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Parasitism by an invasive nest fly reduces future reproduction in Galápagos mockingbirds


Organisms allocate limited resources to competing activities such as reproduction, growth, and defense against parasites and predators. The introduction of a novel parasite may create new life history trade-offs. As hosts increase their investment in self-maintenance or defense, the cost of parasitism may carry over to other aspects of host biology. Here, in an experimental field study, we document delayed effects of an introduced nest parasite, Philornis downsi, on reproduction of Galápagos mockingbirds (Mimus parvulus). Parasitism of first nests reduced both the number and size of chicks that parents hatched when they re-nested several weeks later. The delayed effect of P. downsi on future reproduction may have been mediated by behavioral shifts by the parents to avoid or resist parasitism. Our results demonstrate that effects of parasitism can persist even after immediate exposure ends. We draw attention to the potential implications that introduced parasites have for host reproductive strategies.

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We are grateful to the Galápagos National Park and Charles Darwin Foundation for logistical support and permits (PC-91-14 and PC-41-16). This publication is contribution number 2314 of the Charles Darwin Foundation for the Galapagos Islands. We thank Goberth Cabrera, Monte Neate-Clegg, Scott Villa, Sarah Knutie, Jordan Herman, Wesley Hochachka, Irby Lovette, Dave Slager, Sarah Bush, and Conor Taff for field assistance and/or helpful discussion. This work was supported by NSF grants DEB-0816877 to DHC and DDIG-1701006 grant to SMM and DHC and an NSF Graduate Research Fellowship to SMM.

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SMM and DHC designed the research, SMM, GBG and JYR collected the data, SMM analyzed the data, and SMM and DHC wrote the paper with input from the other authors.

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Correspondence to Sabrina M. McNew.

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The authors declare they have no conflict of interest.

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All applicable institutional guidelines for the care and use of animals were followed.

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Communicated by Robert L. Thomson.

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McNew, S.M., Goodman, G.B., Yépez R, J. et al. Parasitism by an invasive nest fly reduces future reproduction in Galápagos mockingbirds. Oecologia 192, 363–374 (2020).

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  • Life history
  • Philornis downsi
  • Mimus parvulus
  • Parental compensation
  • Tropics