Horseshoe crab body size cline

Aim
Adult body size often exhibits patterns across large-scale environmental gradients, creating ecogeographic clines. However, the form of body size clines varies across taxonomic groups, with linear and non-linear patterns in body size observed in nature. Non-linear body size clines have received less study, and questions remain about how environmental gradients interact to produce non-linear clines. We examined the body size of the American horseshoe crab (Limulus polyphemus), a widely distributed marine arthropod, and evaluated the hypothesis that temperature and active season length can interact multiplicatively to result in a dome-shaped distribution.
Location
Fourteen states in the United States of America and three Mexican states, representing the entire geographic range of the species.
Methods
We compiled environmental data and body size measurements from more than 49,000 individual horseshoe crabs. For each location, we extracted from the literature or calculated from raw data...