Geographical variation in blood parasites in feral pigeons: the role of vectors

Abstract

Prevalence and intensity of blood parasites are known to vary in space within a same species, yet the causes underlying such variation are poorly known. Theoretically, blood parasites variation can be attributed to differences to exposure to parasite vectors and/or to differences in host susceptibility. Here, we show that prevalence of Haemoproteus columbae in feral pigeons Columba livia varied among five near‐by populations (range 15%‐100%), paralleled by variation in the abundance of its main vector, the louse flies Pseudolynchia canariensis. Geographic variation in intensity of blood parasites did not covary with abundance of vectors. Within populations, older individuals had a higher probability of being parasitized than younger ones, whereas younger birds, when infected, suffered higher intensities. Furthermore, we found no evidence of sex‐related differences neither in prevalence nor in intensity of blood parasite infections. To demonstrate that geographical variation in prevalence was actually due to differences in vector exposure, we conducted two experiments based on translocation of unparasitized pigeons from a vector‐free area to an area where both the parasite and vector were abundant. With the first experiment, we demonstrated that unparasitized pigeons were not resistant to the parasite because when transmission was possible pigeons became parasitized in a few months. With the second experiment, in which half of the pigeons were prevented from contacts with the vector, we ruled out the posibility that pigeons we considered as unparasitized would have suffered from latent infections. Therefore, both observational and experimental evidence supports the view that vector abundance is the major factor influencing the spatial variation in prevalence of H. columbae in pigeons.

Avian blood parasites in an endangered columbid:Leucocytozoon marchouxiin the Mauritian Pink PigeonColumba mayeri

“…Our finding of a higher probability of infection in younger pigeons (<1 year old) compared to those aged 1 year and older confirms results of partial screening of the same population earlier in the species recovery programme (Swinnerton et al 2005) but contrasts with the pattern commonly seen in other avian species (e.g. Davidar and Morton, 1993 ;Seutin, 1994 ;Merila et al 1995 ;Sol et al 2000 ;Krone et al 2001 ;Sanz et al 2001). Our negative age-prevalence relationship indicates that individuals are infected at an early age, and this may be because older birds have acquired immunity due to high intensity infections as young birds.…”

“…Our negative age-prevalence relationship indicates that individuals are infected at an early age, and this may be because older birds have acquired immunity due to high intensity infections as young birds. Alternatively, it may reflect age differences in exposure to vectors, although this hypothesis was rejected by Sol et al (2000) in their study of Haemoproteus infection in feral pigeons. We found no significant difference in infection prevalence between any age classes of 1 year and over.…”

“…Sol et al 2000). However, in Mauritius, suitable habitat for simuliid vectors (perennial streams and rivers and temperate, humid climate) occurs at sites of all Pink Pigeon subpopulations except on Ile aux Aigrettes, where there is no natural freshwater.…”

“…Comparative studies of blood parasite infection rates across and within species present methodological problems ; non-circulating chronic infections are difficult to detect in blood smears (Weatherhead and Bennett, 1991 ;Schrader et al 2003), and both temporal and geographical variation in prevalence can be marked even within a single host population Bennett, 1991, 1992 ;Merila et al 1995 ;Sol et al 2000 ;Krone et al 2001 ;Schrader et al 2003). Simultaneous sampling of a large number of individuals in several different localities across a species' range has been recommended to overcome these problems Bennett, 1991, 1992 ;Merila et al 1995).…”

Community interactions govern host-switching with implications for host–parasite coevolutionary history

“…Additional flies were periodically added to maintain fly levels at one to two flies per bird. Fly abundance on wild pigeons ranges from zero to eight flies per bird (47)(48)(49)(50). Host-switching was measured in two stages.…”