Plants at population edges enjoy longer mating distances: Implications for conservation practice

Abstract

Habitat fragmentation and population declines have led to increased population edges, exposing higher proportions of plants to ecotones. However, it remains a challenging question how edge plants perform compared with interior ones, as they usually experience dissimilar abiotic and biotic interactions. To address this question, we performed experiments on a monoecious herb (Sagittaria trifolia) focusing on the reproductive fitness and mating patterns of individuals at the edge of two common gardens established under varied light conditions (open vs. understory) with natural pollination. Plant female fitness was determined by seed production, whereas male fitness and mating patterns were resolved by paternity analysis employing eight microsatellite markers. Results showed that edge plants had lower pollinator visitation frequency than interior ones in both gardens. However, there was no significant reduction in female or male reproductive success of edge plants. Instead, edge plants enjoyed longer distances of effective pollen dispersal when reproduced as males, as well as longer distances of sires when reproduced as females. This pattern was consistent across habitats and years. Together, the results indicate that edge plants not only maintained a comparable level of reproduction as interior ones but also enjoyed greater mating distances, which would likely bring about higher genetic diversity in their offspring. This further implies that edge effects may play an important role in promoting gene exchange and encouraging population recovery.