The evolution of kin recognition

The discovery that many animals are promiscuous has challenged the importance of Hamilton’s Rule because it reduces the net benefits of helping nestmates. To resolve this challenge, biologists have investigated animals’ abilities to determine degrees of relatedness among individuals using kin recognition mechanisms. I conducted a literature review and found that most animals use one of two mechanisms: “familiarity” whereby kin are remembered from interactions early in life, such as in a nest, or “phenotype matching” whereby putative kin are compared to a template of what kin should look, smell, or sound like based on relatives encountered during early life or on one’s own phenotype (called “self-referent phenotype matching”). Theory suggests that familiarity should evolve when being born together is a reliable cue of relatedness, and phenotype matching should evolve when familiarity is unreliable. However, the conditions favouring the evolution of one of these mechanisms over the other has been largely unstudied. In my thesis, I begin to fill this gap using two promiscuous fish species, bluegill (Lepomis macrochirus) and guppies (Poecilia reticulata), and suggest other life history (brood size) and environmental (predation) factors that might influence recognition mechanism. In bluegill, I show that kin recognition can lead to enhanced anti-predator shoaling behaviour, and that high promiscuity, which causes low levels of relatedness within broods, leads to the expression of self-referent phenotype matching. In guppies, I use six guppy populations to show that average brood size and predation regime cannot explain kin recognition mechanism, and in contrast to my findings in bluegill, brood relatedness does not explain recognition mechanism, but it is correlated with the intensity of recognition. Furthermore, I use phylogenetic analysis to show that recognition mechanism is not evolutionarily constrained in guppies. Together, my thesis provides new data on the factors that influence kin recognition mechanism and moves the field beyond the simple observation of what species recognize relatives to the ultimate questions of how these mechanisms evolve