The individual and collective behavior of social organisms across environments

Animals encounter a wide range of ecological conditions, and this diversity can drive behavioral variation. For group-living organisms, this variation is present at both the individual and the collective levels, with individual behavioral phenotypes and interactions among individuals driving collective behavior. However, gaps remain in our understanding of the relationship between collective behavior and the ecological environment. First, more work is needed exploring the role of individual phenotype on collective behavior. Additionally, there is limited research exploring population differences in collective behavior and its role in phenotypic divergence. Addressing these gaps could help us predict the effects of environmental changes on behavioral evolution. In this thesis, I address these questions through the use of two organisms; three-spined stickleback fish (Gasterosteus aculeatus) and odorous house ants (Tapinoma sessile). Both of these species are group-living, exhibit considerable variation in behavior at both the individual and collective level, and have significant population level divergence that is associated with environmental differences. First, I compared individual boldness and social networks between two stickleback ecotypes, the “common” type that exhibits typical paternal care and the “white” ecotype where paternal care is significantly reduced. I found that the white ecotype is bolder than the common ecotype. There were also social network differences, with the white ecotype having lower clustering coefficients, suggesting a more less connected, more cliquish social structure. Additionally, there was an effect of group composition, with groups made up of both ecotypes resembling the common-only groups (high clustering). Second, I explored the relationship between collective behavior and population divergence between the benthic and limnetic ecotypes, which differ significantly in their ecology. I found that benthic fish were bolder, more active, and had deeper bodies than limnetic fish. Group cohesiveness, social interaction rates, and social networks did not differ among ecotypes, but there were population-level differences, suggesting that collective behavior is diverging independently of the benthic-limnetic axis. Third, I investigated the role of exploratory and foraging behavior in the adaptation to urban environments by odorous house ants. I found that colonies from urban environments had more exploratory workers and higher foraging rates than those from “natural”, forested environment. Furthermore, I identified two potential mechanisms driving these behaviors — the social context (whether a worker was foraging, at the nest, or defending territory) and hormones (level of octopamine). Together, these results suggest that behavior is indeed playing a key role in the responses by these animals to their environment and provides a framework for looking at the relationship between behavior and ecology in group-living organisms.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Ecol, Evol, Conservation Biol

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Neumann, Kevin

Contributors dc:contributor

• Bell, Alison M
• Suarez, Andrew V
• Fuller, Becky C
• Bolnick, Daniel I

• Ants
• fish
• odorous house ant
• stickleback
• Gasterosteus aculeatus
• Tapinoma sessile
• collective behavior
• social network
• division of labor
• exploration
• foraging
• hormones, octopamine
• boldness
• behavioral syndrome
• parallel evolution
• population divergence
• clustering
• ecotype
• benthic
• limnetic
• group composition
• behavioral ecology
• urbanization

Statement dc:rights

• Copyright 2025 Kevin Neumann

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132476

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132476