Molecular Ecological Insights into Neotropical Bird–Tick Interactions

Abstract

In the tropics, ticks parasitize many classes of vertebrate hosts. However, because many tropical tick species are only identifiable in the adult stage, and these adults usually parasitize mammals, most attention on the ecology of tick-host interactions has focused on mammalian hosts. In contrast, immature Neotropical ticks are often found on wild birds, yet difficulties in identifying immatures hinder studies of birds’ role in tropical tick ecology and tick-borne disease transmission. In Panama, we found immature ticks on 227 out of 3,498 individually–sampled birds representing 93 host species (24% of the bird species sampled, and 13% of the Panamanian land bird fauna). Tick parasitism rates did not vary with rainfall or temperature, but did vary significantly with several host ecological traits. Likewise, Neotropical–Nearctic migratory birds were significantly less likely to be infested than resident species. Using a molecular library developed from morphologically–identified adult ticks specifically for this study, we identified eleven tick species parasitizing birds, indicating that a substantial portion of the Panamanian avian species pool is parasitized by a diversity of tick species. Tick species that most commonly parasitized birds had the widest diversity of avian hosts, suggesting that immature tick species are opportunistic bird parasites. Although certain avian ecological traits are positively associated with parasitism, we found no evidence that individual tick species show specificity to particular avian host ecological traits. Finally, our data suggest that the four principal vectors of Rocky Mountain Spotted Fever in the Neotropics rarely, if ever, parasitize Panamanian birds. However, other tick species that harbor newly–discovered rickettsial parasites of unknown pathogenicity are frequently found on these birds. Given our discovery of broad interaction between Panamanian tick and avian biodiversity, future work on tick ecology and the dynamics of emerging tropical tick-borne pathogens should explicitly consider wild bird as hosts.

Host body size and the diversity of tick assemblages on Neotropical vertebrates

“…We used data from Dunn, 1923, Fairchild et al., 1966, Bermúdez et al., 2009, Bermúdez et al., 2010, Bermúdez et al., 2011, Bermúdez et al., 2013, Bermúdez et al., 2015b, Bermúdez et al., 2015a, Apanaskevich and Bermúdez, 2013, Murgas et al., 2013, García et al., 2014, Esser et al., 2016, and Miller et al. (2016).…”

“…These earlier studies, however, largely focused on a single tick species, mostly from the Ixodes ricinus species complex, and its distribution across one or two host species. In contrast, only few studies have examined host determinants of tick parasitism for a broader range of host taxa (Gallivan and Horak, 1997, Marsot et al., 2012, Hofmeester et al., 2016, Miller et al., 2016) and the question of how the species diversity of tick assemblages (i.e., the “tick fauna” of a host species, sensu Poulin (2004)) covaries with interspecific host traits such as body size remains unresolved.…”

Avian Migrants Facilitate Invasions of Neotropical Ticks and Tick-Borne Pathogens into the United States

“…Migratory birds that overwinter in Central and South America are frequently infested with Amblyomma tick species (family Ixodidae), which are common carriers of Rickettsia species parasites (8)(9)(10)(11). There are 45 Amblyomma species endemic to the Neotropics (12), where parasitism rates on birds have been found to vary from 6.5% in Panama (10) to 40% in the Brazilian Amazon (9).…”

“…There are 45 Amblyomma species endemic to the Neotropics (12), where parasitism rates on birds have been found to vary from 6.5% in Panama (10) to 40% in the Brazilian Amazon (9). Rickettsia species of bacteria are transmitted to vertebrates by arthropod vectors, including Amblyomma ticks.…”

“…The pathogenicity of many tick-borne Rickettsia species is unknown, but there are Ͼ25 recognized species in the zoonotic spotted fever group, including those that cause Rocky Mountain spotted fever, Mediterranean spotted fever, North Asian tick typhus, and Queensland tick typhus (13). Wild birds have been implicated as hosts of Amblyomma ticks and Rickettsia pathogens in South and Central America (8)(9)(10)(11); however, the significance of wild birds in the epidemiology of these vectors and pathogens remains poorly understood (13).…”