Birds are plagued by an impressive diversity of ectoparasites, ranging from feather-feeding lice, to featherdegrading bacteria. Many of these ectoparasites have severe negative effects on host fitness. It is therefore not surprising that selection on birds has favored a variety of possible adaptations for dealing with ectoparasites. The functional significance of some of these defenses has been well documented. Others have barely been studied, much less tested rigorously. In this article we review the evidence -or lack thereof -for many of the purported mechanisms birds have for dealing with ectoparasites. We concentrate on features of the plumage and its components, as well as anti-parasite behaviors. In some cases, we present original data from our own recent work. We make recommendations for future studies that could improve our understanding of this poorly known aspect of avian biology.
Members of the genus Arsenophonus comprise a large group of bacterial endosymbionts that are widely distributed in arthropods of medical, veterinary, and agricultural importance. At present, little is known about the role of these bacteria in arthropods, because few representatives have been isolated and cultured in the laboratory. In the current study, we describe the isolation and pure culture of an Arsenophonus endosymbiont from the hippoboscid louse fly Pseudolynchia canariensis. We propose provisional nomenclature for this bacterium in the genus Arsenophonus as "Candidatus Arsenophonus arthropodicus." Phylogenetic analyses indicate that "Candidatus Arsenophonus arthropodicus" is closely related to the Arsenophonus endosymbionts found in psyllids, whiteflies, aphids, and mealybugs. The pure culture of this endosymbiont offers new opportunities to examine the role of Arsenophonus in insects. To this end, we describe methods for the culture of "Candidatus Arsenophonus arthropodicus" in an insect cell line and the transformation of this bacterium with a broad-host-range plasmid.Many members of the class Insecta maintain mutualistic associations with one or more specialized symbiotic bacteria (2). Bacteria that participate in these associations are classified either as primary (P) or secondary (S) endosymbionts, because they often coexist in a single insect host. The P-endosymbionts are predicted to be ancient in origin because their phylogenies are concordant with those of their host insects over a substantial period of evolutionary time, indicating long-term coevolution. On the other hand, the S-endosymbionts are predicted to be recent in origin because their phylogenies show little or no concordance with their insect hosts, indicating recent acquisition.While the ancient P-endosymbionts are known to have defined mutualistic functions in their insect hosts, the role of the S-endosymbionts is not yet well understood. From an evolutionary standpoint it seems likely that S-endosymbionts have beneficial (mutualistic) roles in their insect hosts because they are maintained predominantly through a maternal (vertical) transmission strategy. Several recent studies have provided experimental evidence for a number of beneficial effects conferred by the S-endosymbionts of aphids, which recently received new nomenclature (20). These benefits include host plant specialization (17, 27), increased resistance to hymenopteran parasitoids (21, 22), and increased tolerance to heat stress (5, 19). In addition, there is evidence indicating that S-endosymbionts can provide some level of functional compensation for the loss of P-endosymbionts in a laboratory population of aphids (16). While these studies are both exciting and encouraging, the ability to perform experimentation in these systems would be greatly enhanced with the opportunity to genetically manipulate S-endosymbionts. The application of recombinant DNA technology would permit functional analysis of individual genes in the endosymbiont genomes, providing a platform to e...
Competition-colonization trade-off models explain the coexistence of competing species in terms of a trade-off between competitive ability and the ability to colonize competitor-free patches of habitat. A simple prediction of these models is that inferior competitors will be superior dispersers. This prediction has seldom been tested in natural populations because measuring dispersal is difficult. Host-parasite systems are promising in this regard, especially those involving ''permanent'' parasites that complete their entire life cycle on the body of the host. Because of this close association with the host, the dispersal, i.e., transmission, of these parasites can be monitored very accurately. We tested the dispersal prediction of the competition-colonization model by documenting the transmission dynamics of feather-feeding lice, which are permanent, relatively host-specific parasites of birds. We compared two groups known as ''wing'' lice and ''body'' lice that are common parasites of Rock Pigeons (Columba livia Gmelin). The two groups are ecologically similar, and they compete for resources on the host. Previous work shows that body lice are competitively superior to wing lice, leading us to predict that wing lice should be better than body lice at dispersing to new host individuals. We tested this prediction by comparing the ability of wing and body lice to disperse between hosts using vertical-and horizontal-transmission mechanisms, including phoretic hitchhiking on parasitic flies (Diptera: Hippoboscidae). A series of experiments with both captive and wild birds confirmed that wing lice are much better than body lice at colonizing new hosts. Wing lice showed significantly greater vertical transmission to nestlings, and they were quite capable of phoretic transmission to new hosts on flies. In contrast, body lice were not phoretic. These results provide the first rigorous demonstration of phoretic transmission in lice, and they underscore the importance of a community-level approach to understanding the ecology of parasite transmission dynamics.
Reciprocal selective effects between coevolving species are often influenced by interactions with the broader ecological community. Community-level interactions may also influence macroevolutionary patterns of coevolution, such as cospeciation, but this hypothesis has received little attention. We studied two groups of ecologically similar feather lice (Phthiraptera: Ischnocera) that differ in their patterns of association with a single group of hosts. The two groups, "body lice" and "wing lice," are both parasites of pigeons and doves (Columbiformes). Body lice are more host-specific and show greater population genetic structure than wing lice. The macroevolutionary history of body lice also parallels that of their columbiform hosts more closely than does the evolutionary history of wing lice. The closer association of body lice with hosts, compared with wing lice, can be explained if body lice are less capable of switching hosts than wing lice. Wing lice sometimes disperse phoretically on parasitic flies (Diptera: Hippoboscidae), but body lice seldom engage in this behavior. We tested the hypothesis that wing lice switch host species more often than body lice, and that the difference is governed by phoresis. Our results show that, where flies are present, wing lice switch to novel host species in sufficient numbers to establish viable populations on the new host. Body lice do not switch hosts, even where flies are present. Thus, differences in the coevolutionary history of wing and body lice can be explained by differences in host-switching, mediated by a member of the broader parasite community.coevolutionary biology | community ecology | phoresy | ectoparasites
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