Differential Responses of Brain,Gonad and Muscle Steroid Levels to Changes in Social Status and Sex in a Sequential and Bidirectional Hermaphroditic Fish

Sex steroids can both modulate and be modulated by behavior, and their actions are mediated by complex interactions among multiple hormone sources and targets. While gonadal steroids delivered via circulation can affect behavior, changes in local brain steroid synthesis also can modulate behavior. The relative steroid load across different tissues and the association of these levels with rates of behavior have not been well studied. The bluebanded goby (Lythrypnus dalli) is a sex changing fish in which social status determines sexual phenotype. We examined changes in steroid levels in brain, gonad and body muscle at either 24 hours or 6 days after social induction of protogynous sex change, and from individuals in stable social groups not undergoing sex change. For each tissue, we measured levels of estradiol (E₂), testosterone (T) and 11-ketotestosterone (KT). Females had more T than males in the gonads, and more E₂ in all tissues but there was no sex difference in KT. For both sexes, E₂ was higher in the gonad than in other tissues while androgens were higher in the brain. During sex change, brain T levels dropped while brain KT increased, and brain E₂ levels did not change. We found a positive relationship between androgens and aggression in the most dominant females but only when the male was removed from the social group. The results demonstrate that steroid levels are responsive to changes in the social environment, and that their concentrations vary in different tissues. Also, we suggest that rapid changes in brain androgen levels might be important in inducing behavioral and/or morphological changes associated with protogynous sex change.     

A model for the separation of large DNA molecules by crossed field gel electrophoresis.

The idea that large DNA molecules adopt a stretched conformation as they pass through gels suggests a simple mechanism for the separation of DNA by crossed field electrophoresis: at each change in field direction a DNA molecule takes off in the new direction of the field by a movement which is led by what was formerly its back end. The effect of this ratcheting motion is to subtract from the DNA molecule's forward movement, at each step, an amount which is proportional to its length. We find that this model explains most of the features of the separation, and we describe experiments, using a novel electrophoresis apparatus, which support the model. The apparatus turns the gel between two preset orientations in a uniform electric field at preset time intervals. This separation method has the practical advantage over some others that the DNA molecules follow straight tracks. A further advantage is that the parameters which determine the separation are readily predicted from the simple theory describing their motion.     

Density-dependent protogynous sex change in territorial-haremic fishes: models and evidence

Several hypotheses of the proximate control of protogynous (female-to-male)sex change propose that social group composition triggers sexchange, but they do not address how proximate cues are alteredby population density. I present three mutually exclusive encounter-ratethreshold hypotheses that assume that population density determinesrates of contact between social group members and that ratesof contact are cues for sex change. Different densities arepredicted to induce sex change, depending on the encountersassumed to be important in the sex change process (e.g., encounterswith smaller and larger individuals). Tests of the models usea pomacanthid angelfish(Centropyge potten) to show that continuedpresence of a smaller (female) conspecific is needed for sexchange, and that continued presence of a larger (male) conspecificcan either inhibit sex change or prevent its behavioral stimulation.Using constant social group composition, sex change is preventedat higher density but not at a lower density. The absolute encounter-ratethreshold hypothesis, which predicts sex change under intermediate-densityconditions, is the most probable model of the social controlof sex change in C.potteri     

土地利用变化模拟研究进展

土地利用变化研究经历了近30年的快速发展,学者基于不同建模目标构建出多种土地利用变化模型,实现了从数量模拟到时空格局模拟,从单一模型向多种模型耦合的跨越。当前研究主要在元胞自动机(Cellular Automata,CA)模型和CLUE-S (Conversion of Land Use and its Effects at Small region extent)模型的基础上进行改进,马尔科夫模型、系统动力学(System Dynamics,SD)模型、Logistic回归和随机森林等均可计算CA模型和CLUE-S模型中所需的土地利用需求,多标准评价、地理加权回归、多主体模型以及人工神经网络等方法也多被用于CA模型的扩展,而CLUE-S的改进则存在模型本身系列的升级。这些模型广泛应用于各种区域和尺度土地利用变化预测实例研究并研发软件系统和数据集。驱动力分析主要从自然因素与人文因素两方面进行,人文因素是引发土地利用变化的主要因素。在目前的研究中,由于技术手段的限制,仍然存在时空尺度、数据误差、数据整合的不确定性等问题。未来土地利用变化模拟研究应进一步发挥大数据技术优势,推动土地利用变化模拟研究朝向精细化、多元化方向发展。结合生态环境领域实际问题,深挖土地利用变化与其生态环境效应之间的互馈机制,将研究视角从探究人类活动对土地利用变化的影响逐渐转向二者相互作用,最终促进人地关系协调发展。     

A phenomenological model of the perceived intensity of single odorants

The response of a model olfactory system to a single odorant is quantified by interconnecting three separate stimulus-response relationships. Together, these relationships encompass the deposition of odorant molecules onto an olfactory organ, their movement to the dendrite of the olfactory receptor neuron, their subsequent induction of action potentials, and the processing of induced and spontaneous action potentials by the central nervous system, resulting in perception and a behavioral response. Phenomena discussed within the context of the model include the behavioral threshold, central summation of responses from a number of olfactory neurons, and the effect of organ shape on olfactory detection.The intent of the model is to provide a quantitative conceptual framework for designing and interpreting experiments relating sensory input to perception and behavior. Its utility is particularly evident for insect olfaction since it enables insect sex pheromone behavioral thresholds to be estimated from the literature when bioassays or electrophysiological studies are not possible. It also derives a physiologically meaningful method for comparing behavioral thresholds among different animals, and permits comparisons of different kinds of behavioral responses in the same species. Vertebrate olfaction is treated briefly in a discussion of the effect of sniffing on the threshold of detection.     

Will all species with temperature‐dependent sex determination respond the same way to climate change? A reply to Kallimanis (2010)

Recently, Kallimanis (2010) published a paper proposing a mechanism by which temperature‐dependent sex determination (TSD) may play a key role at facilitating species with this strategy to track their climatic niches across space under climate change. Kallimanis hypothesized that TSD species currently inhabiting stable climatic conditions show reduced population growth rates at the edges of their distributional ranges; under warming conditions, these populations will experience faster growth rates and thus are able to colonize new suitable sites. These ideas are based on the assumption that populations of TSD species have balanced sex ratios at the core of their geographic ranges and biased proportions at the edges. However, Kallimanis’ model overlooks complex processes that may produce a more broadly and less predictable aftermath of climate change on TSD species, so we discuss some of his postulates and underlying assumptions. Kallimanis’ model is based only on one of three known TSD strategies in reptiles, thus it lacks generality; and it does not consider the phenological, behavioral, and physiological strategies that TSD species exhibit across their geographic ranges to buffer the potential impacts of climatic variation over the whole reproductive process. We conclude that simple models such as the one proposed by Kallimanis are not broadly applicable; hence, forecasts of TSD species’ responses to climate change will need to be more specific to groups with similar ecologies and modes of TSD.     

Sex ratios when helpers stay at the nest

This study investigates the evolution of the sex ratio (parental investment in sons) when breeding adults are supported by help provided by nonbreeding individuals of one sex. The study also assumes that the helping sex remains on its natal site to compete for the opportunity to breed, whereas the nonhelping sex disperses. Two kin-selection models are presented, both of which incorporate the age structure found in many natural populations where such helping occurs. The first model assumes that helpers increase the survival of their parents. The second model assumes that helpers are indiscriminant: a helper chooses to increase the survival of a random pair of adults breeding on its natal patch. In both models, sex ratios are not always biased toward the sex that provides the most help. When helpers do not discriminate (second model), the direction of sex-ratio bias is determined solely by the size of the benefit of helping behavior. When this benefit is small, sex-ratio evolution is primarily influenced by local resource competition and sex ratios are biased toward the nonhelping (dispersive) sex. If the benefit of help is large enough, the effect of local resource competition is reduced and sex-ratio bias favors the helpful sex. When helpers help only their parents, the same qualitative relationship exists between the direction of sex-ratio bias and the benefit of helping. In this case, however, the direction of sex-ratio bias is also influenced by the size of the social group, mortality, and which individual (mother or father) controls the sex ratio. This study also investigates a sex-ratio conflict that exists between mates. Helping behavior of nonbreeders can act to alleviate the disparities between the optimal sex ratio from the perspective of a mother and that from the perspective of a father. This consequence of helping has not been previously recognized.     

The influence of females on the initiation of female-to-male sex change in a coral reef fish

In the protogynous coral reef fish Anthias squamipinnis (Peters), all males are sex-reversed females. A sexually mature female can be induced to change sex by removing a male from her social group. The influence of non-sex-changing females on the initiation of sex change was evaluated in 109 social groups in the Gulf of Eilat. When the male and largest female were removed from each of 12 single-male groups, the second-largest female changed sex in 9 groups. This result distinguished between two behavioral hypotheses suggested by previous work and made it tenable that a particular behavioral measure, the profile of behavior-received, that depends on adult females, is critical to the initiation of sex change. This species forms all-female groups as well as bisexual groups. All-female groups can be expected to have some mechanism for the production of a male. The removal of the largest female from each of 8 all-female groups failed to induce sex change in any group. The dominant female in these groups thus does not function in the same way as does the male in bisexual groups, at least in terms of the initiation of sex change. Following the removal of the male from each of 8 bisexual groups containing five or fewer adult females, a female changed sex in only 4 groups. This 50% incidence of sex reversal was lower than the 77–80% incidence in control groups containing more than five adult females. Data suggest that a minimum of four adult females is probably required for the probability of sex change after male removal to equal 75%.     

The Dynamics of Sex Ratio Evolution: From the Gene Perspective to Multilevel Selection

The new dynamical game theoretic model of sex ratio evolution emphasizes the role of males as passive carriers of sex ratio genes. This shows inconsistency between population genetic models of sex ratio evolution and classical strategic models. In this work a novel technique of change of coordinates will be applied to the new model. This will reveal new aspects of the modelled phenomenon which cannot be shown or proven in the original formulation. The underlying goal is to describe the dynamics of selection of particular genes in the entire population, instead of in the same sex subpopulation, as in the previous paper and earlier population genetics approaches. This allows for analytical derivation of the unbiased strategic model from the model with rigorous non-simplified genetics. In effect, an alternative system of replicator equations is derived. It contains two subsystems: the first describes changes in gene frequencies (this is an alternative unbiased formalization of the Fisher-Dusing argument), whereas the second describes changes in the sex ratios in subpopulations of carriers of genes for each strategy. An intriguing analytical result of this work is that the fitness of a gene depends on the current sex ratio in the subpopulation of its carriers, not on the encoded individual strategy. Thus, the argument of the gene fitness function is not constant but is determined by the trajectory of the sex ratio among carriers of that gene. This aspect of the modelled phenomenon cannot be revealed by the static analysis. Dynamics of the sex ratio among gene carriers is driven by a dynamic “tug of war” between female carriers expressing the encoded strategic trait value and random partners of male carriers expressing the average population strategy (a primary sex ratio). This mechanism can be called “double-level selection”. Therefore, gene interest perspective leads to multi-level selection.     

Drosophila sex combs as a model of evolutionary innovations

The diversity of animal and plant forms is shaped by nested evolutionary innovations. Understanding the genetic and molecular changes responsible for these innovations is therefore one of the key goals of evolutionary biology. From the genetic point of view, the origin of novel traits implies the origin of new regulatory pathways to control their development. To understand how these new pathways are assembled in the course of evolution, we need model systems that combine relatively recent innovations with a powerful set of genetic and molecular tools. One such model is provided by the Drosophila sex comb—a male‐specific morphological structure that evolved in a relatively small lineage related to the model species D. melanogaster. Our extensive knowledge of sex comb development in D. melanogaster provides the basis for investigating the genetic changes responsible for sex comb origin and diversification. At the same time, sex combs can change on microevolutionary timescales and differ spectacularly among closely related species, providing opportunities for direct genetic analysis and for integrating developmental and population‐genetic approaches. Sex comb evolution is associated with the origin of novel interactions between Hox and sex determination genes. Activity of the sex determination pathway was brought under the control of the Hox code to become segment‐specific, while Hox gene expression became sexually dimorphic. At the same time, both Hox and sex determination genes were integrated into the intrasegmental spatial patterning network, and acquired new joint downstream targets. Phylogenetic analysis shows that similar sex comb morphologies evolved independently in different lineages. Convergent evolution at the phenotypic level reflects convergent changes in the expression of Hox and sex determination genes, involving both independent gains and losses of regulatory interactions. However, the downstream cell‐differentiation programs have diverged between species, and in some lineages, similar adult morphologies are produced by different morphogenetic mechanisms. These features make the sex comb an excellent model for examining not only the genetic changes responsible for its evolution, but also the cellular processes that translate DNA sequence changes into morphological diversity. The origin and diversification of sex combs provides insights into the roles of modularity, cooption, and regulatory changes in evolutionary innovations, and can serve as a model for understanding the origin of the more drastic novelties that define higher order taxa.     

Similarity selection and the evolution of sex: revisiting the red queen

For over 25 years, many evolutionary ecologists have believed that sexual reproduction occurs because it allows hosts to change genotypes each generation and thereby evade their coevolving parasites. However, recent influential theoretical analyses suggest that, though parasites can select for sex under some conditions, they often select against it. These models assume that encounters between hosts and parasites are completely random. Because of this assumption, the fitness of a host depends only on its own genotype (“genotypic selection”). If a host is even slightly more likely to encounter a parasite transmitted by its mother than expected by random chance, then the fitness of a host also depends on its genetic similarity to its mother (“similarity selection”). A population genetic model is presented here that includes both genotypic and similarity selection, allowing them to be directly compared in the same framework. It is shown that similarity selection is a much more potent force with respect to the evolution of sex than is genotypic selection. Consequently, similarity selection can drive the evolution of sex even if it is much weaker than genotypic selection with respect to fitness. Examination of explicit coevolutionary models reveals that even a small degree of mother–offspring parasite transmission can cause parasites to favor sex rather than oppose it. In contrast to previous predictions, the model shows that weakly virulent parasites are more likely to favor sex than are highly virulent ones. Parasites have figured prominently in discussions of the evolution of sex, but recent models suggest that parasites often select against sex rather than for it. With the inclusion of small and realistic exposure biases, parasites are much more likely to favor sex. Though parasites alone may not provide a complete explanation for sex, the results presented here expand the potential for parasites to contribute to the maintenance of sex rather than act against it.     

Consequences of behavioral dynamics for the population dynamics of predator-prey systems with switching

This article explores how different mechanisms governing the rate of change of the predators preference alter the dynamics of predator-prey systems in which the predator exhibits positive frequency-dependent predation. The models assume that individuals of the predator species adaptively adjust a trait that determines their relative capture rates of each of two prey species. The resulting switching behavior does not instantaneously attain the optimum for current prey densities, but instead lags behind it. Several mechanisms producing such lags are discussed and modeled. In all cases examined, our question is whether a realistic behavioral lag can significantly change the dynamics of the system relative to an analogous case in which the predators switching is effectively instantaneous. We also explore whether increasing the rate parameters of dynamic models of behavior results in convergence to the population dynamics of analogous models with instantaneous switching, and whether different behavioral models produce similar population dynamics. The analysis concentrates on systems that undergo endogenously generated predator-prey cycles in the absence of switching behavior. The average densities and the nature of indirect interactions are often sensitive to the rate of behavioral change, and are often qualitatively different for different classes of behavioral models. Dynamics and average densities can be very sensitive to small changes in parameters of either the prey growth or predator switching functions. These differences suggest that an understanding of switching in natural systems will require research into the behavioral mechanisms that govern lags in the response of predator preference to changes in prey density.     

Structure of the Tet repressor and Tet repressor-operator complexes in solution from electrooptical measurements and hydrodynamic simulations

The Tet repressor protein and tet operator DNA fragments and their complexes have been analyzed by electrooptical procedures. The protein shows a positive linear dichroism at 280 nm, a negative linear dichroism at 248 nm, and a strong permanent dipole moment of 3.5 X 10(-27) C m, which is independent of the salt concentration within experimental accuracy. Its rotation time constant of 40 ns indicates an elongated structure, which is consistent with a prolate ellipsoid of 100 A for the long axis and 40 A for the short axis. The time constant can also be fitted by a cylinder of length 78 A and diameter 37 A, which is consistent with nuclease protection data reported on repressor-operator complexes, if the cylinder axis is aligned parallel to the DNA axis. Addition of tetracycline induces changes of the limit dichroism but very little change of the rotation time constant. The rotation time constants observed for the operator DNA fragments show some deviations from the values expected from their contour length; however, these deviations remain relatively small. Formation of repressor-operator complexes leads to some increase of the DNA rotation time constants. Simulations by bead models demonstrate that these time constants can be explained without any major change of the hydrodynamic dimension of the components. The data for the complexes are fitted by bead models with smooth bending of the DNA corresponding to a radius of curvature of 500 A, but at the given accuracy, we cannot rule out that the DNA in the complex remains straight or is bent to a smaller radius of approximately 400 A. Thus, binding of the Tet repressor, which is a helix-turn-helix protein as judged from its sequence, to its operator seems to induce minor bending but does not induce strong bending of the DNA double helix.     

Structural changes and enhancements in DNase I footprinting experiments.

In footprinting experiments, an increase in DNA cleavage with addition of ligand to a system may be due to a ligand-induced structural change. Ligand binding also enhances cleavage by displacing the cleavage agent from ligand-binding sites, thus increasing its concentration elsewhere. The theory and characteristics of this mass-action enhancement are given, and it is shown how it may be recognized. Results of DNase I footprinting of small oligomers, with actinomycin D as ligand, are analyzed to reveal which enhancements are due to mass action, and which can reasonably be ascribed to structural changes. Patterns in the footprinting plots from our experiments on actinomycin D binding to a 139-base-pair DNA fragment (with DNase I as a probe) are studied in the same way. The likely origins of these patterns are discussed, as are enhancements occurring with other probes commonly used in footprinting experiments.     

Correlation between the sexually dimorphic aromatase of the preoptic area and sexual behavior in quail: effects of neonatal manipulations of the hormonal milieu

The aromatase of the preoptic area is significantly more active in males than in females. This sex dimorphism in enzyme activity is still found in birds that have been gonadectomized and treated with a same dose of testosterone. This suggests that the sex difference is not the result of a differential activation by the adult hormonal environment but rather is organized neonatally by steroid hormones. As the central aromatization of testosterone is a limiting step in the activation of copulatory behavior by testosterone, the lower aromatase activity in the preoptic area of females might be responsible, at least in part, for their lower sensitivity to the activating effects of testosterone on behavior. Three experiments were carried out to determine whether early manipulations of the hormonal environment, which are known to differentiate sexual behavior, also affect in a permanent way the aromatase activity in the preoptic area. Injection of estradiol benzoate into male embryos on day 9 of incubation decreased the preoptic aromatase activity in parallel to its demasculinizing effect on behavior. Unexpectedly the same treatment tended to increase enzyme activity in females so that the physiological relevance of the observed enzymatic change remains questionable. In two independent experiments, we confirmed that neonatal ovariectomy of female quail interferes with their behavioral differentiation. Females gonadectomized at 4 days post-hatch showed significantly more male-type sexual behavior as adult in response to testosterone than females gonadectomized at the age of 5 weeks. These experiments also confirmed that the preoptic aromatase activity is higher in males than in females but no evidence for an effect of the age of gonadectomy on the enzyme activity could be obtained. The sex difference and experimental modifications observed in the aromatase activity of the preoptic area were not seen in the posterior hypothalamus demonstrating that these effects are specific. The mechanisms controlling the sex difference in aromatase activity are discussed. The difference might be organized by the action of embryonic steroids as suggested by the changes observed in males injected with estradiol benzoate in egg. Alternatively, activational mechanisms cannot be ruled out at present. In one experiment, the activity of the preoptic aromatase was positively correlated with the sexual activity of the birds.(ABSTRACT TRUNCATED AT 400 WORDS)     

Molecular flexibility in protein-DNA interactions

In living cells protein-DNA interactions are fundamental processes. Here, we compare the 3D structures of several DNA-binding proteins frequently determined with and without attached DNA. We studied the global structure (backbone-traces) as well as the local structure (binding sites) by comparing pair-wise the related atoms. The DNA-interaction sites of uncomplexed proteins show conspicuously high local structural flexibility. Binding to DNA results in specific local conformations, which are clearly distinct from the unbound states. The adaptation of the protein's binding site to DNA can never be described by the lock and key model but in all cases by the induced fit model. Conformational changes in the seven protein backbone traces take place in different ways. Two of them dock onto DNA without a significant change, while the other five proteins are characterized by a backbone conformation change caused by DNA docking. In the case of three proteins of the latter group the DNA-complexed conformation also occurs in a few uncomplexed structures. This behavior can be described by a conformational ensemble, which is narrowed down by DNA docking until only one single DNA-complexed conformation occurs. Different docking models are discussed and each of the seven proteins is assigned to one of them.     

Sex chromosomes and sex determination pathway dynamics in plant and animal models

In this review, we discuss and compare data obtained from animal and plant models, focusing our attention on the mechanisms that affect sex linkage and changes in sex‐determining pathways. Patterns in data across taxa suggest that sex bias and the dynamics that occurs within hybrid zones can play an important role in these processes that enable the spread of some otherwise handicapped genotypes. We discuss the data obtained from several main plant model species in the light of the patterns demonstrated in animal models. In several plant models, we discuss possible differences in the age of their sex‐determining pathways and the age of their current sex chromosomes. We also address an open question: how can an X/A ratio based sex‐determining system evolve from a sex‐determining system based on two genes on the Y chromosome that control two separate sex‐determining pathways (for the control of gynoecium suppression and anther promotion)? Taking inspiration from the well described mechanisms involved in sex determination dynamics in animals, we suggest a hypothetical stepwise scenario of change of the plant sex‐determining system based on two separate sex‐determining pathways (for the control of gynoecium suppression and anther promotion) into the other sex‐determining systems. We suppose that an intermediate step occurs before shift to X/A based sex determination. At that phase, sex determination in plants is still based on an active Y chromosome, although there exists already a connected control of both sex‐determining pathways. We suggest that this connection is enabled by the existence of the genes that control sexual dimorphism in the vegetative state of plant development, and that, in some circumstances, these genes can become sex‐determining genes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 737–752.     

Age-dependent usage of double-strand-break repair pathways

A DNA double-strand break (DSB) can be repaired by any of several alternative and competing mechanisms. The repaired sequences often differ from the original depending on which mechanism was used so that the cell's "choice" of repair mechanism can have profound genetic consequences. DSBs can accumulate with age , and human diseases that mimic some of the effects of aging, such as increased susceptibility to cancer, are associated with certain defects in DSB repair . The premeiotic germ cells of Drosophila provide a useful model for exploration of the connection between aging and DNA repair because these cells are subject to mortality and other age-related changes , and their DNA repair process is easily quantified. We used Rr3, a repair reporter system in Drosophila, to show that the relative usage of DSB repair mechanisms can change substantially as an organism ages. Homologous repair increased linearly in the male germline from 14% in young individuals to more than 60% in old ones, whereas two other pathways showed a corresponding decrease. Furthermore, the proportion of longer conversion tracts (>156 bp) also increased nearly 2-fold as the flies aged. These findings are relevant to the more general question of how DNA damage and repair are related to aging.