鱼类线粒体DNA的遗传与进化

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PLANT POPULATION GENETICS AND EVOLUTION

This paper reviews recent developments in plant population genetics and evolution. Topics discussed include: 1) levels of genetic variation within and among populations; 2) gene flow; 3) mating systems; 4) selection and adaptation; and 5) the genetic structure of natural populations. The current status of each topic is briefly reviewed and suggestions are made of areas where additional research is needed.     

DEVELOPMENTAL QUANTITATIVE GENETICS AND THE EVOLUTION OF ONTOGENIES

A model is presented which permits integration of developmental information into genetic discussions about evolutionary change in morphology. Development of a trait is described in terms of an ontogenetic trajectory whose properties are defined by a small number of parameters. Some evolutionary aspects of development are examined from the perspective of this quantitative genetic model. Particular attention is given to the developmental origin of pleiotropic effects, developmental constraints, heterochrony, and the growth and morphogenesis of complex morphologies. The role of genetic maternal effects in mammalian development is briefly examined, particularly as it relates to selection on developmental traits.     

QUANTITATIVE GENETICS AND THE EVOLUTION OF REACTION NORMS

We extend methods of quantitative genetics to studies of the evolution of reaction norms defined over continuous environments. Our models consider both spatial variation (hard and soft selection) and temporal variation (within a generation and between generations). These different forms of environmental variation can produce different evolutionary trajectories even when they favor the same optimal reaction norm. When genetic constraints limit the types of evolutionary changes available to a reaction norm, different forms of environmental variation can also produce different evolutionary equilibria. The methods and models presented here provide a framework in which empiricists may determine whether a reaction norm is optimal and, if it is not, to evaluate hypotheses for why it is not.     

THE GENETICS AND EVOLUTION OF CANNIBALISM IN FLOUR BEETLES (GENUS TRIBOLIUM)

Cannibalism plays a major role in population regulation in Tribolium confusum, accounting for up to tenfold differences in population size between different genetic strains. I characterized the within- and between-strain genetic variation for cannibalism using standard quantitative-genetic methods. The four laboratory strains studied have similar birth and death rates but differ in their strain-specific cannibalistic tendencies. The cannibalism rates of the strains were stable for more than 60 generations of laboratory husbandry. I found considerable genetic variation for cannibalism within each strain. A genetic analysis of the between-strain differences in each of three types of cannibalism (larvae eating eggs, adults eating eggs, and adults eating pupae) showed that all three cannibalism pathways are autosomally inherited and exhibit minor degrees of dominance. Adult cannibalism of eggs and larval cannibalism of eggs appear to be genetically correlated. The differences between the “high” and “low” cannibalism strains appear to be polygenic for two kinds of cannibalism, larvae eating eggs and adults eating pupae. However, strain differences in adult cannibalism of eggs may be due to only two loci. The stability of the between-strain differences for more than 60 generations, the additive nature of inheritance, and the demonstration of considerable within-strain genetic variation suggest that cannibalism may be selectively neutral or under stabilizing selection with many adaptive peaks.     

THE EVOLUTION OF LANDSCAPE GENETICS

The main objective of this special section is not to review the broad field of landscape genetics, but to provide a glimpse of how the developing landscape genetics perspective has the potential to change the way we study evolution. Evolutionary landscape genetics is the study of how migration and population structure affects evolutionary processes. As a field it dates back to Sewall Wright and the origin of theoretical population genetics, but empirical tests of adaptive processes of evolution in natural landscapes have been rare. Now, with recent developments in technology, methodology, and modeling tools, we are poised to trace adaptive genetic variation across space and through time. Not only will we see more empirical tests of classical theory, we can expect to see new phenomena emerging, as we reveal complex interactions among evolutionary processes as they unfold in natural landscapes.     

EVOLUTION AND CREATIONISM IN MIDDLE EASTERN EDUCATION: A NEW PERSPECTIVE

Statements made in a recent outcry against a creationist in the Israeli Ministry of Education starkly illuminated Western misconceptions about Iranian science education. These misconceptions are perpetuated not only among the general public but also within the international scientific community, where investigations of "Islamic creationism" often incorporate misleading assumptions regarding Islamic religious attitudes toward science as well as the nature of secularism in non‐Western states. In turn, these assumptions have led to superficial analyses that overly rely on state religiosity to explain the treatment of evolution in national science education. Therefore, a new framework accounting for local political and social circumstances is crucial and urgently needed to effectively analyze science education in the Middle East.     

BIOLOGICAL EFFECTS OF ELF-EMF ENHANCED STRESS RESPONSE: NEW INSIGHTS AND NEW QUESTIONS

The effect of extremely low frequency electromagnetic fields (ELF-EMF) on gene expression and early development has been investigated in two different transgenic animals, the nematode Caenorhabditis elegans and Drosophila melanogaster, respectively. ELF-EMF enhanced biological reactions considerably in the presence of a second stressor (mild heat shock). In C. elegans, this effect could be demonstrated at the level of heat shock protein (hsp) gene expression by means of a lacZ reporter gene controlled by an hsp 16 or hsp 70 promoter. In Drosophila, the same experimental strategy led to ELF-EMF induced developmental defects, as well as to a considerable retardation of development. The findings are discussed with respect to possi- ble molecular mechanisms that might explain the observed synergistic ELF-EMF induced enhancement of the stress response. An experimental approach is suggested which may help to unravel the involved signal transduction pathways.     

SUBSTITUTION PROCESSES IN MOLECULAR EVOLUTION. II. EXCHANGEABLE MODELS FROM POPULATION GENETICS

Substitution processes are of two sorts: origination processes record the times at which nucleotide mutations that ultimately fix in the population first appear, and fixation processes record the times at which they actually fix. Substitution processes may be generated by combining models of population genetics—here the symmetrical-neutral, overdominance, underdominance, TIM, and SAS-CFF models—with the infinite-sites, no-recombination model of the gene. This paper is mainly concerned with a computer simulation study of these substitution processes. The rate of substitution is shown to be remarkably insensitive to the strength of selection for models with strong balancing selection caused by the genealogical drift of mutations through alleles held in the population by selection. The origination process is shown to be more regular than Poisson for the overdominance, TIM, and SAS-CFF models but more clustered for the underdominance model. A class of point processes called Sawyer processes is introduced to help explain these observations as well as the observation that the times between successive originations are nearly uncorrelated. Fixation processes are shown to be more complex than origination processes, with regularly spaced bursts of multiple fixations. An approximation to the fixation process is described. One important conclusion is that protein evolution is not easily reconciled with any of these models without adding perturbations that recur on a time scale that is commensurate with that of molecular evolution.     

GENETICS OF HOST-CACTUS RESPONSE AND LIFE-HISTORY EVOLUTION AMONG ANCESTRAL AND DERIVED POPULATIONS OF CACTOPHILIC DROSOPHILA MOJAVENSIS

The extent of host-specific genetic variation for two life-history traits, egg to adult developmental time and viability, and one morphological trait closely tied to fitness, adult thorax size, was exposed by employing a nested half-sib/full-sib breeding design with Baja and mainland populations of Drosophila mojavensis recently extracted from nature. This study was motivated by the presence of substantial variation in life histories among populations of D. mojavensis that use the fermenting tissues of particular species of columnar cacti for feeding and breeding in the Sonoran Desert. Full-sib progeny from all sire-dam crosses were split into cultures of agria cactus, Stenocereus gummosus, and organ pipe cactus, S. thurberi, to examine patterns of genotype-by-environment interaction for these fitness components. Baja flies expressed shorter egg-to-adult developmental times, higher viabilities, and smaller body sizes than mainland flies consistent with previous studies. Significant sire and dam components of variance were exposed for developmental time and thorax size. Genotype-by-environment interactions were significant at the level of dams for developmental time and nearly significant for viability (P = 0.09). Narrow- and broad-sense heritabilities were influenced by host cactus, sex, and population. No strong pattern of genetic correlation emerged among fitness components suggesting that host-range expansion has not been accompanied by formation of coadapted life histories, yet the ability to estimate genetic correlations and their standard errors was compromised by the unbalanced nature of the data set. Genetic correlations in performance across cacti were slightly positive, evidence for ecological generalism among populations explaining the observed pattern of multiple host cactus use within the species range of D. mojavensis.     

CHAOS AND UNPREDICTABILITY IN EVOLUTION

The possibility of complicated dynamic behavior driven by nonlinear feedbacks in dynamical systems has revolutionized science in the latter part of the last century. Yet despite examples of complicated frequency dynamics, the possibility of long‐term evolutionary chaos is rarely considered. The concept of “survival of the fittest” is central to much evolutionary thinking and embodies a perspective of evolution as a directional optimization process exhibiting simple, predictable dynamics. This perspective is adequate for simple scenarios, when frequency‐independent selection acts on scalar phenotypes. However, in most organisms many phenotypic properties combine in complicated ways to determine ecological interactions, and hence frequency‐dependent selection. Therefore, it is natural to consider models for evolutionary dynamics generated by frequency‐dependent selection acting simultaneously on many different phenotypes. Here we show that complicated, chaotic dynamics of long‐term evolutionary trajectories in phenotype space is very common in a large class of such models when the dimension of phenotype space is large, and when there are selective interactions between the phenotypic components. Our results suggest that the perspective of evolution as a process with simple, predictable dynamics covers only a small fragment of long‐term evolution.