Evolution of a hotspot genus: geographic variation in speciation and extinction rates in Banksia (Proteaceae)

Abstract

BackgroundHotspots of angiosperm species richness and endemism in Mediterranean-climate regions are among the most striking, but least well-understood, geographic patterns of biodiversity. Recent studies have emphasized the importance of rapid diversification within hotspots, compared to non-hotspot regions, as a major contributor to these patterns. We constructed the first near-complete phylogeny of Banksia (Proteaceae) to test whether diversification rates have differed between lineages confined to the southwest Australian hotspot and those found throughout southern, eastern and northern Australia. We then tested for variation in diversification rates among the bioclimatic zones within the southwest hotspot itself.ResultsAlthough Banksia species richness in the southwest is ten times that of the rest of the continent, we find little evidence for more rapid diversification in the southwest, although this result is inconclusive. However, we find firmer support for substantial rate variation within the southwest hotspot, with more rapid diversification in the semi-arid heaths and shrublands, compared to the high-rainfall forests. Most of the Banksia diversity of the southwest appears to be generated in the heaths and shrublands, with a high migration rate out of this zone boosting diversity of the adjacent forest zone.ConclusionsThe geographic pattern of diversification in Banksia appears more complex than can be characterized by a simple hotspot vs. non-hotspot comparison, but in general, these findings contrast with the view that the high diversity of Mediterranean hotspots is underpinned by rapid radiations. Steady accumulation of species at unexceptional rates, but over long periods of time, may also have contributed substantially to the great botanical richness of these regions.

Biodiversity hotspots and Ocbil theory

“…Some authors have focused on using hypothesis testing on the origins of biodiversity hotspots (Cook et al 2015), or the origins of selected mesic Australian biota through applying phylogenetic and phylogeographic evidence (Byrne et al 2011). Others have explored relevant aspects of the phylogeny of significant families and genera such as Restionaceae (Litsios et al (2014), Acacia (Miller et al 2013;Bui et al (2014a, b) and Banksia (Cardillo and Pratt 2013).…”

“…inselberg biodiversity and adaptations (Gibson et al 2010;Poot et al 2012;Millar et al 2014;Tapper et al 2014a, b). plant phylogeny (e.g., Smith et al 2011), semiarid speciation processes (Cardillo and Pratt 2013;Ellis et al 2014;Rix et al 2014). paleoendemism (Sole et al 2013;Proches 2014).…”

Could this be Australia’s rarest Banksia? Banksia vincentia (Proteaceae), a new species known from fourteen plants from south-eastern New South Wales, Australia

“…victoriae, B. ilicifolia, B. cuneata, B. pallida, B. sclerophylla, B. kippistiana, B. serratuloides, B. comosa, B. tenuis, B. proteoides, B. octotriginta, B. catoglypta, B. shanklandiorum, B. alliacea, B. pellaeifolia, B. ionthocarpa, B. subulata, B. splendida, B. plumosa, B. pseudoplumosa, B. serra, B. fasciculata, B. densa, B. platycarpa, B. seneciifolia, B. rufistylis, B. insulanemorecincta, B. nana, B. acuminata, B. arcotidis), in the colours themselves (style pale to deep pink or red, but pale in lower half in B. menziesii, cream, often reddish in upper half in B. mucronulata, cream at base, dull yellow above in B. lepidorhiza, maroon in upper half in B. foliolata, cream at base, cream, pink or maroon above, pollen presenter green in B. lindleyana) or in the process by which the colour pattern seems to be induced (style dark red to purple where exposed in B. grossa) (George 1981). These qualitatively different patterns of style coloration are apparently not homologous with that found in the Banksia spinulosa complex, a conclusion that is corroborated by the criterion of congruence when one plots them (results not shown) on to the most recently published phylogenetic tree for Banksia (Cardillo and Pratt 2013).…”

“…This is amply demonstrated by the results of the three explicitly phylogenetic analyses of Banksia that have been published. The morphological analysis of Thiele & Ladiges (1996) returned the following topology: (collina,(spinulosa,(cunninghamii,neoanglica))), which was incongruent with results of the cpDNA analysis of Mast & Givnish (2002): spinulosa,cunninghamii, (collina,neoanglica)), and both of these were incongruent with the resolution found by Cardillo & Pratt (2013) in their cpDNA analysis: (cunninghamii,(spinulosa,(collina,neoanglica))). Consequently, we consider the erection of a highly resolved hierarchical classification within the Banksia spinulosa complex to be premature.…”

Habitat loss is information loss: Species distribution models are compromised in anthropogenic landscapes

“…ARC quantifies the relationship between range overlap of species pairs and their age of divergence, to make inferences about the prevailing geographic mode of speciation within a clade (and other processes: see (Fitzpatrick andTurelli 2006, Warren et al 2008) ). We used the R package `phyloclim` (Heibl and Calenge 2011) to calculate ARC for our control and habitat loss adjusted models for Banksia and Hakea separately, using phylogenies for Banksia from (Cardillo and Pratt 2013) , and for Hakea from (Cardillo et al 2017) .…”