Johanne Brunet ^1* John Kelly ²

• ¹ Brunet Research, Madison, WI, United States
• ² University of Kansas, Lawrence, Kansas, United States

Inbreeding depression (ID) and selfing rate are closely connected. The increase in homozygosity 10 associated with selfing leads to a decrease in fitness and to ID, while ID affects the evolution of 11selfing. By transmitting an extra allele via self-pollen, selfers have a 3:2 genetic advantage over 12 outcrossing. Based on this simple consideration, ID greater than 0.05 favors complete outcrossing; ID 13 less than 0.5 favors complete selfing. 14 15The Research topic comprises six papers that present new theoretical or empirical perspectives on 16 different aspects of ID and mating system evolution and their impact in natural populations. between 10 and 640). They observed a statistically significant interaction between neighborhood and 64 density on plant size. Density dependent effects on plant size were greatest in outcrossed 65 neighborhoods suggesting their superior competitive ability. Variation in size and size inequalities 66 were greatest in mixed relative to homogeneous neighborhoods at the final census, suggesting 67 asymmetric competition. The authors explain how their findings align with the concept of soft 68 selection that can mitigate the genetic load associated with inbreeding depression and its 69 demographic consequences. 70 71 Colonizing species often have small, isolated populations prone to genetic bottlenecks, genetic drift 73 and inbreeding. A mixed mating system, where both selfing and outcrossing can occur, may improve 74 colonizing success. Despite the potential importance of inbreeding depression and mating system in 75 the colonization process, few studies have examined their impact for invasive species. 76Balogh and Barrett estimate the relative fitness of selfed and outcrossed offspring of an invasive 77 plant, Lythrum salicaria, purple loosestrife, a partially self-incompatible tristylous plant species. 78Plants were grown in the presence and absence of intraspecific competition from selfed or outcrossed 79 neighbors. The cumulative inbreeding depression over four years was 48-68% (depending on the 80 method of estimation for multiplicative fitness), lower than many estimates from outcrossing 81 perennial plant species, possibly as a result of the species' autotetraploidy.