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SummarySucculent plants are widely distributed, reaching their highest diversity in arid and semi-arid regions. Their origin and diversification is thought to be associated with a global expansion of aridity. We test this hypothesis by investigating the tempo and pattern of Cactaceae diversification. Our results contribute to the understanding of the evolution of New World Succulent Biomes.We use the most taxonomically complete dataset currently available for Cactaceae. We estimate divergence times and utilize Bayesian and maximum likelihood methods that account for nonrandom taxonomic sampling, possible extinction scenarios and phylogenetic uncertainty to analyze diversification rates, and evolution of growth form and pollination syndrome.Cactaceae originated shortly after the Eocene-Oligocene global drop in CO 2 , and radiation of its richest genera coincided with the expansion of aridity in North America during the late Miocene. A significant correlation between growth form and pollination syndrome was found, as well as a clear state dependence between diversification rate, and pollination and growthform evolution.This study suggests a complex picture underlying the diversification of Cactaceae. It not only responded to the availability of new niches resulting from aridification, but also to the correlated evolution of novel growth forms and reproductive strategies.

A major challenge in evolutionary ecology is to understand how co-evolutionary processes shape patterns of interactions between species at community level. Pollination of flowers with long corolla tubes by long-tongued hawkmoths has been invoked as a showcase model of co-evolution. Recently, optimal foraging models have predicted that there might be a close association between mouthparts' length and the corolla depth of the visited flowers, thus favouring trait convergence and specialization at community level. Here, we assessed whether hawkmoths more frequently pollinate plants with floral tube lengths similar to their proboscis lengths (morphological match hypothesis) against abundance-based processes (neutral hypothesis) and ecological trait mismatches constraints (forbidden links hypothesis), and how these processes structure hawkmoth-plant mutualistic networks from five communities in four biogeographical regions of South America. We found convergence in morphological traits across the five communities and that the distribution of morphological differences between hawkmoths and plants is consistent with expectations under the morphological match hypothesis in three of the five communities. In the two remaining communities, which are ecotones between two distinct biogeographical areas, interactions are better predicted by the neutral hypothesis. Our findings are consistent with the idea that diffuse co-evolution drives the evolution of extremely long proboscises and flower tubes, and highlight the importance of morphological traits, beyond the forbidden links hypothesis, in structuring interactions between mutualistic partners, revealing that the role of niche-based processes can be much more complex than previously known.

In many temperate plants seasonal variation in day length induces flowering at species-specific times each year. Here we report synchronous bud break and flowering of tropical perennials that cannot be explained by seasonal changes in day length. We recorded flushing and flowering of more than 100 tropical trees, succulents and understory herbs over several years. We observed the following phenological patterns throughout the northern Neotropics: wide-ranging trees flush or flower twice a year at the Equator, but annually further north; many trees leaf out in February; in autumn, wide-ranging perennials flower 4 months earlier in Mexico than at the Equator. This latitudinal variation of phenology parallels that of the annual cycle of daily insolation, a function of day length and solar irradiation. Insolation has two annual maxima at the Equator, it rapidly increases in February at all latitudes, and between Mexico and the Equator its maximum shifts from the summer solstice to the autumn equinox. These unique, manifold correlations suggest that throughout the tropics insolation, rather than day length, may control the phenology of many perennials. Our observations significantly extend current knowledge of environmental signals involved in photoperiodic control of plant development.

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Variation in floral phenotype (color, depth, nectar) suggests incipient specialization for bee or hawkmoth pollination across the geographic distribution of Echinopsis ancistrophora, with flower depth ranging from 4.5 to 24 cm. We used chemical and behavioral analyses to test whether fragrance has evolved in concert with morphology in these Andean cacti. Floral scent (145 total compounds) was collected using dynamic headspace methods and analyzed with gas chromatographyÁmass spectrometry, revealing subspecies-specific odors dominated by sesquiterpenes in E. ssp. ancistrophora and arachnacantha and fatty acid derivatives or aromatics in E. ssp. cardenasiana and pojoensis. Compounds indicative of sphingophily were not consistently found in moth-pollinated plants, and total scent emissions were significantly lower in populations with nocturnal anthesis. In wind tunnel assays, Manduca sexta moths were attracted to scent of ssp. ancistrophora from both bee and hawkmoth-pollinated populations, but not to scent of ssp. cardenasiana. However, hawkmoths were most attracted to the methyl benzoate-dominated scent of a distant relative, Echinopsis mirabilis. Thus, hawkmoth-pollinated descendants of the E. ancistrophora lineage may be phylogenetically constrained to emit weak, sesquiterpene-dominated fragrances that are not optimally attractive to hawkmoths, or floral scent may be under stronger selection by destructive flower visitors.

The results suggest incipient differentiation at the population level and local adaptation to either bee or hawkmoth (potentially plus bee) pollination.

The use of evolutionary labile floral traits and growth habit has led to nonnatural classifications. Taxonomic realignments are required, but further study of less evolutionary labile traits suitable for circumscribing genera are needed. Surprisingly, polyploidy seems infrequent in the Echinopsis alliance and hybridization may thus be of minor relevance in the evolution of this clade.