University of British Columbia, British Columbia, Canada
Background/Question/Methods
Despite the knowledge that warming-mediated shifts in insect body size are likely to have significant consequences for many ecological processes, there are few studies that directly link the changes in body size caused by warming to ecological function in natural settings. The existing studies that fall under this broad research umbrella can typically be grouped into those that: (a) use laboratory experiments to examine the effect of temperature on body size, fecundity, and sometimes flight vs. (b) those that examine correlations between insect body size and ecological functions such as pollination, dispersal, and nutrient cycling. Here our goal is to join these two lines of research. We first use laboratory experiments to examine the effects of warming on body size and flight in the widespread butterfly species Pieris rapae (Lepidoptera, Pieridae). We focus on these traits because of their clear links to fecundity, mating success, resource acquisition, dispersal, and plant-insect interactions. Second, we use the results from the experiment to predict how butterfly wing size should affect pollen accumulation and diversity in P. rapae, and we test these predictions using a correlational study on wild-caught P. rapae.
Results/Conclusions
Overall, we found that butterflies were smaller when reared in the lab at warmer temperatures, and when tested on a flight mill, smaller butterflies flew more slowly and tended to fly shorter distances compared to larger butterflies. We predicted that in nature, smaller butterflies with reduced flight capacity may end up visiting fewer flowers and amassing less pollen. Indeed, when we examined the relationship between wing size and pollen number of wild-caught butterflies, wild butterflies of equivalent size to the 30˚C lab-reared butterflies carried 8% and 14% less pollen than did wild butterflies of equivalent size to the 24˚C or 18˚C-reared lab butterflies respectively. Our study thus demonstrates that developmental temperature has predictable effects on P. rapae body size and flight, and that even subtle decreases in wing size in nature have measurable effects on flower visitation and pollen accumulation. This study demonstrates that increased temperatures will likely have important consequences for butterfly-plant interactions in nature.
