Rarity and life-history strategies shape inbreeding and outbreeding effects on early plant fitness

Abstract

Local abundance and regional distribution are two aspects of a species’ rarity. They are suggested to differentially alter genetic processes in plants: Locally rare species are hypothesized to suffer less from inbreeding and outbreeding than locally common species, thanks to genetic purging through long inbreeding histories and weaker local adaptations, respectively. Regionally rare species are hypothesized to be more susceptible to outbreeding, but less to inbreeding, compared to regionally common ones, due to small and declining range size. While this has major implications for plant conservation practices, we lack evidences and general understanding on how breeding effects on a plant’s early life fitness are related to its local and regional rarity. To investigate effects of inbreeding and outbreeding on plants’ early fitness, we performed self-, within- and between-population pollinations in eight pairs of closely related species differing in regional and local rarity. To avoid biases due to context dependency, we took species competitive ability, habitat resource-richness and resource-allocation strategy into account in the analyses. We then tested how inbreeding and outbreeding affected five fruit-, seed- and seedling-related traits. Inbreeding did not generally have more negative effects on early fitness of regionally rare and non-competitive species than on regionally common and competitive ones. Outbreeding was generally beneficial to early fitness of plant species across the gradients of regional rarity, competitive ability and habitat resource-richness. Our results show that outbreeding may be beneficial to the early fitness of plant species, including rare and non-competitive ones and may be considered for conservation strategies.

Keywords

• Competitive ability
• Habitat resource-richness
• Inbreeding
• Outbreeding
• Rarity
• Resource-allocation strategy