Egg Speckling Patterns Do Not Advertise Offspring Quality or Influence Male Provisioning in Great Tits

Many passerine birds lay white eggs with reddish brown speckles produced by protoporphyrin pigment. However, the function of these spots is contested. Recently, the sexually selected eggshell coloration (SSEC) hypothesis proposed that eggshell color is a sexually selected signal through which a female advertises her quality (and hence the potential quality of her future young) to her male partner, thereby encouraging him to contribute more to breeding attempts. We performed a test of the SSEC hypothesis in a common passerine, the great tit Parus major. We used a double cross-fostering design to determine whether males change their provisioning behavior based on eggshell patterns they observe at the nest. We also tested the assumption that egg patterning reflects female and/or offspring quality. Because birds differ from humans in their color and pattern perception, we used digital photography and models of bird vision to quantify egg patterns objectively. Neither male provisioning nor chick growth was related to the pattern of eggs males observed during incubation. Although heavy females laid paler, less speckled eggs, these eggs did not produce chicks that grew faster. Therefore, we conclude that the SSEC hypothesis is an unlikely explanation for the evolution of egg speckling in great tits

Parental-Offspring Conflict

Disputes between parents and their young might seem easy enough to spot in everyday human life, but the notion of a general, evolutionary conflict between offspring and their parents has proved surprisingly slippery (reviewed by Godfray 1995). Nevertheless, today, almost four decades since the concept was first proposed by Trivers (1974), parent-offspring conflict has theoretically robust foundations (reviewed by Godfray 1995; Godfray and Johnstone 2000) and there is diverse evidence that it is a significant selective force in nature (although perhaps not always in the ways initially assumed, reviewed by Kilner and Hinde 2008). In a recent review, we showed how information warfare lies at the heart of parent-offspring conflict in many instances. Readers specifically interested in signalling by young animals and their parents, as well as other uses of personal information, may wish to consult Kilner and Hinde 2008 before ploughing ahead here. Our aim in this chapter is to attempt to reconstruct the evolutionary consequences of this conflict for traits in offspring and their parents, focusing relatively little on signalling this time. We start with a quick recap of basic conflict theory before outlining diverse empirical evidence for an evolutionary conflict between parents and their young. Next we consider how conflict might link pairs of traits in parents and their offspring, showing how co-evolution between the two parties becomes focused on these particular characters. We conclude with a discussion about the outcomes of parent-offspring conflict: does it always end in a stable equilibrium between parents and their young, as predicted by the many ‘resolution’ models of conflict? Or is instability widespread, with parents and offspring frequently alternating in who gains the upperhand

Maternal investment tactics in superb fairy-wrens

In cooperatively breeding species, parents often use helper contributions to offspring care to cut their own costs of investment (i.e. load-lightening). Understanding the process of load-lightening is essential to understanding both the rules governing parental investment and the adaptive value of helping behaviour, but little experimental work has been conducted. Here we report the results of field experiments to determine maternal provisioning rules in cooperatively breeding superb fairy-wrens (Malurus cyaneus). By manipulating carer : offspring ratios, we demonstrate that helpers allow females to reduce the rate at which they provision their brood. Female reductions, however, were less than that provided by helpers, so that chicks still received food at a faster rate in the presence of helpers. Despite this, chicks fed by parents and helpers were not heavier than those provisioned by parents alone. This is because maternal load-lightening not only occurs during the chick provisioning stage, but also at the egg investment stage. Theoretically, complete load-lightening is predicted when parents value themselves more highly than their offspring. We tested this idea by ‘presenting’ mothers with a ‘choice’ between reducing their own levels of care and increasing investment in their offspring. We found that mothers preferred to cut their contributions to brood care, just as predicted. Our experiments help to explain why helper effects on offspring success have been difficult to detect in superb fairy-wrens, and suggest that the accuracy with which theoretical predictions of parental provisioning rules are matched in cooperative birds depends on measuring maternal responses to helper presence at both the egg and chick stages

Nestling cuckoos, Cuculus canorus, exploit hosts with begging calls that mimic a brood

Nestling cuckoos, Cuculus canorus, eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus, as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula, or song thrush, T. philomelos, chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick's rapid begging call ('si, si, si, si ...'), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape

The evolution of egg rejection by cuckoo hosts in Australia and Europe

Exploitation of hosts by brood parasitic cuckoos is expected to stimulate a coevolutionary arms race of adaptations and counteradaptations. However, some hosts have not evolved defenses against parasitism. One hypothesis to explain a lack of host defenses is that the life-history strategies of some hosts reduce the cost of parasitism to the extent that accepting parasitic eggs in the nest is evolutionarily stable. Under this hypothesis, it pays hosts to accept cuckoo eggs if (1) the energetic cost of raising the cuckoo is low, (2) there is time to renest, and (3) clutch size is small. We parasitized the nests of host and nonhost species with nonmimetic model eggs to test whether the evolution of egg recognition by cuckoo hosts could be explained by life-history variables of the host. The most significant factor explaining rates of rejection of model eggs was whether or not a species was a cuckoo host, with hosts rejecting model eggs at a higher rate than nonhosts. Egg-rejection rates were also explained by visibility within the nest and by cuckoo mass. We found little support for the life-history model of egg rejection. Our results suggest that parasitism is always sufficiently costly to select for host defenses and that the evolution of defenses may be limited by proximate constraints such as visibility within the nest. Copyright 2005.brood parasitism; coevolution; cowbirds; cuckoos; life-history strategies

Flow and myocardial interaction: an imaging perspective

Heart failure due to coronary artery disease has considerable morbidity and poor prognosis. An understanding of the underlying mechanics governing myocardial contraction is a prerequisite for interpreting and predicting changes induced by heart disease. Gross changes in contractile behaviour of the myocardium are readily detected with existing techniques. For more subtle changes during early stages of cardiac dysfunction, however, a sensitive method for measuring, as well as a precise criterion for quantifying, normal and impaired myocardial function is required. The purpose of this paper is to outline the role of imaging, particularly cardiovascular magnetic resonance (CMR), for investigating the fundamental relationships between cardiac morphology, function and flow. CMR is emerging as an important clinical tool owing to its safety, versatility and the high-quality images it produces that allow accurate and reproducible quantification of cardiac structure and function. We demonstrate how morphological and functional assessment of the heart can be achieved by CMR and illustrate how blood flow imaging can be used to study flow and structure interaction, particularly for elucidating the underlying haemodynamic significance of directional changes and asymmetries of the cardiac looping. Future outlook on combining imaging with engineering approaches in subject-specific biomechanical simulation is also provided

Juvenile pheomelanin-based plumage coloration has evolved more frequently in carnivorous species

Distinctive pheomelanin-based plumage coloration in juvenile birds has been proposed as a signal of immaturity to avoid aggression by older conspecifics, but recent findings suggest a detoxifying strategy. Pheomelanin synthesis implies the consumption of cysteine, a semi-essential amino acid that is necessary for the synthesis of the antioxidant glutathione (GSH) but that may be toxic if in excess in the diet. As the nestling stage probably represents a low-stress period with limited requirement for GSH protection, the synthesis of pheomelanin in developing birds may help to maintain cysteine homeostasis, particularly in species with a high content of protein in the diet (i.e. carnivores). Here we confirm this hypothesis showing that, among 53 species of Western Palaearctic birds, juvenile pheomelanin-based coloration has evolved more frequently in strictly carnivorous species than in species with other diets