Context-dependent aggression toward non-nestmates in the ant Diacamma sp. from Japan

Jumpei Uematsu,Kazuki Tsuji,Hiroyuki Shimoji,Michel-Olivier Laurent Salazar,Masayuki Hayashi

doi:10.1007/s10164-019-00611-8

Abstract

Aggression toward competitors is a useful measure of resource ownership and defense in animals, but aggressive behavior is costly. Therefore, it is predicted that animals will display aggression only when the expected benefit to individual fitness exceeds the expected cost. In ants, when conspecific individuals belonging to different colonies encounter each other, fighting occurs, seemingly facultatively. However, the context that influences the expression of ants’ aggressive behavior, especially in the field, is still largely unknown. We investigated the plasticity of aggressiveness toward non-nestmates in Diacamma sp. from Japan. Our field experiment clearly showed that the same foragers that were aggressive toward non-nestmates in the vicinity of their nest changed to be non-aggressive at greater distances from the nest. Furthermore, the size of the colony to which the foragers belonged weakly but significantly affected their aggressiveness: foragers belonging to larger colonies behaved more aggressively toward non-nestmates. We discuss the possible adaptive significance of the observed facultative aggression between conspecific non-nestmates. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo190618ds01a and http://www.momo-p.com/showdetail-e.php?movieid=momo190618ds02a.

Highlights

When individuals competing for scarce resources encounter each other, they may fight
The inclusive fitness benefit can be divided into two categories (Tsuji 2010, 2013): (1) the ecological benefit that contributes to obtaining and defending resources such as foods and territories that exist outside the nest, and (2) the social and genetic benefit that prevents unrelated individuals from exploiting the colony properties stored in the nest, such as work force, nutrition and/or the nest itself as a refuge
We collected Diacamma sp. workers from the other colonies nesting within a 3-m radius from the marked colony by using tweezers that had been washed with acetone

Summary

Introduction

When individuals competing for scarce resources encounter each other, they may fight. Social insects such as ants are facultatively hostile toward non-nestmates, which are usually unrelated individuals (Hölldobler and Wilson 1990). The inclusive fitness benefit can be divided into two categories (Tsuji 2010, 2013): (1) the ecological benefit that contributes to obtaining and defending resources such as foods and territories that exist outside the nest, and (2) the social and genetic benefit that prevents unrelated individuals from exploiting the colony properties stored in the nest, such as work force, nutrition (foods and broods) and/or the nest itself as a refuge. Because the balance of those colony-level costs and benefits can change depending on various contexts (Amsalem and Hefetz 2011; Barbieri et al 2015), aggressive behavior of ant workers may be facultative

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Results

Conclusion