Redirected aggression as a conflict management tactic in the social cichlid fish Julidochromis regani.

Conflict management consists of social behaviours that reduce the costs of conflict among group members. Redirected aggression-that is, when a recently attacked individual attacks a third party immediately after the original aggression-is considered a conflict management tactic, as it may reduce the victim's probability of being the object of further aggression. Redirected aggression has been reported in many vertebrates, but few quantitative studies have been conducted on this behaviour in fishes. We examined the function of redirected aggression in Julidochromis regani, a social cichlid fish. Behavioural experiments showed that redirected aggression functioned to divert the original aggressor's attention towards a third party and to pre-empt an attack towards the victim by the third-party individual, specifically among females. We found, however, that redirected aggression did not delay the recurrence of aggression by the original aggressor. These results suggest that a primary function of redirected aggression is to maintain the dominance of its actor against a subordinate occupying an adjacent rank. This study provides, to our knowledge, the first evidence that redirected aggression functions to manage conflict in social fish.

How animals get their skin patterns: fish pigment pattern as a live Turing wave.

It is more than fifty years since Alan Turing first presented the reaction-diffusion (RD) model, to account for the mechanism of biological pattern formation. In the paper entitled "The chemical basis of morphogenesis", Turing concluded that spatial patterns autonomously made in the embryo are generated as the stationary wave of the chemical (cellular) reactions. Although this novel idea was paid little attention by experimental biologists, recent experimental data are suggesting that the RD mechanism really functions in some of the course of animal development. Among the phenomena in which involvement of the RD mechanism is suspected, the striped pigment pattern of zebrafish has been highlighted as an ideal model system for the following reasons: the stationary wave made by the RD mechanism stays alive and can be observed only in the fish skin; and in zebrafish, we can utilize genomic information and molecular genetic techniques to clarify the molecular basis of pattern formation. In this review, we summarize recent progresses in the study of zebrafish pigment pattern formation that is uncovering how the RD wave is made and maintained in the skin.

Pattern regulation in the stripe of zebrafish suggests an underlying dynamic and autonomous mechanism.

The mechanism by which animal markings are formed is an intriguing problem that has remained unsolved for a long time. One of the most important questions is whether the positional information for the pattern formation is derived from a covert prepattern or an autonomous mechanism. In this study, using the zebrafish as the model system, we attempted to answer this classic question. We ablated the pigment cells in limited areas of zebrafish skin by using laser irradiation, and we observed the regeneration of the pigmentation pattern. Depending on the area ablated, different patterns regenerated in a specific time course. The regenerated patterns and the transition of the stripes during the regeneration process suggest that pattern formation is independent of the prepattern; furthermore, pattern formation occurs by an autonomous mechanism that satisfies the condition of "local self-enhancement and long-range inhibition." Because the zebrafish is the only striped animal for which detailed molecular genetic studies have been conducted, our finding will facilitate the identification of the molecular and cellular mechanisms that underlie skin pattern formation.

Major patterns of higher teleostean phylogenies: a new perspective based on 100 complete mitochondrial DNA sequences.

A recent preliminary study using complete mitochondrial DNA sequences from 48 species of teleosts has suggested that higher teleostean phylogenies should be reinvestigated on the basis of more intensive taxonomic sampling. As a second step towards the resolution of higher teleostean phylogenies, which have been described as the "(unresolved) bush at the top of the tree," we reanalyzed their relationships using mitogenomic data from 100 purposefully chosen species that fully represented all of the higher teleostean orders, except for the Batrachoidiformes. Unweighted and weighted maximum parsimony analyses were conducted with the data set that comprised concatenated nucleotide sequences from 12 protein-coding genes (excluding 3rd codon positions) and 21 transfer RNA (tRNA) genes (stem regions only) from each species. The resultant trees were well resolved and largely congruent, with most internal branches being supported by high statistical values. All major, comprehensive groups above ordinal level as currently defined in higher teleosts (with the exception of the Neoteleostei and several monotypic groups), such as the Eurypterygii, Ctenosquamata, Acanthomorpha, Paracanthopterygii, Acanthopterygii, and Percomorpha, appeared to be nonmonophyletic in the present tree. Such incongruities largely resulted from differences in the placement and/or limits of the orders Ateleopodiformes, Lampridiformes, Polymixiiformes, Ophidiiformes, Lophiiformes, Beryciformes, Stephanoberyciformes, and Zeiformes, long-standing problematic taxa in systematic ichthyology. Of these, the resulting phylogenetic positions of the Ophidiiformes and Lophiiformes were totally unexpected, because, although they have consistently been considered relatively primitive groups within higher teleosts (Paracanthopterygii), they were confidently placed within a crown group of teleosts, herein called the Percomorpha. It should be noted that many unexpected, but highly supported relationships were found within the Percomorpha, being highly promising for the next investigative step towards resolution of this remarkably diversified group of teleosts.