Abstract
Life-history theory predicts that the trade-off between parasite defense and other costly traits such as reproduction may be most evident when resources are scarce. The strength of selection that parasites inflict on their host may therefore vary across environmental conditions. Collared flycatchers (Ficedula albicollis) breeding on the Swedish island Öland experience a seasonal decline in their preferred food resource, which opens the possibility to test the strength of life-history trade-offs across environmental conditions. We used nested-PCR and quantitative-PCR protocols to investigate the association of Haemosporidia infection with reproductive performance of collared flycatcher females in relation to a seasonal change in the external environment. We show that despite no difference in mean onset of breeding, infected females produced relatively more of their fledglings late in the season. This pattern was also upheld when considering only the most common malaria lineage (hPHSIB1), however there was no apparent link between the reproductive output and the intensity of infection. Infected females produced heavier-than-average fledglings with higher-than-expected recruitment success late in the season. This reversal of the typical seasonal trend in reproductive output compensated them for lower fledging and recruitment rates compared to uninfected birds earlier in the season. Thus, despite different seasonal patterns of reproductive performance the overall number of recruits was the same for infected versus uninfected birds. A possible explanation for our results is that infected females breed in a different microhabitat where food availability is higher late in the season but also is the risk of infection. Thus, our results suggest that another trade-off than the one we aimed to test is more important for explaining variation in reproductive performance in this natural population: female flycatchers appear to face a trade-off between the risk of infection and reproductive success late in the season.
Highlights
Disease causing micro-parasites can have large negative impacts on the population dynamics of wild plants and animals [1,2,3], via pathogen virulence [4] and/or the costs of resistance [5,6]
We investigated how infection with Haemosporidia parasites was linked with reproductive performance of female collared flycatchers in terms of clutch size, number of fledglings, fledgling condition and number of recruits relative to the timing of breeding
General seasonal pattern of reproductive performance In agreement with previous findings, the reproductive performance of female collared flycatchers breeding in our study sites showed a significant decline with progressing breeding season in terms of clutch size (z1,1849 = 24.89, p,0.0001) and number of fledglings (z1,1624 = 28.82, p,0.0001) produced
Summary
Disease causing micro-parasites can have large negative impacts on the population dynamics of wild plants and animals [1,2,3], via pathogen virulence [4] and/or the costs of resistance [5,6]. For example Trypanosoma prevalence markedly increased in Tengmalm’s owls (Aegolius funereus) during years when their primary prey, Microtus voles, were at low levels [7] and wound healing in tree lizards (Urosaurus ornatus) was compromised when food resources were restricted [13]. These findings are consistent with the idea that trade-offs between immune function and reproduction should be most evident when resources are limited. Understanding how hosts allocate resources between immunity and reproduction across various environmental contexts may be crucial for predicting how particular pathogens influence the host population dynamics and for increasing our general understanding of hostparasite co-evolution
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