Data for: The visual ecology of selective predation: Are unhealthy hosts less stealthy hosts?

Predators can strongly influence disease transmission and evolution,
particularly when they prey selectively on infected hosts. Although
selective predation has been observed in numerous systems, why predators
select infected prey remains poorly understood. Here, we use a
mathematical model of predator vision to test a longstanding hypothesis
about the mechanistic basis of selective predation in a
Daphnia-microparasite system, which serves as a model for the ecology and
evolution of infectious diseases. Bluegill sunfish feed selectively on
Daphnia infected by a variety of parasites, particularly in water
uncolored by dissolved organic carbon. The leading hypothesis for
selective predation in this system is that infection-induced changes in
the transparency of Daphnia render them more visible to bluegill.
Rigorously evaluating this hypothesis requires that we quantify the effect
of infection on the visibility of prey from the predator's
perspective, rather than our own. Using a model of the bluegill visual
system, we show that three common parasites, Metschnikowia bicuspidata,
Pasteuria ramosa and Spirobacillus cienkowskii, decrease the
transparency of Daphnia, rendering infected Daphnia darker
against a background of downwelling light. As a result of this increased
brightness contrast, bluegill can see infected Daphnia at greater
distances than uninfected Daphnia - between 19-33%
further, depending on the parasite. Pasteuria and
Spirobacillus also increase the chromatic contrast of Daphnia.
These findings lend support to the hypothesis that selective predation
by fish on infected Daphnia could result from the
effects of infection on Daphnia's visibility. However, contrary to
expectations, the visibility of Daphnia was not strongly
impacted by water color in our model. Our work demonstrates that models of
animal visual systems can be useful in understanding ecological
interactions that impact disease transmission.