Implications of isolation and low genetic diversity in peripheral populations of an amphi-Atlantic coral

Limited dispersal and connectivity in marine organisms can have negative fitness effects in populations that are small and isolated, but reduced genetic exchange may also promote the potential for local adaptation. Here, we compare the levels of genetic diversity and connectivity in the coral Montastraea cavernosa among both central and peripheral populations throughout its range in the Atlantic. Genetic data from one mitochondrial and two nuclear loci in 191 individuals show that M. cavernosa is subdivided into three genetically distinct regions in the Atlantic: Caribbean-North Atlantic, Western South Atlantic (Brazil) and Eastern Tropical Atlantic (West Africa). Within each region, populations have similar allele frequencies and levels of genetic diversity; indeed, no significant differentiation was found between populations separated by as much as 3000 km, suggesting that this coral species has the ability to disperse over large distances. Gene flow within regions does not, however, translate into connectivity across the entire Atlantic. Instead, substantial differences in allele frequencies across regions suggest that genetic exchange is infrequent between the Caribbean, Brazil and West Africa. Furthermore, markedly lower levels of genetic diversity are observed in the Brazilian and West African populations. Genetic diversity and connectivity may contribute to the resilience of a coral population to disturbance. Isolated peripheral populations may be more vulnerable to human impacts, disease or climate change relative to those in the genetically diverse Caribbean-North Atlantic region.     

Short‐ and long‐term costs of reproduction in a migratory songbird

Costs of reproduction represent a common life‐history trade‐off. Critical to understanding these costs in migratory species is the ability to track individuals across successive stages of the annual cycle. We assessed the effects of total number of offspring fledged and date of breeding completion on pre‐migratory body condition, the schedule of moult and annual survival in a migratory songbird, the Savannah Sparrow Passerculus sandwichensis. Between 2008 and 2010, moult was delayed for individuals that finished breeding later in the breeding period and resulted in reduced lean tissue mass during the pre‐migratory period, suggesting an indirect trade‐off between the timing of breeding completion and condition just prior to migration. Lean tissue mass decreased as the number of offspring fledged increased in 2009, a particularly cool and wet year, illustrating a direct trade‐off between reproductive effort and condition just prior to migration in years when weather is poor. However, using a 17‐year dataset from the same population, we found that parents that fledged young late in the breeding period had the highest survival and that number of offspring fledged did not affect survival, suggesting that individuals do not experience long‐term trade‐offs between reproduction and survival. Taken together, our results suggest that adult Savannah Sparrows pay short‐term costs of reproduction, but that longer‐term costs are mitigated by individual quality, perhaps through individual variation in resource acquisition.     

Breeding success of Spotted Flycatchers Muscicapa striata in southern England – is woodland a good habitat for this species?

The UK population of the Spotted Flycatcher Muscicapa striata has declined markedly in the last 30 years but there have been few recent studies of the species. This study examined the relationship between nest success and the predominant habitat type around Spotted Flycatcher nests in two contrasting areas of England. A breeding population in eastern England, a region where numbers of Spotted Flycatchers are known to have decreased dramatically in recent decades, was compared with another in southwest England, where numbers have remained stable or even increased. Whilst there was no difference in breeding success between the two study areas, there were significant differences between habitats, with garden nests more successful than those in farmland or woodland, at both egg and chick stages. Estimates of productivity per nesting attempt were also lower in farmland and woodland, with nests in gardens fledging twice as many chicks as those in either woodland or farmland. The proximate cause of lower success in farmland and woodland was higher nest predation rates during both egg and chick stages. In terms of nesting success, farmland and woodland appear to be similar in quality for this species, but both appear to be suboptimal habitats when compared with gardens, providing evidence of a problem on the breeding grounds for this species, in at least these two habitats.     

Design and implementation of rapid assessment approaches for water resource monitoring using benthic macroinvertebrates

Abstract Benthic macroinvertebrates are the group of organisms most widely used for assessment of water resources. Rapid assessment approaches are intended to be efficient and cost effective; savings are found in reduced sampling and more efficient data analysis. Rapid bioassessment programmes have been quickly accepted and now cover most of the United States (US) and equivalent programmes cover all of the United Kingdom (UK). Rapid bioassessment programmes are designed to screen large regions, pinpointing trouble spots worthy of more detailed attention. Fundamental to all rapid bioassessment methods is the classification of streams so that comparisons can be made between reference areas and areas of concern, or test sites with similar characteristics. Both the UK and US approaches assess habitat characteristics. These characteristics are used to predict the fauna expected at a test site in the UK approach; in the US they are used as an aid to classification and interpretation of aquatic faunal data. Habitat assessments in the US are also used to determine whether poor water quality or degraded habitat are stressing the invertebrate communities. This is a major development in approaches to water resource assessment. In the UK, a model developed using multivariate statistics uses a few environmental variables thought to be unaffected by human activities to predict the fauna expected at a test site. The US approaches analyse data using several indices (or metrics) presumed to represent ecological features of interest. These indices have a range of sensitivities to different kinds of stress and must be calibrated for the area of interest. The two approaches have been developed in isolation but may have much to offer each other. Developing programmes are advised to consider both. Future needs include: development of procedures that can be applied to large rivers and to lakes; further refinement of ecological principles underlying metric choice; the inclusion of chemical criteria and toxicity tests to establish thresholds that indicate impairment; and development of criteria indicating the necessity for implementation of quantitative assessment studies.     

Century‐scale records of coral growth rates indicate that local stressors reduce coral thermal tolerance threshold

Coral bleaching, during which corals lose their symbiotic dinoflagellates, appears to be increasing in frequency and geographic extent, and is typically associated with abnormally high water temperatures and solar irradiance. A key question in coral reef ecology is whether local stressors reduce the coral thermal tolerance threshold, leading to increased bleaching incidence. Using tree‐ring techniques, we produced master chronologies of growth rates in the dominant reef builder, massive Montastraea faveolata corals, over the past 75–150 years from the Mesoamerican Reef. Our records indicate that the 1998 mass bleaching event was unprecedented in the past century, despite evidence that water temperatures and solar irradiance in the region were as high or higher mid‐century than in more recent decades. We tested the influence on coral extension rate from the interactive effects of human populations and thermal stress, calculated here with degree‐heating‐months (DHM). We find that when the effects of chronic local stressors, represented by human population, are taken into account, recent reductions in extension rate are better explained than when DHM is used as the sole predictor. Therefore, the occurrence of mass bleaching on the Mesoamerican reef in 1998 appears to stem from reduced thermal tolerance due to the synergistic impacts of chronic local stressors.     

Changes in the composition of the auditory bulla in southern Solomon Islands populations of the grey cuscus, Phalanger orientalis breviceps (Marsupialia, Phalangeridae)

The auditory bulla is a much-scrutinized taxonomic character of mammals, which is generally regarded as showing a high degree of structural consistency within higher taxa. Observations of bulla variability in populations of the marsupial Phalanger orientalis from the Solomon Islands demonstrate considerable flexibility in bulla makeup, with variable incorporation of the squamosal into the tympanic floor. Studies of the ontogeny of the bulla in Phalanger show the presence of three ossification centres, including an entotympanic. Squamosal invasion of one of these ossificiation centres is seen as a possible result of inbreeding, arising from the mode of colonization of the Solomon Islands by this species. This suggests that, under certain conditions, considerable morphological plasticity may be induced within the selective constraints of bulla function.