70 search hits
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Behavior and Ecology of Wild Slow Lorises (Nycticebus coucang): Social Organization, Infant Care System, and Diet
(2002)
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Frank Wiens
- In this thesis I describe the social organization, infant care system, and diet of the slow loris Nycticebus coucang, a nocturnal arboreal prosimian primate, in the Malaysian rainforest. Data collected are locational data obtained during 1,000 h of radio-tracking slow lorises, behavioral data from visually observing radio-collared individuals, morphometric data, and records on food remains from fecal analysis. Though close-range encounters were very rare, I observed slow lorises to form stable social units ('social groups') characterized by home range overlap and friendly interactions among members and nonoverlap between groups. Four groups were observed, each consisting of a single adult female, a single adult male and a varying number of younger individuals. Group composition, together with relatively small testis volume and natal dispersal occuring in both sexes, hints towards a monogamous mating system. In one case an extended family group formed by delayed dispersal of a primary pair's offspring. Friendly interactions among group members included allogrooming, following, alternate click-calls, and sleeping in contact. Yet, members did not engage in any co-operative behaviour of the types usually thought to be responsible for group formation in gregarious mammals. One important factor contributing to the sharing of space between slow lorises is probably that chances of successful dispersal are low. However, subtle benefits arising from the presence of conspecifics (allogrooming, transfer of information on food resources) may also be crucial for the formation or maintenance of slow loris spatial groups. The infant care system was also notable for the very low frequency of direct encounters between animals. Active maternal care seemed to be limited to carrying the young to the sleeping place and regular suckling, and grooming of the infant. Non-maternal infant care appeared to be restricted to occasional infant grooming and infant carrying. It has been suggested that young lorises depend on their mothers for information on diet and that they obtain this information by watching their mothers feeding or interacting directly with their mothers over food. I tested this hypothesis on a group including one infant and four older individuals. The infant of the focus group only took food items to the mouth which were also part of its social group's diet and showed concordance in the frequency of use of feeding sites with other members of its group. These results speak against diet learning by trial and error. They indicate that diet learning by infants probably does depend on information obtained from older conspecifics. However, the infant of the focus group was not involved in direct interactions with conspecifics over food and fed mostly alone. It was not within a distance where it could see older conspecifics feeding more often than expected from the configuration and utilization of the individuals` home ranges. When feeding in vicinity of other slow lorises the infant never looked at them. This suggests that, contrary to expectations, visual observation or direct interaction over food are not the mechanisms by which information on food resources is passed from older individuals to young, but that other ways of obtaining such information are used by immature wild slow lorises. The slow loris is a slow-moving animal known to have a very low basal metabolic rate relative to other eutherian species of its body mass. A slow pace of life has been causally linked to a low intake rate of usable energy due to a diet that (1) is generally low in energy, (2) is unpredictably periodically scarce, and (3) contains high amounts of toxins or digestion inhibitors. In order to assess whether the slow loris faces any of these three kinds of limitation in energy supply I studied its dietary habits by direct observations of feeding behavior and by fecal analysis. The diet was composed of five distinct types of food: floral nectar and nectar-producing parts, phloem sap, fruits, gums (another group of plant exudates), and arthropods. The largest proportion of feeding time was spent on phloem sap (34.9%), floral nectar and nectar-producing parts (31.7%), and fruits (22.5%). These food types should provide the slow lorises with high amounts of easily digestible sugars indicating that slow lorises did not face an energy-poor diet. Furthermore, I found no evidence for seasonal food shortages: dietary habits were indistinguishable between rainy- and dry seasons, even though most dry season data were collected during periods of extreme drought induced by the 1997-1998 El Nino Southern-Oscillation event. However, many genera of food plants are known to contain secondary compounds that are toxic or reduce digestibility. I suggest that low metabolism in slow lorises is at least partly related to the need to detoxify secondary compounds in high-energy plant diet.
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Diversity of geometrid moths in a montane rainforest in Ecuador
(2002)
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Gunnar Brehm
- The diversity of the very species-rich family of geometrid moths was investigated in a montane forest at the border of the Podocarpus National Park in southern Ecuador along an altitudinal gradient ranging from 1,040 m to 2,677 m above sea level. This study is part of a larger interdisciplinary project on diversity and functioning of a montane forest ecosystem. A total of 13,938 moths representing 1,010 species were sampled in light-traps at eleven elevational levels (two replicate sites each). Most species belonged to the subfamily Ennominae (500 sp.), followed by Larentiinae (391 sp.), Sterrhinae (58 sp.), Geometrinae (57 sp.), Oenochrominae (3 sp.), and Desmobatrinae (1 sp.). The study covers aspects of host-plant relationships, community structure, endemism, alpha-, beta-, and gamma-diversity. The role of different environmental factors as mechanisms for the diversity of the moths is discussed. Furthermore, methodological aspects of light-trap sampling, and selection of appropriate diversity measures and analytical tools are considered in this study.
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Social life-styles in caterpillars: Behavioral mechanisms and ecological consequences
(2002)
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Claudia Ruf
- The present thesis investigates ecological advantages, ethological adaptations, and behavioral mechanisms connected with sociality in larval Lepidoptera. Data on social thermoregulation, larval communication, developmental benefits, and advantages of survival are presented to contribute to a better understanding of the evolution and maintenance of social systems in caterpillars. I put the main emphasis of this work on the highly social, tent building European lasiocampid moth Eriogaster lanestris. In a comparative study aspects of the social biology of E. lanestris were compared to its congener E. catax and the confamilial species Malacosoma neustria. In addition to these tent building, central-place foraging species a fourth, non-tent building nomadic butterfly species, Araschnia levana (Nymphalidae) was also studied. Caterpillars of E. lanestris are behavioral thermoregulators. In the laboratory (i.e. in the absence of solar radiation) tightly aggregated caterpillars are able to rise their body temperatures compared to ambient temperature for 2.5-3K. Temperature gains are based on metabolic heat production (Chapter 4). Under field conditions grouped caterpillars are able to stabilize their body temperatures between 30-35°C independent of ambient temperature as long as solar radiation is sufficient. Optimal body temperatures are achieved by changing positions in and on the tent frequently. The functionality of the tent is based on the reduction of convective heat exchange (Chapter 5). Foraging bouts of E. lanestris caterpillars are highly synchronized under field conditions. The number of foraging bouts is temperature dependent (influence on speed of digestion and walking). Plasticity in foraging patterns optimizes nutrient uptake and therefore minimize developmental time (Chapter 6). Caterpillars of E. lanestris use trail pheromones for communication. The pheromone is applied by dragging the ventral median sternite of the last abdominal segment over the substrate. Trails contain information about age and suitability of foraging sites, which is encoded by quantitative graduation of the trail marker (opposing processes of aging and (over)marking) (Chapters 7+8). Vibrations of the tent caused by the increasing restlessness of caterpillars at the end of the digestion phase turned out to be tightly linked to the emergence of larvae from the tent and are supposed to play a role for synchronizing the foraging bouts (Chapter 9). Costs of social behavior in E. lanestris are high under field conditions. Total colony mortality (i.e. the complete loss of a female’s offspring) of 100 exposed colonies was 48%. The majority of colony losses was connected to the previous loss of the tent, mostly initiated by heavy rainfalls (Chapter 10). Comparing E. lanestris to E. catax and M. neustria revealed that despite similar life-history traits and overlapping habitat requirements very different ecological strategies evolved with regard to egg size, tent building behavior, foraging strategies, and activity patterns (Chapter 11). Females of A. levana produce several egg clutches of different size over their life time. Caterpillar group size strongly influences development and survival. Single individuals develop more slowly and achieve smaller weights compared to groups of 10, 40 (=mean natural clutch size), or 80 individuals during the social phase of the caterpillars’ life (i.e. first to third instar). Mortality is highest in singly bred individuals and lowest in groups of 40. The advantage of grouping for survival is supposed to result from the strong collective regurgitation behavior which enables the caterpillars to ward off natural enemies (Chapters 12+13). The thesis shows with the example of E. lanestris that highly evolved social systems in larval Lepidoptera afford high parental and larval investment which may in turn lead to high advantages, e.g. with regard to large reductions in developmental time. The extended social phase requires highly sophisticated communication processes. In A. levana flexible egg deposition leads to higher plasticity with regard to the costs of sociality. Nevertheless, physiological and ecological advantages of group living are evident as well.
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Analysis of alkali-inducible genes of Bacillus subtilis
(2003)
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Akram Atalla
- Using the DNA macroarray technique, it could be shown that more than 80 genes induced after alkali shock (Wiegert et al., 2001). While most of them are under the control of the alternative sigma factor (sigmaW), the remaining genes are under the control of one or more unknown regulator(s). By their signature, two of them kipR and yvdT code for regulatory proteins, while pspA, member of the sigmaW regulon, encodes another potential regulator. In this doctoral work, the genes kipR, yvd and pspA were analyzed. The kipR and yvdT genes code for a transcriptional regulator of the IcIR and TetR/AcrR family while the pspA encode a transcriptional anti-activator in E. coli . In Northern blot analyses, it could be shown that all three genes are induced after alkali shock. The transcription start points of the kipR and yvdT genes were identified by primer extension experiments, and it appeared that the transcription is dependent on a vegetative sigma A-like promoter. To identify genes which are under the negative control of the transcriptional anti-activator PspA, a DNA macroarray experiment was carried out. It turned out that several genes are repressed by a factor of at least three under conditions of PspA overproduction. By using the Far-western blot technique, a protein which might interact with the PspA protein was identified. This protein has a molecular weight approximately 50 kDa. In addition, expression of the pst operon ( pst stay for phosphate-specific transport) was analyzed which is induced after phosphate starvation and after alkaline shock. The genes of this operon are involved in the phosphate transport into the cytoplasma. By Northern-blot experiments, it could be shown that all genes of this operon are alkali-inducible. When the transcriptional start point was determined by primer extension, it turned out to be identical to the one determined under phosphate limitation. This transcription start point is preceded by a typical sigmaA-type promoter. Furthermore, alkali-induction is dependent on the PhoP-PhoR two-component signal transduction system. Phosphate-uptake experiments revealed that the uptake of inorganic phosphate was completely abolished after increasing the external pH value.
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QUANTIFYING THE DISTRIBUTION OF FOREST FUNCTIONAL TYPES AND FOREST LEAF AREA INDEX IN THE ALPS
(2003)
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Albena Bobeva
- Land cover change is an important element of global environmental change processes. Most ecosystem processes strongly depend on land cover and its attributes. Mapping land cover, especially in mountain terrain is a difficult and challenging task. Remote sensing is an attractive source of thematic maps, such as those depicting land cover. Thematic mapping from remote sensing data is typically based on image classification. The image classification procedure synthesizes satellite data with field data and other ancillary data derived from a Geographic Information System (GIS - ArcInfo) coverage. The present study combines GIS and remote sensing data to produce a land cover map for the National Park Berchtesgaden and to build an extrapolation for other test areas in the Alps (Stubai and Ötz Valleys). Although a vast GIS data set had been assembled for the National Park, remote sensing was not previously used as a tool for land cover mapping and forest ecosystem analysis. For supervised classification, the maximum likelihood algorithm was used to sort and group data into discrete classes, which can be uniquely identified. Comparison and accuracy assessment with „ground truth“ data was carried out. An overall accuracy of 86% and 87% of the classification results in the National Park Berchtesgaden and in Stubai Valley, respectively, was achieved. Another important parameter determining gas exchange (water loss and carbon gain) of alpine forests is Leaf Area Index (LAI). Remote sensing provides a means to estimate LAI over large areas. To map LAI in mountain regions, Landsat TM NDVI index and SR index were examined together with forest inventory data of the Berchtesgaden National Park. “Ground truth” point grid maps for LAI were obtained through the use of allometric relationships (relating tree size and leaf area) as derived from tree harvests and together with the forest inventory database. On the basis of the forest mask derived from land classification and the Landsat vegetation indices, homogeneous forest polygons were identified. They were used for polygon by polygon correlation between LAI and vegetation indices. Mean forest polygon values were used to determine the relationships. With the derived equations, LAI was mapped at 30m resolution (Landsat data). Using the digital elevation model, the distribution of the vegetation types and LAI along elevation gradients was investigated. The results in National Park Berchtesgaden were further used in an extrapolation to classify land cover in Stubai and Ötz Valleys. Except to detect the distribution of land cover classes, supervised classification was used as a part of the algorithm for predicting forest leaf area index at the investigated sites. The digital LAI map of Stubai Valley was compared with LAI map derived from allometric relationships in Neustift (part of Stubai Valley). A correlation between NDVI and LAI in Neustift was derived. The validation results derived for coniferous forest in Neustift (Stubai Valley) show good correspondence to the results derived in Berchtesgaden. For both investigated sites, leaf area index can successfully be described with simple and reasonable correlation with NDVI.
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How availability and quality of nectar and honeydew shape an Australian rainforest ant community
(2003)
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Nico Blüthgen
- Ant communities visiting nectar and honeydew sources were studied in a tropical lowland rainforest in North Queensland, Australia. The study focused on the hypothesis whether the distribution and composition of nectar and honeydew diets influence resource partitioning and competition in the ant community, and thus regulate community composition. Ants were the most common consumers on all extrafloral nectaries, while they constituted only a minority of floral visitors. In total, 43 ant species were observed to consume nectar from extrafloral nectaries (34 plant species) or from flowers (14 plant species), and wound sap exudates (three plant species). Six nectar-foraging ant species attended trophobionts (including at least 12 species of homopterans and two species of lycaenid caterpillars) for honeydew. Ant species showed a significant compartmentalisation of nectar use across plant species, although most ant species visited a broad spectrum of plants that strongly overlapped between different ants. Trophobioses were much more specialised at the study site, and some ant species attended certain trophobionts exclusively. On each plant individual, only a single ant colony was observed attending trophobionts. In contrast, simultaneous co-occurrences between different ant species foraging for nectar on the same plant individuals were common (observed in 23% of the surveys), although these proportions varied strongly across plant and ant species. The two most dominant ant species (Oecophylla smaragdina and Anonychomyrma gilberti) had mutually exclusive territories, and they were each associated with a significantly different assemblage of other ant species on nectar plants. This community pattern corresponds with the concept of ant mosaics that is based on dominance hierarchies. Honeydew and nectar sources varied substantially in carbohydrate and amino acid concentration and composition (HPLC analyses). There was a strong relationship between the composition of these resources and their use by ants, in particular by the dominant O. smaragdina. Among all 32 nectar and honeydew sources analysed, resources actually consumed by this ant were characterised by relatively similar amino acid profiles and higher total sugar concentration. The most common diets of O. smaragdina included two honeydew sources (Sextius ‘kurandae’ membracids on Entada phaseoloides and Caesalpinia traceyi legume lianas) and two extrafloral nectars (Flagellaria indica and Smilax cf. australis) that had the broadest spectrum of amino acids. Furthermore, these trophobioses on lianas showed a significantly higher per capita recruitment of this ant species (number of workers per individual homopteran) compared to trees. F. indica and S. cf. australis extrafloral nectaries were also commonly monopolised by O. smaragdina in a similar way as trophobioses; co-occurrences were significantly rarer than at other nectar sources. Field experiments on nectar preferences were performed using artificial sugar and amino acid solutions in pairwise comparisons. Preferences among sugars were largely concordant between ant species. For most ant species, sucrose was more attractive than any other sugar, and attractiveness increased with sugar concentration. Most ant species also preferred sugar solutions containing mixtures of amino acids over pure sugar solutions. However, choices between different single amino acids in sugar solutions varied substantially and significantly between species. Preferences between solutions were significantly reduced in the presence of competing ant species. Thus the experiments show that both variability in gustatory preferences, especially for amino acids, and conditional effects of competition may be important for resource selection and partitioning in nectar feeding ant communities. Stable carbon and nitrogen isotope composition was analysed for 50 ant species, and additionally for associated plants, homopterans and other arthropods from the study site. Nitrogen isotope ratios (d15N) of ants were not correlated with those of plant foliage from which the ants were collected. Instead, d15N may represent a powerful indicator of trophic position of omnivorous ants like in other foodweb studies, suggesting that members of the ant community spread out in a continuum between largely herbivorous species, feeding on nectar or honeydew, and predatory taxa. Variability between colonies of the same species was also pronounced. d15N values of O. smaragdina colonies from mature forests, where most of their nectar and honeydew sources are found, indicate lower trophic levels than isotope signatures of colonies from open secondary vegetation. This study demonstrates that the distribution and quality of honeydew and nectar sources have a strong structuring impact in diverse tropical ant communities. Amino acids were found to play a key role for ant species preferences and competition, and for nitrogen fluxes to colonies of the arboreal ant fauna.
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Isolation and characterization of the B-type allatostatin gene of Gryllus bimaculatus de Geer (Ensifera, Gryllidae)
(2004)
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Junling Wang
- 1. Cricket B type allatostatins, which belong to a neuropeptide family sharing the conserved W(X)6Wamide structure, exhibited inhibitory functions on the biosynthesis of juvenile hormones (JH) in vitro in the corpora allata (CA) as well as on ecdysteroid biosynthesis in the ovary of adult crickets (Gryllus bimaculatus). To understand the mechanisms of function of the pleiotropic cricket B type allatostatins, it is necessary to characterize their gene (preprohormone) and study the spatial and temporal expression patterns of the gene. 2. By PCR screening of a random primer cDNA library and by RACE (Rapid Amplification of cDNA Ends), a 535 bp 3´cDNA sequence of the cricket B type allatostatin gene was yielded. This 3´cDNA fragment encodes a putative translation product of 85 amino acids with potential dibasic endoproteolytic cleavage sites, which may allow processing into six peptides including three copies of Grybi-AS B1 (GWQDLNGGWGa) and single copies of Grybi-AS B2 (GWRDLNGGWGa), Grybi-AS B3 (AWRDLSGGWGa), and Grybi-AS B6 (AWNNLGSAWGa), respectively. Three of these deduced peptides were previously isolated from cricket brain extracts by conventional chromatographic techniques and were designated as Grybi-AS B1, Grybi-AS B2, and Grybi-AS B3. The Grybi-AS B6 neuropeptide represents a novel member of the B type allatostatins. 3. The nucleotide sequences encoding the type B allatostatins are high in GC-content and show strong homology. The highest GC-content was found for Grybi-AS B3 with 83.3%. The similarity of the nucleotide sequences encoding Grybi-AS B2 and Grybi-AS B1 is 93.3%, whereas Grybi-AS B2 and B3 share 90% nucleotide identity. 4. By Southern blot analyses, it was proven that the Grybi-AS type B gene is present as a single copy per haploid genome of G. bimaculatus. 5. By RT in situ PCR technique, it could be demonstrated that the Grybi-AS B gene is expressed in various tissues of 1 day old female adult crickets: In the central nervous system the Grybi-AS B gene expression was detected in the brain. In the protocerebrum, strong positive signals were found in the median neurosecretory cells, and to a lesser extent in lateral neurosecretory cells and in neurons. Gene expression was also found in the neurosecretory cells of the deuterocerebrum and the tritocerebrum. Furthermore, Grybi - AS B gene expression was localized in neurosecretory cells of the suboesophageal ganglion (SOG), the thoracic ganglia, and the abdominal ganglia. In the germarium and in primary oocytes of the ovary, Grybi-AS B gene expression was detected as condensed signals in the nuclei, but not in the prefollicular cells or the cytoplasm. With ongoing development of the oocytes, the signals in the nuclei (germinal vesicles) appeared as separated granules with weaker intensity, which finally disappeared, whereas in the follicular cells strong signals became apparent. Grybi-AS B gene expression was also detected in the epithelial cells of the accessory reproductive glands of female crickets. In the caecum and midgut, Grybi-AS B gene expression was found in endocrine secretory and epithelial cells, whereas in the hindgut, positive RT in situ PCR signals were detected in both longitudinal and circular muscles and in the gut epithelial cells. Grybi-AS B gene expression was also found in cells of the fat body and in thoracic (flight) muscles. 6. The results on Grybi-AS B gene expression as obtained by RT in situ PCR were confirmed by RT-PCR and RNA dot blot analyses. The expression of the Grybi-AS B gene in various tissues of adult females varied in an age-dependent manner. In brains of virgin females gene expression increased from the day of emergence until day 8 of adult life. In the ovary of virgin females gene expression showed a maximum at day 4 after ecdysis, whereas in mated females gene expression was high during the first two days and at days 6 to 7, but low inbetween. In caecum and midgut of virgin females gene expression was low during the first 5 days after ecdysis, but peaked at days 6 and 7, whereas in the hindgut gene expression was highest at day 3 of adult life. In the fat body, gene expression showed highest values on day 1 and days 6 to 7 after ecdysis. 7. Gene expression in brain, testes, and accessory reproductive glands of 0 to 3 days old male crickets was also demonstrated by RT-PCR and RNA dot blot analyses.
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The signal transduction of the adipokinetic hormone and regulation of energy metabolism in the cricket, Gryllus bimaculatus de Geer (Ensifera: Gryllidae)
(2004)
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Anurag N. Anand
- The fat body from the cricket, Gryllus bimaculatus incorporates acetate, glycerol or palmitate into lipid in vitro. Adipokinetic hormone (AKH) inhibits acetate incorporation into lipid by the fat body from adult crickets in vitro. AKH inhibits palmitate incorporation into lipid to a small extent, however, it does not influence the incorporation of palmitate into different lipid classes. In the presence of AKH, glycerol incorporation into lipid by the adult cricket fat body increases by several fold. AKH does not influence the incorporation of glycerol into different lipid classes. The fat body incorporates glycerol mainly into triacylglycerol (TAG) and almost exclusively into the backbone. AKH inhibits fatty acid (FA) synthesis but not the coupling of FAs with the glycerol backbone. Triacylglycerol lipase (TGL) from the fat body, in last larval instar and adult crickets, shows an age-dependent pattern of activity. AKH activates TGL, but does not regulate ACCase, ACL and FAS upon treatment of the fat body for a short period, under the assay conditions. The FAS and acetate incorporation activities are highly correlated in an age-dependent manner and are highest on day 2 of the adult stage. The activation of the formation of sn-1,2-DAG from TAG, in the fat body by AKH seems to be via the removal of FAs at positions 1 and 3, followed by reacylation of 2-MAG. The presence of calcium in the incubation medium is crucial for the inhibition of acetate incorporation by AKH; possibly it is essential for the binding of AKH to the receptor. The influx of acetate and calcium into and efflux of calcium from the cytosol are not affected by AKH. The release of calcium from intracellular calcium stores in the fat body, caused by thapsigargin, inhibits acetate incorporation irreversibly and shows a tendency for the activation of TGL. The calcium ionophore ionomycin inhibits acetate incorporation by the fat body reversibly and shows a tendency for TGL activation. Another ionophore, A23187 also inhibits acetate incorporation. Caffeine and theophylline inhibit acetate incorporation by the fat body in a reversible manner and tend to activate TGL. Caffeine seems to act via the release of calcium from intracellular stores and not via increase in the cellular cAMP concentrations. cAMP analogues and agonists do not influence acetate incorporation, however, the agonists, IBMX and forskolin cause a multifold increase in the cAMP concentrations in the fat body. AKH does not affect the cAMP concentrations in the fat body suggesting that cAMP is not involved in the signal transduction. As the activation of protein kinase C by PMA (a phorbol ester) does not affect acetate incorporation, diacylglycerol does not seem to be involved in the AKH signal transduction. The activation and/or translocation of TGL and inhibition of fatty acid synthesis by AKH seems to be via the release of calcium from intracellular calcium stores. Lipid and protein form a major part of the fat body in the penultimate larval instar crickets, while glycogen forms a minor part. However, in comparison with the adult (glycogen content of fat body about 1%) and last larval instar crickets (glycogen content about 3%), the penultimate larval instar crickets contain higher amounts of glycogen (about 9%). AKH inhibits acetate incorporation into lipid by the fat body from penultimate larval instar crickets. The patterns of acetate incorporation and inhibition by AKH are similar in both, males and females. The inhibition is dose-dependent with an EC50 of 79 pM AKH. AKH seems to play an important role in the development and reproduction of insects, in addition to its role during flight metabolism.
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Facultative butterfly-ant interactions - the role of variation in composition of nectar secretions
(2004)
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Holger Daniels
- The significance of variation in nectar secretions of facultatively ant-associated lycaenid butterfly larvae was investigated. The strongly myrmecophilous European Polyommatus coridon, and two moderately myrmecophilous species, the Palaearctic P. icarus and the subtropical Zizeeria knysna were used. Both Polyommatus species are closely related, Z. knysna is a far more distant relative. To obtain high numbers of caterpillars a new method for breaking the egg diapause of the univoltine P. coridon was established, resulting in 65% subitaneously hatching larvae. Based on observations of ants tending caterpillars a new “artificial ant” was assembled, allowing further studies on the ants’ stimulatory antennation pattern. Nectar-harvesting with micro-capillaries from caterpillars attended by ants was optimised and allowed determination of individual secretion droplet size based on large samples. Mean droplet size was 3.7nl in P. coridon, 2nl in P. icarus and 1.4nl in Z. knysna, in the latter two species 65-79% smaller than previously reported. Comparative chemical analyses (HPLC) revealed sucrose as main sugar component in nectar of all three species. In P. coridon it was accompanied by glucose and rarely by further sugars, but never by melezitose. In P. icarus and Z. knysna melezitose was the second most-important component, followed by fructose and glucose. Total sugar contents were 43.6±14.8g/l for P. coridon, 74.2g/l for P. icarus and 68.3±22.6g/l for Z. knysna. P. coridon nectar contained up to 14 amino acids. Major component was always leucine (50% of total), further important were tyrosine, proline, arginine, and phenylalanine. P. icarus nectar comprised up to six amino acids, dominated by tyrosine and phenylalanine. Z. knysna nectar contained only alanine and proline. Total amino acid contents were 9.7±3.4g/l for P. coridon, 1.2g/l for P. icarus and 0.3±0.2g/l for Z. knysna. Nectar composition was considerably different from hemolymph composition. Larval food had minor influence on P. coridon nectar composition. Caterpillars fed with semi-synthetic diet secreted more sucrose, with a trend towards higher total sugar content, and produced nectar with a more homogeneous amino acid pattern than larvae reared on natural host plants. Bioassays with ants from three different subfamilies (Lasius niger (Formicinae), Myrmica rubra (Myrmicinae), Tapinoma melanocephalum (Dolichoderinae)) demonstrated a preference for sucrose (standard concentration 0.1mol/l, as in P. coridon nectar) over monosaccharides. Melezitose in nectar concentration (P. icarus) was not preferred to sucrose. Some single amino acids in sucrose solutions were preferred over pure sucrose, e.g. leucine by L. niger, or phenylalanine and tyrosine by M. rubra. In general, raising amino acid concentration did not enhance preferences and even reduced them in some cases. Mixtures of four or eleven amino acids in sucrose and complete nectar analoga were preferred to sucrose. L. niger preferred a balanced mixture over an energetically similar, less balanced mixture. Due to the tremendous variability in gustatory preferences exhibited by the broad range of largely unpredictable ant visitors, lycaenid caterpillars should either decide on a balanced mixture, containing possible amino acid ‘key compounds’ in moderate concentrations, or if this investment does not pay, should secrete sugar-rich nectars. Using the data from the HPLC analyses and the droplet size measurements combined with published studies on secretion rates allowed estimations of the lifetime energetic value of secretions. One P. coridon caterpillar would deliver 5.5-24.4J, one P. icarus 1.9-14.2J and one Z. knysna 0.7-2.8J. Dissection and gravimetric analysis allowed estimation of the caloric equivalent of larval biomass. One early P. coridon third instar (onset of nectar secretion) would yield 17.6J, and prepupae 656J. Z. knysna second instars would yield 0.95J, third instars 3.2J, and prepupae 83.1J. Thus preying on the caterpillars rather than harvesting their secretions would be of greater energetic benefit. Comparisons of this model with further reports show the rather low benefit accruing to ants from tending facultatively myrmecophilous lycaenids, underpinning that manipulation of ants (by means of still unknown chemicals) must also be involved. The model data also suggest that the mutualistic nature of facultative caterpillar-ant associations will not always be granted, and be strongly conditional. Nectar composition data support the view that in myrmecophilous lycaenids secretions rich in amino acids are related to intimate, often obligate ant-associations, whereas facultative and unspecific myrmecophiles rely more on sugars. Degree of myrmecophily seems to be a better predictor of secretion content than taxonomic relatedness. The low investment costs of the caterpillars into nectar secretions well explain the enormous taxonomic and geographical distribution of facultative myrmecophily.
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Importance of floral scent compounds for the interaction between Silene latifolia (Caryophyllaceae) and the nursery pollinator Hadena bicruris (Lepidoptera: Noctuidae)
(2004)
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Stefan Dötterl
- In the present study, the role of floral volatiles for the interaction between the nocturnal Caryophyllaceae Silene latifolia, and the noctuid moth Hadena bicruris was determined. This insect-plant relationship is one of the known nursery pollination systems, where pollinators reproduce within the flowers they pollinate. Silene latifolia is a dioecious weed, native to Europe and formerly introduced to North America. It is the main larval host plant of H. bicruris, which is distributed in Europe and North Africa. Especially night-active moths, among them H. bicruris, which are attracted by the flower scent, pollinate S. latifolia. However, until now, nothing was known about the role of single flower scent compounds for the attraction of the moths. This thesis describes the chemical composition and the geographical variability in the flower scent of S. latifolia. Furthermore, electrophysiological and behavioural tests with floral scent extracts and single authentic standard compounds were carried out in H. bicruris to identify the attractive compounds of the complex floral scent. To get an insight into the role of floral scent in guiding potential pollinators on flowers, the spatial fragrance pattern within the flowers of S. latifolia was determined, additionally. The variability in floral scent was very high, especially between different populations, and different chemotypes were characterised.Typical compounds in floral scent of S. latifolia were lilac aldehyde isomers, trans-beta-ocimene, benzaldehyde, phenyl acetaldehyde, or veratrole. Some of these compounds are known to attract nocturnal Lepidoptera species. To characterise antennal and behavioural responses of H. bicruris to various floral scent chemotypes of S. latifolia, and to S. vulgaris (which is rarely also used as host plant), different S. latifolia extracts, and a S. vulgaris extract were analysed using GC-MS methods. These extracts were further used in GC-FID/EAG and GC-MS/EAG detections, respectively. Main compounds in the tested extracts often elicited main signals in the antennae (e.g. lilac aldehydes, phenyl acetaldehyde). Some compounds elicited main signals in the antennae, though they were only minor components in the extracts (e.g. 3-methyl-butyl-aldoxime, benzaldehyde). Other compounds elicited only weak signals in the antennae, though they were abundant in the extracts (e.g. myrcene, methyl benzoate). The compounds of the most common chemotypes of S. latifolia were very sensitively detected by Hadena bicruris, whereas compounds of less abundant chemotypes were less sensitively detected. Floral scent blends that were dominated by lilac aldehydes or phenyl acetaldehyde effectively attracted moths. Hadena bicruris can electrophysiologically and behaviourally distinguish between its main host plant, S. latifolia, and the similarly scented S. vulgaris, another rarely used larval host plant, only by their floral scent. To identify floral scent compounds of S. latifolia that are important for the attraction of H. bicruris, the GC-FID/EAD or the GC-MS/EAD method was used in a first step to identify compounds that elicit signals in the antennae of the moth. Electrophysiologically very active compounds were tested in wind tunnel bioassays, and the attractivity of these compounds was compared to the attractivity of the natural scent of whole flowers of S. latifolia. The antennae of H. bicruris detected substances of several compound classes such as monoterpenoids, benzenoids, fatty acid derivatives, and nitrogen-bearing compounds. Lilac aldehydes were the most attractive compounds in wind tunnel bioassays, and attracted 90% of the tested moths, as did the scent of single flowers. Some compounds did not attract any moth, though they elicited significant signals in the antennae. To determine the parts of the female and male flowers responsible for scent emission, volatiles from attached intact flowers were sampled and then single flower parts were progressively removed. After each preparation step, volatiles were collected from the remaining “flower”. Especially the petals and the anthophore emitted the typical flower volatiles of S. latifolia; and compounds emitted from the petals differed from the compounds emitted by the anthophore. The anthophore emitted only lilac aldehydes and alcohols. Lilac aldehydes are known to be behaviourally very attractive for noctuid Lepidoptera such as Autographa gamma and Hadena bicruris, and they may serve as nectar guides in S. latifolia.
