Gender dimorphism in Corema album across its biogeographical area and implications under a scenario of extreme drought events

In dioecious species, traits may have evolved because of significantly different resource demands associated with male versus female sexual reproduction. It is generally assumed that females have higher reproductive costs, thereafter in long-lived species, males often exceed females in vigour and suffer lower physiological limitations under stress. However, large-scale studies of gender dimorphism and the link between survival and physiological responses and compensation mechanisms are still lacking. In this study, we compared canopy performance, photochemical efficiency, leaf water potential, Delta C-13, leaf nitrogen content and delta N-15 in both genders of the dioecious species Corema album (Ericaceae) across all the species' biogeographical distribution. This area corresponds to a wide climatic gradient, from temperate and humid to Mediterranean, across the Atlantic coast of the Iberian Peninsula. Our results evidenced that the species responds to the bioclimatic gradient, and most variables were significantly correlated with annual rainfall and bioclimatic indices, although gender dimorphism was only manifested in Delta C-13 and in leaf water potential at the peak of the drought season. Female plants have significantly higher values of Delta C-13, which could be attributed to lower water use efficiency; however, male plants presented more negative leaf water potentials than females, especially in the populations with the warmest and most arid climate. We concluded that C. album populations adjust to the climatic gradient at different hierarchical scales, from physiological instantaneous to time-integrated traits, with gender dimorphism only occurring in sub-optimal environments The absence of morphological differences between genders and the maintenance of a less negative water potential in females in the dry period in southern more arid populations, suggests the existence of compensatory mechanisms at underground level.