Inter-specific competitive stress does not affect the magnitude of inbreeding depression

Abstract

Hypothesis: Stressful inter-specific competition enhances inbreeding depression.<br />Organisms: Creeping spearwort (Ranunculus reptans L.) and its common competitor, the<br />creeping bentgrass (Agrostis stolonifera L.).<br />Field site: Outdoor common garden experiment at the University of Potsdam.<br />Methods: We collected plants of 12 natural populations of R. reptans differing in mean parental inbreeding coefficient (0.01–0.26). We performed within-population crosses for two<br />generations and kept the offspring in a common environment. In the second generation, we raised plants in the presence or absence of the grass competitor A. stolonifera. After 2 months,<br />we assessed survival and growth of two replicate plants per seed family and treatment. To compare our results with those of previous investigations, we compiled a list of studies on<br />inbreeding and competition.<br />Conclusions: Both population mean inbreeding and inter-specific competition led to a significant reduction in plant performance (survival and growth) and were therefore sources of stress. However, inbreeding and competition did not interact in their effects on plant<br />performance or developmental instability (estimated by within-family coefficient of variation in performance). Inter-specific competition did not enhance inbreeding depression, which is in line<br />with the results of most previous studies.