Evol Ecol Res 15: 189-198 (2013)     Full PDF if your library subscribes.

No evidence that stickleback spines directly increase risk of predation by an invertebrate predator

Kenyon B. Mobley1,2, Rocio Colas Ruiz1, Frank Johansson1,3, Göran Englund1 and Folmer Bokma1

1Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden,  2Department of Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, Plön, Germany and  3Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden

Correspondence: K. Mobley, Department of Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, August-Thienemann-Strasse 2, 24306 Plön, Germany.
e-mail: mobley@evolbio.mpg.de


Background: Some populations of stickleback have a reduced number and/or relative size of spines.

Hypothesis: Macroinvertebrate predators such as dragonfly larvae cause selective pressure against spines by capturing more stickleback with pelvic spines than stickleback that are spineless.

Organisms: Ninespine stickleback (Pungitius pungitius) and dragonfly larvae (Aeshna grandis).

Methods: We used 10 stickleback, five with pelvic spines and five with their pelvic spines removed. We put them in containers with two dragonfly larvae. Every day for 4 days we monitored how many stickleback were captured by the larvae. We repeated this experiment ten times at two different densities of fish and predators. We also developed a model to determine whether selection for spinelessness can be distinguished from drift.

Results: Dragonfly larvae caught as many stickleback with spines as without. The absence of spines was not associated with a decrease in predation risk. We substituted Bayesian estimates of the selection coefficient into quantitative genetic models of allele frequency change, and the results of the models suggest that the selective advantage of spine loss is so small that its effects cannot be distinguished from drift.

Keywords: Aeshna, dragonfly larvae, Pungitius, morphological defence, predation, prey capture, stickleback.

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