Insularity effects on bird immune parameters: A comparison between island and mainland populations in West Africa

Abstract

Oceanic islands share several environmental characteristics that have been shown to drive convergent evolutionary changes in island organisms. One change that is often assumed but has seldom been examined is the evolution of weaker immune systems in island species. The reduction in species richness on islands is expected to lead to a reduced parasite pressure and, given that immune function is costly, island animals should show a reduced immune response. However, alternative hypotheses exist; for example, the slower pace of life on islands could favor the reorganization of the immune system components (innate vs. acquired immunity) on islands. Thus far, few island species have been studied and no general patterns have emerged. Here, we compared two immune parameters of birds from São Tomé and Príncipe islands to those of their close relatives at similar latitudes on the mainland (Gabon, West Africa). On islands, the acquired humoral component (total immunoglobulins) was lower for most species, whereas no clear pattern was detected for the innate component (haptoglobin levels). These different responses did not seem to arise from a reorganization of the two immune components, as both total immunoglobulins and haptoglobin levels were positively associated. This work adds to the few empirical studies conducted so far which suggest that changes in immune parameters in response to insularity are not as straightforward as initially thought.

Insularity effects on the assemblage of the blood parasite community of the birds from the Gulf of Guinea

“…If the closest relative did not occur in the sampling site on the mainland, we used the congeneric species present (e.g. Estrilda spp; see also Lobato et al , 2017). In addition, Ploceus cucullatus is the closest mainland relative of both the São Tomé endemic P. grandis and the Príncipe endemic P. princeps (Staffan Andersson, Göteborg University, pers.…”

“…Estrilda spp. ; see also Lobato, Doutrelant, Melo, Reis, & Covas, 2017). In addition, Ploceus cucullatus is the closest mainland relative of both the São Tom e F I G U R E 1 Map of the Gulf of Guinea, in central-west Africa, illustrating the seven regions sampled within the five islands and the mainland sampling areas (located in Cameroon and Gabon).…”

Convergence in reduced body size, head size, and blood glucose in three island reptiles

“…For instance, numerous studies have shown that island populations of a wide range of plants and animals differ from mainland populations with regard to traits such as body size, reproduction, dispersal ability, woodiness, and aggression (reviewed in Whitakker & Fernández-Palacios 2007). Study of physiological differences between island and mainland populations has been more limited, and has focused primarily on tests for differences in immune function with respect to island size and/or parasite diversity (Beadell, Atkins, Cashion, Jonker, & Fleischer, 2007;Lobato, Doutrelant, Melo, Reis, & Covas, 2017;Matson, 2006;Matson & Beadell, 2010;Tompkins, Mitchell, & Bryant, 2006), levels of hormone corticosterone as an index of stress (Müller et al, 2007;Rödl, Berger, Michael Romero, & Wikelski, 2007), digestion efficiency (Sagonas, Pafilis, & Valakos, 2015), and thermoregulatory strategy (Sagonas, Valakos, & Pafilis, 2013).…”

Evolution of immune genes in island birds: reduction in population sizes can explain island syndrome

“…Reduced immune function has also been hypothesized to be an island syndrome trait, directly linked to reduced parasite pressure on islands (Lobato et al, 2017; Matson and Beadell, 2010; Wikelski et al, 2004). Island parasite communities are i) less diverse (Beadell et al, 2006; Illera et al, 2015; Loiseau et al, 2017; Maria et al, 2009; Pérez-Rodríguez et al, 2013), and ii) could be less virulent due to the expansion of the ecological niche expected by the theory of island biogeography.…”