Biological Sciences, School of


Date of this Version

Summer 5-2013


Melie, A.J. 2013. Predation and behavioral plasticity in green swordtails: mate choice in females and exploratory behavior in males. MS Thesis, University of Nebraska-Lincoln.


A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Biological Sciences, Under the Supervision of Professor Alexandra Basolo. Lincoln, Nebraska: May, 2013

Copyright (c) 2013 Andrew J. Melie


Two studies were carried out with green swordtails, Xiphophorus helleri, to investigate the effect of predation on swordtail behavior, and to determine how behavioral plasticity operates in both a mate choice and an anti-predator context. Male green swordtails vary in colorful conspicuous traits, e.g. the colorful dorsal fin and sword. Female swordtails have a preexisting bias for males with a sword, and prefer long-sworded males to short-sworded males, but this preference is plastic. The first study examined predator-related plasticity in the behavior of males differing in size. Smaller males showed greater behavioral plasticity; they were more active in the absence of a predator, but reduced activity in the presence of a predator, while larger males maintained lower activity levels regardless of predation environment. Males, regardless of size, entered the area nearest to where a predator had been, shortly after it had swam off. Males also utilized refuges furthest from a successful predator while the predator was visible, but did not differentially use refuges after the predator departed, regardless of male size. The second study examined whether different predation environments differ in their effects on female sword responses. Females switched their preference to short-sworded males, regardless of whether the predator was a large cichlid chasing and consuming a male swordtail with a short sword, a large cichlid alone, or a small cichlid alone. We also looked at the lasting effect of predation environment on sword response and found that the preference for short-sworded males persisted to the following day. To our knowledge, this is the first example of enduring plasticity in a receiver bias. Finally, we addressed whether females respond differently to differing predation environments in a non-mating context. Females perceived large cichlid predators alone to be as dangerous as successful predators, but not small cichlids. The results of these studies indicate that predation can have a profound influence on the expression of suites of behaviors, in both mating and non-mating contexts.

Advisor: Alexandra L. Basolo