南京直立人的高鼻梁是由于对寒冷气候的适应吗?

有人质疑南京直立人的高耸鼻梁的成因,认为高鼻梁是对寒冷和干燥气候的适应,有两篇论文被引用来作为支持。本文指出那两篇论文讨论的是鼻高,鼻宽与纬度的关系,结论是纬度较高者鼻宽较小,并没有论证高鼻梁是对寒冷和干燥气候的适应。本文还援引其他不同纬度地区人群反映鼻的不同部分向前方突出程度的资料,指出目前很难看出鼻的突出程度与气候如何相关。这些资料和寒带因纽特人的扁鼻梁与热带的Bodo化石头骨的高鼻梁的对比以及南京直立人1号头骨所在的堆积物反映温带或亚热带气候,都反对或至少是不支持高耸鼻梁是适应寒冷和干燥气候结果的观点。目前也还没有证据表明南京直立人的高鼻梁可以在东亚的人类谱系上溯源到某些曾经由于对寒冷气候的适应而具有高鼻梁的古人类。     

Adaptation to host plants may prevent rapid insect responses to climate change

We must consider the role of multitrophic interactions when examining species' responses to climate change. Many plant species, particularly trees, are limited in their ability to shift their geographic ranges quickly under climate change. Consequently, for herbivorous insects, geographic mosaics of host plant specialization could prohibit range shifts and adaptation when insects become separated from suitable host plants. In this study, we examined larval growth and survival of an oak specialist butterfly (Erynnis propertius) on different oaks (Quercus spp.) that occur across its range to determine if individuals can switch host plants if they move into new areas under climate change. Individuals from Oregon and northern California, USA that feed on Q. garryana and Q. kelloggii in the field experienced increased mortality on Q. agrifolia, a southern species with low nutrient content. In contrast, populations from southern California that normally feed on Q. agrifolia performed well on Q. agrifolia and Q. garryana and poorly on the northern, high elevation Q. kelloggii. Therefore, colonization of southern E. propertius in higher elevations and some northern locales may be prohibited under climate change but latitudinal shifts to Q. garryana may be possible. Where shifts are precluded due to maladaptation to hosts, populations may not accrue warm‐adapted genotypes. Our study suggests that, when interacting species experience asynchronous range shifts, historical local adaptation may preclude populations from colonizing new locales under climate change.     

Climate shaped the worldwide distribution of human mitochondrial DNA sequence variation

There is an ongoing discussion in the literature on whether human mitochondrial DNA (mtDNA) evolves neutrally. There have been previous claims for natural selection on human mtDNA based on an excess of non-synonymous mutations and higher evolutionary persistence of specific mitochondrial mutations in Arctic populations. However, these findings were not supported by the reanalysis of larger datasets. Using a geographical framework, we perform the first direct test of the relative extent to which climate and past demography have shaped the current spatial distribution of mtDNA sequences worldwide. We show that populations living in colder environments have lower mitochondrial diversity and that the genetic differentiation between pairs of populations correlates with difference in temperature. These associations were unique to mtDNA; we could not find a similar pattern in any other genetic marker. We were able to identify two correlated non-synonymous point mutations in the ND3 and ATP6 genes characterized by a clear association with temperature, which appear to be plausible targets of natural selection producing the association with climate. The same mutations have been previously shown to be associated with variation in mitochondrial pH and calcium dynamics. Our results indicate that natural selection mediated by climate has contributed to shape the current distribution of mtDNA sequences in humans.     

The role of climate in human mitochondrial DNA evolution: a reappraisal

Previous studies have proposed that selection has been involved in the differentiation of human mitochondrial DNA (mtDNA) and climate was the main driving force. This viewpoint, however, gets no support from the subsequent studies and remains controversial thus far. To clarify this issue, a total of 237 complete mtDNA sequences belonging to autochthonous lineages from South Asia, Oceania, and East Asia were collected to seek for the imprint of selection. Based on nonsynonymous (N) and synonymous (S) substitutions analysis, our results confirmed that purifying selection was the predominant force during the evolution of human mtDNA. However, no significant and extensive difference was detected among these three regions, which did not support the climate adaptation hypothesis but preferred random genetic drift to be the main factor in shaping the current landscape of human mtDNA, at least those from Asian and Oceanian regions.     

Mitochondrial DNA inherited variants are associated with successful aging and longevity in humans.

Mitochondrial DNA (mtDNA) is characterized by high variability, maternal inheritance, and absence of recombination. Studies of human populations have revealed ancestral associated polymorphisms whose combination defines groups of mtDNA types (haplogroups) that are currently used to reconstruct human evolution lineages. We used such inherited mtDNA markers to compare mtDNA population pools between a sample of individuals selected for successful aging and longevity (212 subjects older than 100 years and in good clinical condition) and a sample of 275 younger individuals (median age 38 years) carefully matched as to sex and geographic origin (northern and southern Italy). All nine haplogroups that are typical of Europeans were found in both samples, but male centenarians emerged in northern Italy as a particular sample: 1) mtDNA haplogroup frequency distribution was different between centenarians and younger individuals (P=0.017 by permutation tests); and 2) the frequency of the J haplogroup was notably higher in centenarians than in younger individuals (P=0.0052 by Fisher exact test). Since haplogroups are defined on the basis of inherited variants, these data show that mtDNA inherited variability could play a role in successful aging and longevity.     

Extreme climate,rather than population history,explains mid‐facial morphology of northern asians

Previous studies have examined mid‐facial cold adaptation among either widely dispersed and genetically very diverse groups of humans isolated for tens of thousands of years, or among very closely related groups spread over climatically different regions. Here we present a study of one East Asian and seven North Asian populations in which we examine the evidence for convergent adaptations of the mid‐face to a very cold climate. Our findings indicate that mid‐facial morphology is strongly associated with climatic variables that contrast the temperate climate of East Asians and the very cold and dry climate of North Asians. This is also the case when either maxillary or nasal cavity measurements are considered alone. The association remains significant when mtDNA distances among populations are taken into account. The morphological contrasts between populations are consistent with physiological predictions and prior studies of mid‐facial cold adaptation in more temperate regions, but among North Asians there appear to be some previously undescribed morphological features that might be considered as adaptive to extreme cold. To investigate this further, analyses of the seven North Asian populations alone suggest that mid‐facial morphology remains strongly associated with climate, particularly winter precipitation, contrasting coastal Arctic and continental climates. However, the residual covariation among North Asian mid‐facial morphology and climate when genetic distances are considered, is not significant. These findings point to modern adaptations to extreme climate that might be relevant to our understanding of the mid‐facial morphology of fossil hominins that lived during glaciations. Am J Phys Anthropol 153:449–462, 2014. © 2013 Wiley Periodicals, Inc.     

Is Gene Flow Promoting the Reversal of Pleistocene Divergence in the Mountain Chickadee (Poecile gambeli)?

The Pleistocene glacial cycles left a genetic legacy on taxa throughout the world; however, the persistence of genetic lineages that diverged during these cycles is dependent upon levels of gene flow and introgression. The consequences of secondary contact among taxa may reveal new insights into the history of the Pleistocene’s genetic legacy. Here, we use phylogeographic methods, using 20 nuclear loci from regional populations, to infer the consequences of secondary contact following divergence in the Mountain Chickadee (Poecile gambeli). Analysis of nuclear data identified two geographically-structured genetic groups, largely concordant with results from a previous mitochondrial DNA (mtDNA) study. Additionally, the estimated multilocus divergence times indicate a Pleistocene divergence, and are highly concordant with mtDNA. The previous mtDNA study showed a paucity of sympatry between clades, while nuclear patterns of gene flow show highly varied patterns between populations. The observed pattern of gene flow, from coalescent-based analyses, indicates southern populations in both clades exhibit little gene flow within or between clades, while northern populations are experiencing higher gene flow within and between clades. If this pattern were to persist, it is possible the historical legacy of Pleistocene divergence may be preserved in the southern populations only, and the northern populations would become a genetically diverse hybrid species.     

PHYLOGEOGRAPHY OF THE SARDINES (SARDINOPS SPP.): ASSESSING BIOGEOGRAPHIC MODELS AND POPULATION HISTORIES IN TEMPERATE UPWELLING ZONES

Sardines (Sardinops spp.) occupy temperate upwelling zones in the coastal regions of the Indian and Pacific Oceans, including locations in Japan, California, Chile, Australia, and South Africa. East and West Pacific populations are separated by vast expanses of open ocean, and northern and southern hemisphere populations are separated by tropical waters which are lethal to sardines. The relative importance of these barriers has been the focus of a longstanding debate between vicariance and dispersal schools in biogeography. Comparisons of a 500 bp fragment of the mitochondrial (mt) DNA control region reveal strong geographic structuring of mtDNA lineages but shallow divergence both within and between regional populations. Regional populations are related to one another in a stepping-stone pattern, the apparent result of a series of Pleistocene dispersal events around the continental margins of the Indian-Pacific Basin. These mtDNA data, combined with an electrophoretic survey of variability at 34 nuclear loci (Grant and Leslie 1996), indicate that the five regional forms of Sardinops (considered separate taxa by most authorities) probably diverged within 500,000 years BP, a much shorter timeframe than predicted by vicariance models based on plate tectonics. High mtDNA haplotype diversity, coupled with an excess of rare alleles in the protein electrophoretic dataset, may indicate exponential growth from a small ancestral population. The mtDNA and allozyme data are concordant with climate records and fossil evidence in portraying regional populations as recent, unstable, and ephemeral. Regional populations of sardines have probably been extinguished and recolonized over short evolutionary timescales in response to changes in climate and the oceanography of coastal upwelling zones.     

Mitochondrial DNA Variant in COX1 Subunit Significantly Alters Energy Metabolism of Geographically Divergent Wild Isolates in Caenorhabditis elegans

Mitochondrial DNA (mtDNA) sequence variation can influence the penetrance of complex diseases and climatic adaptation. While studies in geographically defined human populations suggest that mtDNA mutations become fixed when they have conferred metabolic capabilities optimally suited for a specific environment, it has been challenging to definitively assign adaptive functions to specific mtDNA sequence variants in mammals. We investigated whether mtDNA genome variation functionally influences Caenorhabditis elegans wild isolates of distinct mtDNA lineages and geographic origins. We found that, relative to N2 (England) wild-type nematodes, CB4856 wild isolates from a warmer native climate (Hawaii) had a unique p.A12S amino acid substitution in the mtDNA-encoded COX1 core catalytic subunit of mitochondrial complex IV (CIV). Relative to N2, CB4856 worms grown at 20 °C had significantly increased CIV enzyme activity, mitochondrial matrix oxidant burden, and sensitivity to oxidative stress but had significantly reduced lifespan and mitochondrial membrane potential. Interestingly, mitochondrial membrane potential was significantly increased in CB4856 grown at its native temperature of 25 °C. A transmitochondrial cybrid worm strain, chpIR (M, CB4856 > N2), was bred as homoplasmic for the CB4856 mtDNA genome in the N2 nuclear background. The cybrid strain also displayed significantly increased CIV activity, demonstrating that this difference results from the mtDNA-encoded p.A12S variant. However, chpIR (M, CB4856 > N2) worms had significantly reduced median and maximal lifespan relative to CB4856, which may relate to their nuclear–mtDNA genome mismatch. Overall, these data suggest that C. elegans wild isolates of varying geographic origins may adapt to environmental challenges through mtDNA variation to modulate critical aspects of mitochondrial energy metabolism.     

ADAPTATION TO DIFFERENT RATES OF ENVIRONMENTAL CHANGE IN CHLAMYDOMONAS

We investigate how different rates of environmental change affect adaptive outcomes and dynamics by selecting Chlamydomonas populations for over 200 generations in environments where the rate of change varies. We find that slower rates of environmental change result in end populations that grow faster and pay a lower cost of adaptation than populations that adapt to a sudden change of the same magnitude. We detected partial selective sweeps in adapting populations by monitoring changes in marker frequency in each population. Although populations adapting to a sudden environmental change showed evidence of mutations of large effect segregating early on, populations adapting to slow rates of change showed patterns that were consistent with mutations of relatively small effect occurring at less predictable times. This work suggests that rates of environmental change may fundamentally alter adaptive dynamics and outcomes of adaptation by changing the size and timing of fitness increases. We suggest that using mutations of smaller effect during adaptation may result in lower levels of pleiotropy and historical constraints, which could in turn result in higher fitness by the end of the experiment.     

Topographic,latitudinal and climatic distribution of Pinus coulteri: geographic range limits are not at the edge of the climate envelope

With changing climate, many species are projected to move poleward or to higher elevations to track suitable climates. The prediction that species will move poleward assumes that geographically marginal populations are at the edge of the species' climatic range. We studied Pinus coulteri from the center to the northern (poleward) edge of its range, and examined three scenarios regarding the relationship between the geographic and climatic margins of a species' range. We used herbarium and iNaturalist.org records to identify P. coulteri sites, generated a species distribution model based on temperature, precipitation, climatic water deficit, and actual evapotranspiration, and projected suitability under future climate scenarios. In fourteen populations from the central to northern portions of the range, we conducted field studies and recorded elevation, slope and aspect (to estimate solar insolation) to examine relationships between local and regional distributions. We found that northern populations of P. coulteri do not occupy the cold or wet edge of the species' climatic range; mid‐latitude, high elevation populations occupy the cold margin. Aspect and insolation of P. coulteri populations changed significantly across latitudes and elevations. Unexpectedly, northern, low‐elevation stands occupy north‐facing aspects and receive low insolation, while central, high‐elevation stands grow on more south‐facing aspects that receive higher insolation. Modeled future climate suitability is projected to be highest in the central, high elevation portion of the species range, and in low‐lying coastal regions under some scenarios, with declining suitability in northern areas under most future scenarios. For P. coulteri, the lack of high elevation habitat combined with a major dispersal barrier may limit northward movement in response to a warming climate. Our analyses demonstrate the importance of distinguishing geographically vs. climatically marginal populations, and the importance of quantitative analysis of the realized climate space to understand species range limits.     

Mitochondrial DNA mutation and the ageing process: bioenergy and pharmacological intervention.

A comprehensive hypothesis concerning the contribution of mitochondrial DNA (mtDNA) mutations to the human ageing process is reviewed and the implications for cellular bioenergy loss and pharmacological therapy are considered. The central idea is that random mutations in the population of mtDNA molecules of each cell occur throughout life, and that this is a major contributor to the gradual loss of cellular bioenergy capacity within tissues and organs, associated with general senescence and diseases of ageing. An elaboration of four major aspects of the general proposition, together with relevant supporting data, is presented. (1) An extensive array of deletions in mtDNA of many tissues of humans and other mammals has been observed to occur in an age-related manner. (2) The preservation and selection of fully functional mtDNA molecules in the female germ line cells is proposed to occur via a human mtDNA cycle, in which selective amplification of a limited number of mtDNA templates occurs during oocyte development. This proposal explains the endowment of normal neonates with a mtDNA complement minimally contaminated by damaged mtDNA molecules. The phenomena of maternal inheritance and rapid fixation of sequence variants of mtDNA in mammals, as well as selection of cells based on mitochondrial function, are taken into account. (3) Tissue bioenergy mosaics result from accumulated mtDNA damage during ageing, representing different rates of cellular bioenergy loss within individual cells of a tissue. The random segregation of mtDNA during cell division will also further contribute to the tissue energy mosaic. Cells unable to meet their particular bioenergy demand will become non-functional, leading to cell death; the bioenergy threshold is different for the various cell types in the tissues of the body. (4) In order to bioenergetically resuscitate cells and tissues suffering from impaired mitochondrial functions as a result of the ageing process, we propose that redox compounds may be used therapeutically in the pharmacological configurations of a by-pass strategy or as a redox sink therapy. The role of these compounds is to maintain at least part of the mitochondrial respiratory chain function (by-pass) as well as to maintain adequate levels of cellular NAD+ (redox sink) for ATP synthesis, predominantly by the cytosolic glycolytic pathway, with some contribution from mitochondrial oxidative phosphorylation.     

Quantifying the impact of gene flow on phenotype-environment mismatch: a demonstration with the scarlet monkeyflower Mimulus cardinalis

Geographic range margins offer testing grounds for limits to adaptation. If range limits are concordant with niche limits, range expansions require the evolution of new phenotypes that can maintain populations beyond current range margins. However, many species' range margins appear static over time, suggesting limits on the ability of marginal populations to evolve appropriate phenotypes. A potential explanation is the swamping gene flow hypothesis, which posits that asymmetrical gene flow from large, well-adapted central populations prevents marginal populations from locally adapting. We present an empirical framework for combining gene flow, environment, and fitness-related phenotypes to infer the potential for maladaptation, and we demonstrate its application using the scarlet monkeyflower Mimulus cardinalis. We grew individuals sampled from populations on a latitudinal transect under varied temperatures and determined the phenotypic deviation (PD), the mismatch between phenotype and local environment. We inferred gene flow among populations and predicted that populations receiving the most temperature- or latitude-weighted immigration would show the greatest PD and that these populations were likely marginal. We found asymmetrical gene flow from central to marginal populations. Populations with more latitude-weighted immigration had significantly greater PD but were not necessarily marginal. Gene flow may limit local adaptation in this species, but swamping gene flow is unlikely to explain its northern range limit.     

Evidence for parallel adaptation to climate across the natural range of Arabidopsis thaliana

How organisms adapt to different climate habitats is a key question in evolutionary ecology and biological conservation. Species distributions are often determined by climate suitability. Consequently, the anthropogenic impact on earth's climate is of key concern to conservation efforts because of our relatively poor understanding of the ability of populations to track and evolve to climate change. Here, we investigate the ability of Arabidopsis thaliana to occupy climate space by quantifying the extent to which different climate regimes are accessible to different A. thaliana genotypes using publicly available data from a large‐scale genotyping project and from a worldwide climate database. The genetic distance calculated from 149 single‐nucleotide polymorphisms (SNPs) among 60 lineages of A. thaliana was compared to the corresponding climate distance among collection localities calculated from nine different climatic factors. A. thaliana was found to be highly labile when adapting to novel climate space, suggesting that populations may experience few constraints when adapting to changing climates. Our results also provide evidence of a parallel or convergent evolution on the molecular level supporting recent generalizations regarding the genetics of adaptation.     

Phylogeography of the black fly Simulium tani (Diptera: Simuliidae) from Thailand as inferred from mtDNA sequences

Intraspecific phylogeography has been used widely as a tool to infer population history. However, little attention has been paid to Southeast Asia despite its importance in terms of biodiversity. Here we used the cytochrome oxidase I gene of mitochondrial DNA (mtDNA) for a phylogeographic study of 147 individuals of the black fly Simulium tani from Thailand. The mtDNA revealed high genetic differentiation between the major geographical regions of north, east and central/south Thailand. Mismatch distributions indicate population expansions during the mid-Pleistocene and the late Pleistocene suggesting that current population structure and diversity may be due in part to the species' response to Pleistocene climatic fluctuations. The genealogical structure of the haplotypes, high northern diversity and maximum-likelihood inference of historical migration rates, suggest that the eastern and central/southern populations originated from northern populations in the mid-Pleistocene. Subsequently, the eastern region had had a largely independent history but the central/southern population may be largely the result of recent (c. 100,000 years ago) expansion, either from the north again, or from a relictual population in the central region. Cytological investigation revealed that populations from the south and east have two overlapping fixed chromosomal inversions. Since these populations also share ecological characteristics it suggests that inversions are involved in ecological adaptation. In conclusion both contemporary and historical ecological conditions are playing an important role in determining population genetic structure and diversity.     

Cold adaptive thermogenesis in small mammals from different geographical zones of China

The mechanisms of thermogenesis and thermoregulation were studied in the tree shrew (Tupaia belangeri) and greater vole (Eothenomys miletus) of the subtropical region, and Brandt's vole (Microtus brandti), Mongolian gerbil (Meriones unguiculatus), Daurian ground squirrel (Spermophilus dauricus) and plateau pika (Ochotona curzoniae) of the northern temperate zone. Resting metabolic rate (RMR) and non-shivering thermogenesis (NST) increased significantly in T. belangeri, E. miletus, M. brandti and M. unguiculatus after cold acclimation (4 degrees C) for 4 weeks. In T. belangeri, the increase in RMR and thermogenesis at liver cellular level were responsible for enhancing the capacity of enduring cold stress, and homeothermia was simultaneously extended. Stable body temperature in M. brandti, E. miletus, M. unguiculatus and O. curzoniae was maintained mainly through increase in NST, brown adipose tissue (BAT) mass and its mitochondrial protein content, and the upregulation of uncoupling protein (UCP1) mRNA, as well as enhancement of the activity of cytochrome C oxidase, alpha-glycerophosphate oxidase and T(4) 5'-deiodinase in BAT mitochondria. The RMR in O. curzoniae and euthermic S. dauricus was not changed, while NST significantly increased during cold exposure; the former maintained their stable body temperature and mass, while body temperature in the latter declined by 4.8 degrees C. The serum T(3) concentration or ratio of T(3)/T(4) in all the species was enhanced after cold acclimation. Results indicated that: (1) the adaptive mechanisms of T. belangeri residing in the subtropical region to cold are primarily by increasing RMR and secondly by increasing NST, and the mechanisms of thermogenesis are similar to those in tropical mammals; (2) in small mammals residing in northern regions, the adaptation to cold is chiefly to increase NST; (3) the mechanism of cold-induced thermogenesis in E. miletus residing in subtropical and high mountain regions is similar to that in the north; (4) a low RMR in warm environments and peak RMR and NST in cold environments enabled M. unguiculatus to tolerate a semi-desert climate; (5) O. curzoniae has unusually high RMR and high NST, acting mainly via increasing NST to adapt to extreme cold of the Qinghai-Tibet Plateau; (6) the adaptation of euthermic S. dauricus to cold is due to an increase in NST and a relaxed homeothermia; and lastly (7) the thyroid hormone is involved in the regulation of cold adaptive thermogenesis in all the species studied.     

Adaptation strategies to climate change in marine systems

The world's oceans are highly impacted by climate change and other human pressures, with significant implications for marine ecosystems and the livelihoods that they support. Adaptation for both natural and human systems is increasingly important as a coping strategy due to the rate and scale of ongoing and potential future change. Here, we conduct a review of literature concerning specific case studies of adaptation in marine systems, and discuss associated characteristics and influencing factors, including drivers, strategy, timeline, costs, and limitations. We found ample evidence in the literature that shows that marine species are adapting to climate change through shifting distributions and timing of biological events, while evidence for adaptation through evolutionary processes is limited. For human systems, existing studies focus on frameworks and principles of adaptation planning, but examples of implemented adaptation actions and evaluation of outcomes are scarce. These findings highlight potentially useful strategies given specific social–ecological contexts, as well as key barriers and specific information gaps requiring further research and actions.     

Ancient DNA Reveals That the Genetic Structure of the Northern Han Chinese Was Shaped Prior to 3,000 Years Ago

The Han Chinese are the largest ethnic group in the world, and their origins, development, and expansion are complex. Many genetic studies have shown that Han Chinese can be divided into two distinct groups: northern Han Chinese and southern Han Chinese. The genetic history of the southern Han Chinese has been well studied. However, the genetic history of the northern Han Chinese is still obscure. In order to gain insight into the genetic history of the northern Han Chinese, 89 human remains were sampled from the Hengbei site which is located in the Central Plain and dates back to a key transitional period during the rise of the Han Chinese (approximately 3,000 years ago). We used 64 authentic mtDNA data obtained in this study, 27 Y chromosome SNP data profiles from previously studied Hengbei samples, and genetic datasets of the current Chinese populations and two ancient northern Chinese populations to analyze the relationship between the ancient people of Hengbei and present-day northern Han Chinese. We used a wide range of population genetic analyses, including principal component analyses, shared mtDNA haplotype analyses, and geographic mapping of maternal genetic distances. The results show that the ancient people of Hengbei bore a strong genetic resemblance to present-day northern Han Chinese and were genetically distinct from other present-day Chinese populations and two ancient populations. These findings suggest that the genetic structure of northern Han Chinese was already shaped 3,000 years ago in the Central Plain area.     

Range margin populations show high climate adaptation lags in European trees

How populations of long‐living species respond to climate change depends on phenotypic plasticity and local adaptation processes. Marginal populations are expected to have lags in adaptation (i.e. differences between the climatic optimum that maximizes population fitness and the local climate) because they receive pre‐adapted alleles from core populations preventing them from reaching a local optimum in their climatically marginal habitat. Yet, whether adaptation lags in marginal populations are a common feature across phylogenetically and ecologically different species and how lags can change with climate change remain unexplored. To test for range‐wide patterns of phenotypic variation and adaptation lags of populations to climate, we (a) built model ensembles of tree height accounting for the climate of population origin and the climate of the site for 706 populations monitored in 97 common garden experiments covering the range of six European forest tree species; (b) estimated populations' adaptation lags as the differences between the climatic optimum that maximizes tree height and the climate of the origin of each population; (c) identified adaptation lag patterns for populations coming from the warm/dry and cold/wet margins and from the distribution core of each species range. We found that (a) phenotypic variation is driven by either temperature or precipitation; (b) adaptation lags are consistently higher in climatic margin populations (cold/warm, dry/wet) than in core populations; (c) predictions for future warmer climates suggest adaptation lags would decrease in cold margin populations, slightly increasing tree height, while adaptation lags would increase in core and warm margin populations, sharply decreasing tree height. Our results suggest that warm margin populations are the most vulnerable to climate change, but understanding how these populations can cope with future climates depend on whether other fitness‐related traits could show similar adaptation lag patterns.     

Inferring temperature adaptation from thermal performance curves of somatic growth rate: The importance of growth measurements and mortality

When comparing somatic growth thermal performance curves (TPCs), higher somatic growth across experimental temperatures is often observed for populations originating from colder environments. Such countergradient variation has been suggested to represent adaptation to seasonality, or shorter favourable seasons in colder climates. Alternatively, populations from cold climates may outgrow those from warmer climates at low temperature, and vice versa at high temperature, representing adaptation to temperature. Using modelling, we show that distinguishing between these two types of adaptation based on TPCs requires knowledge about (i) the relationship between somatic growth rate and population growth rate, which in turn depends on the scale of somatic growth (absolute or proportional), and (ii) the relationship between somatic growth rate and mortality rate in the wild. We illustrate this by quantifying somatic growth rate TPCs for three populations of Daphnia magna where population growth scales linearly with proportional somatic growth. For absolute somatic growth, the northern population outperformed the two more southern populations across temperatures, and more so at higher temperatures, consistent with adaptation to seasonality. In contrast, for the proportional somatic growth TPCs, and hence population growth rate, TPCs tended to converge towards the highest temperatures. Thus, if the northern population pays an ecological mortality cost of rapid growth in the wild, this may create crossing population growth TPCs consistent with adaptation to temperature. Future studies within this field should be more explicit in how they extrapolate from somatic growth in the lab to fitness in the wild.