Contrasted patterns of hyperdiversification in Mediterranean hotspots

Abstract

Dating the Tree of Life has now become central to relating patterns of biodiversity to key processes in Earth history such as plate tectonics and climate change. Regions with a Mediterranean climate have long been noted for their exceptional species richness and high endemism. How and when these biota assembled can only be answered with a good understanding of the sequence of divergence times for each of their components. A critical aspect of dating by using molecular sequence divergence is the incorporation of multiple suitable age constraints. Here, we show that only rigorous phylogenetic analysis of fossil taxa can lead to solid calibration and, in turn, stable age estimates, regardless of which of 3 relaxed clock-dating methods is used. We find that Proteaceae, a model plant group for the Mediterranean hotspots of the Southern Hemisphere with a very rich pollen fossil record, diversified under higher rates in the Cape Floristic Region and Southwest Australia than in any other area of their total distribution. Our results highlight key differences between Mediterranean hotspots and indicate that Southwest Australian biota are the most phylogenetically diverse but include numerous lineages with low diversification rates. biodiversity ͉ diversification rates ͉ fossil calibration ͉ molecular dating ͉ Proteaceae

Flammable biomes dominated by eucalypts originated at the Cretaceous–Palaeogene boundary

“…Multiple crown-group eucalypt lineages were also present in Patagonia during the early Eocene 31 . They persist in Southeast Asia today, but have since gone extinct in New Zealand and Patagonia, likely as a result of climate change to wetter and colder conditions that are no longer so prone to fire 19,32 . Dispersal limitation may account for the lack of spread of eucalypts beyond the immediate region since the end of the Eocene, when Australia separated from East Gondwana.…”

“…Sclerophyllous morphology is often assumed to be an adaptation to fire and a driver of diversification 13,19,20 , but sclerophylly has diverse functions and is not necessarily an indicator of climates in general or fire-prone vegetation in particular 2,21,22 . Nevertheless, in Australia, the unique epicormic anatomy (types A and B: Supplementary Table S1) of Myrtaceae, especially eucalypts, is known to be responsible for post-fire recovery 8,9,11 .…”

“…= 2.5 (Supplementary Table S2). We used the fossil Myrtaceidites mesonesus (61 Ma) to calibrate the crown of Myrtaceae instead of M. lisamae (~86 Ma), used previously 45 , because the backbone-constraint test 19 indicated that the latter was probably misplaced as a member of the Myrtaceae crown. Recently, 52-Ma Eucalyptus macrofossils were discovered in Patagonia 31 and are older than our 37 Ma constraint (M. eucalyptoides, Supplementary Table S2) for the crown node of the genus.…”

“…The phylogenetic placement of each fossil on the unconstrained molecular phylogeny was estimated using heuristic parsimony searches of 100 random-addition replicates with tree-bisection-reconnection in PAUP* 44 , with the tree-search constrained by the molecular phylogeny estimated without internal calibrations. As suggested 19 , the most parsimonious + 1 and + 2 trees were also saved, to assess confidence of fossil placements. The test identified seven fossils as suitable for calibration (Supplementary Table S2).…”

“…To estimate absolute divergence times, the analysis was calibrated using pollen fossils of known age placed at seven internal nodes. Fossil pollens suitable for calibration were identified using a backbone-constraint test 19 . This method searches for the most parsimonious placement of fossil pollens on a molecular phylogeny, using a pollen character data matrix scored for the terminal taxa.…”