Stock markets are dynamic. Therefore, investors hedge their bets or “don’t put all of their eggs in one basket” by investing in multiple stocks simultaneously. This reduces the chance of complete loss due to a stock crash but also reduces potential gains when a stock dramatically rises. Similarly, organisms may have evolved bet-hedging strategies that allow them to cope with dynamic environments. However, evidence supporting the existence of biological bet-hedging strategies stems primarily from theoretical work; that is, only a handful of good examples have been found in nature. Here we investigate bet hedging in a seed heteromorphic species or one that produces multiple morphologically different diaspores simultaneously. Preliminary work has shown that our species, Pectocarya heterocarpa, produces low dispersing/more dormant basal seeds and highly dispersing/quick germinating aerial seeds simultaneously. We collected specimens across an aridity gradient in the southwestern United States to test whether the ratios of the different seeds produced follow expectations from bet hedging theory. Furthermore, we germinated and raised the field collected offspring in a common garden environment to examine germination differences between populations as well as the level of plasticity associated with the ratio of basal to aerial seeds produced.
Results/Conclusions
Across the aridity gradient we found that, in agreement with bet hedging theory, the ratio of basal to aerial seeds significantly increases with increasing rainfall variation. However, when we grew F1 individuals from six extreme populations in a common garden environment, the pattern was reversed. A close look at this pattern revealed that the plants from less variable habitats did not alter their seed ratios very much between the field and greenhouse assessments but the plants from the more variable sites did so dramatically. This suggests that the plants from sites with high rainfall variability have greater plasticity in their ability to produce aerial seeds during periods of favorable conditions. Furthermore, we assessed the germination time and fractions of the seeds produced by the field collected plants. Interestingly we found that germination time in the growth chamber was fastest for plants from more variable rainfall sites, though their germination fractions were lowest as expected from bet hedging theory. These results suggest that plants from more variable sites may have the lowest field germination rates but this may be masked in germination trials with ample water because they have to be much more sensitive to water availability to achieve any germination in their natural habitat.