Microevolution in island rodents

We perform a meta-analysis on morphological data from four island rodent populations exhibiting microevolution (>100 years). Data consisting of incidences of skeletal variants, cranial, and external measurements are from house mice (Mus musculus) on one Welsh and one Scottish island, black rats (Rattus rattus) on two Galapagos islands, and deer mice (Peromyscus maniculatus) on three California Channel islands. We report extremely high rates of microevolution for many traits; 60% of all mensural traits measured changed at a rate of 600 d or greater (max. 2682 d). The proportion of all mensural traits evolving at 600–800 d (23%) was idiosyncratic and departed from an expected negative exponential distribution. We argue that selection, rather than founder events, is largely responsible for the substantial shifts in morphology seen among insular rodents. Examining individual traits, there is a trend towards the nose becoming longer and wider, while the skull becomes shallower, shown by both rats and mice on five different islands. We found a significant correlation between island size and degree of skeletal variant evolution and between island distance from the mainland (or nearest island) and degree of cranial and external character evolution. Thus, microevolution of rodents is greater on smaller and more remote islands.     

Evolution of specialists in an experimental microcosm

The impact of adaptation on the persistence of a balanced polymorphism was explored using the lactose operon of Escherichia coli as a model system. Competition in chemostats for two substitutable resources, methylgalactoside and lactulose, generates stabilizing frequency-dependent selection when two different naturally isolated lac operons (TD2 and TD10) are used. The fate of this balanced polymorphism was tracked over evolutionary time by monitoring the frequency of fhuA-, a linked neutral genetic marker that confers resistance to the bacteriophage T5. In four out of nine chemostats the lac polymorphism persisted for 400-600 generations when the experiments were terminated. In the other five chemostats the fhuA polymorphism, and consequently the lac operon polymorphism, was lost between 86 and 219 generations. Four of 13 chemostat cultures monomorphic for the lac operon retained the neutral fhuA polymorphism for 450-550 generations until they were terminated; the remainder became monomorphic at fhuA between 63 and 303 generations. Specialists on each galactoside were isolated from chemostats that maintained the fhuA polymorphism, whether polymorphic or monomorphic at the lac operon. Strains isolated from three of four chemostats in which the lac polymorphism was preserved had switched their galactoside preference. Most of the chemostats where the fhuA polymorphism was lost also contained specialists. These results demonstrate that the initial polymorphism at lac was of little consequence to the outcome of long-term adaptive evolution. Instead, the fitnesses of evolved strains were dominated by mutations arising elsewhere in the genome, a fact confirmed by showing that operons isolated from their evolved backgrounds were alone unable to explain the presence of both specialists. Our results suggest that, once stabilized, ecological specialization prevented selective sweeps through the entire population, thereby promoting the maintenance of linked neutral polymorphisms.     

Harvest reserves reduce extinction risk in an experimental microcosm

Overharvesting by humans threatens a substantial fraction of endangered species. Reserves have recently received enormous attention as a means of better conserving harvested resources, despite limited empirical evidence of their efficacy. We used manipulated microcosms to test whether reserves reduce extinction risk in mobile populations of harvested Tetrahymena thermophila , a ciliate. Here we show that patterns of population distribution inside and outside reserves can be accurately predicted on the basis of simple models of diffusion coupled with logistic controls on local population growth. No extinctions occurred in eight experimental trials with reserves, whereas extinction occurred in seven of eight trials without reserves, as predicted by population viability models based on stochastic population processes. These results suggest that marine reserves may be an effective means of improving long-term viability in heavily harvested fish species.     

Population dynamics and nutrient fluxes in an aquatic microcosm

An aquatic microcosm, consisting of three spatially separated yet mutually dependent trophic levels, was established in the laboratory and monitored for 310 days. A three-fold research approach evaluates the experimental potential of this large, multicompartmental microecosystem. Realistic biological and chemical features and nutrient fluxes parallel identifiable patterns observed in natural aquatic ecosystems as well as in published laboratory observations. Two successional patterns developed in the autotrophic community: a sequential change in species composition and a progression from a one-compartment planktonic situation to a two-phased planktonic-attached system. Although the microcosm was initially seeded with an axenic culture of Cryptomonas ovata var. palustris Ehr, contamination by Chlorella, Scenedesmus, Closterium, and Anabaena occurred within 41 days. The appearance of attached algae, noted on day 5, marked the transition from a planktonically-based ecosystem to a heterogeneous system. Crashes in the cladoceran population occurred on days 103 and 202. The second collapse was final. Repeated attempts to reestablish Daphnia middendorffiana failed. Mineralization and nutrient cycling are recognizable properties of the microcosm. Ammonification, nitrification, and nitrogen assimilation occurred predominantly in the decomposer tank as did the regeneration of inorganic phosphorus. A peak on day 205 in the ammonia input to the algal tank drawn from beneath the bacterial filter bed followed a peak in total Kjeldahl nitrogen (TKN) (day 135) and preceded peaks in nitrate (day 219) and TKN (day 233). Although levels in the algal tank were undetectable after three weeks, dissolved orthophosphate was actively regenerated in the decomposer bed, recycled to the autotroph unit, and rapidly assimilated by the algae. Characteristic patterns of radiotracer circulation also were evident. Sequential movement of ³²P from the dissolved compartment to phytoplankton to attached algae was proposed. Conversely, ¹⁴C was steadily incorporated into the phytoplankton compartment; filtrate activities fluctuated. Tracer behaviors in the cladoceran compartment were superficially cyclic. Carbon turnover times in the algal and zooplankton compartments were 17 and 11.11 hours, respectively. Indicative of the greater biological mobility of phosphorus, respective turnover times of 2.50 and 2.44 hours were similarly calculated for phosphorus. Unlike dissolved carbon which had a turnover time of 625 hours, dissolved phosphorus was rapidly cycled into the algae (turnover time = 0.58 h).     

Microbial degradation of four Nigerian crude oils in an estuarine microcosm

Four Nigerian crude oils (Bonny Light, Bonny Medium, Escravos Light and Forcados Blend) that differ substantially in fractional composition were exposed to the Lagos Lagoon waters in microcosm experiments with oil-impregnated membrane filters. Changes in microbial numbers on the membranes and in the residual oil concentration showed a relationship between the fractional composition and the biodegradation rates of the oils, with the lighter oils disappearing more rapidly. After 10 weeks exposure in the lagoon, only 15% (w/w) of the Bonny Light crude remained on the filters as compared with 20, 32 and 45% (w/w) for Escravos Light, Bonny Medium and Forcados Blend respectively. The hydrocarbon-utilizing microbial colonizers of the oil-impregnated membranes were Micrococcus, Bacillus, Pseudomonas, Flavobacterium, Alcaligenes and Aspergillus niger.     

Microevolution of Aedes aegypti

Scientific research into the epidemiology of dengue frequently focuses on the microevolution and dispersion of the mosquito Aedes aegypti. One of the world’s largest urban agglomerations infested by Ae. aegypti is the Brazilian megalopolis of Sao Paulo, where >26,900 cases of dengue were reported until June 2015. Unfortunately, the dynamics of the genetic variability of Ae. aegypti in the Sao Paulo area have not been well studied. To reduce this knowledge gap, we assessed the morphogenetic variability of a population of Ae. aegypti from a densely urbanised neighbourhood of Sao Paulo. We tested if allelic patterns could vary over a short term and if wing shape could be a predictor of the genetic variation. Over a period of 14 months, we examined the variation of genetic (microsatellites loci) and morphological (wing geometry) markers in Ae. aegypti. Polymorphisms were detected, as revealed by the variability of 20 microsatellite loci (115 alleles combined; overall F_st = 0.0358) and 18 wing landmarks (quantitative estimator Q_st = 0.4732). These levels of polymorphism are higher than typically expected to an exotic species. Allelic frequencies of the loci changed over time and temporal variation in the wing shape was even more pronounced, permitting high reclassification levels of chronological samples. In spite of the fact that both markers underwent temporal variation, no correlation was detected between their dynamics. We concluded that microevolution was detected despite the short observational period, but the intensities of change of the markers were discrepant. Wing shape failed from predicting allelic temporal variation. Possibly, natural selection (Q_st>F_st) or variance of expressivity of wing phenotype are involved in this discrepancy. Other possibly influential factors on microevolution of Ae. aegypti are worth searching. Additionally, the implications of the rapid evolution and high polymorphism of this mosquito vector on the efficacy of control methods have yet to be investigated.     

乳酸菌微进化的研究进展

摘要:乳酸菌是食品工业中重要的微生物,乳酸菌微进化研究有助于深入解析其生物学功能与机制。随着分子生物学的发展,多位点序列分型(Multi-locus Sequence Typing,MLST)及基因组重测序(Whole-genome resequencing)等技术手段应运而生,使得从分子水平上阐述乳酸菌的系统发育和种群进化关系成为可能。MLST已被广泛用于乳酸菌遗传多样性和种群结构等微进化研究中,近期,测序成本的锐减使全基因组测序技术在乳酸菌微进化研究中的优势日益突显。本文对乳酸菌微进化的理论基础、研究方法和意义进行了阐述,并介绍了全基因组测序技术在乳酸菌微进化方面的应用,旨在为乳酸菌微进化分析研究提供新思路。     

Cranial Variation and Microevolution in Arikara Skeletal Populations

Abstract

Crania from six archaeological sites in South Dakota are analyzed. Chronologically the sites fall into two groups, an early group and a late group, with A.D. 1750 as the approximate boundary between them. It is shown that the late group is morphologically diverse, while the early group is relatively homogeneous. The morphological pattern is related to the increasing intensity of evolutionary processes as the contact period progressed.     

Microevolution of African American dental morphology

The African American (AA) gene pool is primarily the result of gene flow between two biologically disparate groups: West Africans (WA) and Americans of western European descent (EA). This research utilizes characteristics of dental morphology to trace genetic relationships among WA, western Europeans (EU), AA, and European Americans. Dental morphological traits are useful for this purpose because they are heritable, do not remodel during life (although they can be lost to wear or pathology), and can be compared equally among samples from past and present populations. The results of this research provide new information about human microevolution through time and space in a biocultural setting. The mean measure of divergence is used to analyze dental morphological data from 1,265 individuals in 25 samples grouped by ancestry and time. Three hypotheses associated with admixture in AA are tested. When compared with known history, results from dental morphological data are equivocal in documenting admixture in AA. Dental morphological traits do appear to reflect admixture in AA. However, changes in trait frequencies do not closely correspond with important cultural events and trends such as the institutionalized racism of the Civil War and Jim Crow era. Results are mixed concerning whether AA with greater admixture were more likely to take part in the Great Migration to southern urban centers and to the North.     

Detection of bacteria associated with harmful algal blooms from coastal and microcosm environments using electronic microarrays

With the global expansion of harmful algal blooms (HABs), several measures, including molecular approaches, have been undertaken to monitor its occurrence. Many reports have indicated the significant roles of bacteria in controlling algal bloom dynamics. Attempts have been made to utilize the bacteria/harmful algae relationship in HAB monitoring. In this study, bacterial assemblages monitored during coastal HABs and bacterial communities in induced microcosm blooms were investigated. Samples were analysed using denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA gene. DGGE bands with peculiar patterns before, during, and after algal blooms were isolated and identified. Probes for six ribotypes representing organisms associated with Chatonella spp., Heterocapsa circularisquama, or Heterosigma akashiwo were used for analysis on NanoChip electronic microarray. In addition, a new approach using cultured bacteria species was developed to detect longer (533 bp) polymerase chain reaction-amplified products on the electronic microarray. The use of fluorescently labelled primers allowed the detection of individual species in single or mixed DNA conditions. The developed approach enabled the detection of the presence or absence and relative abundance of the HAB-related ribotypes in coastal and microcosm blooms. This study indicates the ability of electronic microarray platform to detect or monitor bacteria in natural and induced environments.     

Microevolution of the Chibcha-speaking peoples of lower Central America: rare genes in an Amerindian complex.

Models are developed for the survival, history, and spread of variant alleles, in order to consider what can, and what cannot, be inferred from this type of data. The high variances of the processes involved, and questions of sampling, place severe limitations on inferences. Nonetheless, by combining information on a number of rare variants observed in a group of interrelated populations, reliable qualitative inferences are possible. These ideas and models are developed in the context of data on five rare variants and six private polymorphisms observed in eight Chibcha-speaking tribes of Costa Rica and Panama. The decline and fragmentation of the Amerindian populations of Central America over the last 300 years create considerable difficulties in attempting inference of past genetic events. However, these tribes have been well studied genetically, anthropologically, and linguistically and thus provide an excellent framework for the study of rare-variant spread.     

Electricity generation by microorganisms in the sediment-water interface of an extreme acidic microcosm

The attachment of microorganisms to electrodes is of great interest for electricity generation in microbial fuel cells (MFC) or other applications in bioelectrochemical systems (BES). In this work, a microcosm of the acidic ecosystem of Río Tinto was built and graphite electrodes were introduced at different points. This allowed the study of electricity generation in the sediment/water interface and the involvement of acidophilic microorganisms as biocatalysts of the anodic and cathodic reactions in a fuel-cell configuration. Current densities and power outputs of up to 3.5 A/m2 and 0.3 W/m2, respectively, were measured at pH 3. Microbial analyses of the electrode surfaces showed that Acidiphilium spp., which uses organic compounds as electron donors, were the predominant biocatalysts of the anodic reactions, whereas the aerobic iron oxidizers Acidithiobacillus ferrooxidans and Leptospirillum spp. were detected mainly on the cathode surface.     

Conjugal transfer at natural population densities in a microcosm simulating an estuarine environment

Abstract Estuarine microcosms were used to follow conjugal transfer of a broad host range IncP1 plasmid from a Pseudomonas putida donor to indigenous bacteria. Donor cells were added at a concentration similar to the natural abundance of bacteria in the water column (10⁶ cells ml⁻¹). Transfer was not detected in any of the test microcosms (calculated limit of detection of 10⁻⁷ and 10⁻⁴ transconjugants donor⁻¹ in water column and sediment, respectively), with the exception of transfer to an isogenic recipient (added at 10⁵ cells ml⁻¹) in sediments of controls that had been inoculated with both donors and recipients. The same plasmid was transferred with high efficiencies (10⁻¹ to 10⁻³) to a variety of recipients in filter and broth matings. These results suggest that if conjugal gene transfer occurred, it was at efficiencies that were not detectable in estuarine microcosms simulating natural population densities.     

A gnotobiotic plant microcosm

Summary A chamber for growing plants gnotobiotically in soil for an extended period of time can be constructed with readily available materials.     

Microevolution of neuroendocrine mechanisms regulating reproductive timing in Peromyscus leucopus

A key question in the evolution of life history and in evolutionary physiology asks how reproductive and other life-history traits evolve. Genetic variation in reproductive control systems may exist in many elements of the complex inputs that can affect the hypothalamic-pituitary-gonadal (HPG) or reproductive axis. Such variation could include numbers and other traits of secretory cells, the amount and pattern of chemical message released, transport and clearance mechanisms, and the number and other traits of receptor cells. Selection lines created from a natural population of white-footed mice (Peromyscus leucopus) that contains substantial genetic variation in reproductive inhibition in response to short winter daylength (SD) have been used to examine neuroendocrine variation in reproductive timing. We hypothesized that natural genetic variation would be most likely to occur in the inputs to GnRH neurons and/or in GnRH neurons themselves, but not in elements of the photoperiodic pathway that would have pleiotropic effects on nonreproductive functions as well as on reproductive functions. Significant genetic variation has been found in the GnRH neuronal system. The number of GnRH neurons immunoreactive to an antibody to mature GnRH peptide under conditions maximizing detection of stained neurons was significantly heritable in an unselected control (C) line. Furthermore, a selection line that suppresses reproduction in SD (photoperiod responsive, R) had fewer IR-GnRH neurons than a selection line that maintains reproduction in SD (photoperiod nonresponsive, NR). This supports the hypothesis that genetic variation in characteristics of GnRH neurons themselves may be responsible for the observed phenotypic variation in reproduction in SD. The R and NR lines differ genetically in food intake and iodo-melatonin receptor binding, as well as in other characteristics. The latter findings are consistent with the hypothesis that genetic variation occurs in the nutritional and hormonal inputs to GnRH neurons. Genetic variation also exists in the phenotypic plasticity of responses to two combinations of treatments, (1) food and photoperiod, and (2) photoperiod and age, indicating genetic variation in individual norms of reaction within this population. Overall, the apparent multiple sources of genetic variation within this population suggest that there may be multiple alternative combinations of alleles for both the R and NR phenotypes. If that interpretation is correct, we suggest that this offers some support for the evolutionary "potential" hypothesis and is inconsistent with the evolutionary "constraint" and "symmorphosis" hypotheses for the evolution of complex neuroendocrine pathways.