Growth form evolution and hybridization in Senecio (Asteraceae) from the high equatorial Andes

Abstract

Changes in growth forms frequently accompany plant adaptive radiations, including páramo–a high‐elevation treeless habitat type of the northern Andes. We tested whether diverse group of Senecio inhabiting montane forests and páramo represented such growth form changes. We also investigated the role of Andean geography and environment in structuring genetic variation of this group. We sampled 108 populations and 28 species of Senecio (focusing on species from former genera Lasiocephalus and Culcitium) and analyzed their genetic relationships and patterns of intraspecific variation using DNA fingerprinting (AFLPs) and nuclear DNA sequences (ITS). We partitioned genetic variation into environmental and geographical components. ITS‐based phylogeny supported monophyly of a Lasiocephalus‐Culcitium clade. A grade of herbaceous alpine Senecio species subtended the Lasiocephalus‐Culcitium clade suggesting a change from the herbaceous to the woody growth form. Both ITS sequences and the AFLPs separated a group composed of the majority of páramo subshrubs from other group(s) comprising both forest and páramo species of various growth forms. These morphologically variable group(s) further split into clades encompassing both the páramo subshrubs and forest lianas, indicating independent switches among the growth forms and habitats. The finest AFLP genetic structure corresponded to morphologically delimited species except in two independent cases in which patterns of genetic variation instead reflected geography. Several morphologically variable species were genetically admixed, which suggests possible hybrid origins. Latitude and longitude accounted for 5%–8% of genetic variation in each of three AFLP groups, while the proportion of variation attributed to environment varied between 8% and 31% among them. A change from the herbaceous to the woody growth form is suggested for species of high‐elevation Andean Senecio. Independent switches between habitats and growth forms likely occurred within the group. Hybridization likely played an important role in species diversification.

Pleistocene glacial cycles drive isolation, gene flow and speciation in the high‐elevation Andes

“…In this regard, it is noteworthy that our demographic modelling detected recent episodes of postsplit gene flow associated with both lineage pairs analysed. These results are in line with recent studies suggesting that gene flow may have occurred between currently geographically isolated Andean cordilleras (Kolar et al ., ) and that hybridization may have played an important role in other Andean plant radiations (Duskova et al ., ; Vargas et al ., ; Pouchon et al ., ).…”

“…The relative contributions of Andean orogeny and more recent Pleistocene glacial cycles in driving diversification of highelevation Andean plants remain unclear, partly because of the difficulties associated with reconstructing the evolutionary history of rapidly diversifying clades. However, 'next generation' sequencing (NGS) datasets for high-elevation Andean plants are providing phylogenetic resolution in these groups for the first time (Nevado et al, 2016;Uribe-Convers et al, 2016;Vargas et al, 2017;Contreras-Ortiz et al, 2018), and recent studies suggest that interspecific gene flow may have occurred in some Andean radiations (Kolar et al, 2016;Duskova et al, 2017;Vargas et al, 2017;Pouchon et al, 2018). While these reports are at odds with a strict allopatric speciation scenario driven by Andean orogeny, thus far the timing of species divergence and hybridization, and the effect of gene flow between species at a genome-wide scale have not been studied.…”

The flickering connectivity system of the north Andean páramos

“…Where isolation resulted in allopatric, in situ speciation, connectivity triggered diversification through dispersal and settlement in new areas (‘dispersification’, Moore & Donoghue, ), and hybridization of previously isolated populations (Grant, ; Petit et al., ). Much evidence suggests that hybridization is not the processes of species becoming ‘reabsorbed’ into their parental forms but contributes by bringing evolutionary novelty and gene flow operating at different introgression rates (Dušková et al., ; Nevado, Contreras‐Ortiz, Hughes, & Filatov, ; Pouchon et al., ), and thus a likely trigger of speciation and morphological diversity. Interestingly, population‐level processes such as gene flow, dispersification and hybridization, alongside periods of isolation, have been increasingly recognized to play out at the phylogenetic scale, leading to (rapid) lineage diversification, for example in mountains (e.g.…”

Climate Vulnerability Assessment of the Espeletia Complex on Páramo Sky Islands in the Northern Andes

“…However, in order to gather a more comprehensive view of climate change responses in the high mountain ecosystems of the northern Andes, other diverse and highly abundant plant genera in the Páramo (Hughes et al, 2013) should be considered under a similar analytical framework as the described here. Immediate candidates to follow up this approach are Bartsia (Uribe-Convers and Tank, 2015), Chusquea (Ely et al, 2019), Diplostephium (Vargas et al, 2017), Hypericum (Nürk et al, 2013), Loricaria (Kolar et al, 2016), Lupinus (Hughes and Eastwood, 2006;Vásquez et al, 2016;Contreras-Ortiz et al, 2018), Oreobolus (Chacón et al, 2006;Gómez-Gutiérrez et al, 2017), Puya (Jabaily and Sytsma, 2013), and Senecio (Duskova et al, 2017;Walter et al, 2020). These combined efforts would ultimately reveal whether the fastest evolving biodiversity hotspot on earth, and in general tropical high mountain ecosystems (Hedberg, 1964;Sklenáø et al, 2014;Chala et al, 2016), have a chance to persist under current environmental and anthropogenic threats.…”