Abstract
In holometabolous insects, larval nutrition is a key factor underpinning development and fitness. Heterogeneity in the nutritional environment and larval competition can force larvae to forage in suboptimal diets, with potential downstream fitness effects. Little is known about how larvae respond to competitive heterogeneous environments, and whether variation in these responses affects current and next generations. Here, we designed nutritionally heterogeneous foraging arenas by modifying nutrient concentration, where groups of the polyphagous fruit fly Bactrocera tryoni could forage freely at various levels of larval competition. Larval foraging preferences were highly consistent and independent of larval competition, with greatest foraging propensity for high (100%) followed by intermediate (80% and 60%) nutrient concentration diets, and avoidance of lower concentration diets (less than 60%). We then used these larval preferences (i.e. 100%, 80% and 60% diets) in fitness assays in which larvae competition was maintained constant, and showed that nutrient concentrations selected by the larvae in the foraging trials had no effect on fitness-related traits such as egg hatching and pupation success, adult flight ability, sex ratio, percentage of emergence, nor on adult cold tolerance, fecundity and next-generation pupal weight. These results support the idea that polyphagous species can exploit diverse hosts and nutritional conditions with minimal fitness costs to thrive in new environments.
Highlights
In holometabolous insects, nutritional stress at the larval stage can have long-lasting fitness implications [1,2,3,4]
If suboptimal feeding is sustained throughout development, this can lead to downstream effects on developmental time, body size and tolerance to environmental stresses, and fecundity [23,34,35,36], with unknown trans-generational effects
There has been no detailed investigation of the behavioural responses and potential costs associated with foraging in competitive heterogeneous nutritional environment
Summary
Nutritional stress at the larval stage can have long-lasting fitness implications [1,2,3,4]. Larvae commonly forage in aggregations which may vary in size, both because females oviposit eggs in batches and because larvae may have a common affinity for a particular location [21,26,27,28] This creates the potential for larval competition and socially dependent larval dietary choices. Key questions remain unanswered, such as ‘How do individuals adjust their foraging behaviour in competitive heterogeneous environments?’; and ‘What are the potential fitness costs of foraging choices made in heterogeneous environments?’ The answer to these questions can help us better understand how polyphagous insect larvae forage under different competition levels and in nutritionally heterogeneous environments, and how larval foraging patterns can support individual development and adult performance in changing environmental conditions
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