Abstract
Background and Aims Organismal evolution tends to be closely associated with ecological conditions. However, the extent to which this association constrains adaptation or diversification into new habitats remains unclear. We studied habitat evolution in the hyper-diverse angiosperm clade Saxifragales. Methods We used species-level phylogenies for approx. 950 species to analyse the evolution of habitat shifts as well as their influence on plant diversification. We combined habitat characterization based on floristic assignments and state-of-the art phylogenetic comparative methods to estimate within- and across-habitat diversification patterns. Key Results Our analyses showed that Saxifragales diversified into multiple habitats from a forest-inhabiting ancestor and that this diversification is governed by relatively rare habitat shifts. Lineages are likely to stay within inferred ancestral ecological conditions. Adaptation to some habitat types (e.g. aquatic, desert) may be canalizing events that lineages do not escape. Although associations between increased diversification rates and shifts in habitat preferences are occasionally observed, extreme macroevolutionary rates are closely associated with specific habitats. Lineages occurring in shrubland, and especially tundra and rock cliffs, exhibit comparatively high diversification, whereas forest, grassland, desert and aquatic habitats are associated with low diversification. Conclusions The likelihood of occupation of new habitats appears to be asymmetric. Shifts to aquatic and desert habitats may be canalizing events. Other habitats, such as tundra, might act as evolutionary sources, while forests provide the only habitat seemingly colonized easily by lineages originating elsewhere. However, habitat shifts are very rare, and any major environmental alteration is expected to have dramatic evolutionary consequences.
Highlights
Modern evolutionary ecology has been strongly influenced by the idea that most diversification tends to occur within ancestral ecological conditions
We addressed these objectives by analysing: (a) the evolutionary history of habitat occupation in Saxifragales, to determine the habitat of the most recent common ancestor (MRCA) of the group; (b) the relative diversification rates associated with each habitat type and the consequences for diversification of habitat shifts, whether anagenetic or cladogenetic; and (c) the evolutionary dynamics across the five focal habitat boundaries
Most diversification occurs within the ancestral ecological conditions; niche conservatism is of major evolutionarily importance in this clade
Summary
Modern evolutionary ecology has been strongly influenced by the idea that most diversification tends to occur within ancestral ecological conditions. It has been argued that current human-induced climate change might lead to widespread extinction because it outpaces both the rate of adaptation in situ and the ability of organisms to track moving habitat boundaries (Corlett and Westcott, 2013; Kubisch et al, 2013; Quintero and Wiens, 2013). At this point, we cannot make general predictions about the consequences of habitat changes for the conservation of biodiversity above the species level (Wiens et al, 2010). We studied habitat evolution in the hyper-diverse angiosperm clade Saxifragales
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