Universität zu Köln

Mölzner, Jana (2014). Role of volatile infochemicals in snail-periphyton interactions. PhD thesis, Universität zu Köln.

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Abstract

The fitness of consumers varies widely in aquatic and terrestrial habitats depending on resource quantity and quality. In aquatic food webs, herbivores are most affected by a variable resource quality, which is caused by considerable spatial and seasonal variations of nutrient availability in an ecosystem. Herbivores underlie a particularly high pressure in terms of their ability to acquire a sufficient nutrient supply in order to maintain high rates of growth and reproduction in heterogeneous environments. Particularly for organisms with limited motility such as gastropods, food searching is a very cost-intensive process. The effectiveness of food searching could be increased through the perception of diet-derived infochemicals that convey information about a food resource’s quality over a certain distance. Chemical information transfer is a major agent in the regulation of interspecific and intraspecific interactions in natural ecosystems. The information transmission via chemical cues, like volatile organic compounds (VOCs) would clearly help to optimize foraging processes of herbivores and it would be adaptive for them to have efficient chemoreceptive mechanisms to locate food resources over distances. Despite the importance of the interaction of primary producers and grazers for the structure of a benthic natural system there is little knowledge about factors and mechanisms that allow the communication of these organisms. This study aimed to elucidate important aspects and mechanisms of a snail-periphyton interaction, mediated by the transmission of volatile infochemicals from algae and this study highlights the natural relevance. As model organisms, the common pond snail Lymnaea stagnalis and the benthic green alga Uronema/ Ulothrix fimbriata were used for investigations like growth and behavioural assays but also for GC-MS analyses. I was able to show that the availability of essential macro-elements Nitrogen and Phosphorous in benthic algae lead to reduced fitness of juvenile L. stagnalis and additionally to qualitative and quantitative changes in the algal VOCs bouquet. The results of the behavioural assays revealed that VOCs extracted from U. fimbriata serve as foraging cues for L. stagnalis. Further, I was able to demonstrate for the first time that snails are able to differentiate between high and low quality food sources just by the perception of food odours released from benthic green algae after cell wounding. In field experiments I tested whether this foraging strategy is relevant on a larger spatial scale. The data of the field experiments showed that L. stagnalis is able to recognise algal odour bouquets as foraging infochemicals under natural conditions. Further findings gave also strong evidence that the feeding style of snails (radular cell damage) leads to VOC release under natural conditions because the grazing of L. stagnalis caused an aggregation of conspecifics under natural conditions. Furthermore, L. stagnalis appear to be able to distinguish between high and low quality food resources based on resource-quality specific odour bouquets under natural conditions. My results suggest that the perception of volatile cues is a process relevant on environmental scales and thus a possible mechanism to explain the frequently observed patchy distribution of grazers in ecosystems. The results of a VOCs liberation experiment demonstrated that gastropod grazing indeed leads to VOCs release. Further, I was able to show that a certain threshold of VOCs level is necessary for L. stagnalis which induces a directed foraging behaviour towards the odour. Finally, a mass balance model demonstrated that the grazer mediated VOC release is able to yield signal concentrations sufficient for the recognition by other lymnaeids which then utilize these cues as foraging infochemicals. The emission of ecologically relevant volatiles through snail grazing with subsequent attraction of other gastropod grazers to algal biofilms indicates an important but so far understudied chemical signalling mechanism of ecological importance.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Mölzner, Jana UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-59409
Date:	1 October 2014
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language Aquatic chemical ecology, Lymnaea stagnalis, volatile organic compounds, VOCs, behaviour UNSPECIFIED
Date of oral exam:	9 December 2014
Referee:	Name Academic Title Elert, Eric von Prof. Dr. Bonkowski, Michael Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/5940