Protocalliphora larvae: moderate but lasting carry-over effects on yearling and mother coloration

Parasites play a significant role in the evolution of their hosts,
influencing a wide range of traits, including animal signals such as
coloration. While the direct effects of parasitism on coloration are
well-documented, it remains unclear whether these effects persist beyond
the parasitized phase, leading to direct carry-over effects. Additionally,
the impact of parasitism on parental investment may have indirect
consequences for the parents themselves, potentially affecting their
coloration. We analyzed a 20-year dataset to estimate both direct and
indirect long-term effects of the ectoparasite Protocalliphora sp. on blue
tit (Cyanistes caeruleus) and their plumage color. This ectoparasite only
affects the nestling stage but is also known to increase parental care. We
measured the impact of ectoparasites on nestlings' condition, and
then quantified their long-term effects on the colorations produced during
the subsequent molt in i) parasitized individuals at their yearling stage,
and ii) parents that had reared parasitized nestlings. Our analyses
focused on a carotenoid-based (yellow patch) and a structural (blue patch)
plumage coloration. Our findings revealed that parasite load was
negatively correlated with nestling condition. We also found long-term
effects of Protocalliphora larvae on yearling coloration, reducing the
brightness of the yellow patch in individuals from large broods. In
parents that reared parasitized nestlings, we observed lasting
consequences in coloration, reducing brightness of the yellow patch in
both parents but decreasing blue patch intensity only in mothers. This
study supports the hypothesis that early life parasitism can have a
lasting effect on ornaments of parasitized individuals, as well as
carry-over indirect effects on parent ornaments.