Contributions to Zoology, 86 (2) – 2017Gerrit Potkamp; Mark J.A. Vermeij; Bert W. Hoeksema: Genetic and morphological variation in corallivorous snails (Coralliophila spp.) living on different host corals at Curaçao, southern Caribbean
Results

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Allometry

Allometric patterns were important in determining the shell shape in both C. galea and C. caribaea. In both species, shell length explained minor variation in shell shape (R2 = 0.072; p = 0.001 and R2 = 0.041; p = 0.049 for C. galea and C. caribaea, respectively), and these relationships depended on the host on which snails were found (shell length and host species interaction, R2 = 0.046; p = 0.001 and R2 = 0.133; p = 0.004 for C. galea and C. caribaea, respectively). The presence of such host-associated differences was also implied by the regressions between the CAC and shell length, where the slope of these linear regressions varied among snails associated with different host species (regressions were only done for hosts with ≥ 5 specimens; Fig. 11). Post-hoc tests further confirmed the presence of host-associated differences in allometric patterns in both C. galea and C. caribaea. Predicting the hypothetical shell shape of shells associated with a certain host species for a specific shell length, based on linear regressions of PC scores against shell length, clearly showed these differences (Fig. 12). Allometric patterns were subtler in C. caribaea compared to C. galea. In case of C. galea, both the distance (i.e., amount of change per unit of growth) and correlation (i.e., the direction of change) among vectors of shell length were, after Bonferroni corrections (n = 45), different for six pairs of host species (Fig. 12a; Table S6 in Online Supplementary Material 4). In C. caribaea, the correlation of vectors differed for a single pair of host species, while no differences were observed in the distances among vectors (Fig. 12b; Table S7 in Online Supplementary Material 4).

FIG2

Fig. 11. Allometric patterns in Coralliophila galea (a) and C. caribaea (b). Common allometric component (CAC) is plotted against shell length (a). Separate regressions for host species with five or more specimens are plotted, symbols on the lines represent the R2-value (first symbol) and p-value (second symbol) of the regression: ns: p > 0.05; *: R2 < 0.1, p < 0.05; **: R2 ≥ 0.1, p < 0.01; ***: R2 ≥ 0.5, p < 0.001; ****: R2 ≥ 0.75, p < 0.0001. Points and regression lines per host are colour-coded as in Figs. 9-10. Shell length is plotted on a logarithmic scale.

FIG2

Fig. 12. Predicted shell shape of Coralliophila galea (a) and C. caribaea (b) shells of different shell lengths associated with different host species, based on principal component scores of repeatable axes. Grids show the predicted shape of the largest specimen collected from the respective host, warped against the predicted shape of the smallest specimen collected. Black arrows indicate significant differences in the amount of change in shell shape per unit of growth, red arrows indicate significant differences in the direction of change in shell shape. Significant differences: *: p < 0.05; **: p < 0.01.