Breeding System Diversification and Evolution in American Poa supersect. Homalopoa (Poaceae: Poeae: Poinae)

GIUSSANI, LILIANA MÓNICA; GILLESPIE, LYNN; SCATAGLINI, M. AMALIA; NEGRITO, MARIA; ANTÓN ANA; SORENG, ROBERT

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2016 vol. 118 p. 281 - 303

0305-7364

Background and Aims Poa subgenus Poa supersect. Homalopoa has diversified extensively in the Americas.Over half of the species in the supersection are diclinous; most of these are from the New World, while a few arefrom South-East Asia. Diclinism in Homalopoa can be divided into three main types: gynomonoecism, gynodioecismand dioecism. Here the sampling of species of NewWorld Homalopoa is expanded to date its origin and diversificationin North and South America and examine the evolution and origin of the breeding system diversity. Methods A total of 124 specimens were included in the matrix, of which 89 are species of Poa supersect.Homalopoa sections Acutifoliae, Anthochloa, Brizoides, Dasypoa, Dioicopoa, Dissanthelium, Homalopoa sensulato (s.l.), Madropoa and Tovarochloa, and the informal Punapoa group. Bayesian and parsimony analyses wereconducted on the data sets based on four markers: the nuclear ribosomal internal tanscribed spacer (ITS) and externaltranscribed spacer (ETS), and plastid trnT-L and trnL-F. Dating analyses were performed on a reduced Poa matrixand enlarged Poaceae outgroup to utilize fossils as calibration points. A relaxed Bayesian molecular clockmethod was used. Key Results Hermaphroditism appears to be pleisiomorphic in the monophyletic Poa supersect. Homalopoa,which is suggested to have originated in Eurasia 84?42 million years ago (Mya). The ancestor of Poa supersect.Homalopoa radiated throughout the New World in the Late Miocene?Early Pliocene, with major lineagesoriginating during the Pliocene to Pleistocene (5?2 Mya). Breeding systems are linked to geographic areas, showingan evolutionary pattern associated with different habitats. At least three major pathways from hermaphroditism todiclinism are inferred in New World Homalopoa: two leading to dioecism, one via gynodioecism in South Americaand another directly from hermaphroditism in North America, a result that needs to be checked with a broader samplingof diclinous species in North America. A third pathway leads from hermaphroditism to gynomonoecism inAndean species of South America, with strictly pistillate species evolving in the highest altitudes. Conclusions Divergence dating provides a temporal context to the evolution of breeding systems in New WorldPoa supersect. Homalopoa. The results are consistent with the infrageneric classification in part; monophyleticsections are confirmed, it is proposed to reclassify species of sect. Acutifoliae, Dasypoa and Homalopoa s.l. and it isacknowledged that revision of the infrageneric taxonomy of the gynomonoecious species is needed.