Abstract
Scale-eating cichlid fishes, Perissodus spp., in Lake Tanganyika have laterally asymmetrical bodies, and each population is composed of righty and lefty morphs. Righty morphs attack the right side of prey and lefty morphs do the opposite. This anti-symmetric dimorphism has a genetic basis. Temporal changes in the frequencies of morphs in two cohabiting scale-eating species (Perissodus microlepis and P. straeleni) were investigated over a 31-year period on a rocky shore at the southern end of the lake. Dimorphism was maintained dynamically during the period in both species, and the frequencies oscillated with a period of about four years in a semi-synchronized manner. Recent studies have indicated that this type of anti-symmetric dimorphism is shared widely among fishes, and is maintained by frequency-dependent selection between predator and prey species. The combinations of laterality in each scale-eater and its victim were surveyed. The results showed that “cross-predation”, in which righty predators catch lefty prey and lefty predators catch righty prey, occurred more frequently than the reverse combination (“parallel-predation”). The cause of the predominance of cross-predation is discussed from the viewpoint of the physical and sensory abilities of fishes.
Highlights
Lateral bias of behavior has been observed in various animals, vertebrates
Results showed that the lateral dimorphism of two species of scale-eater cohabiting in a rocky
The ratios of Results showed that the lateral two species of period scale-eater a rocky the two species oscillated during the dimorphism
Summary
Lateral bias of behavior has been observed in various animals, vertebrates. Many studies on morphological asymmetry have been conducted in both invertebrates and vertebrates including fish, from which three types of asymmetry have been categorized based on the frequency distribution of measured laterality: fluctuating asymmetry (unimodal and symmetrical distribution), directional asymmetry (unimodal distribution shifted from symmetry) and anti-symmetry (bimodal distribution) [9]. The relationship between behavioral laterality and morphological asymmetry, especially for anti-symmetry, had rarely been investigated aside from asymmetry of the brain [6,10,11]. Some theoretical and/or empirical studies have investigated the mechanism that is responsible for maintaining the lateralization in one population from the viewpoint of cerebral lateralization [12,13,14], but few studies have been done to analyze the mechanism that maintains the anti-symmetric dimorphism in one population. The population in which the dimorphism is maintained dynamically, Symmetry 2019, 11, 119; doi:10.3390/sym11010119 www.mdpi.com/journal/symmetry
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