Pathogen transmission as a selective force against cannibalism

Area of Science:

• Ecology
• Evolutionary Biology
• Behavioral Ecology

Background:

• Cannibalism, despite offering nutritional and competitive benefits, is taxonomically widespread yet uncommon in most species.
• A prevailing hypothesis suggests that increased pathogen transmission risk from genetically similar conspecifics deters cannibalism.

Purpose of the Study:

• To test the hypothesis that pathogen transmission is a significant cost of cannibalism.
• To investigate the fitness consequences of consuming diseased versus healthy conspecifics and heterospecifics.

Main Methods:

• Experimental predation trials using cannibalistic tiger salamander (Ambystoma tigrinum) larvae.
• Larvae were fed diseased conspecifics, healthy conspecifics, diseased heterospecifics (A. texanum), or healthy heterospecifics.
• Survival to metamorphosis and growth rates were measured for each treatment group.

Main Results:

• Larvae consuming diseased conspecifics exhibited significantly lower survival and reduced growth compared to those eating diseased heterospecifics.
• No significant differences were observed between other feeding groups (healthy conspecifics, healthy heterospecifics, diseased heterospecifics).
• Tiger salamander larvae showed a preference for preying on heterospecifics over conspecifics when given a choice.

Conclusions:

• Pathogen transmission from diseased conspecifics represents a substantial fitness cost, explaining the rarity of cannibalism.
• This finding provides a general ecological explanation for the infrequent occurrence of cannibalism across diverse species.
• Behavioral avoidance of conspecifics, particularly when diseased, is a likely strategy to mitigate disease risk.