Social and environmental factors in the evolution of signalling

Thesis

Offspring across the animal kingdom have evolved a variety of vocalizations, postures and structural ornaments to help them solicit more food from their parents. These signals are typically assumed to convey information about offspring state that helps parents decide which offspring to feed, and the dominant framework holds that begging is a signal of need. However, species differ both in how they beg and how they respond to begging, and signalling theory has been unable to account for this variation. In this thesis, I use a combination of comparative, observational and theoretical data to explore how the degree of within-family conflict leads to differences in parent-offspring signalling systems both across and within bird species. I also explore the possibility that some signalling systems function differently because the information they transmit is not cryptic. Specifically: 1) I show that offspring signals of need are more likely to evolve in species living in predictable and/or unusually good environments, while signals or cues of quality are more likely to evolve in unpredictable and/or unusually poor environments, when conflict over food is greater because brood reduction is probable; 2) I show that the same patterns hold within-species, indicating that parents can facultatively adjust their responsiveness based on the risk of brood reduction; 3) I show that offspring signals of need are less honest when sibling competition is greater, due to offspring number and/or relatedness; 4) I argue, using a simple game, that signals of non-cryptic condition can be stable if signalling provides an efficiency benefit compared to parents’ using cues; and 5) I provide a potential example of such a signal in nature, gape size, and show that its honesty fluctuates based on local conditions.

Authors: Caro, SM

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: parental care; social evolution; communication
• Subjects: Biology