Linking breeding and wintering ranges of a migratory songbird using stable isotopes

We used the natural abundance of stable isotopes (carbon and hydrogen) in the feathers of a neotropical migrant songbird to determine where birds from particular breeding areas spend the winter and the extent to which breeding populations mix in winter quarters. We show that most birds wintering on western Caribbean islands come from the northern portion of the species' North American breeding range, whereas those on more easterly islands are primarily from southern breeding areas. Although segregated by breeding latitude, birds within local wintering areas derive from a wide range of breeding longitudes, indicating considerable population mixing with respect to breeding longitude. These results are useful for assessing the effects of wintering habitat loss on breeding population abundances and for predicting whether the demographic consequences will be concentrated or diffuse.     

Habitat fragmentation, species loss, and biological control

Fragmentation of habitats in the agricultural landscape is a major threat to biological diversity, which is greatly determined by insects. Isolation of habitat fragments resulted in decreased numbers of species as well as reduced effects of natural enemies. Manually established islands of red clover were colonized by most available herbivore species but few parasitoid species. Thus, herbivores were greatly released from parasitism, experiencing only 19 to 60 percent of the parasitism of nonisolated populations. Species failing to successfully colonize isolated islands were characterized by small and highly variable populations. Accordingly, lack of habitat connectivity released insects from predator control.     

A localized negative genetic correlation constrains microevolution of coat color in wild sheep

The evolutionary changes that occur over a small number of generations in natural populations often run counter to what is expected on the basis of the heritability of traits and the selective forces acting upon them. In Soay sheep, dark coat color is associated with large size, which is heritable and positively correlated with fitness, yet the frequency of dark sheep has decreased. This unexpected microevolutionary trend is explained by genetic linkage between the causal mutation underlying the color polymorphism and quantitative trait loci with antagonistic effects on size and fitness. As a consequence, homozygous dark sheep are large, but have reduced fitness relative to phenotypically indistinguishable dark heterozygotes and light sheep. This result demonstrates the importance of understanding the genetic basis of fitness variation when making predictions about the microevolutionary consequences of selection.     

Sustaining fisheries yields over evolutionary time scales

Fishery management plans ignore the potential for evolutionary change in harvestable biomass. We subjected populations of an exploited fish (Menidia menidia) to large, small, or random size-selective harvest of adults over four generations. Harvested biomass evolved rapidly in directions counter to the size-dependent force of fishing mortality. Large-harvested populations initially produced the highest catch but quickly evolved a lower yield than controls. Small-harvested populations did the reverse. These shifts were caused by selection of genotypes with slower or faster rates of growth. Management tools that preserve natural genetic variation are necessary for long-term sustainable yield.     

Reconstructing the origin of Andaman Islanders

The origin of the Andaman "Negrito" and Nicobar "Mongoloid" populations has been ambiguous. Our analyses of complete mitochondrial DNA sequences from Onges and Great Andaman populations revealed two deeply branching clades that share their most recent common ancestor in founder haplogroup M, with lineages spread among India, Africa, East Asia, New Guinea, and Australia. This distribution suggests that these two clades have likely survived in genetic isolation since the initial settlement of the islands during an out-of-Africa migration by anatomically modern humans. In contrast, Nicobarese sequences illustrate a close genetic relationship with populations from Southeast Asia.     

Unpredictable evolution in a 30-year study of Darwin's finches

Evolution can be predicted in the short term from a knowledge of selection and inheritance. However, in the long term evolution is unpredictable because environments, which determine the directions and magnitudes of selection coefficients, fluctuate unpredictably. These two features of evolution, the predictable and unpredictable, are demonstrated in a study of two populations of Darwin's finches on the Galápagos island of Daphne Major. From 1972 to 2001, Geospiza fortis (medium ground finch) and Geospiza scandens (cactus finch) changed several times in body size and two beak traits. Natural selection occurred frequently in both species and varied from unidirectional to oscillating, episodic to gradual. Hybridization occurred repeatedly though rarely, resulting in elevated phenotypic variances in G. scandens and a change in beak shape. The phenotypic states of both species at the end of the 30-year study could not have been predicted at the beginning. Continuous, long-term studies are needed to detect and interpret rare but important events and nonuniform evolutionary change.     

大豆异地衍生RIL群体主要数量性状的自然选择效应

 【目的】探明大豆杂交组合在不同生态条件下衍生重组自交系群体的遗传结构的差异及其成因。【方法】以Peking×7605、RN-9×7605两个组合分别在南京和济南衍生的RIL群体为材料,比较同一杂交组合在两地衍生群体主要数量性状的表型差异,鉴别大豆主要数量性状不同生态环境条件下的自然选择效应。【结果】Peking×7605组合衍生的两个群体在南京和济南种植,其株高和分枝数均表现出显著差异;RN-9×7605组合衍生的两个RIL群体在南京和济南种植,其分枝数、有效荚数、单株粒数和百粒重等表现均差异显著。【结论】上述性状发生了明显的自然选择效应,经表型方差分解证实性状差异由群体间遗传结构存在的真实差异造成。     

桃果实单果重及可溶性固形物含量的全基因组选择分析

【背景】桃单果重和可溶性固形物含量（SSC）是育种家关注的两个重要的数量性状,受到多个微效基因的控制,难以通过单个标记进行早期筛选。全基因组选择作为一种新颖的数量性状早期预测工具,在果树上已经有了初步应用,但其在桃上的应用效果以及影响预测准确性的因素仍需要深入探讨。【目的】建立桃单果重和SSC的全基因组选择技术,为桃高效分子育种技术体系的建立奠定基础。【方法】以520株训练自然群体为试材,通过重测序筛选出的48 398个SNP进行分型,在11个全基因组预测模型中分别筛选出两个数量性状适宜的模型,进而在56株自然群体和1 145株杂交群体上进行应用。【结果】3类群体的平均测序数据量在1.95—3.52 Gb,测序深度为5.29—10.79×。训练自然群体经与参考基因组比对,共得到5 065 726个SNP,去除缺失率较高（>20%）、最小等位基因频率过低（<0.05）的位点后,随机挑选基因组上48 398个SNP用于训练群体的全基因组选择模型构建。单果重预测精度最高的模型是BayesA,SSC预测精度最高的模型为randomforest。分别利用两个数量性状最适的模型进行预测...     

生境片段化对千岛湖岛屿上黄足厚结猛蚁遗传多样性的影响

利用相关序列扩增多态性(SRAP)分子标记法,对千岛湖片段化生境中14个岛屿上的黄足厚结猛蚁(Pachycondyla luteipes)种群遗传结构和多样性进行研究。利用5对SRAP引物对42份材料的基因组进行扩增,共得到大小在50-800 bp之间的71个可重复位点,其中63个为多态性位点,多态性比率达88.73%。AMOVA分析结果显示,65.03%的遗传变异存在于种群间,34.97%的遗传变异来自种群内(P < 0.001)。利用PopGene Version 1.32软件对SRAP多态性数据进行分析,不同岛屿种群的多态位点比例和Nei''s基因多样性指数变化范围分别介于35.21%-91.55%和0.2662-0.4905之间,平均值分别为58.25%和0.3729,其中多态位点比率最高的岛屿为面积最大的JSE岛。多态位点比例和Nei''s基因多样性指数与岛屿面积、海拔均无显著相关性,但与隔离度呈显著正相关关系。种群间遗传分化指数介于0.0777-0.9328之间,平均值为0.4419,基因流值介于0.0360-5.9350之间,平均值为1.0451,种群间遗传分化程度较高,基因流较低。利用UPGMA聚类分析法对14岛屿上的42个个体进行遗传聚类分析,表明地理距离较近的个体和岛屿具有优先聚在一起的趋势。Mantel 检验表明黄足厚结猛蚁各种群间地理距离与遗传距离间存在显著相关性(r=0.7757,P < 0.01)。以上结果表明地理隔离是影响千岛湖黄足厚结猛蚁种群遗传结构和多样性的主要因素。     

Evolution of character displacement in Darwin's finches

Competitor species can have evolutionary effects on each other that result in ecological character displacement; that is, divergence in resource-exploiting traits such as jaws and beaks. Nevertheless, the process of character displacement occurring in nature, from the initial encounter of competitors to the evolutionary change in one or more of them, has not previously been investigated. Here we report that a Darwin's finch species (Geospiza fortis) on an undisturbed Galápagos island diverged in beak size from a competitor species (G. magnirostris) 22 years after the competitor's arrival, when they jointly and severely depleted the food supply. The observed evolutionary response to natural selection was the strongest recorded in 33 years of study, and close to the value predicted from the high heritability of beak size. These findings support the role of competition in models of community assembly, speciation, and adaptive radiations.     

中国水仙野生居群形态变异及其南麂水仙分类地位的研究

[目的]研究我国沿海岛屿归化的中国水仙的形态变异,探讨中国水仙在地理隔离状态下的遗传及其浙江南麂岛产水仙的分类地位。[方法]采用居群取样法采集8个居群的野生样品和2个居群栽培样品,并对其进行形态测量。然后,使用SPSS Statistics 19.0以及Excel软件对数据进行统计分析。[结果]福建平潭、上海崇明、浙江舟山和南麂4个岛屿8个居群的水仙由于长期的地理隔离,它们之间发生了一定的形态变异;南麂列岛上的水仙高矮2个类型是环境差异引起的环境饰变;南麂产水仙仍然属于多花水仙的变种——中国水仙;南麂产的中国水仙具有植株小、花朵大的特点,且其种群规模较小,资源数量极其有限。[结论]南麂产的中国水仙是一种珍稀遗传资源,应当予以重点保护。     

Admixture studies and the detection of selection

Three methods can be used to search for evidence of natural selection from admixture studies. These include classification of the admixture estimates into two groups; calculation of the rank correlation between estimates from more than one population; and the testing of admixture estimates for homogeneity. The use of these methods is discussed with special reference to black-white admixture in the United States. Using revised estimates of African gene frequencies, derived from a consideration of the geographical origin of the slaves, we calculated admixture estimates and their variances for five U.S. black populations; Claxton (Georgia); Sapelo Island (Georgia); James Island (South Carolina); Charleston (South Carolina); Oakland (California). Two out of the five populations yielded heterogeneous admixture estimates but all other tests were non-significant. The data provide little evidence for the action of selection. The few, inconsistent significant results are more indicative of the action of random drift or biased gene frequency estimates than natural selection, and in general these effects cannot be differentiated. It seems doubtful that admixture studies can ever provide unequivocal evidence for the action of natural selection in human populations. In the search for natural selection, perhaps admixture studies should only be used as a preliminary screening device.     

Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles

Major phenotypic changes evolve in parallel in nature by molecular mechanisms that are largely unknown. Here, we use positional cloning methods to identify the major chromosome locus controlling armor plate patterning in wild threespine sticklebacks. Mapping, sequencing, and transgenic studies show that the Ectodysplasin (EDA) signaling pathway plays a key role in evolutionary change in natural populations and that parallel evolution of stickleback low-plated phenotypes at most freshwater locations around the world has occurred by repeated selection of Eda alleles derived from an ancestral low-plated haplotype that first appeared more than two million years ago. Members of this clade of low-plated alleles are present at low frequencies in marine fish, which suggests that standing genetic variation can provide a molecular basis for rapid, parallel evolution of dramatic phenotypic change in nature.     

The dynamics of cooperative bacterial virulence in the field

Laboratory experiments have shown that the fitness of microorganisms can depend on cooperation between cells. Although this insight has revolutionized our understanding of microbial life, results from artificial microcosms have not been validated in complex natural populations. We investigated the sociality of essential virulence factors (crystal toxins) in the pathogen Bacillus thuringiensis using diamondback moth larvae (Plutella xylostella) as hosts. We show that toxin production is cooperative, and in a manipulative field experiment, we observed persistent high relatedness and frequency- and density-dependent selection, which favor stable cooperation. Conditions favoring social virulence can therefore persist in the face of natural population processes, and social interactions (rapid cheat invasion) may account for the rarity of natural disease outbreaks caused by B. thuringiensis.     

Reduced responses to selection after species range expansion

Species range expansion reduces genetic variation at the margins of a species range and should thus compromise the adaptive potential of its marginal populations. Remarkably, this prediction has not previously been tested. Here, we show that populations of the plant Mercurialis annua, which expanded its range into Spain and Portugal from North Africa after the Pleistocene glaciation, respond to selection on a key life-history trait less well than populations from the species' historical refugium. Our results provide direct evidence of a decline in adaptive potential across the geographic range of a species after a shift in its distribution. Predicting evolutionary responses to environmental change will thus need to account for the genetic heterogeneity of species and the spatial dynamics of their geographic distributions.     

Natural selection and the reinforcement of mate recognition

Natural selection on mate recognition may often contribute to speciation, resulting in reproductive character displacement. Field populations of Drosophila serrata display reproductive character displacement in cuticular hydrocarbons when sympatric with Drosophila birchii. We exposed field sympatric and allopatric populations of D. serrata to experimental sympatry with D. birchii for nine generations. Cuticular hydrocarbons of field allopatric D. serrata populations evolved to resemble the field sympatric populations, whereas field sympatric D. serrata populations remained unchanged. Our experiment indicates that natural selection on mate recognition resulted in the field pattern of reproductive character displacement.     

Rapid evolution of egg size in captive salmon

Captive breeding and release programs, widely used to supplement populations of declining species, minimize juvenile mortality to achieve rapid population growth. However, raising animals in benign environments may promote traits that are adaptive in captivity but maladaptive in nature. In chinook salmon, hatchery rearing relaxes natural selection favoring large eggs, allowing fecundity selection to drive exceptionally rapid evolution of small eggs. Trends toward small eggs are also evident in natural populations heavily supplemented by hatcheries, but not in minimally supplemented populations. Unintentional selection in captivity can lead to rapid changes in critical life-history traits that may reduce the success of supplementation or reintroduction programs.     

Population cycles in small rodents

We conclude that population fluctuations in Microtus in southern Indiana are produced by a syndrome of changes in birth and death rates similar to that found in other species of voles and lemmings. The mechanisms which cause the changes in birth and death rates are demolished by fencing the population so that no dispersal can occur. Dispersal thus seems critical for population regulation in Microtus. Because most dispersal occurs during the increase phase of the population cycle and there is little dispersal during the decline phase, dispersal is not directly related to population density. Hence the quality of dispersing animals must be important, and we have found one case of increased dispersal tendency by one genotype. The failure of population regulation of Microtus in enclosed areas requires an explanation by any hypothesis attempting to explain population cycles in small rodents. It might be suggested that the fence changed the predation pressure on the enclosed populations. However, the fence was only 2 feet (0.6 meter) high and did not stop the entrance of foxes, weasels, shrews, or avian predators. A striking feature was that the habitat in the enclosures quickly recovered from complete devastation by the start of the spring growing season. Obviously the habitat and food quality were sufficient to support Microtus populations of abnormally high densities, and recovery of the habitat was sufficiently quick that the introduction of new animals to these enclosed areas resulted in another population explosion. Finally, hypotheses of population regulation by social stress must account for the finding that Microtus can exist at densities several times greater than normal without "stress" taking an obvious toll. We hypothesize that the prevention of dispersal changes the quality of the populations in the enclosures in comparison to those outside the fence. Voles forced to remain in an overcrowded fenced population do not suffer high mortality rates and continue to reproduce at abnormally high densities until starvation overtakes them. The initial behavioral interactions associated with crowding do not seem sufficient to cause voles to die in situ. What happens to animals during the population decline? Our studies have not answered this question. The animals did not appear to disperse, but it is possible that the method we used to measure dispersal (movement into a vacant habitat) missed a large segment of dispersing voles which did not remain in the vacant area but kept on moving. Perhaps the dispersal during the increase phase of the population cycle is a colonization type of dispersal, and the animals taking part in it are likely to stay in a new habitat, while during the population decline dispersal is a pathological response to high density, and the animals are not attracted to settling even in a vacant habitat. The alternative to this suggestion is that animals are dying in situ during the decline because of physiological or genetically determined behavioral stress. Thus the fencing of a population prevents the change in rates of survival and reproduction, from high rates in the increase phase to low rates in the decline phase, and the fenced populations resemble "mouse plagues." A possible explanation is that the differential dispersal of animals during the phase of increase causes the quality of the voles remaining at peak densities in wild populations to be different from the quality of voles at much higher densities in enclosures. Increased sensitivity to density in Microtus could cause the decline of wild populations at densities lower than those reached by fenced populations in which selection through dispersal has been prevented. Fencing might also alter the social interactions among Microtus in other ways that are not understood. The analysis of colonizing species by MacArthur and Wilson (27) can be applied to our studies of dispersal in populations of Microtus. Groups of organisms with good dispersal and colonizing ability are called r strategists because they have high reproductive potential and are able to exploit a new environment rapidly. Dispersing voles seem to be r strategists. Young females in breeding condition were over-represented in dispersing female Microtus (17). The Tf(C)/Tf(E) females, which were more common among dispersers during the phase of population increase (Fig. 6), also have a slight reproductive advantage over the other Tf genotypes (19). Thus in Microtus populations the animals with the highest reproductive potential, the r strategists, are dispersing. The segment of the population which remains behind after the selection-via-dispersal are those individuals which are less influenced by increasing population densities. These are the individuals which maximize use of the habitat, the K strategists in MacArthur and Wilson's terminology, or voles selected for spacing behavior. Thus we can describe population cycles in Microtus in the same theoretical framework as colonizing species on islands. Our work on Microtus is consistent with the hypothesis of genetic and behavioral effects proposed by Chitty (6) (Fig. 7) in that it shows both behavioral differences in males during the phases of population fluctuation and periods of strong genetic selection. The greatest gaps in our knowledge are in the area of genetic-behavioral interactions which are most difficult to measure. We have no information on the heritability of aggressive behavior in voles. The pathways by which behavioral events are translated into physiological changes which affect reproduction and growth have been carefully analyzed by Christian and his associates (28) for rodents in laboratory situations, but the application of these findings to the complex field events described above remains to be done. Several experiments are suggested by our work. First, other populations of other rodent species should increase to abnormal densities if enclosed in a large fenced area (29). We need to find situations in which this prediction is not fulfilled. Island populations may be an important source of material for such an experiment (30). Second, if one-way exit doors were provided from a fenced area, normal population regulation through dispersal should occur. This experiment would provide another method by which dispersers could be identified. Third, if dispersal were prevented after a population reached peak densities, a normal decline phase should occur. This prediction is based on the assumption that dispersal during the increase phase is sufficient to ensure the decline phase 1 or 2 years later. All these experiments are concerned with the dispersal factor, and our work on Microtus can be summarized by the admonition: study dispersal.     

Rapid temporal reversal in predator-driven natural selection

As the environment changes, will species be able to adapt? By conducting experiments in natural environments, biologists can study how evolutionary processes such as natural selection operate through time. We predicted that the introduction of a terrestrial predator would first select for longer-legged lizards, which are faster, but as the lizards shifted onto high twigs to avoid the predator, selection would reverse toward favoring the shorter-legged individuals better able to locomote there. Our experimental studies on 12 islets confirmed these predictions within a single generation, thus demonstrating the rapidity with which evolutionary forces can change during times of environmental flux.