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Dispersal of coral reef fish: Post-settlement selection processes shape the population genetic structure

Fachliche Zuordnung Evolution, Anthropologie
Förderung Förderung von 2009 bis 2014
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 125398870
 
Erstellungsjahr 2014

Zusammenfassung der Projektergebnisse

Understanding the mechanisms that drive and maintain population divergence, evolutionary branching and potential speciation is a fundamental challenge for evolutionary theory. In the marine environment, isolation of populations caused by geographic barriers alone cannot explain high speciation rates and biodiversity. In this project we show that incipient speciation can be observed in adjacent reef habitats. Analyzing the cardinalfish Ostorhinchus doederleini over ten generations at the Capricorn- Bunker group in the Great Barrier Reef (GBR), Australia, we detected five phenotypically indistinguishable clades that can be considered incipient species. Sequence data of two mitochondrial gene fragments as well as microsatellite markers indicated almost complete genetic isolation, although rare interbreeding between some clades could be observed. Surprisingly, partial habitat overlap could be observed between clade 1 and 2 at reef slopes which were found within the same cave (<1 m3). Apparently recognition processes avoid intermingling. In behavioral experiments we could show that individuals of different clades can recognize each other based on visual as well as olfactory cues. Since our age determination based on otolith analysis showed that O. doederleini become only one year old the relative stable population structure at reefs over years indicate some selfrecruitment. Genetically we could show that 60 % of settling larvae originated from the reefs where they intended to settle. To understand successful self-recruitment, we studied sensory capabilities of settling larvae that might guide them back to their natal reef. We showed evidence for a sun compass mechanism that can bring larvae to the vicinity of their natal reef. In a circular arena, pre-settlement larvae and early settlers (< 24 hours) of the cardinal fish, showed a strong SSE directional swimming response, which most likely has evolved to compensate for the locally prevailing large scale NNW current drift. The suggested sun compass guided swimming response is likely to continue until the larvae recognize the odor halo and/or sound of their natal reef, which present a much larger homing target for returning larvae than the reef itself. The use of a sun compass adds a missing long-distance link to the hierarchy of other sensory abilities that can direct larvae to the region of origin, including their natal reef. Once close to the natal reef we could provide the first in-situ evidence that pelagic reef fish larvae discriminate reef odor and respond by changing their swimming speed and direction. It concludes that reef fish larvae smell the presence of coral reefs from several kilometers offshore and this odor is a primary component of their navigational system and activates other directional sensory cues. Our results help to understand speciation in the marine environment and reveal sensory mechanism involved in orientation and recognition processes that might be key factors in migration not only in coral reefs but in many marine organisms. • Geruchssinn und Sonnenkompass: Wie Fische ihren Weg finden, PRESSE & KOMMUNIKATION Uni Oldenburg, Juni 2013; die Meldung wurde von zahlreichen deutschen Zeitungen aufgegriffen • Kommunikation unter Wasser: Fische können sich gut riechen, Nolte PR, IVH-PD, Nr.: 17_18/12

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