Supergenes offer spectacular examples of long-term balancing selection in nature, but their origin and maintenance remain a mystery. Reduced recombination between arrangements, a critical aspect of... Show moreSupergenes offer spectacular examples of long-term balancing selection in nature, but their origin and maintenance remain a mystery. Reduced recombination between arrangements, a critical aspect of many supergenes, protects adaptive multi-trait phenotypes but can lead to mutation accumulation. Mutation accumulation can stabilize the system through the emergence of associative overdominance (AOD), destabilize the system, or lead to new evolutionary outcomes. One outcome is the formation of maladaptive balanced lethal systems, where only heterozygotes remain viable and reproduce. We investigated the conditions under which these different outcomes occur, assuming a scenario of introgression after divergence. We found that AOD aided the invasion of a new supergene arrangement and the establishment of a polymorphism. However, this polymorphism was easily destabilized by further mutation accumulation, which was often asymmetric, disrupting the quasi-equilibrium state. Mechanisms that accelerated degeneration tended to amplify asymmetric mutation accumulation between the supergene arrangements and vice-versa. As the evolution of balanced lethal systems requires symmetric degeneration of both arrangements, this leaves only restricted conditions for their evolution, namely small population sizes and low rates of gene conversion. The dichotomy between the persistence of polymorphism and degeneration of supergene arrangements likely underlies the rarity of balanced lethal systems in nature. Show less
Avian vocalizations function in mate attraction and territorial defence. Vocalizations can act as behavioural barriers and play an important role in speciation processes. Hybrid zones illustrate... Show moreAvian vocalizations function in mate attraction and territorial defence. Vocalizations can act as behavioural barriers and play an important role in speciation processes. Hybrid zones illustrate behavioural barriers are not always impermeable and provide a natural laboratory to examine the role of vocalizations in the causes and consequences of hybridization. This thesis examines a hybrid zone between two species of African doves: the vinaceous (Streptopelia vinacea) and ring-necked dove (S.capicola) by investigating its composition and history with molecular techniques, the mechanisms underlying the variation in dove coos and the response to hybrid signals within and outside the hybrid zone. The variation in hybrid signals and the possibility of learning which vocalizations to respond to can play an important role in facilitating further introgression between the two species. Show less