Paternal effects in the initiation of migratory behaviour in birds

What determines why some birds migrate and others do not? This question is fundamental to understanding how migratory systems are responding to environmental changes, but the causes of individual migratory behaviours have proven difficult to isolate. We show that, in a partially migratory population of Eurasian oystercatchers (Haematopus ostralegus), the migratory behaviour of progeny follows paternal but not maternal behaviour, and is unrelated to timing of hatching or fledging. These findings highlight the key role of social interactions in shaping the migratory behaviour of new generations, and thus the spatio-temporal distribution of migratory populations.

Corresponding morphological and molecular indicators of crude oil toxicity to the developing hearts of mahi mahi

Crude oils from distinct geological sources worldwide are toxic to developing fish hearts. When oil spills occur in fish spawning habitats, natural resource injury assessments often rely on conventional morphometric analyses of heart form and function. The extent to which visible indicators correspond to molecular markers for cardiovascular stress is unknown for pelagic predators from the Gulf of Mexico. Here we exposed mahi (Coryphaena hippurus) embryos to field-collected crude oil samples from the 2010 Deepwater Horizon disaster. We compared visible heart defects (edema, abnormal looping, reduced contractility) to changes in expression of cardiac-specific genes that are diagnostic of heart failure in humans or associated with loss-of-function zebrafish cardiac mutants. Mahi exposed to crude oil during embryogenesis displayed typical symptoms of cardiogenic syndrome as larvae. Contractility, looping, and circulatory defects were evident, but larval mahi did not exhibit downstream craniofacial and body axis abnormalities. A gradation of oil exposures yielded concentration-responsive changes in morphometric and molecular responses, with relative sensitivity being influenced by age. Our findings suggest that 1) morphometric analyses of cardiac function are more sensitive to proximal effects of crude oil-derived chemicals on the developing heart, and 2) molecular indicators reveal a longer-term adverse shift in cardiogenesis trajectory.

Enforced expression of Simian virus 40 large T-antigen leads to testicular germ cell tumors in zebrafish

Testicular germ cell tumors (TGCTs) are the most common malignancy in young men. However, there are few in vivo animal models that have been developed to study this disease. We have used the pufferfish (fugu) lymphocyte-specific protein tyrosine kinase (flck) promoter, which has been shown to enforce high-level expression in the testes of transgenic mice, to express Simian virus 40 large T-antigen in zebrafish testes. Zebrafish that express T-antigen develop TGCTs after a long latency of >1 year. Although overt TGCTs are only evident in 20% of the fish, occult TGCTs can be detected in 90% of the transgenic fish by 36 month of age. The TGCTs resemble the human disease in terms of morphology and gene expression pattern, and can be transplanted to healthy wild-type recipient fish. In addition, enforced expression of the zebrafish stem cell leukemia (scl) gene in the zebrafish testes also generated TGCTs in transgenic fish. These results demonstrate the feasibility of studying TGCTs in a model organism.

Measuring coral reef decline through meta-analyses

Coral reef ecosystems are in decline worldwide, owing to a variety of anthropogenic and natural causes. One of the most obvious signals of reef degradation is a reduction in live coral cover. Past and current rates of loss of coral are known for many individual reefs; however, until recently, no large-scale estimate was available. In this paper, we show how meta-analysis can be used to integrate existing small-scale estimates of change in coral and macroalgal cover, derived from in situ surveys of reefs, to generate a robust assessment of long-term patterns of large-scale ecological change. Using a large dataset from Caribbean reefs, we examine the possible biases inherent in meta-analytical studies and the sensitivity of the method to patchiness in data availability. Despite the fact that our meta-analysis included studies that used a variety of sampling methods, the regional estimate of change in coral cover we obtained is similar to that generated by a standardized survey programme that was implemented in 1991 in the Caribbean. We argue that for habitat types that are regularly and reasonably well surveyed in the course of ecological or conservation research, meta-analysis offers a cost-effective and rapid method for generating robust estimates of past and current states.

Pair bonds: arrival synchrony in migratory birds

Synchronous arrival of pairs of migratory birds at their breeding grounds is important for maintaining pair bonds and is achieved by pairs that remain together all year round. Here we show that arrival is also synchronized in paired individuals of a migratory shorebird, the black-tailed godwit (Limosa limosa islandica), even though they winter hundreds of kilometres apart and do not migrate together. The mechanisms required to achieve this synchrony and prevent 'divorce' illustrate the complexity of migratory systems.

The buffer effect and large-scale population regulation in migratory birds

Buffer effects occur when sites vary in quality and fluctuations in population size are mirrored by large changes in animal numbers in poor-quality sites but only small changes in good-quality sites. Hence, the poor sites 'buffer' the good sites, a mechanism that can potentially drive population regulation if there are demographic costs of inhabiting poor sites. Here we show that for a migratory bird this process can apply on a country-wide scale with consequences for both survival and timing of arrival on the breeding grounds (an indicator of reproductive success). The Icelandic population of the black-tailed godwit, Limosa limosa islandica, wintering in Britain has increased fourfold since the 1970s (ref. 5) but rates of change within individual estuaries have varied from zero to sixfold increases. In accordance with the buffer effect, rates of increase are greater on estuaries with low initial numbers, and godwits on these sites have lower prey-intake rates, lower survival rates and arrive later in Iceland than godwits on sites with stable populations. The buffer effect can therefore be a major process influencing large-scale population regulation of migratory species.

Depletion models can predict shorebird distribution at different spatial scales

Predicting the impact of habitat change on populations requires an understanding of the number of animals that a given area can support. Depletion models enable predictions of the numbers of individuals an area can support from prey density and predator searching efficiency and handling time. Depletion models have been successfully employed to predict patterns of abundance over small spatial scales, but most environmental change occurs over large spatial scales. We test the ability of depletion models to predict abundance at a range of scales with black-tailed godwits, Limosa limosa islandica. From the type II functional response of godwits to their prey, we calculated the handling time and searching efficiency associated with these prey. These were incorporated in a depletion model, together with the density of available prey determined from surveys, in order to predict godwit abundance. Tests of these predictions with Wetland Bird Survey data from the British Trust for Ornithology showed significant correlations between predicted and observed densities at three scales: within mudflats, within estuaries and between estuaries. Depletion models can thus be powerful tools for predicting the population size that can be supported on sites at a range of scales. This greatly enhances our confidence in predictions of the consequences of environmental change.