Figure 8. Alternative interpretations of the heterogeneous response to stress by individual nematodes.

At permissive temperatures (≤25°C) brood sizes are well described as normal distributions (as shown in Figure 2). However, at higher temperatures (≥28°C), the brood size distributions diverge from normal, and a mixture of two distributions is required to describe the data. Two different combinations of distributions could account for the observations. In both cases a fraction of the overall population consists of worms reproducing robustly; these are described by a normal distribution (blue). An exponential distribution (red) could indicate that chronic stress causes random reproductive failure among individuals in the population (A). A normal distribution (red) would suggest that subpopulations of individuals deploy qualitatively distinct reproductive strategies (B). Regardless of the explanation, there is a dichotomy of reproductive behaviors among individuals within populations under temperature stress.