Integrating environmental, molecular, and morphological data to unravel an ice‐age radiation of arctic‐alpine Campanula in western North America

Abstract

Many arctic-alpine plant genera have undergone speciation during the Quaternary. The bases for these radiations have been ascribed to geographic isolation, abiotic and biotic differences between populations, and/or hybridization and polyploidization. The Cordilleran Campanula L. (Campanulaceae Juss.), a monophyletic clade of mostly endemic arctic-alpine taxa from western North America, experienced a recent and rapid radiation. We set out to unravel the factors that likely influenced speciation in this group. To do so, we integrated environmental, genetic, and morphological datasets, tested biogeographic hypotheses, and analyzed the potential consequences of the various factors on the evolutionary history of the clade. We created paleodistribution models to identify potential Pleistocene refugia for the clade and estimated niche space for individual taxa using geographic and climatic data. Using 11 nuclear loci, we reconstructed a species tree and tested biogeographic hypotheses derived from the paleodistribution models. Finally, we tested 28 morphological characters, including floral, vegetative, and seed characteristics, for their capacity to differentiate taxa. Our results show that the combined effect of Quaternary climatic variation, isolation among differing environments in the mountains in western North America, and biotic factors influencing floral morphology contributed to speciation in this group during the mid-Pleistocene. Furthermore, our biogeographic analyses uncovered asynchronous consequences of interglacial and glacial periods for the timing of refugial isolation within the southern and northwestern mountains, respectively. These findings have broad implications for understanding the processes promoting speciation in arctic-alpine plants and the rise of numerous endemic taxa across the region.

Molecular insights into the lichen genusAlectoria(Parmeliaceae) in North America

“…Indeed, it is possible that, as has been suspected in the past (Brodo and Hawksworth 1977), the A. sarmentosa group is affected by phenomena such as hybridization. Similarly, it is possible the high concentration of the morphological and chemical variation in western North America reflects a recent rapid radiation as has been documented in vascular plants (Abbott et al 2000;Brochmann and Brysting 2008;Brochmann et al 2004;DeChaine et al 2013DeChaine et al , 2014. As is the case in other regions such as the southern Appalachians of eastern North America (Wen 1999), albeit on a much younger scale, the Pacific Northwest has had a dynamic environmental and geological history characterized by periods of isolated refugia followed by rapid expansion of available habitat (Beatty and Provan 2010;Brunsfeld and Sullivan 2005;Brubaker et al 2005;Godbout et al 2008).…”

Has past climate change affected cold‐specialized species differentially through space and time?

“…There is widespread support for a general model of alpine population history in temperate regions (Schoville & Roderick, ), from both genetic and palaeontological data (DeChaine & Martin, ; Frenzel, ; Knowles & Carstens, ; Birks, ; Galbreath et al ., ), wherein cold‐specialized species track favourable climate conditions downslope during glacial episodes and upslope during warmer interglacial periods. Across a wide variety of taxa and in alpine habitats globally, past climate change has led to rapid lineage diversification and the formation of new species (Knowles, ; Comes & Kadereit, ; Buckley & Simon, ; Schoville & Roderick, ; DeChaine et al ., ; Hedin et al ., ), exemplifying the so‐called ‘Pleistocene species pump’ (Terborgh, ; Schoville et al ., ). Speciation is not the only outcome, however, as highly dispersive species experience secondary contact during climate fluctuations, leading to admixture of divergent genomes that formed during periods of isolation (e.g.…”

The genetic differentiation of a cricket (Velarifictorus micado) with two modes of life cycle in East Asia after the middle Pleistocene and the invasion origin of the United States of America

“…Glacial cycles had an important impact on the distribution and genetic structure of a species (Hewitt, 2000(Hewitt, , 2004. Climate oscillation occurred in Asia during Pleistocene has affected the current distribution of species (Jia & Zhang, 2019;Ye et al, 2014;Qu et al, 2011), leading to genetic differentiation in species (Gu et al, 2013;Hazlitt et al, 2014;Rodrigues et al, 2014;Xu et al, 2009;Ye et al, 2018) and speciation in Asia (Bao et al, 2010;DeChaine et al, 2014;Lin et al, 2016;Shih et al, 2011). Individuals colonized to new habitat due to the environmental changes in original habitat or population expansion.…”