No evidence of assortative mating on the basis of putative ornamental traits in Long‐tailed Finches Poephila acuticauda

When multiple ornaments are expressed in both sexes, they are generally assumed to be maintained by mutual sexual selection and have a function in mate choice. In the Long‐tailed Finch Poephila acuticauda both sexes exhibit multiple ornaments that vary in their expression in either size (pintail and throat patch) or colour (bill) between individuals and sexes. We assessed whether these ornaments are maintained by mutual sexual selection by exploring whether individuals in a wild population paired assortatively with respect to these ornamental traits, and the degree to which the expression of these ornamental traits was indicative of reproductive success. We found no evidence of assortative pairing with respect to variation in homologous ornaments or body condition in the two sexes. In addition, we found no effect of ornament expression on the reproductive success of either males or females. Our findings suggest that the expression of these apparently ornamental traits in both sexes of this species may play no current role in mutual mate selection or as indicator traits of reproductive performance. We are currently unable to identify any function for these very elaborate ornaments in either sex of this species and suggest that the typical assumption that all such traits have an ornamental function may need further examination.     

Complex trait differentiation between host-populations of the pea aphid Acyrthosiphon pisum (Harris): implications for the evolution of ecological specialisation

Variation in traits affecting preference for, and performance on, new habitats is a key factor in the initiation of ecological specialisation and adaptive speciation. However, habitat and resource use also involves other traits whose influence on ecological and genetic divergence remains poorly understood. In the present study, we investigated the extent of variation of life-history traits among sympatric populations of the pea aphid Acyrthosiphon pisum , which shows several host races that are specialised on various plants of the family Fabaceae plants and is an established model for ecological speciation. First, we assessed the community structure of microbial partners within host populations of the pea aphid. The effect of these microbes on host fitness is uncertain, although there is growing evidence that they may modulate various important adaptive traits of their host such as plant utilisation and resistance against natural enemies. Second, we performed a multivariate analysis on several ecologically relevant features of host populations recorded in the present and previous studies (including microbial composition, colour morph, reproductive mode, and male dispersal phenotype), enabling the identification of correlations between phenotypic traits. We discuss the ecological significance of these associations of traits in relation to the habitat characteristics of pea aphid populations, and their consequences for the evolution of ecological specialisation and sympatric speciation.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 718–727.     

Sudden expansion of a single brown bear maternal lineage across northern continental Eurasia after the last ice age: a general demographic model for mammals?

The brown bear has proved a useful model for studying Late Quaternary mammalian phylogeography. However, information is lacking from northern continental Eurasia, which constitutes a large part of the species' current distribution. We analysed mitochondrial DNA sequences (totalling 1943 bp) from 205 bears from northeast Europe and Russia in order to characterize the maternal phylogeography of bears in this region. We also estimated the formation times of the sampled brown bear lineages and those of its extinct relative, the cave bear.
Four closely related haplogroups belonging to a single mitochondrial subclade were identified in northern continental Eurasia. Several haplotypes were found throughout the whole study area, while one haplogroup was restricted to Kamchatka. The haplotype network, estimated divergence times and various statistical tests indicated that bears in northern continental Eurasia recently underwent a sudden expansion, preceded by a severe bottleneck. This brown bear population was therefore most likely founded by a small number of bears that were restricted to a single refuge area during the last glacial maximum. This pattern has been described previously for other mammal species and as such may represent one general model for the phylogeography of Eurasian mammals. Bayesian divergence time estimates are presented for different brown and cave bear clades. Moreover, our results demonstrate the extent of substitution rate variation occurring throughout the phylogenetic tree, highlighting the need for appropriate calibration when estimating divergence times.     

Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity

Lions were the most widespread carnivores in the late Pleistocene, ranging from southern Africa to the southern USA, but little is known about the evolutionary relationships among these Pleistocene populations or the dynamics that led to their extinction. Using ancient DNA techniques, we obtained mitochondrial sequences from 52 individuals sampled across the present and former range of lions. Phylogenetic analysis revealed three distinct clusters: (i) modern lions, Panthera leo ; (ii) extinct Pleistocene cave lions, which formed a homogeneous population extending from Europe across Beringia (Siberia, Alaska and western Canada); and (iii) extinct American lions, which formed a separate population south of the Pleistocene ice sheets. The American lion appears to have become genetically isolated around 340 000 years ago, despite the apparent lack of significant barriers to gene flow with Beringian populations through much of the late Pleistocene. We found potential evidence of a severe population bottleneck in the cave lion during the previous interstadial, sometime after 48 000 years, adding to evidence from bison, mammoths, horses and brown bears that megafaunal populations underwent major genetic alterations throughout the last interstadial, potentially presaging the processes involved in the subsequent end-Pleistocene mass extinctions.     

The challenges of conservation for declining migrants: are reserve‐based initiatives during the breeding season appropriate for the Pied Flycatcher Ficedula hypoleuca?

Creating conservation policies for declining migrant species in response to global change presents a considerable challenge. Migrant species are affected by factors at breeding grounds, overwintering areas and during migration. Accordingly, reserve-based management during the breeding season is not always a suitable conservation strategy. Recent Pied Flycatcher population decline typifies the pattern for many migrants. The UK population has declined by 43% in the past decade, but explanations, and possible solutions, remain elusive. We use 15 years of data (1990–2004) from a declining British population to establish possible reasons for decline, considering: (1) breeding performance (including the influences of competition and predation); (2) weather patterns caused by the winter phase (December–March) of the North Atlantic Oscillation (NAO), which modify conditions experienced at wintering grounds and on migration; and (3) possible impacts of climate change on spring temperatures. We conclude that decreasing breeding performance is contributing to decline, but that non-breeding factors are more important. Winter NAO index is a strong predictor of breeding population, probably because it influences food abundance in Africa and at migratory stopover points. Importantly, however, year itself enhances the predictive model, indicating that influences on population remain unaccounted for by current research. Management strategies based on increasing breeding productivity cannot fully address population decline because non-breeding factors appear important. However, as breeding performance is declining, breeding-based strategies remain useful conservation tools. To this end, our research indicates that optimal placement of nestboxes as regards orientation and habitat management to increase larval food supplies could increase productivity significantly.     

Hatching asynchrony and growth trade‐offs within domesticated and wild zebra finch,Taeniopygia guttata,broods

The Australian zebra finch, Taeniopygia guttata, is a widely used model organism, yet few studies have compared domesticated and wild birds with the aim of examining its relevance as an evolutionary model species. Domestic and wild broods hatch over approximately 4 and 2 days, respectively, which is important given that nestlings can fledge after as little as 12 days, although 16–18 days is common. We aimed to evaluate the extent to which the greater hatching asynchrony in domestic stock may effect reproductive success through greater variance in size hierarchies, variance in within‐brood growth rates, and partial brood mortality. Therefore, by simultaneously controlling brood sizes and experimentally manipulating hatching intervals in both domesticated and wild birds, we investigated the consequences of hatching intervals for fledging success and nestling growth patterns, as well as trade‐offs. Fledging success was similarly high in domestic and wild broods of either hatching pattern. Nonetheless, between‐brood analyses revealed that domestic nestlings had significantly higher masses, larger skeletal characters, and longer wings than their wild counterparts, although wild nestlings had comparable wing lengths at the pre‐fledging stage. Moreover, within‐brood analyses revealed only negligible differences between domestic and wild nestlings, and larger effects of hatching order and hatching pattern. Therefore, despite significant differences in the hatching intervals, and the ultimate size achieved by nestlings, the domestication process does not appear to have significantly altered nestling growth trade‐offs. The present study provides reassuring evidence that studies involving domesticated zebra finches, or other domesticated model organisms, may provide reasonable adaptive explanations in behavioural and evolutionary ecology. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 763–773.     

Palaeoenvironmental implications of the ichnology and geochemistry of the Westbury Formation (Rhaetian), Westbury‐on‐Severn,south‐west England

Abstract: The Westbury Formation (Rhaetian) beds of Westbury Garden Cliff, Westbury‐on‐Severn, west of Gloucester, Britain, show an unusual combination of features. Both deep water and emergent characteristics are present within the sediments and the trace fossils. The ichnoassemblage consists of abundant Selenichnites, Planolites beverlyensis and Lockeia with rarer Oniscoidichnus, Chondrites, Rhizocorallium irregulare, Taenidium serpentium, an unusual form of Walcottia and Merostomichnites‐like traces. These trace fossils display an interesting relationship with the sediments: low‐energy Cruziana ichnofacies is found within high‐energy sandstones. The sandstones are interbedded with laminated mudstones, apparently deposited in deep water, but some aspects of the ichnoassemblage, preservation and sedimentation indicate shallower water. One new trace fossil, Radichnus allingtona igen. et isp. nov., closely resembles the traces of modern fiddler crabs and imply emergence, by analogy. This ichnofauna is similar to early stage disaster colonisation in recent experiments in Long Island Sound (south of Connecticut, USA) and with storm‐influenced deposits within the Cardium Formation (Seebe, Alberta, Canada). This indicates a lagoonal environment with influxes of sand and oxygen. Total organic carbon levels were found to fluctuate greatly between stratigraphic layers but remained relatively high. This implies low oxygen conditions. The abundance of sulphur (in pyrite) also supports an interpretation of anoxic conditions, and low sedimentation rates within the shale layers. A restricted shallow basin or lagoonal environment is proposed for the palaeoenvironment, with fluctuating oxygen influencing diversity.     

Hydraulic acclimation to shading in boreal conifers of varying shade tolerance

The purpose of this study was to determine how shading affects the hydraulic and wood‐anatomical characteristics of four boreal conifers (Pinus banksiana, Pinus contorta, Picea glauca and Picea mariana) that differ in shade tolerance. Plants were grown in an open field and under a deciduous‐dominated overstory for 6 years. Sapwood‐ and leaf‐area specific conductivity, vulnerability curves, and anatomical measurements (light and scanning electron microscopy) were made on leading shoots from six to nine trees of each treatment combination. There was no difference in sapwood‐area specific conductivity between open‐grown and understory conifers, although two of four species had larger tracheid diameters in the open. Shaded conifers appeared to compensate for small diameter tracheids by changes in pit membrane structure. Scanning electron microscopy revealed that understory conifers had thinner margo strands, greater maximum pore size in the margo, and more torus extensions. All of these trends may contribute to inadequate sealing of the torus. This is supported by the fact that all species showed increased vulnerability to cavitation when grown in the understory. Although evaporative demand in an understory environment is low, a rapid change into fully exposed conditions could be detrimental for shaded conifers.     

Use and misuse of the IUCN Red List Criteria in projecting climate change impacts on biodiversity

Recent attempts at projecting climate change impacts on biodiversity have used the IUCN Red List Criteria to obtain estimates of extinction rates based on projected range shifts. In these studies, the Criteria are often misapplied, potentially introducing substantial bias and uncertainty. These misapplications include arbitrary changes to temporal and spatial scales; confusion of the spatial variables; and assume a linear relationship between abundance and range area. Using the IUCN Red List Criteria to identify which species are threatened by climate change presents special problems and uncertainties, especially for shorter‐lived species. Responses of most species to future climate change are not understood well enough to estimate extinction risks based solely on climate change scenarios and projections of shifts and/or reductions in range areas. One way to further such understanding would be to analyze the interactions among habitat shifts, landscape structure and demography for a number of species, using a combination of models. Evaluating the patterns in the results might allow the development of guidelines for assigning species to threat categories, based on a combination of life history parameters, characteristics of the landscapes in which they live, and projected range changes.     

Elimination of a specialised facultative symbiont does not affect the reproductive mode of its aphid host

Abstract.  1. Microorganisms that manipulate the reproduction of their hosts through diverse mechanisms including the induction of parthenogenesis are widespread among arthropods.
2. The pea aphid, Acyrthosiphon pisum , shows a variation in its reproductive mode, with lineages reproducing by cyclical parthenogenesis (obligate alternation of parthenogenetic and sexual generations each year) and others by obligate parthenogenesis (continuous asexual reproduction all year round). In addition, the pea aphid harbours, along with Buchnera the primary aphid endosymbiont, several facultative symbionts whose prevalence differs among host populations.
3. The possible influence of a Rickettsia facultative symbiont on the reproductive mode of its host was tested on two pea aphid clones by comparing the response of infected and uninfected individuals with the same genetic background to conditions that typically induce the production of sexual morphs.
4. No significant effect of the Rickettsia infection was found on the type of reproductive morphs produced (sexual vs. asexual) or on their quantities for the two clones.
5. However, the Rickettsia had a detrimental effect on the fitness of its aphid host, in apparent contradiction to the high prevalence of this symbiont in some host populations. It is suggested that this negative impact may disappear under specific environmental conditions, transforming a parasitic association into a mutualistic one.