An individual’s lifetime fitness and patterns of mating between individuals are interdependent features of sexual organisms. Mating systems (outcrossing vs. selfing or mating between close rela-tives) can affect the distribution of offspring fitness, which generally declines with inbreeding, which in turn is related to a population’s genetically effective size (Ne). Fitness and mating patterns are also expected to vary with proximity of mates (i.e., population density). Consequently, density and Ne may influence demographic and genetic changes over generations and interact in their effects. Here, we report an experiment designed to assess the influence of these two population-level properties on mating system and lifetime fitness. In experimental arrays under quasi-natural conditions, we varied the density and Ne of the hermaphroditic annual legume Chamaecrista fasciculata. We recorded components of fitness for each individual and employed microsatellite markers to estimate outcrossing and assign paternity. We used aster analyses to estimate lifetime fitness for genetic families using female (seeds set) and male (seeds sired) reproduction as fitness measures. With estimates from these analyses, we assessed the evidence for a trade-off between fitness attained through female versus male function, but we found none. Lifetime fitness increased with density, especially under high Ne. Outcrossing rates increased with density under high Ne but declined modestly with density under low Ne. Our results show that density and Ne have strong direct effects on fitness and mating systems, with negative fitness effects of low Ne limiting the positive effects of increasing density. These findings highlight the importance of the interactive effects of density and Ne on lifetime fitness.
Bibliographical noteFunding Information:
We thank Bailey Choudhury, Lauren Sawich, Shelby Flint, and Daniel Wright for field and logistical expertise; Charles Geyer and Frank Shaw for assistance with aster modeling; Anna Peschel for pedigreed Chamaecrista fasciculata seeds; Nicholas Deacon, Sarah Jordan, and Jennine Cavender-Bares for molecular lab equipment and assistance; and Mabi Hos-seinalizadehnobarinezhad and Lisa Wallace for kindly supplying microsatellite primer sequences and polymerase chain reaction conditions. We thank Chris Caruso and Michael Whitehead for comments and criticisms that greatly improved the manuscript. Finally, we thank two anonymous reviewers, Lynda Delph, and Daniel Bolnick for suggestions that improved the manuscript. This work was funded by a National Science Foundation grant (DEB-1257462) to R.G.S.
© 2021 by The University of Chicago.
- Chamaecrista fasciculata
- Mating system
- Population density
- Siring success
- Soft selection