Genetic composition of social groups influences male aggressive behaviour and fitness in natural genotypes ofDrosophila melanogaster

Abstract

Indirect genetic effects (IGEs) describe how an individual's behaviour-which is influenced by his or her genotype-can affect the behaviours of interacting individuals. IGE research has focused on dyads. However, insights from social networks research, and other studies of group behaviour, suggest that dyadic interactions are affected by the behaviour of other individuals in the group. To extend IGE inferences to groups of three or more, IGEs must be considered from a group perspective. Here, I introduce the 'focal interaction' approach to study IGEs in groups. I illustrate the utility of this approach by studying aggression among natural genotypes of Drosophila melanogaster. I chose two natural genotypes as 'focal interactants': the behavioural interaction between them was the 'focal interaction'. One male from each focal interactant genotype was present in every group, and I varied the genotype of the third male-the 'treatment male'. Genetic variation in the treatment male's aggressive behaviour influenced the focal interaction, demonstrating that IGEs in groups are not a straightforward extension of IGEs measured in dyads. Further, the focal interaction influenced male mating success, illustrating the role of IGEs in behavioural evolution. These results represent the first manipulative evidence for IGEs at the group level.

The development of collective personality: the ontogenetic drivers of behavioral variation across groups

“…It is currently unknown why some social groups develop social niches while others do not; though social niches are expected in groups with relatively stable social structures (i.e., little fission or fusion). Within a group, it has been shown that specific genotypes may predispose some individuals to occupy specific social niches over others (Saltz, 2013;Saltz and Nuzhdin, 2014). Genetic variation is also one proximate explanation for division of labor in social insects (Page and Robinson, 1991;Robinson, 1992;Beshers and Fewell, 2001;LeBoeuf and Grozinger, 2014).…”

“…For example, in a group of Drosophilia males, aggressive behavior (influenced by genotype) of one individual can influence the interactions between the others, and impact mating success (Saltz, 2013). Therefore, understanding the genetic make-up of the group, and how that changes over time, may influence the developmental trajectory of the collective personality.…”

Genetic variation in social environment construction influences the development of aggressive behavior in Drosophila melanogaster

“…Natural genetic variation in aggressiveness influences group formation, including group size (Saltz and Foley, 2011), through processes that are not yet fully understood (Foley et al, 2015). Males from natural genotypes modulate their aggressive behavior in response to local ecology and sex ratio (Cacoyianni and Hoffmann, 1990), and natural genotypes show indirect genetic effects, whereby the aggressiveness of a male depends on the genotype of his opponent (Cabral et al, 2008;Saltz, 2013). Complementary work on laboratory genotypes has shown that prior exposure to males (Yurkovic et al, 2006;Wang et al, 2008) and females (Yuan et al, 2014;Baxter et al, 2015) can influence males' later aggression.…”

“…All focal flies were male. Flies were reared under standard conditions that minimize variation in larval density (Saltz and Foley, 2011;Saltz, 2011Saltz, , 2013.…”

“…First, naive males of natural fly genotypes differ in the social group sizes that they prefer (Saltz, 2011). Second, short-term aggressive interactions influence behavioral dynamics within and among groups (Saltz and Foley, 2011;Saltz, 2013). Here I measured the consequences of genetic variation in these two types of social environment construction for the development of aggressive behavior.…”