Aggression in larval Hynobius leechii: Kin discrimination of polymorphic larvae and relatedness as a factor in pathogen transmission

Abstract

Larvae of some amphibians can develop into two distinct morphological types, a large-headed morph adapted to cannibalize the other, small-headed morph. Cannibalism confers nutritional benefits that can accelerate development, essential for survival in transient environments, but incurs potential inclusive fitness costs. Selective cannibalism of non-kin thus should be favored, but siblings share immunological defenses. Thus subjects may be more vulnerable to pathogens of non-siblings, to which they are naïve. I investigated kin discrimination and pathogen transmission among Korean salamander (Hynobius leechii) larvae. I placed large-headed morph larvae into a circular arena together with two small headed-morph larvae, one sibling and one non-sibling, recorded behavioral interactions among them, and scored the aggressiveness of their interactions. In a second experiment, I fed large-headed morph larvae either a sibling or non-sibling small-headed morph larva that I had previously infected with the pathogenic bacterium Aeromonas hydrophila. Two days after ingestion, I euthanized the cannibals and determined by qPCR whether the bacterium had infected their hearts. Large-headed morph larvae behaved more aggressively toward siblings than non-siblings but only late in development. Some large-headed morph larvae that ate non-siblings had higher infection loads than those that ate siblings, but infection loads varied more widely when non-siblings were cannibalized. Cannibalizing non-siblings thus may increase the risk of contracting disease. However, large-headed morph larvae do not discriminate between siblings and non-siblings until late in development when inclusive fitness costs of cannibalizing siblings may be diminishing.