Contemporary evolution of an invasive plant is associated with climate but not with herbivory

Colomer-Ventura F., Martínez-Vilalta J., Zuccarini P., Escolà A., Armengot L., Castells E. (2015) Contemporary evolution of an invasive plant is associated with climate but not with herbivory. Functional Ecology. 29: 1475-1485.
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Doi: 10.1111/1365-2435.12463

Resum:

Divergence in plant traits and trait plasticity after invasion has been proposed as mechanisms favouring invasion success. Current hypotheses predict a rapid evolution in response to changes in the abiotic conditions in the area of introduction or to differences in the herbivore consumption pressure caused by a decrease in the enemies associated with the area of origin [e.g. evolution of increased competitive ability (EICA) hypothesis]. The importance of these factors in determining plant geographical divergence has not been yet simultaneously evaluated. Senecio pterophorus (Asteraceae) is a perennial shrub native to eastern South Africa and a recent invader in western South Africa (since ~100 years ago), Australia (>70-100 years) and Europe (>30 years). These areas differ in their summer drought stress [measured as the ratio of summer precipitation to potential evapotranspiration (P/PET)] and their interactions with herbivores. We performed a common garden experiment with S. pterophorus sampled throughout its entire known distributional area to determine (i) whether native and non-native populations diverge in their traits, as well as the plasticity of these traits in response to water availability and (ii) whether climate and herbivory play a role in the genetic differentiation across regions. Plants from the non-native regions were smaller and had a lower reproductive output than plants from the indigenous area. No geographical differences in phenotypic plasticity were found in response to water availability. Herbivory was not related to the plant geographical divergence. In contrast, our results are consistent with the role of climate as a driver for postinvasive evolution, as suggested by adaptation of plants to a drought cline in the native range, the analogous change in plant traits in independently invaded regions and the convergence of vegetative traits between non-native plants and native plants under similar drought conditions. Native and non-native populations of S. pterophorus differed in plant traits, but not in trait plasticity, in response to their local climatic conditions. Our results are contrary to the role of herbivory as a selective factor after invasion and highlight the importance of climate driving rapid evolution of exotic plants. © 2015 The Authors.

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Female reproductive success in gynodioecious Thymus vulgaris: Pollen versus nutrient limitation and pollinator foraging behaviour

Arnan X., Escola A., Rodrigo A., Bosch J. (2014) Female reproductive success in gynodioecious Thymus vulgaris: Pollen versus nutrient limitation and pollinator foraging behaviour. Botanical Journal of the Linnean Society. 175: 395-408.
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Doi: 10.1111/boj.12173

Resum:

Gynodioecy is a dimorphic breeding system in which female individuals coexist with hermaphroditic individuals in the same population. Females only contribute to the next generation via ovules, and many studies have shown that they are usually less attractive than hermaphrodites to pollinators. Several mechanisms have been proposed to explain how females manage to persist in populations despite these disadvantages. The 'resource reallocation hypothesis' (RRH) states that females channel resources not invested in pollen production and floral advertisement towards the production of more and/or larger seeds. We investigated pollination patterns and tested the RRH in a population of Thymus vulgaris. We measured flower display, flower size, nectar production, visitation rates, pollinator constancy and flower lifespan in the two morphs. In addition, we measured experimentally the effects of pollen and resource addition on female reproductive success (fruit set, seed set, seed weight) of the two morphs. Despite lower investment in floral advertisement, female individuals were no less attractive to pollinators than hermaphrodites on a per flower basis. Other measures of pollinator behaviour (number of flowers visited per plant, morph preference and morph constancy) also showed that pollinators did not discriminate against female flowers. In addition, stigma receptivity was longer in female flowers. Accordingly, and contrary to most studies on gynodioecious species, reproductive success of females was not pollen limited. Instead, seed production was pollen limited in hermaphrodites, suggesting low levels of cross-pollination in hermaphrodites. Seed production was resource limited in hermaphrodites, but not in females, thus providing support for the RRH. © 2014 The Linnean Society of London.

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