Genetic diversity enhanced by ancient introgression and secondary contact in East Pacific black mangroves

Abstract

Regional distribution of genetic diversity in widespread species may be influenced by hybridization with locally restricted, closely related species. Previous studies have shown that Central American East Pacific populations of the wide-ranged Avicennia germinans, the black mangrove, harbour higher genetic diversity than the rest of its range. Genetic diversity in this region might be enhanced by introgression with the locally restricted Avicennia bicolor. We tested the hypotheses of ancient hybridization using phylogenetic analysis of the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA and intergenic chloroplast DNA; we also tested for current hybridization by population level analysis of nuclear microsatellites. Our results unveiled ancient ITS introgression between a northern Pacific Central American A. germinans lineage and A. bicolor. However, microsatellite data revealed contemporary isolation between the two species. Polymorphic ITS sequences from Costa Rica and Panama are consistent with a zone of admixture between the introgressant ITS A. germinans lineage and a southern Central American lineage of A. germinans. Interspecific introgression influenced lineage diversity and divergence at the nuclear ribosomal DNA; intraspecific population differentiation and secondary contact are more likely to have enhanced regional genetic diversity in Pacific Central American populations of the widespread A. germinans.

Multiple-Geographic-Scale Genetic Structure of Two Mangrove Tree Species: The Roles of Mating System, Hybridization, Limited Dispersal and Extrinsic Factors

“…marina [51–53] and A . bicolor [15] are consistent with these findings. However, we did not observe evidence for large amounts of inbreeding in the southernmost samples of A .…”

“…However, at smaller geographic scales, substantial genetic structure is also observed among different genera [10,13]. Another important recent advance is that ancient and ongoing interspecific hybridization has now been recorded [8,11,14], including between taxa for which no morphologically intermediate individuals have been found [15]. …”

“…schaueriana in the lower Lesser Antilles [1,16]. Preliminary evidence of chloroplast capture between these species has been found within their sympatry zone [15]. This interaction is biologically feasible as both these species present a generalist pollination system and share pollinators [17,18].…”

Evolutionary Hotspots in the Mojave Desert

“…Geographic areas that support divergent populations may harbor greater evolutionary potential, as they can represent places where divergent lineages now meet (suture zones) or reflect abiotic drivers of adaptive variation (e.g., an ecotone of steep environmental gradients). High levels of intrapopulation genetic diversity may also provide a rich resource for evolutionary resilience, and can reflect large effective population sizes [7][8][9], the presence of a historical refuge with environmentally stable conditions [10], or a zone of mixing between previously isolated gene pools [11,12]. Conversely, low or reduced genetic diversity is generally associated with reductions in fitness and survival [13,14].…”

Light intensity on two mangrove species as an indicator of regeneration in a disturbed forest in Campeche, Mexico

“…According to some estimations, mangroves in Mexico occur on about 9,140 km 2 [4]. And the most important species are Rhizophora mangle L. (Red mangrove), Laguncularia racemosa (White mangrove), Avicennia germinans (Black mangrove), Conocarpus erectus L. (Button mangrove), and only in the state of Chiapas, Rhizophora harrisonii Leechm and Avicennia bicolor L. [5]. Mexico is the second place of distribution and extension of mangroves in America, mangroves occurs in 17 states of the country, in the Yucatan Peninsula has the 55% of the total extension, followed by the North Pacific region with about 24.5%; the Gulf of Mexico with 11%, and South Pacific region, 8.6% [6].…”