Environmental variation influences the magnitude of inbreeding depression in Cucurbita pepo ssp. texana (Cucurbitaceae)


C. Nelson Hayes, Department of Biology, 208 Mueller Lab, The Pennsylvania State University, University Park, PA 16802, USA.
Tel.: 814 863 6360; fax: 814 865 9131; e-mail: cnh1@psu.edu


We grew inbred and outcrossed Cucurbita pepo ssp. texana plants and measured inbreeding depression for several male and female fitness traits 4 years in a row in adjacent fields at the same field station under the same cultivation conditions. We found that the magnitude of inbreeding depression varied from 0.16 to 0.53 from year to year and that those traits which were most affected tended to vary with year. We also grew inbred and outcrossed C. pepo ssp. texana plants in two adjacent fields differing only in the presence of nitrogen fertilizer to examine the effect of nutrient limitation as a form of environmental stress on the magnitude of inbreeding depression. We found that inbreeding depression was more severe in the unfertilized field. Overall, this study illustrates the notion that any estimate of inbreeding depression represents a single point in a cluster of possible estimates that can vary (often dramatically) with growing conditions.