Not all jellyfish are equal: isotopic evidence for inter- and intraspecific variation in jellyfish trophic ecology

Jellyfish are highly topical within studies of pelagic food-webs and there is a growing realisation that their role is more complex than once thought. Efforts being made to include jellyfish within fisheries and ecosystem models are an important step forward, but our present understanding of their underlying trophic ecology can lead to their oversimplification in these models. Gelatinous zooplankton represent a polyphyletic assemblage spanning >2,000 species that inhabit coastal seas to the deep-ocean and employ a wide variety of foraging strategies. Despite this diversity, many contemporary modelling approaches include jellyfish as a single functional group feeding at one or two trophic levels at most. Recent reviews have drawn attention to this issue and highlighted the need for improved communication between biologists and theoreticians if this problem is to be overcome. We used stable isotopes to investigate the trophic ecology of three co-occurring scyphozoan jellyfish species (Aurelia aurita, Cyanea lamarckii and C. capillata) within a temperate, coastal food-web in the NE Atlantic. Using information on individual size, time of year and δ 13 C and δ 15 N stable isotope values, we examined: (1) whether all jellyfish could be considered as a single functional group, or showed distinct inter-specific differences in trophic ecology; (2) Were size-based shifts in trophic position, found previously in A. aurita, a common trait across species?; (3) When considered collectively, did the trophic position of three sympatric species remain constant over time? Differences in δ 15 N (trophic position) were evident between all three species, with size-based and temporal shifts in δ 15 N apparent in A. aurita and C. capillata. The isotopic niche width for all species combined increased throughout the season, reflecting temporal shifts in trophic position and seasonal succession in these gelatinous species. Taken together, these findings support previous assertions that jellyfish require more robust inclusion in marine fisheries or ecosystem models

Winter ecology of specialist and generalist morphs of European whitefish, Coregonus lavaretus, in subarctic Northern Europe

European whitefish is a model species for adaptive radiation of fishes in temperate and subarctic lakes. In northern Europe the most commonly observed morphotypes are a generalist (LSR) morph and a pelagic specialist (DR) morph. The evolution of a pelagic specialist morph is something of an enigma, however, as this region is characterized by long, dark winters with pelagic primary production limited to a brief window in late summer. We conducted the first winter-based study of polymorphic whitefish populations to determine the winter ecology of both morphs, and we combined seasonal diet and stable isotope analysis with several proxies of condition in three polymorphic whitefish populations. The generalist LSR morph fed on benthic and pelagic prey in summer but was solely reliant on benthic prey in winter. This was associated with a noticeable but moderate reduction in condition, lipid content and stomach fullness in winter relative to summer. In contrast, the DR whitefish occupied a strict pelagic niche in both seasons. A significant reduction in pelagic prey during winter resulted in severe decrease in condition, lipid content and stomach fullness in DR whitefish in winter relative to summer, with the pelagic morph apparently approaching starvation in winter. We suggest that this divergent approach to seasonal foraging is associated with the divergent life-history traits of both morphs.Peer reviewe

Sequential sampling of domestic and wild camelids’ teeth in the highlands of Atacama: First results on carbon and nitrogen stable isotope compositions

El objetivo de este trabajo consiste en establecer si la señal isotópica del carbono y el nitrógeno medida sobre piezas dentales de camélidos modernos de las tierras altas de Atacama refleja las variaciones en la dieta, la movilidad y la territorialidad de estos animales a nivel diacrónico. Se busca explorar el correlato isotópico de la variación estacional en la dieta de los rebaños de camélidos domésticos determinada por la movilidad trashumante que practican los grupos pastoriles en el área de estudio, así como también la señal isotópica de las variaciones estacionales en la dieta y la movilidad de las poblaciones de camélidos silvestres condicionadas por las fluctuaciones climáticas características de este ambiente. Para ello se obtuvieron valores isotópicos (d13C y d15N, medidos en colágeno de dentina) de manera secuencial y perpendicular al eje de crecimiento de las piezas dentales consideradas, los cuales revelaron la existencia de una variación acotada. La trascendencia de esta investigación radica en proveer un marco de referencia para la discusión de las composiciones isotópicas medidas a partir del muestreo secuencial de piezas dentales de camélidos recuperados en contextos arqueológicos de la puna de Atacama.The goal of this paper is to establish if the variation manifested in the carbon and nitrogen stable isotope compositions measured on modern camelids’ teeth from the highlands of Atacama reflects how the diet, mobility, and territoriality of these animals vary through time. The study seeks to determine if the isotopic signal shows the seasonal variation in the diet of the domestic camelid herds conditioned by the transhumant mobility practiced by the local herders, as well as the seasonal variation in the diet and mobility of the wild camelid populations related to the environmental fluctuations typical of this area. For this purpose, isotopic values (d13C and d15N measured on dentin collagen) were obtained sequentially and perpendicularly to the growth axis of the teeth considered, which revealed the existence of a limited variation. The significance of this research lies in providing a frame of reference for the discussion of the stable isotope compositions obtained from the sequential sampling of dental samples of camelids recovered from archaeological contexts in the Puna de Atacama.Fil: Samec, Celeste Tamara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina. Max Planck Institute For The Science Of Human History; AlemaniaFil: Harrod, Chris. Universidad de Antofagasta (uantof)

Unravelling the macro-evolutionary ecology of fish–jellyfish associations: life in the ‘gingerbread house’

Fish–jellyfish interactions are important factors contributing to fish stock success. Jellyfish can compete with fish for food resources, or feed on fish eggs and larvae, which works to reduce survivorship and recruitment of fish species. However, jellyfish also provide habitat and space for developing larval and juvenile fish which use their hosts as means of protection from predators and feeding opportunities, helping to reduce fish mortality and increase recruitment. Yet, relatively little is known about the evolutionary dynamics and drivers of such associations which would allow for their more effective incorporation into ecosystem models. Here, we found that jellyfish association is a probable adaptive anti-predator strategy for juvenile fish, more likely to evolve in benthic (fish living on the sea floor), benthopelagic (fish living just above the bottom of the seafloor), and reef-associating species than those adapted to other marine habitats. We also found that jellyfish association likely preceded the evolution of a benthic, benthopelagic, and reef-associating lifestyle rather than its evolutionary consequence, as we originally hypothesized. Considering over two-thirds of the associating fish identified here are of economic importance, and the wide-scale occurrence and diversity of species involved, it is clear the formation of fish–jellyfish associations is an important but complex process in relation to the success of fish stocks globally

Ecological speciation in a generalist consumer expands the trophic niche of a dominant predator

Ecological speciation - whereby an ancestral founder species diversifies to fill vacant niches - is a phenomenon characteristic of newly formed ecosystems. Despite such ubiquity, ecosystem-level effects of such divergence remain poorly understood. Here, we compared the trophic niche of European whitefish (Coregonus lavaretus) and their predators in a series of contrasting subarctic lakes where this species had either diversified into four ecomorphologically distinct morphs or instead formed monomorphic populations. We found that the trophic niche of whitefish was almost three times larger in the polymorphic than in the monomorphic lakes, due to an increase in intraspecific specialisation. This trophic niche expansion was mirrored in brown trout (Salmo trutta), a major predator of whitefish. This represents amongst the first evidence for ecological speciation directly altering the trophic niche of a predator. We suggest such mechanisms may be a common and important - though presently overlooked - factor regulating trophic interactions in diverse ecosystems globally.Peer reviewe

Tracing early stages of species differentiation: ecological, morphological and genetic divergence of Galápagos sea lion populations

Wolf JBW, Harrod C, Brunner S, Salazar S, Trillmich F, Tautz D. Tracing early stages of species differentiation: ecological, morphological and genetic divergence of Galápagos sea lion populations. BMC Evolutionary Biology. 2008;8(1): 150.Background: Oceans are high gene flow environments that are traditionally believed to hamper the build-up of genetic divergence. Despite this, divergence appears to occur occasionally at surprisingly small scales. The Galápagos archipelago provides an ideal opportunity to examine the evolutionary processes of local divergence in an isolated marine environment. Galápagos sea lions (Zalophus wollebaeki) are top predators in this unique setting and have an essentially unlimited dispersal capacity across the entire species range. In theory, this should oppose any genetic differentiation. Results: We find significant ecological, morphological and genetic divergence between the western colonies and colonies from the central region of the archipelago that are exposed to different ecological conditions. Stable isotope analyses indicate that western animals use different food sources than those from the central area. This is likely due to niche partitioning with the second Galápagos eared seal species, the Galápagos fur seal (Arctocephalus galapagoensis) that exclusively dwells in the west. Stable isotope patterns correlate with significant differences in foraging-related skull morphology. Analyses of mitochondrial sequences as well as microsatellites reveal signs of initial genetic differentiation. Conclusion: Our results suggest a key role of intra- as well as inter-specific niche segregation in the evolution of genetic structure among populations of a highly mobile species under conditions of free movement. Given the monophyletic arrival of the sea lions on the archipelago, our study challenges the view that geographical barriers are strictly needed for the build-up of genetic divergence. The study further raises the interesting prospect that in social, colonially breeding mammals additional forces, such as social structure or feeding traditions, might bear on the genetic partitioning of populations

Total mercury concentrations in liver and muscle of European whitefish (Coregonus lavaretus (L.)) in a subarctic lake - Assessing the factors driving year-round variation

Subarctic lakes are characterised by extreme seasonal variation in light and temperature which influences growth, maturation, condition and resource use of fishes. However, our understanding of how seasonal changes affect mercury concentrations of fishes is limited. We conducted a year-round study (3 ice-covered months, 3 open-water months) with open-water inter-annual aspect (3 years: samples from August/September), focusing on total mercury (THg) concentrations and ecological characteristics of a common freshwater fish, European whitefish (Coregonus lavaretus (L.)) from a subarctic lake. We measured THg concentrations from tissues with fast (liver, n = 164) and moderate (muscle, n = 225) turnover rates, providing information on THg dynamics over different temporal scales. In both tissues, lipid-corrected THg concentrations were highest in winter (liver: 1.70 +/- 0.88 mu g/g, muscle: 0.24 +/- 0.05 mu g/g) and lowest in summer (liver: 0.87 +/- 0.72 mu g/g, muscle: 0.19 +/- 0.04 mu g/g). THg concentrations increased in winter following the summer-autumn dietary shift to pelagic zooplankton and starvation after spawning. Whitefish THg concentrations decreased towards summer, and were associated with consumption of benthic macroinvertebrates and subsequent growth dilution. Mercury bio-accumulated in both tissues with age, both showing the strongest regression slopes in winter and lowest in summer. THg concentrations in liver and muscle tissue were correlated throughout the year, however the correlation was lowest in summer, indicating high metabolism during somatic growing season in summer and growth dilution. Multiple linear regression models explained 50% and 55% of the THg variation in liver and muscle both models dominated by seasonally-variable factors i.e. sexual maturity, delta C-13, and condition factor. Seasonally varying bioaccumulation slopes and the higher level of intra-annual variation (21%) in whitefish THg concentration in muscle than the inter-annual accumulation (8%) highlight the importance of including seasonal factors in future THg studies. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Competition between co-occurring invasive and native consumers switches between habitats

1.The introduction of a non‐native species frequently has adverse direct effects on native species. The underlying mechanisms, however, often remain unclear, in particular where native and invasive species are taxonomically similar. 2.We found evidence of direct competitive interactions between a globally distributed invasive species (the Pacific oyster, Magallana gigas) and its native counterpart (the European oyster, Ostrea edulis). We also discovered that the competitive outcome differed between different habitat types and orientation by identifying context‐dependent responses driven by environmental conditions and stress (i.e. intertidal compared to subtidal habitats; and vertical versus horizontal substratum). This is particularly important because the European oyster is threatened, or in decline, throughout most of its range and restoration efforts are underway in many regions. 3.We combined experimental manipulations and stable isotope analysis (SIA) to identify the direct effects of competition and the mechanisms by which the invasive and native species compete. We identified negative effects of the invasive species on the native oyster but these were limited to the subtidal habitat (lower stress environment) and determined by substratum orientation (habitat structure). Crucially, we found that effects of the invasive species on the native species were not always negative and under certain conditions (e.g. on vertical substrata) were positive. Shifts in isotopic niches of both species when co‐occurring, alongside mixing models, indicate that exploitative competition for food is most likely to underpin niche partitioning between both species. 4.We have identified different foraging strategies under different contexts and our findings highlight the importance of exploitative competition as a driving mechanism behind the co‐occurrence of two seemingly functionally similar consumers. The combination of experimental manipulations with SIA is a powerful tool and we illustrate how this approach should be incorporated, into multiple environmental contexts at appropriate scales, to more accurately predict impacts of the spread of invasive species on native communities

Adaptive Radiation along a Thermal Gradient : Preliminary Results of Habitat Use and Respiration Rate Divergence among Whitefish Morphs

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