Recent accelerated diversification in rosids occurred outside the tropics

Abstract

Conflicting relationships have been found between diversification rate and temperature across disparate clades of life. Here, we use a supermatrix comprising nearly 20,000 species of rosids-a clade of~25% of all angiosperm species-to understand global patterns of diversification and its climatic association. Our approach incorporates historical global temperature, assessment of species' temperature niche, and two broad-scale characterizations of tropical versus non-tropical niche occupancy. We find the diversification rates of most subclades dramatically increased over the last 15 million years (Myr) during cooling associated with global expansion of temperate habitats. Climatic niche is negatively associated with diversification rates, with tropical rosids forming older communities and experiencing speciation rates~2-fold below rosids in cooler climates. Our results suggest long-term cooling had a disproportionate effect on non-tropical diversification rates, leading to dynamic young communities outside of the tropics, while relative stability in tropical climes led to older, slower-evolving but still species-rich communities.

Angiosperms at the edge: Extremity, diversity, and phylogeny

“…Cold adaptations are also highly prevalent among the superrosids and well-studied. Much like arid-adapted groups (above), radiation of cold-adapted superrosids is largely of Miocene date (Folk et al, 2019;Sun et al, 2020). Saxifragales are particularly well-studied and stand as perhaps the oldest known large radiation in angiosperms (~113 million years ago) that is almost entirely limited to temperate and cold environments (but see Ranunculales, the other contender, above).…”

“…Saxifragales are particularly well-studied and stand as perhaps the oldest known large radiation in angiosperms (~113 million years ago) that is almost entirely limited to temperate and cold environments (but see Ranunculales, the other contender, above). (Sun et al, 2020;Töpel, Antonelli, Yesson, & Eriksen, 2012;Zhang et al, 2017). across the clade, the occurrence of these adaptations to extreme environments reflects recurrent evolutionary events.…”

“…Ultimately, global cooling and aridification promoted the evolution of recognizably modern terrestrial biomes, including grasslands and deserts over large areas of Eurasia, North America, Africa, and Australia, as well as an expansive arctic-alpine flora (Herbert et al, 2016;Holbourn et al, 2018;Potter & Szatmari, 2009;Pound, Haywood, Salzmann, & Riding, 2012). Concomitant with this cooling and aridification was the radiation of many familiar extreme-adapted plants, such as most of the world's succulents and alpine cushion plants (Arakaki et al, 2011;Folk et al, 2019;Hernández-Hernández, Brown, Schlumpberger, Eguiarte, & Magallón, 2014;Sun et al, 2020).…”

Ambiguous support for extra-tropical accelerated diversification of rosids

“…The authors assessed the relationship between tropicality/non-tropicality and diversification under a model comparison framework using four alternative BiSSE/HiSSE models. According to the authors, under both definitions of tropicality (Köppen-Geiger and geographic) the full HiSSE model fitted best, which would indicate that higher diversification of non-tropical species is modulated by an unobserved trait (Sun et al 1 and their Supplemental Table 4). However, when the analyses are repeated by running the authors' code 10 a different picture emerges (Table 1).…”

Evolution of environmental stress responses in plants

“…Bottom left inset: a confocal microscopic image of A. thaliana stomata stained with the florescence dye H2DCFDA for monitoring reactive oxygen species in cells. Bottom right inset: an electrophoresis image for gene cloning aridification during the mid-Miocene promoted the radiation of many extreme-adapted flowering plants (Folk et al, 2019;Sun et al, 2020).…”