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. Size-corrected 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.
Highlights
The timing of the onset of reproduction and the number of offspring produced by an individual are two fundamental life-history traits closely linked to fitness in an environment (Stearns, 1992; Braendle et al, 2011)
We focus on phenotypic plasticity and among-populations genetic variation in plasticity for reproductive allometry in range-wide P. halepensis populations assessed in a common garden experiment replicated in two contrasted sites
We found that plants in the high-stress site had lower biomass and height compared with those in the lowstress site, confirming that overall environmental differences between both sites had an effect on vegetative growth (Table 3, Fig. 2)
Summary
The timing of the onset of reproduction and the number of offspring produced by an individual are two fundamental life-history traits closely linked to fitness in an environment (Stearns, 1992; Braendle et al, 2011). According to life-history theory, individuals that a 2013 THE AUTHORS. 26 (2013) 1912–1924 JOURNAL OF EVOLUTIONARY BIOLOGY a 2013 EUROPEAN SOCIETY FOR EVOLUTIONARY BIOLOGY expected that plants, long-lived perennials, will delay reproduction in favourable environments until they reach an optimal size for reproduction both by means of genetic change and phenotypic plasticity provided that selective forces act at local and broad scales (Kozłowski, 1992; Roff, 1992) BIOL. 26 (2013) 1912–1924 JOURNAL OF EVOLUTIONARY BIOLOGY a 2013 EUROPEAN SOCIETY FOR EVOLUTIONARY BIOLOGY expected that plants, long-lived perennials, will delay reproduction in favourable environments until they reach an optimal size for reproduction both by means of genetic change and phenotypic plasticity provided that selective forces act at local and broad scales (Kozłowski, 1992; Roff, 1992)
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