Abstract
Background fecundity and viability selections on phenological traits are difficult to distinguish in plants, where vegetative and reproductive phenologies are closely synchronized. Moreover, interference with sexual selection may arise from assortative mating (the positive correlation between mates for flowering time). This study aims at disentangling these components of selection on spring phenology in European beech.
Methods the timing of budburst (TBB) was surveyed in 147 and 192 adult trees in two natural populations at low and high elevation respectively along an altitudinal gradient. Male and female individual fecundities were estimated using paternity and parentage analyses of 1414 seeds and 473 seedlings, which also allowed mating networks to be inferred. Morever, TBB and growth was surveyed in 1552 and 1709 seedlings originating from the same populations and planted in a common garden.
Results assortative mating occurred only at low elevation, where spring phenology was also more spread out. Phenological mismatch reduced male but not female fecundities at both plots, indicating sexual selection to maximize mating opportunities. At high elevation, directional fecundity selection for earlier TBB occurred both through male and female fecundities. At low elevation, directional fecundity selection for earlier spring phenology was mitigated by a positive association between TBB and fecundity in the smaller trees. In the common garden, early budburst was associated to higher seedling growth.
Discussion This study showed that sexual selection arising from assortative mating could drive stabilizing selection on TBB through the male function, while selection through female fecundity predominantly selects for earlier TBB. This intertwining of sexual and fecundity selection calls for an integrative approach to predict the evolution of spring phenology under changing climate.
Competing Interest Statement
The authors have declared no competing interest.
