Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential ω-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene Fads2 in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of Fads2 in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in Fads2 copies, indicating its key role in freshwater colonization.

An experimental forest ecosystem drought Drought is affecting many of the world’ s forested ecosystems, but it has proved challenging to develop an ecosystem-level mechanistic understanding of the ways that drought affects carbon and water fluxes through forest ecosystems. Werner et al . used an experimental approach by imposing an artificial drought on an entire enclosed ecosystem: the Biosphere 2 Tropical Rainforest in Arizona (see the Perspective by Eisenhauer and Weigelt). The authors show that ecosystem-scale plant responses to drought depend on distinct plant functional groups, differing in their water-use strategies and their position in the forest canopy. The balance of these plant functional groups drives changes in carbon and water fluxes, as well as the release of volatile organic compounds into the atmosphere. —AMS

The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. The omega‐3 long‐chain polyunsaturated fatty acids eicosapentaenoic acid (EPA; 20:5n‐3) and docosahexaenoic acid (DHA; 22:6n‐3) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer fatty acid distributions amongst major ecosystems, between habitats and amongst species within habitats. We highlight some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal and community‐level variation of resource quality. We propose a hierarchical trait‐based approach for studying the evolution of consumers’ metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to EPA and DHA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment‐dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification.

Please cite this article as: Nemiah Ladd, S., Sachs, J.P., Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia, Geochimica et Cosmochimica Acta (2015), doi: http://dx. AbstractHydrogen isotope ratios ( 2 H/ 1 H or δ 2 H) of plant leaf waxes typically covary with those of precipitation, and are therefore used as a proxy for past hydrologic variability. Mangroves present an important exception to this relationship, as salinity can strongly influence 2 H fractionation in leaf lipids. To better understand and calibrate this effect, δ 2 H values of taraxerol and n-alkanes were measured in the leaves of Rhizophora spp. (red mangroves) from three estuaries and four brackish lakes on the Micronesian islands of Pohnpei and Palau, and compared to the δ 2 H and δ 18 O values of leaf water, xylem water and surface water. Net 2 H discrimination between surface water and taraxerol increased by 0.9 ± 0.2‰ per part per thousand (ppt -1 ) over a salinity range of 1-34 ppt. Xylem water was always depleted in 2 H relative to surface water, and the magnitude of this depletion increased with salinity, which is most likely due to a combination of greater 2 H discrimination by roots during water uptake and opportunistic use of freshwater.Changes in the 2 H content of xylem water can account for up to 43% of the change in net taraxerol fractionation with salinity. Leaf water isotopes were minimally enriched relative to xylem water and there was not significant variability in leaf water enrichment with salinity, which is consistent with a Péclet-modified Craig-Gordon model of leaf water enrichment. As leaf 2 water enrichment is therefore unlikely to be responsible for increased 2 H/ 1 H fractionation in mangrove leaf lipids at elevated salinities, the majority of this signal is most likely explained either by changes in biosynthetic fractionation in response to salt stress or by salinity influenced changes in the timing of water uptake and lipid synthesis.