Effects of environmental variation on fitness of singly and multiply sired progenies of Raphanus sativus (Brassicaceae)

Two hypotheses have been proposed concerning possible fitness advantages of multiple paternity. According to the Elbow Room hypothesis, the magnitude of resource partitioning is positively correlated with the genetic diversity of competitors. This leads to the prediction that the mean fitness of competing half‐siblings will exceed the mean fitness of competing full‐siblings. The Lottery hypothesis suggests that in a patchy environment a genetically diverse sibship increases the probability that a mother will produce winning phenotypes for each of several different microsites. Both hypotheses were tested in a greenhouse experiment with wild radish, Raphanus sativus. Progeny derived from factorial crosses were raised in competition as full‐ or half‐siblings. To simulate environmental variation, the experiment was replicated across a gradient of nutrient concentrations. After 9 weeks, the aboveground biomass of all plants was harvested and oven‐dried. Although dry weights were strongly influenced by nutrient level, within nutrient classes there were no significant differences in the mean dry weight of full‐ and half‐sib competitors. Thus, there was no evidence for the Elbow Room hypothesis. In addition, there were no significant differences in numbers of winning phenotypes in the two competition regimes. Therefore, there was also no support for the Lottery hypothesis. Although competition regime did not influence the mean fitness of competing progeny, it significantly affected variation in dry weight of seedlings within pots. Higher coefficients of variation in half‐sib pots suggest that interference competition may be greater in genetically diverse sibships.