Latitudinal cline in morph frequency. Morph frequencies for each local population were shown as a pie chart (blue: andromorph; red: gynomorph). The frequency of andromorphs increased with latitude. The inset Figure shows the logistic regression with the latitude (t = 8.15, df = 21, P < 0.001), excluding the northernmost population (solid plot).
Takahashi et al. BMC Evolutionary Biology 2011 11:256 doi:10.1186/1471-2148-11-256