African geoxyles evolved in response to fire; frost came later

Abstract

Pagel M (1994) Detecting correlated evolution on phylogenies: a general method for the comparative analysis of discrete characters. Proceedings of the Royal Society B 255: 37-45. Pagel M, Meade A (2006) Bayesian analysis of correlated evolution of discrete characters by reversible jump markov chain monte carlo. The American Naturalist 167: 808-825.

Unearthing belowground bud banks in fire‐prone ecosystems

“…While Maurin et al . () placed the geoxyles that they studied in south–central Africa under the general umbrella of xylopodia, our literature search indicated that they are more likely to be lignotubers, woody rhizomes and/or taproot tubers (Lamont et al ., ). In general terms, lignotubers are associated with larger woody shrubs and mallees occurring under high‐intensity fire regimes, whereas xylopodia tend to occur among smaller shrubs and forbs, often with seasonal stems, under frequent low‐intensity fires in grasslands and savannas; however, without a detailed inspection it is often difficult to ascertain the actual type of basal burl.…”

“…Fire‐prone ecosystems are rich in species with BBBs, as the protection of the buds by the soil provides fitness benefits in the presence of frequent fires (Flinn & Wein, ; Schimmel & Granstrom, ; Vesk et al ., ). Some structures may have been selected for by recurrent fire, as with many lignotubers, woody rhizomes and xylopodia (Maurin et al ., ; Paula et al ., ; Lamont et al ., ). Others have come from lineages that had traits for lateral spreading (colonization) or for seasonal dynamics that were later conserved in fire‐prone communities thanks to their capacity to withstand recurrent fires (fleshy underground swellings, bud‐bearing roots).…”

“…The sequence of these two processes is not easy to identify as both may have occurred simultaneously or certainly contemporaneously, or alternated in different periods (Keeley et al ., ). There is increasing evidence that many fire‐adaptive traits arose as a direct response to fire rather than seasonality that developed later (Lamont & He, ; Lamont et al ., ). Basal resprouting may have been selected for by a range of disturbances in early ecosystems that included floods, strong winds, drought, grazing and fires, and thus it can be considered an ancient and widespread functional trait (Pausas & Keeley, ).…”

“…The Protea ancestor arose 28 Ma in the Cape region (South Africa) and was a nonresprouter, with the lignotuberous form first arising 18.7 Ma (Lamont et al ., ). Invasion of the savanna grasslands by proteas was delayed until 12.5 Ma, and diversification began 5 Ma later again, when a lignotuberous subclade evolved from a nonresprouting ancestor that was adapted to the much more frequent fires there (Lamont et al ., ).…”

“…By contrast, the Microlicieae tribe of Melastomataceae arose at 17.2 Ma and began to diversify at 9.9 Ma with the most recent speciation event at 0.67 Ma among five genera. It is instructive to compare these data with the equivalent growth form (subshrub geoxyles) in a matched environment (tropical grasslands) in southern Africa: a mean of 3.6 Ma with a maximum at 15.2 Ma and a minimum at 0.3 Ma (data for 22 families collated from Maurin et al ., ; see Lamont et al ., ). Thus, even though the African species are probably lignotuberous‐rhizomatous (Table S1; Lamont et al ., ), this evidence of their coincident origins can be attributed to the rise of highly fire‐prone, tropical grasslands worldwide c .…”