Genetic consequences of plant facilitation

Abstract

Facilitation, the positive interaction where a nurse plant provides regeneration niches for other plants (beneficiary), can increase both the species diversity and the phylogenetic diversity of the communities where it is prevalent. The underlying causes are mostly related to improved environmental conditions for regeneration. Because these improved conditions can affect plant populations at the same temporal scales, facilitation could also have potential genetic effects at the intra-population level of beneficiary species. These within-species genetic consequences of facilitation have not yet been explored. We tested whether facilitation can lead to increased genetic diversity and structuring of a beneficiary species, Euphorbia nicaeensis. This species is abundant at a high-altitude community where it is benefitted from Juniperus sabina cushions, which also act as nurses for many other species. As in other communities, phylogenetic diversity of the community is higher under J. sabina cushions. We found that a parallel situation of increased intra-population genetic diversity under nurse trees is not present for Euphorbia nicaeensis, as measured with AFLP markers. However, facilitation does lead to genetic structuring of kinship relationships among individuals: a spatially controlled analysis showed that individuals growing under nurse trees have higher kinship coefficients among them than with individuals growing in open areas, and vice versa. For this species, facilitation seems to promote a mating separation of facilitated individuals from non-facilitated congeners even at small spatial scales. We explore the possible ecological mechanisms behind this genetic pattern.