Browsing by Subject "diversification"

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    Adaptation to hummingbird pollination is associated with reduced diversification in Penstemon.
    (Evolution letters, 2019-10) Wessinger, Carolyn A; Rausher, Mark D; Hileman, Lena C
    A striking characteristic of the Western North American flora is the repeated evolution of hummingbird pollination from insect-pollinated ancestors. This pattern has received extensive attention as an opportunity to study repeated trait evolution as well as potential constraints on evolutionary reversibility, with little attention focused on the impact of these transitions on species diversification rates. Yet traits conferring adaptation to divergent pollinators potentially impact speciation and extinction rates, because pollinators facilitate plant reproduction and specify mating patterns between flowering plants. Here, we examine macroevolutionary processes affecting floral pollination syndrome diversity in the largest North American genus of flowering plants, Penstemon. Within Penstemon, transitions from ancestral bee-adapted flowers to hummingbird-adapted flowers have frequently occurred, although hummingbird-adapted species are rare overall within the genus. We inferred macroevolutionary transition and state-dependent diversification rates and found that transitions from ancestral bee-adapted flowers to hummingbird-adapted flowers are associated with reduced net diversification rate, a finding based on an estimated 17 origins of hummingbird pollination in our sample. Although this finding is congruent with hypotheses that hummingbird adaptation in North American Flora is associated with reduced species diversification rates, it contrasts with studies of neotropical plant families where hummingbird pollination has been associated with increased species diversification. We further used the estimated macroevolutionary rates to predict the expected pattern of floral diversity within Penstemon over time, assuming stable diversification and transition rates. Under these assumptions, we find that hummingbird-adapted species are expected to remain rare due to their reduced diversification rates. In fact, current floral diversity in the sampled Penstemon lineage, where less than one-fifth of species are hummingbird adapted, is consistent with predicted levels of diversity under stable macroevolutionary rates.
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    Divergence times and the evolution of epiphytism in filmy ferns (Hymenophyllaceae) revisited
    (International Journal of Plant Sciences, 2008-11-01) Hennequin, S; Schuettpelz, E; Pryer, KM; Ebihara, A; Dubuisson, J
    Although the phylogeny of the filmy fern family (Hymenophyllaceae) is rapidly coming into focus, much remains to be uncovered concerning the evolutionary history of this clade. In this study, we use two data sets (108-taxon rbcL+ rps4, 204-taxon rbcL) and fossil constraints to examine the diversification of filmy ferns and the evolution of their ecology within a temporal context. Our penalized likelihood analyses (with both data sets) indicate that the initial divergences within the Hymenophyllaceae (resulting in extant lineages) and those within one of the two major clades (trichomanoids) occurred in the early to middle Mesozoic. There was a considerable delay in the crown group diversification of the other major clade (hymenophylloids), which began to diversify only in the Cretaceous. Maximum likelihood and Bayesian character state reconstructions across the broadly sampled single-gene (rbcL) phylogeny do not allow us to unequivocally infer the ancestral habit for the family or for its two major clades. However, adding a second gene (rps4) with a more restricted taxon sampling results in a hypothesis in which filmy ferns were ancestrally terrestrial, with epiphytism having evolved several times independently during the Cretaceous. © 2008 by The University of Chicago. All rights reserved.
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    Guyanagaster, a New Wood-Decaying Sequestrate Fungal Genus Related to Armillaria (Physalacriaceae, Agaricales, Basidiomycota)
    (2010) Henkel, TW; Smith, ME; Aime, MC
    Premise of the study : Sequestrate basidiomycete fungi (e. g. "gasteromycetes") have foregone ballistospory and evolved alternative, often elaborate mechanisms of basidiospore dispersal with highly altered basidioma morphology. Sequestrate fungi have independently evolved in numerous Agaricomycete lineages, confounding taxonomic arrangements of these fungi for decades. Understanding the multiple origins and taxonomic affinities of sequestrate fungi provides insight into the evolutionary forces that can drastically alter basidioma morphology. In the neotropical rainforests of the Guiana Shield, we encountered a remarkable sequestrate fungus fruiting directly on decaying hardwood roots. The fungus 'singular combination of traits include a wood-decaying habit; black, verrucose peridium; reduced stipe; and gelatinized basidiospore mass. Methods : Guyanagaster necrorhiza gen. et sp. nov. is described. Macro-and micromorphological characters were assessed and compared to most similar taxa. To determine the phylogenetic affinities of the fungus, DNA sequence data were obtained for the 18S, ITS, and 28S rDNA, RBP2, and EF1 alpha regions and subjected to single-and multi-gene analyses. DNA sequences from fungal vegetative organs growing on decaying woody roots confirmed the wood-inhabiting lifestyle of Guyanagaster. Key results : Guyanagaster is morphologically unique among sequestrate fungi worldwide. Phylogenetic evidence places Guyanagaster in close relation to the wood-decaying mushroom genus Armillaria in the Physalacriaceae (Agaricales, Agaricomycetes, Basidiomycota). Conclusions : Guyanagaster represents an independently evolved sequestrate form within the Physalacriaceae. Although molecular data confirm that Guyanagaster is closely related to Armillaria, the unusual features of this fungus suggest a case of radically divergent morphological evolution.
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    Testing the adaptive radiation hypothesis for the lemurs of Madagascar.
    (Royal Society open science, 2017-01-18) Herrera, James P
    Lemurs, the diverse, endemic primates of Madagascar, are thought to represent a classic example of adaptive radiation. Based on the most complete phylogeny of living and extinct lemurs yet assembled, I tested predictions of adaptive radiation theory by estimating rates of speciation, extinction and adaptive phenotypic evolution. As predicted, lemur speciation rate exceeded that of their sister clade by nearly twofold, indicating the diversification dynamics of lemurs and mainland relatives may have been decoupled. Lemur diversification rates did not decline over time, however, as predicted by adaptive radiation theory. Optimal body masses diverged among dietary and activity pattern niches as lineages diversified into unique multidimensional ecospace. Based on these results, lemurs only partially fulfil the predictions of adaptive radiation theory, with phenotypic evolution corresponding to an 'early burst' of adaptive differentiation. The results must be interpreted with caution, however, because over the long evolutionary history of lemurs (approx. 50 million years), the 'early burst' signal of adaptive radiation may have been eroded by extinction.