Total-evidence framework reveals complex morphological evolution in nightbirds (Strisores)

Strisores is a clade of neoavian birds that include diurnal aerial specialists such as swifts and hummingbirds, as well as several predominantly nocturnal lineages such as nightjars and potoos. Despite the use of genome-scale molecular datasets, the phylogenetic interrelationships among major strisorean groups remain controversial. Given the availability of next-generation sequence data for Strisores and the clade’s rich fossil record, we reassessed the phylogeny of Strisores by incorporating a large-scale sequence dataset with anatomical data from living and fossil strisoreans within a Bayesian total-evidence framework. Combined analyses of molecular and morphological data resulted in a phylogenetic topology for Strisores that is congruent with the findings of two recent molecular phylogenomic studies, supporting nightjars (Caprimulgidae) as the extant sister group of the remainder of Strisores. This total-evidence framework allowed us to identify morphological synapomorphies for strisorean clades previously recovered using molecular-only datasets. However, a combined analysis of molecular and morphological data highlighted strong signal conflict between sequence and anatomical data in Strisores. Furthermore, simultaneous analysis of molecular and morphological data recovered differing placements for some fossil taxa compared with analyses of morphological data under a molecular scaffold, highlighting the importance of analytical decisions when conducting morphological phylogenetic analyses of taxa with molecular phylogenetic data. We suggest that multiple strisorean lineages have experienced convergent evolution across the skeleton, obfuscating the phylogenetic position of certain fossils, and that many distinctive specializations of strisorean subclades were acquired early in their evolutionary history. Despite this apparent complexity in the evolutionary history of Strisores, our results provide fossil support for aerial foraging as the ancestral ecological strategy of Strisores, as implied by recent phylogenetic topologies derived from molecular data.Parts of this project were supported by Systematics Research Fund awards to A.C. and D.J.F. by the Linnean Society of London and the Systematics Association. D.J.F. also acknowledges support from the Isaac Newton Trust early career support scheme. Parts of this project were also funded by the European Union’s Horizon 2020 research and innovation program 2014–2018 under grant agreement 677774 (European Research Council [ERC] Starting Grant: TEMPO) to R.B.J.B. N.D.W. and M.J.B. received Smithsonian Institution support through the Predoctoral Fellowship Program (N.D.W.), the Frontiers in Phylogenetics Program, the Scholarly Studies Program, and the Consortium for Understanding and Sustaining a Biodiverse Planet

The Evolution and Fossil Record of Palaeognathous Birds (Neornithes: Palaeognathae)

The extant diversity of the avian clade Palaeognathae is composed of the iconic flightless ratites (ostriches, rheas, kiwi, emus, and cassowaries), and the volant tinamous of Central and South America. Palaeognaths were once considered a classic illustration of diversification driven by Gondwanan vicariance, but this paradigm has been rejected in light of molecular phylogenetic and divergence time results from the last two decades that indicate that palaeognaths underwent multiple relatively recent transitions to flightlessness and large body size, reinvigorating research into their evolutionary origins and historical biogeography. This revised perspective on palaeognath macroevolution has highlighted lingering gaps in our understanding of how, when, and where extant palaeognath diversity arose. Towards resolving those questions, we aim to comprehensively review the known fossil record of palaeognath skeletal remains, and to summarize the current state of knowledge of their evolutionary history. Total clade palaeognaths appear to be one of a small handful of crown bird lineages that crossed the Cretaceous-Paleogene (K-Pg) boundary, but gaps in their Paleogene fossil record and a lack of Cretaceous fossils preclude a detailed understanding of their multiple transitions to flightlessness and large body size, and recognizable members of extant subclades generally do not appear until the Neogene. Despite these knowledge gaps, we combine what is known from the fossil record of palaeognaths with plausible divergence time estimates, suggesting a relatively rapid pace of diversification and phenotypic evolution in the early Cenozoic. In line with some recent authors, we surmise that the most recent common ancestor of palaeognaths was likely a relatively small-bodied, ground-feeding bird, features that may have facilitated total-clade palaeognath survivorship through the K-Pg mass extinction, and which may bear on the ecological habits of the ancestral crown bird.</jats:p

New material of Paleocene-eocene pellornis (aves: Gruiformes) clarifies the pattern and timing of the extant gruiform radiation

Pellornis mikkelseni is an early gruiform from the latest Paleocene-earliest Eocene Fur Formation of Denmark. At approximately 54 million years old, it is among the earliest clear records of the Gruiformes. The holotype specimen, and only material thus far recognised, was originally considered to comprise a partial postcranial skeleton. However, additional mechanical preparation of the nodule containing the holotype revealed that the skeleton is nearly complete and includes a well-preserved skull. In addition to extracting new information from the holotype, we identify and describe two additional specimens of P. mikkelseni which reveal further morphological details of the skeleton. Together, these specimens show that P. mikkelseni possessed a schizorhinal skull and shared many features with the well-known Paleogene Messelornithidae (“Messel rails”). To reassess the phylogenetic position of P. mikkelseni, we modified an existing morphological dataset by adding 20 characters, four extant gruiform taxa, six extinct gruiform taxa, and novel scorings based on the holotype and referred specimens. Phylogenetic analyses recover a clade containing P. mikkelseni, Messelornis, Songzia and crown Ralloidea, supporting P. mikkelseni as a crown gruiform. The phylogenetic position of P. mikkelseni illustrates that some recent divergence time analyses have underestimated the age of crown Gruiformes. Our results suggest a Paleocene origin for this important clade, bolstering evidence for a rapid early radiation of Neoaves following the end-Cretaceous mass extinction.</jats:p

Sex-biased parental care and sexual size dimorphism in a provisioning arthropod

The diverse selection pressures driving the evolution of sexual size dimorphism (SSD) have long been debated. While the balance between fecundity selection and sexual selection has received much attention, explanations based on sex-specific ecology have proven harder to test. In ectotherms, females are typically larger than males, and this is frequently thought to be because size constrains female fecundity more than it constrains male mating success. However, SSD could additionally reflect maternal care strategies. Under this hypothesis, females are relatively larger where reproduction requires greater maximum maternal effort – for example where mothers transport heavy provisions to nests. To test this hypothesis we focussed on digger wasps (Hymenoptera: Ammophilini), a relatively homogeneous group in which only females provision offspring. In some species, a single large prey item, up to 10 times the mother’s weight, must be carried to each burrow on foot; other species provide many small prey, each flown individually to the nest. We found more pronounced female-biased SSD in species where females carry single, heavy prey. More generally, SSD was negatively correlated with numbers of prey provided per offspring. Females provisioning multiple small items had longer wings and thoraxes, probably because smaller prey are carried in flight. Despite much theorising, few empirical studies have tested how sex-biased parental care can affect SSD. Our study reveals that such costs can be associated with the evolution of dimorphism, and this should be investigated in other clades where parental care costs differ between sexes and species

Analysis of the atmospheric distribution, sources, and sinks of oxygenated volatile organic chemicals based on measurements over the Pacific during TRACE-P

Airborne measurements of a large number of oxygenated volatile organic chemicals (OVOC) were carried out in the Pacific troposphere (0.1 - 12 km) in winter/spring of 2001 (24 February to 10 April). Specifically, these measurements included acetone (CH3COCHA3), methylethyl ketone (CH3COC2H5, MEK), methanol (CH3OH), ethanol (C2H5OH), acetaldehyde (CH3CHO), propionaldehyde C2H 5CHO), peroxyacylnitrates (PANs) (CnH 2n+1COO2NO2), and organic nitrates (CnH2n+1ONO2). Complementary measurements of formaldehyde (HCHO), methyl hydroperoxide (CH 3OOH), and selected tracers were also available. OVOC were abundant in the clean troposphere and were greatly enhanced in the outflow regions from Asia. Background mixing ratios were typically highest in the lower troposphere and declined toward the upper troposphere and the lowermost stratosphere. Their total abundance (ΣOVOC) was nearly twice that of nonmethane hydrocarbons (Σ C2-C8 NMHC. Throughout the troposphere, the OH reactivity of OVOC is comparable to that of methane and far exceeds that of NMHC. A comparison of these data with western Pacific observations collected some 7 years earlier (February-March 1994) did not reveal significant differences. Mixing ratios of OVOC were strongly correlated with each other as well as with tracers of fossil and biomass/biofuel combustion. Analysis of the relative enhancement of selected OVOC with respect to CH 3Cl and CO in 12 plumes originating from fires and sampled in the free troposphere (3-11 km) is used to assess their primary and secondary emissions from biomass combustion. The composition of these plumes also indicates a large shift of reactive nitrogen into the PAN reservoir thereby limiting ozone formation. A three-dimensional global model that uses state of the art chemistry and source information is used to compare measured and simulated mixing ratios of selected OVOC. While there is reasonable agreement in many cases, measured aldehyde concentrations are significantly larger than predicted. At their observed levels, acetaldehyde mixing ratios are shown to be an important source of HCHO (and HOx) and PAN in the troposphere. On the basis of presently known chemistry, measured mixing ratios of aldehydes and PANs are mutually incompatible. We provide rough estimates of the global sources of several OVOC and conclude that collectively these are extremely large (150-500 Tg C yr-1) but remain poorly quantified. Copyright 2004 by the American Geophysical Union

Photodissociation and the Morphology of HI in Galaxies

Young massive stars produce Far-UV photons which dissociate the molecular gas on the surfaces of their parent molecular clouds. Of the many dissociation products which result from this ``back-reaction'', atomic hydrogen \HI is one of the easiest to observe through its radio 21-cm hyperfine line emission. In this paper I first review the physics of this process and describe a simplified model which has been developed to permit an approximate computation of the column density of photodissociated \HI which appears on the surfaces of molecular clouds. I then review several features of the \HI morphology of galaxies on a variety of length scales and describe how photodissociation might account for some of these observations. Finally, I discuss several consequences which follow if this view of the origin of HI in galaxies continues to be successful.Comment: 18 pages, 7 figures in 8 files, invited review paper for the conference "Penetrating Bars Through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes a New Note", South Africa, June 2004. Proceedings to be published by Kluwer, eds. D.L. Block, K.C. Freeman, I. Puerari, R. Groess, & E.K. Bloc

Functional complementarity of ancient plant–fungal mutualisms: contrasting nitrogen, phosphorus and carbon exchanges between Mucoromycotina and Glomeromycotina fungal symbionts of liverworts

Liverworts, which are amongst the earliest divergent plant lineages and important ecosystem pioneers, often form nutritional mutualisms with arbuscular mycorrhiza‐forming Glomeromycotina and fine‐root endophytic Mucoromycotina fungi, both of which coevolved with early land plants. Some liverworts, in common with many later divergent plants, harbour both fungal groups, suggesting these fungi may complementarily improve plant access to different soil nutrients. We tested this hypothesis by growing liverworts in single and dual fungal partnerships under a modern atmosphere and under 1500 ppm [CO2], as experienced by early land plants. Access to soil nutrients via fungal partners was investigated with 15N‐labelled algal necromass and 33P orthophosphate. Photosynthate allocation to fungi was traced using 14CO2. Only Mucoromycotina fungal partners provided liverworts with substantial access to algal 15N, irrespective of atmospheric CO2 concentration. Both symbionts increased 33P uptake, but Glomeromycotina were often more effective. Dual partnerships showed complementarity of nutrient pool use and greatest photosynthate allocation to symbiotic fungi. We show there are important functional differences between the plant–fungal symbioses tested, providing new insights into the functional biology of Glomeromycotina and Mucoromycotina fungal groups that form symbioses with plants. This may explain the persistence of the two fungal lineages in symbioses across the evolution of land plants

Dynamics of trimming the content of face representations for categorization in the brain

To understand visual cognition, it is imperative to determine when, how and with what information the human brain categorizes the visual input. Visual categorization consistently involves at least an early and a late stage: the occipito-temporal N170 event related potential related to stimulus encoding and the parietal P300 involved in perceptual decisions. Here we sought to understand how the brain globally transforms its representations of face categories from their early encoding to the later decision stage over the 400 ms time window encompassing the N170 and P300 brain events. We applied classification image techniques to the behavioral and electroencephalographic data of three observers who categorized seven facial expressions of emotion and report two main findings: (1) Over the 400 ms time course, processing of facial features initially spreads bilaterally across the left and right occipito-temporal regions to dynamically converge onto the centro-parietal region; (2) Concurrently, information processing gradually shifts from encoding common face features across all spatial scales (e.g. the eyes) to representing only the finer scales of the diagnostic features that are richer in useful information for behavior (e.g. the wide opened eyes in 'fear'; the detailed mouth in 'happy'). Our findings suggest that the brain refines its diagnostic representations of visual categories over the first 400 ms of processing by trimming a thorough encoding of features over the N170, to leave only the detailed information important for perceptual decisions over the P300

Adaptive Filtering Enhances Information Transmission in Visual Cortex

Sensory neuroscience seeks to understand how the brain encodes natural environments. However, neural coding has largely been studied using simplified stimuli. In order to assess whether the brain's coding strategy depend on the stimulus ensemble, we apply a new information-theoretic method that allows unbiased calculation of neural filters (receptive fields) from responses to natural scenes or other complex signals with strong multipoint correlations. In the cat primary visual cortex we compare responses to natural inputs with those to noise inputs matched for luminance and contrast. We find that neural filters adaptively change with the input ensemble so as to increase the information carried by the neural response about the filtered stimulus. Adaptation affects the spatial frequency composition of the filter, enhancing sensitivity to under-represented frequencies in agreement with optimal encoding arguments. Adaptation occurs over 40 s to many minutes, longer than most previously reported forms of adaptation.Comment: 20 pages, 11 figures, includes supplementary informatio

Neural Decision Boundaries for Maximal Information Transmission

We consider here how to separate multidimensional signals into two categories, such that the binary decision transmits the maximum possible information transmitted about those signals. Our motivation comes from the nervous system, where neurons process multidimensional signals into a binary sequence of responses (spikes). In a small noise limit, we derive a general equation for the decision boundary that locally relates its curvature to the probability distribution of inputs. We show that for Gaussian inputs the optimal boundaries are planar, but for non-Gaussian inputs the curvature is nonzero. As an example, we consider exponentially distributed inputs, which are known to approximate a variety of signals from natural environment.Comment: 5 pages, 3 figure