Comparative Analysis of the Pattern of Population Genetic Diversity in Three Indo-West Pacific Rhizophora Mangrove Species

Abstract

Rhizophora species are the most widely distributed mangrove trees in the Indo-West Pacific (IWP) region. Comparative studies of these species with shared life history traits can help identify evolutionary factors that have played most important roles in determining genetic diversity within and between populations in ocean-current dispersed mangrove tree species. We sampled 935 individuals from 54 natural populations for genotyping with 13 microsatellite markers to investigate the level of genetic variation, population structure, and gene flow on a broad geographic scale in Rhizophora apiculata, Rhizophora mucronata, and Rhizophora stylosa across the IWP region. In contrast to the pattern expected of long-lived woody plants with predominant wind-pollination, water-dispersed seeds and wide geographic range, genetic variation within populations was generally low in all the three species, especially in those peripheral populations from geographic range limits. Although the large water-buoyant propagules of Rhizophora have capacity for long distance dispersal, such events might be rare in reality, as reflected by the low level of gene flow and high genetic differentiation between most of population pairs within each species. Phylogeographic separation of Australian and Pacific island populations from SE Asian lineages previously revealed with DNA sequence data was still detectable in R. apiculata based on genetic distances, but this pattern of disjunction was not always evident in R. mucronata and R. stylosa, suggesting that fast-evolving molecular markers could be more suitable for detecting contemporary genetic structure but not deep evolutionary divergence caused by historical vicariance. Given that mangrove species generally have small effective population sizes, we conclude that genetic drift coupled with limited gene flow have played a dominant role in producing the current pattern of population genetic diversity in the IWP Rhizophora species, overshadowing the effects of their life history traits. Recent population fragmentation and disturbances arising from human activities could further endanger genetic diversity in mangrove trees.

Molecular responses to freshwater limitation in the mangrove tree Avicennia germinans (Acanthaceae)

“…The genetic structure inferred by genome-wide SNPs (Figure 3 tating the accumulation of random genetic divergences (Francisco et al, 2018;Wee et al, 2014;Yan, Duke, & Sun, 2016). Our results also suggest that the lower precipitation of the warmest quarter in northern sites (AMMC and Northeast Brazil regions; Figure 1) may play an additional, nonneutral role in shaping this north-south divergence.…”

Contrasting colonization patterns of black mangrove (Avicennia germinans (L.) L.) gene pools along the Mexican coasts

“…Isolation by distance seem typical of mangroves (Cerón‐Souza et al., ; Kennedy et al., ; Sandoval‐Castro et al., ). However, it has been suggested that factors other than absolute geographic distance should be also considered, including water velocity (Nathan et al., ), the retention of propagules by roots (Van der Stocken et al., ), tides (Ngeve, van der Stocken, Sierens, Koedam, & Triest, ), the direction of wind and local currents, and coastal topography (Yan, Duke, & Sun, ). We hypothesized that the level of genetic structure found on each coast would be related to differences in each coast's features.…”

“…GM56), probably following the Gulf current during the Holocene. Previous studies proposed two recolonization routes for the northern parts of the Gulf of Mexico and Florida (Sherrod & McMillan, 1985), from sources in the Yucatan Peninsula and the Caribbean coasts in Central America (McMillan, 1986 along the Gulf of Mexico, which is further backed by the lack of correlation between latitude and heterozygosity along this coast (which remained non-significant even after taking the concave shape of this basin into account; r s = 0.309, P = 0.538; see also (Yan, Duke, & Sun, 2016). We hypothesized that the level of genetic structure found on each coast would be related to differences in each coast's features.…”

Population genetic structure, introgression, and hybridization in the genus Rhizophora along the Brazilian coast

“…(Wee et al., ). Although this pattern is not universal—for instance, it was not detected in other Rhizophora (Yan et al., ) and Sonneratia (Yang et al., ) species—it indicates that common extrinsic factors, such as superficial ocean currents (Wee et al., ) and sea‐level fluctuations (Yan et al., ), have shaped the organization and distribution of genetic diversity.…”

“…(Rhizophoraceae; Minobe et al, 2010), Excoecaria agallocha L. (Euphorbiaceae; Zhang et al, 2008), Lumnitzera racemosa Willd. (Combretaceae; Li et al, 2016), Rhizophora apiculata Blume (Rhizophoraceae; Yahya et al, 2014;Yan, Duke, & Sun, 2016), and R. mucronata Lam. (Wee et al, 2014).…”