Avian Malaria and Interspecific Interactions in Ficedula Flycatchers

Abstract: Parasitism is a core theme in ecological and evolutionary studies. Despite this, there are still gaps in our knowledge regarding host-parasite interactions in nature. Furthermore, in an era of human-induced, global climatic and environmental change revealing the roles that parasites play in host life-histories, interspecific interactions and host distributions is of the utmost importance. In this thesis, I explore avian malaria parasites (haemosporidians) in two species of passerine birds: the collared flycatcher Ficedula albicollis and the pied flycatcher F. hypoleuca. In Paper I, I show that an increase in spring temperature has led to rapid divergence in breeding times for the two flycatcher species, with collared flycatchers breeding significantly earlier than pied flycatchers. This has facilitated regional coexistence through the build up of temporal isolation. In Paper II, I explore how malaria assemblages across the breeding ranges of collared and pied flycatchers vary. I find that pied flycatcher populations have significantly higher infection prevalence than collared flycatchers, but collared flycatchers have a higher diversity of parasites. Additionally, I find that recently colonised flycatchers have kept their original parasite assemblages while gaining further parasites from native pied flycatchers. In Paper III, I explore age-related patterns of malaria infections in collared flycatchers. I find that female collared flycatchers have higher overall infection rates than males and that infected female collared flycatchers have significantly higher mortality rates than uninfected females while males pay no survival cost. Despite this, female collared flycatchers do not pay a fitness cost, despite their shorter lifespans. In Paper IV, I explore nest defence behaviours of infected and uninfected collared flycatchers. I find that malaria infection significantly interacts with age and that young, infected collared flycatchers have a lower intensity of defence behaviours than uninfected individuals, while the opposite pattern is present in older collared flycatchers, with infected birds having higher defence behaviours. Therefore, I argue that Papers III and VI suggest patterns of terminal investment are present in collared flycatchers. Finally, in Paper V, I investigate parasite transmission in pied and collared flycatchers. I find that infected individuals of both species produce higher quantities of volatile organic compounds (VOCs) than uninfected individuals. Additionally, there is a significant increase in VOCs produced when the number of malaria gametocytes is higher. This suggests that malaria parasites are able to manipulate their hosts into producing insect-vector attracting compounds and that this is further increased at peak infectivity. These findings help to fill in some of the gaps in the literature regarding host-parasite relationships and the role of environmental change on hosts.