Abstract
BackgroundA central question for understanding the evolutionary responses of plant species to rapidly changing environments is the assessment of their potential for short-term (in one or a few generations) genetic change. In our study, we consider the case of Pinus pinaster Aiton (maritime pine), a widespread Mediterranean tree, and (i) test, under different experimental conditions (growth chamber and semi-natural), whether higher recruitment in the wild from the most successful mothers is due to better performance of their offspring; and (ii) evaluate genetic change in quantitative traits across generations at two different life stages (mature trees and seedlings) that are known to be under strong selection pressure in forest trees.ResultsGenetic control was high for most traits (h2 = 0.137-0.876) under the milder conditions of the growth chamber, but only for ontogenetic change (0.276), total height (0.415) and survival (0.719) under the more stressful semi-natural conditions. Significant phenotypic selection gradients were found in mature trees for traits related to seed quality (germination rate and number of empty seeds). Moreover, female relative reproductive success was significantly correlated with offspring performance for specific leaf area (SLA) in the growth chamber experiment, and stem mass fraction (SMF) in the experiment under semi-natural conditions, two adaptive traits related to abiotic stress-response in pines. Selection gradients based on genetic covariance of seedling traits and responses to selection at this stage involved traits related to biomass allocation (SMF) and growth (as decomposed by a Gompertz model) or delayed ontogenetic change, depending also on the testing environment.ConclusionsDespite the evidence of microevolutionary change in adaptive traits in maritime pine, directional or disruptive changes are difficult to predict due to variable selection at different life stages and environments. At mature-tree stages, higher female effective reproductive success can be explained by differences in their production of offspring (due to seed quality) and, to a lesser extent, by seemingly better adapted seedlings. Selection gradients and responses to selection for seedlings also differed across experimental conditions. The distinct processes involved at the two life stages (mature trees or seedlings) together with environment-specific responses advice caution when predicting likely evolutionary responses to environmental change in Mediterranean forest trees.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0200-5) contains supplementary material, which is available to authorized users.
Highlights
A central question for understanding the evolutionary responses of plant species to rapidly changing environments is the assessment of their potential for short-term genetic change
Microevolutionary change due to differences in maternal reproductive success and early selection is expected in Mediterranean maritime pine populations, and could be an important mechanism mitigating the negative consequences of climate change
Substantial genetic variation was detected for adaptive traits related to growth, ontogenetic change and biomass allocation in maritime pine, but no clear differences in phenotypic plasticity among seedlings when two different factors were considered
Summary
A central question for understanding the evolutionary responses of plant species to rapidly changing environments is the assessment of their potential for short-term (in one or a few generations) genetic change. [7,8]) They pose, some limitations derived from (i) potential trait multicollinearity, (ii) biases introduced by failure to include traits that covary with fitness, (iii) deviations of response variables from multivariate normality assumed for hypothesis testing, and (iv) failure to consider environmental factors that may induce spurious correlations [9]. It is not clear what the implications are of such selection gradients for a population’s adaptive potential, i.e. its ability to respond to selective pressures [10]. This component is difficult to estimate, especially for long-lived organisms in natural conditions ([11]; see [12] for some estimates in different organisms and the problems involved)
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