Fig. 2.
Relationships between geographic isolation, habitat area, and genetics of Mastigias populations. (A) Genetic distances between marine lake and lagoon populations of Mastigias medusae are positively correlated with the shortest geographic distances from the lakes to the lagoon. Regression of mean pairwise sequence difference corrected for intrapopulation variation (y) against log10-transformed shortest geographic distance (x) of lake populations from the lagoon gives y = 2.332 log10[x] -9.436 (SE on m ± 0.4752, c ± 2.380), R2 = 0.858, F1,4 = 24.072, P = 0.008. Linear regression by using untransformed geographic distances produced a weaker but still significant fit, y = 0.015x -0.177 (SE on m ± 0.004, c ± 0.642), R2 = 0.797, F1,4 = 15.741, P = 0.017. (B) Genetic diversity (#/n) of Mastigias populations is positively correlated with habitat area (Spearman's Rank correlation r = 0.975, P = 0.005, excluding OTM, which was decimated by the 1998 La Niña; ref. 28). Including OTM, r = 0.812, P = 0.050. Diversity in the lagoon (mean ± SE, n = 3) is shown for comparison but was not used to calculate correlation coefficients. Linear regression of genetic diversity on habitat area (m2) for the five lake populations excluding OTM gives y = (2.944 × 10-7)x + 0.119 (SE on m ± 0.000, c ± 0.037), R2 = 0.482, F1,3 = 2.791, P = 0.193. Linear regression of log10[diversity] on log10[area] for the five lake populations excluding OTM gives y = 0.352x -2.513 (SE on m ± 0.145, c ± 0.679), R2 = 0.662, F1,3 = 5.880, P = 0.094. (Insets) Expectations given genetic and phylogenetic consequences of island biogeography. (B Inset) Plotted on continuous linear axes (26).