Perumytilus purpuratus

García-Huidobro, M. R., Varas, O., George-Nascimento, M., Pulgar, J., Aldana, M., Lardies, M. A. & Lagos, N. A., 2019, Role of temperature and carbonate system variability on a host-parasite system: Implications for the gigantism hypothesis, International Journal for Parasitology: Parasites and Wildlife 9, pp. 7-15 : 10-11

3.2. Parasite effect on adults of P. purpuratus

The prevalence of undetermined trematode in P. purpuratus was 11.1% and 18.5% for the central and southern site, respectively. The shell length of the adult fraction of P. purpuratus (> 20 mm) (sexual maturity in this species is reached at 10 mm), was higher in parasitized than non-parasitized mussels, and this pattern was independent of the collection sites (see Fig. 1 in supplementary material). The mature portion of the population of P. purpuratus collected at both sites, also showed geographic variability patterns, in which mussels from southern Chile (Concepción) evidenced a significant increase in shell length compared to those collected from Central Chile (Quintay; Fig. 2 . Table 2). Both factors operate additively, evidenced by a non-significant Site × Parasite condition (p = 0.102, Table 2).

Comparing morphological variables between mussels with different parasite conditions at the mean shell length (i.e., LSM value of the covariate in ANCOVA), the total weight and volume increased significantly in parasitized compared to non-parasitized mussels at both study sites ( Fig. 3A, D . Table 3). In addition, the total weight and volume of the mussels were higher in the southern site than in the central site ( Fig. 3A, D ). The soft tissue weight was lower in parasitized than non-parasitized individuals in both study sites. Additionally, the soft tissue weight was lower in the central than in the southern population ( Fig. 3B . Table 3). Furthermore, shell weight was higher in parasitized than in non-parasitized individuals at the central site, but in the southern site, the individuals did not show differences between parasitized conditions ( Fig. 3C ). The CaCO 3 content was similar between parasitized conditions, but higher in the southern site than in the central Chile site ( Fig. 3E . Table 3). The total weight, soft tissue weight, shell weight and volume correlated positively with the shell length of P. purpuratus , but not the CaCO 3 content (see Figs. 2 and 3 in supplementary material).

Shell thickness was higher in parasitized individuals than in non-parasitized individuals at the central site ( Fig. 3F . Table 3), but an inverse pattern was recorded at the southern Chile site ( Fig. 3F . Table 3). In both sites, the shell weight scaled positively with the shell surface (see Fig. 3 in supplementary material) .

For the acute exposition period used in this study, the growth rate was higher in parasitized than non-parasitized mussels, and this effect was independent of temperature treatments ( Fig. 4A . Table 4). However, oxygen consumption showed no difference between parasitism and experimental temperatures ( Fig. 4B . Table 4).

Figures

Fig. 1. Study sites along the Chilean coast (Quintay and Concepción), and variability in temperature, pH, salinity, total alkalinity, partial pressure of CO2, and aragonite saturation state. Bars indicate ± 1 standard error. Asterisk represents significant differences between sites (p <0.001).

Fig. 2. Total shell length of adults parasitized (gray bars) and non-parasitized (white bars) individuals of P. purpuratus from central (Quintay) and southern populations (Concepción). Bars indicate ± 1 standard error. Asterisk indicates significant differences between parasitism condition (p <0.001).

Fig. 3. Least square means (LSM), the predicted value of the response variable at the mean value of the covariate (Shell Length) in ANCOVA. Responses are (A) total weight, (B) soft tissue weight, (C) shell weight, (D) volume, (E) CaCO3, and (D) LSM of the shell surface of P. purpuratus from central (Quintay) and southern populations (Concepción). Gray bars represent parasitized individuals and white bars, non-parasitized individuals. Asterisk indicates significant differences between parasitism condition, and letter indicates significant differences between sites (p <0.001).

Fig. 4. (A) Growth and (B) metabolic rates of parasitized (gray bars) and nonparasitized (white bars) of P. purpuratus from central site (Quintay), subject to 12 and 18 ̊C. Bars indicate ± 1 standard error. Asterisk indicates significant differences between parasitism condition (p <0.001).