The relationship between genetic diversity and fitness has important implications in evolutionary and conservation biology. This relationship has been widely investigated at the individual level in studies of heterozygosity-fitness correlations (HFC). General effects caused by inbreeding and/or local effects at single loci have been used as explanations of HFC, but the debate about the causes of HFC in open, natural populations is still ongoing. Study designs that control for variation in the inbreeding level of the individuals, and knowledge on the function and location of the markers used to measure heterozygosity, are fundamental to understand the causes of HFC. Here we investigated correlations between individual heterozygosity and estimates of survival at different life-history stages in an open population of blue tits (Cyanistes caeruleus). For survival at the embryo, nestling and fledgling stage, we used a full-sibling approach, i.e. we controlled for the level of inbreeding. We genotyped 1496 individuals with 79 microsatellites mapped across 25 chromosomes in the zebra finch (Taeniopygia guttata) that were classified either as potentially functional (58 loci) or as neutral (21 loci). We found different effects of standardized multilocus heterozygosity (SH): SH(functional) had a negative effect on the probability of hatching and local recruitment of females, whereas SH(neutral) had a positive effect on adult survival. The negative effects of functional loci are better explained by local effects, whereas the positive effects of neutral markers could reflect inbreeding effects in the population. Our results highlight the importance of considering the characteristics of the markers used in HFC studies and confirm the mixed effects of heterozygosity in different contexts (e.g. sex and life-history stage).

To understand the mechanisms behind heterozygosity-fitness correlations (HFC), it is necessary to employ large numbers of markerswith known function and independently estimate the variation in inbreeding in the population. Here we genotyped 794 blue tits with 79 microsatellites that were distributed across 25 chromosomes and that were classified either as "functional" (N = 58) or "neutral" (N = 21). We found a positive effect of individual heterozygosity at multiple loci on clutch size, on the number of eggs sired by males, and on the number of recruits produced by males and females. We documented the occurrence of some consanguineous matings and found evidence for a particular type of population structure that can contribute to the occurrence of inbreeding. As the set of "neutral" loci provided more power to detect HFC and identity disequilibrium, we argue that "neutral" markers are better predictors of the effects of inbreeding. The number of significant effects at single loci did not exceed the expected number of false positives and no strong effects were associated with heterozygosity at "functional" markers. Thus, the HFC found here cannot be attributed to strong effects of the loci under study. K E Y W O R D S :EST-SSR, heterozygosity-fitness correlation, identity disequilibrium, microsatellites, population structure.

Investigations of heterozygosity-fitness correlations (HFCs) are central to the understanding how genetic diversity is maintained in natural populations. Advanced genome-wide approaches will enrich the number of functional loci to be tested. We argue that a combined analysis of the genetic mechanisms of HFCs and selection signals at single loci will allow researchers to better understand the micro-evolutionary basis of HFCs. Different dominance relationships among the alleles at the locus can lead to positive, negative or null HFCs depending on the allele frequency distribution. These scenarios differ in the temporal stability of the HFCs and in the patterns of allele frequency changes over time. Here, we describe a simple theoretical framework that links the analyses of heterozygosity-fitness associations (ecological timescale) with tests for selection signals (evolutionary timescale). Different genomic footprints of selection can be expected for the different underlying genetic mechanisms of HFCs, and this information can be independently used for the classification of HFCs. We suggest that in addition to inbreeding and single-locus overdominant effects also loci under directional selection could play a significant role in the development of heterozygosity-fitness effects in large natural populations under recent or fluctuating ecological changes.

We have characterized a set of 106 microsatellite markers in 26-127 individual blue tits (Cyanistes caeruleus), and assigned their location on the zebra finch (Taeniopygia guttata) and on the chicken (Gallus gallus) genome on the basis of sequence homology. Thirty-one markers are newly designed from zebra finch EST (expressed sequence tags) sequences, 22 markers were developed by others from EST sequences using different methods and the remaining 53 loci were previously designed or modified passerine markers. The 106 microsatellite markers are distributed over 26 and 24 chromosomes in the zebra finch and in the chicken genome respectively and the number of alleles varies between 2 and 49. Eight loci deviate significantly from Hardy-Weinberg equilibrium and show a high frequency of null alleles, and three pairs of markers located in the same chromosome appear to be in linkage disequilibrium. With the exception of these few loci, the polymorphic microsatellite markers presented here provide a useful genome-wide resource for population and evolutionary genetic studies of the blue tit, in addition to their potential utility in other passerine birds.

Decision-making during different life-history stages requires information, which is obtained through own or others' experience and interaction with the environment. In birds, song is important for territory defense and mate attraction. Although song has evolved to purposely convey information, it can be inadvertently exploited by conspecifics. Experiments attempting to attract focal species by playing back their song are numerous, yet the consequences for reproductive performance remain little understood. In 2013 and 2014, settlement, reproduction, and extrapair paternity of Phylloscopus sibilatrix were assessed in a randomized experiment. We hypothesized that territory number, reproductive performance, and extrapair paternity would be higher on song plots (wood warbler song playbacks during prebreeding periods) than on control plots (no wood warbler song playback). On song plots, 3 times more territories were established, settlement occurred faster, and maximum plot occupancy was higher compared with control plots. Pairing rate, daily nest survival rate, mean clutch size, mean number of nestlings and fledglings, rates of extrapair young, nest abandonment, and nest predation did not differ between treatments, but fledging success was lower on song plots compared with control plots. This study shows the important role social cues can play for territory selection of birds, but also exemplifies the necessity for postattraction evaluation of reproduction to rule out negative effects of artificial attraction. Decreased fledging success on song plots and ambiguity about consequences of artificial attraction for distribution and settling dynamics of the species give reason to further evaluate whether acoustic attraction represents a suitable method for songbird conservation.