Diversification in North American arid lands: Niche conservatism, divergence and expansion of habitat explain speciation in the genus Ephedra

Biología Evolutiva, Instituto de Ecología A.C., Apartado Postal 63, 91000 Xalapa, Veracruz, Mexico.
Molecular Phylogenetics and Evolution (Impact Factor: 3.92). 07/2012; 65(2):437-50. DOI: 10.1016/j.ympev.2012.06.025
Source: PubMed


A lineage of 12 arid land shrubby species in the gymnosperm genus Ephedra (Gnetales) from North America is used to evaluate the influence of climate on speciation. With a long evolutionary history, and a well documented fossil record this lineage is an ideal model for understanding the process of speciation under a niche conservatism scenario. Using seven DNA molecular markers, Bayesian inference is carried out to uncover sister species and to estimate time of divergence of the lineages. Ecological niche models are generated for four parapatric and sympatric sister species and two analyses of niche evolution are performed, one based on ecological niche models and another using raw data and multivariate analysis. As previous analyses suggest, the diversification of North America Ephedra species may be the result of a recent secondary radiation. Both parapatric and sympatric species diverged mostly in a scenario of climatic niche conservatism. However, we also found strong evidence for niche divergence for one of the sister species pairs (E. californica-E. trifurca). Moreover, the multivariate analysis found environmental differences for some variables between sister species. The estimated divergence time of three pairs of sister species distributed in southwestern North America (E. cutleri-E. aspera, E. californica-E. trifurca and E. torreyana-E. viridis) is inferred to have occurred in the Late Miocene to Pliocene and for the sister species pair E. antisyphilitica-E. coryi distributed in the southern United States and northeastern Mexico, it was inferred from the Pliocene to Pleistocene. The orogenetic and climatic changes documented for these regions related to expansion of arid lands, may have contributed to the diversification in North American Ephedra, rather than adaptations to new climatic conditions.

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    • "A complex set of geologic, climatic, genetic and stochastic events may act alone or in combination to promote divergence among populations and species (Ayoub and Riechert, 2004; Hope et al., 2012; Loera et al., 2012; Blair et al., 2014). Barriers to gene flow and reproductive isolation may develop in allopatry, parapatry or sympatry (Schluter, 2001; Losos and Glor, 2003). "
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    ABSTRACT: The hypothesis that endemic species could have originated by the isolation and divergence of peripheral populations of widespread species can be tested through the use of ecological niche models (ENMs) and statistical phylogeography. The joint use of these tools provides complementary perspectives on historical dynamics and allows testing hypotheses regarding the origin of endemic taxa. We used this approach to infer the historical processes that have influenced the origin of a species endemic to the Mexican Plateau (Cynomys mexicanus) and its divergence from a widespread ancestor (Cynomys ludovicianus), and to test whether this endemic species originated through peripatric speciation. We obtained genetic data for 295 individuals for two species of black-tailed prairie dogs (C. ludovicianus and C. mexicanus). Genetic data consisted of mitochondrial DNA sequences (cytochrome b and control region), and 10 nuclear microsatellite loci. We estimated dates of divergence between species and between lineages within each species and performed ecological niche modelling (Present, Last Glacial Maximum and Last Interglacial) to determine changes in the distribution range of both species during the Pleistocene. Finally, we used Bayesian inference methods (DIYABC) to test different hypotheses regarding the divergence and demographic history of these species. Data supported the hypothesis of the origin of C. mexicanus from a peripheral population isolated during the Pleistocene [∼230,000 years ago (0.1 – 0.43 Ma 95% HPD)], with a Pleistocene-Holocene (∼9,000 − 11,000 years ago) population expansion (∼10-fold increase in population size). We identified the presence of two possible refugia in the southern area of the distribution range of C. ludovicianus and another, consistent with the distribution range of C. mexicanus. Our analyses suggest that Pleistocene climate change had a strong impact in the distribution of these species, promoting peripatric speciation for the origin of C. mexicanus and lineage divergence within C. ludovicianus.
    Molecular Phylogenetics and Evolution 09/2015; DOI:10.1016/j.ympev.2015.08.027 · 3.92 Impact Factor
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    • "Our molecular divergence time estimates suggest that the evolutionary history of Ephedra species in North and South America might be associated with the expansion of arid habitats since the Oligocene – Miocene (Axelrod 1979, Wilson and Pitts 2010a, Palazessi and Barreda 2012) given that most lineage divergences fall within this time frame. In North America, most of the speciation events occurred in the southwest after or during the Miocene orogenic activity that favored the expansion of arid habitats and the radiation of biotas adapted to these ecological conditions (Axelrod 1979, Moore and Jansen 2006, Wilson and Pitts 2010b, Loera et al. 2012, Bryson et al. 2013). Th erefore, vicariance processes due to geographic barriers in addition to habitat expansion may be involved in speciation events in N. Am. "
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    ABSTRACT: In this study we selected the New World species of Ephedra to understand the ecological consequences of different dispersal syndromes. The twenty-three species of Ephedra in the New World have a disjunct distribution in North and South American arid and semi-arid habitats, exhibiting three dispersal syndromes related to dispersal by birds, wind and rodents. Using DNA sequence data we inferred phylogenetic relationships and lineage divergence times, and used these estimates to test different ecological assumptions. Using comparative methods we tested for correlations between dispersal syndromes and a set of ecological variables (niche breadth, niche evolution, distributional ranges and niche position). We found that speciation events in the New World coincided with the expansion of arid habitats in this region. We suggest that the bird dispersal syndrome is related with higher rates of climatic niche evolution for all variables used, including aridity index, mean annual temperature and mean annual precipitation. Distribution ranges were correlated with niche breadth, they were however not significantly different between dispersal syndromes. Species inhabiting the extremely arid regions on niche axes had narrower niche breadths. We conclude that species whose seeds are dispersed by birds have colonized a broader set of habitats and that those with wind and rodent dispersal syndromes might have promoted the colonization of more arid environments.
    Ecography 02/2015; 38. DOI:10.1111/ecog.01264 · 4.77 Impact Factor
    • "Nakazato et al. (2010) found a complex pattern of niche evolution among Solanum species separated between 1 and 4 myr, with cases of niche divergence, conservatism and specialization. Loera et al. (2012) found niche conservatism and divergence in species of Ephedra distant between 1 and 5 myr. European columbines began to diversify between 1 and 4 myr ago (Bastida et al. 2010), achieving high diversification rates which, according to the present study, were accompanied by complex patterns of niche evolution. "
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