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Many critical cellular processes, including cell proliferation and tissue repair, exhibit melatonin sensitivity. We examined the effects of exogenous melatonin, photoperiod and temperature on regeneration in Phagocata gracilis, a common North American turbellarian. Planarian regeneration involves the proliferation and migration of pluripotent stem cells capable of replacing missing body components. A characteristic mass of cells (blastema) forms during planarian regeneration, and its formation, growth and differentiation provide reliable endpoints for the study of regenerative processes. We tested the effects of exogenous melatonin at two concentrations and three photoperiods on both head and tail regenerates under seasonal diurnal temperature regimes. High temperatures and melatonin treatment increased mortality in P. gracilis, and surviving melatonin-treated subjects exhibited delayed regeneration. Asymmetrical and deficient regeneration was more common in melatonin-treated, high temperature and dark treated subjects. Additionally, high temperature and melatonin induced a novel locomotor dysfunction. [ABSTRACT FROM AUTHOR]

In many aquatic animals, predator avoidance can be stimulated by chemical cues, including those released by injured prey (alarm cues). Alarm cues of both conspecific and heterospecific origin have been identified within several fish taxa, where phylogenetic conservation of the cue-response complex is common. Turbellarian flatworms (planaria) are among the simplest animals known to respond to chemical cues released by injured conspecifics. We examined how two locally sympatric planaria species respond to conspecific and heterospecific chemical cues using macerated tissue suspensions. Brown (Girardia tigrina) and black (Dugesia dorotocephala) planaria both exhibited avoidance behavior when presented conspecific cues. Despite a significant twofold difference in body size (black > brown), stimulus prepared from a single (1×) individual of either species elicited avoidance. Increasing brown planaria cue concentration by macerating two individuals (2×) produced a significant increase in conspecific avoidance. Heterospecific stimuli produced asymmetric results. Black planaria avoided the brown planaria stimulus, but only in the higher concentration (2×) trials. Brown planaria did not consistently exhibit avoidance of the black planaria stimulus and some brown subjects approached and consumed black planarian tissues. Our results expand the demonstrated occurrence of alarm cues among planaria and suggest that avoidance behavior can be mediated by multiple environmental and intrinsic factors in freshwater Turbellaria. [ABSTRACT FROM AUTHOR]

Color pattern changes in fishes can vary from nearly instantaneous changes to long term, developmental (ontogenetic) changes. Species-typical patterns of ontogenetic color change (OCC) can provide insight regarding the behavior, ecology, and evolution of a taxon. Observations performed on laboratory-reared Firemouth Cichlids, Thorichthys meeki, from hatching to age 205 days, revealed 16 dynamic color pattern elements. Color pattern changes were correlated with age, but a significantly better correlation was found with body size. Ontogenetic color change in the Firemouth Cichlid featured the expression of some transitory color pattern elements not found in adults, and several elements and their sequence of expression were similar to those previously described for other cichlid species. [ABSTRACT FROM AUTHOR]

Presents a study which tested the behavioral significance of the orange ventral coloration observed in female convict cichlids, Cichlasoma nigrofasciatum, in relation to role of sexual selection in the evolution of sexual dichromatism. Methodology used to conduct the study; Relationship between a female's color and behavior; Discussion based on the study.