Population history and seed dispersal in widespread Central AmericanBegoniaspecies (Begoniaceae) inferred from plastome-derived microsatellite markers

Abstract

Seven plastid microsatellite markers derived from plastome sequence data were used to study the population genetic structure in two widespread Begonia spp. from Central America. In B. nelumbiifolia, no variation was found at any locus. In contrast, significant haplotype diversity was found in B. heracleifolia (hT = 0.937, hS = 0.444, 39 haplotypes, mean of 3.3 haplotypes per population), and populations showed high absolute levels of genetic differentiation (G'ST = 0.829, D = 0.407). The distribution of haplotypes showed strong phylogeographical structure (GST = 0.526, RST = 0.737, GST < RST, P < 0.05), but this pattern was poorly accounted for by commonly studied historical scenarios, such as Pleistocene refugia or Pliocene differentiation at the Isthmus of Tehuantepec. Instead, subdivision into a large number of regions, each containing local populations (e.g. when k = 9, FCT = 0.749, P < 0.05), best explained the haplotype distribution. The lack of haplotype diversity in B. nelumbiifolia, a moist adapted species, suggests that it may have been severely restricted in range during dry spells in the Pleistocene, and has subsequently expanded from this recent population bottleneck. The high haplotype diversity in B. heracleifolia may indicate that its adaptation to drought enabled it to survive in small, but ecologically suitable, pockets of isolated habitat throughout the Pleistocene. Limited seed exchange between B. heracleifolia populations is likely to be responsible for its high population substructure, and provided the opportunity for divergence through genetic drift. This interpretation is consistent with previous population genetic studies in Begonia, and suggests a common pattern of extremely low genetic exchange among a series of small, but long‐lived, populations that may predispose the genus to rapid speciation. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 00, 000–000.

Genetic diversity and structure of wild populations ofCarica papayain Northern Mesoamerica inferred by nuclear microsatellites and chloroplast markers

“…Probably, because of the pioneer/nomadic behaviour of wild C. papaya, and its short life cycle, populations could have established and expanded rapidly after the Isthmus of Tehuantepec arose, erasing any sign of past genetic break. Another study has shown similar results; Twyford et al (2013) found low F CT values between populations east and west from the isthmus for Begonia heracleifolia, a neotropical lowland plant. In contrast, Gutiérrez-Rodr ıguez et al (2011) found a phylogeographical break at the Isthmus of Tehuantepec, with private haplotypes at either side of the isthmus for Palicourea padifolia, a cloud forest herb.…”

“…For tropical lowland species like C. papaya, responses to historical climatic fluctuations may depend on species-specific adaptations, therefore making the identification of refugia for complex tropical species assemblages difficult (Poelchau and Hamrick, 2012). Generalizations about refugia may apply only for species with similar ecological preferences, rather than at broad taxonomic scales (Twyford et al, 2013).…”

“…This could promote a latitudinal gradient with a stronger phylogeographical structure in tropical lowland species than in temperate plants (Dick and Heuertz, 2008), and several studies have documented phylogeographical structure of Neotropical trees sampled around geographical barriers (Aide and Rivera, 1998;Cavers et al, 2003;Dick et al, 2003;Novick et al, 2003), and higher F ST values in tropical trees than in trees from temperate and/or boreal forests (Dick and Heuertz, 2008). Finally, current environmental features may drive patterns of gene flow and genetic structure of tropical plants (Poelchau and Hamrick, 2012); in particular, habitat fragmentation in recent times may also have played a role in structuring genetic diversity (Twyford et al, 2013).…”

“…The Isthmus of Tehuantepec forms a narrow piece of lowland that separates the southcentral Mexican highlands (Sierra de Ju arez and Sierra Madre del Sur) from the highlands of Chiapas (Ornelas et al, 2010). It has been suggested that the isthmus was a seaway for much of the Pliocene (Morrone, 2006), and therefore a major barrier to gene flow during this period (Twyford et al, 2013). Moreover, if the Pleistocene refugia theory is correct, some regions in south-eastern Mexico might have acted as Pleistocene refuges in the past, as suggested by Toledo (1982).…”

“…There is a relative dearth of detailed phylogeographical information on Neotropical lowland plant species (but see: Cavers et al, 2003;Novick et al, 2003;Poelchau and Hamrick, 2012;Twyford et al, 2013), even though lowland tropical vegetation covers most of the Mesoamerican landscape. Although the vast majority of the world's tree diversity lies in the tropics, most of the evolutionary history and genetic knowledge comes from temperate and boreal forests, with a marked emphasis on pines, poplars and oaks (Dick, 2010).…”