Long‐term variation in environmental conditions influences host–parasite fitness

Musgrave, Karen; Bartlow, Andrew W.; Fair, Jeanne M.

doi:10.1002/ece3.5321

Cited by 23 publications

(17 citation statements)

References 57 publications

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“…Global climate change is known to affect host–parasite dynamics in various (and often poorly understood) ways (Poulin 2006, Rohr et al 2011, Musgrave et al 2019). A long‐term advancement in Cliff Swallow breeding date has occurred during this study, attributable to warmer and drier conditions (Brown and Brown 2014).…”

Section: Discussionmentioning

confidence: 99%

The cost of ectoparasitism in Cliff Swallows declines over 35 years

Brown

Hannebaum

O’Brien

et al. 2021

Ecological Monographs

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Host-parasite dynamics often vary over time, brought about by changes in the parasite's virulence or the host's ability to resist or tolerate the parasite. Although virulence evolution in microparasites is well studied, we know little about temporal change in the pathogenicity of macroparasites such as blood-feeding insects. Using data collected over 35 yr, we report a reduction in pathogenicity of the hematophagous swallow bug (Cimex vicarius) on its Cliff Swallow (Petrochelidon pyrrhonota) host. Relative to experimentally fumigated, parasite-free nests, the negative effects of bugs on nestling swallow body mass and survival were less in the later years of the study than in the earlier years, and the negative relationship between nestling body mass and bug abundance became weaker over time. The survival of adult birds exposed to swallow bugs increased throughout the study, while survival of birds from parasitefree nests decreased over time. Swallow bug abundance per nest, bug body size, and bug age ratios did not change during the study. Between-colony transmission of bugs showed less immigration into larger colonies than in earlier studies, but there was no net change in transmission. Cliff Swallows did not reduce their exposure to bugs over time by being more likely to avoid infested nest or colony sites. Parents increased the number of food deliveries to their offspring over time in the presence of parasites, but the total amount of food delivered was unchanged. The reduced cost of swallow bug ectoparasitism does not seem related to changes in parasite narrow-sense virulence, the host's avoidance of parasites, the presence of alternative hosts for bugs, or climate-driven phenological mismatches. The results probably reflect the Cliff Swallow's evolving of greater tolerance to swallow bugs, brought about by the bird's shift from natural cliff nesting sites to artificial structures that may harbor more bugs than natural cliffs. This study shows that hosts can respond relatively rapidly to high levels of parasitism, and provides support for models that suggest the evolution of tolerance should be expected in some host-parasite systems.

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Section: Discussionmentioning

confidence: 99%

The cost of ectoparasitism in Cliff Swallows declines over 35 years

Brown

Hannebaum

O’Brien

et al. 2021

Ecological Monographs

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“…Our results suggest that different host species can defend themselves similarly and differently to the same parasite, which is likely due to variation in host ecology and life history. Future studies are needed to determine if there is long‐term interannual variation in these host–parasite relationships and whether environmental factors, such as precipitation, could affect them (Musgrave, Bartlow, & Fair, ).…”

Section: Discussionmentioning

confidence: 99%

Host tolerance and resistance to parasitic nest flies differs between two wild bird species

Grab

Hiller

Hurlbert

et al. 2019

Ecology and Evolution

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Hosts have developed and evolved defense strategies to limit parasite damage. Hosts can reduce the damage that parasites cause by decreasing parasite fitness (resistance) or without affecting parasite fitness (tolerance). Because a parasite species can infect multiple host species, determining the effect of the parasite on these hosts and identifying host defense strategies can have important implications for multi‐host–parasite dynamics. Over 2 years, we experimentally manipulated parasitic flies (Protocalliphora sialia) in the nests of tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis). We then determined the effects of the parasites on the survival of nestlings and compared defense strategies between host species. We compared resistance between host species by quantifying parasite densities (number of parasites per gram of host) and measured nestling antibody levels as a mechanism of resistance. We quantified tolerance by determining the relationship between parasite density and nestling survival and blood loss by measuring hemoglobin levels (as a proxy of blood recovery) and nestling provisioning rates (as a proxy of parental compensation for resources lost to the parasite) as potential mechanisms of tolerance. For bluebirds, parasite density was twice as high as for swallows. Both host species were tolerant to the effects of P. sialia on nestling survival at their respective parasite loads but neither species were tolerant to the blood loss to the parasite. However, swallows were more resistant to P. sialia compared to bluebirds, which was likely related to the higher antibody‐mediated immune response in swallow nestlings. Neither blood recovery nor parental compensation were mechanisms of tolerance. Overall, these results suggest that bluebirds and swallows are both tolerant of their respective parasite loads but swallows are more resistant to the parasites. These results demonstrate that different host species have evolved similar and different defenses against the same species of parasite.

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“…Nestboxes were added in new watersheds over the years to 2017, resulting in over 800 nestboxes (see Musgrave et al . 2019 for a map of the study site and nestbox locations). Nestboxes were placed approximately 2 m off the ground on Ponderosa Pine and Piñon Pine trees and spaced approximately 50–75 m apart, spanning an elevation gradient from 1890 to 2305 m.…”

Section: Methodsmentioning

confidence: 99%

Sex ratio of Western Bluebirds (Sialia mexicana) is mediated by phenology and clutch size

Bartlow

Jankowski

Hathcock

et al. 2021

Ibis

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Mothers may produce more of one sex to maximize their fitness if there are differences in the cost of producing each sex or there are differences in their relative reproductive value. Breeding date and clutch size are known to influence offspring sex ratios in birds through sex differences in dispersal, social behaviours, differential mortality and available food resources. We tested whether breeding date, clutch size and drought conditions influenced offspring sex ratios in a sexually size‐monomorphic species, the Western Bluebird Sialia mexicana, by interrogating a 21‐year dataset. After controlling for differential mortality, we found that hatch dates late in the breeding season were associated with the production of more females, suggesting that the value of producing males declines as the breeding season progresses. When clutch size was taken into account, small clutches yielded significantly more females late in the breeding season than in the early and middle parts of the breeding season, which produced significantly more males. Large clutches early in the season tended to produce more females, although this was not significant. Drought severity was not correlated with sex ratio adjustment. We propose and discuss several explanations for these patterns, including male offspring, but not female offspring, acting as helpers, increased female nestling provisioning late in the breeding season, differences in food abundance and egg‐laying order. Future work will help to uncover the mechanisms leading to these patterns. Identifying patterns and mechanisms of sex ratio skew from long‐term datasets is important for informing predictions regarding life‐history trade‐offs in wildlife populations.

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Long‐term variation in environmental conditions influences host–parasite fitness

Cited by 23 publications

References 57 publications

The cost of ectoparasitism in Cliff Swallows declines over 35 years

The cost of ectoparasitism in Cliff Swallows declines over 35 years

Host tolerance and resistance to parasitic nest flies differs between two wild bird species

Sex ratio of Western Bluebirds (Sialia mexicana) is mediated by phenology and clutch size

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