2.5 Statistical analyses
(i) The effect of L. intestinalis infection on host fecundity was tested using a generalized linear mixed-effects model (glmmPQL) fitted with Quasi-Poisson distribution with fecundity as a response variable, and maturity stage and infection status as predictor variables. Because the data were collected over a 10-year period, year of sampling was included as a random effect factor in the model.
(ii) To test whether reproductive investment at maturity has increased over time, we used a generalized linear model (glm) fitted with a binomial distribution. The binomial response variable combined gonadal weight of uninfected E. sardella and somatic weight. We chose to use relative gonad weight at stage IV because this is the stage whereE. sardella reach reproductive maturity. Year was included as a covariate.
(iii) To test whether size of E. sardella at maturity has decreased over time, we used a linear model (lm) including body length of uninfected E. sardella at stage IV as a response variable and year as a covariate. To explore whether body growth after maturity decreased over time we also tested whether body length at stage V decreased over time. All statistics and graphics were carried out using R, version 3.2.5 (http://r-project.org).