Is spatial autocorrelation an intrinsic property of territory size?

In animals, competition for space and resources often results in territorial behaviour. The size of a territory is an important correlate of fitness and is primarily determined by the spatial distribution of resources and by interactions between competing individuals. Both of these determinants, alone or in interaction, could lead to spatial non-independence of territory size (i.e. spatial autocorrelation). We investigated the presence and magnitude of spatial autocorrelation (SAC) in territory size using Monte Carlo simulations of the most widely used territory measures. We found significant positive SAC in a wide array of competition-simulated conditions. A meta-analysis of territory size data showed that SAC is also a feature of territories mapped based on behavioural observations. Our results strongly suggest that SAC is an intrinsic trait of any territory measure. Hence, we recommend that appropriate statistical methods should be employed for the analysis of data sets where territory size is either a dependent or an explanatory variable

Evidence for increased olfactory receptor gene repertoire size in two nocturnal bird species with well-developed olfactory ability

<p>Abstract</p> <p>Background</p> <p>In vertebrates, the molecular basis of the sense of smell is encoded by members of a large gene family, namely olfactory receptor (OR) genes. Both the total number of OR genes and the proportion of intact OR genes in a genome may indicate the importance of the sense of smell for an animal. There is behavioral, physiological, and anatomical evidence that some bird species, in particular nocturnal birds, have a well developed sense of smell. Therefore, we hypothesized that nocturnal birds with good olfactory abilities have evolved (i) more OR genes and (ii) more intact OR genes than closely related and presumably less 'olfaction-dependent' day-active avian taxa.</p> <p>Results</p> <p>We used both non-radioactive Southern hybridization and PCR with degenerate primers to investigate whether two nocturnal bird species that are known to rely on olfactory cues, the brown kiwi (<it>Apteryx australis</it>) and the kakapo (<it>Strigops habroptilus</it>), have evolved a larger OR gene repertoire than their day-active, closest living relatives (for kiwi the emu <it>Dromaius novaehollandiae</it>, rhea <it>Rhea americana</it>, and ostrich <it>Struthio camelus </it>and for kakapo the kaka <it>Nestor meridionalis </it>and kea <it>Nestor notabilis</it>). We show that the nocturnal birds did not have a significantly higher proportion of intact OR genes. However, the estimated total number of OR genes was larger in the two nocturnal birds than in their relatives.</p> <p>Conclusion</p> <p>Our results suggest that ecological niche adaptations such as daily activity patterns may have shaped avian OR gene repertoires.</p

Playback of predator calls inhibits and delays dawn singing in a songbird community

Recent studies have demonstrated that experimental increases in perceived predation risk can substantially impair breeding behavior and reduce reproductive success. Perceived predation risk may also occur in the context of sexual signaling, with potential consequences for sexual selection. In songbirds, singing at dawn is an important sexual signal but may also attract predators. Here, we report on 2 experiments designed to test whether perceived predation risk affects the occurrence and timing of dawn singing in a songbird community. In a pilot experiment, we broadcast predator playbacks intermittently across half a forest plot and nonpredator playbacks across the other half throughout early spring. In the second experiment, we repeated the treatments in 16 independent but smaller plots (8 with predator calls and 8 with nonpredator calls). In the predator treatment, most species were less likely to sing at dawn (small, nonsignificant effects) and started later if they did sing (significant for 2 species). Meta-analyses combining the data from both experiments showed an overall significant effect of the treatment on both the likelihood and timing of singing. Species that were less likely to sing also sang later if they did sing, corroborating that an increase in perceived predation risk was the common cause of the effects on both measures

Paternity in mallards: effects of sperm quality and female sperm selection for inbreeding avoidance

Postcopulatory processes might play an important role in sexual selection. In theory, fertilization success could be controlled by females via selection of particular sperm within their reproductive tract, or it could be determined by sperm competition per se. In practice, these two mechanisms are difficult to disentangle. To assess the relative importance of both mechanisms we used artificial insemination in combination with measurements of sperm quality (swimming speed and motility) in mallards. In this species, females often lack behavioral control over copulations and hence may use postcopulatory mechanisms to optimize their reproductive output. One important factor affecting female fitness may be selection of genetically compatible males. To investigate the influence of sperm quality and parental relatedness on paternity we inseminated 12 groups of related females with a sperm mixture containing equal numbers of sperm from a brother and from an unrelated male. Paternity was independent of the relatedness of the siring male to the female but was significantly affected by long-term sperm swimming speed and motility. No interaction between relatedness and sperm quality on paternity was observed. These results suggest that female mallards are not able to select sperm on a purely genetic basis and emphasize the importance of sperm quality in gaining paternit

Within- and between-year variation in the presence of individually marked Ruff <i>Calidris pugnax</i> at a stopover site during northward migration

Ruffs Calidris pugnax migrate from wintering areas in West-Africa and Europe tobreeding grounds in northern Eurasia, using stopover sites along the way. At onesuch stopover site in southwest Friesland (53°N, The Netherlands), we studiedvariation in the timing of individual stopover based on 6474 Ruffs colour-ringedin 2004–2012. 43% of males and 22% of females were recorded in the studyarea in March–May the years following marking. Minimal stopover duration ofreturning individuals showed substantial within-year heterogeneity. We distinguishedtwo classes: (1) ‘transient’ individuals were observed only on a singleday in the study area within a season (51% of observed males and 79% offemales), and (2) ‘staging’ individuals were observed on multiple days. Weobserved two seasonal peaks in the presence of transient Ruffs, typically coincidingwith the peak of arrival and departure of staging birds. Males known towinter in Europe were more likely to be observed in the study area and arrivedearlier than males of unknown winter origin (3.1 days and 3.7 days earlier fortransient and staging males, respectively), but departure was unrelated to winterorigin. Staging and transient females arrived later than males. Between-yearrepeatability of individual behaviour was low, and individuals did not significantlyadvance their arrival date over the course of years, in contrast with a pattern ofshifting arrival dates at the population level. The observation that a large proportionof Ruffs visit southwest Friesland for only a short stop suggests that manyindividuals rely on other sites for moulting and refuelling during spring migration.Resightings of marked individuals elsewhere in western Europe indicated thatthese sites are largely located between 51° and 54°N. Thus, during springmigration, Ruffs marked in southwest Friesland displayed high between- andwithin-individual variation in minimal stopover duration

Sources of individual variation in plasma testosterone levels

The steroid hormone testosterone (T) plays a central role in the regulation of breeding in males, because many physiological, morphological and behavioural traits related to reproduction are T dependent. Moreover, in many seasonally breeding vertebrates, male plasma T levels typically show a pronounced peak during the breeding season. While such population-level patterns are fairly well worked out, the sources and the implications of the large variability in individual T levels within the seasonal cycle remain surprisingly little understood. Understanding the potential sources of individual variation in T levels is important for behavioural and evolutionary ecologists, for at least two reasons. First, in ‘honest signalling’ theory, T is hypothesized to play a critical role as the assumed factor that enforces honesty of the expression of sexually selected quality indicators. Second, T is often considered a key mediator of central life-history trade-offs, such as investment in survival versus reproduction or in mating versus parental care. Here, we discuss the patterns of within- and between-individual variation in male plasma T levels in free-living populations of birds. We argue that it is unclear whether this variability mainly reflects differences in underlying individual quality (intrinsic factors such as genetic or maternal effects) or in the environment (extrinsic factors including time of day, individual territorial status and past experience). Research in avian behavioural endocrinology has mainly focused on the effects of extrinsic factors, while other sources of variance are often ignored. We suggest that studies that use an integrative approach and investigate the relative importance of all potential sources of variation are essential for the interpretation of data on individual plasma T levels

Genetic Correlates of Individual Differences in Sleep Behavior of Free-Living Great Tits (Parus major)

Within populations, free-living birds display considerable variation in observable sleep behaviors, reflecting dynamic interactions between individuals and their environment. Genes are expected to contribute to repeatable between-individual differences in sleep behaviors, which may be associated with individual fitness. We identified and genotyped polymorphisms in nine candidate genes for sleep, and measured five repeatable sleep behaviors in free-living great tits (Parus major), partly replicating a previous study in blue tits (Cyanistes caeruleus). Microsatellites in the CLOCK and NPAS2 clock genes exhibited an association with sleep duration relative to night length, and morning latency to exit the nest box, respectively. Furthermore, microsatellites in the NPSR1 and PCSK2 genes associated with relative sleep duration and proportion of time spent awake at night, respectively. Given the detection rate of associations in the same models run with random markers instead of candidate genes, we expected two associations to arise by chance. The detection of four associations between candidate genes and sleep, however, suggests that clock genes, a clock-related gene, or a gene involved in the melanocortin system, could play key roles in maintaining phenotypic variation in sleep behavior in avian populations. Knowledge of the genetic architecture underlying sleep behavior in the wild is important because it will enable ecologists to assess the evolution of sleep in response to selection

Morph-dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards <i>Buteo buteo</i>

How genetic polymorphisms are maintained in a population is a key question in evolutionary ecology. Previous work on a plumage colour polymorphism in the common buzzard Buteo buteo suggested heterozygote advantage as the mechanism maintaining the co-existence of three morphs (light, intermediate and dark). We took advantage of 20 years of life history data collected in a Dutch population to replicate earlier studies on the relationship between colour morph and fitness in this species. We examined differences between morphs in adult apparent survival, breeding success, annual number of fledglings produced and cumulative reproductive success. We found that cumulative reproductive success differed among morphs, with the intermediate morph having highest fitness. We also found assortative mating for colour morph, whereby assortative pairs were more likely to produce offspring and had longer-lasting pair bonds than disassortative pairs. Over the 20-year study period, the proportion of individuals with an intermediate morph increased. This apparent evolutionary change did not just arise from selection on individual phenotypes, but also from fitness benefits of assortative mating. The increased frequency of intermediates might also be due to immigration or drift. We hypothesize that genetic variation is maintained through spatial variation in selection pressures. Further studies should investigate morph-dependent dispersal behaviour and habitat choice

Drd4 gene polymorphisms are associated with personality variation in a passerine bird

Polymorphisms in several neurotransmitter-associated genes have been associated with variation in human personality traits. Among the more promising of such associations is that between the human dopamine receptor D4 gene (Drd4) variants and novelty-seeking behaviour. However, genetic epistasis, genotype–environment interactions and confounding environmental factors all act to obscure genotype–personality relationships. Such problems can be addressed by measuring personality under standardized conditions and by selection experiments, with both approaches only feasible with non-human animals. Looking for similar Drd4 genotype–personality associations in a free-living bird, the great tit (Parus major), we detected 73 polymorphisms (66 SNPs, 7 indels) in the P. major Drd4 orthologue. Two of the P. major Drd4 gene polymorphisms were investigated for evidence of association with novelty-seeking behaviour: a coding region synonymous single nucleotide polymorphism (SNP830) and a 15 bp indel (ID15) located 5′ to the putative transcription initiation site. Frequencies of the three Drd4 SNP830 genotypes, but not the ID15 genotypes, differed significantly between two P. major lines selected over four generations for divergent levels of ‘early exploratory behaviour’ (EEB). Strong corroborating evidence for the significance of this finding comes from the analysis of free-living, unselected birds where we found a significant association between SNP830 genotypes and differing mean EEB levels. These findings suggest that an association between Drd4 gene polymorphisms and animal personality variation predates the divergence of the avian and mammalian lineages. Furthermore, this work heralds the possibility of following microevolutionary changes in frequencies of behaviourally relevant Drd4 polymorphisms within populations where natural selection acts differentially on different personality types