Intraguild predation (IGP) is a commonly recognized mechanism influencing the community structure of predators, but the complex interactions are notoriously difficult to disentangle. The mesopredator ...suppression hypothesis predicts that a superpredator may either simultaneously repress two mesopredators, restrain the dominant one and thereby release the subdominant mesopredator, or elicit different responses by both mesopredators. We show the outcome arising from such conditions in a three‐level predator assemblage (Eurasian eagle owl Bubo bubo L., northern goshawk Accipiter gentilis L. and common buzzard Buteo buteo L.) studied over 25 years. In the second half of the study period, the eagle owl re‐colonized the study area, thereby providing a natural experiment of superpredator introduction. We combined this set‐up with detailed GIS analysis of habitat use and a field experiment simulating intrusion by the superpredator into territories of the subdominant mesopredator, the buzzard. Although population trends were positive for all three species in the assemblage, the proportion of failed breeding attempts increased significantly in both mesopredators after the superpredator re‐colonized the area. We predicted that superpredator‐induced niche shifts in the dominant mesopredator may facilitate mesopredator coexistence in superpredator‐free refugia. We found significant changes in nesting habitat choice in goshawk, but not in buzzard. Since competition for enemy‐free refugia and the rapid increase in population density may have constrained niche shifts of the subdominant mesopredator, we further predicted behavioural changes in response to the superpredator. The field experiment indeed showed a significant increase in aggressive response of buzzards towards eagle owl territory intrusion over the course of 10 years, probably due to phenotypic plasticity in the response towards superpredation risk. Overall, our results show that intraguild predation can be a powerful force of behavioural change, simultaneously influencing habitat use and aggressiveness in predator communities. These changes might help to buffer mesopredator populations against the negative effects of intraguild predation.
Polymorphic genes involved in the conserved molecular signalling of circadian and circannual clocks may play important roles in governing the timing of breeding and dispersal and thereby affect ...fitness in vertebrates. However, relatively few studies have explored associations between phenological candidate genes and behaviour, and these are somewhat biased towards particular taxonomic groups such as passerine birds and salmonid fish. Consequently, we assayed microsatellite polymorphisms within the exonic and 3′ untranslated regions of the regulatory genes CLOCK, NPAS2, ADCYAP1 and CREB1 in the common buzzard (Buteo buteo), a polymorphic raptor species with three plumage morphs that differ in key life history traits including lifetime reproductive success. In contrast to studies of passerines, CLOCK poly‐glutamine (poly‐Q) was found to be monomorphic in 976 common buzzard nestlings as well as in three other Buteo species. Moreover, none of the candidate genes were significantly associated with fledging dates, although intermediately melanized females were found to lay earlier on average than light or dark morph individuals, and their offspring carried longer ADCYAP1 alleles. In contrast, all three candidate genes explained significant variation in one or more measures of juvenile buzzard dispersal (resighting probability, timing of dispersal and distance dispersed). Our findings contribute towards a broader body of work on the adaptive significance of CLOCK polymorphism, while also building upon previous studies that have documented links between ADCYAP1 variability and the timing of migration.
The effect of changing climatic conditions on wild populations has been the subject of much recent research. Most attention has been on the direct effects of climate changes on species of lower ...trophic levels and on the negative consequences of climate change. However, a deeper understanding of how climate change affects apex predators is vital, as they are keystone species that have a disproportionate effect on ecosystems. Studying survival in an apex predator requires individual‐based data from long‐term studies and is complicated by the integration of climatic effects on lower trophic levels. Here we assess how climate affects the survival of the Common Buzzard
B
uteo buteo
. We analysed the survival of 670 males and 669 females over the period 1989–2011, during which time our study population quadrupled. We used mark–recapture survival analysis of individual resightings of breeding adults to identify the environmental factors best explaining survival. A decrease in the North Atlantic Oscillation (
NAO
) index increased survival to an extent that largely explains the population increase. This might be caused by higher Common Vole
M
icrotus arvalis
survival in drier conditions and under snow cover. Buzzard survival appeared to increase more for males than for females, possibly due to the males' higher sensitivity to winter food availability resulting from their smaller body mass. However, we also found that the effect of
NAO
strongly depended on the area in which individuals lived, especially for females. This may have been caused by the recolonization of Eagle Owls
B
ubo bubo
in some parts of our study area. This study suggests that climatic changes can have complex effects on species of higher trophic levels via an interaction with their prey.
Blood parasite prevalence in two related warbler species (Acrocephalus arundinaceus and A. scirpaceus) was studied at three Bulgarian sites that differed mainly in altitude and weather. The ...prevalence of Haemoproteus, the most common parasite genus, was significantly lower at the highest altitude site (730 m above sea level, asl). Such a pattern was not found in ectoparasite-transmitted Hepatozoon. This can be explained with worsening conditions for the development of free-flying vectors with altitude and suggests loosening of the host-parasite conflict at higher breeding sites. The total heamatozoan prevalence was significantly higher in great reed warbler, compared with reed warbler especially as regards Haemoproteus parasites.
Abstract
Nuclear copies of mitochondrial genes (numts) are commonplace in vertebrate genomes and have been characterized in many species. However, relatively little attention has been paid to ...understanding their evolutionary origins and to disentangling alternative sources of insertions. Numts containing genes with intact mitochondrial reading frames represent good candidates for this purpose. The sequences of the genes they contain can be compared with their mitochondrial homologs to characterize synonymous to nonsynonymous substitution rates, which can shed light on the selection pressures these genes have been subjected to. Here, we characterize 25 numts in the Antarctic fur seal (Arctocephalus gazella) genome. Among those containing genes with intact mitochondrial reading frames, three carry multiple substitutions in comparison to their mitochondrial homologs. Our analyses reveal that one represents a historic insertion subjected to strong purifying selection since it colonized the Otarioidea in a genomic region enriched in retrotransposons. By contrast, the other two numts appear to be more recent and their large number of substitutions can be attributed to noncanonical insertions, either the integration of heteroplasmic mtDNA or hybridization. Our study sheds new light on the evolutionary history of pinniped numts and uncovers the presence of hidden sources of mitonuclear variation.
The effect of changing climatic conditions on wild populations has been the subject of much recent research. Most attention has been on the direct effects of climate changes on species of lower ...trophic levels and on the negative consequences of climate change. However, a deeper understanding of how climate change affects apex predators is vital, as they are keystone species that have a disproportionate effect on ecosystems. Studying survival in an apex predator requires individual‐based data from long‐term studies and is complicated by the integration of climatic effects on lower trophic levels. Here we assess how climate affects the survival of the Common Buzzard Buteo buteo. We analysed the survival of 670 males and 669 females over the period 1989–2011, during which time our study population quadrupled. We used mark–recapture survival analysis of individual resightings of breeding adults to identify the environmental factors best explaining survival. A decrease in the North Atlantic Oscillation (NAO) index increased survival to an extent that largely explains the population increase. This might be caused by higher Common Vole Microtus arvalis survival in drier conditions and under snow cover. Buzzard survival appeared to increase more for males than for females, possibly due to the males' higher sensitivity to winter food availability resulting from their smaller body mass. However, we also found that the effect of NAO strongly depended on the area in which individuals lived, especially for females. This may have been caused by the recolonization of Eagle Owls Bubo bubo in some parts of our study area. This study suggests that climatic changes can have complex effects on species of higher trophic levels via an interaction with their prey.
Studies of non-model species are important for understanding the molecular processes underpinning phenotypic variation under natural ecological conditions. The common buzzard (Buteo buteo; Aves: ...Accipitriformes) is a widespread and common Eurasian raptor with three distinct plumage morphs that differ in several fitness-related traits, including parasite infestation. To provide a genomic resource for plumage polymorphic birds in general and to search for candidate genes relating to fitness, we generated a transcriptome from a single dead buzzard specimen plus easily accessible, minimally invasive samples from live chicks.
We not only de novo assembled a near-complete buzzard transcriptome, but also obtained a significant fraction of the transcriptome of its malaria-like parasite, Leucocytozoon buteonis. By identifying melanogenesis-related transcripts that are differentially expressed in light ventral and dark dorsal feathers, but which are also expressed in other regions of the body, we also identified a suite of candidate genes that could be associated with fitness differences among the morphs. These include several immune-related genes, providing a plausible link between melanisation and parasite load. qPCR analysis of a subset of these genes revealed significant differences between ventral and dorsal feathers and an additional effect of morph.
This new resource provides preliminary insights into genes that could be involved in fitness differences between the buzzard colour morphs, and should facilitate future studies of raptors and their malaria-like parasites.
1. The habitat heterogeneity (HHH) and individual adjustment (IAH) hypotheses are commonly proposed to explain a decrease in reproduction rate with increasing population density. Higher numbers of ...low-quality territories with low reproductive success as density increases lead to a decrease in reproduction under the HHH, while more competition at high density decreases reproduction across all territories under the IAH. 2. We analyse the influence of density and habitat heterogeneity on reproductive success in eight populations of long-lived territorial birds of prey belonging to four species. Sufficient reliability in distinguishing between population-wide, site-specific and individual quality effects on reproduction was granted through the minimal duration of 20 years of all data sets and the ability to control for individual quality in five of them. 3. Density increased in five populations but reproduction did not decrease in these. Territory occupancy as a surrogate of territory quality correlated positively with reproductive success but only significantly so in large data sets with more than 100 territories. 4. Reproductive success was always best explained by measures of territory quality in multivariate models. Direct or delayed (t-1) population density entered very few of the best models. Mixed models controlling for individual quality showed an increasing reproductive performance in older individuals and in those laying earlier, but measures of territory quality were also always retained in the best models. 5. We find strong support for the habitat heterogeneity hypothesis but weak support for the individual adjustment hypothesis. Both individual and site characteristics are crucial for reproductive performance in long-lived birds. Proportional occupancy of territories enables recognition of highquality territories as preferential conservation targets.
Density‐dependent reproduction is commonly explained by either the habitat heterogeneity (HHH) or individual adjustment (IAH) hypothesis. Under the HHH, high quality territories are assumed to be ...occupied first. At higher density, occupation of low‐quality territories increases due to lower availability of high‐quality territories, which reduces mean reproductive success. Alternatively, the IAH assumes that increased competition at higher densities reduces reproductive success in all territories. For birds of prey, HHH plays an important role in territorial species, and IAH in socially breeding species. To test the generality of this hypothesis, we studied the mechanism behind density dependence in raven Corvus corax, a long‐lived passerine bird, using long‐term population data from a large number of territories. Population density decreased reproduction, which was explained by increased usage of low quality territories at higher density, supporting the HHH. Density reduced reproduction in low quality territories, but not in high and intermediate quality territories. We additionally compared the explanatory power of different models describing brood size, representing IAH, HHH, or a combination of both. The best model represented a combination of both hypotheses, in which the effect of density depended on territory quality. Our conclusion that both IAH and HHH are supported can be explained by the biology of ravens, where territorial adults not only experience interference competition with other territorial adults, but also with social groups of juveniles and floaters. We conclude that the relative importance of IAH and HHH may depend on variation in territory quality and social structure.
The group of haemosporidian parasites is of general interest to basic and applied science, since several species infect mammals, leading to malaria and associated disease symptoms. Although the great ...majority of haemosporidian parasites appear in bird hosts, as in the case of Leucocytozoon buteonis, there is little genomic information about genetic aspects of their co-evolution with hosts. Consequently, there is a high need for parasite-enrichment strategies enabling further analyses of the genomes, namely without exposure to DNA-intercalating dyes. Here, we used flow cytometry without an additional labelling step to enrich L. buteonis from infected buzzard blood. A specific, defined area of two-dimensional scattergramms was sorted and the fraction was further analysed. The successful enrichment of L. buteonis in the sorted fraction was demonstrated by Giemsa-staining and qPCR revealing a clear increase of parasite-specific genes, while host-specific genes were significantly decreased. This is the first report describing a labelling-free enrichment approach of L. buteonis from infected buzzard blood. The enrichment of parasites presented here is free of nucleic acid-intercalating dyes which may interfere with fluorescence-based methods or subsequent sequencing approaches.
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