Abstract
Many species of social hymenoptera demonstrate behavioral flexibility, where older workers that typically forage can revert to younger worker tasks, such as nursing, when these are absent. This flexibility is typical of the sterile worker class, yet rare in queens. In the little fire ant (Wasmannia auropunctata) queens have been reported to perform only egg laying. We examined behavior of queens of W. auropunctata after demographic manipulation. When half of the workers were removed from the colony, queens were observed caring for eggs, larvae and pupae as well as eating outside of the nest, like forager workers. We examined the relationship between these atypical queen behaviors and their juvenile hormone binding protein (JHbp) and vitellogenin (Vg) expression via QRT-PCR method. JHbp and Vg expression decreased when queens were performing worker tasks, resembling the expected expression pattern of typical sterile workers. Flexibility in queen behaviors in the little fire ant may be an important adaptation to changing environments. As a significant invasive species, such adaptation may increase the probability of colony survival during propagation. Our results not only present new insights in behavioral flexibility in social insects, but also increases our understanding of the success of this significant invasive species.
Highlights
Eusocial insects are characterized by having reproductive division of labor (Wilson, 1971)
We examined queen behavior in Wasmannia auropunctata, the little fire ant, a native of South America and an aggressive invasive species on all other continents except Antarctica (Le Breton et al, 2003; Wetterer and Porter, 2003; Mikheyev et al, 2008)
During the period after worker removal in which queens behaved as workers, egg laying decreased significantly (Figure 1A: W = 62.5, p-value = 0.01) while nursing and foraging behaviors increased significantly (Figure 1B: W = 2.5, p-value = 0.002; Figure 1C: W = 15, p-value = 0.04)
Summary
Eusocial insects are characterized by having reproductive division of labor (Wilson, 1971). Within the colony one or more individuals carry out egg laying while sterile workers perform nest related tasks including queen and brood care (i.e., nursing), defense and foraging (Gordon, 1996). Division of labor in workers may be associated with age or morphological differences (Hölldobler and Wilson, 1990). There are species where workers show behavioral flexibility, performing tasks that are not typical of their age or morphology. Workers of the ant Pheidole dentata are found to increase their behavioral repertory as they age, where older workers perform tasks typical to younger individuals, yet the young workers are not proficient in older worker tasks (Calabi and Traniello, 1989; Seid and Traniello, 2006; Mertl and Traniello, 2009). Behavioral flexibility in workers is an important adaptation that increases the chances
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