The evolution of defence systems: theory and experiment

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2016

End date

12/31/2022

Budget

1,094,208 EUR

Fundings

Abstract

An organism may use many types of defences to protect itself against its natural enemies. The different defence traits are often best understood as parts of more complex defence systems involving many traits. A central focus in the project has been to understand how costs associated with production and maintenance of defence traits might constrain the ability to express other traits, leading to evolutionary compromises. In the theoretical part of the project, we have developed mathematical models of organismal defence systems relevant for several empirical systems. Many animal and plant studies describe how different defence traits are correlated across populations or species, but these correlative patterns are not well understood. We have investigated selective conditions under which defences should correlate positively or negatively. We have in addition modelled how animals respond to danger, including the response of prey to increased predation and the response of predators to defended prey. This work has been based on signal detection models used within evolutionary ecology, and has also led to novel methodological insights that allows several classic models from the literature to be analysed as variants of the same general model, leading to additional insight into the predictions of these models. Moreover, we have modelled specific systems, including brood parasitism and aposematism. Aposematism is the combination of a secondary defence such as a toxin with a primary defence (a warning signal) that advertises it, and we study how these and other associated defences covary and interact. Defensive signals are themselves often multi-component, and we have studied the selective conditions that favour such signals. We have also conducted experiments to understand the properties of defence systems and how they evolve under different selective conditions. Daphnia are small freshwater crustaceans that can modify aspects of their morphology, behaviour, and life-history strategy in response to chemical cues (kairomones) from predators. A comprehensive experiment was conducted in which clones of Daphnia magna were first exposed to a gradient of kairomones from predatory Chaoborus larva during development, and then later exposed to the bacterial parasite Pasteuria ramosa, to see how they cope with multiple threats.