Date of Award

8-2026

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Kaitlin M. Baudier

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Christoph Grüter

Committee Member 3

Kellie M. Kuhn

Committee Member 4

Fabio Santos do Nascimento

Committee Member 5

Donald A. Yee

Committee Member 5 School

Biological, Environmental, and Earth Sciences

Abstract

Eusocial insects rely on division of labor to achieve high colony efficiency and provide essential ecosystem services, but specialization may also constrain colony resilience when workers operate near their physiological or behavioral limits under abiotic and biotic stressors. How specialization mediates these responses remains poorly understood, particularly in stingless bees (Tribe: Meliponini). Using the agriculturally relevant stingless bee Tetragonisca angustula, which possesses a specialized soldier subcaste, I investigated how a high degree of worker specialization influences physiological tolerance and predator responses across worker subcastes.

In this dissertation, I quantified variation in thermal tolerance and desiccation resistance among worker subcastes differing in age, size, task, and environmental exposure (foragers, hovering guards, and standing guards). Foragers exhibited a broader thermal tolerance breadth, but upper and lower thermal limits and desiccation resistance did not differ among subcastes, suggesting limited physiological differentiation to compensate for differences in environmental exposure. At the colony-level, I found a trade-off between heat tolerance and desiccation resistance, potentially further constraining colony performance under climate stress.

I also characterized ant predation and behavioral responses to predator cues. Ant predation occurred primarily during the daytime. In laboratory assays, bees reduced movement in response to visual ant stimuli but showed no response to olfactory cues. In the field, responses varied: foragers responded cautiously to all stimuli but most strongly to live ants, hovering guards—known to specialize in responding to heterospecific bee threats—showed no response to ants, and standing guards occasionally respond when ants attack but generally avoid live ant predator stimuli. This suggests a trade-off in defensive investment, with a higher threshold to attack ant threats compared with previous work investigating bee threats.

Together, these findings demonstrate that worker specialization does not necessarily confer improved tolerance to environmental stress and may constrain colony responses to multiple challenges. These constraints may reduce colony flexibility under simultaneous environmental and biotic stressors, increasing vulnerability under changing conditions and highlighting the importance of incorporating social organization into predictions of resilience for social systems.

ORCID ID

0009-0004-1696-6202

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