Impact of Late Pleistocene-Holocene climatic fluctuations on the phylogeographic structure and historical demographics of Zamia prasina (Cycadales: Zamiaceae)

Abstract

Background: Glacial periods during the Pleistocene have been hypothesized to have greatly influenced geographical patterns of genetic structure and demography of many tropical species. The Glacial Refugium Hypothesis proposes that, during cold, dry glacial periods, populations of moisture-affinities tropical species were restricted to sheltered, humid areas and that, during warmer and more humid interglacial periods, these populations expanded. Some mountain regions in the tropics acted as refugia during the cold, dry periods of the Pleistocene for several temperate forest taxa, which recolonized the humid areas farther north during the interglacial periods.
 Questions: (1) Did Late Pleistocene-Holocene climate changes affect the historical demophraphy of Zamia prasina ? (2) Does the historical distribution of Zamia prasina agree with the Glacial Refugium Hypothesis?
 Study species: Zamia prasina W.Bull. (Zamiaceae), the only cycad native to the Yucatan Peninsula Biotic Province (YPBP).
 Methods: Five individuals were collected in 23 populations and characterized using two DNA regions: plastid atpF-atpH , and nuclear ITS2. Genetic diversity, phylogeographic structure, historical demography, and potential distributions were assessed. 
 Results: Our results showed moderately high genetic diversity and low, but significant, phylogeographic structure. Two genetic groups were identified, one in the eastern part of the Peninsula, the other in the western. The changes in historical demography suggest that Z. prasina experienced a population expansion following the warm conditions of the Holocene.
 Conclusions: The population dynamics of Zamia prasina are in accordance with the Glacial Refugium Hypothesis.