The role of ultraviolet coloration in intrasexual interactions in a colonial fish
Anne C.Sabol, Jennifer K. Hellmann, Suzanne M.Gray, Ian M.Hamilton. 2017. Animal Behaviour. 131: 99-106. https://doi.org/10.1016/j.anbehav.2017.06.027
Ultraviolet (UV) coloration varies drastically across species and likely plays fundamentally different roles in facilitating social communication depending on the ecological or social context. While it is well known that UV coloration serves important social functions in species that school and flock, far less is known about the role of UV coloration in group-territorial and colonial species, where individuals have long-lasting and potentially cooperative relationships with many neighbours. We measured spectral reflectance in Neolamprologus pulcher, a group-living, colonial Tanganyikan cichlid fish, and found prominent UV coloration on both sexes. We manipulated the visibility of this UV coloration using a clear UV-blocking filter or a UV-transparent filter during behavioural contests across a barrier. We found that trials between similarly sized same-sex opponents involved significantly lower frequencies of aggression when opponents' UV coloration was obscured compared to when opponents' UV coloration was visible. As aggression is typically high between similarly sized same-sex individuals in N. pulcher, this reduction in aggression suggests that UV coloration aids in motivating individuals to engage in conspecific intrasexual interactions. We found no difference in aggression in trials between familiar and unfamiliar opponents in female–female and male–female trials, regardless of the presence of UV coloration. In male–male trials, we found significantly higher frequencies of aggression in contests between familiar male opponents than in contests between unfamiliar male opponents, but only when UV coloration was visible. Collectively, these results suggest that UV coloration is important for intrasexual interactions and prompts further investigation as to the benefits of having visual signals of communication extend into the ultraviolet spectrum.
Reactive oxygen species extend insect life span using components of the insulin-signaling pathway
Xiao-Shuai Zhang, Tao Wang, Xian-Wu Lin, David L. Denlinger, and Wei-Hua Xu. 2017. http://www.pnas.org/content/114/37/E7832.abstract
Reactive oxygen species (ROS) are well-known accelerants of aging, but, paradoxically, we show that physiological levels of ROS extend life span in pupae of the moth Helicoverpa armigera, resulting in the dormant state of diapause. This developmental switch appears to operate through a variant of the conventional insulin-signaling pathway, as evidenced by the facts that Akt, p-Akt, and PRMT1 are elevated by ROS, but not insulin, and that high levels of p-Akt fail to phosphorylate FoxO through PRMT1-mediated methylation. These results suggest a distinct signaling pathway culminating in the elevation of FoxO, which in turn promotes the extension of life span characteristic of diapause.
Size-mediated control of perch–midge coupling in Lake Erie transient dead zones
Daisuke Goto, James J. Roberts, Steven A. Pothoven, Stuart A. Ludsin, Henry A. Vanderploeg, Stephen B. Brandt, Tomas O. Höök. Environ Biol Fish. 2017. https://doi.org/10.1007/s10641-017-0667-1
Transient ecosystem-level disturbances such as oxygen depletion (hypoxia) in aquatic systems modulate species distributions and interactions. In highly eutrophic systems, hypoxic areas (“dead zones”) have expanded around the world, temporarily preventing many demersal predators from accessing their food resources. Here, we investigate how yellow perch (Perca flavescens), an exploited, cool-water mesopredator, interact with their dominant invertebrate prey in benthic habitat–non-biting midge (chironomid) larvae–as bottom-water hypoxia develops in central Lake Erie (United States–Canada) during summer. We apply linear mixed-effects models to individual-level data from basin-wide field surveys on size-based interactions between perch and midge larvae under varying habitat conditions and resource attributes. We test if 1) midge populations (larval body size and density) differ among habitat states (unstratified normoxia, stratified normoxia, and stratified hypoxia); and 2) size-based perch–midge interactions (predator–prey mass ratio or PPMR) differ among habitat states with varying temperature and midge density. Midge populations remained highly abundant after bottom-water oxygen depletion. Despite their high densities, midge larvae also maintained their body size in hypoxic water. In contrast, perch on average consumed relatively smaller (by up to ~64%) midges (higher PPMR) in warmer and hypoxic water, while prey size ingested by perch shrunk less in areas with higher midge density. Our analysis shows that hypoxia-tolerant midges largely allow perch to maintain their consumer–resource relationships in contracted habitats through modified size-mediated interactions in dead zones during summer, revealing plasticity of their trophic coupling in the chronically perturbed ecosystem.
Atmospheric deposition, CO2, and change in the land carbon sink.
Fernández-Martínez M, Vicca S, Janssens IA, Ciais P, Obersteiner M, Bartrons M, Sardans J, Verger A, Canadell JG, Chevallier F, Wang X, Bernhofer C, Curtis PS, Gianelle D, Grünwald T, Heinesch B, Ibrom A, Knohl A, Laurila T, Law BE, Limousin JM, Longdoz B, Loustau D, Mammarella I, Matteucci G, Monson RK, Montagnani L, Moors EJ, Munger, Papale D, Piao SL, Peñuelas J. 2017. Sci Rep. Aug 29;7(1):9632. doi: 10.1038/s41598-017-08755-8.
Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modeling.
Objective choice of phylogeographic models
Bryan C.Carstens, Ariadna E.Morales, Nathan D.Jackson, Brian C.O'Meara. 2017. Molecular Phylogenetics and Evolution. 116: 136-140. https://doi.org/10.1016/j.ympev.2017.08.018
Phylogeography seeks to discover the evolutionary processes that have given rise to organismal and genetic diversity. This requires explicit hypotheses (i.e., models) to be evaluated with genetic data in order to identify those hypotheses that best explain the data. In recent years, advancements in the model-based tools used to estimate phylogeographic parameters of interest such as gene flow, divergence time, and relationships among groups have been made. However, given the complexity of these models, available methods can typically only compare a handful of possible hypotheses, requiring researchers to specify in advance the small set of models to consider. Without formal quantitative approaches to model selection, researchers must rely on their intuition to formulate the model space to be explored.
We explore the adequacy of intuitive choices made by researchers during the process of data analysis by reanalyzing 20 empirical phylogeographic datasets using PHRAPL, an objective tool for phylogeographic model selection. We show that the best models for most datasets include both gene flow and population divergence parameters, and that species tree methods (which do not consider gene flow) tend to be overly simplistic for many phylogeographic systems. Objective approaches to phylogeographic model selection offer an important complement to researcher intuition.
Increased resource use efficiency amplifies positive response of aquatic primary production to experimental warming
James M. Hood, Jonathan P. Benstead, Wyatt F. Cross, Alexander D. Huryn, Philip W. Johnson, Gísli M. Gíslason, James R. Junker, Daniel Nelson, Jón S. Ólafsson, Chau Tran. 2017. DOI: 10.1111/gcb.13912
Climate warming is affecting the structure and function of river ecosystems, including their role in transforming and transporting carbon (C), nitrogen (N), and phosphorus (P). Predicting how river ecosystems respond to warming has been hindered by a dearth of information about how otherwise well-studied physiological responses to temperature scale from organismal to ecosystem levels. We conducted an ecosystem-level temperature manipulation to quantify how coupling of stream ecosystem metabolism and nutrient uptake responded to a realistic warming scenario. A ~3.3°C increase in mean water temperature altered coupling of C, N, and P fluxes in ways inconsistent with single-species laboratory experiments. Net primary production tripled during the year of experimental warming, while whole-stream N and P uptake rates did not change, resulting in 289% and 281% increases in autotrophic dissolved inorganic N and P use efficiency (UE), respectively. Increased ecosystem production was a product of unexpectedly large increases in mass-specific net primary production and autotroph biomass, supported by (a) combined increases in resource availability (via N mineralization and N2 fixation) and (b) elevated resource use efficiency, the latter associated with changes in community structure. These large changes in C and nutrient cycling could not have been predicted from the physiological effects of temperature alone. Our experiment provides clear ecosystem-level evidence that warming can shift the balance between C and nutrient cycling in rivers, demonstrating that warming will alter the important role of in-stream processes in C, N, and P transformations. Moreover, our results reveal a key role for nutrient supply and use efficiency in mediating responses of primary producers to climate warming.
Habitat restoration and native grass conservation: a case study of switchgrass (Panicum virgatum)
Hsiaochi Chang, Helen M. Alexander, Evans Mutegi, Allison A. Snow. 2017. Restor Ecol. DOI: 10.1111/rec.12599
Switchgrass (Panicum virgatum) has been planted extensively for habitat restoration across the United States, such as with the Conservation Reserve Program (CRP). However, genetic profiles of these populations have never been studied nor compared with those of remnant prairies or cultivars. In this study, we sampled 16 CRP and 17 prairie populations across eastern Kansas. We assessed ploidy levels of all populations and compared genetic diversity and structure of 10 prairies, 10 CRP areas, and 5 standard cultivars, using nine simple sequence repeat (SSR) DNA markers. All CRP and prairie populations were octaploid (8x), except two prairies with both hexaploid (6x) and octaploid (8x) individuals. Based on the results of SSR analyses, there were no significant differences between CRP and prairie populations in genetic diversity, and 94% of total variation was partitioned within populations. Similarities among prairie and CRP populations were also observed in Bayesian clustering algorithms and principal coordinate analysis, suggesting that they had similar genetic compositions. In addition, positive spatial autocorrelations were detected up to 42 and 46 km among prairie and among CRP populations, respectively. To conclude, the CRP and prairie populations shared similar genetic profiles. However, remnant prairies still harbored unique genotypes and a high level of genetic diversity, highlighting the importance of seed sources for restoration efforts, that is using local wild seeds or cultivars from the same geographical region. A popular tetraploid (4x) cultivar known as “Kanlow” was genetically distinct from the prairie populations and therefore is not recommended for habitat restoration in this region.