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The evolution of variance in sequential defences.

Lingzi Wang1, Stephen J Cornell1, Michael P Speed1

  • 1Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, Faculty of Health & Life Sciences, University of Liverpool, Liverpool L69 7ZB, UK.

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|October 10, 2018
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Summary
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Organisms show varied anti-predator defenses. Mathematical models reveal that the effectiveness and tolerance of a species

Keywords:
HerbivoryMultiple defencesPhenotypic variationPredationSelection

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Area of Science:

  • Evolutionary biology
  • Animal behavior
  • Mathematical modeling

Background:

  • Organisms exhibit significant variability in anti-predator defense strategies, both among individuals and within a single individual.
  • Understanding the evolutionary origins of this defense variability is crucial for comprehending species' survival mechanisms.

Purpose of the Study:

  • To investigate the evolutionary dynamics of defense variability in species employing sequential anti-predator defenses using a mathematical model.
  • To determine how factors like defense effectiveness, tolerance to phenotypic deviation, mutation rate, and fitness costs influence defense variance.

Main Methods:

  • Development and analysis of a mathematical model incorporating mutation and selection.
  • Simulation of a population with sequential 'first' and 'second' line defenses against predators.
  • Examination of equilibrium variances in defense phenotypes under varying parameter conditions.

Main Results:

  • Typically, the first defense evolves lower variance than the second, even if its failure incurs greater fitness loss.
  • The first defense can evolve higher variance if it is less effective or less tolerant of phenotypic deviation.
  • Increased mutation rates lead to higher equilibrium variances; increased fitness importance of one defense reduces its relative variance.

Conclusions:

  • Defense variability is shaped by a complex interplay of selection, mutation, and the specific characteristics of sequential defenses.
  • Theoretical predictions regarding defense variance warrant empirical testing in organisms with sequentially acting anti-predator mechanisms.