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Abstract Detail


Monteverde Suarez, María Jose [1], McIntyre, Patrick [2], Cacho, N.Ivalu [3].

Parallel evolution in floral morphology in a plant ring-species, the Caribbean Euphorbia tithymaloides.

Ring-species are formed when a population expands along two geographic fronts surrounding a geographic barrier in such way that when the terminal forms of each front come into secondary contact they show divergence. Parallel evolution may be a more common feature of ring species than is currently recognized, as divergence around geographic barriers may extend along common environmental gradients associated with longitude, latitude, or elevation. Because, by definition, both geographic fronts come into secondary contact, the evolutionary table is set for a scenario of convergence based on shared environmental characteristics in the area of contact. The Caribbean slipper-spurge, Euphorbia tithymaloides L., to date seems to be the only plant that conforms to a ring-species model, having colonized the Antilles from Mexico/ Guatemala along two fronts: one that expanded east through the Greater Antilles, and another that expanded south through Central America, and then east and north through South America and the Lesser Antilles, respectively. The two forms in the Antilles differ morphologically and genetic data available suggests barriers to gene flow between them. The biogeographical history of E. tithymaloides, in combination with morphological variation within the species complex, raises intriguing questions about morphological evolution in these lineages. In particular, the floral involucres of Antillean E. tithymaloides seem to have shortened compared to the mainland populations, while such a pattern of possible convergence has not been documented in vegetative morphology. Here, we examine floral and leaf traits in the context of geography across populations spanning the range of E. tithymaloides in the Caribbean to investigate whether patterns of morphological variation support a parallel shortening of the inflorescence along the Greater and Lesser Antillean expansion fronts towards the Caribbean. Using georeferenced data available for E. tithymaloides and regression, we document geographical patterns of morphological variation across the Caribbean basin. Our results suggest that there has been a parallel reshaping of the cyathium in both range expansion fronts where populations closer to the Anegada passage in the Antilles tend to have shorter cyathia. While convergence in floral morphology has been detected, climatic preferences do not seem to have a clear role in shaping such patterns along the geographic range of E. tithymaloides. Finally, we outline potential factors that could be involved in generating and maintaining such patterns.

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1 - Instituto de Biología, UNAM, Botany, 3er Circuito de CU s/n, Universidad Nacional Autónoma de México, Del. Coyoacán. México DF 04510, Mexico, 04510, Mexico
2 - NatureServe, 1680 38th St., Suite 120, Boulder, CO, 80301, USA
3 - Instituto de Biología, UNAM, Botany, 3er Circuito de Ciudad Universitaria s/n. Universidad Nacional Autónoma de México, Del. Coyoacán, Mexico, DF, 04510, Mexico

morphological clinal variation
climatic preferences.

Presentation Type: Oral Paper
Session: 19, ASPT Cooley Awards I
Location: 110/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 8:30 AM
Number: 19003
Abstract ID:162
Candidate for Awards:George R. Cooley Award

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