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Complex offspring size effects: variations across life stages and between species
Zhao Sun1, Jean-François Hamel2, Christopher C Parrish1
1Department of Ocean Sciences, Memorial University St. John's, Newfoundland and Labrador, A1C 5S7, Canada.
Ecology and Evolution
|March 24, 2015
Summary
Offspring size impacts aquatic animal performance differently across life stages and species. Larger larvae may perform better, but smaller juveniles can have survival advantages against certain predators.
Area of Science:
- Marine biology
- Evolutionary ecology
- Life history theory
Background:
- Classical models link offspring size to performance, assuming a consistent positive relationship.
- Aquatic organisms with complex life cycles present challenges in understanding size-performance dynamics due to varied metrics and ontogenetic shifts.
- Brooding marine animals offer a model to study size effects across larval and juvenile stages.
Purpose of the Study:
- To investigate how offspring size influences performance in premetamorphic (larval) and postmetamorphic (juvenile) stages of marine invertebrates.
- To determine if the size-performance relationship is consistent across ontogeny, species, and ecological contexts.
- To explore the underlying mechanisms, such as lipid content and predation susceptibility, driving size-dependent performance.
Main Methods:
- Examined size effects in larval and juvenile stages of the sea anemone Urticina felina and the species Aulactinia stella.
- Assessed larval performance metrics including settlement and survival rates under suboptimal conditions.
- Evaluated juvenile susceptibility to predation by different sizes of nudibranch predators.
- Quantified larval lipid content and analyzed predation rates in relation to offspring size.
Main Results:
- Larger Urticina felina larvae generally showed better performance (settlement, survival), with parentage mediating this relationship.
- Juvenile U. felina showed size-dependent predation: smaller individuals were less vulnerable to subadult nudibranchs, while both sizes performed similarly against adults.
- Juvenile Aulactinia stella exhibited context-dependent predation, with smaller individuals having lower mortality against adult nudibranchs.
- Larval size-performance in U. felina correlated with lipid content; juvenile predation aligned with optimal foraging predictions.
Conclusions:
- The size-performance relationship in marine organisms with complex life cycles is highly variable and context-dependent, challenging simple monotonic models.
- Parentage, ontogeny, and predator-prey interactions significantly mediate the fitness consequences of offspring size.
- Empirical support for a universally positive monotonic size-performance function is difficult to obtain in species with complex life histories, which are prevalent in marine ecosystems.
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