A fly's eye view of circadian entrainment

The Drosophila circadian clock is an ideal model system for teasing out the molecular mechanisms of circadian behavior and the means by which animals synchronize to day-night cycles. The clock that drives behavioral rhythms, located in the lateral neurons in the central brain, consists of a feedback loop of the circadian genes period (per) and timeless (tim). The molecular cycle, roughly 24 h long, is constantly reset by the environment. This review focuses on the main input pathways of the dominant circadian zeitgeber, light. Light acts directly on the clock primarily through cryptochrome (cry), a deep brain blue-light photoreceptor. CRY activation causes rapid TIM degradation, which is a predicted means of resetting the clock both on a daily basis at dawn and on an acute basis following an entraining light pulse during the night hours. In the absence of cry, the clock can still be driven by photic input through the visual system, though the mechanisms underlying this entrainment are unclear. Temperature can also entrain the clock, although the mechanisms by which this occurs are also unclear.     

Sociality, mating system and reproductive skew in marmots: evidence and hypotheses

Marmot species exhibit a great diversity of social structure, mating systems and reproductive skew. In particular, among the social species (i.e. all except Marmota monax), the yellow-bellied marmot appears quite different from the others. The yellow-bellied marmot is primarily polygynous with an intermediate level of sociality and low reproductive skew among females. In contrast, all other social marmot species are mainly monogamous, highly social and with marked reproductive skew among females. To understand the evolution of this difference in reproductive skew, I examined four possible explanations identified from reproductive skew theory. From the literature, I then reviewed evidence to investigate if marmot species differ in: (1) the ability of dominants to control the reproduction of subordinates; (2) the degree of relatedness between group members; (3) the benefit for subordinates of remaining in the social group; and (4) the benefit for dominants of retaining subordinates. I found that the optimal skew hypothesis may apply for both sets of species. I suggest that yellow-bellied marmot females may benefit from retaining subordinate females and in return have to concede them reproduction. On the contrary, monogamous marmot species may gain by suppressing the reproduction of subordinate females to maximise the efficiency of social thermoregulation, even at the risk of departure of subordinate females from the family group. Finally, I discuss scenarios for the simultaneous evolution of sociality, monogamy and reproductive skew in marmots.     

The current state and problems of circadian clock studies in cyanobacteria

Circadian rhythms have been observed in innumerable physiological processes in most of organisms. Recent molecular and genetic studies on circadian clocks in many organisms have identified and characterized several molecular regulatory factors that contribute to generation of such rhythms. The cyanobacterium is the simplest organism known to harbor circadian clocks, and it has become one of most successful model organisms for circadian biology. In this review, we will briefly summarize physiological observations and consideration of circadian rhythms in cyanobacteria, molecular genetics of the clock using Synechococcus, and current knowledge of the input and output pathways that support the cellular circadian system. Finally, we will document some current problems in the studies on the cyanobacterial circadian clock.     

Sexual differentiation of the zebra finch song system: Positive evidence,negative evidence,null hypotheses,and a paradigm shift

Permanent sex differences in the brain are found in many vertebrates, and are thought to be induced by sex differences in secretion of gonadal steroid hormones during critical periods of early development. This theory has received support primarily from many experiments conducted on mammals, but also from studies on other vertebrate classes, including birds. The only avian neural dimorphism that has allowed extensive tests of this hypothesis is the neural circuit for song in passerine birds, which is much larger in males than in females. Experiments in zebra finches have yielded contradictory results. Although it is relatively easy to induce masculine patterns of development in genetic females with estrogen, it has not been possible to induce feminine patterns of development in males with any treatments, including antiestrogens and inhibitors of estrogen synthesis. Moreover, genetic females that develop with large amounts of functional testicular tissue but with virtually no ovarian tissue nevertheless have a feminine song circuit. The latter studies fail to support the idea of steroid induction of sexual differentiation. An alternative to the steroidal control hypothesis is that nonhormonal gene products expressed in the brain early in development trigger sexually dimorphic patterns of development. Although current evidence in several neural and nonneural systems indicates that sexual differentiation of some somatic phenotypes cannot be explained by the actions of gonadal steroids, the idea of direct genetic (nonhormonal) induction of sexual differentiation has yet to be proved. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 572–584, 1997     

Pest problems: The view of an environmentalist

Abstract

The key issue for me is the great need I see for enhanced public awareness of the significance of pests and of the importance of controlling or managing them. Without such clear public understanding, it is difficult to see how we, as a society, can stimulate the level of effort, commitment, and financial resources that is required of us at every level—from Central Government and Regional Councils to individual land owners. Reflecting on this has stimulated me to think about the ambivalence of the conservation and environment movement on this issue.     

The molecular mechanism and cellular functions of mitochondrial division

Mitochondria are highly dynamic organelles that continuously divide and fuse. These dynamic processes regulate the size, shape, and distribution of the mitochondrial network. In addition, mitochondrial division and fusion play critical roles in cell physiology. This review will focus on the dynamic process of mitochondrial division, which is highly conserved from yeast to humans. We will discuss what is known about how the essential components of the division machinery function to mediate mitochondrial division and then focus on proteins that have been implicated in division but whose functions remain unclear. We will then briefly discuss the cellular functions of mitochondrial division and the problems that arise when division is disrupted.