Contents 516 I. 516 II. 518 III. 518 IV. 521 V. 523 VI. 523 VII. 526 526 References 526 SUMMARY: The relevance of infochemicals in the relationships between organisms is emerging as a fundamental aspect of aquatic ecology. Exchanges of chemical cues are likely to occur not only between organisms of different species, but also between conspecific individuals. Especially intriguing is the investigation of chemical communication in microalgae, because of the relevance of these organisms for global primary production and their key role in trophic webs. Intraspecific communication between algae has been investigated mostly in relation to sexuality and mating. The literature also contains information on other types of intraspecific chemical communication that have not always been explicitly tagged as ways to communicate to conspecifics. However, the proposed role of certain compounds as intraspecific infochemicals appears questionable. In this article, we make use of this plethora of information to describe the various instances of intraspecific chemical communication between conspecific microalgae and to identify the common traits and ecological significance of intraspecific communication. We also discuss the evolutionary implications of intraspecific chemical communication and the mechanisms by which it can be inherited. A special focus is the genetic diversity among conspecific algae, including the possibility that genetic diversity is an absolute requirement for intraspecific chemical communication.

Division of Plant Sciences University of Dundee at The James Hutton Institute Dundee Invergowrie DD2 5DA UK Functional Plant Biology and Climate Change Cluster University of Technology Sydney Ultimo NSW 2007 Australia

Laboratory of Algal and Plant Physiology Dipartimento di Scienze della Vita e dell'Ambiente Università Politecnica delle Marche 60131 Ancona Italy

Laboratory of Algal and Plant Physiology Dipartimento di Scienze della Vita e dell'Ambiente Università Politecnica delle Marche 60131 Ancona Italy Institute of Microbiology Academy of Sciences of the Czech Republic Algatech 379 81 Trebon Czech Republic National Research Council Institute of Marine Science 30122 Venice Italy

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