Predation on guppies (Poecilia reticulata) by oscar cichlids (Astronotus ocellatus): effects of varying prey color and prey size

Jason Fowler, Department of Biology, York College

Introduction

Color is a sexually selected trait in guppies. Female guppies prefer to mate with brightly colored males over plain, grey colored ones. Color seems to be an indicator of the quality of the male guppy, with colored ones showing greater boldness toward predators and a superior ability to escape from them (Godin and Dugatkin 1996). However, color can also make the guppies more visible and thus attract more predators. Field and laboratory studies have been performed to examine predator preferences for guppies containing various intensities of color. In the field, researchers have observed the color intensities of guppies in high and low predation areas. In the lab, they have exposed predator fish to guppies and studied their behaviors. Similar experiments have also been done looking at predator preferences for different sizes of guppies.

Predators seem to prefer: 1) Brightly colored over plain (Godin and McDonough 2003). 2) Large over small (Johansson et al. 2004).

Limitations in previous research: 1) A small number of predator fish species have been thoroughly studied. 2) In the lab, predators have always been tested individually. 3) Predator preferences for different characteristics have never been directly compared.

OBJECTIVES

1) To study predator preferences in a new species (Astronotus ocellatus).

2) To test predators as a group.

3) To determine whether prey color or prey size is a more preferred characteristic.

Methods

The aquarium was 205 liters, with 2 plastic guppy containers on opposite ends and a 30 cm line marked from each end.

Figure 1. The set-up of the aquarium (overhead view).

12 oscars were split into 2 equal groups.

Placed one guppy into each container and subjected both groups to 5 tests: 1) Small Plain vs. Small Plain 2) Small Colored vs. Small Plain 3) Small Plain vs. Big Plain 4) Big Plain vs. Small Colored 5) Big Colored vs. Small Colored

3 measurements made during the testing period: 1) Number of approaches to each guppy 2) Number of attacks on each guppy 3) Time spent within each 30 cm line

Oscar acclimation period1 day

Guppy acclimation period5 minutes

Testing period5 minutes

After both groups were done testing, the groups were rearranged and tested again. The groups were then rearranged and tested for a third time. Therefore, a total of 6 groups were tested.

Results

Based on the results of the five tests, the oscars preferred: 1) Colored over plain 2) Big over small 3) Small colored over big plain 4) Big colored over small colored

These results were consistent across the three measurements.

CONCLUSIONS

1) Predator fish tested in groups display similar preferences to those previously tested individually.

2) Prey color and prey size are both important factors in the selection of guppies by oscars.

3) Prey color seems to play a larger role in attracting oscars to the guppies.

4) Once the guppy is visible, prey size seems to be important in the decision of whether or not to attack.

Future Studies

This study contained a very limited sample size, so testing a larger number of fish will lead to an even greater understanding of their preferences. Also, future studies could examine predator preferences for additional guppy characteristics, such as group size.

Literature Cited

Godin, J.J. and Dugatkin, L.A. 1996. Female mating preference for bold males in the guppy, Poecilia reticulata. Proceedings of the National Academy of Sciences of the United States of America 93:10262-10267. Godin, J.J. and McDonough, H.E. 2003. Predator preference for brightly colored males in the guppy: a viability cost for a sexually selected trait. Behavioral Ecology 14(2):194-200.

Johansson, J., Turesson, H. and Persson, A. 2004. Active selection for large guppies, Poecilia reticulata, by the pike cichlid, Crenicichla saxatilis. Oikos 105:595-605.

Acknowledements

I would like to thank Dr. Rehnberg for his guidance throughout this project.

Results

Figure 2. Means for the three measurements made during the five-minute testing period. Six groups of oscars were tested. The four types of guppy: small plain (SP), small colored (SC), big plain (BP), and big colored (BC). Error bars represent one standard error of the mean. (a) Number of approaches to each guppy. (b) Number of attacks on each guppy. (c) The total amount of time spent within each 30 cm line. (d) Number of attacks per approach to each guppy.

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