Abstracts (first author)

Poster 

The evolution of sexual segregation within inflorescences: the role of resource competition by flowers

Author(s): Afonso A, Castro S, Méndez M, Gómez J, Anderberg AA, Torices R

Summary:

Spatial segregation of sexual functions within inflorescences has been explained as a mechanism of avoiding self-fertilization reducing the negative effects of inbreeding. However, many species with sexual functions separated in different flowers also have self-incompatibility systems making difficult generalizations of this hypothesis. An alternative hypothesis for this pattern is that flowers within inflorescences compete by resources, and that the sequential development of flowers and architectural constraints lead to a gradient on resource availability. For instance, fruit size also follows a positional pattern within inflorescences supporting this resource gradient. This variation on resource availability produces distinct optima for sex allocation accordingly with the position of the flower within an inflorescence, potentially driving the evolution of sexual specialization on separated flowers. Using as a model the largest family of flowering plants, Asteraceae, we explored whether floral specialization in sex functions (either male or female unisexual flowers) within inflorescences was related with higher levels of floral aggregation and therefore with higher resource competition between different flowers within the inflorescence. We measured number of flowers and capitulum size to estimate flower density in 101 species with different levels of sexual specialization: hermaphroditic (only bisexual flowers), gynomonoecious (bisexual and female flowers) and monoecious species (female and male flowers), using herbarium specimens from Swedish Natural History Museum and Coimbra University Herbarium. Statistical differences were assessed with phylogenetic generalized least squared models. Flower number and flower density at inflorescence level was correlated with the specialization degree on floral gender, suggesting that the increase of floral competition might favor sex specialization of male and female functions on different flowers within inflorescences.



Abstracts (coauthor)

Summary:

Hybridization can create natural hybrid zones where two related species mate and produce (some) viable hybrids. These areas are natural laboratories to investigate evolutionary processes and mechanisms operating in the organisms integrating them, especially gene flow and selective pressures on phenotypic traits. For example, hybrid zones often present a striking profusion of flower morphologies and floral traits may profoundly influence both formation and fitness of hybrids primarily through the effect on pollinator behaviour. Within the Circum-Mediterranean genus Anacyclus, the rayed-head species A. clavatus co-exists with the rayless-head A. valentinus along the Western Mediterranean coast. In these mixed populations, a high phenotypic diversity in the number and size of ray florets has been observed revealing the existence of a dynamic hybrid zone. The presence of rays has been shown to have significant consequences on pollination, primarily enhancing the attractiveness of heads and consequently influencing the levels of outcrossing. These species show a generalist pollination syndrome since they are commonly visited by more than 80 species of insects. However, the role of pollinator preferences in hybrid zones between highly generalist species remains unknown and its study might help understanding how generalist interactions exert selection of floral phenotypes. Hence, this hybrid zone provides an exceptional microevolutive framework to explore how generalist pollinators are driving the evolution of floral phenotypes. To explore the role of pollinator preferences on floral traits we investigated floral trait variation on a natural hybrid zone of A. clavatus and A. valentinus and assessed the number and type of pollinator visits on each phenotype. Furthermore, we performed phenotypic manipulations of floral morphologies for a better understanding of pollinator preferences

Contacts

Chairman: Octávio S. Paulo
Tel: 00 351 217500614 direct
Tel: 00 351 217500000 ext22359
Fax: 00 351 217500028
email: mail@eseb2013.com

Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

Website

Computational Biology & Population Genomics Group 
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