Could a Factor That Does Not Affect Egg Recognition Influence the Decision of Rejection?

Rejection of the parasitic egg is the most important defence of hosts against brood parasites. However, this response is variable among and within species, and egg discrimination is not always followed by egg rejection. Low risk of parasitism and high risk of rejection costs may lead to the acceptance of the parasitic egg even if it has been previously recognized. The main aim of this paper is to answer a relevant question: can a single egg trait provoke the acceptance of an experimental egg previously recognized as foreign? Increased egg mass should hamper the ejection of an egg that has been discriminated because ejection of a heavy egg may imply higher rejection costs for hosts. We have tested this prediction by experimentally parasitizing natural nests of Common Blackbirds (Turdus merula) with non-mimetic model eggs of different mass (heavy, normal-weight, and light) while controlling for potential confounding factors such as egg size and colour. Our results showed that blackbirds more frequently accepted heavy eggs, even when previously recognized. This differential acceptance may be related to insufficient motivation to assume the higher costs that the ejection of a heavy egg could impose.Financial support has been provided by the Consejería Economía, Innovación, Ciencia y Empleo, Junta de Andalucia (research project CVI-6653)

Sadržaj

AG is supported by a NERC Independent Research Fellowship (NE/K009524/1).Insects are often chemically-defended against predators. There is considerable evidence for a group-beneficial element to their defences, and an associated potential for individuals to curtail their own investment in costly defence whilst benefitting from the investments of others, termed “automimicry”. Although females in chemically-defended taxa often lay their eggs in clusters, leading to siblings living in close proximity, current models of automimicry have neglected kin-selection effects, which may be expected to curb the evolution of such selfishness. Here we develop a general theory of automimicry that explicitly incorporates kin selection. We investigate how female promiscuity modulates intragroup and intragenomic conflicts over investment into chemical defence, finding that individuals are favoured to invest less than is optimal for their group, and that maternal-origin genes favour greater investment than do paternal-origin genes. We translate these conflicts into readily-testable predictions concerning gene-expression patterns and the phenotypic consequences of genomic perturbations, and discuss how our results may inform gene discovery in relation to economically-important agricultural products.Publisher PDFPeer reviewe

Egg rejection in blackbirds Turdus merula: a by-product of conspecific parasitism or successful resistance against interspecific brood parasites?

Traditional theory assumes that egg recognition and rejection abilities arise as a response against interspecific brood parasitism (IBP). However, rejection also appears in some species that are currently not exploited by interspecific parasites, such as Turdus thrushes. Recent evidences suggest that rejection abilities evolved in these species as a response to conspecific brood parasitism (CBP). To test these two alternative hypotheses, we performed an experimental study by parasitizing nests of the common blackbird (Turdus merula) with conspecifics or heterospecific eggs under different risk of parasitism (presence of interspecific or conspecific parasites near the nest). Common blackbird is a potential host of the common cuckoo (Cuculus canorus) but suffers low levels of CBP too. Results: We found that blackbirds were able to recognize and eject heterospecific eggs at high rates whereas most of conspecifics eggs were not recognized and, therefore, accepted. Ejection rates of conspecific eggs did not exceed 13 %, even in situations of high risk of CBP (blackbird female placed near the nest), which contradict the main prediction derived from the CBP hypothesis. Conversely, ejection rates of experimental eggs simulating IBP were much higher (80–100 %). Furthermore, female blackbirds were more aggressive towards cuckoos than towards blackbird dummies. Conclusions: Our results considered together support the IBP hypothesis, indicating that recognition and rejection of parasitic eggs in blackbirds have probably evolved due to previous cuckoo parasitism. The current absence of IBP in blackbirds may be due to the highly efficient rejection abilities in this species. Thus, these abilities have been retained in absence of brood parasitism as a consequence of the low costs involved for blackbirds, resulting in a successful resistance against interspecific brood parasitism.Financial support has been provided by the Consejería Economía, Innovación, Ciencia y Empleo. Junta de Andalucia (research project CVI-6653)

Diversity in warning coloration: selective paradox or the norm?

Aposematic theory has historically predicted that predators should select for warning signals to converge on a single form, as a result of frequency-dependent learning. However, widespread variation in warning signals is observed across closely related species, populations and, most problematically for evolutionary biologists, among individuals in the same population. Recent research has yielded an increased awareness of this diversity, challenging the paradigm of signal monomorphy in aposematic animals. Here we provide a comprehensive synthesis of these disparate lines of investigation, identifying within them three broad classes of explanation for variation in aposematic warning signals: genetic mechanisms, differences among predators and predator behaviour, and alternative selection pressures upon the signal. The mechanisms producing warning coloration are also important. Detailed studies of the genetic basis of warning signals in some species, most notably Heliconius butterflies, are beginning to shed light on the genetic architecture facilitating or limiting key processes such as the evolution and maintenance of polymorphisms, hybridisation, and speciation. Work on predator behaviour is changing our perception of the predator community as a single homogenous selective agent, emphasising the dynamic nature of predator-prey interactions. Predator variability in a range of factors (e.g. perceptual abilities, tolerance to chemical defences, and individual motivation), suggests that the role of predators is more complicated than previously appreciated. With complex selection regimes at work, polytypisms and polymorphisms may even occur in Mullerian mimicry systems. Meanwhile, phenotypes are often multifunctional, and thus subject to additional biotic and abiotic selection pressures. Some of these selective pressures, primarily sexual selection and thermoregulation, have received considerable attention, while others, such as disease risk and parental effects, offer promising avenues to explore. As well as reviewing the existing evidence from both empirical studies and theoretical modelling, we highlight hypotheses that could benefit from further investigation in aposematic species. Finally by collating known instances of variation in warning signals, we provide a valuable resource for understanding the taxonomic spread of diversity in aposematic signalling and with which to direct future research. A greater appreciation of the extent of variation in aposematic species, and of the selective pressures and constraints which contribute to this once-paradoxical phenomenon, yields a new perspective for the field of aposematic signalling.Peer reviewe

From pattern to process : extracting ecology from time series

Abstract Patterns in time series are observational records of past ecological processes, and identifying these processes remains a major challenge to population ecologists. Until recently, analysis of time series has concentrated on statistical description of density dependent structure of patterns, while the ecological factors that underlie the structure remain to a large part unknown. In this thesis, mechanistic properties of a model building on existing statistical framework are explored and discussed. By incorporating a two species trophic interaction and seasonality, the model may allow for direct ecological interpretation of density dependence. General model dynamics are explored and the biologically relevant parameter space identified. It is further shown that the relative length of summer/winter can have profound consequences for model dynamics, and very possibly force populations between regions of stable, cyclic and unstable dynamics. Supposing that the model can adequately describe the outcome of biological interactions, it is fitted to a large set of time series of voles from Hokkaido, Japan. From qualitative properties of six independent estimates of model coefficients, inferences are done about the parameter aggregates that constitute these coefficients. Inferences from two different ecological scenarios; predator-prey and grazer-vegetation, are then compared with the parameter space found appropriate from when studying the general model dynamics. Under specified assumptions, support is found for that signals in the time series are a result of an interaction between vole and its food resource

Structure, setting, and petrography of the Raudvatnet sulphide deposit, Hattfjelldal, Northern Norway

The Raudvatnet massive sulphide deposit is located in Hattfjelldal in Nordland, Northern Norway. Deposit investigations have been made by mining companies Boliden AB and Aspro AS in the 1960’s and 1980’s respectively. The Deposit lies in the Bjørkvatnet Nappe belonging to the Lower Køli Nappes of the Upper Allochthon in the North Central Caledonides. Brief structural investigations in the area along with petrographic, geochemical studies were conducted on a selection of samples collected in the field, both from mineralized ore horizons and adjacent lithologies. Geological mapping was conducted to produce an updated geological map of the area along with creation of 4 cross section profile sketches produced from the combined impressions of surface mapping and 4 of the logged drill cores. Geochemical analysis of the host rock of the mineralisation yields a sericite altered quartz keratophyre, which in turn is an altered felsic metavolcanite. The associated metabasites in which the felsic sequence is situated yields anN-MORB type geochemistry. The deposit contains abundant Zn andCu and is classified as a Zn-Cu compositional type. In addition, there are substantial amounts of Pb, Ag and Au as found in various phases associated with the massive mineralisations present. The deposit is characterized as a Kuroko type VMS deposit and is recognized as being a Bimodal mafic type in terms of lithostratigraphic classification