a separate species A. africana.

Genetic variation of Avicennia marina (Forsk.) Vierh. (Avicenniaceae) in Vietnam revealed by microsatellite and AFLP markers

“…In general, both the proportion of polymorphic loci (P) and the average heterozygosity (H) for over all populations (P= 0.601 and H=0.086) was lower than the values found by Maguire et al (2002)(P = 1.000 and H = 0.193). They were also lower than the values reported by Dodd et al (2002) for populations of A. germinans (P = 0.980 and H = 0.212). This result is in congruent with that of microsatellite.…”

“…Similarly, high values of genetic differentiation have been found in worldwide populations of A. marina using microsatellite analysis (F ST = 0.410, Maguire et al, 2000b) and allozyme analysis (F ST = 0.384, Duke et al, 1998), and AFLP analysis for Avicennia germinans (F ST = 0.410, Dodd et al, 2002). These values are higher than that found by AFLP analysis in land tree species (e.g., F ST = 0.083 in Quercus mongolica var.…”

“…In our study, the populations were discrete and separated by at least 100 kilometers. Additionally, because of the root system in A. marina, fruits that fall from trees are trapped in the pneumatophores, resulting in local retention of propagules (Rabinowitz, 1978;Maguire et al, 2000b;Dodd et al, 2002). This will limit the dispersal of propagules and creates high rates of inbreeding.…”

“…Several studies have been carried out on mangrove species in order to assess genetic diversity using genetic markers such as allozymes (McMillan, 1986;Ballment et al, 1989;Duke et al, 1998), random amplified polymorphic DNA (RAPD), restriction fragment length polymorphism (RFLP) (Balakrishma, 1995;Parani et al, 1997), and recently microsatellite and amplified fragment length polymorphism (AFLP) (Maguire et al, 2000b;Maguire et al, 2002;Dodd et al, 2002;Harada et al, 2002). Duke et al (1998) studied the worldwide genetic diversity of Avicennia marina using allozyme markers and showed that A. marina generally has high levels of genetic diversity with low levels of inbreeding.…”

Vicariance and Oceanic Barriers Drive Contemporary Genetic Structure of Widespread Mangrove Species Sonneratia alba J. Sm in the Indo-West Pacific

“…The SCS populations (east coast Malay Peninsula) were represented by MA3, TH3, VIE, MA4, PH1 and PH2. In the predictor matrix, population pairs from different coasts were coded 1 (high expected genetic differentiation), while population pairs from the same coast were coded 0 (low expected genetic differentiation) [7,36]. A Mantel R statistic based on Pearson's product-moment correlation between the pairwise genetic distance matrix and the predictor matrix was performed with 999 permutations using the package "vegan" [37] implemented in the R statistical platform.…”