title: A blurring of life-history lines: Immune function, molt and reproduction in a highly stable environment.
abstract: Rufous-collared sparrows (Zonotrichia capensis peruviensis) from valleys in the Atacama Desert of Chile, live in an extremely stable environment, and exhibit overlap in molt and reproduction, with valley-specific differences in the proportion of birds engaged in both. To better understand the mechanistic pathways underlying the timing of life-history transitions, we examined the relationships among baseline and stress-induced levels of corticosterone (CORT), testosterone, and bacteria-killing ability of the blood plasma (BKA), as well as haemosporidian parasite infections and the genetic structure of two groups of sparrows from separate valleys over the course of a year. Birds neither molting nor breeding had the lowest BKA, but there were no differences among the other three categories of molt-reproductive stage. BKA varied over the year, with birds in May/June exhibiting significantly lower levels of BKA than the rest of the year. We also documented differences in the direction of the relationship between CORT and BKA at different times during the year. The direction of these relationships coincides with some trends in molt and reproductive stage, but differs enough to indicate that these birds exhibit individual-level plasticity, or population-level variability, in coordinating hypothalamo-pituitary-adrenal axis activity with life-history stage. We found weak preliminary evidence for genetic differentiation between the two populations, but not enough to indicate genetic isolation. No birds were infected with haemosporidia, which may be indicative of reduced parasite pressure in deserts. The data suggest that these birds may not trade off among different life-history components, but rather are able to invest in multiple life-history components based on their condition.
authors.affiliation: Illinois Natural History Survey, University of Illinois, Urbana-Champaign, IL 61820, USA. Electronic address: loren21@illinois.edu.
authors.forename: Loren
authors.initials: L
authors.lastname: Merrill
authors.affiliation: Instituto de Filosofia y Ciencias de la Complejidad (IFICC), Santiago, Chile. Electronic address: plgonzalezgomez@gmail.com.
authors.forename: Paulina L
authors.initials: PL
authors.lastname: González-Gómez
authors.affiliation: Department of Biology, University of Missouri, St. Louis, MO 63121, USA. Electronic address: vincenzoellis@mail.umsl.edu.
authors.forename: Vincenzo A
authors.initials: VA
authors.lastname: Ellis
authors.affiliation: Department of Biology, Grinnell College, Grinnell, IA 50112, USA; Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Boulder, CO 80309, USA(1). Electronic address: Iris.Levin@colorado.edu.
authors.forename: Iris I
authors.initials: II
authors.lastname: Levin
authors.affiliation: Instituto de Ecología y Biodiversidad, IEB, Universidad de Chile, Santiago, Chile. Electronic address: rvasquez@uchile.cl.
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Vásquez
authors.affiliation: University of California Davis, Davis, CA 95616, USA. Electronic address: jcwingfield@ucdavis.edu.
authors.forename: John C
authors.initials: JC
authors.lastname: Wingfield
mesh_terms: D000818:Animals; D001715:Bird Diseases / Q000276:immunology* / Q000469:parasitology; D001947:Breeding; D003345:Corticosterone / Q000097:blood; D004777:Environment; D016787:Haemosporida / Q000276:immunology*; D006790:Host-Parasite Interactions; D008018:Life Cycle Stages / Q000502:physiology*; D018978:Molting; D010913:Pituitary-Adrenal System / Q000378:metabolism; D011528:Protozoan Infections / Q000276:immunology* / Q000469:parasitology; D012098:Reproduction; D012621:Seasons; D046370:Sparrows / Q000276:immunology* / Q000378:metabolism / Q000469:parasitology; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D003345:Corticosterone
keywords: Bacteria-killing ability; Corticosterone; Hypothalamo–pituitary–adrenal axis; Rufous-collared sparrow; Trade-off; Zonotrichia