Browsing by Autor "F. Ollevier"

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Correcting the short‐term effect of food deprivation in a damselfly: mechanisms and costs
(Wiley, 2007) Melina Campero; Marjan De Block; F. Ollevier; Robby Stoks
1. Mass at emergence is a life-history trait strongly linked to adult fitness. Therefore, when faced with transient food shortage in the larval stage, mass-correcting mechanisms are common. 2. These correcting mechanisms may carry costs with them. On one hand, these costs may be overestimated because they can be confounded with the direct effects of the transient food shortage itself. On the other hand, costs may be underestimated by ignoring physiological costs. Another largely neglected topic is that correcting mechanisms and costs may critically depend upon other stressors that often co-occur. 3. Here, we identify the mass-correcting mechanisms and their associated costs at emergence in the damselfly Coenagrion puella, after being stressed by a transient period of starvation and a subsequent exposure to pesticide stress during the larval stage. We introduce path analysis to disentangle direct costs of starvation and the mass-correcting mechanisms in terms of immune response. 4. As predicted, we found no differences in mass at emergence. Starvation directly resulted in a costly delayed emergence and a decreased immune response at emergence. Mass-correcting mechanisms included a prolonged post-starvation period, reduced mass loss at emergence and compensatory growth, although the latter only in females under pesticide stress. 5. The mass-correcting mechanisms were associated with beneficial effects on investment in immune response, but only in the absence of pesticide stress. Under pesticide stress, these beneficial effects were mostly undone or overruled, resulting in negative effects of the mass-correcting mechanisms in terms of immune response. 6. Our results stress the importance of and introduce a statistical way of disentangling direct costs of starvation and the mass-correcting mechanisms themselves, and the importance of including physiological endpoints in this kind of studies.
Diel vertical migration of zooplankton in an Amazonian várzea lake (Laguna Bufeos, Bolivia)
(Taylor & Francis, 2006) Danny Rejas; Luc De Meester; Lena Ferrufino; Mabel Maldonado; F. Ollevier
We studied diel vertical migration (DVM) of a variety of zooplanktonic taxa. Our results fit the predictions of the predator avoidance hypothesis, with larger taxa performing normal migrations to avoid fish predation and smaller taxa performing reversed migrations, probably to avoid predation by Chaoborus. Cladocerans and adults of copepods displayed normal DVM, whereas cyclopoid copepodites did not migrate. Five rotifer taxa migrated in a normal pattern whereas four taxa migrated in a reverse pattern. Our results suggest that during the day microcrustaceans moved close to the bottom, while rotifers showed narrower migration amplitudes. Larvae of the invertebrate predator Chaoborus displayed strong normal DVM, and appeared to synchronize its life cycle with the lunar cycle, with mass emergence of adults around New Moon.
Ecological relevance and sensitivity depending on the exposure time for two biomarkers
(Wiley, 2007) Melina Campero; F. Ollevier; Robby Stoks
Biomarkers are widely used to assess pesticide stress, but their ecological relevance and exposure time dependent sensitivity is still heavily debated. We studied both aspects in larvae of the damselfly Coenagrion puella, comparing the impact of low doses of atrazine, carbaryl, and endosulfan on two key biomarkers (acetylcholinesterase [AChE] activity and fluctuating asymmetry [FA]) and their relationship with life history traits (mortality, development time, growth rate, and body size). Larvae exposed to the pesticides had, in general, longer development times. Size, growth rate, and mortality were not affected by any of the pesticides. In the long-term exposure, AChE activity was diminished by atrazine treatments and stimulated by carbaryl treatments, and was not affected in the endosulfan treatments. FA decreased with increasing endosulfan concentrations and showed no reaction to atrazine or carbaryl. Overall, short-term exposure tended to overestimate the results of long-term exposure decreasing growth rates and enhancing inhibition of AChE activity in atrazine and carbaryl treatments. In line with its ecological relevance, relationship between biomarkers and life history traits showed that AChE inhibition was positively correlated with mortality, while FA was traded off with size. These results show that caution should be exerted when using these biomarkers to assess pesticide pollution in field situations.
Metamorphosis offsets the link between larval stress, adult asymmetry and individual quality
(Wiley, 2008) Melina Campero; Marjan De Block; F. Ollevier; Robby Stoks
1 It is poorly understood which traits translate larval stressors into adult fitness in animals where larval and adult stages are separated by metamorphosis. Although fluctuating asymmetry (FA) is often assumed to do so, especially in insects the relationship between larval stress, adult FA and individual quality is often absent. One suggested hypothesis for this is the higher mortality of low quality (hence more asymmetric) animals during metamorphosis (i.e. developmental selection hypothesis). 2 Here we test this hypothesis and also propose and test an alternative hypothesis where metamorphosis is stressful but not lethal and increases FA of all animals up to a certain level (i.e. stressful metamorphosis hypothesis). 3 We manipulated larval stress (food stress and pesticide stress) and measured FA before and after metamorphosis in the damselfly Coenagrion puella. Additionally, we assessed the relationship between FA and individual quality variables measured at metamorphosis (age, mass and two immune variables: phenoloxidase (PO) and haemocyte number). 4 Before metamorphosis, FA reflected the combination of food and pesticide stress and was negatively related with mass and both immune variables after metamorphosis. These patterns were, however, offset after metamorphosis. Low mortality, not linked to FA during metamorphosis, indicates that developmental selection cannot explain this. Instead, the strong increase in FA up to equal levels across treatments during metamorphosis supports the stressful metamorphosis hypothesis. 5 Taken together, the developmental stage in which FA is measured may critically determine the reliability of FA as an indicator of stress and of individual quality in insects.
SUBLETHAL PESTICIDE CONCENTRATIONS AND PREDATION JOINTLY SHAPE LIFE HISTORY: BEHAVIORAL AND PHYSIOLOGICAL MECHANISMS
(Wiley, 2007) Melina Campero; Stefanie Slos; F. Ollevier; Robby Stoks
Despite their relevance for risk assessment, the interactive effects of pesticide and predation cues are poorly understood because the underlying behavioral and physiological mechanisms are largely unknown. To explore these mechanisms, we reared larvae of the damselfly Coenagrion puella at three different predation risk levels and a range of environmentally realistic concentrations of three pesticides used worldwide (atrazine, carbaryl, and endosulfan). We compared key development responses (growth rate, developmental time, and final size) against food ingestion, assimilation, and conversion efficiency, and acetylcholinesterase (AChE) activity. Predation risk impaired all endpoints, including AChE activity, while the effects of pesticide stress were smaller for atrazine and endosulfan and absent for carbaryl. The effects of both stressors and their interaction on life history were mostly indirect through resource acquisition and energy allocation. Compensatory physiological mechanisms to pesticide stress (atrazine and endosulfan) were present in larvae reared in the absence of predation stress but were offset under predation stress. As a result, smaller size (atrazine and endosulfan) and lower growth rate (endosulfan) from pesticide stress were only found in the highest predation risk treatment. Our results provide insight as to the conditions under which interactions between stressors are likely to occur: damselfly populations at high density and living in fish ponds will be more affected by pesticides than populations at low densities in fishless ponds. By identifying variables that may shape the interaction between predation stress and other stressors such as pesticides, our mechanistic approach may help to bridge the gap between laboratory and field studies.
Trace Metal Levels in Chironomid Larvae and Sediments from a Bolivian River: Impact of Mining Activities
(Elsevier BV, 1998) Lieven Bervoets; Danilo Solis; Ana Romero; Paul A. Van Damme; F. Ollevier