Eocyzicus argillaquus

Hethke, Manja & Weeks, Stephen C., 2020, Fig. 25 in Fig. 20. Sesarmops mora n in Paralbunea dayriti, Zoological Studies 59 (33), pp. 1-11 : 10-13

Eocyzicus argillaquus

Shape

PC1, PC2, and PC3 explain 30.0%, 18.3%, and 14.1% of the variance in the Fourier dataset ( Fig. 9B , Table S4, Fig. S2 ). Ordinary least squares regression of PC1 and PC2 scores versus H / L ( Fig. 11 ) indicates that PC1 is driven by that ratio (compare specimens in Fig. 10A and B ). According to Fourier shape analysis (NPMANOVA in Table 6), there is an overall significant population density effect on carapace shape (p (same) = 0.0021). However, that difference in shape is driven by the distinct shape of clam shrimp in single-individual cups, reflecting the size results in table 5.

Burnaby transformation of linear measurements

NPMANOVA of the multivariate size dataset that has been transformed using Burnaby’s method was not distinct ( Table 7; p (same) = 0.1275), with only two significant pairwise comparisons (cups 10 and 1; 10 and 3). Fourier shape analysis seems superior for shape discrimination in clam shrimp.

Size and shape comparison

We tested the overprint of population density on inter-species variability by combining the size and shape datasets, respectively. In the size analysis ( Fig. 12A ), PC1 (75.2%) discriminates between the two species, whereas the population density effect on size is mostly picked up by PC2 (19.2%). Also, size variation is larger in Eulimnadia texana than in Eocyzicus argillaquus . Inter-species shape distinction is even more pronounced ( Fig. 12B ); PC1 (86.6%) represents the distinction between two species whereas the population density effect on shape is only represented by higher principle components. The perfect distinction between the two species is due to inter-family size and shape variability. Intra-family variability will be subtler.

Figures

Fig. 9. Population density effect on size and shape in Eocyzicus argillaquus. A, Biplot of principal component scores and variable vectors (loadings) on PC1 and PC2 of a set of log-transformed linear measurements. Outlines scaled to size. B, Population density effect on shape in Eocyzicus argillaquus based on Fourier shape analysis. Outlines represent shape only.

Fig. 2. Eulimnadia texana experiment (number of individuals = 49). Individuals were transferred into cups of various population densities three days after hydration (1, 5, 10 and 15 individuals/400 ml). A, Population survival. All individuals in cup 5.2 and in the four single-individual cups survived, while density declined fast in cups 10.2 and 15. B, Superimposed growth curves for all nine cups (compare with Fig. 3).

Fig. 11. A, B, Ordinary least squares regression of PC1 and PC2 scores (shape analysis) by the H/L ratio, which drives shape variable PC1.

Fig. 10. Shape dependency on population density in Eocyzicus argillaquus. A–D, 1.1_1 (1 inds/400 ml), 7.1_3 (6.6 inds/400 ml), 15.1_6, 15.1_7 (both 14 inds/400 ml). A and B, Shape variable PC1 in figure 9B represents the difference between elongate and more oval carapaces (= positive and negative scores along PC1, respectively). C, 14.1% of the shape variability (PC3; Fig. S1) represents the difference between an oval and a subquadratic outline (shown here). D, Aberrant growth affected one third (7/21) of the photographed clam shrimp in cups 15.1 and 15.2. A shift in growth modified carapace proportions and the dorsal margin.

Fig. 12. Comparison of size and shape morphospaces. Red dots represent single-individual cups.A, Biplot on PC1 and PC2 of eight log-transformed linear variables. 95% concentration ellipses show that size analysis separates both species well: Eulimnadia texana occupies negative values on PC1, while Eocyzicus argillaquus occupies positive values on PC1. Eulimnadia texana is driven by larger Ch values (dorsal margin) and Eocyzicus argillaquus by larger Av and Arr values. B, Biplot on PC1 and PC2 of the combined Fourier datasets. Eulimnadia texana occupies negative values on PC1, while Eocyzicus argillaquus occupies positive values on PC1. The density effect is represented by PC2.