Phenotypic tradeoffs between egg number and egg size in three parasitic anisakid nematodes

Abstract

Phenotypic tradeoffs between number and size of eggs were tested in three component populations of three marine anisakid nematodes: Anisakis simplex , Pseudoterranova decipiens and Contracaecum osculatum . Body and uterine volumes (as proxies of female size), and egg number, mean egg volume and clutch volume (as descriptors of reproductive output) were measured in 50 females of each species. Evidence of a phenotypic tradeoff was detected only in A. simplex ; the first time that has been found in a parasite population. Comparison of feasible values inferred from the van Noordwijk and de Jong's model and current data showed that interindividual variation in egg size was narrower than expected in the three populations. Structural constrictions in response to optimal allocation rules might account for this pattern. In P. decipiens and C. osculatum variation in egg size was the lowest and independent of female size, suggesting that the tradeoff is absent, rather than being present but masked by unaccounted variables. Spatial constrictions imposed by uterine size seemed to play an important role determining the emergence of the tradeoffs. So factors accounting for the tradeoff in A. simplex are probably constructional rather than physiological. Individual variability in investment in clutch volume was similar to previous studies but variation in allocation between number and size of eggs was much smaller than that reported previously. Perhaps differences in life-history strategies might explain this because the nematodes studied are either semelparous or short-lived iteroparus organisms whereas previous data derive from long-lived iteroparous ones. Despite the perception that parasites live in resource-rich habitats, the present study indicates that patterns relating number and size of eggs might not differ much from those observed in free-living populations and thus the same range of factors would operate in both types of organisms.

Zoonotic Anisakidae Nematodes - Emerging Pathogens in Salmon and Other Commercially Important Fish Species from Polish Marine Waters

“…Studies on the presence of nematodes in Baltic Sea seals (H. grypus, P. vitulina and P. hispida) reported that each seal was infected with Anisakidae nematodes, with one grey seal showing an intensity of infection of up to 590 nematodes [59]. It is worth emphasizing that C. osculatum and P. decipiens females are very productive: one female P. decipiens produces on average about 60,000 eggs, while a female C. osculatum produces on average about 9,000 eggs [60]. If we multiply the number of grey seals by the number of nematodes in each seal and by the number of eggs that might be produced by each mature female parasite, we end up with a extremely high load of nematodes shed into the environment.…”

To live free or being a parasite: The optimal foraging behavior may favor the evolution of entomopathogenic nematodes

“…For instance, long-lived nematodes tend to achieve larger sizes and extended reproductive periods, especially in iteroparous species. Larger adult sizes are associated with increased reproductive capacity, such as higher egg production [54,55]. Additionally, larger adults have greater access to food, occupy better places to live as parasites, and have more reproductive opportunities compared to smaller ones [53].…”