Most ectothermic organisms mature at smaller body sizes when reared in warmer conditions. This phenotypically plastic response, known as the "temperature-size rule" (TSR), is one of the most taxonomically widespread patterns in biology. However, the TSR remains a longstanding life-history puzzle for which no dominant driver has been found. We propose that oxygen supply plays a central role in explaining the magnitude of ectothermic temperature-size responses. Given the much lower oxygen availability and greater effort required to increase uptake in water vs. air, we predict that the TSR in aquatic organisms, especially larger species with lower surface area-body mass ratios, will be stronger than in terrestrial organisms. We performed a meta-analysis of 1,890 body mass responses to temperature in controlled experiments on 169 terrestrial, freshwater, and marine species. This reveals that the strength of the temperature-size response is greater in aquatic than terrestrial species. In animal species of ∼100 mg dry mass, the temperature-size response of aquatic organisms is 10 times greater than in terrestrial organisms (−5.0%°C −1 vs.). Moreover, although the size response of small (<0.1 mg dry mass) aquatic and terrestrial species is similar, increases in species size cause the response to become increasingly negative in aquatic species, as predicted, but on average less negative in terrestrial species. These results support oxygen as a major driver of temperaturesize responses in aquatic organisms. Further, the environment-dependent differences parallel latitudinal body size clines, and will influence predicted impacts of climate warming on food production, community structure, and food-web dynamics.physiology | aerobic scope | scaling | plasticity E ctothermic organisms, which comprise over 99% of species, usually mature at a smaller body size when reared in warmer conditions (1-3). This response, called the "temperature-size rule" (TSR) (1, 2), is one of the most widespread patterns in biology (4, 5) and is found in organisms as diverse as bacteria, protists, invertebrates, plants, and ectothermic vertebrates (1, 6). The TSR contributes to reduced crop yields in warm years (7), and accords with the recently described ecological response of declining body size associated with global warming (8, 9). Despite the widespread importance of both temperature and body size in ecosystem functioning (10), the effect of temperature on organism size remains poorly understood (5), with no dominant driver having been identified (4, 5, 11).To reveal the major influences on temperature-size responses across the whole of the ectotherms, analysis of the quantitative variation in body size responses among all taxa and environments is required. So far, many size-and temperature-dependent influences on growth, reproduction, and survival have been proposed to explain the variation in size responses to temperature, but no dominant cause or mechanism has been confirmed (1-6). No systematic differences in the strength of the TSR, for e...

Decline-diseases are complex and becoming increasingly problematic to tree health globally. Acute Oak Decline (AOD) is characterized by necrotic stem lesions and galleries of the bark-boring beetle, Agrilus biguttatus, and represents a serious threat to oak. Although multiple novel bacterial species and Agrilus galleries are associated with AOD lesions, the causative agent(s) are unknown. The AOD pathosystem therefore provides an ideal model for a systems-based research approach to address our hypothesis that AOD lesions are caused by a polymicrobial complex. Here we show that three bacterial species, Brenneria goodwinii, Gibbsiella quercinecans and Rahnella victoriana, are consistently abundant in the lesion microbiome and possess virulence genes used by canonical phytopathogens that are expressed in AOD lesions. Individual and polyspecies inoculations on oak logs and trees demonstrated that B. goodwinii and G. quercinecans cause tissue necrosis and, in combination with A. biguttatus, produce the diagnostic symptoms of AOD. We have proved a polybacterial cause of AOD lesions, providing new insights into polymicrobial interactions and tree disease. This work presents a novel conceptual and methodological template for adapting Koch’s postulates to address the role of microbial communities in disease.

Growth and development rates are fundamental to all living organisms. In a warming world, it is important to determine how these rates will respond to increasing temperatures. It is often assumed that the thermal responses of physiological rates are coupled to metabolic rate and thus have the same temperature dependence. However, the existence of the temperature-size rule suggests that intraspecific growth and development are decoupled. Decoupling of these rates would have important consequences for individual species and ecosystems, yet this has not been tested systematically across a range of species. We conducted an analysis on growth and development rate data compiled from the literature for a well-studied group, marine pelagic copepods, and use an information-theoretic approach to test which equations best describe these rates. Growth and development rates were best characterized by models with significantly different parameters: development has stronger temperature dependence than does growth across all life stages. As such, it is incorrect to assume that these rates have the same temperature dependence. We used the best-fit models for these rates to predict changes in organism mass in response to temperature. These predictions follow a concave relationship, which complicates attempts to model the impacts of increasing global temperatures on species body size.

Summary1. The temperature-size rule (TSR) is a widespread phenomenon, which describes the phenotypic plastic response of species' size to temperature: individuals reared at colder temperatures mature as larger adults than at warmer temperatures. 2. The TSR is driven by an unequal thermal response of growth and development rates. However, we currently lack an understanding of how these rates change through ontogeny and their decoupling. Further, we do not know how this decoupling varies across generations. 3. Using the brine shrimp Artemia franciscana as a model, we examine growth and development rates through ontogeny at different temperatures across two generations. 4. The slopes of natural-logged weight-specific growth rates against temperature are steeper in earlier than later larval stages, indicating their greater temperature dependence, whereas development rates maintain the same temperature dependence across life stages. An inverse TSR is generated in early larval stages; the typical TSR (smaller size at warmer temperatures) is only established later in ontogeny. 5. Phase-specific temperature dependence of growth and development rates is not significantly different across the 1st and 2nd generation, suggesting the TSR is primarily a within-generation outcome. 6. Ontogenetic size responses in Artemia are compared to other crustacean species to identify patterns within this subphylum. Data for a range of crustaceans follow the same ontogenetic pattern: early larval stages show an inverse or no TSR, with TSR being only established in later stages. Adults often, but not always, show the greatest response.

Summary1. The 'temperature-size rule' (TSR) is a widely observed phenomenon within ectothermic species: individuals reared at lower temperatures grow more slowly, but are larger as adults than individuals reared at warmer temperatures. Although the TSR is common and of widespread ecological importance, it is not known whether there is a general physiological mechanism causing the TSR or even if species share a similar pattern of thermal response across ontogeny. 2. We constructed a conceptual model to show that binary division forces growth (g) and development (D) rates to return to a fixed ratio in unicellular organisms exposed to a change in temperature. After a period of decoupling during thermal acclimation, these rates must be restored to maintain a fixed ratio of adult:progeny size. However, the relationship between adult and progeny size need not be fixed in multicellular organisms at different temperatures, and hence growth and development rates need not have a fixed ratio either. 3. We conducted a meta-analysis on data of metazoan ontogenetic responses to temperature which demonstrates that adult size shows a much stronger temperature-size response than progeny size, and reveals variation in size response among other life cycle phases. 4. This study shows fundamental differences in the operation of the TSR in unicellular and multicellular organisms, suggesting that a general physiological mechanism causing the TSR is unlikely. Our findings also reveal the value of analysing shifts in size through the life cycle and across generations: these will yield a more complete quantitative description of how, and potentially provide clues to why, body size responds to temperature.

Forests and woodlands worldwide are being severely impacted by invasive Phytophthora species, with initial outbreaks in some cases occurring on host trees located in public parks and gardens. These highly disturbed sites with diverse planting practices may indeed act as harbours for invasive Phytophthora pathogens which are particularly well adapted to surviving in soil. High throughput Illumina sequencing was used to analyse Phytophthora species diversity in soil samples collected from 14 public garden/amenity woodland sites in northern Britain. Bioinformatic analyses revealed some limitations to using internal transcribed spacer as the barcode region; namely reporting of false positives and ambiguous species matches. Taking this into account, 35 distinct sequences were amplified across the sites, corresponding to 23 known Phytophthora species as well as twelve oomycete sequences with no match to any known Phytophthora species. Phytophthora pseudosyringae and P. austrocedri, both of which cause serious damage to trees and are regarded as fairly recent introductions to Britain, were the two most abundant Phytophthora species detected. There was no evidence that any of the detected Phytophthora species were more associated with any one type of host, healthy or otherwise. This study has demonstrated the ubiquity and diversity of Phytophthora species endemic in highly managed, extensively planted soil environments in Britain. Suggested improvements to the methodology and the practical implications of the findings in terms of mitigating Phytophthora spread and impact are discussed.

The temperature-size rule (TSR) is an intraspecific phenomenon describing the phenotypic plastic response of an organism size to the temperature: individuals reared at cooler temperatures mature to be larger adults than those reared at warmer temperatures. The TSR is ubiquitous, affecting &gt;80% species including uni- and multicellular groups. How the TSR is established has received attention in multicellular organisms, but not in unicells. Further, conceptual models suggest the mechanism of size change to be different in these two groups. Here, we test these theories using the protist Cyclidium glaucoma. We measure cell sizes, along with population growth during temperature acclimation, to determine how and when the temperature-size changes are achieved. We show that mother and daughter sizes become temporarily decoupled from the ratio 2:1 during acclimation, but these return to their coupled state (where daughter cells are half the size of the mother cell) once acclimated. Thermal acclimation is rapid, being completed within approximately a single generation. Further, we examine the impact of increased temperatures on carrying capacity and total biomass, to investigate potential adaptive strategies of size change. We demonstrate no temperature effect on carrying capacity, but maximum supported biomass to decrease with increasing temperature.

The devil is in the detail: Metabarcoding of arthropods provides a sensitive 2 measure of biodiversity response to forest stand composition compared with 3 surrogate measures of biodiversity 4 5