Match and mismatch between dietary switches and microbial partners in plant sap-feeding insects

Some animal groups associate with the same vertically transmitted microbial symbionts over extended periods of evolutionary time, punctuated by occasional symbiont switches to different microbial taxa. Here we test the oft-repeated suggestion that symbiont switches are linked with host diet changes, focusing on hemipteran insects of the suborder Auchenorrhyncha. These insects include the only animals that feed on plant xylem sap through the life cycle, as well as taxa that feed on phloem sap and plant parenchyma cells. Ancestral state reconstruction provides strong statistical support for a xylem feeding auchenorrhynchan ancestor bearing the dual symbiosis with the primary symbiont Sulcia (Bacteroidetes) and companion symbiont ‘β-Sym’ (β-proteobacteria). We identified seven dietary transitions from xylem feeding (six to phloem feeding, one to parenchyma feeding), but no reversions to xylem feeding; five evolutionary losses of Sulcia, including replacements by yeast symbionts, exclusively in phloem/parenchyma-feeding lineages; and 14–15 losses of β-Sym, including nine transitions to a different bacterial companion symbiont. Our analysis indicates that, although companion symbiont switching is not associated with shifts in host diet, Sulcia is probably required for xylem-feeding. Furthermore, the ancestral auchenorrhynchan bearing Sulcia and β-Sym probably represents the sole evolutionary origin of xylem feeding in the animal kingdom

Misconceptions on the application of biological market theory to the mycorrhizal symbiosis

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Justice in climate policy:Distributing climate costs fairly

This open access book is looking into ways to achieve just climate policy within a country. The authors of this monograph share a unique, timely and original vision: continuous support for climate policy is more likely to emerge when citizens find that the distribution of the bill for climate costs is fair. But what is a fair distribution of climate costs? This is an important question because financial costs of mitigation (reducing greenhouse gases), adaptation (adapting to climate change) and damage (compensating or compensating after weather extremes) increase significantly in the coming decades. Drawing on philosophy and ethics, the authors propose ten principles for achieving just distributions of domestic climate costs. Examples of such principles are individual responsibility, the polluter pays, greatest utility and capacity to pay. Yet what a fair distribution is, depends on, for example, political preferences and the policy issue at hand. Empirical research on designing climate policies, however, shows that distributive principles are not part of the political, policy, and public discussions. The authors therefore argue that explicit attention to principles of just distribution at the start of a policy process contributes to support for climate policy. This book provides tools to professionals and students to achieve justice in climate policy

Larger colony sizes favoured the evolution of more worker castes in ants

The size–complexity hypothesis is a leading explanation for the evolution of complex life on earth. It predicts that in lineages that have undergone a major transition in organismality, larger numbers of lower-level subunits select for increased division of labour. Current data from multicellular organisms and social insects support a positive correlation between the number of cells and number of cell types and between colony size and the number of castes. However, the implication of these results is unclear, because colony size and number of cells are correlated with other variables which may also influence selection for division of labour, and causality could be in either direction. Here, to resolve this problem, we tested multiple causal hypotheses using data from 794 ant species. We found that larger colony sizes favoured the evolution of increased division of labour, resulting in more worker castes and greater variation in worker size. By contrast, our results did not provide consistent support for alternative hypotheses regarding either queen mating frequency or number of queens per colony explaining variation in division of labour. Overall, our results provide strong support for the size–complexity hypothesis

Rechtvaardigheid in klimaatbeleid:Over de verdeling van klimaatkosten

We zijn op een nieuw punt aanbeland in het debat over klimaatbeleid. Ooit ging het over de vraag of de aarde daadwerkelijk opwarmt door menselijk toedoen. Vervolgens ging het over de vraag wat daaraan te doen valt. Nu gaat het steeds vaker over de vraag wie de kosten van klimaatmaatregelen en van klimaatschademoet betalen. De protesten van de ‘gele hesjes’ in Frankrijk hebben laten zien hoe belangrijk het is dat de verdeling van zulke klimaatkosten als rechtvaardig gezien wordt. Als dat niet het geval is, dan kan het draagvlak voor klimaatbeleid afkalven. Hoe kunnen rechtvaardige verdelingen eruit zien? Dat analyseert de Wetenschappelijke Raad voor het Regeringsbeleid (wrr) in dit rapport. De hoofdboodschap van dit rapport is dat er in klimaatbeleid stelselmatige aandacht moet zijn voor de rechtvaardigheid van verdelingen. Maatregelen dienen niet alleen beoordeeld te worden vanuit het perspectief van doelmatigheid en rechtmatigheid, maar ook vanuit het perspectief van rechtvaardigheid. Onze belangrijkste boodschap is daarom dat de mogelijke verdelingen van klimaatkosten al vooraf expliciet op tafel komen en worden doordacht. Dat helptbeleidsmakers om meer oog te krijgen voor mogelijke onbedoelde en ongewensteneveneffecten. Het leidt ook tot een meer afgewogen en transparanter politiek debat. En het zorgt ervoor dat het draagvlak voor klimaatbeleid op peil blijft. De wrr doet drie aanbevelingen hoe de overheid rechtvaardige verdelingen in het klimaatbeleid tot stand kan brengen: zorg voor (1) inhoudelijke verbreding, (2) procedurele verankering en (3) institutionele borging

Dominance and rarity in tree communities across the globe: Patterns, predictors and threats

Aim: Ecological and anthropogenic factors shift the abundances of dominant and rare tree species within local forest communities, thus affecting species composition and ecosystem functioning. To inform forest and conservation management it is important to understand the drivers of dominance and rarity in local tree communities. We answer the following research questions: (1) What are the patterns of dominance and rarity in tree communities? (2) Which ecological and anthropogenic factors predict these patterns? And (3) what is the extinction risk of locally dominant and rare tree species? Location: Global. Time period: 1990–2017. Major taxa studied: Trees. Methods: We used 1.2 million forest plots and quantified local tree dominance as the relative plot basal area of the single most dominant species and local rarity as the percentage of species that contribute together to the least 10% of plot basal area. We mapped global community dominance and rarity using machine learning models and evaluated the ecological and anthropogenic predictors with linear models. Extinction risk, for example threatened status, of geographically widespread dominant and rare species was evaluated. Results: Community dominance and rarity show contrasting latitudinal trends, with boreal forests having high levels of dominance and tropical forests having high levels of rarity. Increasing annual precipitation reduces community dominance, probably because precipitation is related to an increase in tree density and richness. Additionally, stand age is positively related to community dominance, due to stem diameter increase of the most dominant species. Surprisingly, we find that locally dominant and rare species, which are geographically widespread in our data, have an equally high rate of elevated extinction due to declining populations through large‐scale land degradation. Main conclusions: By linking patterns and predictors of community dominance and rarity to extinction risk, our results suggest that also widespread species should be considered in large‐scale management and conservation practices

Native diversity buffers against severity of non-native tree invasions

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies. Here, leveraging global tree databases, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions

Evenness mediates the global relationship between forest productivity and richness

1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions