Why are fruit traits of Cistus ladanifer (Cistaceae) so variable: A multi-level study across the western Mediterranean region

Variation is the raw material for evolution. Differences among populations in the expression of traits related to plant fitness may result from natural selection, phenotypic plasticity (in response to local conditions), and developmental instability (manifested as high intra-individual variation in repeated patterns or characters). Cistus ladanifer is a highly polymorphic plant distributed in the Mediterranean and the only species in the family (Cistaceae, 180 species) with a variable number of valves per fruit. We herein analysed the variation in the number of valves (5-12) and seeds (318-1185) per fruit in 36 populations (607 individuals, 1821 fruits) at different levels: temporal, geographical, ecogeographical, taxonomic, and phylogeographical. In addition, we tested whether an increased number of fruit valves influences pre-dispersal seed predation. Large variation in the number of valves and seeds per fruit among populations, individuals, and years was reported. The number of ovules and seeds per valve increased with a higher number of fruit valves. Geographical and taxonomic variables did not significantly explained this fruit variation. On the contrary, we found a negative relationship between the number of fruit valves and altitude and a positive relationship with precipitation. We argue that ecogeographical factors, in addition to some phylogeographical and phylogenetic signals, are involved in the multiplication of carpels during the development of the ovary wall. This, coupled with the results of the evolutionary history of Cistus in previous studies, indicates active evolutionary processes in C. ladanifer populations.