Heterogeneous environments can select for complex growth patterns

Anna Ejsmond, Jan Kozłowski, Maciej J. Ejsmond

A female of Daphnia magna. Daphnia magna is an exemplary crustacean species with biology that correspond well with life histories and growth strategies modelled in our work. Image credit: Dieter Ebert, The University of Basel, Switzerland (CC BY-SA 4.0).
A female of Daphnia magna. Daphnia magna is an exemplary crustacean species with biology that correspond well with life histories and growth strategies modelled in our work. Image credit: Dieter Ebert, The University of Basel, Switzerland (CC BY-SA 4.0).

In many organisms such as annual plants, mollusks, crustaceans, amphibians, reptiles and fish, growth accompanies reproduction throughout life. The growth patterns of these organisms are often complex, with episodic cessations or accelerations of growth occurring long after maturation. These episodic cessations of growth in annuals and other short lived-organisms are usually associated with adverse conditions.

The most important consequence of growth is an increased fecundity in the future due to greater body size. However, investment in future reproduction through growth must be discounted by the chances that the organism dies before reproduction. In a heterogeneous environment in which habitats differ with respect to mortality risk, staying alive makes an organism more optimistic about its fate as it becomes more likely that the organism occupies a safe spot. Our model shows that when risky sites are frequent, females are first pessimistic about their survival prospects and mature early.

However, by living longer they become optimistic about local conditions and the allocation of resources to growth accelerates in the middle of the lifespan. The acceleration of growth is more likely to occur in species that grow only after changing their exoskeletons (moulting). In line with our results, many crustaceans that display complex growth patterns, such as water flies or scuds (freshwater shrimps), can grow only after moulting.

In conclusion, our work shows that spatially heterogeneous environments can select for complex growth strategies and simultaneous allocation of resources to growth and reproduction in short lived organisms.

Read the paper in full here.

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