Neri et al. 2015 (Conference Paper) Vriesea

Reproductive isolation between incipient outcrossing and selfing Vriesea species (Bromeliaceae)

Author(s):—J. Neri, H. Moura-Neto, A.Y. Maêda, T. Wendt & C. Palma-Silva in Benko-Iseppon, A.M.; Alves, M. & Louzada, R. (2015) An overview and abstracts of the First World Congress on Bromeliaceae Evolution. Rodriguésia 66(2): A1-A66.

Publication:— (2015).

Abstract:—Speciation requires the evolution of reproductive isolation mechanisms that provide barriers to hybridization between diverging lineages. Patterns of gene flow in hybrid zones are often observed to be asymmetrical and these asymmetries can arise from variations in the strength and direction of isolation barriers in the species involved. Incipient species can be reproductively isolated effectively by one or multiple prezygotic or postzygotic mechanisms as long as they provide a strong barrier to gene flow. We aim to study the consequences of hybridization in the process of speciation-with-gene-flow between Vriesea simplex and Vriesea scalaris. These species have similar morphology, overlap in flowering phenology, and share hummingbird pollinators. Putative hybrids are reported when bromeliads occur in sympatry. Here, we will present: 1) a description of themating systems of both species and results of inter-specific manual-crossing; 2) genetic structure of sympatricand allopatric populations and genetic composition of hybrids, using 15 nuclear SSR loci. The intra-specific manual-crossing, revealed that V. simplex is predominantly outcrossing, whereas V. scalaris is predominantlyof selfing. Seed viability from selfing treatments in V. simplex (4.0±7.34) was much smaller than in V. scalaris (64.57±43.56), indicating that V. simplex is partially self-compatible and pollinator-dependent. The inter-specific manual-crossing treatments revealed higher fruit (F=3.597, p=0.064) and significantly seed set (F=5.702, p=0.022) for V. simplex, when receiving pollen of V. scalaris, (93.02%, and 581.43±235.56, respectively) than for V. scalaris when receiving pollen of V. simplex (74.07% and 422.43±180.35, respectively). These results may suggest hybridization is asymmetrical from V. scalaris to V. simplex. However, the percentage of seed germination was very low but similar among species (V. simplex = 26.60±38.24 and V. scalaris = 26.75±37.71),suggesting that postzygotic barriers can act at different stages. The analysis of genetic admixture, based on nuclear microsatellites, in three sympatric populations identified a total of 30 hybrids. The genetic diversity parameters in the outcrosser V. simplex were higher than in the selfer V. scalaris. V. scalaris species is more highly structured (FST =0.483) than V. simplex (FST=0.120). Furthermore, the inbreeding coefficient (FIS) of V. scalaris was higher (0.526) than in V. simplex (0.170). These data are consistent with the species? mating
system. The AMOVA analysis showed low genetic differentiation between species (7.12%). Collectively,
the results indicate mating system is a potential prezygotic barrier between these two species, and pointed to
the important role of postzygotic barriers to maintain species integrity.

Keywords:—Hybridization and Introgression; Speciation-with-gene-flow; Mating Systems.