| 1. |
- Hambäck, Peter A, et al.
(författare)
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Asymmetric indirect interactions mediated by a shared parasitoid: connecting species traits and local distribution patterns for two chrysomelid beetles
- 2006
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 148:3, s. 475-481
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on an asymmetric indirect interaction between two chrysomelid beetles where one species (Galerucella tenella) experiences higher parasitization, and the other species (Galerucella calmariensis) lower parasitization, in mixed compared with monospecific populations. This pattern is likely to be a consequence of differences in life history characteristics, where the inferior species has a smaller body size, a lower fecundity and supports a lower parasitoid density than the superior species. This connection between life history characteristics and interspecific dominance in host–parasitoid systems corresponds to predictions from current community ecology theory, and provides a useful building-block in the development of a predictive theory of parasitoid effects on host coexistence.
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| 2. |
- Jivegård, Lennart, 1950, et al.
(författare)
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Effects of three months of low molecular weight heparin (dalteparin) treatment after bypass surgery for lower limb ischemia--a randomised placebo-controlled double blind multicentre trial.
- 2005
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Ingår i: European journal of vascular and endovascular surgery : the official journal of the European Society for Vascular Surgery. - : Elsevier BV. - 1078-5884. ; 29:2, s. 190-8
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To test the hypothesis that long-term postoperative dalteparin (Fragmin), Pharmacia Corp) treatment improves primary patency of peripheral arterial bypass grafts (PABG) in lower limb ischemia patients on acetylsalicylic acid (ASA) treatment. DESIGN: Prospective randomised double blind multicenter study. MATERIALS AND METHODS: Using a computer algorithm 284 patients with lower limb ischemia, most with pre-operative ischemic ulceration or partial gangrene, from 12 hospitals were randomised, after PABG, to 5000 IU dalteparin or placebo injections once daily for 3 months. All patients received 75 mg of ASA daily for 12 months. Graft patency was assessed at 1, 3 and 12 months. RESULTS: At 1 year, 42 patients had died or were lost to follow-up. Compliance with the injection schedule was 80%. Primary patency rate, in the dalteparin versus the control group, respectively, was 83 versus 80% (n.s.) at 3 months and 59% for both groups at 12 months. Major complication rates and cardiovascular morbidity were not different between the two groups. CONCLUSIONS: In patients on ASA treatment, long-term postoperative dalteparin treatment did not improve patency after peripheral artery bypass grafting. Therefore, low molecular weight heparin treatment cannot be recommended for routine use after bypass surgery for critical lower limb ischemia.
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| 3. |
- Stenberg, Johan A., et al.
(författare)
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Herbivore-induced "rent rise" in the host plant may drive a diet breadth enlargement in the tenant
- 2008
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Ingår i: Ecology. - : Ecological Society of America (ESA). - 0012-9658 .- 1939-9170. ; 89:1, s. 126-133
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Tidskriftsartikel (refereegranskat)abstract
- Inter- and intraspecies variations in host plant traits are presumably involved in many host shifts by insect herbivores, and elucidating the mechanisms involved in such shifts has been a crucial goal in insect-plant research for several decades. Here we propose that herbivore-induced evolutionary increases in host plant resistance may cause oligophagous insect herbivores to shift to other sympatric plants as currently preferred host plants become increasingly unpalatable. We tested this hypothesis in a system based on the perennial herb Filipendula uhnaria (Rosaceae), whose herbivory defense has become gradually stronger due to prolonged selection by Galerucella tenella (Coleoptera: Chrysomelidae) herbivory in a boreal archipelago. We. show that Galerucella gradually increases its use of the alternative host plant Rubus arcticus (Rosaceae) in parallel to gradually increased resistance in Filipendula. Our results imply that, by driving the evolutionary increase in Filipendula resistance, Galerucella is also gradually making the original host species more unpalatable and thereby driving its own host-breadth enlargement. We argue that such self-inflicted "rent rises" may be an important mechanism behind host plant shifts, which in turn are believed to have preceded the speciation of many phytophagous insects.
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| 4. |
- Halitschke, Rayko, et al.
(författare)
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Shared signals -'alarm calls' from plants increase apparency to herbivores and their enemies in nature.
- 2008
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Ingår i: Ecology letters. - : Wiley. - 1461-0248 .- 1461-023X. ; 11:1, s. 24-34
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Tidskriftsartikel (refereegranskat)abstract
- The attraction of natural enemies of herbivores by volatile organic compounds as an induced indirect defence has been studied in several plant systems. The evidence for their defensive function originates mainly from laboratory studies with trained parasitoids and predators; the defensive function of these emissions for plants in natural settings has been rarely demonstrated. In native populations and laboratory Y-tube choice experiments with transgenic Nicotiana attenuata plants unable to release particular volatiles, we demonstrate that predatory bugs use terpenoids and green leaf volatiles (GLVs) to locate their prey on herbivore-attacked plants. By attracting predators with volatile signals, this native plant reduces its herbivore load - demonstrating the defensive function of herbivore-induced volatile emissions. However, plants producing GLVs are also damaged more by flea beetles. The implications of these conflicting ecological effects for the evolution of induced volatile emissions and for the development of sustainable agricultural practices are discussed.
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| 5. |
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| 6. |
- Stenberg, Johan A
(författare)
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Predictable evolution of plant defense on uplift islands
- 2009
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Konferensbidrag (refereegranskat)abstract
- Background/Question/Methods When blank patches are uncovered to neighboring ecological communities they are often colonized by plants, herbivores, and carnivores in a highly predictable temporal order, which is the case in species-poor Bothnian land-uplift archipelagos. This implies that colonizing plants first will experience a time window of herbivore-free space, selecting for reduced resistance in favor of growth, followed by a time period of strong herbivory selecting for increased resistance at the expense of growth. To demonstrate this phenomenon I used an archipelago where young islands early become suitable for establishment of the perennial herb Meadowsweet, while selective leaf beetles cannot establish until the islands reach such a height (age) that the beetles are not washed away from their overwintering sites. Results/Conclusions I show that the mean phenotypic resistance against leaf beetles increases with island age, corresponding to the fitness reduction selectively imposed on susceptible host plants during historic herbivory. I further show that the raised resistance on old islands complicates the lives of the beetles which gradually become more prone to utilize a less suitable alternative host-plant species. These results demonstrate the possibility to study evolutionary interactions in rising archipelagos
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| 7. |
- Stenberg, Johan A., et al.
(författare)
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Presence of Lythrum salicaria enhances the bodyguard effects of the parasitoid Asecodes mento for Filipendula ulmaria
- 2007
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 116:3, s. 482-490
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports significant effects of a co-occurring plant species (Lythrum salicaria, Lythraceae) on the reproductive success of the perennial herb Filipendula ulmaria (Rosaceae). We studied 15 Filipendula populations in the Skeppsvik Archipelago; seven of which were monospecific and eight mixed with Lythrum. All the Filipendula populations studied harbored the chrysomelid beetle Galerucella tenella, and in 2005 seed set was strongly negatively correlated with the percentage leaf area consumed. Moreover, data from 2004 showed that 25–100% of the G. tenella larvae were parasitized by the hymenopteran parasitoid Asecodes mento, and we found a strong cascading top-down effect of parasitism in 2004 on Filipendula seed set in 2005. In 2004, parasitism (at the population level) was negatively correlated with percentage leaf area consumed and positively correlated with seed set in 2005. The parasitoid Asecodes also parasitized G. calmariensis, which is monophagous on Lythrum. Mixed populations of Filipendula and Lythrum supported higher densities of their shared ‘bodyguard’Asecodes. Further, Y-tube bioassays showed that floriferous Filipendula attracted more than twice as many gravid Asecodes females as floriferous Lythrum. Taken together, these findings suggest that coexistence of the two plants results in ‘associational resistance’ for Filipendula and ‘associational susceptibility’ for Lythrum. This scenario was supported for Filipendula since, for this species, we found lower leaf consumption followed by higher seed production in mixed than in monospecific populations. Considered together, our results show that bodyguards may increase the reproductive fitness of a perennial herb, and that the strength of the cascading ‘bodyguard’ effect can be strongly influenced by co-occurring plants through ‘apparent competition’. This is the first paper to demonstrate that, in the wild, plant species may use odors to compete for ‘bodyguards’, thereby causing asymmetrical ‘apparent competition’ between the herbivores involved. Our data emphasize the need to consider community factors in studies of trophic interactions.
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| 8. |
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| 9. |
- Stenberg, Johan A, et al.
(författare)
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Tall herb herbivory resistance reflects historic exposure to leaf beetles in a boreal archipelago age-gradient.
- 2006
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 148:3, s. 414-425
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we introduce the coevolution-by-coexistence hypothesis which predicts that the strength of a coevolutionary adaptation will become increasingly apparent as long as the corresponding selection from an interacting counterpart continues. Hence, evolutionary interactions between plants and their herbivores can be studied by comparing discrete plant populations with known history of herbivore colonization. We studied populations of the host plant, Filipendula ulmaria (meadow sweet), on six islands, in a Bothnian archipelago subject to isostatic rebound, that represent a spatio-temporal gradient of coexistence with its two major herbivores, the specialist leaf beetles Galerucella tenella and Altica engstroemi. Regression analyses showed that a number of traits important for insect-plant interactions (leaf concentrations of individual phenolics and condensed tannins, plant height, G. tenella adult feeding and oviposition) were significantly correlated with island age. First, leaf concentrations of condensed tannins and individual phenolics were positively correlated with island age, suggesting that plant resistance increased after herbivore colonization and continued to increase in parallel to increasing time of past coexistence, while plant height showed a reverse negative correlation. Second, a multi-choice experiment with G. tenella showed that both oviposition and leaf consumption of the host plants were negatively correlated with island age. Third, larvae performed poorly on well-defended, older host populations and well on less-defended, younger populations. Thus, no parameter assessed in this study falsifies the coevolution-by-coexistence hypothesis. We conclude that spatio-temporal gradients present in rising archipelagos offer unique opportunities to address evolutionary interactions, but care has to be taken as abiotic (and other biotic) factors may interact in a complicated way.
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| 10. |
- Stenberg, Johan A., et al.
(författare)
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Visual cues override olfactory cues in the host-finding process of the monophagous leaf beetle Altica engstroemi
- 2007
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Ingår i: Entomologia Experimentalis et Applicata. - : Wiley. - 0013-8703 .- 1570-7458. ; 125:1, s. 81-88
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Tidskriftsartikel (refereegranskat)abstract
- It is generally assumed that specialist insect herbivores utilize plant odours to find their particular host plants and that visual cues are of minor importance in the host-finding process. We performed Y-tube olfactometer bioassays and small-scale field experiments to determine whether, under laboratory and field conditions, the monophagous herbivore Altica engstroemi J. Sahlberg (Coleoptera: Chrysomelidae: Alticinae) is guided to its host plant Filipendula ulmaria (L.) Maxim. (Rosaceae) by visual or olfactory cues. The olfactometer tests showed that A. engstroemi was never attracted to odours, either from undamaged or from damaged plants. Even starvation for 24 h did not change this behaviour. However, the field experiment showed that visual cues alone were sufficient to attract a significant number of starved beetles when offered a choice between bagged host plants and bagged green plastic control ‘plants’. Our findings contrast with the general view that plant odours constitute the major cue in the host-finding process among specialized phytophagous insects. A review of the literature for the period 1986–2006 inclusive, relating to host-plant finding in hrysomelidae, identified studies of 19 chrysomelid species, all of which were guided by olfactory cues. No species were guided to their host by visual cues. Although some studies demonstrated that chrysomelids may exhibit orientation responses to colour or contrast, our study on A. engstroemi is the only one demonstrating that visual cues affect host-plant selection in a chrysomelid species. We suggest that the use of visual cues in host-finding may evolve among chrysomelids with limited dispersal ability in persistent habitats and may be found among species monophagous on abundant host plants that dominate the structure of the plant community, that is, where the host plant’s presence is predictable in time and space.
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