Uterine size can constrain egg number and size in nematodes

What is it about?

Individuals have to partition their reproductive output between number and size of their offspring. We studied the relationship between egg number and egg volume in three populations of three marine nematode species. We found evidence of a tradeoff only in Anisakis simplex. Factors accounting for this pattern were probably constructional (uterine size) 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.

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Why is it important?

The relationship between egg size and egg number in parasites was poorly understood. The perception was that that parasites live in resource-rich habitats, where such tradeoffs are unlikely to occur. However, this study represents the first demonstration of such a tradeoff. In addition, our results indicated that patterns of resource allocation relating number and size of eggs did not differ much from those observed in free-living populations and thus the same range of factors would operate in both types of organisms.