title: Geographic distribution of suitable hosts explains the evolution of specialized gentes in the European cuckoo Cuculus canorus.
abstract: BACKGROUND
  Several types of selective forces can act to promote parasite specialization. Parasites might specialize on some suitable hosts at the cost of decreasing effectiveness when exploiting other species of hosts, and specialization can be more easily selected for in hosts that the parasites will easily find. Thus demographic characteristics of suitable hosts such as population density and its spatial consistency could be key factors predicting probability of parasite specialization and speciation. Here, we explore this hypothesis by studying the relationship between occurence of specialized races of the European cuckoo (Cuculus canorus) (i.e. gentes) and mean and coefficient of variation in population density estimated for 12 different European regions.
  
  
  RESULTS
  The results were in accordance with the hypothesis because specialized cuckoo egg morphs were more common in suitable hosts with high population density and low variation in population density at the level of host species or genera.
  
  
  CONCLUSIONS
  We have presented evidence suggesting that population density and homogeneity of geographic distribution of hosts explain, at least partly, the evolution of specialized egg-morphs of the European cuckoo. These results are consistent with the hypothesis that resource (i.e., host) predictability explains the evolution of host races and species of parasites.
authors.affiliation: Departamento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Aridas (CSIC), General Segura 1, Almería E-04001, Spain. jsoler@eeza.csic.es
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Soler
authors.forename: Manuel Martín
authors.initials: MM
authors.lastname: Vivaldi
authors.forename: Anders Pape
authors.initials: AP
authors.lastname: Møller
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000145:classification / Q000502:physiology*; D004531:Eggs; D005060:Europe; D005260:Female; D005843:Geography; D009425:Nesting Behavior; D011156:Population Density; D012098:Reproduction / Q000502:physiology*; D013045:Species Specificity