Herbivores affect natural selection for floral‐sex ratio in a field population of horsenettle, Solanum carolinense

Abstract

Although aspects of a plant's breeding system are generally believed to have evolved in response to selection for effective pollination, herbivores may also play a selective role. Here we report on a field experiment involving 960 transplanted ramets of the andromonoecious herb Solanum carolinense in which the pattern of natural selection for an important breeding-system trait was influenced by naturally occurring herbivores. As the level of flower and fruit herbivory increased, the pattern of selection on floral-sex ratio went from stabilizing (with an optimum of 29% male flowers), to directional toward a lower proportion of males, with the optimum bottoming at 0% male. This pattern of selection likely helped generate the broad-sense genetic correlation (r = 0.42) between floral-sex ratio and resistance to herbivory. These results contribute to the growing awareness that herbivores can be important influences not only on plant resistance traits, but also on the evolution of their hosts' breeding system.

Temporal variation in extrafloral nectar secretion in different ontogenic stages of the fruits ofAlibertia verrucosaS. Moore (Rubiaceae) in a Neotropical savanna

“…Several authors have demonstrated that the damage caused by predators is greater in young fruits, mainly due to their physical properties, which make them softer (Reuveni & Reuveni 1995;Alford 2007;Ferna´ndez et al 2008;Wise & He´bert 2010). However, sometimes the predators do not have a special preference for young fruit (Clarke 1992;Lenzi et al 2006;Silva et al 2007), mainly because in some plant species the young fruits contain high levels of tannins compared with ripe fruits (Dement & Mooney 1974).…”

Pollinators exert natural selection on flower size and floral display inPenstemon digitalis

“…Six additional studies explicitly tested, by manipulating the pollination environment, whether pollinators were agents of selection (Andersson, 1996;Galen, 1996;Totland et al, 1998;Fishman & Willis, 2008;Parachnowitsch & Caruso, 2008;Sandring & Å gren, 2009), five studies manipulated herbivory (Juenger & Bergelson, 1998Gómez, 2003;Juenger et al, 2005;Wise & Cummins, 2007) and a further four studies manipulated the presence of co-flowering species (Caruso, 2000(Caruso, , 2001Moeller & Geber, 2005;Smith & Rausher, 2008), although one study examined facilitation by congeners rather than competition for pollinators (Moeller & Geber, 2005). Measures of flower morphology were by far the most common, followed by display and phenology.…”

Variation in floral sex allocation, female success, and seed predation within racemiform synflorescence in the gynomonoecious Ligularia virgaurea (Asteraceae)

“…Some researches have already suggested that floral traits or reproductive investment might also be subject to the action of antagonistic non-pollinator agents, especially herbivores (Ashman 2002;Herrera et al 2002;Kliber and Eckert 2004;Wise and Hèbert 2010). Evidences have been presented that andromonoecy, gynodioecy and dioecy may be selected, because they reduce the impacts of floral herbivory or pre-dispersal seed predation on reproductive success (Ashman 2002(Ashman , 2006Strauss and Whittall 2006;Wise and Hèbert 2010).…”