An alternative pattern of head expansion during feeding in cichlids

Specialized feeding methods evolved repeatedly from a suction-feeding strategy in cichlids. How algae-eaters altered their suction mechanics to transport detached algae efficiently, and how this may hinder capturing larger prey, remains unclear. Here, we study the kinematics and time-resolved volumetrics of a piscivore, an algae picker/nibbler, and an algae scraper from Lake Malawi feeding on attached algae tablets and free pieces of shrimp. Algae specialists lack the common anterior-to-posterior expansion and compression waves of the head, instead exhibiting a synchronous expansion pattern. This alternative pattern may allow algae retention due to low-amplitude dilation of the gill rakers, maximized suction flow speeds for a given local expansion amplitude, and rapid sequences of suction cycles. The trade-off between powerful suction and efficient feeding on algae may explain why algae scrapers' opportunistic switching to suction feeding can only be successful on easy prey, and may have impacted cichlid diversification and trophic niche constraining.