Understanding how environmental variation influences the distribution of parasite diversity is critical if we are to anticipate disease emergence risks associated with global change. However, choosing the relevant variables for modelling current and future parasite distributions may be difficult: candidate predictors are many, and they seldom are statistically independent. This problem often leads to simplistic models of current and projected future parasite distributions, with climatic variables prioritized over potentially important landscape features or host population attributes. We studied avian blood parasites of the genera Plasmodium, Haemoproteus and Leucocytozoon (which are viewed as potential emergent pathogens) in 37 Iberian blackcap Sylvia atricapilla populations. We used Partial Least Squares regression to assess the relative importance of a wide array of putative determinants of variation in the diversity of these parasites, including climate, landscape features and host population migration. Both prevalence and richness of parasites were predominantly related to climate (an effect which was primarily, but not exclusively driven by variation in temperature), but landscape features and host migration also explained variation in parasite diversity. Remarkably, different models emerged for each parasite genus, although all parasites were studied in the same host species. Our results show that parasite distribution models, which are usually based on climatic variables alone, improve by including other types of predictors. Moreover, closely related parasites may show different relationships to the same environmental influences (both in magnitude and direction). Thus, a model used to develop one parasite distribution can probably not be applied identically even to the most similar host-parasite systems.

AimThe study of parasite biogeography on islands is important for our understanding of both the processes involved in the evolution of parasite assemblages worldwide and the ecology and conservation of insular communities. By studying the haemosporidian blood parasites of a bird that has recently colonized a number of oceanic islands, we were able to test hypotheses relating to the processes of parasite colonization and community assembly prior to the permanent isolation of host species on islands.Location The Atlantic Ocean archipelagos of Madeira and the Canary Islands. MethodsWe used cytochrome b DNA sequences to determine the prevalence and richness of parasites of the genera Haemoproteus, Plasmodium and Leucocytozoon in blackcaps, Sylvia atricapilla, a widespread passerine that colonized these archipelagos during the Last Glacial Maximum. We compared insular blackcap parasite assemblages with those observed in 37 blackcap populations sampled on mainland Europe. ResultsThe insular parasite assemblage was impoverished, containing c. 10% of the parasites found on the continent. None of the parasites observed on the islands were blackcap specific. Some of the observed parasites appear to have switched from blackcaps to other Macaronesian host species, whereas others were of Afrotropical origin and were acquired after blackcaps colonized the islands. The prevalence of parasites in the island populations of blackcaps was lower than in mainland blackcap populations and parasite richness decreased with increasing island distance to the continent.Main conclusions Macaronesian blackcaps do not face the strong parasite load encountered by their mainland counterparts despite the fact that blackcap migration from the continent may directly transport mainland blackcap parasites to the islands. This supports the idea that normal mainland host-parasite associations are compromised on islands and that parasite island syndromes (low richness, frequent host-switching and reduced specialization) evolve even before insular host populations become completely isolated from their mainland counterparts.

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Aim We examined dorsal coloration in and genetic relationships among Iberian populations of the lizard Psammodromus algirus to determine the extent to which the current distribution of phenotypic variation is correlated with phylogeographical history or local environmental conditions. Location Iberian Peninsula, western Palaearctic. MethodsWe sequenced mitochondrial DNA (ND4 and adjacent tRNAs genes) in 36 populations, and seven microsatellite loci in eight representative populations. In 23 populations, lizards were classified according to the presence and intensity of a dorsal striped pattern, the heritability of which was estimated by means of mother-offspring regressions. To determine whether colour pattern is an adaptation for crypsis, we compared the time taken by humans to detect striped and unstriped lizards in different environments.Results The analysis of mtDNA revealed an ancient split between a western clade, subdivided into south-and north-western haplogroups, and an eastern clade with central, south-eastern and eastern haplogroups. In contrast, nuclear markers showed a post-glacial admixture of central and western haplogroups, with the central haplogroup apparently isolated from the rest of its clade. This was consistent with variation in the dorsal striped pattern, a heritable phenotypic trait: central and western lizards were unstriped, whereas eastern lizards were striped. We then suggest that dorsal coloration promotes crypsis: in eastern locations detection times were longer for striped than for unstriped lizards, whereas the opposite was true in western and central locations. Main conclusionsOur results indicate that natural selection for crypsis may promote not only divergence within clades, as suggested by the apparent isolation between unstriped central lizards and striped members of eastern haplogroups, but also admixture between them. We conclude that ecologically driven selection is crucial for understanding the phylogeographical background of phenotypic variation, because recent adaptation to the environment can blur the effects of ancestral isolation.