Plumage Ornaments Signal Male Physiological Quality in Common Yellowthroats

Elaborate ornaments are thought to honestly signal quality to potential mates. These ornaments may signal a variety of physiological processes that affect health and fitness. I examined the relationship between ornaments and physiological quality in a bird, the common yellowthroat (Geothlypis trichas). Male common yellowthroats have two plumage ornaments, a black (eumelanin-based) mask and a yellow (carotenoid-based) bib. Males with larger masks are preferred by females for both extra-pair and social mates. I found that both the mask and the bib of male common yellowthroats honestly signal their ability to resist oxidative stress. Males with larger masks and more colorful bibs also produce a greater amount of corticosterone, a hormone that releases stored energy and induces adaptive behavioral changes, during a short-term stress response. This suggests that these ornaments signal how well males cope with stressful situations. In contrast, neither the mask or the bib signal the infection intensity of haemosporidian parasites across males in the population. However, haemosporidian infection intensity was not related to overwinter survival or body mass, suggesting that these parasites may not be very costly. Together, these results suggest that both melanin- and carotenoid-based plumage ornaments honestly signal male physiological quality in common yellowthroats

Understanding the evolution of immune genes in jawed vertebrates

Driven by co-evolution with pathogens, host immunity continuously adapts to optimize defence against pathogens within a given environment. Recent advances in genetics, genomics and transcriptomics have enabled a more detailed investigation into how immunogenetic variation shapes the diversity of immune responses seen across domestic and wild animal species. However, a deeper understanding of the diverse molecular mechanisms that shape immunity within and among species is still needed to gain insight into-and generate evolutionary hypotheses on-the ultimate drivers of immunological differences. Here, we discuss current advances in our understanding of molecular evolution underpinning jawed vertebrate immunity. First, we introduce the immunome concept, a framework for characterizing genes involved in immune defence from a comparative perspective, then we outline how immune genes of interest can be identified. Second, we focus on how different selection modes are observed acting across groups of immune genes and propose hypotheses to explain these differences. We then provide an overview of the approaches used so far to study the evolutionary heterogeneity of immune genes on macro and microevolutionary scales. Finally, we discuss some of the current evidence as to how specific pathogens affect the evolution of different groups of immune genes. This review results from the collective discussion on the current key challenges in evolutionary immunology conducted at the ESEB 2021 Online Satellite Symposium: Molecular evolution of the vertebrate immune system, from the lab to natural populations

Data from: The relationship between blood parasites and ornamentation depends on the level of analysis in the common yellowthroat

The Hamilton–Zuk hypothesis predicts that ornament expression is a signal of the ability of individuals to resist parasite infection. Thus, across a population (i.e. between-individuals) more ornamented individuals should have lower levels of parasitism. Numerous studies have tested this prediction and the results are mixed. One reason for these conflicting results may be that many studies have examined this relationship at the between-individual level, which may be affected by confounding factors such as selective mortality. Using within-subject centering we examined the relationship between male ornamentation and avian blood parasites at both the between- and within-individual levels. These relationships focus on differences in genetically-based resistance to parasites and the trade-off in resource allocation between parasite resistance and ornament expression within an individual, respectively. We studied male common yellowthroats Geothlypis trichas, which have two plumage ornaments, a yellow, carotenoid-based bib (throat and chest) and a black, melanin-based facial mask. Surprisingly, within-individuals, an increase in parasitism between years was associated with an increase in mask size and, potentially, greater concentration of carotenoids in the yellow feathers. This suggests that males may be able to tolerate an increase in parasitism and still increase ornament expression. In contrast, ornamentation was not related to parasitism at the between-individual level. Thus, our study revealed relationships between ornaments and parasitism at the within-individual level that were not present at the between-individual level. Our results highlight the importance of examining both within- and between-individual relationships as correlations between variables, such as ornaments and parasites, may depend on the level of analysis (i.e. within- or between-individuals)

Data from: Male stress response is related to ornamentation but not resistance to oxidative stress in a warbler

1. Ornaments are thought to honestly signal individual quality to potential mates. Individual quality may include the ability to cope with stress through the production of glucocorticoids (GCs), which help to redirect resources from growth or reproduction to survival during an acute stress response. However, elevated levels of GCs may also increase oxidative stress and reduce immune function. Thus, an important question is whether high quality individuals, with more elaborate ornaments, signal their ability to produce a strong stress response and mitigate some of the negative effects of doing so through higher resistance to oxidative stress. 2. We tested whether ornamentation and resistance to oxidative stress were related to the magnitude of the increase in corticosterone (CORT), the main GC in birds, during an acute stress response in common yellowthroats (Geothlypis trichas). Males in this species have two plumage ornaments, a black (eumelanin-based) facial mask and a yellow (carotenoid-based) bib. We measured the increase in CORT in response to capture and handling. 3. Males with more elaborate ornaments (larger masks and more colourful bibs) had a greater increase in CORT during an acute stress response. However, the increase in CORT was not related to resistance to oxidative stress. 4. These results suggest that both melanin- and carotenoid-based plumage ornaments can signal the ability of a male to cope with stressors through a greater increase in CORT. Thus, the association between ornamentation and stress induced CORT is not likely due to a mechanism specific to a particular colour (melanin or carotenoid), but instead may result from more general interactions between CORT and health or condition

OxidativeStress & GSH data

Tab delimited file with 14 columns (variables) and 52 rows (top row contains the variable names). Variables are: Band Number (band number of individual bird [4 digit prefix and 5 digit suffix, after the decimal point]) Capture Date(1=1May) Breed Experience (see KRL file for description) Exper Group (see KRL file for description) Mask (see KRL file for description) bib size (see KRL file for description) Yellow Brightness (see KRL file for description) Ccar (see KRL file for description) Tarsus (mm) Weight pre (g, prior to bird being put in an aviary, if part of the LPS experiment) GSH pre (see Methods for GSH; "pre" refers to estimate prior to LPS experiment) ROMs/TAC_pre (see Methods; "pre" refers to estimate prior to LPS experiment) GSH post-pre (see Methods; "pre" refers to estimate prior to LPS experiment) ROMs/TAC post-pre (see Methods; "pre" refers to estimate prior to LPS experiment

KRL data

Time to hemolysis for 50% of red blood cells in the KRL assay. File is tab-delimited text file with 11 variables (columns). The first row is the headers for each column and there are 39 subsequent rows of data.Variables names are:Band No Breed Experience (Experienced = known prior breeding experience; inexperienced = no known prior breeding experience on the main study area; blanks indicate unknown because the bird was captured off the main study area) Time to 50% hemolysis (the response variable) Jdate for KRL (date blood was sampled for KRL assay; 1=1 May) Tarsus (tarsus length of bird, mm) Mass (total body mass of bird, g) Mask (facial mask size of bird, mm^2) bib size (size of yellow throat patch, mm^2) Yellow brightness (see Methods) Ccar (see Methods) N replicates (number of different assays performed; see Methods

Rapid adaptation to a novel pathogen through disease tolerance in a wild songbird

Animal hosts can adapt to emerging infectious disease through both disease resistance, which decreases pathogen numbers, and disease tolerance, which limits damage during infection without limiting pathogen replication. Both resistance and tolerance mechanisms can drive pathogen transmission dynamics. However, it is not well understood how quickly host tolerance evolves in response to novel pathogens or what physiological mechanisms underlie this defense. Using natural populations of house finches (Haemorhous mexicanus) across the temporal invasion gradient of a recently emerged bacterial pathogen (Mycoplasma gallisepticum), we find rapid evolution of tolerance (\u3c25 years). In particular, populations with a longer history of MG endemism have less pathology but similar pathogen loads compared with populations with a shorter history of MG endemism. Further, gene expression data reveal that more-targeted immune responses early in infection are associated with tolerance. These results suggest an important role for tolerance in host adaptation to emerging infectious diseases, a phenomenon with broad implications for pathogen spread and evolution

Understanding the evolution of immune genes in jawed vertebrates.

Driven by co-evolution with pathogens, host immunity continuously adapts to optimize defence against pathogens within a given environment. Recent advances in genetics, genomics and transcriptomics have enabled a more detailed investigation into how immunogenetic variation shapes the diversity of immune responses seen across domestic and wild animal species. However, a deeper understanding of the diverse molecular mechanisms that shape immunity within and among species is still needed to gain insight into-and generate evolutionary hypotheses on-the ultimate drivers of immunological differences. Here, we discuss current advances in our understanding of molecular evolution underpinning jawed vertebrate immunity. First, we introduce the immunome concept, a framework for characterizing genes involved in immune defence from a comparative perspective, then we outline how immune genes of interest can be identified. Second, we focus on how different selection modes are observed acting across groups of immune genes and propose hypotheses to explain these differences. We then provide an overview of the approaches used so far to study the evolutionary heterogeneity of immune genes on macro and microevolutionary scales. Finally, we discuss some of the current evidence as to how specific pathogens affect the evolution of different groups of immune genes. This review results from the collective discussion on the current key challenges in evolutionary immunology conducted at the ESEB 2021 Online Satellite Symposium: Molecular evolution of the vertebrate immune system, from the lab to natural populations