New uses for ancient middens: bridging ecological and evolutionary perspectives

Rodent middens provide a fine-scale spatiotemporal record of plant and animal communities over the late Quaternary. In the Americas, middens have offered insight into biotic responses to past environmental changes and historical factors influencing the distribution and diversity of species. However, few studies have used middens to investigate genetic or ecosystem level responses. Integrating midden studies with neoecology and experimental evolution can help address these gaps and test mechanisms underlying eco-evolutionary patterns across biological and spatiotemporal scales. Fully realizing the potential of middens to answer cross-cutting ecological and evolutionary questions and inform conservation goals in the Anthropocene will require a collaborative research community to exploit existing midden archives and mount new campaigns to leverage midden records globally.

White Paper: An Integrated Perspective on the Causes of Hypometric Metabolic Scaling in Animals

Larger animals studied during ontogeny, across populations, or across species, usually have lower mass-specific metabolic rates than smaller animals (hypometric scaling). This pattern is usually observed regardless of physiological state (e.g. basal, resting, field, maximally-active). The scaling of metabolism is usually highly correlated with the scaling of many life history traits, behaviors, physiological variables, and cellular/molecular properties, making determination of the causation of this pattern challenging. For across-species comparisons of resting and locomoting animals (but less so for across populations or during ontogeny), the mechanisms at the physiological and cellular level are becoming clear. Lower mass-specific metabolic rates of larger species at rest are due to a) lower contents of expensive tissues (brains, liver, kidneys), and b) slower ion leak across membranes at least partially due to membrane composition, with lower ion pump ATPase activities. Lower mass-specific costs of larger species during locomotion are due to lower costs for lower-frequency muscle activity, with slower myosin and Ca++ ATPase activities, and likely more elastic energy storage. The evolutionary explanation(s) for hypometric scaling remain(s) highly controversial. One subset of evolutionary hypotheses relies on constraints on larger animals due to changes in geometry with size; for example, lower surface-to-volume ratios of exchange surfaces may constrain nutrient or heat exchange, or lower cross-sectional areas of muscles and tendons relative to body mass ratios would make larger animals more fragile without compensation. Another subset of hypotheses suggests that hypometric scaling arises from biotic interactions and correlated selection, with larger animals experiencing less selection for mass-specific growth or neurolocomotor performance. A additional third type of explanation comes from population genetics. Larger animals with their lower effective population sizes and subsequent less effective selection relative to drift may have more deleterious mutations, reducing maximal performance and metabolic rates. Resolving the evolutionary explanation for the hypometric scaling of metabolism and associated variables is a major challenge for organismal and evolutionary biology. To aid progress, we identify some variation in terminology use that has impeded cross-field conversations on scaling. We also suggest that promising directions for the field to move forward include: 1) studies examining the linkages between ontogenetic, population-level, and cross-species allometries, 2) studies linking scaling to ecological or phylogenetic context, 3) studies that consider multiple, possibly interacting hypotheses, and 4) obtaining better field data for metabolic rates and the life history correlates of metabolic rate such as lifespan, growth rate and reproduction.

The road to a larger brain

Ecological opportunities in the early Cenozoic favored larger, not smarter, mammals.

Response to Comment on "The influence of juvenile dinosaurs on community structure and diversity"

The analysis of dinosaur ecology hinges on the appropriate reconstruction and analysis of dinosaur biodiversity. Benson et al. question the data used in our analysis and our subsequent interpretation of the results. We address these concerns and show that their reanalysis is flawed. Indeed, when occurrences are filtered to include only valid taxa, their revised dataset strengthens our earlier conclusions.

A Framework for Investigating Rules of Life by Establishing Zones of Influence

The incredible complexity of biological processes across temporal and spatial scales hampers defining common underlying mechanisms driving the patterns of life. However, recent advances in sequencing, big data analysis, machine learning, and molecular dynamics simulation have renewed the hope and urgency of finding potential hidden rules of life. There currently exists no framework to develop such synoptic investigations. Some efforts aim to identify unifying rules of life across hierarchical levels of time, space, and biological organization, but not all phenomena occur across all the levels of these hierarchies. Instead of identifying the same parameters and rules across levels, we posit that each level of a temporal and spatial scale and each level of biological organization has unique parameters and rules that may or may not predict outcomes in neighboring levels. We define this neighborhood, or the set of levels, across which a rule functions as the zone of influence. Here, we introduce the zone of influence framework and explain using three examples: (Smocovitis, 1992) randomness in biology, where we use a Poisson process to describe processes from protein dynamics to DNA mutations to gene expressions, (Leroi, 2014) island biogeography, and (Gropp, 2016) animal coloration. The zone of influence framework may enable researchers to identify which levels are worth investigating for a particular phenomenon and reframe the narrative of searching for a unifying rule of life to the investigation of how, when, and where various rules of life operate.

The influence of juvenile dinosaurs on community structure and diversity

Despite dominating biodiversity in the Mesozoic, dinosaurs were not speciose. Oviparity constrained even gigantic dinosaurs to less than 15 kg at birth; growth through multiple morphologies led to the consumption of different resources at each stage. Such disparity between neonates and adults could have influenced the structure and diversity of dinosaur communities. Here, we quantified this effect for 43 communities across 136 million years and seven continents. We found that megatheropods (more than 1000 kg) such as tyrannosaurs had specific effects on dinosaur community structure. Although herbivores spanned the body size range, communities with megatheropods lacked carnivores weighing 100 to 1000 kg. We demonstrate that juvenile megatheropods likely filled the mesocarnivore niche, resulting in reduced overall taxonomic diversity. The consistency of this pattern suggests that ontogenetic niche shift was an important factor in generating dinosaur community structure and diversity.

The relationship between molar morphology and ecology within Neotoma

The extensive diversity in dental form across mammals and its strong relationship with function provides insights into the diet, habitat, and behavior, of both extant and extinct taxa. Understanding the extent of variation in dental morphology across species allows for more accurate identification of fossils and a better ability to infer relationships between form and function and ecology. We examined variation in the size and shape of the first upper molar among the genus Neotoma. We employed elliptical Fourier analysis to quantify differences in the shape of 2D outlines for 23 populations and six species of Neotoma, varying in body size and habitat preference. As expected, molar length is a strong predictor of body size and is significantly and negatively correlated with temperature, particularly in species whose ranges span large latitudinal gradients. We found that differences in molar shape separate species into three general morpho-groups, with no evidence of a phylogenetic signal. While outline analysis could not robustly classify all molars to the species level, it did perform well for Neotoma cinerea, probably because of the greater degree of folding and more acute angling of molar lophs. In contrast, wider lophs with shallower enamel infolding was characteristic of species specializing on softer, more succulent resources (i.e., Neotoma albigula and Neotoma micropus). Neotoma floridana were inaccurately classified to species in the majority of cases, but were the only molars correctly identified to locality 100% of the time, suggesting that dietary specializations at a local level may drive morphological changes within the species as well as across the genus.

Investigating the role of environment in pika (Ochotona) body size patterns across taxonomic levels, space, and time

Body size is an important trait in animals because it influences a multitude of additional life history traits. The causal mechanisms underlying body size patterns across spatial, temporal, and taxonomic hierarchies are debated, and of renewed interest in this era of climate change. Here, we tested multiple hypotheses regarding body mass patterns at the intraspecific and interspecific levels. We investigated body size patterns within a climate-sensitive small mammal species, Ochotona princeps (n = 2,873 individuals), across their range with local environmental variables. We also examined body mass of populations over time to determine if body size has evolved in situ in response to environmental change. At the interspecific level we compared the mean mass of 26 pika species (genus Ochotona) to determine if environmental temperatures, food availability, habitat variability, or range area influence body size. We found correlations between temperature, vegetation, and particularly precipitation variables, with body mass within O. princeps, but no linear relationship between body size and any climate or habitat variable for Ochotona species. Body size trends in relation to climate were stronger at the intraspecific than the interspecific level. Our results suggest that body size within O. princeps likely is related to food availability, and that body size evolution is not always a viable response to temperature change. Different mechanisms may be driving body size at the interspecific and intraspecific levels and factors other than environment, such as biotic interactions, may also be influential in determining body size over space and time.

Metabolic asymmetry and the global diversity of marine predators

Species richness of marine mammals and birds is highest in cold, temperate seas—a conspicuous exception to the general latitudinal gradient of decreasing diversity from the tropics to the poles. We compiled a comprehensive dataset for 998 species of sharks, fish, reptiles, mammals, and birds to identify and quantify inverse latitudinal gradients in diversity, and derived a theory to explain these patterns. We found that richness, phylogenetic diversity, and abundance of marine predators diverge systematically with thermoregulatory strategy and water temperature, reflecting metabolic differences between endotherms and ectotherms that drive trophic and competitive interactions. Spatial patterns of foraging support theoretical predictions, with total prey consumption by mammals increasing by a factor of 80 from the equator to the poles after controlling for productivity.

Trophic rewilding as a climate change mitigation strategy?

The loss of megafauna at the terminal Pleistocene has been linked to a wide range of Earth-system-level changes, such as altered greenhouse gas budgets, fire regimes and biome-level vegetation changes. Given these influences and feedbacks, might part of the solution for mitigating anthropogenic climate change lie in the restoration of extant megafauna to ecosystems? Here, we explore the potential role of trophic rewilding on Earth's climate system. We first provide a novel synthesis of the various ways that megafauna interact with the major drivers of anthropogenic climate change, including greenhouse gas storage and emission, aerosols and albedo. We then explore the role of rewilding as a mitigation tool at two scales: (i) current and near-future opportunities for national or regional climate change mitigation portfolios, and (ii) more radical opportunities at the global scale. Finally, we identify major knowledge gaps that complicate the complete characterization of rewilding as a climate change mitigation strategy. Our perspective is urgent since we are losing the Earth's last remaining megafauna, and with it a potential option to address climate change.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Body size downgrading of mammals over the late Quaternary

Since the late Pleistocene, large-bodied mammals have been extirpated from much of Earth. Although all habitable continents once harbored giant mammals, the few remaining species are largely confined to Africa. This decline is coincident with the global expansion of hominins over the late Quaternary. Here, we quantify mammalian extinction selectivity, continental body size distributions, and taxonomic diversity over five time periods spanning the past 125,000 years and stretching approximately 200 years into the future. We demonstrate that size-selective extinction was already under way in the oldest interval and occurred on all continents, within all trophic modes, and across all time intervals. Moreover, the degree of selectivity was unprecedented in 65 million years of mammalian evolution. The distinctive selectivity signature implicates hominin activity as a primary driver of taxonomic losses and ecosystem homogenization. Because megafauna have a disproportionate influence on ecosystem structure and function, past and present body size downgrading is reshaping Earth's biosphere.

Hierarchical complexity and the size limits of life

Over the past 3.8 billion years, the maximum size of life has increased by approximately 18 orders of magnitude. Much of this increase is associated with two major evolutionary innovations: the evolution of eukaryotes from prokaryotic cells approximately 1.9 billion years ago (Ga), and multicellular life diversifying from unicellular ancestors approximately 0.6 Ga. However, the quantitative relationship between organismal size and structural complexity remains poorly documented. We assessed this relationship using a comprehensive dataset that includes organismal size and level of biological complexity for 11 172 extant genera. We find that the distributions of sizes within complexity levels are unimodal, whereas the aggregate distribution is multimodal. Moreover, both the mean size and the range of size occupied increases with each additional level of complexity. Increases in size range are non-symmetric: the maximum organismal size increases more than the minimum. The majority of the observed increase in organismal size over the history of life on the Earth is accounted for by two discrete jumps in complexity rather than evolutionary trends within levels of complexity. Our results provide quantitative support for an evolutionary expansion away from a minimal size constraint and suggest a fundamental rescaling of the constraints on minimal and maximal size as biological complexity increases.

The changing role of mammal life histories in Late Quaternary extinction vulnerability on continents and islands

Understanding extinction drivers in a human-dominated world is necessary to preserve biodiversity. We provide an overview of Quaternary extinctions and compare mammalian extinction events on continents and islands after human arrival in system-specific prehistoric and historic contexts. We highlight the role of body size and life-history traits in these extinctions. We find a significant size-bias except for extinctions on small islands in historic times. Using phylogenetic regression and classification trees, we find that while life-history traits are poor predictors of historic extinctions, those associated with difficulty in responding quickly to perturbations, such as small litter size, are good predictors of prehistoric extinctions. Our results are consistent with the idea that prehistoric and historic extinctions form a single continuing event with the same likely primary driver, humans, but the diversity of impacts and affected faunas is much greater in historic extinctions.

The fossil record of the sixth extinction

Comparing the magnitude of the current biodiversity crisis with those in the fossil record is difficult without an understanding of differential preservation. Integrating data from palaeontological databases with information on IUCN status, ecology and life history characteristics of contemporary mammals, we demonstrate that only a small and biased fraction of threatened species (< 9%) have a fossil record, compared with 20% of non-threatened species. We find strong taphonomic biases related to body size and geographic range. Modern species with a fossil record tend to be large and widespread and were described in the 19(th) century. The expected magnitude of the current extinction based only on species with a fossil record is about half of that of one based on all modern species; values for genera are similar. The record of ancient extinctions may be similarly biased, with many species having originated and gone extinct without leaving a tangible record.

The importance of considering animal body mass in IPCC greenhouse inventories and the underappreciated role of wild herbivores

Methane is an important greenhouse gas, but characterizing production by source sector has proven difficult. Current estimates suggest herbivores produce ~20% (~76-189 Tg yr(-1) ) of methane globally, with wildlife contributions uncertain. We develop a simple and accurate method to estimate methane emissions and reevaluate production by wildlife. We find a strikingly robust relationship between body mass and methane output exceeding the scaling expected by differences in metabolic rate. Our allometric model gives a significantly better fit to empirical data than IPCC Tier 1 and 2 calculations. Our analysis suggests that (i) the allometric model provides an easier and more robust estimate of methane production than IPCC models currently in use; (ii) output from wildlife is much higher than previously considered; and (iii) because of the allometric scaling of methane output with body mass, national emissions could be reduced if countries favored more, smaller livestock, over fewer, larger ones.

Response to Comments on "Evidence for mesothermy in dinosaurs"

D'Emic and Myhrvold raise a number of statistical and methodological issues with our recent analysis of dinosaur growth and energetics. However, their critiques and suggested improvements lack biological and statistical justification.

Dinosaur physiology. Evidence for mesothermy in dinosaurs

Were dinosaurs ectotherms or fast-metabolizing endotherms whose activities were unconstrained by temperature? To date, some of the strongest evidence for endothermy comes from the rapid growth rates derived from the analysis of fossil bones. However, these studies are constrained by a lack of comparative data and an appropriate energetic framework. Here we compile data on ontogenetic growth for extant and fossil vertebrates, including all major dinosaur clades. Using a metabolic scaling approach, we find that growth and metabolic rates follow theoretical predictions across clades, although some groups deviate. Moreover, when the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms and ectotherms and closest to those of extant mesotherms. Our results suggest that the modern dichotomy of endothermic versus ectothermic is overly simplistic.

Opening the black box: outcomes of interactions between arbuscular mycorrhizal (AM) and non-host genotypes of Medicago depend on fungal identity, interplay between P uptake pathways and external P supply

We investigated the physiology that underlies the influence of arbuscular mycorrhizal (AM) colonization on outcomes of interactions between plants. We grew Medicago truncatula A17 and its AM-defective mutant dmi1 in intragenotypic (two plants per pot of the same genotype, x2) or intergenotypic (one plant of each genotype, 1 + 1) combinations, inoculated or not with Rhizophagus irregularis (formerly Glomus intraradices) or Gigaspora margarita. We measured plant growth, colonization, contributions of AM and direct P uptake pathways using (32)P, and expression of plant Pi transporter genes at two levels of P supply. A17 (x2) responded positively to inoculation only at low P. The response was enhanced with 1 + 1 even at high P where colonization in A17 was reduced. With R. irregularis P uptake by the AM pathway was unaffected by P supply, whereas with G. margarita, the AM pathway was lower at high P, and direct uptake higher. Gene expression varied and was unrelated to P uptake through the two pathways. There was no evidence of plant control of P uptake via R. irregularis at high P but there was via G. margarita. Importantly, growth responses of plant genotypes grown alone did not predict outcomes of intergenotypic interactions.

Patterns of maximum body size evolution in Cenozoic land mammals: eco-evolutionary processes and abiotic forcing

There is accumulating evidence that macroevolutionary patterns of mammal evolution during the Cenozoic follow similar trajectories on different continents. This would suggest that such patterns are strongly determined by global abiotic factors, such as climate, or by basic eco-evolutionary processes such as filling of niches by specialization. The similarity of pattern would be expected to extend to the history of individual clades. Here, we investigate the temporal distribution of maximum size observed within individual orders globally and on separate continents. While the maximum size of individual orders of large land mammals show differences and comprise several families, the times at which orders reach their maximum size over time show strong congruence, peaking in the Middle Eocene, the Oligocene and the Plio-Pleistocene. The Eocene peak occurs when global temperature and land mammal diversity are high and is best explained as a result of niche expansion rather than abiotic forcing. Since the Eocene, there is a significant correlation between maximum size frequency and global temperature proxy. The Oligocene peak is not statistically significant and may in part be due to sampling issues. The peak in the Plio-Pleistocene occurs when global temperature and land mammal diversity are low, it is statistically the most robust one and it is best explained by global cooling. We conclude that the macroevolutionary patterns observed are a result of the interplay between eco-evolutionary processes and abiotic forcing.

Effects of allometry, productivity and lifestyle on rates and limits of body size evolution

Body size affects nearly all aspects of organismal biology, so it is important to understand the constraints and dynamics of body size evolution. Despite empirical work on the macroevolution and macroecology of minimum and maximum size, there is little general quantitative theory on rates and limits of body size evolution. We present a general theory that integrates individual productivity, the lifestyle component of the slow-fast life-history continuum, and the allometric scaling of generation time to predict a clade's evolutionary rate and asymptotic maximum body size, and the shape of macroevolutionary trajectories during diversifying phases of size evolution. We evaluate this theory using data on the evolution of clade maximum body sizes in mammals during the Cenozoic. As predicted, clade evolutionary rates and asymptotic maximum sizes are larger in more productive clades (e.g. baleen whales), which represent the fast end of the slow-fast lifestyle continuum, and smaller in less productive clades (e.g. primates). The allometric scaling exponent for generation time fundamentally alters the shape of evolutionary trajectories, so allometric effects should be accounted for in models of phenotypic evolution and interpretations of macroevolutionary body size patterns. This work highlights the intimate interplay between the macroecological and macroevolutionary dynamics underlying the generation and maintenance of morphological diversity.

Estimating the influence of the thermal environment on activity patterns of the desert woodrat (Neotoma lepida) using temperature chronologies

Environmental temperature influences the ecology and life history of animals. In habitats near the thermal range boundary, fluctuations in temperature may influence the ability of species to persist. Desert woodrats ( Neotoma lepida Thomas, 1893) occupy one of the hottest and most extreme environments in the western hemisphere, Death Valley, California, despite limited adaptations for water conservation or efficient heat dissipation. Moreover, N. lepida have a relatively low tolerance for high temperature. Thus, we hypothesized temperature might influence both the timing and the duration of activity. To test this idea, we attached iButton sensors to 56 animals over a 2-year period and recorded activity. Each sensor was set to record at 5 or 15 min intervals and stored approximately 2000 records before retrieval. We found a strong relationship between ambient temperature and onset and duration of activity, influenced by both body size and gender. Neotoma lepida did not emerge until air temperature fell below 42 °C. As daily high temperatures increased, both sexes had fewer nightly activity bouts of shorter duration. Our results suggest that activity of N. lepida is constrained during the climatically intense summer months. Animals face a trade-off between remaining in the thermal safety of the den vs. emerging to obtain resources.

Evolution. Some like it hot

A study of horse evolution illustrates the connection between environmental temperature and mammal body size.

How big should a mammal be? A macroecological look at mammalian body size over space and time

Macroecology was developed as a big picture statistical approach to the study of ecology and evolution. By focusing on broadly occurring patterns and processes operating at large spatial and temporal scales rather than on localized and/or fine-scaled details, macroecology aims to uncover general mechanisms operating at organism, population, and ecosystem levels of organization. Macroecological studies typically involve the statistical analysis of fundamental species-level traits, such as body size, area of geographical range, and average density and/or abundance. Here, we briefly review the history of macroecology and use the body size of mammals as a case study to highlight current developments in the field, including the increasing linkage with biogeography and other disciplines. Characterizing the factors underlying the spatial and temporal patterns of body size variation in mammals is a daunting task and moreover, one not readily amenable to traditional statistical analyses. Our results clearly illustrate remarkable regularities in the distribution and variation of mammalian body size across both geographical space and evolutionary time that are related to ecology and trophic dynamics and that would not be apparent without a broader perspective.

The evolutionary consequences of oxygenic photosynthesis: a body size perspective

The high concentration of molecular oxygen in Earth's atmosphere is arguably the most conspicuous and geologically important signature of life. Earth's early atmosphere lacked oxygen; accumulation began after the evolution of oxygenic photosynthesis in cyanobacteria around 3.0-2.5 billion years ago (Gya). Concentrations of oxygen have since varied, first reaching near-modern values ~600 million years ago (Mya). These fluctuations have been hypothesized to constrain many biological patterns, among them the evolution of body size. Here, we review the state of knowledge relating oxygen availability to body size. Laboratory studies increasingly illuminate the mechanisms by which organisms can adapt physiologically to the variation in oxygen availability, but the extent to which these findings can be extrapolated to evolutionary timescales remains poorly understood. Experiments confirm that animal size is limited by experimental hypoxia, but show that plant vegetative growth is enhanced due to reduced photorespiration at lower O(2):CO(2). Field studies of size distributions across extant higher taxa and individual species in the modern provide qualitative support for a correlation between animal and protist size and oxygen availability, but few allow prediction of maximum or mean size from oxygen concentrations in unstudied regions. There is qualitative support for a link between oxygen availability and body size from the fossil record of protists and animals, but there have been few quantitative analyses confirming or refuting this impression. As oxygen transport limits the thickness or volume-to-surface area ratio-rather than mass or volume-predictions of maximum possible size cannot be constructed simply from metabolic rate and oxygen availability. Thus, it remains difficult to confirm that the largest representatives of fossil or living taxa are limited by oxygen transport rather than other factors. Despite the challenges of integrating findings from experiments on model organisms, comparative observations across living species, and fossil specimens spanning millions to billions of years, numerous tractable avenues of research could greatly improve quantitative constraints on the role of oxygen in the macroevolutionary history of organismal size.

The Evolution of Maximum Body Size of Terrestrial Mammals

The extinction of dinosaurs at the Cretaceous/Paleogene (K/Pg) boundary was the seminal event that opened the door for the subsequent diversification of terrestrial mammals. Our compilation of maximum body size at the ordinal level by sub-epoch shows a near-exponential increase after the K/Pg. On each continent, the maximum size of mammals leveled off after 40 million years ago and thereafter remained approximately constant. There was remarkable congruence in the rate, trajectory, and upper limit across continents, orders, and trophic guilds, despite differences in geological and climatic history, turnover of lineages, and ecological variation. Our analysis suggests that although the primary driver for the evolution of giant mammals was diversification to fill ecological niches, environmental temperature and land area may have ultimately constrained the maximum size achieved.

Arbuscular mycorrhizal colonization reduces arsenate uptake in barley via downregulation of transporters in the direct epidermal phosphate uptake pathway

*Here, we used barley (Hordeum vulgare) grown in normal and compartmented pots to investigate sensitivity to arsenic (As) in the absence of a positive growth response to arbuscular mycorrhizas (AM). *We tested the hypothesis that upon inoculation with AM fungi downregulation of HvPht1;1 and HvPht1;2 genes (encoding high-affinity inorganic orthophosphate (P(i))-uptake systems in a direct pathway via root epidermis and root hairs) and upregulation of the AM-induced HvPht1;8 (encoding the P(i)-uptake system responsible for transfer of P(i) from the symbiotic interface to cortical cells) play a role in decreased As uptake and hence reduced As sensitivity in AM plants. *Barley did not respond, or responded negatively to colonization by Glomus intraradices in terms of growth. In terms of specific phosphorus (P) uptake (P uptake per g of root) barley was nonresponsive. There was a significant interaction between As treatment and colonization, resulting in a lower As concentration and uptake in AM compared with nonmycorrhizal (NM) plants. *The decreased uptake of As and higher P : As molar ratios in the AM barley can be explained by the operation of the AM pathway as indicated by induction of HvPht1;8 and by down-regulation of HvPht1;1 and HvPht1;2.

Mustela or Vison? Evidence for the taxonomic status of the American mink and a distinct biogeographic radiation of American weasels

The American mink's relationship to the weasels in Mustela has been uncertain. Karyological, morphological, and phylogenetic comparisons to Eurasian Mustela support placing the mink outside the genus as Neovison vison. However, genetic comparisons that incorporate other endemic American Mustela suggest the interpretation of N. vison's position to Mustela has been handicapped by biased geographic sampling. Here, we analyzed mitochondrial cytochrome-b from all weasels endemic to the Americas, including two poorly known South American species (M. felipei, M. africana), weasels native to North America (M. vison, M. frenata, M. nigripes), Mustela migrant to North America (M. erminea, M. nivalis), palearctic Mustela, and other American members of Mustelidae. Bayesian and likelihood inference methods were used to construct a phylogeny of Mustela, and relaxed Bayesian phylogenetic techniques estimated ages of divergence within the genus using priors calibrated by fossil ages. Our analyses show that the American mink and the smaller Mustela endemic to the Americas represent a distinct phylogenetic heritage apart from their Eurasian cousins, and biogeographic barriers like the Bering and Panamanian land bridges have influenced the evolutionary history of Mustela in the Americas.

No evidence for competition between arsenate and phosphate for uptake from soil by medic or barley

We investigated the effects of phosphorus (P) supply on the uptake and toxicity of arsenate (As(V)) in two plant species (Medicago truncatula and Hordeum vulgare) grown in soil/sand mixes. Our initial hypothesis was that competition between phosphate (Pi) and As(V) for uptake would be observed, and that this would be the basis for the 'protective' effect of P with respect to As toxicity, as shown in solution culture. Addition of P to the soil/sand mixes did not have major effects on water extractable As, or vice versa. We observed that toxic effects of As(V) on plant growth were ameliorated by increased P in both plant species. However, we found no evidence that increased P supply reduced specific uptake of As(V) on a molar basis, so that competition with Pi could not be the basis for the effect. A more complex mechanism of protection is indicated which might relate to different Pi transport systems being expressed at different P levels.

Arbuscular mycorrhizal inhibition of growth in barley cannot be attributed to extent of colonization, fungal phosphorus uptake or effects on expression of plant phosphate transporter genes

Here, we used phosphorus-32 (32P) labelling in compartmented pots combined with quantitative real-time polymerase chain reaction (PCR) analysis of phosphate(Pi) transporter gene expression to investigate regulation of Pi uptake pathways in barley (Hordeum vulgare), an arbuscular mycorrhizal (AM) plant that does not show strong positive growth responses to colonization.Barley was colonized well by Glomus intraradices and poorly by Glomus geosporum,but both fungi induced significant and similar growth depressions compared with non mycorrhizal controls. The lack of correlation between per cent colonization and extent of growth depression suggests that the latter is not related to carbon drain to the fungus. The contribution of the AM Pi uptake pathway for the two fungi was, in general,related to per cent colonization and expression of the AM-inducible Pi transporter gene, HvPT8, but not to plant responsiveness. Glomus intraradices contributed 48%of total plant P whereas G. geosporum contributed very little.The growth depression in plants where the AM uptake pathway was functional suggests that the contribution of the direct Pi uptake pathway via root hairs and epidermis was decreased. This decrease was not correlated with downregulation of the epidermal-expressed Pi transporter genes, HvPT1 and HvPT2. We hypothesize post-transcriptional or post-translational control of this transport process by AM colonization.

Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity

The maximum size of organisms has increased enormously since the initial appearance of life >3.5 billion years ago (Gya), but the pattern and timing of this size increase is poorly known. Consequently, controls underlying the size spectrum of the global biota have been difficult to evaluate. Our period-level compilation of the largest known fossil organisms demonstrates that maximum size increased by 16 orders of magnitude since life first appeared in the fossil record. The great majority of the increase is accounted for by 2 discrete steps of approximately equal magnitude: the first in the middle of the Paleoproterozoic Era (approximately 1.9 Gya) and the second during the late Neoproterozoic and early Paleozoic eras (0.6-0.45 Gya). Each size step required a major innovation in organismal complexity--first the eukaryotic cell and later eukaryotic multicellularity. These size steps coincide with, or slightly postdate, increases in the concentration of atmospheric oxygen, suggesting latent evolutionary potential was realized soon after environmental limitations were removed.

Structural differences in arbuscular mycorrhizal symbioses: more than 100 years after Gallaud, where next?

This review commemorates and examines the significance of the work of Isobel Gallaud more than 100 years ago that first established the existence of distinct structural classes (Arum-type and Paris-type) within arbuscular mycorrhizal (AM) symbioses. We add new information from recent publications to the previous data last collated 10 years ago to consider whether any patterns have emerged on the basis of different fungal morphology within plant species or families. We discuss: (1) possible control exerted by the fungus over AM morphology; (2) apparent lack of plant phylogenetic relationships between the classes; (3) functions of the interfaces in different structural classes in relation to nutrient transfer in particular; and (4) the occurrence of plants with both of the major classes, and with intermediate AM structures, in different plant habitats. We also give suggestions for future research to help remove uncertainties about the functional and ecological significance of differences in AM morphology. Lastly, we urge retention of the terms Arum- and Paris-type, which are now well recognised by those who study AM symbioses.

Arbuscular mycorrhizal fungi can induce the production of phytochemicals in sweet basil irrespective of phosphorus nutrition

The potential of three arbuscular mycorrhizal fungi (AMF) to enhance the production of antioxidants (rosmarinic and caffeic acids, RA and CA) was investigated in sweet basil (Ocimum basilicum). After adjusting phosphorus (P) nutrition so that P concentrations and yield were matched in AM and non-mycorrhizal (NM) plants we demonstrated that Glomus caledonium increased RA and CA production in the shoots. Glomus mosseae also increased shoot CA concentration in basil under similar conditions. Although higher P amendments to NM plants increased RA and CA concentrations, there was higher production of RA and CA in the shoots of AM plants, which was not solely due to better P nutrition. Therefore, AMF potentially represent an alternative way of promoting growth of this important medicinal herb, as natural ways of growing such crops are currently highly sought after in the herbal industry.

Uptake of oxytetracycline and its phytotoxicity to alfalfa (Medicago sativa L.)

A series of experiments were conducted in a hydroponic system to investigate the uptake of oxytetracycline (OTC) and its toxicity to alfalfa (Medicago sativa L.). OTC inhibited alfalfa shoot and root growth by up to 61% and 85%, respectively. The kinetics of OTC uptake could be well described by Michaelis-Menten equation with Vmax of 2.25 micromol g-1 fresh weight h-1, and Km of 0.036 mM. The uptake of OTC by alfalfa was strongly inhibited by the metabolic inhibitor, 2,4-DNP (2,4-dinitrophenol), at pH 3.5 and 6.0, but not by the aquaporin competitors, glycerol and Ag+. OTC uptake, however, was significantly inhibited by Hg2+, suggesting that the inhibition of influx was due to general cellular stress rather than the specific action of Hg2+ on aquaporins. Results from the present study suggested that OTC uptake into alfalfa is an energy-dependent process.

Pleistocene Rewilding: An Optimistic Agenda for Twenty‐First Century Conservation

Large vertebrates are strong interactors in food webs, yet they were lost from most ecosystems after the dispersal of modern humans from Africa and Eurasia. We call for restoration of missing ecological functions and evolutionary potential of lost North American megafauna using extant conspecifics and related taxa. We refer to this restoration as Pleistocene rewilding; it is conceived as carefully managed ecosystem manipulations whereby costs and benefits are objectively addressed on a case-by-case and locality-by-locality basis. Pleistocene rewilding would deliberately promote large, long-lived species over pest and weed assemblages, facilitate the persistence and ecological effectiveness of megafauna on a global scale, and broaden the underlying premise of conservation from managing extinction to encompass restoring ecological and evolutionary processes. Pleistocene rewilding can begin immediately with species such as Bolson tortoises and feral horses and continue through the coming decades with elephants and Holarctic lions. Our exemplar taxa would contribute biological, economic, and cultural benefits to North America. Owners of large tracts of private land in the central and western United States could be the first to implement this restoration. Risks of Pleistocene rewilding include the possibility of altered disease ecology and associated human health implications, as well as unexpected ecological and sociopolitical consequences of reintroductions. Establishment of programs to monitor suites of species interactions and their consequences for biodiversity and ecosystem health will be a significant challenge. Secure fencing would be a major economic cost, and social challenges will include acceptance of predation as an overriding natural process and the incorporation of pre-Columbian ecological frameworks into conservation strategies.

Pleistocene rewilding: an optimistic agenda for twenty-first century conservation

Large vertebrates are strong interactors in food webs, yet they were lost from most ecosystems after the dispersal of modern humans from Africa and Eurasia. We call for restoration of missing ecological functions and evolutionary potential of lost North American megafauna using extant conspecifics and related taxa. We refer to this restoration as Pleistocene rewilding; it is conceived as carefully managed ecosystem manipulations whereby costs and benefits are objectively addressed on a case-by-case and locality-by-locality basis. Pleistocene rewilding would deliberately promote large, long-lived species over pest and weed assemblages, facilitate the persistence and ecological effectiveness of megafauna on a global scale, and broaden the underlying premise of conservation from managing extinction to encompass restoring ecological and evolutionary processes. Pleistocene rewilding can begin immediately with species such as Bolson tortoises and feral horses and continue through the coming decades with elephants and Holarctic lions. Our exemplar taxa would contribute biological, economic, and cultural benefits to North America. Owners of large tracts of private land in the central and western United States could be the first to implement this restoration. Risks of Pleistocene rewilding include the possibility of altered disease ecology and associated human health implications, as well as unexpected ecological and sociopolitical consequences of reintroductions. Establishment of programs to monitor suites of species interactions and their consequences for biodiversity and ecosystem health will be a significant challenge. Secure fencing would be a major economic cost, and social challenges will include acceptance of predation as an overriding natural process and the incorporation of pre-Columbian ecological frameworks into conservation strategies.

Arsenic sequestration in iron plaque, its accumulation and speciation in mature rice plants (Oryza sativa L.)

A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order: iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain.

Arsenic sequestration in iron plaque, its accumulation and speciation in mature rice plants (Oryza sativa L.)

A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order: iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain.

Ecotypic variation in the context of global climate change: revisiting the rules

Patterns of ecotypic variation constitute some of the few 'rules' known to modern biology. Here, we examine several well-known ecogeographical rules, especially those pertaining to body size in contemporary, historical and fossil taxa. We review the evidence showing that rules of geographical variation in response to variation in the local environment can also apply to morphological changes through time in response to climate change. These rules hold at various time scales, ranging from contemporary to geological time scales. Patterns of body size variation in response to climate change at the individual species level may also be detected at the community level. The patterns underlying ecotypic variation are complex and highly context-dependent, reducing the 'predictive-power' of ecogeographical rules. This is especially true when considering the increasing impact of human activities on the environment. Nonetheless, ecogeographical rules may help interpret the likely influences of anthropogenic climate change on ecosystems. Global climate change has already influenced the body size of several contemporary species, and will likely have an even greater impact on animal communities in the future. For this reason, we highlight and emphasise the importance of museum specimens and the continued need for documenting the earth's biological diversity.

Rapid screening for major depression in post-myocardial infarction patients: an investigation using Beck Depression Inventory II items

OBJECTIVE

To determine the ability of three questions from the Beck Depression Inventory II (BDI-II) to detect major depressive disorder (MDD) in a cohort of patients hospitalised for acute myocardial infarction (MI).

DESIGN

Prospective observational study.

SETTING

Coronary care unit and cardiac step-down unit of an urban academic medical centre.

PATIENTS

131 post-MI patients within 72 h of symptom onset.

INTERVENTIONS

Patients were administered the BDI-II and participated in a structured diagnostic interview for MDD. Three individual BDI-II items (regarding sadness, loss of interest and loss of pleasure) were examined individually and in two-question combinations to determine their ability to screen for MDD.

MAIN OUTCOME MEASURES

Sensitivity, specificity, negative and positive predictive values and proportion of patients with MDD correctly identified.

RESULTS

The individual items and two-question combinations had good sensitivity (76-94%), specificity (70-88%) and negative predictive values (97-99%). Item 1 (sadness) performed the best of the individual items (48% with a positive response to the item had MDD; 3% with a negative response had MDD; over 80% of patients with MDD were correctly identified). A combination of questions about sadness and loss of interest performed best among the two-question combinations (37% with positive response had MDD v 1% with a negative response; 94% of patients with MDD were identified).

CONCLUSIONS

One to two questions regarding sadness and loss of interest serve as simple and effective screening tools for post-MI depression.

Effects of arbuscular mycorrhizal inoculation on uranium and arsenic accumulation by Chinese brake fern (Pteris vittata L.) from a uranium mining-impacted soil

A glasshouse experiment was conducted to investigate U and As accumulation by Chinese brake fern, Pteris vittata L., in association with different arbuscular mycorrhizal fungi (AMF) from a U and As contaminated soil. The soil used contains 111 mg U kg(-1) and 106 mg As kg(-1). P. vittata L. was inoculated with each of three AMF, Glomus mosseae, Glomus caledonium and Glomus intraradices. Two harvests were made during plant growth (two and three months after transplanting). Mycorrhizal colonization depressed plant growth particularly at the early stages. TF (transfer factor) values for As from soil to fronds were higher than 1.0, while those for roots were much lower. Despite the growth depressions, AM colonization had no effect on tissue As concentrations. Conversely, TF values for U were much higher for roots than for fronds, indicating that only very small fraction of U was translocated to fronds (less than 2%), regardless of mycorrhizal colonization. Mycorrhizal colonization significantly increased root U concentrations at both harvests. Root colonization with G. mosseae or G. intraradices led to an increase in TF values for U from 7 (non-inoculation control) to 14 at the first harvest. The highest U concentration of 1574 mg kg(-1) was recorded in roots colonized by G. mosseae at the second harvest. The results suggested that P. vittata in combination with appropriate AMF would play very important roles in bioremediation of contaminated environments characterized by a multi-pollution.

Arsenate (As) uptake by and distribution in two cultivars of winter wheat (Triticum aestivum L.)

Two cultivars of winter wheat (Triticum aestivum L.) (Jing 411 and Lovrin 10) were used to investigate arsenate (As) uptake and distribution in plants grown in hydroponic culture and in the soil. Results showed that without As addition, Lovrin 10 had higher biomass than Jing 411 in the soil pot experiment; in the hydroponic experiment Lovrin 10 had similar root biomass to and lower shoot biomass than Jing 411. Increasing P supply from 32 to 161 microM resulted in lower tissue As concentrations, and increasing As supply from 0 to 2,000 microM resulted in lower tissue P concentrations. Increasing P supply tended to increase shoot-to-root ratios of As concentrations, and increasing As supply tended to decrease shoot-to-root ratios of As concentrations. Both cultivars invested more in root production under P deficient conditions than under P sufficient conditions. Lovrin 10 invested more biomass production to roots than Jing 411, which might be partly responsible for higher shoot P and As concentrations and higher shoot-to-root ratios of As concentrations. Moreover, Lovrin 10 allocated less As to roots than Jing 411 and the difference disappeared with decreasing P supply.

Do iron plaque and genotypes affect arsenate uptake and translocation by rice seedlings (Oryza sativa L.) grown in solution culture?

The effects of Fe concentrations in the pretreatment solution on the induction of plaque and the differences between genotypes on arsenate uptake by and translocation within rice seedlings grown in nutrient solution in the greenhouse were investigated. After iron plaque on rice roots was induced in solutions containing 20, 40, 60, 80, and 100 mg Fe2+ l(-1), seedlings were transplanted into nutrient solution with 0.5 mg As l(-1). The formation of iron plaque was clearly visible as a reddish coating on the root surface after 12 h induction. Fe2+ concentrations in the pretreatment solution and 0.5 mg As l(-1) in the treatment solutions did not significantly affect rice growth. There was a significant correlation between the concentrations of Fe and As in iron plaque on the root surface for the three genotypes. About 75-89% of total As was concentrated in iron plaque (DCB-extracts). There were no significant differences in As concentrations in the roots between the three genotypes; however, As concentrations in shoots differed significantly between them. Arsenic concentrations in shoots were positively correlated with iron concentrations in the shoots. The results suggest that iron plaque may act as a 'buffer' for As in the rhizosphere.