| 1. |
- Berdan, Emma L, 1983, et al.
(author)
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Genetic divergence and phenotypic plasticity contribute to variation in cuticular hydrocarbons in the seaweed fly Coelopa frigida
- 2019
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In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 9:21, s. 12156-12170
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Journal article (peer-reviewed)abstract
- Cuticular hydrocarbons (CHCs) form the boundary between insects and their environments and often act as essential cues for species, mate, and kin recognition. This complex polygenic trait can be highly variable both among and within species, but the causes of this variation, especially the genetic basis, are largely unknown. In this study, we investigated phenotypic and genetic variation of CHCs in the seaweed fly, Coelopa frigida, and found that composition was affected by both genetic (sex and population) and environmental (larval diet) factors. We subsequently conducted behavioral trials that show CHCs are likely used as a sexual signal. We identified general shifts in CHC chemistry as well as individual compounds and found that the methylated compounds, mean chain length, proportion of alkenes, and normalized total CHCs differed between sexes and populations. We combined these data with whole genome resequencing data to examine the genetic underpinnings of these differences. We identified 11 genes related to CHC synthesis and found population-level outlier SNPs in 5 that are concordant with phenotypic differences. Together these results reveal that the CHC composition of C. frigida is dynamic, strongly affected by the larval environment, and likely under natural and sexual selection.
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| 2. |
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| 3. |
- Enge, Swantje, 1981, et al.
(author)
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An exotic chemical weapon explains low herbivore damage in an invasive alga
- 2012
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In: Ecology. - : Wiley. - 0012-9658. ; 93:12, s. 2736-2745
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Journal article (peer-reviewed)abstract
- Invasion success of introduced species is often attributed to a lack of natural enemies as stated by the enemy release hypothesis (ERH). The ERH intuitively makes sense for specialized enemies, but it is less evident why invaders in their new area escape attacks by generalist enemies. A recent hypothesis explains low herbivore damage on invasive plants with plant defense chemicals that are evolutionarily novel to native herbivores. Support for this novel weapon hypothesis (NWH) is so far based on circumstantial evidence. To corroborate the NWH, there is a need for direct evidence through explicit characterizations of the novel chemicals and their effects on native consumers. This study evaluated the NWH using the highly invasive red alga Bonnemaisonia hamifera. In pairwise feeding experiments, preferences between B. hamifera and native competitors were assessed for four common generalist herbivores in the invaded area. Through a bioassay-guided fractionation, we identified the deterrent compound and verified its effect in an experiment with the synthesized compound at natural concentrations. The results showed that native herbivores strongly preferred native algae to B. hamifera. The resistance against herbivores could be tracked down to the algal metabolite 1,1,3,3-tetrabromo-2-heptanone, a compound not known from native algae in the invaded area. The importance of the chemical defense was further underlined by the feeding preference of herbivores for individuals with a depleted content of 1,1,3,3-tetrabromo-2-heptanone. This study thus provides the first conclusive example of a highly successful invader where low consumption in the new range can be directly attributed to a specific chemical defense against evolutionarily naive native generalists. In conclusion, our results support the notion that novel chemical weapons against naive herbivores can provide a mechanistic explanation for plant invasion success.
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| 4. |
- Enge, Swantje, 1981, et al.
(author)
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Native generalist herbivores promote invasion of a chemically defended seaweed via refuge-mediated apparent competition
- 2013
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In: Ecology Letters. - 1461-023X .- 1461-0248. ; 16:4, s. 487-492
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Journal article (peer-reviewed)abstract
- Refuge-mediated apparent competition was recently suggested as a mechanism that enables plant invasions. The refuge characteristics of introduced plants are predicted to enhance impacts of generalist herbivores on native competitors and thereby result in an increased abundance of the invader. However, this prediction has so far not been experimentally verified. This study tested if the invasion of a chemically defended seaweed is promoted by native generalist herbivores via refuge-mediated apparent competition. The invader was shown to offer herbivores a significantly better refuge against fish predation compared with native seaweeds. Furthermore, in an experimental community, the presence of herbivores decreased the performance of neighbouring native seaweeds, but increased growth and relative abundance of the invader. These results provides the first experimental evidence that native generalist herbivores can shift a community towards a dominance of a well-defended invader, inferior to native species in direct competitive interactions, by means of refuge-mediated apparent competition.
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| 5. |
- Enge, Swantje, 1981
(author)
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Seaweed Invasions and Novel Chemical Defences
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Biological invasions pose a risk to the biodiversity and the functioning of ecosystems in invaded areas. The reasons why some introduced species become dominant and widespread in their new environments is still largely an unsettled question. It has commonly been predicted that introduced plants will invade when they are less affected by herbivores, since this will provide the introduced species with a competitive advantage over native plants. Furthermore, it has been suggested that introduced species with chemical defences that are novel to native herbivores in the new range are most likely to become successful invaders. The scope of this thesis was to investigate ecological processes that underlie the successful invasion of plant/seaweed species and how chemical compounds mediate these processes, using the filamentous red alga Bonnemaisonia hamifera as a model organism. Having its origin in the Northwest Pacific, this alga has invaded large parts of the North Atlantic rocky shores and became dominant in many seaweed communities. Feeding preference experiments showed that native generalist herbivores explicitly preferred native seaweeds to the invader (paper I). Using a bioassay-guided fractionation, B. hamifera was found to be chemically defended against native herbivores by producing 1,1,3,3-tetrabromo-2-heptanone as the main feeding deterrent compound (paper I). The production of this compound was demonstrated to be costly, but also to increase the fitness of the invader by reducing the impact of pathogenic bacteria (paper IV) in addition to the shown reduced herbivory. Resource allocation to a chemical defence may also explain the relatively poor performance (in terms of growth) of B. hamifera in direct interactions with native seaweeds when herbivores were absent in experimental algal communities (paper II, III). In the presence of herbivores, however, the abundance of B. hamifera increased in the community as a result of both consumption of neighbouring algal competitors and an enhanced performance of the invader (paper III). In return, the invasive species was found to provide a superior refuge to herbivores from fish predation compared to native seaweeds, which may explain the previously observed rich species diversity and abundance of invertebrates associated with the alga. Overall, these results suggest that the invasion of B. hamifera has been facilitated by refuge-mediated apparent competition (paper III). In conclusion, B. hamifera provides a remarkable example of how a novel chemical defence can drive different ecological processes in the new community and how this jointly contributes to the invasiveness of the introduced species. The further development of the invaded community is difficult to predict and depends on the ability of the native species to adapt to the chemical defence of the invader, as well as on the potential of the invader to respond to the novel selection regimes in the invaded area. Sufficient genetic variation is generally considered essential for the potential of adaptations. In Swedish waters, B. hamifera mainly propagates asexually by fragmentation, which suggests that the alga should be highly clonal with low genetic diversity within these introduced populations. Preliminary results from 83 amplified fragment length polymorphism markers analysed for 44 individuals indicated reduced genetic diversity in Swedish populations compared to populations from the native range in Korea. No clones were found in the Swedish population, although the low degree of differentiation and high similarity between the Swedish individuals suggests that the individuals belong to a single clonal lineage, that is well intermixed by fragment dispersal (paper V).
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| 6. |
- Hargrave, Matthew, et al.
(author)
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Co-cultivation with blue mussels increases yield and biomass quality of kelp
- 2022
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In: Aquaculture. - : Elsevier BV. - 0044-8486. ; 550
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Journal article (peer-reviewed)abstract
- Integrated multi-trophic aquaculture (IMTA) has to date largely centred on a fed species, often finfish or shrimps, alongside which extractive species, such as bivalves or seaweeds, have been placed. In comparison, IMTA systems excluding a fed component have received little research. Here we report a field study of an IMTA cultivation of the sugar kelp, Saccharina latissima, and the blue mussel, Mytilus edulis, on the Swedish west coast. Kelp were cultivated at two depths, 1-2 m and 3-4 m, either 10 m downstream of commercial scale blue mussel farms, or at control (monoculture) sites at least 500 m from the nearest farm. Significant enhancement of kelp yields in terms of both blade length and biomass was observed in IMTA treatments compared to monoculture, with a mean increase in length of 22% and biomass of 38%. Moreover, kelps co-cultivated with mussels displayed an epiphyte reduction of more than half compared to kelps grown in monoculture, with a 15% coverage in monoculture compared to 6% in co-culture. Significant increases in pigment content were also detected, with higher levels of chlorophyll a, fucoxanthin and phaeophytin in IMTA treatment kelps in comparison to monoculture. This study provides evidence for the potential of IMTA systems containing solely extractive species and presents factors beyond nutrient enrichment as drivers for enhanced growth in these systems. © 2021 The Authors
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| 7. |
- Nylund, Göran M., 1974, et al.
(author)
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Costs and Benefits of Chemical Defence in the Red Alga Bonnemaisonia hamifera
- 2013
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In: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 8:4
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Journal article (peer-reviewed)abstract
- A number of studies have shown that the production of chemical defences is costly in terrestrial vascular plants. However, these studies do not necessarily reflect the costs of defence production in macroalgae, due to structural and functional differences between vascular plants and macroalgae. Using a specific culturing technique, we experimentally manipulated the defence production in the red alga Bonnemaisonia hamifera to examine if the defence is costly in terms of growth. Furthermore, we tested if the defence provides fitness benefits by reducing harmful bacterial colonisation of the alga. Costly defences should provide benefits to the producer in order to be maintained in natural populations, but such benefits through protection against harmful bacterial colonisation have rarely been documented in macroalgae. We found that algae with experimentally impaired defence production, but with an externally controlled epibacterial load, grew significantly better than algae with normal defence production. We also found that undefended algae exposed to a natural epibacterial load experienced a substantial reduction in growth and a 6-fold increase in cell bleaching, compared to controls. Thus, this study provides experimental evidence that chemical defence production in macroalgae is costly, but that the cost is outweighed by fitness benefits provided through protection against harmful bacterial colonisation.
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| 8. |
- Pavia, Henrik, 1964, et al.
(author)
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Chemical defences against herbivores
- 2012
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In: Chemical ecology in aquatic systems. - New York, US : Oxford University Press. - 9780199583096 ; , s. 210-235
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Book chapter (peer-reviewed)abstract
- In recent years it has become increasingly clear that chemical interactions play a fundamental role in aquatic habitats and have far-reaching evolutionary and ecological consequences. A plethora of studies have shown that aquatic organisms from most taxa and functional groups respond to minute concentrations of chemical substances released by other organisms. However, our knowledge of this 'chemical network' is still negligible. Chemical interactions can be divided into two larger sub-areas based on the function of the chemical substance. First, there are interactions where chemical substances are toxic to other organisms and are used as a defense against consumers (including both herbivores and predators) or a weapon against competitors (allelopathy). Second, chemical substances mey be used as a source for information of the environment; for example: how can I find the optimal habitat, the best food, the nicest partner, and avoid being eaten? Aquatic organisms are able to detect and respond to extremely low concentrations of chemical cues to answer all these questions. The book aims at connecting these intriguing chemical interactions with traditional knowledge of organism interactions. Chemical ecology in aquatic systems covers a wide range of studies, both plant and animal, from different geographic regions and habitats-pelagic as well as benthic. Most of the chemical interactions are similar in freshwater and marine habitats and this book therefor strives at integrating work on both systems. This accessible, research-level text is aimed at graduate students and professional researchers in the fields of limnology, marine ecology, evolutionary biology, behavioral ecology, and chemical ecology.
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| 9. |
- Rugiu, Luca, et al.
(author)
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Kelp in IMTAs: small variations in inorganic nitrogen concentrations drive different physiological responses of Saccharina latissima
- 2021
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In: Journal of Applied Phycology. - : Springer Science and Business Media LLC. - 0921-8971 .- 1573-5176. ; 33, s. 1021-1034
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Journal article (peer-reviewed)abstract
- © 2020, The Author(s). Kelps can be included in integrated multitrophic aquaculture (IMTA) where their growth and quality might benefit from the nutrient load released by other species like finfish and mussels transforming effluents from the cultured animals into valuable products. We studied how different nutrient concentrations affect growth, photosynthesis, chemical composition and pigment content of the kelp Saccharina latissima. We exposed kelps to natural seawater, water enriched to levels of ammonium and nitrate simulating finfish cage waste (IMTA1) and a combination of such enrichment with natural effluents coming from mussels (IMTA2). The algal biomass was higher and produced elevated total organic content when exposed to both IMTA1 and IMTA2. The photosynthetic responses in terms of relative electron transfer rate (rETRmax), PSII saturation irradiance (Ek) and total nitrogen content were also positively affected by both IMTA1 and IMTA2. We found a significant enhancement in pigment content only when algae were exposed to the strongest enrichment of our study (IMTA2). Finally, we found a positive relationship between rETRmax and growth, and the content of chlorophyll a and fucoxanthin. Our results show significant physiological responses of S. latissima to nutrient enrichment mimicking IMTA settings, as well as the benefit of added nutrients through a boost in photosynthetic activity that leads to higher kelp biomass and pigment production. This study suggests that modest nitrogen enrichment such as the one in our IMTA2 setup is enough to generate not only higher kelp biomass, but also an increased biomass quality with potentially higher market value.
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| 10. |
- Sagerman, Josefin, et al.
(author)
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Divergent ecological strategies determine different impacts on community production by two successful non-native seaweeds
- 2014
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In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 175:3, s. 937-946
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Journal article (peer-reviewed)abstract
- The consequences of plant introductions into ecosystems are frequently reported from terrestrial environments, but little is known about the effects on ecosystem functioning caused by non-native primary producers in marine systems. In this study we explored the effects of the invasion by the two filamentous red algae Heterosiphonia japonica and Bonnemaisonia hamifera on the primary production of seaweed communities by using single and mixed cultures of non-native and native red algae. The experiments were conducted both in the presence and absence of herbivores. Biomass production of the invaded community increased more than four times in mixed cultures with H. japonica, while introduction by B. hamifera had no significant effect. The different impact on community production could be explained by differences in life history strategies between the invaders; H. japonica grew considerably faster than the native seaweeds which directly increased the community production, while B. hamifera showed a relatively slow growth rate and therefore had no effect. From previous studies it is known that B. hamifera produces a highly deterrent, but also costly, chemical defence. The assessment of survival and growth of a native generalist herbivore further corroborated that the biomass produced by B. hamifera constitutes a very low-quality food, whereas the performance of herbivores on a diet of H. japonica was comparable to that on native algal diets. In summary, this study demonstrates that successful invaders belonging to the same functional group (filamentous red algae) may have distinctly different impacts on productivity in the recipient community, depending on their specific life history traits.
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