Postcranial stem tetrapod remains from the Devonian of Scat Craig, Morayshire, Scotland

The postcranial stem tetrapod remains from Scat Craig include a neural arch, humerus, tibia, femur, and incomplete pectoral girdles and ilia. These elements are all large or very large compared with the corresponding bones of other stem tetrapods. They correlate well in size with the proportions of Elginerpeton , the known stem tetrapod from Scat Craig, and probably belong to this genus. The neural arch has weak zygapophyses, and the ilia and shoulder girdles resemble those of Ichthyostega . The femur is strongly twisted, with the intercondylar fossa facing anteroventrally, so the hind limb probably functioned as a paddle. The tibia is broad, as in Acanthostega and Ichthyostega . The humerus is approximately intermediate in shape between those of osteolepiforms and later stem tetrapods, but seems to have a ventral radial facet like Ichthyostega . Overall, the postcranial bones combine apparent synapomorphies with Ichthyostega and characters which are uniquely primitive among stemgroup tetrapods. This character combination is incongruent. A recently discovered postorbital bone from the site is, strictly speaking, indeterminable but may belong to Elginerpeton ; it broadly resembles the postorbitals of Ichthyostega and Acanthostega , and demonstrates that the typical stem tetrapod facial morphology had evolved before the end of the Frasnian.     

The postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev

Postcranial remains of the Russian Late Devonian tetrapod Tulerpeton include the hexadactylous fore limb, hind limb, anocleithral pectoral girdle, squamation, and associated disarticulated postcranial bones. A cladistic analysis indicates that Tulerpeton is a reptiliomorph stem-group amniote and the earliest known crown-group tetrapod: Acanthostega and Ichthyostega are successively more derived plesion stem-group tetrapods and do not consititute a monophyletic ichthyostegalian radiation. Previous analyses suggesting a profound split in tetrapod phylogeny are thereby corroborated, and likewise the interpretation of Westlothiana as a stem-group amniote. The divergence of reptiliomorphs from batrachomorphs occurred before the Devonian-Carboniferous boundary. Tulerpeton originates from an entirely aquatic environment with a diverse fish fauna. The morphologies of its limbs and those of Devonian stem-tetrapods suggest that dactyly predates the elaboration of the carpus and tarsus, and that Polydactyly persisted after the evolutionary divergence of the principal lineages of living tetrapods. The apparent absence of a branchial lamina and gill skeleton suggests that Tulerpeton was primarily air-breathing, whereas contemporary stem-group tetrapods and more recent batrachomorphs retained greater emphasis on gill-breathing.     

Devonian tetrapod trackways and trackmakers; a review of the fossils and footprints

The earliest tetrapods are known from the Upper Devonian. Their remains are becoming better known from increasing numbers of specimens, localities, environments and ichnofossils. Each of the eight (or possibly nine) genera now represented by skeletal fossils is reviewed in its sedimentological, faunal and stratigraphic context, with an assessment of what might be inferred about the habitus and locomotory capabilities of each. Fossil trackways and their interpretations are then re-examined in the context of the known body forms, and consideration given to the degree of fit between the skeletal fossils, the trackways and their interpretations. The currently known Devonian tetrapods are unlikely to have made any of the known tracks, unless they were produced under water. Neither the skeletal fossils nor the trackways show good evidence of terrestrial locomotion among Devonian tetrapods. When the fossil material and recent phylogenetic analyses are taken in combination, it appears that neither tetrapods nor limbs with digits are likely to have arisen before the Frasnian. This should be borne in mind in palaeoecological studies of these animals.     

四足动物起源研究的新进展

四足动物的起源是生物进化过程中的关键问题之一。2006年,美国学者Daeschler E B和Shubin N H在加拿大努纳武特地区南部的埃勒斯米尔岛上发掘了一系列距今3.75亿年的Tiktaalik鱼化石。该鱼与希望螈（Elpisto-stegalian）一样均没有背鳍、没有鳃盖、子鳃盖、外肩胛骨;而具有宽大的背腹性明显的扁平颅骨,以及位于颅骨背面的眼睛,还具有成对的额骨、微鼻孔和位于末端的口,并具备了四足动物的一些特征,诸如较大的通气孔、可活动的颈部、伏瓦状排列的肋骨,胸鳍出现了挠骨的分化,并有骨质关节。这一发现填补了从海洋动物到四足动物的空白。     

Development of limbs in urodeles and the origin of tetrapod limbs

On the basis of studies on serial sections of larval Ranodon sibiricus limbs and published data, the hypothesis of the origin of tetrapod limbs from the biserial archipterygium is proposed. The mesomeres of the central axis of the biserial fin correspond (in proximodistal direction) to the humerus, ulna, ulnare, all carpalia distalia, metacarpale 1, and phalanges of the first digit in the forelimb of caudate amphibians and to the femur, fibula, fibulare, tarsalia distalia, metatarsale 1, and phalanges of the first digit in the hind limb. The preaxial elements of the zygopodium and autopodium, which are positioned proximal to the digital arch, correspond to the preaxial rays of the biserial fin, and digits 2–5 correspond to its postaxial rays. As the fin transformed into the limb, the central axis curved preaxially, forming the digital arch and resulting in partial reduction and fusion of preaxial rays.     

Uricoteley:its nature and origin during the evolution of tetrapod vertebrates

The hepatic mechanism for detoxication of ammonia formed during amino acid gluconeogenesis in uricotelic vertebrates requires the intramitochondrial synthesis of glutamine by glutamine synthetase. This glutamine then serves as a precursor of uric acid in the cytosol. The evolutionary development of uricoteley thus required the localization of glutamine synthetase in liver mitochondria. The mechanism for the mitochondrial import of glutamine synthetase in uricotelic vertebrate liver is not yet known. Tortoises, extant relatives of the stem reptiles, possess both the ureotelic and uricotelic hepatic systems. It therefore seems likely that the genetic events allowing the mitochondrial localization of glutamine synthetase in liver occurred in the amniote amphibian ancestors of the stem reptiles. The selection of ureoteley by the theropsids and of uricoteley by the sauropsids were major events in the divergence and subsequent evolution of these two lines. Once established in the sauropsid line, uricoteley has persisted through to the higher reptiles, crocodilians, and birds. Uricoteley was in part responsible for the radiation of the archosaurs during the Triassic as a water-conserving mechanism in the adult, thereby allowing them to invade the arid environments of that period. Contrary to dogma, uricoteley was probably of minor significance in the development of the cleidoic egg. Neither mammalian nor avian embryonic liver tissues catabolize amino acids to any great extent, so it is inappropriate to attribute to them a kind of "waste" nitrogen metabolism.     

Prehistorical climate change increased diversification of a group of butterflies

Satyrinae butterflies (Lepidoptera: Nymphalidae) and grasses (Poaceae) are very diverse and distributed worldwide. Most Satyrinae use grasses as host plants, but the temporal scale of this tight association is not known. Here, we present a phylogenetic study of Satyrinae butterflies and related groups, based on 5.1 kilobases from six gene regions and 238 morphological characters for all major lineages in the 'satyrine clade'. Estimates of divergence times calibrated using a fossil from the Late Oligocene indicate that the species-rich tribe Satyrini diversified to its current 2200 species simultaneously with the expansion and radiation of grasses during the dramatic cooling and drying up of the Earth in the Oligocene. We suggest that the adaptive radiation of grass feeders in Satyrini has been facilitated by the ubiquitousness of grasses since 25Myr ago, which was triggered by a change in global climate.     

Flying in the face of climate change: a review of climate change, past, present and future

The distribution and abundance of birds is known to depend critically upon climate variability at a range of temporal and spatial scales. In this paper we review historical changes in climate in the context of what is known about climate variability over the last millennium, with particular reference to the British Isles. The climate of Britain is now warmer than it has been in at least 340 years, with the 1990s decade 0.5 °C warmer than the 1961–1990 average. In addition, the frequency of cold days (mean temperature below 0 °C), particularly during March and November, has declined and there has been a marked shift in the seasonality of precipitation, with winters becoming substantially wetter and summers becoming slightly drier. Current understanding is that the rate of future warming is likely to accelerate with more frequent and more intense summer heatwaves, milder winters, an increase in winter rainfall, an increased risk of winter river floods, and an increase in mean sea-level and associated coastal flooding. All of these aspects of climate change are likely to impact on coastal birds. A range of potential future climate scenarios for the British Isles are presented derived from recently completed global climate model experiments. For migrant bird species, changes in the British climate have also to be seen within the context of remote climate change in both the breeding and the overwintering grounds.     

Patterns of mechanical energy change in tetrapod gait: pendula, springs and work

Kinematic and center of mass (CoM) mechanical variables used to define terrestrial gaits are compared for various tetrapod species. Kinematic variables (limb phase, duty factor) provide important timing information regarding the neural control and limb coordination of various gaits. Whereas, mechanical variables (potential and kinetic energy relative phase, %Recovery, %Congruity) provide insight into the underlying mechanisms that minimize muscle work and the metabolic cost of locomotion, and also influence neural control strategies. Two basic mechanisms identified by Cavagna et al. (1977. Am J Physiol 233:R243-R261) are used broadly by various bipedal and quadrupedal species. During walking, animals exchange CoM potential energy (PE) with kinetic energy (KE) via an inverted pendulum mechanism to reduce muscle work. During the stance period of running (including trotting, hopping and galloping) gaits, animals convert PE and KE into elastic strain energy in spring elements of the limbs and trunk and regain this energy later during limb support. The bouncing motion of the body on the support limb(s) is well represented by a simple mass-spring system. Limb spring compliance allows the storage and return of elastic energy to reduce muscle work. These two distinct patterns of CoM mechanical energy exchange are fairly well correlated with kinematic distinctions of limb movement patterns associated with gait change. However, in some cases such correlations can be misleading. When running (or trotting) at low speeds many animals lack an aerial period and have limb duty factors that exceed 0.5. Rather than interpreting this as a change of gait, the underlying mechanics of the body's CoM motion indicate no fundamental change in limb movement pattern or CoM dynamics has occurred. Nevertheless, the idealized, distinctive patterns of CoM energy fluctuation predicted by an inverted pendulum for walking and a bouncing mass spring for running are often not clear cut, especially for less cursorial species. When the kinematic and mechanical patterns of a broader diversity of quadrupeds and bipeds are compared, more complex patterns emerge, indicating that some animals may combine walking and running mechanics at intermediate speeds or at very large size. These models also ignore energy costs that are likely associated with the opposing action of limbs that have overlapping support times during walking. A recent model of terrestrial gait (Ruina et al., 2005. J Theor Biol, in press) that treats limb contact with the ground in terms of collisional energy loss indicates that considerable CoM energy can be conserved simply by matching the path of CoM motion perpendicular to limb ground force. This model, coupled with the earlier ones of pendular exchange during walking and mass-spring elastic energy savings during running, provides compelling argument for the view that the legged locomotion of quadrupeds and other terrestrial animals has generally evolved to minimize muscle work during steady level movement.     

Hydrologic refugia,plants, and climate change

Climate, physical landscapes, and biota interact to generate heterogeneous hydrologic conditions in space and over time, which are reflected in spatial patterns of species distributions. As these species distributions respond to rapid climate change, microrefugia may support local species persistence in the face of deteriorating climatic suitability. Recent focus on temperature as a determinant of microrefugia insufficiently accounts for the importance of hydrologic processes and changing water availability with changing climate. Where water scarcity is a major limitation now or under future climates, hydrologic microrefugia are likely to prove essential for species persistence, particularly for sessile species and plants. Zones of high relative water availability – mesic microenvironments – are generated by a wide array of hydrologic processes, and may be loosely coupled to climatic processes and therefore buffered from climate change. Here, we review the mechanisms that generate mesic microenvironments and their likely robustness in the face of climate change. We argue that mesic microenvironments will act as species‐specific refugia only if the nature and space/time variability in water availability are compatible with the ecological requirements of a target species. We illustrate this argument with case studies drawn from California oak woodland ecosystems. We posit that identification of hydrologic refugia could form a cornerstone of climate‐cognizant conservation strategies, but that this would require improved understanding of climate change effects on key hydrologic processes, including frequently cryptic processes such as groundwater flow.     

Protandry, sexual selection and climate change

Protandry refers to the earlier appearance of males before females at sites of reproduction. Sexual selection has been hypothesized to give rise to sex differences in benefits and costs of early arrival, thereby selecting for earlier appearance by the sex subject to more intense sexual selection. If sexual selection is more intense, there is a greater premium on early arrival among individuals of the chosen sex because of direct selection for earlier arrival. This hypothesis leads to the prediction that changes in the costs and benefits of early arrival related to changes in environmental conditions should particularly affect the sex that arrives first and hence the degree of protandry. I tested this hypothesis using the Barn Swallow Hirundo rustica. During 1971–2003, the degree of protandry increased significantly in a Danish population because males advanced arrival date while females did not. This earlier arrival by males compared with females was correlated with a significant increase by over 1.2 standard deviations in the length of the outermost tail feathers of males, a secondary sexual character, suggesting direct selection on both protandry and the secondary sexual character. Environmental conditions during spring migration in Northern Africa, as reflected by the normalized difference vegetation index, have deteriorated since 1984, resulting in increased mortality among males during spring migration, but not among females, and this deterioration of climatic conditions was positively correlated with an increasing degree of protandry. Likewise, an increase in April temperatures at the breeding grounds during recent decades is positively correlated with increased protandry, apparently because males can arrive earlier without increasing the fitness cost of early arrival. Local population size did not predict changes in arrival date. These findings suggest that rapid changes in climate can cause a change in degree of protandry and secondary sexual characters.     

Invertebrates,ecosystem services and climate change

The sustainability of ecosystem services depends on a firm understanding of both how organisms provide these services to humans and how these organisms will be altered with a changing climate. Unquestionably a dominant feature of most ecosystems, invertebrates affect many ecosystem services and are also highly responsive to climate change. However, there is still a basic lack of understanding of the direct and indirect paths by which invertebrates influence ecosystem services, as well as how climate change will affect those ecosystem services by altering invertebrate populations. This indicates a lack of communication and collaboration among scientists researching ecosystem services and climate change effects on invertebrates, and land managers and researchers from other disciplines, which becomes obvious when systematically reviewing the literature relevant to invertebrates, ecosystem services, and climate change. To address this issue, we review how invertebrates respond to climate change. We then review how invertebrates both positively and negatively influence ecosystem services. Lastly, we provide some critical future directions for research needs, and suggest ways in which managers, scientists and other researchers may collaborate to tackle the complex issue of sustaining invertebrate‐mediated services under a changing climate.     

Plantation forests,climate change and biodiversity

Nearly 4 % of the world’s forests are plantations, established to provide a variety of ecosystem services, principally timber and other wood products. In addition to such services, plantation forests provide direct and indirect benefits to biodiversity via the provision of forest habitat for a wide range of species, and by reducing negative impacts on natural forests by offsetting the need to extract resources. There is compelling evidence that climate change is directly affecting biodiversity in forests throughout the world. These impacts occur as a result of changes in temperature, rainfall, storm frequency and magnitude, fire frequency, and the frequency and magnitude of pest and disease outbreaks. However, in plantation forests it is not only the direct effects of climate change that will impact on biodiversity. Climate change will have strong indirect effects on biodiversity in plantation forests via changes in forest management actions that have been proposed to mitigate the effects of climate change on the productive capacity of plantations. These include changes in species selection (including use of species mixtures), rotation length, thinning, pruning, extraction of bioenergy feedstocks, and large scale climate change driven afforestation, reforestation, and, potentially deforestation. By bringing together the potential direct and indirect impacts of climate change we conclude that in the short to medium term changes in plantation management designed to mitigate or adapt to climate change could have a significantly greater impact on biodiversity in such plantation forests than the direct effects of climate change. Although this hypothesis remains to be formally tested, forest managers worldwide are already considering new approaches to plantation forestry in an effort to create forests that are more resilient to the effects of changing climatic conditions. Such change presents significant risks to existing biodiversity values in plantation forests, however it also provides new opportunities to improve biodiversity values within existing and new plantation forests. We conclude by suggesting future options, such as functional zoning and species mixtures applied at either the stand level or as fine-scale mosaics of single-species stands as options to improve biodiversity whilst increasing resilience to climate change.     

A new genus of Devonian tetrapod from North‐East Greenland,with new information on the lower jaw of Ichthyostega

Abstract: A new genus and species of Devonian tetrapod has been identified from material collected in 1947 from the southern slope of Mt. Celsius, Ymer Ø, North‐East Greenland. The specimen preserves both lower jaws, partial palate, premaxillae and maxillae, with a natural mould of parts of the shoulder girdle. The new taxon, Ymeria denticulata, shows differences in dentition, skull ornament and lateral line expression from both Acanthostega and Ichthyostega, but it shows a closer resemblance to the latter. A cladistic analysis not only suggests that Ymeria lies adjacent to Ichthyostega on the tetrapod stem, but also reveals substantial topological instability. As the third genus and the fifth species of tetrapod identified from North‐East Greenland, it demonstrates the high diversity of Devonian tetrapods in that region.     

Interval between clutches, fitness, and climate change

Timing of optimal reproduction can be affected by the presenceof multiple broods, with multi-brooded species breeding earlier(and later) than the optimal timing of breeding as comparedwith single-brooded species that only need to optimize the timingof a single brood. Approximately two-thirds of barn swallowsHirundo rustica produce 2 broods per year, and I tested whetherthe constraints on timing of reproduction were affected by climatechange because climatic amelioration would allow both an earlierstart and a later termination of reproduction. The durationof the interval between first and second clutches and the variancein the duration increased during 1971–2005 when temperatureduring spring, but not summer, increased rapidly. Interclutchinterval was shorter when mean date of breeding was late andalso among late-breeding individuals during individual years.When clutch size and brood size of the first clutch were large,interval until the second brood increased. Pairs with a longinterval produced more fledglings than pairs with a short interval.Pairs with first broods with strong mean T-cell–mediatedimmune responses took shorter time to start their second clutch,whereas mean body mass or tarsus length of first broods werenot significantly related to interclutch interval. Interclutchinterval increased with the size of a secondary sexual character,the length of the outermost tail feathers of adult male barnswallows, but not with tail length of females, or with sizeof several other phenotypic characters in either sex. Thesefindings are consistent with the hypothesis that the durationof the interclutch interval is determined by a combination ofenvironmental conditions, reproductive effort, and sexual selection.     

Rubisco, Rubisco activase, and global climate change

Global warming and the rise in atmospheric CO(2) will increase the operating temperature of leaves in coming decades, often well above the thermal optimum for photosynthesis. Presently, there is controversy over the limiting processes controlling photosynthesis at elevated temperature. Leading models propose that the reduction in photosynthesis at elevated temperature is a function of either declining capacity of electron transport to regenerate RuBP, or reductions in the capacity of Rubisco activase to maintain Rubisco in an active configuration. Identifying which of these processes is the principal limitation at elevated temperature is complicated because each may be regulated in response to a limitation in the other. Biochemical and gas exchange assessments can disentangle these photosynthetic limitations; however, comprehensive assessments are often difficult and, for many species, virtually impossible. It is proposed that measurement of the initial slope of the CO(2) response of photosynthesis (the A/C(i) response) can be a useful means to screen for Rubisco activase limitations. This is because a reduction in the Rubisco activation state should be most apparent at low CO(2) when Rubisco capacity is generally limiting. In sweet potato, spinach, and tobacco, the initial slope of the A/C(i) response shows no evidence of activase limitations at high temperature, as the slope can be accurately modelled using the kinetic parameters of fully activated Rubisco. In black spruce (Picea mariana), a reduction in the initial slope above 30 degrees C cannot be explained by the known kinetics of fully activated Rubisco, indicating that activase may be limiting at high temperatures. Because black spruce is the dominant species in the boreal forest of North America, Rubisco activase may be an unusually important factor determining the response of the boreal biome to climate change.