Selection patterns on early‐life phenotypic traits in Pinus sylvestris are associated with precipitation and temperature along a climatic gradient in Europe

Abstract

Summary Understanding the dynamics of selection is key to predicting the response of tree species to new environmental conditions in the current context of climate change. However, selection patterns acting on early recruitment stages and their climatic drivers remain largely unknown in most tree species, despite being a critical period of their life cycle. We measured phenotypic selection on Pinus sylvestris seed mass, emergence time and early growth rate over 2 yr in four common garden experiments established along the latitudinal gradient of the species in Europe. Significant phenotypic plasticity and among‐population genetic variation were found for all measured phenotypic traits. Heat and drought negatively affected fitness in the southern sites, but heavy rainfalls also decreased early survival in middle latitudes. Climate‐driven directional selection was found for higher seed mass and earlier emergence time, while the form of selection on seedling growth rates differed among sites and populations. Evidence of adaptive and maladaptive phenotypic plasticity was found for emergence time and early growth rate, respectively. Seed mass, emergence time and early growth rate have an adaptive role in the early stages of P. sylvestris and climate strongly influences the patterns of selection on these fitness‐related traits.

Latitudinal and Longitudinal Trends of Seed Traits Indicate Adaptive Strategies of an Invasive Plant

“…may also influence seed traits and germination progress, which needs further studies. But several studies have demonstrated that temperature and precipitation are the major factors affecting seed traits, plant performance, and distribution (Chamorro et al, 2018;Ramírez-Valiente et al, 2020;Zhou et al, 2020), as reported in the present study. Furthermore, the SEM analysis in this study indicated that the seed traits affected by MAT was stronger than MAP, which in line with previous study based on a worldwide meta-analysis (Moles et al, 2014).…”

Adaptive responses to temperature and precipitation variation at the early‐life stages of Pinus sylvestris

“…sylvestris have found positive associations between seed mass and emergence (Reich et al ., 1994; Castro, 1999; Ramírez‐Valiente & Robledo‐Arnuncio, 2015). Consistent with this finding, our previous phenotypic selection analyses showed directional selection for higher seed mass when considering the emergence rate as a fitness measure (Ramírez‐Valiente et al ., 2021). Heavier seeds have more reserves, which should favor successful embryo development, germination and seedling emergence (Castro et al ., 2006).…”

“…This design had a two‐fold rationale. First, replicating half‐sib families in four populations maximized their sample to conduct the phenotypic selection analyses used in a previous study (see Ramírez‐Valiente et al ., 2021). Second, it maximized the number of populations (18) to implement the fitness–climate regressions and mixed models of climatic transfer distances of the present study (see next sections).…”

“…Ramírez‐Valiente et al . (2021) examined how climatic conditions at the experimental sites during the study period affected fitness and altered the direction and magnitude of contemporary selection, using only the four populations for which individual seed mass, emergence time and developmental time were measured for phenotypic selection analyses. The present study uses all 18 populations available in the trials to assess population‐level variation in fitness and growth as a function of seed transfer distance.…”

“…sylvestris to examine the role of temperature‐ and precipitation‐related climatic variables as selective factors driving adaptive divergence at early‐life stages among populations of this widespread conifer, and to evaluate to what extent population differences in emergence, survival and early growth are consistent with a productivity–persistence trade‐off. A previous phenotypic selection study based on part of this same common garden network revealed that high temperatures, low precipitation and heavy rainfall events were associated with lower survival during the summer months, indicating that climate is an important driver of selection for P. sylvestris during the first life stages (Ramírez‐Valiente et al ., 2021). Other studies have reported high intraspecific variation in fitness and phenotypic traits during early‐life stages in this species (e.g.…”