Tropical forests are both evolutionary cradles and museums of leaf beetle diversity

Abstract

The high extant species diversity of tropical lineages of organisms is usually portrayed as a relatively recent and rapid development or as a consequence of the gradual accumulation or preservation of species over time. These explanations have led to alternative views of tropical forests as evolutionary ''cradles'' or ''museums'' of diversity, depending on the organisms under study. However, biogeographic and fossil evidence implies that the evolutionary histories of diversification among tropical organisms may be expected to exhibit characteristics of both cradle and museum models. This possibility has not been explored in detail for any group of terrestrial tropical organisms. Cephaloleia ͉ diversification ͉ evolutionary radiation ͉ phylogeny T he extraordinarily high species diversity of tropical forest floras and faunas is often attributed to the recent and rapid accumulation of species via high speciation rates (1-4) or the gradual accumulation and͞or preservation of species over time via low extinction rates (5-8). These observations have led to the widespread belief that tropical forests are evolutionary ''cradles'' of diversity for some lineages and ''museums'' of diversity for others (6, 7).Evidence in support of cradle models comes largely from geographic patterns of distribution, species richness, and endemism of extant tropical organisms. These patterns are often ascribed to evolutionary radiation in response to relatively recent climatic, tectonic, or biotic events; e.g., Pleistocene [Ϸ1.8-0.01 mega-annum (Ma) ago] glaciation or Pliocene (Ϸ5.3-1.8 Ma ago) bridging of the Isthmus of Panama (1-4). However, paleontological evidence implies that many of the evolutionary radiations that account for the present diversity (''crown diversification'') of taxonomically disparate groups of tropical organisms may have occurred comparatively early, during the late Paleocene and early to middle Eocene (Thanetian, Ypresian, and Lutetian Ages, Ϸ58.7-40.4 Ma ago) (9-17), associated with global warming, Cenozoic maximum global temperatures (18), and the latitudinal expansion (16, 19) and taxonomic diversification (9,11,14,16,17) of characteristically tropical lineages of plants, consistent with museum models of diversification. Although cradle and museum models are often presented as temporal alternatives (4, 7), their predictions are not mutually exclusive, and, as the aforementioned observations suggest, the evolutionary histories of tropical lineages of organisms may be expected to exhibit features of both kinds of models. However, this possibility has not been explored in detail for any group of terrestrial tropical organisms.Using molecular genetic, paleontologic, and biogeographic evidence, we investigated timing and tempo in the diversification of Cephaloleia, a species-rich genus of herbivorous Neotropical leaf beetles (Chrysomelidae: Cassidinae). Our goals were to determine (i) whether the evolutionary history of Cephaloleia diversification (speciation-extinction) departs significantly from a constant rate m...

Phylogenetic diversity as a window into the evolutionary and biogeographic histories of present-day richness gradients for mammals

“…Globally, tropical rates are predicted to be high, but with faster rates in the Neotropics, supporting evidence that they represent a speciation pump for many taxa (e.g. plants [95 -97], insects [98,99], birds [73,100], fish and mammals [52,60], T. J. Davies & L. B. Buckley 2011, unpublished data). However, our model also predicts fast rates in Southeast Asia, which has a high richness of old lineages.…”

'Moa's Ark' or 'Goodbye Gondwana': is the origin of New Zealand's terrestrial invertebrate fauna ancient, recent or both?

“…Brown et al 1999;Buckley and Simon 2007), the cases reviewed here indicate that, for at least a few groups, vicariance is still a plausible biogeographical scenario. In fact, the combination of a few ancient divergences with more recent diversifications is not very different from the model proposed for the leaf beetle diversity of the Neotropics (McKenna and Farrell 2006), a combination of 'evolutionary cradles' and 'museums of diversity'. Having an unbalanced mix of old species-poor lineages and a larger proportion of recent radiations may actually be expected even in stable parts of our planet.…”

Repeated climate-linked host shifts have promoted diversification in a temperate clade of leaf-mining flies

“…Contrary to our findings on host shifts, we can see no clear evidence of a direct effect of major Oligocene climate events on Phytomyza diversification. Despite much recent interest in such questions (5,40,41), there is still very little quantitative evidence on the degree to which global climate events have affected insect diversification.…”

“…Strong examples support the operation of intrinsic and extrinsic forces in isolation (4). Only recently, however, has the debate moved toward synthesis, i.e., joint estimation of the relative importance of each, and their interaction, at different time scales (2,4,5). In this study we compare the effects of a major intrinsic factor (shift to a novel host plant clade) and a major extrinsic factor (global climate change) on the macroevolutionary dynamics of a temperate, Cenozoic radiation of phytophagous insects, the leaf-mining fly genus Phytomyza (Diptera: Agromyzidae).…”

“…Despite a recent surge of interest in insect diversification rates (9), however, there is still little evidence on the degree to which changes in either plant defense or insect ''offense'' promote diversification (7). Progress on the insect side has come from several recent reports plausibly attributing an instance of significantly elevated insect diversity to a co-occurring shift to a new host taxon (5,10,11). Any single instance of elevated diversification, however, could reflect other influences that happen to be confounded with the host shift.…”