| 1. |
- Flenner, Ida, 1976-, et al.
(författare)
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Predator-induced spine length and exocuticle thickness in Leucorrhinia dubia (Insecta : Odonata): a simple physiological trade-off?
- 2009
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Ingår i: Ecological Entomology. - Oxford : Wiley. - 0307-6946 .- 1365-2311. ; 34:6, s. 735-740
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Tidskriftsartikel (refereegranskat)abstract
- 1. Morphological defence structures evolve against predators but are costly to the individual, and are induced only when required. A well-studied example is the development of longer abdominal spines in dragonfly larvae in the presence of fish. Numerous attempts to discover trade-offs between spine size and behaviour, development time or body size have, however, produced little evidence. 2. We considered a physiological trade-off. Spines consist of cuticle and using material to build longer structures may result in less material remaining elsewhere. We therefore measured exocuticle thickness at nine locations on Leucorrhinia dubia larvae from habitats with and without fish. 3. Our results show a significant effect of the interaction between fish presence and spine length on head and fore leg exocuticle thickness. Relative thickness increased with relative length of lateral spine 9 in the absence of fish, whereas no such relationship existed with fish. Hence, synthesis and secretion of cuticle material occur as a trade-off when larvae react to fish presence. 4. We assume the mechanism to be a selective synthesis of material with different responses in different parts of the larval body. These findings offer a new angle to the fish/spine trade off debate.
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| 2. |
- Mühle, Lesley, et al.
(författare)
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Atmungsverhalten von Orthetrum cancellatum–Larven: Einfluss der aktuellen Temperatur und der Aufzuchtsbedingungen (Odonata: Libellulidae)
- 2009
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Ingår i: Libellula. - Börnsen : Gesellschaft deutschsprachiger Odonatologen. - 0723-6514. ; 28:1-2, s. 59-68
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Tidskriftsartikel (refereegranskat)abstract
- Ventilation behaviour of Orthetrum cancellatum larvae: influence of the current temperature and rearing conditions (Odonata: Libellulidae) — The intensity of respiration of larval Anisoptera can be determined by observing the frequency of abdominal movements. We used this to study the influence of the current temperature on the larval respiration of O. cancellatum. We assumed that (1) the breathing rate of the larvae increases with rising temperature and that (2) the response to the current temperature depends on the rearing conditions. The larvae were kept for nine months under four different rearing conditions. The egg clutches originated from two countries in different climate zones, from southern France in the Mediterranean area and from northern Germany in the temperate zone. Our experiment revealed that the ventilation rate increased with increasing temperature. This was more pronounced with higher rearing temperatures that the larvae experienced. We interpreted this as a habituation effect. The size of the larvae influenced the ventilation rate as well. On the other hand, the genetic and geographic origin of the larvae had no significant effect.
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| 3. |
- Sahlén, Göran, et al.
(författare)
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Morphology of dragonfly larvae along a habitat gradient : interactions with feeding behaviour and growth (Odonata: Libellulidae)
- 2008
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Ingår i: International Journal of Odonatology. - Abingdon, Oxfordshire : Taylor & Francis. - 1388-7890. ; 11:2, s. 225-240
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown that life history, behavioural as well as morphological traits vary with the habitats occupied by odonate larvae. Here we ask the following questions: (1) Are the morphological traits, which are associated with perception and foraging, related to the larval habitat? (2) Do these traits influence foraging success and growth rate? We analysed the morphology of species pairs belonging to the genera Crocothemis, Orthetrum and Trithemis; one species in each pair occurring in perennial spring-fed streams, the other able to develop in temporary waters. A PCA reveals four principal components of morphological characters which may be expressed as PC1: prey handling, PC2: visual perception, and PC3 and PC4: density of long and short setae on the feet. The variances of PC1, PC2 and PC3 were affected by phylogeny. PC1, PC2 and PC4 differed between habitats. Species of perennial springs had larger values for visual perception. These waters are clear and larger eyes should be beneficial. But, a high PC2 value was associated with low growth rate and did not affect foraging success. We therefore conclude that investment in better sight made by perennial water species may reflect the need of avoiding predators. Development in temporary waters mainly requires rapid growth and species may not be capable to invest also in visual perception. PC1 was negatively correlated with foraging behaviour and PC3 was positively so. This indicates the importance of prey capture mode to foraging success, which may, however, not translate into a higher growth rate.
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| 4. |
- Suhling, Frank, et al.
(författare)
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Behavioural and life history traits in temporary and perennial waters : comparisons among three pairs of sibling dragonfly species
- 2005
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Ingår i: Oikos. - : Blackwell Publishing. - 0030-1299 .- 1600-0706. ; 108:3, s. 609-617
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Tidskriftsartikel (refereegranskat)abstract
- Identifying and examining traits that influence the distribution of species is crucial to the understanding of community structure. Theory predicts that traits should differ between species that live in temporary and permanent waters because of differing major environmental variables; viz drying out and predator presence, respectively. Species, however, will also be influenced by their evolutionary history, i.e. by the traits of their common ancestors. We studied differences in life history and behaviour traits in a series of laboratory experiments using pairs of dragonfly species out of three genera of Namibian Libellulidae (Odonata) with one species from each type of habitat. As predicted, growth rates were significantly higher in the temporary water species compared to the permanent water species. Activity and foraging, in contrast, differed between the genera, but did not differ between the habitat types. Hence, our study implies that the behavioural traits are influenced by phylogenetic inertia rather than by the habitat variables, while growth rate is adapted to the habitat. We argue that in all three genera one species has diverged recently from a sister species that lives in the original habitat of the genus, which may be temporary waters in Crocothemis Brauer and in Orthetrum Newman, and permanent waters in Trithemis Brauer. The behavioural traits may therefore be less well adapted. Rapid growth may be the more relevant trait because it is crucial to survival in temporary waters.
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| 5. |
- Suhling, Frank, et al.
(författare)
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Dragonfly Assemblages in Arid Tropical Environments : A Case Study from Western Namibia
- 2006
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Ingår i: Biodiversity and Conservation. - : Springer Netherlands. - 0960-3115 .- 1572-9710. ; 15:1, s. 311-332
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Tidskriftsartikel (refereegranskat)abstract
- Dragonflies have been proposed as indicators for the ecosystem health of freshwater wetlands. For their useful functioning as indicators it is, however, necessary to identify species compositions in specific habitats and species-habitat associations, particularly in the tropics, where such knowledge is still weak. We examined the dragonfly species composition of 133 localities in the arid environment of western Namibia. An analysis of nestedness indicated that distinct, and predictable patterns of species associations can be expected. Discriminant analyses revealed that most of the nine habitat types separated by structural and hydrological parameters are well discriminated by their dragonfly assemblages. Spring brooks in particular host a specific assemblage, which is threatened due to the habitat restriction of several species, as well as by recent habitat loss and degradation. Using a hierarchical method of several criteria we demonstrated the selection of a set of potential indicator species from the species set, most of these being useful indicators for spring brook assemblages. The conservation status of certain habitats and species is discussed. We propose that dragonflies will have a high indicator potential for threatened freshwater wetlands in such areas and may also serve as an indication of the sustainable use of water resources including evaluating measures to rehabilitate environments.
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