Experimental manipulation of Blue Tit nest height does not support the thermoregulation hypothesis

Birds show immense variation in nest sizes within species. At least six different hypotheses have been forwarded to explain intraspecific variation in nest size in cavity nesting species, but very few of those hypotheses have been tested experimentally. In our study, when nestlings were 2 days old, we manipulated the height of 182 Blue Tit (Cyanistes caeruleus) nests to either 5 cm or 11 cm while standardising their ectoparasite load and genetic and maternal background. In line with the hypothesis that larger nests provide thermoregulatory benefits, we expected experimentally enlarged nests to show increased growth of nestlings compared to shallow nests, or to improve female somatic condition. We found that the nest height manipulation affected the tail length of 16-day old nestlings, but did not affect any other morphometric measure (tarsus length, body mass, head size and wing length). In addition nest height manipulation had no impact on nestling survival and did not affect female body condition. Our results do not therefore provide strong support for the thermoregulatory hypothesis and suggest regional differences in the relationship between nest size and reproductive success.Peer reviewe

Reed Warbler Hosts Do Not Fine-Tune Mobbing Defenses During the Breeding Season, Even When Cuckoos Are Rare

Hosts of brood parasitic cuckoos often employ mobbing attacks to defend their nests and, when mobbing is costly, hosts are predicted to adjust their mobbing to match parasitism risk. While evidence exists for fine-tuned plasticity, it remains unclear why mobbing does not track larger seasonal changes in parasitism risk. Here we test a possible explanation from parental investment theory: parents should defend their current brood more intensively as the opportunity to replace it declines (re-nesting potential), and therefore “counteract” any apparent seasonal decline to match parasitism risk. We take advantage of mobbing experiments conducted at two sites where reed warblers (Acrocephalus scirpaceus) experience (in Italy), or do not experience (in Finland), brood parasitism. We predicted that mobbing of cuckoos should be higher overall in Italy, but remain constant over the season as in other parasitised sites, whereas in Finland where cuckoos do not pose a local threat, we predicted that mobbing should be low at the beginning of the season but increase as re-nesting potential declined. However, while cuckoos were more likely to be mobbed in Italy, we found little evidence that mobbing changed over the season at either the parasitized or non-parasitized sites. This suggests that re-nesting potential has either little influence on mobbing behavior, or that its effects are obscured by other seasonal differences in ecology or experience of hosts

From the animal house to the field : are there consistent individual differences in immunological profile in wild populations of field voles (Microtus agrestis)?

Inbred mouse strains, living in simple laboratory environments far removed from nature, have been shown to vary consistently in their immune response. However, wildlife populations are typically outbreeding and face a multiplicity of challenges, parasitological and otherwise. In this study we seek evidence of consistent difference in immunological profile amongst individuals in the wild. We apply a novel method in this context, using longitudinal (repeated capture) data from natural populations of field voles, Microtus agrestis, on a range of life history and infection metrics, and on gene expression levels. We focus on three immune genes, IFN-γ, Gata3, and IL-10, representing respectively the Th1, Th2 and regulatory elements of the immune response. Our results show that there was clear evidence of consistent differences between individuals in their typical level of expression of at least one immune gene, and at most all three immune genes, after other measured sources of variation had been taken into account. Furthermore, individuals that responded to changing circumstances by increasing expression levels of Gata3 had a correlated increase in expression levels of IFN-γ. Our work stresses the importance of acknowledging immunological variation amongst individuals in studies of parasitological and infectious disease risk in wildlife populations

Pedigree_BT

Pedigree of the blue tit population (2003-2010

Supplementary textR2

R codes used for performing quantitative genetic analyses (with asreml-R), structural equation models (with lavaan) and simulation

WingWebs

Multiple measures of nestling wing webs (in mm) before (2 times on day 13) and after PHA injection (3 time on day 14)

Data from: Tail color signals performance in blue tit nestlings

Indirect sexual selection arises when reproductive individuals choose their mates based on heritable ornaments that are genetically correlated to fitness. Evidence for genetic associations between ornamental coloration and fitness remain scarce. In this study we investigate the quantitative genetic relationship between different aspects of tail structural coloration (brightness, hue and UV chroma) and performance (cell mediated immunity, body mass and wing length) in blue tit (Cyanistes caeruleus) nestlings. In line with previous studies, we find low heritability for structural coloration and moderate heritability for performance measures. Multivariate animal models show positive genetic correlations between the three measures of performance, indicating quantitative genetic variation for overall performance while tail brightness and UV chroma, two genetically independent color measures, are genetically correlated with performance (positively and negatively respectively). Our results suggest that mate choice based on independent aspects of tail coloration can have fitness payoffs in blue tits and provide support for the indirect benefits hypothesis. However, low heritability of tail structural coloration implies that indirect sexual selection on mate choice for this ornament will be a weak evolutionary force

NestConstructionPed

Pedigree of blue tits with IDs encountered in NestConstructionData. To be used for quantitative genetic analyse

Data from: Low heritability of nest construction in a wild bird

In birds and other taxa, nest construction varies considerably between and within populations. Such variation is hypothesized to have an adaptive (i.e. genetic) basis, but estimates of heritability in nest construction are largely lacking. Here, we demonstrate with data collected over 10 years of 1010 nests built by blue tits in nest boxes that nest size (height of nest material) and nest composition (proportion of feathers in the nest) are repeatable but only weakly (12-13%) heritable female traits. These findings imply that nest construction may evolve but only if subjected to strong and consistent selection pressures