Studies in Royal Society journals include stress in birds and depletion of medieval fish stocks

November 23, 2004

Biology Letters

Temperature-dependent sex ratio in a bird by Dr A Göth and Dr DT Booth

Incubation temperature is known to determine sex ratios in reptiles, but not in birds. We show that incubation temperature affects sex ratios in megapode birds, which are exceptional because they use environmental heat sources for incubation. In a megapode species, the Australian brush-turkey (Alectura lathami), more males hatch at low and more females hatch at high incubation temperatures, while the proportion is 1:1 at the average temperature found in natural incubation mounds. Chicks from lower temperatures weigh less, but are not smaller, which affects offspring survival. This is the first report for an incubation temperature dependent sex bias in birds.
Contact: Dr Ann Göth, Psychology, Macquarie University, North Ryde, SYDNEY, 2109, Australia

Community response to enrichment is highly sensitive to model structure by Dr GF Fussmann and Dr B Blasius
Biologists use mathematical expressions to model, understand, and predict nature. Often several mathematical expressions are available to describe biological processes. The uptake of food, for instance, can be described by at least three mathematical functions that are indistinguishable for all practical purposes. If, however, used in a standard predator-prey model these functions may lead to drastically different predictions of the population dynamics in this system. Predictive models should be analyzed and interpreted with great caution whenever the mathematical functions used in them are approximations of biological processes.
Contact: Dr Gregor Fussmann, McGill University, Department of Biology, 1205, ave. Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada

Resistance of flight feathers to mechanical fatigue covaries with moult strategy in two warbler species by Dr TP Weber, Dr J Borgudd, Dr A Hedenstrom, Dr K Persson and Dr G Sandberg
Most bird species replace their flight feathers once every year, but for so far unknown reasons some species moult these feathers twice. We investigated feathers of two closely related songbirds, the chiffchaff, which moults once, and the willow warbler, which moults twice. We found that the willow warblers' relatively thick feather shafts are damaged much faster than the thinner chiffchaff feather shafts when bent repeatedly. Willow warblers may have to built strong, thick shafts out of weak material. This may lead to more damage build-up in the outer layers of the shaft when feathers are bent during flight.
Contact: Dr Thomas Weber, Dep. of Animal Ecology, Lund University, Sölvegatan, LUND, S-22362, Sweden

Proceedings of The Royal Society B: Biological Sciences

Balancing food and predator pressure induces chronic stress in songbirds by Dr M Clinchy, Dr L Zanette, Professor R Boonstra, Professor JC Wingfield and Dr JNM Smith

'Kill or be killed' combat stress can have life-long consequences. Wild animals experience something similar in daily having to find food (ie kill or maim) while avoiding being killed by predators. We show that food and predators together affect measures of chronic stress in song sparrows. These inseparable effects on the individual's physiology provide a link between the well-known effects of food and predators on behaviour and inseparable food and predator effects on demography we previously demonstrated in song sparrows. We suggest inseparable food and predator effects on both physiology and demography may be the norm in birds and mammals.
Contact: Dr Michael Clinchy, Biology, University of Western Ontario, LONDON, ONTARIO, N6A 5B7, Canada

The origins of intensive marine fishing in medieval Europe: the English evidence by Dr JH Barrett, Dr AM Locker and Professor CM Roberts
The catastrophic impact of fishing pressure on commercial species is well documented, but the antiquity of their intensive exploitation has been poorly understood. Archaeology now shows that the clearest changes in marine fishing in England between AD 600 and 1600 occurred rapidly around AD 1000 and involved large increases in catches of herring and cod. Surprisingly, this revolution predated the documented post-medieval expansion of England's sea fisheries and coincided with a warm period when natural herring and cod stocks were probably low. This discovery shows that human impact on aquatic ecosystems could be far more ancient than is usually assumed.
Contact: Dr JH Barrett, Department of Archaelogy, University of York, York, YA1 7EP, UK

The fitness cost of extended lifespan in Caenorhabditis elegans by Dr GJ Lithgow, Dr NL Jenkins and Dr G McColl
Is it possible for lifespan to be extended without negative effects? Evolutionary theory predicts that extending lifespan will lead to reduced fitness. However, some mutants of the nematode Caenorhabditis elegans have a doubled lifespan without obvious side effects on development and fertility. We made such long-lived worms directly compete with normal worms over a number of generations. The apparently healthy long-lived worms, known as daf-2 mutants, actually became extinct after only four generations in the presence of normal worms. It seems longevity does come at a cost, just as predicted by evolutionary theories of aging. This finding may have implications for future interventions in human aging.
Contact: Dr NL Jenkins, Buck Insitute fo Age Research, 8001 Redwood Blvd, Novato, CA 94945, USA

Impulsiveness without discounting: the ecological rationality hypothesis by Dr DW Stephens, Dr B Kerr and Dr E Fernandez-Juricic
Animals make impulsive choices: preferring small but immediate food rewards even when waiting leads to more food over the same time interval. Why would evolution engineer animals to choose smaller benefits? The traditional answer is that delay reduces, or discounts, value in the same way that $10 today is worth more than $10 next month. We explain how impulsiveness can be beneficial without discounting. Many natural choice situations have a structure that can reduce or eliminate the long-term costs of impulsiveness. In addition, impulsive rules have a discrimination advantage over far-sighted rules. This may have practical implications because scientists believe that impulsiveness limits cooperation and may cause addiction.
Contact: Dr David Stephens, Ecology, Evolution & Behaviour, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108, USA

Tolerance of pollination networks to species extinctions by Dr J Memmott, Professor NM Waser and Dr MV Price
Humans rely on pollination of plants by insects, but human activities threaten pollinators and plants with extinction. This paper combines computer models with extensive records of pollination to explore vulnerability of plants to extinction of their pollinators. Many plants are pollinated by a diversity of insect species, and those that are specialised (use few pollinators) tend to use pollinators that themselves are generalists. These features confer relative tolerance to extinction for plant species. But tolerance is not immunity, and it is essential to conserve pollinators that are generalised, including bumblebees and some other types of bees.
Contact: Dr Jane Memmott, School of Biological Sciences, University of Bristol, Woodland Road, BRISTOL, BS8 1UG

Predicting shifts in dynamics of cannibalistic field populations using individual-based models by Dr L Persson, Dr AMD de Roos and Dr A Bertolo
Gape constraints determine the population dynamics of cannibalistic fish populations. Implementing individual life history characteristics of three cannibalistic fish species - the yellow perch, the Eurasian perch, and the northern pike - into an individual-based model shows that the population dynamics of these three species can be predicted based on the smallest and largest victim the cannibal can take. For the species studied, the predicted and observed dynamics shifted from cycles driven by competition among size cohorts to non cyclic dynamics regulated by cannibalism with increasing cannibal efficiency. Predicted and observed population dynamics for the three species were traced via growth curves of different age cohorts over time.
Contact: Dr Lennart Persson, Department of Ecology and Environmental Science, Umea University, SE-90187 UMEA, Sweden

The impact of cross-immunity and demographic stochasticity on pathogen diversity by Dr LJ Abu-Raddad and Professor NM Ferguson This work is the first to explore the nature of multiple-strain pathogen diseases such as influenza, malaria and HIV using a mathematical model at an arbitrarily large number of strains interacting via cross-immunity and in the presence of mutations and extinctions. Cross immunity is a phenomenon where infection by one strain induces partial immunity to future infections by other strains. Our analysis quantifies the role that world population size and cross immunity play in determining the level of strain diversity. Equilibrium dynamics fall into three classes: systems where global extinction is likely, stable single-strain persistence, and multiple strain persistence with stable diversity.
Contact: Dr LJ Abu-Raddad, Department of Infectious Deisease Epidemiology, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK

A selection mosaic in the facultative mutualism between ants and wild cotton by Dr JA Rudgers and Dr SY Strauss
Wild cotton plants bear extrafloral nectaries on their leaves that provide a nutritional resource for ants. In some populations of wild cotton, this army of ant visitors protects the plants against insect herbivores. In other populations, however, ants are less abundant and confer no benefits. Little is known about how variation in indirect interactions, such as those between ants and plants, affects the evolution of plant traits in different populations. Experimentally excluding ants from wild cotton revealed that variation among populations in protection by ants creates a mosaic of different patterns of selection on extrafloral nectary traits across the landscape.
Contact: Dr JA Rudgers, Department of Biology, Indiana University, Bloomington, IN 47405, USA

Do aposematism and Batesian mimicry require bright colours? A test, using European viper markings by Dr W Wuster, Dr CSE Allum, Dr IB Bjargardottir, Dr K Bailey, Dr KJ Dawson, Dr J Guenioui, Dr J lewis, Dr J McGurk, Dr AG Moore, Dr M Niskanen and Dr CP Pollard
Well-defended animals often advertise their dangerous nature through bright colours and patterns, which are recognised and avoided by predators. However, other well-defended animals have inconspicuous, but sometimes highly characteristic patterns. Can predators learn to avoid such well-defended but inconspicuous prey? Using plasticine snake models, Wüster and colleagues showed that wild birds avoid the characteristic but inconspicuous zigzag band of the venomous adder. This shows that bright colours are not necessary to generate predator avoidance of noxious prey. It also demonstrates that Batesian mimicry of inconspicuous but characteristic patterns is possible, and may have been important in the evolution of snakes.
Contact: Dr Wolfgang Wuster, School of Biological Sciences, University of Wales Bangor, BANGOR, LL57 2UW

Empirically inspired electromechanical model of the rat mystacial folliclesinus complex by Dr B Mitchinson, Dr T Prescott, Dr K Gurney, Dr P Redgrave, Dr C Melhuish, Dr T Pipe, Dr M Pearson and Dr I Gilhespy
Rat whiskers form a powerful sensory system that works where eyes do not, for instance in dark or smoky environments; the benefits to robotics of reproducing this system are clear. Previously, it has not been understood how the whisker and follicle transform stimuli into nerve impulses, so we have built a computer model of these parts, the first of its kind, and validated it against observations from biologists. This model is already helping us to better understand sensory systems, which is invaluable in our wider project, the construction of a whiskered robot that can navigate and explore like a real rat.
Contact: Dr Ben Mitchinson, Adaptive Behaviour Research Group, University of Sheffield, SHEFFIELD, S10 2TP

Female preference for multiple condition-dependent components of a sexually selected signal by Dr H Scheuber, Dr A Jacot and Dr MWG Brinkhof
Males of many animal species use multiple signals to secure their mating success, but it is far from clear how choosy females use distinct signals to evaluate males. We investigated the preference of female field crickets for carrier frequency and chirp rate, two components of the calling song that indicate male nutritional condition during juvenile development and at present, respectively. In a choice experiment, females preferred playbacks of lower carrier frequency and higher chirp rate, but prioritised the carrier frequency over the chirp rate. Thus, our results indicate that females integrate information from distinct cues when choosing a mate.
Contact: Dr MWG Brinkhof, Social and Preventive Medicine, Division of Epidemiology and Biostatistics, University of Bern, Finkenhubelweg 11, BERN, CH - 3012 Switzerland

Spatially explicit analyses unveil density dependence by Dr MA McGeoch and Dr R Veldtman
A question that has intrigued ecologists for decades is how the size of populations is regulated. Predators sometimes attack proportionally more prey individuals in high than in low prey density areas. This attack pattern is widely thought to be necessary for population regulation. However, until now it has been found comparatively rarely in nature. Using an African wild silk moth and its natural enemies as a case study, a new analytical technique was applied to the problem. The results show that this phenomenon (called 'spatial density dependence') is probably far more common than previously thought.
Contact: Dr Melodie McGeoch, Department of Conservation Ecology, University of Stellenbosch, PrivateX1, MATIELAND, 7602, South Africa

Intraspecific sexual selection on a speciation trait, male coloration, in the Lake Victoria cichlid Pundamilia nyererei by Dr ME Maan, Dr O Seehausen, Dr L Soderberg, Dr L Johnson, Dr EAP Ripmeester, Dr HDJ Mrosso, Dr TJM van Dooren, Dr JJM van Alphen and Dr MI Taylor
In Lake Victoria (East-Africa), hundreds of cichlid species have evolved rapidly. Mainly males are very colourful, and choosy females use these colours to choose conspecific males. Selective mate choice may have driven the diversification of these fish. A requirement for such a process to work is that females also select for extreme coloured males within their own species. We tested this in a species with red males of varying brightness, using mate-choice experiments in aquaria and ponds, and behavioural observations in the lake. We found that females indeed prefer the reddest males, supporting the hypothesis that female choice is important in cichlid diversification.
Contact: Dr ME Mann, Department of Animal Ecology, Institute of Biology, University of Leiden, PO Box 9516, Leiden, 2300 RA, The Nethlands

Seasonality and wildlife disease: how seasonal birth, aggregation and variation in immunity affect the dynamics of Mycoplasma gallisepticum in house finches by Dr PR Hosseini, Professor AA Dhondt and Professor AP Dobson
A key result from the Cornell Lab of Ornithology's House Finch Disease Survey is that the prevalence of disease varies seasonally. Diseased birds are rare during the summer breeding season, rises to a peak in the autumn, declines to a midwinter minimum, increases again to an early spring peak, then declines back to rare during the summer. To complicate the story even further, the seasonal pattern varies with latitude. In the South, the autumn peak occurs earlier, and a higher proportion of birds show disease symptoms, whereas farther north the peak occurs later, and fewer birds show symptoms. This paper identifies a number of potentially important conditions that could cause this behaviour. For the model to generate seasonal variation in disease prevalence that mimics the observed data, some birds must gain partial immunity, recover from the disease, breed seasonally, and aggregate more in the winter than during the summer. Longer breeding seasons generate patterns more like those in the South, whereas shorter ones generate the kind of patterns seen in the north. Seasonal aggregation along with a population of partially immune birds drives the early spring resurgence of the disease. Thus by looking at mathematical what-if scenarios, we have found some likely causes of these seasonal and latitudinal variations in disease dynamics.
Contact: Dr Parviez Hosseini, Lab of Ornithology, Cornell University, 159, Sapsuckerwoods Road, Ithaca, NY 14850,USA

Royal Society

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