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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Sex ratios

Sex could be determined for 609 specimens of C. galea and 115 specimens of C. caribaea. In C. galea, 74.4% were male. With 64.3%, the fraction of males in C. caribaea was lower (p = 0.030). Females were larger than males in both C. galea2 = 133.9; p < 0.0001) and C. caribaea (F = 35.1; p < 0.0001). Both males and females were found on all but one host species (C. caribaea on Porites furcata Lamarck, 1816, on which only female specimens were found). Sex ratios within C. galea differed among snails associated with different host species (p = 0.0004; only including hosts with ≥ 5 specimens; Fig. 13a). After Bonferroni correction of p-values (n = 78) one pair remained significant: snails associated with Agaricia humilis Verrill, 1901 had a higher male to female ratio than snails associated with Colpophyllia natans (Houttuyn, 1772) (p = 0.032). Within C. caribaea, no variation in sex ratios between host species existed (p = 0.975; only including hosts with ≥ 5 specimens; Fig. 13b). Sex ratio of C. caribaea associated with alcyonaceans (66.0% male) and scleractinians (63.1% male) was similar as well (p = 0.845).

FIG2

Fig. 13. Sex ratios of Coralliophila galea (a) and C. caribaea (b) associated with different host species. Host species are ranked based on the fraction of males. After Bonferroni correction for multiple pairwise comparisons, no significant differences remained in C. caribaea. Significant differences: *: p < 0.05.

Within C. galea, mean length of females per host species correlated with the mean length of males (R2 = 0.707; p = 0.0002) (Fig. 14a). The same was observed in C. caribaea (R2 = 0.614; p = 0.011) (Fig. 14b).

FIG2

Fig. 14. Mean shell length against the proportion of male snails per host species of Coralliophila galea (a) and C. caribaea (b). Regression was not significant for C. caribaea (b). In the linear regression, individual points were weighed per number of observations per host species. Number of observations is represented by the size of points. Points are coloured by host order (b), blue for Alcyonacea, red for Scleractinia.