Variability in timing of egg hatch of Triaenophorus crassus Forel (Cestoda: Pseudophyllidea) as a mechanism increasing temporal dispersion of coracidia

Eggs collected from 174 Triaenophorus crassus Forel over 3 years were maintained under a 12-h photocycle at 15 °C to quantify variability in three egg hatching characteristics. The percentage of eggs hatching to release coracidia varied from 20 to 90% (mean 82%). The median hatch time (time from egg release to hatch) varied from 4.3 to 14.2 days (mean 8.3 days). The duration of the egg hatching period (the time between hatch of 10 and 90% of eggs) varied from 1 to 17 days (mean 4.6 days). These three characteristics varied among years, among worms from different hosts, and among worms from the same host. Variability in egg hatching characteristics was not correlated with egg size or fecundity of the parent, but a consideration of this variability within the context of the hierarchical nature of parasite populations suggested that this variability resulted from genotypic and environmental contributions to parasite phenotype. Results of a simulation study suggested that naturally occurring levels of variability in egg hatching characteristics could increase temporal dispersion of coracidia beyond that resulting solely from temporal variation in egg release from adult worms. The time at which peak densities of coracidia occurred was affected little by variability in egg hatching characteristics. However, peak densities of coracidia were reduced because the period of egg hatching began earlier and ended later compared with expectations in the absence of variability in egg hatching characteristics.