A genome-wide set of 106 microsatellite markers for the blue tit (Cyanistes caeruleus)

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.     

Experimentally increased reproductive effort alters telomere length in the blue tit (Cyanistes caeruleus)

Telomeres have recently been suggested to play important role in ageing and are considered to be a reliable ageing biomarkers. The life history theory predicts that costs of reproduction should be expressed in terms of accelerated senescence, and some empirical studies do confirm such presumption. Thus, a link between reproductive effort and telomere dynamics should be anticipated. Recent studies have indeed demonstrated that reproduction may trigger telomere loss, but actual impact of reproductive effort has not received adequate attention in experimental studies. Here, we experimentally manipulated reproductive effort by increasing the brood size in the wild blue tit (Cyanistes caeruleus). We show that parents attending enlarged broods experienced larger yearly telomere decay in comparison to control birds attending unaltered broods. In addition, we demonstrate that the change in telomere length differs between sexes, but this effect was independent from our treatment. To our knowledge, this is the first experimental study in the wild revealing that telomere dynamics may be linked to reproductive effort. Thus, telomere shortening may constitute one of the potential proximate mechanisms mediating the costs of reproduction.     

Heterozygosity-based assortative mating in blue tits (Cyanistes caeruleus): implications for the evolution of mate choice

The general hypothesis of mate choice based on non-additive genetic traits suggests that individuals would gain important benefits by choosing genetically dissimilar mates (compatible mate hypothesis) and/or more heterozygous mates (heterozygous mate hypothesis). In this study, we test these hypotheses in a socially monogamous bird, the blue tit (Cyanistes caeruleus). We found no evidence for a relatedness-based mating pattern, but heterozygosity was positively correlated between social mates, suggesting that blue tits may base their mating preferences on partner''s heterozygosity. We found evidence that the observed heterozygosity-based assortative mating could be maintained by both direct and indirect benefits. Heterozygosity reflected individual quality in both sexes: egg production and quality increased with female heterozygosity while more heterozygous males showed higher feeding rates during the brood-rearing period. Further, estimated offspring heterozygosity correlated with both paternal and maternal heterozygosity, suggesting that mating with heterozygous individuals can increase offspring genetic quality. Finally, plumage crown coloration was associated with male heterozygosity, and this could explain unanimous mate preferences for highly heterozygous and more ornamented individuals. Overall, this study suggests that non-additive genetic traits may play an important role in the evolution of mating preferences and offers empirical support to the resolution of the lek paradox from the perspective of the heterozygous mate hypothesis.     

Narrow-sense heritability of body size and its response to different developmental temperatures in Culex quinquefasciatus (Say 1923)

Body size is an important trait involved in overall fitness through its effects on mating success, fecundity, resource acquisition and mortality, and desiccation resistance. In this study, we raised inbred Culex quinquefasciatus mosquito cohorts at different developmental temperatures of 20°, 23°, and 27° C. As an indicator of the amount of genetic variation in body size, we estimated the narrow-sense heritability of body sizes defined as wing aspect ratios. Our results show that narrow-sense heritability of the body size increased as the developmental temperature increased. We also detected the presence of strong genotype-by-environment (G × E) interaction from low cross-environmental correlations. The body size of each temperature regime followed the general rule that higher temperatures produce smaller individuals. We suggest that the increase in genetic variation with increasing temperature might be due to an unleashing of the cryptic genetic variation of the putative genes affecting body size. We conclude that this increase in genetic variation tracking the environmental (developmental temperature) change could have considerable implications for the distribution and range expansion of Cx. quinquefasciatus, especially in warmer environments.     

The role of genotype‐by‐environment interactions in sexual selection

Genotype‐by‐environment interactions (GxEs) in naturally selected traits have been extensively studied, but the impact of GxEs on sexual selection has only recently begun to receive attention. Here, we review recent models and consider how GxEs might affect the evolution of sexual traits through influencing sexual signal reliability and also how GxEs may influence variation in sexually selected traits and the process of reproductive isolation. We then assess the current empirical literature on GxEs in sexual selection and conclude by highlighting areas that need additional work. Research on GxEs and sexual selection is an important new area of study for the discipline, which has largely focused on relatively simple mate choice/competition scenarios to date. Investigators now need to apply this knowledge to more complex, but realistic, situations, to more fully explore the evolution of sexual traits, and in this review we suggest potentially useful directions for future research.     

Correlations between heterozygosity and reproductive success in the blue tit (Cyanistes caeruleus): an analysis of inbreeding and single locus effects

To understand the mechanisms behind heterozygosity-fitness correlations (HFC), it is necessary to employ large numbers of markers with 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.     

No effect of parental quality or extrapair paternity on brood sex ratio in the blue tit (Parus caeruleus)

Sex allocation theory predicts that parents should manipulatebrood sex ratio in order to maximise the combined reproductivevalue of their progeny. Females mating with high quality malesshould, therefore, be expected to produce brood sex ratiosbiased towards sons, as male offspring would receive a relativelygreater advantage from inheritance of their father's characteristicsthan would their female siblings. Furthermore, it has been suggested that sex allocation in chicks fathered through extrapair fertilizations should also be biased towards sons. Contraryto these predictions, we found no evidence that the distributionof sex ratios in a sample of 1483 chicks from 154 broods ofblue tits (Parus caeruleus) deviated significantly from thatof a binomial distribution around an even sex ratio. In addition,we found no significant effect on brood sex ratio of the individualquality of either parent as indicated by their biometrics, feather mite loads, time of breeding, or parental survival. This suggeststhat females in our population were either unable to manipulateoffspring sex allocation or did not do so because selectionpressures were not strong enough to produce a significant shiftaway from random sex allocation. The paternity of 986 chicks from 103 broods was determined using DNA microsatellite typing.Extrapair males sired 115 chicks (11.7%) from 41 broods (39.8%).There was no significant effect of paternity (within-pair versusextrapair) on the sex of individual offspring. We suggest that,in addition to the weakness of selection pressures, the possiblemechanisms responsible for the allocation of sex may not besufficiently accurate to control offspring sex at the levelof the individual egg.     

Genetic and environmental components of growth in nestling blue tits (Parus caeruleus)

We investigated the effect of brood‐size mediated food availability on the genetic and environmental components of nestling growth in the blue tit (Parus caeruleus), using a cross‐fostering technique. We found genetic variation for body size at most nestling ages, and for duration of mass increase, but not of tarsus growth. Hence, nestling growth in our study population seems to have the potential to evolve further. Furthermore, significant genotype–environment interactions indicated heritable variation in reaction norms of growth rates and growth periods, i.e. that our study population had a heritable plasticity in the growth response to environmental conditions. The decreasing phenotypic variance with nestling age indicated compensatory growth in all body traits. Furthermore, the period of weight increase was longer for nestlings growing up in enlarged broods, while there was no difference to reduced broods in the period of tarsus growth. At fledging, birds in enlarged broods had shorter tarsi and lower weights than birds in reduced broods, but there was no difference in wing length or body condition between the two experimental groups. The observed flexibility in nestling growth suggests that growing nestlings are able to respond adaptively to food constraint by protecting the growth of ecologically important traits.     

Causes and consequences of individual variation in the extent of post‐juvenile moult in the blue tit Cyanistes caeruleus (Passeriformes: Paridae)

Moult, comprising the growth or replacement of feathers in birds, is an energetically demanding process. As a result, in many species, the extent of the post‐juvenile moult can vary substantially. However, the reasons underlying this variation remain poorly understood, and the potential life‐history consequences of variation in moult extent are even less clear. In the present study, we aimed to use individual‐specific data to identify factors affecting the extent of the post‐juvenile moult in a population of over 2500 blue tits Cyanistes caeruleus Linnaeus 1758, and to assess the consequences of individual variation in moult extent on reproduction in the first year of life. There was a substantial sex difference in post‐juvenile moult extent, with males moulting more extensively than females. Putative immigrant birds had moulted on average less than those born locally. However, there was little evidence of carry‐over effects of the natal environment on moult extent because we found no relationship between moult extent and fledging date or nestling mass. Evidence that moult extent, and hence feather brightness, affected subsequent reproductive success was limited. Moult extent had no effect on recruitment in males, although female recruits had moulted significantly less than nonbreeders. Because it was not influenced by features of the natal environment, moult extent may not be an honest signal of individual quality in C. caeruleus. As a result, the potential consequences of variation in moult extent for fitness are likely to be small.     

Quantitative genetic parameters of agronomic and quality traits in a global germplasm collection reveal excellent breeding perspectives for Jatropha curcas L.

Jatropha curcas L. (jatropha) is an undomesticated plant, which has received great attention in recent years for its potential in biofuel production and in greening and rehabilitation of wastelands. Yet the absence of improved cultivars and the lack of agronomic knowledge are limiting factors for successful jatropha cultivation. The objectives of the present study were to investigate the perspectives of a worldwide jatropha breeding program and specifically to (i) estimate variance components and heritabilities for agronomic and quality traits in the early phase of cultivation; (ii) assess phenotypic and genetic correlations among those traits; and (iii) discuss strategies for breeding high yielding jatropha cultivars. Data on various traits was collected from 375 jatropha genotypes, which were tested at seven locations during the first 3 years of growth. The accumulated seed yields and the seed yields per harvest year differed significantly among the testing locations. The estimates of genetic and genotype‐by‐environment interaction variances were significant and estimates of heritabilities were high for all yield parameters. The estimates of genetic correlations indicated a strong association among yield parameters. Oil yield was strongly correlated with seed yield and only weakly with oil content in seeds. The perspectives of a jatropha breeding program are excellent. Improved cultivars, definition of favorable environmental factors and refinement of agronomic management practices are needed to secure sustainable jatropha cultivation.     

Secondary phytohaemagglutinin (PHA) swelling response is a good indicator of T‐cell‐mediated immunity in free‐living birds

The validity of using the phytohaemagglutinin (PHA) test to measure acquired immunity, one of the most widely used methods, is currently being debated due to new knowledge on the complex physiology of the process. As a greater secondary response to repeated challenges linked to increases of circulating lymphocyte levels would be indicative of a T‐cell‐mediated immune response, we performed for the first time an experiment under natural conditions with repeated PHA challenges in free‐living adult birds and chicks to shed light on this topic. We found significantly stronger secondary response to PHA injection independent of sex or age, while controlling for body condition, the second response being on average 90% larger than the first. Likewise, lymphocyte counts were significantly higher in the second PHA challenge, whereas no significant differences were found among untreated birds. Significant positive correlations between the PHA response and both lymphocyte counts and plasma protein levels (mainly albumin, globulin precursor) were recovered, whereas no significant differences were recovered in plasma protein levels between challenges. Our results are consistent with those from captive birds, supporting the validity of the PHA skin‐swelling test as an accurate gauge of acquired T‐cell‐mediated immunity in birds.     

Sex‐specific compensatory growth in the larvae of the greater wax moth Galleria mellonella

Deficiency of food resources in ontogeny is known to prolong an organism's developmental time and affect body size in adulthood. Yet life‐history traits are plastic: an organism can increase its growth rate to compensate for a period of slow growth, a phenomenon known as ‘compensatory growth’. We tested whether larvae of the greater wax moth Galleria mellonella can accelerate their growth after a fast of 12, 24 or 72 h. We found that a subgroup of female larvae showed compensatory growth when starved for 12 h. Food deficiency lasting more than 12 h resulted in longer development and lower mass gain. Strength of encapsulation reactions against a foreign body inserted in haemocoel was the weakest in females that showed compensatory growth, whereas the strongest encapsulation was recorded in the males and females that fasted for 24 and 72 h. More specifically, we found sex‐biased immune reactions so that females had stronger encapsulation rates than males in one group that fasted for 72 h. Overall, rapidly growing females had a short larval development period and the shortest adult lifespan. These results suggest that highly dynamic trade‐offs between the environment, life‐history traits and sex lead to plasticity in developmental strategies/growth rates in the greater wax moth.     

Quantitative genetic and translocation experiments reveal genotype‐by‐environment effects on juvenile life‐history traits in two populations of Chinook salmon (Oncorhynchus tshawytscha)

Understanding the genetic architecture of phenotypic plasticity is required to assess how populations might respond to heterogeneous or changing environments. Although several studies have examined population‐level patterns in environmental heterogeneity and plasticity, few studies have examined individual‐level variation in plasticity. Here, we use the North Carolina II breeding design and translocation experiments between two populations of Chinook salmon to detail the genetic architecture and plasticity of offspring survival and growth. We followed the survival of 50 800 offspring through the larval stage and used parentage analysis to examine survival and growth through freshwater rearing. In one population, we found that additive genetic, nonadditive genetic and maternal effects explained 25%, 34% and 55% of the variance in larvae survival, respectively. In the second population, these effects explained 0%, 24% and 61% of the variance in larvae survival. In contrast, fry survival was regulated primarily by additive genetic effects, which indicates a shift from maternal to genetic effects as development proceeds. Fry growth also showed strong additive genetic effects. Translocations between populations revealed that offspring survival and growth varied between environments, the degree of which differed among families. These results indicate genetic differences among individuals in their degree of plasticity and consequently their ability to respond to environmental variation.     

Parental effort and response to nestling begging in the house sparrow: repeatability,heritability and parent–offspring co‐evolution

Parental effort has a direct impact on individual fitness. Theoretical models exploring how parental effort evolves to cope with offspring demand and sexual conflicts may differ in the assumptions they make in respect to the genetic heritability of parental behaviours. Only a few attempts, however, have been made to estimate the heritability of parental behaviours and their possible co‐evolution with offspring solicitation behaviour. Analysing parent and offspring behaviours in four generations of cross‐fostered broods of house sparrows, we found that parental effort (food delivery rate) was repeatable across consecutive broods and heritable across generations. In contrast, parental response to experimentally induced changes in nestling begging was neither repeatable across broods nor heritable across generations or correlated to nestling begging. Thus, the results give no indication for genetic covariance between begging intensity and parental response, but provide the first cross‐fostering‐based evidence for the heritability of parental investment levels across generations.     

Characterization of 20 microsatellite loci in the long‐tailed tit Aegithalos caudatus (Aegithalidae,AVES)

We characterized 20 microsatellite loci in the long‐tailed tit, Aegithalos caudatus. Polymorphic loci were identified by testing 114 loci that had been originally isolated in other avian species. The loci were characterized in 23–163 unrelated long‐tailed tits from a British population and displayed between two and 42 alleles, with observed heterozygosity ranging between 0.09 and 0.97.     

Sex‐linked microsatellite marker detected in the female gametophytes of Undaria pinnatifida (Phaeophyta)

In our microsatellite analysis of three male and three female gametophytes of Undaria pinnatifida (Harv.) Suringar, a microsatellite marker (part of the locus Up‐AC‐2A8, GenBank accession no. AY738602.1) was only polymerase chain reaction‐amplified in three female gametophytes. This putative female‐specific marker was further tested by the use of 32 male and 21 female gametophytes maintained in the Marine Biological Culture Collection Centre, China. In addition, three sporophytes were included for confirmation. Results showed that the marker was present in all of the female gametophytes and sporophyte cultures, but absent in all of the male gametophytes. To our knowledge, this is the first sex‐related marker ever reported in U. pinnatifida. The discovery of this marker will accelerate gender identification and shed light on our understanding of the mechanisms of sex determination at a molecular level in this commercially important seaweed.     

Application of Concanavalin A during immune responsiveness skin‐swelling tests facilitates measurement interpretation in mammalian ecology

The skin‐swelling test is a simple and widespread method used in field ecological research to estimate cellular immune responsiveness in animals. This immunoecological test is based on measuring the magnitude of tissue swelling response at specific times following subcutaneous application of an experimental pro‐inflammatory stimulant. In the vast majority of studies across vertebrate taxa, phytohemagglutinin (PHA) is used as a universal stimulant. Given the complexity of immune response activation pathways of PHA, however, interpretation of test results can be ambiguous. Goal of this study was to improve methodology of the skin‐swelling test to decrease this ambiguity. Here, we present an alternative protocol aimed at facilitating interpretation of skin‐swelling data for mammals. Based on previous evidence suggesting that mammalian T cells are readily activated by Concanavalin A (ConA) in vitro, we compared cellular immune responses in vivo to PHA and ConA as an alternative pro‐inflammatory stimulant in mice. We measured magnitude of tissue swelling and compared it with intensity of blood cell infiltration into tissue over a 72‐hour interval. Our results corroborate that PHA and ConA show important differences in both dynamics and response amplitude in rodents. ConA induces stronger swelling with a distinct leukocyte activity pattern and higher pro‐inflammatory cytokine (interleukin 6 [IL‐6] and interferon gamma[IFN‐γ]) expression than PHA during peak response (24‐h post‐treatment). Furthermore, unlike PHA, magnitude of swelling was positively associated with cellular activity (number of neutrophils infiltrating tissue) following ConA injection. We conclude that ConA is the more suitable stimulant for skin‐swelling tests in mammals. This is because of the molecular binding specificity in the two lectins, that is, ConA specifically activates T cells while PHA also triggers erythroagglutination. We propose that ConA be used in all future ecological testing in mammals as it exhibits better performance and its application facilitates immunological interpretation of skin‐swelling test results.     

Sex‐specific estimates of dispersal show female philopatry and male dispersal in a promiscuous amphibian,the alpine salamander (Salamandra atra)

Amphibians display wide variations in life‐history traits and life cycles that should prove useful to explore the evolution of sex‐biased dispersal, but quantitative data on sex‐specific dispersal patterns are scarce. Here, we focused on Salamandra atra, an endemic alpine species showing peculiar life‐history traits. Strictly terrestrial and viviparous, the species has a promiscuous mating system, and females reproduce only every 3 to 4 years. In the present study, we provide quantitative estimates of asymmetries in male vs. female dispersal using both field‐based (mark–recapture) and genetic approaches (detection of sex‐biased dispersal and estimates of migration rates based on the contrast in genetic structure across sexes and age classes). Our results revealed a high level of gene flow among populations, which stems exclusively from male dispersal. We hypothesize that philopatric females benefit from being familiar with their natal area for the acquisition and defence of an appropriate shelter, while male dispersal has been secondarily favoured by inbreeding avoidance. Together with other studies on amphibians, our results indicate that a species' mating system alone is a poor predictor of sex‐linked differences in dispersal, in particular for promiscuous species. Further studies should focus more directly on the proximate forces that favour or limit dispersal to refine our understanding of the evolution of sex‐biased dispersal in animals.