Lay mistletoes on the Yucatán Peninsula: post-glacial expansion and genetic differentiation of Psittacanthus mayanus (Loranthaceae)

Abstract

We evaluate phylogeographical patterns of Psittacanthus mayanus (Loranthaceae), a widely distributed mistletoe species on the Yucatán Peninsula and Chiapas, using nuclear and plastid markers. An analysis of phylogeographic population structure and demography and Bayesian inference methods were conducted on P. mayanus from 16 localities across the range of the species. To assess the historical processes and changes through the Pleistocene climatic cycles that may have affected the distribution and demographic history of the species, the current potential distribution of the species was modelled using ecological niche modelling (ENM) and projected onto the mid Holocene (MH), Last Glacial Maximum (LGM) and Last Inter Glacial (LIG). Psittacanthus mayanus exhibited higher haplotype and nucleotide diversity in the southern part of its distribution than in the northern part. Two divergent lineages were revealed in the phylogenetic and phylogeographical analyses of ribotypes and haplotypes. Populations from the northern portion of the Yucatán Peninsula probably experienced a recent population growth, whereas populations from the southern portion of the Peninsula and Chiapas are marked by historical demographic stability and isolation. Approximate Bayesian computation (ABC) analyses strongly supported a scenario of post-glacial population growth. ENM results indicate that the distribution of P. mayanus expanded and was connected into the southern portion of the Yucatán Peninsula during LGM conditions and colonized the northern portion of the Peninsula and fragmented during MH conditions. According to the ABC and ENM results, the genetic differentiation of P. mayanus may be linked to the effects of the glacial/interglacial cycles and environmental factors, in which populations of P. mayanus expanded during the LGM into the Petén province currently covered with semideciduous tropical rain forest followed by northward expansion, southwards contractions and post-glacial colonization of the northernmost portion of the Yucatán province, a region currently covered with seasonally dry tropical deciduous forest. Our results highlight the influence of Pleistocene events in shaping the geographical distribution of genetic variation in Neotropical lowland forest. The phylogeographic and environmental patterns in P. mayanus provide an opportunity to investigate further the evolution of Mexican lowland forest biodiversity.