Seabirds, a key factor in the dispersal of parasites

The research, led by Elena Gómez-Díaz, researcher from the Institute of Evolutionary Biology (CSIC-UPF), analyses the genetic diversity of Ornithodoros capensis ticks from a variety of seabird species, such as Sula leucogaster and Cape Verde shearwaters, on several islands within the Cape Verde Archipelago. Researchers from Queen’s University, in Canada, and from the National Centre for Scientific Research (CNRS), in France, have also taken part in the research.

Coexisting lineages   The study reveals that multiple species of this tick complex belonging to lineages which are genetically very different coexist within the Cape Verde Archipelago. Coexisting lineages also occur on different host species in distant geographical locations across the Pacific, Atlantic and Indian Oceans. As professor Jacob González-Solís states, “the most surprising result is the great diversity found in ticks within the Cape Verde Archipelago, which is unexpectedly high. It demonstrates that several cryptic ticks may coexist in one place, which have been dispersed by seabirds, as they can travel enormous distances and often breed in areas which are very distant from each other, such as the Galápagos Islands (in the Pacific Ocean) or Réunion (in the Indian Ocean). In a broader sense, this result shows the importance of host mobility in parasite dispersal, as well as the capacity some seabirds have to disperse parasites and other diseases around the world”.       

The researchers’ hypothesis is that this genetic diversity cannot have arisen by evolution on the islands from an original host lineage alone but as a result of multiple independent colonization events via seabird dispersal. Young seabirds carry parasites from a more distant origin    Another striking result is related to the migratory movements of seabirds and their fidelity to breeding sites. According to recent studies, Sula leucogaster and Cape Verde shearwaters can travel long distances. For example, Cape Verde shearwaters cross the Atlantic during migration as they travel from the Cape Verde Archipelago, in front of the Senegal coast, to Brazil. However, during the breeding season these birds come back to the same islands to nest. As a result of this fidelity, a certain genetic structure can be found in their colonies. Therefore, populations in the Atlantic are genetically very different from those in the Pacific or Indian Oceans.

According to the researcher Elena Gómez, “it is thought that immature non-breeding seabirds, known to move more erratically, are responsible for bringing these lineages from very distant origins to the archipelago”. This research, which is a pioneering study on the dispersal of seabird ectoparasites between archipelagos in different oceans, demonstrates that seabirds regularly disperse parasites over extreme spatial scales. According to professor González-Solís, “seabird dispersal capacity is almost unbeatable in the animal world”. Although Ornithodoros capensis ticks do not carry any disease, as it is currently known, the study demonstrates the influence migratory seabirds have on dispersing pathogens and determining the evolutionary ecology and epidemiology of these organisms.