Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands

Abstract

Historic demography changes of plant species adapted to New World arid environments could be consistent with either the Glacial Refugium Hypothesis (GRH), which posits that populations contracted to refuges during the cold-dry glacial and expanded in warm-humid interglacial periods, or with the Interglacial Refugium Hypothesis (IRH), which suggests that populations contracted during interglacials and expanded in glacial times. These contrasting hypotheses are developed in the present study for the giant columnar cactus Cephalocereus columna-trajani in the intertropical Mexican drylands where the effects of Late Quaternary climatic changes on phylogeography of cacti remain largely unknown. In order to determine if the historic demography and phylogeographic structure of the species are consistent with either hypothesis, sequences of the chloroplast regions psbA-trnH and trnT-trnL from 110 individuals from 10 populations comprising the full distribution range of this species were analysed. Standard estimators of genetic diversity and structure were calculated. The historic demography was analysed using a Bayesian approach and the palaeodistribution was derived from ecological niche modelling to determine if, in the arid environments of south-central Mexico, glacial-interglacial cycles drove the genetic divergence and diversification of this species. Results reveal low but statistically significant population differentiation (FST = 0.124, P < 0.001), although very clear geographic clusters are not formed. Genetic diversity, haplotype network and Approximate Bayesian Computation (ABC) demographic analyses suggest a population expansion estimated to have taken place in the Last Interglacial (123.04 kya, 95% CI 115.3–130.03). The species palaeodistribution is consistent with the ABC analyses and indicates that the potential area of palaedistribution and climatic suitability were larger during the Last Interglacial and Holocene than in the Last Glacial Maximum. Overall, these results suggest that C. columna-trajani experienced an expansion following the warm conditions of interglacials, in accordance with the GRH.

Pleistocene diversification in an ancient lineage: a role for glacial cycles in the evolutionary history of Dioon Lindl. (Zamiaceae)

“…In contrast to the previous suggestions that Dioon species ranges contracted to refugia in response to cooler temperatures, our hypothesis describes an expansion, or at least a joining, of populations during glacial maxima. This is akin to the Interglacial Refugial Hypothesis (Haffer, ; Bonatelli et al., ; Cornejo‐Romero et al., ) wherein species are restricted in range during the interglacials and then expand into secondary contact during glacial periods. However, a key component of Dioon ecology related to the process of lineage spitting due to range shifts is its relative restriction to ecotone habitats that currently occur at mid‐elevations.…”

“…However, a key component of Dioon ecology related to the process of lineage spitting due to range shifts is its relative restriction to ecotone habitats that currently occur at mid‐elevations. Other taxa that occur at lower elevations in southern Mexico have contracted to smaller refugial ranges during glacial periods and then expanded in the interglacial (Cornejo‐Romero et al., ) perhaps because there was nowhere lower and warmer to go. Species that cannot migrate to alternate elevations, whether because of dispersal limitations or because of a lack of habitat, will be unlikely to experience a similar diversification process in the mountains of Mexico.…”

Pleistocene refugia in the Chihuahuan Desert: the phylogeographic and demographic history of the gymnosperm Ephedra compacta

“…Many of these endemic species have speciation dates or show evidence of demographic expansion during the Pleistocene (e.g. Cornejo‐Romero et al., ; Fernández, Cervantes & Hafner, ; Gándara & Sosa, ). Moreover, in some cases sister species and genetically differentiated populations are allopatrically distributed among some of these adjacent areas (Castoe, Spencer & Parkinson, ; Fernández, ; Hernández‐Hernández, Colorado & Sosa, ; Ruiz‐Sanchez & Specht, ; Vásquez‐Cruz & Sosa, ).…”

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

“…We propose that the absence of environmental suitability in the YPBP for the establishment of Z. prasina in the Last Interglacial (≈ 120 ka) could be due to some Zamia species needing a seasonal climate, while others have a tree habit and are adapted to very humid, woodland habitats (Nicolalde-Morejón et al 2011). It is possible that the last interglacial was warmer, humid and without seasonality, in comparison with the Holocene (Walker et al 2012, Cornejo-Romero et al 2017, and thus was not propitious for the growth of Z. prasina.…”

“…This hypothesis is widely accepted for temperate species such as subtropical columnar cacti in the mid latitudes of the Northern Hemisphere (Soltis et al 2006). In contrast, the Interglacial Refugium Hypothesis (IRH) suggests that in the intertropical open dry vegetation of South America (Caatinga, Cerrado and Chaco biomes), populations of some species contracted to warm and humid refugia during the interglacials and expanded outward under the cold/ dry climate of the Ultimate Glacial Maximum (LGM) (≈ 80 Ka) (Cornejo-Romero et al 2017). Several authors have proposed a refugium theory as the underlying model for glacial and postglacial population dynamics of tropical species during the LGM (Farrera et al 1999, Ramírez-Barahona & Eguiarte 2013, Cornejo-Romero et al 2017.…”