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Ann Bot

Title:		Pollinator convergence and the nature of species' boundaries in sympatric Sardinian Ophrys (Orchidaceae)
Author(s):		Cortis P; Vereecken NJ; Schiestl FP; Barone Lumaga MR; Scrugli A; Cozzolino S;
Address:		"Dipartimento di Scienze Botaniche, Universita degli Studi di Cagliari, I-09123 Cagliari, Italy"
Journal Title:		Ann Bot
Year:		2009
Volume:		20081110
Issue:		3
Page Number:		497 - 506
DOI:		10.1093/aob/mcn219
ISSN/ISBN:		1095-8290 (Electronic) 0305-7364 (Print) 0305-7364 (Linking)
Abstract:		"BACKGROUND AND AIMS: In the sexually deceptive Ophrys genus, species isolation is generally considered ethological and occurs via different, specific pollinators, but there are cases in which Ophrys species can share a common pollinator and differ in pollen placement on the body of the insect. In that condition, species are expected to be reproductively isolated through a pre-mating mechanical barrier. Here, the relative contribution of pre- vs. post-mating barriers to gene flow among two Ophrys species that share a common pollinator and can occur in sympatry is studied. METHODS: A natural hybrid zone on Sardinia between O. iricolor and O. incubacea, sharing Andrena morio as pollinator, was investigated by analysing floral traits involved in pollinator attraction as odour extracts both for non-active and active compounds and for labellum morphology. The genetic architecture of the hybrid zone was also estimated with amplified fragment length polymorphism (AFLP) markers, and pollination fitness and seed set of both parental species and their hybrids in the sympatric zone were estimated by controlled crosses. KEY RESULTS: Although hybrids were intermediate between parental species in labellum morphology and non-active odour compounds, both parental species and hybrids produced a similar odour bouquet for active compounds. However, hybrids produced significantly lower fruit and seed set than parental species, and the genetic architecture of the hybrid zone suggests that they were mostly first-generation hybrids. CONCLUSIONS: The two parental species hybridize in sympatry as a consequence of pollinator overlap and weak mechanical isolation, but post-zygotic barriers reduce hybrid frequency and fitness, and prevent extensive introgression. These results highlight a significant contribution of late post-mating barriers, such as chromosomal divergence, for maintaining reproductive isolation, in an orchid group for which pre-mating barriers are often considered predominant"
Keywords:		"Animals Flowers/anatomy & histology/ultrastructure Fruit/growth & development Hybridization, Genetic Odorants Orchidaceae/classification/genetics/*parasitology/ultrastructure Pollination/*physiology Seeds/growth & development Species Specificity;"
Notes:		"MedlineCortis, P Vereecken, N J Schiestl, F P Barone Lumaga, M R Scrugli, A Cozzolino, S eng Research Support, Non-U.S. Gov't England 2008/11/13 Ann Bot. 2009 Aug; 104(3):497-506. doi: 10.1093/aob/mcn219. Epub 2008 Nov 10"