Evolutionary and demographic history of the Californian scrub white oak species complex: an integrative approach

Abstract

Understanding the factors promoting species formation is a major task in evolutionary research. Here, we employ an integrative approach to study the evolutionary history of the Californian scrub white oak species complex (genus Quercus). To infer the relative importance of geographical isolation and ecological divergence in driving the speciation process, we (i) analysed inter- and intraspecific patterns of genetic differentiation and employed an approximate Bayesian computation (ABC) framework to evaluate different plausible scenarios of species divergence. In a second step, we (ii) linked the inferred divergence pathways with current and past species distribution models (SDMs) and (iii) tested for niche differentiation and phylogenetic niche conservatism across taxa. ABC analyses showed that the most plausible scenario is the one considering the divergence of two main lineages followed by a more recent pulse of speciation. Genotypic data in conjunction with SDMs and niche differentiation analyses support that different factors (geography vs. environment) and modes of speciation (parapatry, allopatry and maybe sympatry) have played a role in the divergence process within this complex. We found no significant relationship between genetic differentiation and niche overlap, which probably reflects niche lability and/or that multiple factors, have contributed to speciation. Our study shows that different mechanisms can drive divergence even among closely related taxa representing early stages of species formation and exemplifies the importance of adopting integrative approaches to get a better understanding of the speciation process.

Genomic data reveal cryptic lineage diversification and introgression in Californian golden cup oaks (section Protobalanus)

“…1.8–1.0 Ma) (Table ). Note, however, that our estimates of divergence time must be interpreted with extreme caution due to the wide confidence intervals around our point estimates and considerable uncertainty in mutation rates and generation time for long‐lived tree species (Table ) (see Ortego et al ., ; Tsuda et al ., ). Migration rates per generation ( m ) were estimated to be significantly higher (i.e.…”

Genetic Structure and Evolutionary History of Three Alpine Sclerophyllous Oaks in East Himalaya-Hengduan Mountains and Adjacent Regions

“…Therefore, the probability of incomplete lineage sorting depends on both the effective population size ( Ne ) in the ancestral population of species, which determines the rate of coalescence of lineages, and the time between successive speciation events (Hudson, 1990; Degnan and Salter, 2005). While the introgression is mostly detected in zones of sympatry/parapatry between two or more species, in other words, it occurs in co-distributed populations belong to different species [Ortego et al, 2015; also see review by Abbott et al (2013) and references therein].…”

“…For instance, in western Eurasia, species retreated into southern refuges during glacial episodes and recolonized during warmer interglacials; this periodical process created a frequently observed south-north gradient in genetic diversity (southern richness, northern purity) during postglacial re-expansion (Hewitt, 1996). Other researches have suggested that environmental heterogeneity may also contribute to the genetic differentiation among species or populations (e.g., Ortego et al, 2012, 2015; Guichoux et al, 2013). In China, phylogeographic studies have focus mainly on the roles of historical orogenesis, climatic oscillations and environmental heterogeneity in evolutionary history of biotas in Qinghai-Tibet Plateau (QTP) and adjacent regions (Qiu et al, 2011; Liu et al, 2012; Wen et al, 2014).…”

“…Weak reproductive isolation, frequent interspecies gene exchange and high phenotypic variation result in diffuse species boundaries within the genus causing much debate about species concepts (Burger, 1975; Rushton, 1993). Up to date, numerous studies in Europe and America have focused on the impact of climate change on their evolutionary history (e.g., Ortego et al, 2012, 2015; Guichoux et al, 2013; Cavender-Bares et al, 2015). Within our scope, few reports concerned oak species in China (Zeng et al, 2010, 2011, 2015), and even less alpine sclerophyllous oaks.…”

Effects of Geological and Environmental Events on the Diversity and Genetic Divergence of Four Closely Related Pines: Pinus koraiensis, P. armandii, P. griffithii, and P. pumila

“…Nucleotide diversity levels within populations and spatial patterns, as well as species divergence are of great importance in the field of evolutionary biology (Coyne and Orr, 2004; Hao et al, 2015; Ortego et al, 2015). Mountain uplift and past environmental oscillations may have been largely responsible for shaping the spatial patterns of diversity and genetic divergence among species (Coyne and Orr, 2004; Wachowiak et al, 2009).…”