Imperfect past and present progressive: beak color reflects early-life and adult exposure to antigen

Abstract

Secondary sexual traits may convey information about individual condition. We assessed the capacity for immune challenge with lipopolysaccharide (LPS) or keyhole limpet hemocyanin (KLH) during the prenatal and early postnatal stages to impact beak color development and expression in captive zebra finches. In addition, we tested whether adult immune challenge impacted beak color, and if early-life experience was influential. Immune challenge with KLH early in life slowed development of red beak coloration, and males challenged with KLH as nestlings had reduced red coloration as adults. Following adult KLH challenge, males exhibited a decline in beak redness. Birds challenged with KLH during development produced more anti-KLH antibodies after adult challenge. There was a significant interaction between young treatment and anti-KLH antibody production; for males not challenged with KLH early in life, individuals that mounted a weaker antibody response lost more red coloration after challenge than males mounting a stronger antibody response. Based on models of avian vision, these differences in beak coloration should be detectable to the finches. In contrast to previous studies, we found no effect of early-life or adult challenge with LPS on any aspects of beak coloration. These results provide evidence that beak color reflects developmental and current conditions, and that the signal is linked to critical physiological processes.

Early‐life immune activation increases song complexity and alters phenotypic associations between sexual ornaments

“…Males treated with KLH as nestlings had reduced beak colour expression as adults (Merrill et al., ) whereas for song, males treated with KLH as nestlings had greater song complexity as adults. Similar to beak coloration, some components of song were more strongly impacted by KLH treatment (unique elements, song phrases), having higher effect sizes, whereas others were less impacted (total elements, song duration).…”

“…For details of beak colour assessment, see Merrill et al. (). In brief, we used a portable spectrophotometer (USB 4000; Ocean Optics) with a deuterium‐halogen light source (DH‐2000‐BAL; Ocean Optics) to measure beak colour reflectance between 320 and 700 nm on the left and right side of the upper mandible of adult (3+ years) male finches.…”

“…We examined the role of early‐life immune challenge on song complexity in adult male zebra finches ( Taeniopygia guttata Vieillot 1817), and whether song complexity was related to baseline beak coloration. Our prior work has shown that post natal immune challenge reduces baseline beak redness across the birds’ life span (3+ years), and that adult immune activation reduces beak redness temporarily (8+ days) (Merrill, Naylor, & Grindstaff, ). To the best of our knowledge, previous studies have not addressed the effect of early‐life immune challenge on independent static and dynamic signals.…”

“…This work builds on previous research examining the effects of early‐life immune activation on physiological, cognitive, and sexual signalling traits in zebra finches. Early‐life immune challenge impairs ability to learn a novel task and growth rates (Grindstaff, Hunsaker, & Cox, ), permanently alters stress responsiveness (Merrill & Grindstaff, ), reduces production of anti‐KLH antibodies during development (Merrill & Grindstaff, ), slows development of red beak coloration during development, and produces permanently duller “baseline” beak coloration in adulthood (Merrill et al., ). Here, we expand upon this work to examine the impact of early‐life immune activation on male song complexity.…”

Carotenoids buffer the acute phase response on fever, sickness behavior, and rapid bill color change in zebra finches

“…The dynamic nature of carotenoid-based integuments, such as bills and legs, suggests that they represent a condition-based signal potentially different from more-frequently considered feather color ornaments. However, the rapid changing of bill color suggests that the long-term signaling value of sensitive, real-time indicators may be low and/or different, as integrated phenotypic traits, such as feathers, may better reflect overall condition or quality (Merrill et al, 2016).…”