Enhancement of Allee effects in plants due to self-incompatibility alleles

Authored by Sahotra Sarkar, Donald A Levin, Christopher D Kelley

Date Published: 2009

DOI: 10.1111/j.1365-2745.2009.01499.x

Sponsors: No sponsors listed

Platforms: No platforms listed

Model Documentation: Other Narrative

Model Code URLs: Model code not found

Abstract

Founder populations of plants are usually small and may become extinct due to many factors including inbreeding and low pollen transfer besides stochastic factors. This positive relationship between population size and individual fitness is taken as evidence of an Allee effect. Very few studies have quantitatively compared the influence of self-incompatibility systems and S-allele counts on the magnitude of observed Allee effects for different population sizes and seed and pollen dispersal distances. This paper uses a stochastic, spatially explicit, individual-based cellular automaton model to simulate the dynamics of newly established plant populations with sporophytic or gametophytic self-incompatibility (SI) alleles and compares these to a null (Mendelian) population. Parameters varied in model simulation are the S-allele count, the initial population size, and the pollen and seed dispersal distances. These parameters were studied over a wide range to assess their relative impact on population viability compared to the null case in order to model the effect of self-incompatibility on population fitness. The results indicate that Allee effects are enhanced and growth rates are slowed in newly established populations of species with S-alleles relative to Mendelian populations, leading to enhanced extinction risk. They also show the importance of the relationship between pollen and seed dispersal ranges on the fitness of the population. Populations with sporophytic self-incompatibility were more extinction-prone than those with gametophytic SI, and the latter more so than Mendelian populations when all other factors were held constant. Synthesis. Overall, the simulation results indicate that Allee effects in small populations are enhanced in plants with S-alleles. Even in relatively large populations, S-allele count controls the strength of observed Allee effects. A high S-allele count is able to compensate for lower initial population size. Pollen and seed dispersal ranges had a similarly strong effect on the viability of populations with S-alleles. These effects are stronger in populations with sporophytic self-incompatibility than in those with gametophytic SI. Simulation results also indicate that S-alleles were not lost to genetic drift over time, in contrast with some earlier studies of S-allele systems displaying Allee effects.

Tags

Habitat fragmentation Reproductive success Natural-populations Ranunculus-reptans Population-size Inbreeding depression Species brassica-insularis Genetic rescue Cross-compatibility Seed production