Phylogeography of Plathymenia reticulata (Leguminosae) reveals patterns of recent range expansion towards northeastern Brazil and southern Cerrados in Eastern Tropical South America

Abstract

Little is known about past vegetation dynamics in Eastern Tropical South America (ETSA). Here we describe patterns of chloroplast (cp) DNA variation in Plathymenia reticulata, a widespread tree in the ETSA Atlantic Forest and Cerrado biomes, but not found in the xeromorphic Caatinga. Forty one populations, comprising 220 individuals, were analysed by sequencing the trnS-trnG and trnL-trnL-trnF cpDNA regions. Combined, they resulted in 18 geographically structured haplotypes. The central region of the sampling area, comprising Minas Gerais and Goiás Brazilian states, is a centre of genetic diversity and probably the most longstanding area of the distribution range of the species. In contrast, populations from northeastern Brazil and the southern Cerrados showed very low diversity levels, almost exclusively with common haplotypes which are also found in the central region. Coupled with a long-branched star-like network, these patterns suggest a recent range expansion of P. reticulata to those regions from central region sources. The recent origin of the species (in the early Pleistocene) or the extinction of some populations due to drier and cooler climate during the last glacial maximum could have been responsible for that phylogeographic pattern. The populations from northeastern Brazil originated from two colonization routes, one eastern (Atlantic) and one western (inland). Due to its high diversity and complex landscape, the central region, especially central-north Minas Gerais (between 15 degrees -18 degrees S and 42 degrees -46 degrees W), should be given the highest priority for conservation.

A large historical refugium explains spatial patterns of genetic diversity in a Neotropical savanna tree species

“…In contrast, more unstable areas would exhibit lower genetic diversity due to a population bottleneck. Furthermore, because the geographical distribution of D. mollis is included in the geographic range of other Cerrado legume tree species with phylogeographical patterns which are already known (Ramos et al, 2007;Novaes et al, 2010Novaes et al, , 2013Colevatti et al, 2013b), we expected a similar phylogeographical structure for D. mollis. Since savanna species have shown evidence of range retraction during the LGM followed by expansion after climate amelioration (e.g.…”

“…In contrast to D. mollis, strong phylogeographical structure and high genetic divergence among populations were found with ITS sequences in D. miscolobium (Novaes et al, 2013), as well as in two other legume tree species with chloroplast DNA, Hymenaea stigonocarpa (Ramos et al, 2007) and Plathymenia reticulata (Novaes et al, 2010). These differences can be due to different effects of Quaternary climatic changes on D. mollis in comparison with these species, since they showed genetic evidence of strong range retraction and recent population expansion, whereas D. mollis presented only slight range retraction, with a large stable area maintained since the LGM.…”

“…The few studies on phylogeography and demographic history performed with Cerrado plant species have shown some congruencies. High levels of genetic differentiation among populations, evidence of reduction in species range during the Last Glacial Maximum (LGM), and recent colonization of the southern Cerrado from northern sources were found (Collevatti et al, 2003(Collevatti et al, , 2013bRamos et al, 2007;Novaes et al, 2010Novaes et al, , 2013. Most species have also shown a striking phylogeographical structure, with a somewhat similar subdivision between groups of populations (eg.…”

“…Phylogeographical studies with Cerrado species have shown that Pleistocene climatic changes have shaped the demographic history of populations and the geographical range of species of plants (e.g. Collevatti et al, 2003Collevatti et al, , 2013bRamos et al, 2007;Novaes et al, 2010Novaes et al, , 2013, as well as animals (e.g. Prado et al, 2012;Santos et al, 2014;Gonzalez et al, 2015).…”

“…Most species have also shown a striking phylogeographical structure, with a somewhat similar subdivision between groups of populations (eg. Ramos et al, 2007;Novaes et al, 2010Novaes et al, , 2013.…”