Master of Science (MSc)
Faculty of Science
Tristan A.F. Long
The fruit fly Drosophila melanogaster has a long history as a research model for studies on behaviour and group dynamics. When individuals are grouped in an environment and resources decrease, then they may behave co-operatively with one another or antagonistically compete. Hamilton’s Law states that if the benefit of helping a related individual out-weighs the cost to its direct fitness, then the individual’s indirect fitness will increase when they help their kin compared to helping an unrelated stranger. Yet it is unknown whether kinship mediates larval behaviour to encourage co-operation and/or lessen antagonistic behaviours between consanguineous individuals. In this thesis I set out to examine and understand how kinship might be important to the evolution of sociality and anti-social behaviours in Drosophila melanogaster larvae. First, I set out to determine if kinship mediates the co-operative feeding cluster behaviour between 3rd instar larvae and whether there are evolutionary benefits to co-operating with kin over unrelated conspecifics in three separate assays. I changed the average degree of relatedness between individuals in the social environment and measured the characteristics of the feeding cluster (size, frequency and number of larvae) in the first assay. In the second assay I measured the weight and survivorship of the matured adult flies, and in the third assay I measured the proportion of related individuals in the clusters. From these assays, I was able to determine that the higher the degree of relatedness between individuals resulted: in increasing clusters with relatives, in increasing cooperation between related individuals in cluster formation, and evidence of benefits to co-operating with kin than strangers (with increased survivorship and weight in females as a predictor of fecundity). Secondly, I also examined how kinship might affect the expression of cannibalistic behaviour towards related individuals compared to unrelated conspecifics. I conducted assays with 2nd instar larvae, giving them the choice to cannibalize related eggs or unrelated eggs. I was able to determine that there is some evidence of cannibalism occurring with larvae more often eating unrelated eggs, however there were also some unexpected results which occurred. For example, there was no difference in the median time to the first incidence of cannibalism nor differences in the duration of the cannibalistic interactions. As such, more experiments need to be conducted to support this hypothesis and to better understand any underlining mechanisms that might be in play. Kinship selection might be the key to unlocking the underlining factors of why individuals behave pleasantly towards one another and antagonistically with rivals; and eventually understanding the genes behind those behaviours might also help us understand our own evolutionary origins of sociality.
Khodaei, Lucas, "Happy or Hangry Families: Does kinship mediate cooperation and cannibalism in Drosophila melanogaster larvae?" (2019). Theses and Dissertations (Comprehensive). 2185.
Available for download on Sunday, October 20, 2019