Search publications of the members of the Royal Belgian institute of natural Sciences
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Relationship between fluctuating asymmetry and fitness within and between stressed and unstressed populations of the wolf spider Pirata piraticus
- Although developmental instability, measured as fluctuating asymmetry (FA), is expected to be positively related to stress and negatively to fitness, empirical evidence is often lacking or contradictory when patterns are compared at the population level. We demonstrate that two important properties of stressed populations may mask such relationships: (i) a stronger relationship between FA and fitness, resulting in stronger selection against low quality (i.e. developmental unstable) individuals and (ii) the evolution of adaptive responses to environmental stress. In an earlier study, we found female wolf spiders Pirata piraticus from metal exposed populations to be characterized by both reduced clutch masses and increased egg sizes, the latter indicating an adaptive response to stress. By studying the relationship between these two fitness related traits and levels of FA at individual level, we here show a significant negative correlation between FA and clutch mass in metal stressed populations but not in unstressed reference populations. As a result, levels of population FA may be biased downward under stressful conditions because of the selective removal of developmentally unstable (low quality) individuals. We further show that females that produced larger eggs in stressed populations exhibited lower individual FA levels. Such interaction between individual FA and fitness with stress may confound the effect of metal stress on FA, resulting in an absence of relationships between FA, fitness and stress at the population level.
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Response of snails and slugs to fragmentation of lowland forests in NW Germany
- Habitat fragmentation is a major cause for species loss, but its effect on invertebrates with low active dispersal power, like terrestrial gastropods, has rarely been studied. Such species can not cross a hostile habitat matrix, for which the predictions of island theory, such as positive relations between species richness and patch size, should apply. In order to test this prediction, we studied gastropod species diversity by assessing gastropod assemblage characteristics from 35 sites in 19 fragments of deciduous old-growth forests in the Lower Rhine Embayment, Germany. Assemblages differed between larger (a parts per thousand yen700 ha) and smaller forests ( 400 ha), those of large forests held a higher percentage of forest species. Although alpha-diversity was similar between the two forest size classes, small forests often comprised matrix species, resulting in a higher beta-diversity. Edge effects on the species richness of matrix species were noticeable up to 250 m into the forest. Hierarchical partitioning revealed that distance to disturbances (external edge, internal edges like roads) explained most assemblage variables, whereas forest size and woodland cover within a 1 km radius from the sites explained only a few assemblage variables. Densities of two forest-associated species, Discus rotundatus and Arion fuscus, decreased with forest size. Yet, forest size was positively correlated with richness of typical forest species and densities of Limax cinereoniger. The latter species seems to need forests of 1,000 ha, i.e., well above the size of most fragments. In conclusion, the prediction is valid only for forest species. The response to fragmentation is species specific and seems to depend on habitat specialization and macroclimatic conditions.
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Site Fidelity of Formica rufa: Micro-Scaled and Persistent Despite Disturbance (Hymenoptera: Formicidae)
- Long-term site fidelity or Ortstreue is an individual foraging strategy typical of ants exploiting stable and predictable food sources in space and time. Red wood ant workers (Formica s. str.) are central-place foragers feeding on honeydew secreted by stable aphid populations. In this field study, temporal site fidelity of Formica rufa honeydew tenders was investigated on a micro-scaled level for a period of time. Additionally, the effect of exchanging honeydew workers between two trees on site fidelity was examined. Site fidelity of the honeydew tenders was very high and they returned repeatedly to particular micro-sites (branches, set of leaves) on a tree. The transfer to a new feeding site apparently did not influence site fidelity as honeydew tenders mainly return to their initial tree. Small-scale site fidelity decreased with time and was not so rigid as larger-scale fidelity. We discuss how site fidelity on one hand and flexibility in foraging and recruiting on the other hand promote foraging efficiency of the colony.
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Spiders do not escape reproductive manipulations by Wolbachia
- Background: Maternally inherited bacteria that reside obligatorily or facultatively in arthropods can increase their prevalence in the population by altering their hosts' reproduction. Such reproductive manipulations have been reported from the major arthropod groups such as insects (in particular hymenopterans, butterflies, dipterans and beetles), crustaceans (isopods) and mites. Despite the observation that endosymbiont bacteria are frequently encountered in spiders and that the sex ratio of particular spider species is strongly female biased, a direct relationship between bacterial infection and sex ratio variation has not yet been demonstrated for this arthropod order. Results: Females of the dwarf spider Oedothorax gibbosus exhibit considerable variation in the sex ratio of their clutches and were infected with at least three different endosymbiont bacteria capable of altering host reproduction i.e. Wolbachia, Rickettsia and Cardinium. Breeding experiments show that sex ratio variation in this species is primarily maternally inherited and that removal of the bacteria by antibiotics restores an unbiased sex ratio. Moreover, clutches of females infected with Wolbachia were significantly female biased while uninfected females showed an even sex ratio. As female biased clutches were of significantly smaller size compared to non-distorted clutches, killing of male embryos appears to be the most likely manipulative effect. Conclusions: This represents to our knowledge the first direct evidence that endosymbiont bacteria, and in particular Wolbachia, might induce sex ratio variation in spiders. These findings are pivotal to further understand the diversity of reproductive phenotypes observed in this arthropod order.
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Spinnen en zware metalen: 1. Een kort overzicht van de literatuur
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Storage mediums affect metal concentration in woodlice (Isopoda)
- Terrestrial invertebrates are becoming widely established as tools to assess heavy metal pollution at contaminated sites. A practical and time saving method to sample terrestrial invertebrates consist of pitfall traps, often filled with a 4\% formaldehyde solution and some detergent. The reliability of metal concentrations based on organisms captured and stored in this solution might however be questioned and we therefore tested the effect of formaldehyde on Zn, Cu, Cd and Pb concentration experimentally in three isopod species. Our results showed that in many cases, significant decreases in Cu concentrations compared to animals stored in a freezer were observed that could be as high as 40\%, while Zn, Cd and Ph concentrations increased. A regression analysis of individual dry weight on individual size revealed that formaldehyde decreases the dry weight substantially and in that way causes increased measurements of Zn, Cd and Pb concentrations. We conclude that pitfall traps with formaldehyde should better not be used to collect animals in which concentrations of heavy metals or other toxic substances will be determined. (C) 2002 Elsevier Science Ltd. All rights reserved.
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Survival differences of the two male morphs in the dwarf spider Oedothorax gibbosus Blackwall, 1841 (Erigoninae, Linyphiidae, Araneae)
- Oedothorax gibbosus is a rare dwarf spider species in Flanders bound to oligo- and mesotrophic alder carrs. This dwarf spider is characterised by the appearance of a male dimorphism; there is a gibbosus male morph with a hunch on the last third of the carapace, anterior to which is a hairy groove, and a tuberosus morph without these features. Earlier studies have already indicated some differences between both male morphs. According to VANACKER et al. (2001) the juvenile phase (the period between the emergence of the spiders and the last moult) of the gibbosus morph is significantly longer than the juvenile phase of the tuberosus morph, and this is presumably necessary for the production of the hunch and the hairy groove. This hairy groove probably secretes a fluid that is important for the gustatoric courtship behaviour and gibbosus would therefore have a reproductive advantage (HEINEMANN & UHL, 2000). In this paper we report another interesting difference between both morphs. To examine if the male morphs also differ in survival, some survival experiments, in normal food and moisture conditions and in two extreme conditions, namely in foodless and low moisture environments, were set up. The gibbosus male is significantly more susceptible to foodless conditions than the tuberosus male, and also in normal conditions tuberosus lives significantly longer than gibbosus. This is demonstrated by means of survival curves. In low moisture conditions, however, we could not prove that survival rate differs between both male morphs. The higher survival rate of tuberoses is a possible explanation for the morph ratio in favour of tuberosus in the studied field population.
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Synecology of spiders of gravel banks and environmental constraints along a lowland river system, the Intermeuse (Belgium, the Netherlands) (Araneae)
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The effect of successional stage and salinity on the vertical distribution of seeds in salt marsh soils
- Seed bank density and similarity between above-ground vegetation and seed bank with depth were compared between two adjacent salt marshes that differ in age. In addition, the effect of salinity on the variation in seed bank density and similarity between above-ground vegetation and seed bank with depth was compared between euhaline against mesohaline conditions in three salt marshes. Ten plots of 2 m x 2 m were situated in a new salt marsh (existing since 2002) and 80 plots in three old salt marshes. Soil samples were collected at three different depths (0-5, 5-10, 10-15 cm) in spring 2006. Soil seed bank was investigated in germination experiments under greenhouse conditions. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Above-ground vegetation composition was determined during the growing season in all plots. Viable seed density was calculated for each plot and for the three different depths; the similarity between seed bank and floristic composition of the above-ground vegetation was calculated. A general linear model was used to investigate the effect of soil depth, salinity and age of the salt marsh on density and similarity between seed bank and above-ground vegetation. The results showed that seed density decreased with depth in all salt marshes, irrespective of their age and soil salinity. Seed density and similarity between seed bank and above-ground vegetation were higher in the new salt marsh than in the old one in the same study area. This is because in young as well as in old successional stages, the seed bank was mostly composed of new colonizers, while most perennial species were absent from the soil seed bank, although they were dominant in the standing vegetation of the old salt marsh. The characteristics of the seed bank of a mesohaline salt marsh were found not to be fundamentally different from that of both euhaline salt marshes. (C) 2010 Elsevier GmbH. All rights reserved.
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The effects of forest patch size and matrix type on changes in carabid beetle assemblages in an urbanized landscape
- In this study we compared ground beetles (Carabidae) from a range of different forest fragments along an urbanization gradient in Brussels, Belgium. We address the following questions: (i) How does the degree of urbanization in the surrounding habitat affect forest beetles, and does it interact with the effects of patch size and distance to forest edge? (ii) Do these factors have a different effect at the level of individual species, habitat affinity groups or total community? During 2002 we sampled 13 forest plots in 10 forest patches, ranging in size from 5.27 to 4383 ha. The beetles were captured using transects of pitfall traps from the edge to a distance of 100 m into each woodland and identified to species level. Effects of urbanization, forest size and forest edge were evaluated on total species number, abundance and habitat affinity groups and ten abundant, widespread model carabid species. Overall, the effects of urbanization, forest size and edge effects slightly influenced total species richness and abundance but appeared to have a major effect on ground beetle assemblages through species specific responses. More urbanized sites had significantly fewer forest specialists and more generalist species. Large forest fragments were favoured by forest specialist species while generalist species and species frequently associated with forest (forest generalists) dominated the smaller forests. Forest edges mainly harboured generalist species while forest specialist species were more frequent into the forests if the forest patches were large enough, otherwise they disappeared due to the destruction or impoverishment of their habitat. Our results show the importance of differentiating between habitat affinity, especially habitat generalists versus specialists, the latter having a higher value in nature conservation, and merely the quantity of species represented in human-dominated areas. (c) 2008 Elsevier Ltd. All rights reserved.
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The importance of biological factors affecting trace metal concentration as revealed from accumulation patterns in co-occurring terrestrial invertebrates
- As physicochemical properties of the soil highly influence the bioavailable fraction of a particular trace metal, measured metal body burdens in a particular species are often assumed to be more reliable estimators of the contamination of the biota. To test this we compared the Cd, Cu and Zn content of three spiders (generalist predators) and two amphipods (detritivores), co-occurring in seven tidal marshes along the river Schelde, between each other and with the total metal concentrations and the concentrations of four sequential extractions of the soils. Correlations were significant in only one case and significant site x species interactions for all metals demonstrate that factors affecting metal concentration were species and site specific and not solely determined by site specific characteristics. These results emphasize that site and species specific biological factors might be of the utmost importance in determining the contamination of the biota, at least for higher trophic levels. A hypothetical example clarifies these findings. (C) 2003 Elsevier Ltd. All rights reserved.
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The richness and paucity of the spider fauna of the Belgian coast.
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La Formation des schistes noires de Matagne et l'extinction du Dévonien Supérieur
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A single tooth replacement pattern generates diversity in the dentition in cichlids of the tribe Eretmodini, endemic to Lake Tanganyika.pdf
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Biology of the Soricidae
- Crocidura is the largest shrew genus, and occurs in most of the Old World. Its taxonomy is complex, and some species are morphologically so similar that they are allocated to “species groups”. Among the African Crocidura, several species are in need of taxonomic revision or are known by a few speci- mens only. Additional sampling is necessary to in- crease the number of specimens available in order to perform multivariate analyses of morphological characters. Meanwhile, molecular tools might help solve taxonomical difficulties and select specimens for further analyses. We used a combined morpho- logical and molecular approach to investigate spe- cies boundaries and phylogenetic relationships within African Crocidura species groups. We se- quenced part of the 16s rRNA mitochondrial gene of 131 specimens, representing a minimum of 30 morphologically defined species. Mitochondrial DNA sequences confirmed the distinctness of spe- cies in groups where cranio-dental characters allow reliable specific identification, but failed to confirm the differentiation of species within the most com- plex species groups. Within two of these groups, haplotypes tended to cluster by localities rather than by putative species, suggesting potential synonymy. We also detected three potentially new or unrecog- nized species. Our findings are encouraging, but will have to be further investigated using multivariate analyses of morphological characters and additional molecular analyses.
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Chapter 14 Genetic Traces Of Environmental Variations In Ancient Lakes
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De la phylogénie comparée à la biogéographie historique l'exemple des quelques mammifères forestiers d'Afrique Centrale
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Lake level fluctuations and speciation in rock-dwelling cichlid fish in lake Tanganyika, East Africa
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Mitochondrial Phylogeny of African woord mice, genus Hylomyscus (Rodentia, Muridae): Implications for their taxonomy and biogeography
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Mitochondrial phylogeny reveals differential modes of chromosomal evolution in ther genus tatera (Rodentia: Gerbillinae) in Africa
