Plasticity in reproduction and growth among 52 range‐wide populations of aMediterranean conifer: adaptive responses to environmental stress

Abstract

A plastic response towards enhanced reproduction is expected in stressful environments, but it is assumed to trade off against vegetative growth and efficiency in the use of available resources deployed in reproduction [reproductive efficiency (RE)]. Evidence supporting this expectation is scarce for plants, particularly for long-lived species. Forest trees such as Mediterranean pines provide ideal models to study the adaptive value of allocation to reproduction vs. vegetative growth given their among-population differentiation for adaptive traits and their remarkable capacity to cope with dry and low-fertility environments. We studied 52 range-wide Pinus halepensis populations planted into two environmentally contrasting sites during their initial reproductive stage. We investigated the effect of site, population and their interaction on vegetative growth, threshold size for female reproduction, reproductive-vegetative size relationships and RE. We quantified correlations among traits and environmental variables to identify allocation trade-offs and ecotypic trends. Genetic variation for plasticity was high for vegetative growth, whereas it was nonsignificant for reproduction. Sizecorrected reproduction was enhanced in the more stressful site supporting the expectation for adverse conditions to elicit plastic responses in reproductive allometry. However, RE was unrelated with early reproductive investment. Our results followed theoretical predictions and support that phenotypic plasticity for reproduction is adaptive under stressful environments. Considering expectations of increased drought in the Mediterranean, we hypothesize that phenotypic plasticity together with natural selection on reproductive traits will play a relevant role in the future adaptation of forest tree species.

Dioecious plants are more precocious than cosexual plants: A comparative study of relative sizes at the onset of sexual reproduction in woody species

“…(2009) suggested precocious reproduction as a mechanism of compensation for the disadvantages. Although the reproductive size thresholds of long‐lived plants has been studied in several studies (Barot et al., 2005; Davies & Ashton, 1999; Santos‐del‐Blanco et al., 2013; Thomas, 1996; Wright et al., 2005), Bruijning et al. (2017) are the only one to examine the association between the sex expression of plants and their size at the onset of flowering.…”

Ecological and association genetics in two Mediterranean pine species

“…As found in previous studies, areas with milder temperatures and higher rainfall selected for high growth rates, non-conservative water use efficiency and low reproductive investment (Ferrio et al 2003;Voltas et al 2008Voltas et al , 2015Santos-del-Blanco et al 2013). This could be explained by selective pressures favouring a competitive strategy, involving more investment in vegetative growth in order to outcompete neighbouring trees (Grime 1977;Falster and Westoby 2003).…”

“…Previous studies had already found intraspecific genetic variability in the species for growth traits (Voltas et al 2008;Esteban et al 2010;Santos-del-Blanco et al 2013;De La Mata et al 2014), water use efficiency (Ferrio et al 2003;Chambel et al 2007;Voltas et al 2008Voltas et al , 2015 and morphometric and anatomical traits (Esteban et al 2010). We did not find Table 2.2).…”

“…is a long-lived conifer, widely distributed across the Mediterranean Basin, where it can be found across environments encompassing a broad range of moisture and thermal conditions. It has also remarkable capacity to cope with dry and low-fertility environments (Voltas et al 2008;Santos-del-Blanco et al 2013). Previous studies suggest that Aleppo pine populations expanded westwards all around the Mediterranean basin from some refugia located in the southern part of the Balkan Peninsula (Grivet et al 2009).…”

“…And second, ecotypic trends or clinal variation, i.e. continuous genetically-based phenotypic variation along environmental gradients (Santos-del-Blanco et al 2013;De La Mata et al 2014;Gauli et al 2015). The combined study of growth, wood quality, stress response and reproductive trait phenotypes at the individual and population level can shed light on the complex patterns of adaptation in forest trees.…”