Same prey, different strategies: how sensory morphology and behavior differ between two species of Lake Malawi cichlids.
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1
University of Rhode Island, Department of Biological Sciences, United States
The iconic adaptive radiations of cichlids in the Rift Lakes of East Africa resulted in a diversity of morphological features and feeding strategies, which allow taxa to presumably avoid competition for resources. For instance, the Lake Malawi genera Aulonocara and Tramitichromis both feed on invertebrates in sandy substrates, but use two distinct foraging strategies. Aulonocara slowly swim just above the sand to detect the hydrodynamic stimuli generated by buried prey and directly strike at prey (previously determined), whereas Tramitichromis engulfs mouthfuls of sand and sifts out prey. Interestingly, these two taxa have different cranial lateral line canal morphologies and these morphologies most likely influence the ability to detect hydrodynamic stimuli generated by live prey. All species of Aulonocara have widened lateral line canals, which are thought to be more sensitive to water flows than the narrow canals found in species of Tramitichromis. We asked how prey detection behavior in Tramitichromis compares to that in Aulonocara when both taxa were presented with the same live tethered (benthic) prey in an experimental arena with sandy substrate. We evaluated the ability of A. stuartgranti and T. intermedius to feed on tethered live and dead adult Artemia (brine shrimp) under light and dark conditions using HD video. We compared several aspects of prey detection behavior: number of prey strikes, detection distance and angle, prey preference (live vs. dead), and the phase of search behavior (thrust, glide, or pause) during which prey was detected. Both species readily ate in the light; however, in the dark, Tramitichromis tended not to feed while Aulonocara actively fed (especially on live prey). While differences were found in each component of prey detection behavior, the largest differences involved detection distance and angle. In the light, Tramitichromis detected prey further away (10.3±0.4 cm, two prey types combined) but over a narrower range of angles (±40° from the long axis of the fish) than Aulonocara (7.7±0.4 cm, ±60° from the long axis of the fish). In the dark, Aulonocara located prey from a greater distance (4.4±0.3 cm) than Tramitichromis (2.3±0.3 cm) and performed 180° swimming reversals when prey were detected beneath them. These results suggest that Aulonocara uses both its lateral line system and vision to detect prey in the light, and only its lateral line system in the dark. In contrast, Tramitichromis appears to depend mostly on vision, and most fish did not feed in the dark. Thus, sensory capabilities appear to define two different niches for these sand-feeding taxa. This study provides novel insights into the ecological significance of lateral line-mediated feeding behavior, the potential for nocturnal feeding in cichlid fishes, and how the adaptive evolution of the lateral line system may have contributed to niche partitioning among these fishes.
Keywords:
Cichlid,
Feeding Behavior,
Lateral Line,
Mechanoreception
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for participant symposium and student poster award)
Topic:
Sensory: Mechanosensation
Citation:
Schwalbe
MA and
Webb
JF
(2012). Same prey, different strategies: how sensory morphology and behavior differ between two species of Lake Malawi cichlids..
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00092
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Received:
04 Jul 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Ms. Margot A Schwalbe, University of Rhode Island, Department of Biological Sciences, Kingston, RI - Rhode Island, 02881, United States, mbergstrom@my.uri.edu