Behaviourally specialized foragers are less efficient and live shorter lives than generalists in wasp colonies

Davide Santoro,Stephen Hartley,Philip J Lester

doi:10.1038/s41598-019-41791-0

Davide Santoro, Stephen Hartley + Show 1 more

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https://doi.org/10.1038/s41598-019-41791-0

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Journal: Scientific Reports	Publication Date: Mar 29, 2019
Citations: 18	License type: open-access

Affiliation: Victoria University of Wellington

Abstract

A widely held assumption in ecology is that specialists are more efficient than generalists. However, empirical evidence for this fundamental assumption is surprisingly scarce and often contradictory. Theoretically, the evolution of alternative life history strategies is underpinned by a trade-off between activity levels and survival. We investigated the consequences of specialization in a foraging context, by comparing the performance and longevity of closely related individuals in a social insect, the common wasp (Vespula vulgaris). Using radio-frequency identification technology, we monitored the lifetime foraging activity of individual wasps from three colonies kept under natural foraging conditions. Returning foragers were video-recorded as they passed the nest entrance so that their foraging load could be assessed. There were substantial differences in foraging activity and survival within and between colonies. At the colony level, foraging specialization was weak. Yet, workers within each nest demonstrated a remarkable range of foraging specialization levels (defined as the degree of overlap between individual and colony-level task allocation) and efficiencies (defined by the number of successful trips and trip duration). We found that specialist foragers were less efficient than generalist siblings within the same colony. Behavioural specialists accomplished fewer successful trips per foraging day, and their trips were typically relatively longer. Specialized foragers also showed reduced life expectancy. The mortality risk was higher for individuals spending relatively more time in the field, yet we found no link between the level of specialization and relative field exposure. Our extensive dataset of unprecedented detail provides strong empirical evidence that behavioural specialization is not associated with a better lifetime performance, on the contrary, the opposite appears true for the common wasp. We also show that the survival of genetically similar individuals can be linked to life-long differences in behaviour according to classical life-history theory predictions.

Highlights

A fundamental assumption in ecological and evolutionary studies is that specialists are more efficient than generalists[1]
The prevalent foraging task at the colony level was represented by fluid foraging, with 55% of the returning foragers showing a swollen abdomen and no solid loads in their mandibles
Common wasp colonies showed a weak degree of foraging specialization

Summary

Introduction

A fundamental assumption in ecological and evolutionary studies is that specialists are more efficient than generalists[1]. Very few empirical studies have investigated the efficiency of individual workers and how individual efficiency relates to their task specialization[11,20,21]. Both in ant and bumble bee colonies, workers’ specialization in particular tasks was unrelated to their ability to perform them[11,21]. Precocious honey bee foragers show higher risk of death in their first flights[23] From their age at first foraging, wasp workers from Polybia colonies lived an average of six days after foraging onset, and the length of their foraging career did not decrease as age of first foraging increased[24]. Consistent with a trade-off between foraging activity and lifespan, foraging seems to be undertaken by individuals with reduced life expectancy and residual value[28], e.g. older honey bees[23], or wasps in subordinate social positions[29]

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