What determines the impact of alien birds and mammals in Europe?

An often-cited reason for studying the process of invasion by alien species is that the understanding sought can be used to mitigate the impacts of the invaders. Here, we present an analysis of the correlates of local impacts of established alien bird and mammal species in Europe, using a recently described metric to quantify impact. Large-bodied, habitat generalist bird and mammal species that are widespread in their native range, have the greatest impacts in their alien European ranges, supporting our hypothesis that surrogates for the breadth and the amount of resources a species uses are good indicators of its impact. However, not all surrogates are equally suitable. Impacts are generally greater for mammal species giving birth to larger litters, but in contrast are greater for bird species laying smaller clutches. There is no effect of diet breadth on impacts in birds or mammals. On average, mammals have higher impacts than birds. However, the relationships between impact and several traits show common slopes for birds and mammals, and relationships between impact and body mass and latitude do not differ between birds and mammals. These results may help to anticipate which species would have large impacts if introduced, and so direct efforts to prevent such introductions.     

What is comparable in comparative cognition?

To understand how complex, or 'advanced' various forms of cognition are, and to compare them between species for evolutionary studies, we need to understand the diversity of neural-computational mechanisms that may be involved, and to identify the genetic changes that are necessary to mediate changes in cognitive functions. The same overt cognitive capacity might be mediated by entirely different neural circuitries in different species, with a many-to-one mapping between behavioural routines, computations and their neural implementations. Comparative behavioural research needs to be complemented with a bottom-up approach in which neurobiological and molecular-genetic analyses allow pinpointing of underlying neural and genetic bases that constrain cognitive variation. Often, only very minor differences in circuitry might be needed to generate major shifts in cognitive functions and the possibility that cognitive traits arise by convergence or parallel evolution needs to be taken seriously. Hereditary variation in cognitive traits between individuals of a species might be extensive, and selection experiments on cognitive traits might be a useful avenue to explore how rapidly changes in cognitive abilities occur in the face of pertinent selection pressures.     

Re‐evaluating the distribution of cooperative breeding in birds: is it tightly linked with altriciality?

The evolution of cooperative breeding (CB) in birds has aroused intensive interest for decades, largely due to the paradox that some adults forgo independent breeding to help others. While much effort has been directed at understanding the adaptive significance of CB behavior, much less effort has been spent on understanding its origin. Ligon and Burt argued that the evolution of altriciality played a key role in the origin of CB since CB occurs more frequently in altricial lineages than expected if developmental mode and CB evolved independently and that both traits arose early in the avian tree of life. We mapped presence or absence of CB, and precocial or altricial development on a recent phylogeny of all birds to re‐evaluate their conclusions. Our results suggest altriciality may be more recently derived than previously thought, and that CB species clustered in a derived land bird clade (especially within Passeriformes) where we reconstructed many gains and losses. We did find a link between cooperative breeding and altriciality. However, since CB also occurs in precocial species, has not evolved in many altricial clades, and may have evolved prior to altriciality (based on some classifications of which species have CB), it is not clear whether altriciality is linked to other factors, such as benefits to group living, that are necessary for the acquisition of CB behavior, or whether altriciality may have been a driving force in the evolution of CB itself. The relative importance of these other factors versus altriciality for the origin of CB needs to be considered.     

Why is limb regeneration possible in amphibians but not in reptiles,birds, and mammals?

The capacity to regenerate limbs is very high in amphibians and practically absent in other tetrapods despite the similarities in developmental pathways and ultimate morphology of tetrapod limbs. We propose that limb regeneration is only possible when the limb develops as a semiautonomous module and is not involved in interactions with transient structures. This hypothesis is based on the following two assumptions: To an important extent, limb development uses the same developmental mechanisms as normal limb development and developmental mechanisms that require interactions with transient structures cannot be recapitulated later. In amniotes limb development is early, shortly after neurulation, and requires inductive interactions with transient structures such as somites. In amphibians limb development is delayed relative to amniotes and has become decoupled from interactions with somites and other transient structures that are no longer present at this stage. The limb develops as a semi-independent module. A comparison of the autonomy and timing of limb development in different vertebrate taxa supports our hypothesis and its assumptions. The data suggest a good correlation between self-organizing and regenerative capacity. Furthermore, they suggest that whatever barriers amphibians overcame in the evolution of metamorphosis, they are the same barriers that need to be overcome to make limb regeneration possible in other taxa.     

What is menstruation for? On the projectibility of functional predicates in menstruation research

In 1993, biologist Margie Profet captured the attention of the popular press with the publication of her radical thesis: menstruation has a function. Traditional theories, she claims, typically view menstruation as a functionless by-product of cyclic flux. The details of Profet’s functional account are similarly radical: she argues that menstruation has been naturally selected to defend the female reproductive tract from sperm-borne pathogens. There are a number of weaknesses in Profet’s evolutionary analysis. However, I focus on a set of pragmatic problems that arise prior to any details of her evolutionary account. In arguing for the importance of pragmatic considerations, I draw from the linguistic analyses of Nelson Goodman. I conclude that critical investigation of the evolutionary details of Profet’s pathogen defense account will be more feasible if and when biologists more frequently feature the female system of pathogen defense in their inductive generalisations. The system needs to be better entrenched before its functional components, such as menstruation, can be thoroughly investigated.     

The rise of birds and mammals: are microevolutionary processes sufficient for macroevolution?

It is a basis of darwinian evolution that the microevolutionary mechanisms that can be studied in the present are sufficient to account for macroevolution. However, this idea needs to be tested explicitly, as highlighted here by the example of the superceding of dinosaurs and pterosaurs by birds and placental mammals that occurred near the Cretaceous/Tertiary boundary approximately 65 million years ago. A major problem for testing the sufficiency of microevolutionary processes is that independent ideas (such as the existence of an extraterrestrial impact, and the extinction of dinosaurs) were linked without the evidence for each idea being evaluated separately. Here, we suggest and discuss five testable models for the times and divergences of modern mammals and birds. Determination of the model that best represents these events will enable the role of microevolutionary mechanisms to be evaluated. The question of the sufficiency of microevolutionary processes for macroevolution is solvable, and available evidence supports an important role for biological processes in the initial decline of dinosaurs and pterosaurs.     

What is Causal Specificity About,and What is it Good for in Philosophy of Biology?

Acta Biotheoretica - The concept of causal specificity is drawing considerable attention from philosophers of biology. It became the rationale for rejecting (and occasionally, accepting) a thesis...     

What is clinical malaria? Finding case definitions for field research in highly endemic areas

In non-endemic areas, the diagnosis of clinical malaria may be made on the basis of fever and a positive blood film. However, in areas of high endemicity, asymptomatic parasitaemia is very common: to assume that a child who presents with fever and parasitaemia is ill from malaria will result in overdiagnosis. In this article, Jo Schellenberg, Tom Smith, Pedro Alonso and Richard Hayes discuss the relationship between fever and parasite density in such areas, and show how the proportion of fevers due to malaria (the attributable fraction) can be estimated and used to evaluate case definitions for use in field trials.     

Are changes in breeding habitat responsible for recent population changes of long-distance migrant birds?

Capsule: The direction and magnitude of changes in structure of UK woodlands since the 1980s, are inconsistent with them playing a causative role in the declines of four migrant bird species in upland oak woods.

Aims: To investigate whether changes in woodland structure were a possible cause of population changes of four Afro-Palearctic migrants (Wood Warbler Phylloscopus sibilatrix, Tree Pipit Anthus trivialis, Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus) in the upland oakwoods of western and northern Britain.

Methods: Bird population estimates and measures of woodland structure were recorded in two time periods 1982–85 and 2003–04 across six regions of the UK. We modelled the effect of habitat change and initial habitat state on population changes between the two time periods. The predicted effects of habitat change on populations were then compared with observed population changes across the different regions.

Results: All four species underwent population declines; there were also significant increases in ground cover and understorey cover. The number of birds in 2003–04 was influenced by habitat structure at this time in addition to showing regional differences. Change in bird numbers varied between regions and was affected by both the initial habitat state and change in habitat structure, with regional variation in the effect of habitat change. There was however no relationship between the predicted effect of change in habitat structure on population size and observed regional population changes.

Conclusions: Changes in woodland structure are unlikely to be the main driver of population change in these four migrant bird species, and large-scale factors affecting demographics in other parts of their breeding range or in their wintering areas are likely reasons for local population declines.     

CMA restricted to mammals and birds: myth or reality?

Chaperone-mediated autophagy (CMA) is a major pathway of lysosomal proteolysis essential for the control of intermediary metabolism. So far, the absence of any identifiable LAMP2A – a necessary and limiting protein for CMA – outside of the tetrapod clade, led to the paradigm that this cellular function was (presumably) restricted to mammals and birds. However, after we identified expressed sequences displaying high sequence homology with the mammalian LAMP2A in several fish species, our findings challenge that view and suggest that CMA likely appeared much earlier during evolution than initially thought. Hence, our results do not only shed an entirely new light on the evolution of CMA, but also bring new perspectives on the possible use of complementary genetic models, such as zebrafish or medaka for studying CMA function from a comparative angle/view.     

Are European starlings breeding in the Azores archipelago genetically distinct from birds breeding in mainland Europe?

The European starling (Sturnus vulgaris) has recently been found to eat eggs of the endangered roseate tern (Sterna dougallii) in the Azores. Azorean starlings are considered an endemic subspecies (S. vulgaris granti), so we investigated how much genetic divergence has accumulated between the Azores and other European populations in order to assess whether lethal control measures might be possible, as previous experiments have found that taste aversion is not likely to be successful. For this purpose, we sequenced a region of the protein-coding mitochondrial gene ND2 for samples from six different populations. Of the 1,026 base pairs sequenced, 19 (1.7%) were variable and formed 15 different haplotypes. The Azores had high and significant genetic differentiation from all the other populations studied. Haplotype diversity was high in the mainland populations studied, ranging from 0.767 to 0.900, but there was no variation among the Azores samples, which were collected from a geographically broad region. Given the lack of genetic variability in the Azores birds and their abundance throughout the archipelago, lethal control on a local basis and as part of an integrated control plan can be seen as a reasonable measure to protect tern colonies.     

How widespread is adult neurogenesis in mammals?

It is now widely accepted that neurogenesis occurs in two regions of the adult mammalian brain--the hippocampus and the olfactory bulb. There is evidence for adult neurogenesis in several additional areas, including the neocortex, striatum, amygdala and substantia nigra, but this has been difficult to replicate consistently other than in the damaged brain. The discrepancies may be due to variations in the sensitivity of the methods used to detect new neurons.     

Local sleep homeostasis in the avian brain: convergence of sleep function in mammals and birds?

The function of the brain activity that defines slow wave sleep (SWS) and rapid eye movement (REM) sleep in mammals is unknown. During SWS, the level of electroencephalogram slow wave activity (SWA or 0.5-4.5 Hz power density) increases and decreases as a function of prior time spent awake and asleep, respectively. Such dynamics occur in response to waking brain use, as SWA increases locally in brain regions used more extensively during prior wakefulness. Thus, SWA is thought to reflect homeostatically regulated processes potentially tied to maintaining optimal brain functioning. Interestingly, birds also engage in SWS and REM sleep, a similarity that arose via convergent evolution, as sleeping reptiles and amphibians do not show similar brain activity. Although birds deprived of sleep show global increases in SWA during subsequent sleep, it is unclear whether avian sleep is likewise regulated locally. Here, we provide, to our knowledge, the first electrophysiological evidence for local sleep homeostasis in the avian brain. After staying awake watching David Attenborough's The Life of Birds with only one eye, SWA and the slope of slow waves (a purported marker of synaptic strength) increased only in the hyperpallium--a primary visual processing region--neurologically connected to the stimulated eye. Asymmetries were specific to the hyperpallium, as the non-visual mesopallium showed a symmetric increase in SWA and wave slope. Thus, hypotheses for the function of mammalian SWS that rely on local sleep homeostasis may apply also to birds.