Feeding-Entrained Circadian Rhythms in Fishes

There has been sufficient work done in fishes to warrant a review of feeding-entrained rhythmicity, if only for comparative reasons. Relative to the extensive work with laboratory mammals, however, information on this topic in fishes is meager. An attempt at a broad overview at this point is fated from the outset to be data poor and speculation rich; hopefully this paper will, nevertheless, serve a heuristic role. Specifically, the paper addresses five questions regarding feeding entrainment of circadian rhythms in fishes: Does feeding entrain rhythms in fishes? How? Why? So what? and What next?https://nsuworks.nova.edu/occ_facbooks/1020/thumbnail.jp

Evolution of circadian organization in vertebrates

Circadian organization means the way in which the entire circadian system above the cellular level is put together physically and the principles and rules that determine the interactions among its component parts which produce overt rhythms of physiology and behavior. Understanding this organization and its evolution is of practical importance as well as of basic interest. The first major problem that we face is the difficulty of making sense of the apparently great diversity that we observe in circadian organization of diverse vertebrates. Some of this diversity falls neatly into place along phylogenetic lines leading to firm generalizations: i) in all vertebrates there is a "circadian axis" consisting of the retinas, the pineal gland and the suprachiasmatic nucleus (SCN), ii) in many non-mammalian vertebrates of all classes (but not in any mammals) the pineal gland is both a photoreceptor and a circadian oscillator, and iii) in all non-mammalian vertebrates (but not in any mammals) there are extraretinal (and extrapineal) circadian photoreceptors. An interesting explanation of some of these facts, especially the differences between mammals and other vertebrates, can be constructed on the assumption that early in their evolution mammals passed through a "nocturnal bottleneck". On the other hand, a good deal of the diversity among the circadian systems of vertebrates does not fall neatly into place along phylogenetic lines. In the present review we will consider how we might better understand such "phylogenetically incoherent" diversity and what sorts of new information may help to further our understanding of the evolution of circadian organization in vertebrate