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).