PRIMARY RESEARCH PAPER Alternative egg-feeding tactics in Telmatherina sarasinorum, a trophic specialist of Lake Matano’s evolving sailfin silversides fish radiation Alexander F. Cerwenka • Juliane D. Wedekind • Renny K. Hadiaty • Ulrich K. Schliewen • Fabian Herder Received: 21 July 2011 / Revised: 16 March 2012 / Accepted: 22 March 2012 / Published online: 10 April 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Feeding specialisation is a typical feature of adaptive animal radiations. Different kinds of feeding specialisations have evolved in the endemic sailfin silversides species flock in Lake Matano (Central Sulawesi, Indonesia), including egg-feeding. The present study focuses on Telmatherina sarasino- rum, a sailfin silverside species feeding on the eggs of related Telmatherina antoniae. Stomach content anal- yses supported T. antoniae eggs to be the dominant food item, independent of daytime. We hypothesized that the egg-feeders use alternative tactics for maxi- mising egg consumption under varying densities of both, spawning T. antoniae pairs and competing conspecific egg-feeders. Focal behavioural observa- tions were applied to describe different feeding tactics and to analyse feeding success and the related costs in terms of competitive interactions. Egg-feeders fol- lowed single courting pairs of T. antoniae or, alterna- tively, they switched between different spawning pairs. Following-behaviour, covering one or more spawning events of the host species, was positively related to enhanced egg consumption. Compared to feeding by switching frequently among different spawning pairs, the following tactic came at the cost of likewise increased competition. Behavioural obser- vations suggest that some males monopolize courting pairs of T. antoniae and gain increased amounts of eggs compared to others avoiding competition by switching among pairs. The present results confirm that egg-feeding is a distinct trophic specialisation in T. sarasinorum and increase the scale of behavioural specialisation in Lake Matano’s evolving Telmatheri- na radiation. Keywords Oophagy Á Trophic ecology Á Malili Lakes Á Indonesia Á Telmatherinidae Á Adaptive radiation Introduction Adaptive radiation predicts specialisation to trophic resources and the evolution of alternative strategies for exploiting them (Schluter, 2000). There are various animals that are oophagous (feed on eggs), a behaviour that is in most reported cases facultative (e.g. Randall, Handling editor: I. A. Nagelkerken A. F. Cerwenka (&) Á J. D. Wedekind Á U. K. Schliewen Department of Ichthyology, Bavarian State Collection of Zoology (ZSM), Mu ¨nchhausenstr. 21, 81247 Munich, Germany e-mail: cerwenka@zsm.mwn.de R. K. Hadiaty Ichthyology Laboratory, Division of Zoology, Research Center for Biology, Indonesian Institute of Sciences (LIPI), Jl. Raya Bogor Km 46, Cibinong 16911, Indonesia F. Herder Sektion Ichthyologie, Zoologisches Forschungsmuseum Alexander Koenig, Adenauerallee 160, 53113 Bonn, Germany 123 Hydrobiologia (2012) 693:131–139 DOI 10.1007/s10750-012-1099-8