Putative floral brood-site mimicry, loss of autonomous selfing, and reduced vegetative growth are significantly correlated with increased diversification in Asarum (Aristolochiaceae).
The drivers of angiosperm diversity have long been sought and the flower-arthropod association has often been invoked as the most powerful driver of the angiosperm radiation. We now know that features that influence arthropod interactions cannot only affect the diversification of lineages, but also expedite or constrain their rate of extinction, which can equally influence the observed asymmetric richness of extant angiosperm lineages. The genus Asarum (Aristolochiaceae; ∼100 species) is widely distributed in north temperate forests, with substantial vegetative and floral divergence between its three major clades, Euasarum, Geotaenium, and Heterotropa. We used Binary-State Speciation and Extinction Model (BiSSE) Net Diversification tests of character state distributions on a Maximum Likelihood phylogram and a Coalescent Bayesian species tree, inferred from seven chloroplast markers and nuclear rDNA, to test for signal of asymmetric diversification, character state transition, and extinction rates of floral and vegetative characters. We found that reduction in vegetative growth, loss of autonomous self-pollination, and the presence of putative fungal-mimicking floral structures are significantly correlated with increased diversification in Asarum. No significant difference in model likelihood was identified between symmetric and asymmetric rates of character state transitions or extinction. We conclude that the flowers of the Heterotropa clade may have converged on some aspects of basidiomycete sporocarp morphology and that brood-site mimicry, coupled with a reduction in vegetative growth and the loss of autonomous self-pollination, may have driven diversification within Asarum.
The Ohio State University Museum of Biological Diversity, Dept. of Evolution, Ecology, and Organismal Biology, 1315 Kinnear Road, Columbus, OH 43212, United States. Electronic address: sinn.6@buckeyemail.osu.edu.
Brandon T
BT
Sinn
The New York Botanical Garden, 2900 Southern Boulevard, Bronx, NY 10458, United States.
Lawrence M
LM
Kelly
The Ohio State University Museum of Biological Diversity, Dept. of Evolution, Ecology, and Organismal Biology, 1315 Kinnear Road, Columbus, OH 43212, United States.
John V
JV
Freudenstein
D030023:Asarum / Q000145:classification* / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D001487:Basidiomycota; D001499:Bayes Theorem; D044822:Biodiversity; D000067558:Biological Mimicry / Q000235:genetics / Q000502:physiology; D053476:Extinction, Biological; D035264:Flowers / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology; D049810:Genetic Speciation; D014644:Genetic Variation; D010802:Phylogeny; D054817:Pollination; D057945:Self-Fertilization
Asarum; Binary-state speciation and extinction; Brood-site mimicry; Diversification; Magnoliid; Piperales