NO EFFECT OF ENVIRONMENTAL HETEROGENEITY ON THE MAINTENANCE OF GENETIC VARIATION IN WING SHAPE IN DROSOPHILA MELANOGASTER

Theory suggests that heterogeneous environments should maintain more genetic variation within populations than homogeneous environments, yet experimental evidence for this effect in quantitative traits has been inconsistent. To examine the effect of heterogeneity on quantitative genetic variation, we maintained replicate populations of Drosophila melanogaster under treatments with constant temperatures, temporally variable temperature, or spatially variable temperature with either panmictic or limited migration. Despite observing differences in fitness and divergence in several wing traits between the environments, we did not find any differences in the additive genetic variance for any wing traits among any of the treatments. Although we found an effect of gene flow constraining adaptive divergence between cages in the limited migration treatment, it did not tend to increase within‐population genetic variance relative to any of the other treatments. The lack of any clear and repeatable patterns of response to heterogeneous versus homogeneous environments across several empirical studies suggests that a single general mechanism for the maintenance of standing genetic variation is unlikely; rather, the relative importance of putative mechanisms likely varies considerably from one trait and ecological context to another.     

Heterochrony, maternal effects, and phenotypic variation among sympatric pupfishes

Variation in ontogeny can produce phenotypic variation both within and among species. I investigated whether changes in timing and rate of growth were a source of phenotypic variation in a putative incipient species group of pupfish (Cyprinodon spp.). On San Salvador Island, Bahamas, sympatric forms of pupfish differ in morphology but show only partial reproductive isolation in the laboratory. Offspring from two forms and two geographical areas and their hybrids were bred in the laboratory, and ontogenetic trajectories of their feeding morphology were followed until maturity. In the Bahamian pupfish the two forms grow along similar size but not shape trajectories. Two heterochronic parameters, onset and rate of growth, alter shape trajectories in the Bahamian pupfish. Similar forms from different geographical areas (Florida and the Bahamas) grow along parallel shape trajectories, differing only in one heterochronic parameter, the onset shape. Hybrids within and between the pupfish forms produced intermediate feeding morphologies that were influenced by their maternal phenotype, suggesting that maternal effects may be a source of phenotypic variation in shape that can persist to maturity. In Cyprinodon, small changes in multiple heterochronic parameters translate into large phenotypic differences in feeding morphology.     

REINFORCEMENT AND REPRODUCTIVE CHARACTER DISPLACEMENT IN GASTROPHRYNE CAROLINENSIS AND G. OLIVACEA (ANURA: MICROHYLIDAE): A REEXAMINATION

Tape-recorded advertisement calls of Gastrophryne carolinensis and G. olivacea, obtained in Texas and southern Louisiana, were analyzed by means of an analogue audiospectrograph. Samples were grouped into four areas: allopatric and sympatric for G. carolinensis, and combined adjacent allopatric/shallow sympatric, and sympatric for G. olivacea. Three attributes of the advertisement call (call duration, pulse rate, and dominant frequency) were investigated, with water temperature at the calling site as the independent variable. Values for dominant frequency do not overlap between species, across the full range of recording temperatures, and those of sympatric G. carolinensis are displaced away from those of both groups of G. olivacea (which are very similar)—thus indicating a pattern of geographic variation consistent with reproductive character displacement. There is considerable overlap in the values for duration and for pulse rate of each species when considered alone, but there is only slight overlap of the scatters of points for the pairs of values. For both species, no consistent patterns of correlation were detected between the three attributes of the call and the snout–vent length of the emitter, thus reducing the likelihood that the divergence in calls is due to pleiotropic effects of body size.     

Experimental heating reveals nest temperature affects nestling condition in tree swallows (Tachycineta bicolor)

Investment in one life-history stage can have delayed effects on subsequent life-history stages within a single reproductive bout. We experimentally heated tree swallow (Tachycineta bicolor) nests during incubation to test for effects on parental and nestling conditions. Females incubating in heated boxes maintained higher body condition and fed nestlings at higher rates. We cross-fostered nestlings and found that young nestlings (4-7 days old) incubated in heated nests had higher body condition and body mass, regardless of treatment status of their rearing parent. However, older nestlings which were fed by heated females maintained higher condition and body mass regardless of treatment status of their incubating parent. These results indicate that investment in one life-history stage can have multiple pathways of carry-over effects on future life-history stages.     

FINE-GRAINED SPATIAL AND TEMPORAL VARIATION IN SELECTION DOES NOT MAINTAIN GENETIC VARIATION IN ERIGERON ANNUUS

Because interactions among plants are spatially local, the scale of environmental heterogeneity can have large effects on evolutionary dynamics. However, very little is known about the spatial patterns of variation in fitness and the relative magnitude of spatial and temporal variation in selection. Replicates of 12 genotypes of Erigeron annuus (Asteraceae) were planted in 288 locations within a field, separated by distances of 0.1 to 30.0 m, and replicated in two years. In a given year, most spatial variation in relative fitness (genotype-environment [G × E] interactions for fitness) occurred over distances of only 50 cm. Year effects were as large or larger than the spatial variation in fitness; in particular there was a large, three-way, genotype-year-environment interaction at the smallest spatial scale. The genetic correlation of fitness across years at a given location was near zero, 0.03. Thus, the relative fitness of genotypes is spatially unpredictable and a map of the selective environment has constantly shifting locations of peaks and valleys. Including measurements of soil nutrients as covariates in the analysis removed most of the spatial G × E interaction. Vegetation and microtopography had no effect on the G × E terms, suggesting that differential response to soil nutrients is the cause of spatial variation in fitness. However, the slope of response to NH₄ and P0₄ was negative; therefore the soil nutrients are probably just indicators of other, unknown, environmental factors. We explored via simulation the evolutionary consequences of spatial and temporal variation in fitness and showed that, for this system, the spatial scale of variation was too fine grained (by a factor of 3 to 5) to be a powerful force maintaining genetic variation in the population. The inclusion of both spatial and temporal variation in fitness actually reduced the coexistence of genotypes compared to pure spatial models. Thus the presence of spatial or temporal variation in selection does not guarantee that it is an effective evolutionary force maintaining diversity. Instead the pattern of selection favors generalist genotypes.     

PEMPHIGUS REVISITED: CHANGES IN GEOGRAPHIC VARIATION BUT CONSTANCY IN VARIABILITY AND COVARIATION

Samples of the gall-forming aphids Pemphigus populicaulis and P. populitransversus (both elongate and globular morphs) were re-collected at sites in eastern North America after 13 to 16 years. Twenty-three morphometric characters of the galls, stem mothers, and alate fundatrigeniae were analyzed by univariate and multivariate methods. Varying proportions of the variance of each character are attributable to the four levels of variation—locality, year, year by locality interaction, and among galls (within one year and locality). The year by locality interaction level generally has the greatest variation and is highly significant. Year and locality effects tend to be lower and not significant. The variance components do not exhibit trends with time. Geographic variation patterns of single variables or factor scores in the original and revisited populations show significant spatial structure overall but lack clear-cut spatial patterns, especially clines. Observable patterns of variation match results of the spatial analyses: most characters lack clear trends; patterns in the revisited data do not resemble patterns for the same variables in the original data. Variability profiles for characters change little over the time span and are comparable among and within localities. Covariation among characters over localities is largely maintained during the time interval despite the changes in patterns. Fluctuating interclonal competition among aphids on secondary hosts is believed to cause the marked heterogeneity in space and time among the aphids in the galls.     

理化诱变引起的小麦再生株染色体变异

小麦幼胚和愈伤组织经理化诱变后形成的再生株M_1R_1和C_1R_1,具有比R_1株高的染色体变异频率,其染色体数目变化于35—46之间,但无倍数变异。理化诱变处理提高了再生株中含非整倍体、棒状二价体、单价体、等臂环和四价体的细胞频率,其中以1000伦琴γ射线照射未成熟胚处理的再生株染色体变异频率为最高。其次为2 mmol/L叠氮化钠处理愈伤组织的再生株。经过二倍体和单倍体选择,染色体变异大为减少,但仍保有较高频率的单价体。     

RESPONSE TO NATURAL ENVIRONMENTAL HETEROGENEITY: MATERNAL EFFECTS AND SELECTION ON LIFE-HISTORY CHARACTERS AND PLASTICITIES IN MIMULUS GUTTATUS

Recent studies in plant populations have found that environmental heterogeneity and phenotypic selection vary at local spatial scales. In this study, I ask if there is evolutionary change in response to environmental heterogeneity and, if so, whether the response occurs for characters or character plasticities. I used vegetative clones of Mimulus guttatus to create replicate populations of 75 genotypes. These populations were planted into the natural habitat where they differed in mean growth, flowering phenology, and life span. This phenotypic variation was used to define selective environments. There was variation in fitness (flower production) among genotypes across all planting sites and in genotype response to the selective environment. Offspring from each site were grown in the greenhouse in two water treatments. Because each population initially had the same genetic composition, variation in the progeny between selective environments reveals either evolutionary change in response to environmental heterogeneity or environmental maternal effects. Plants from experimental sites that flowered earlier, had shorter life spans and were less productive, produced offspring that had more flowers, on average, and were less plastic in vegetative allocation than offspring of longer-lived plants from high-productivity areas. However, environmental maternal effects masked phenotypic differences in flower production. Therefore, although there was evidence of genetic differentiation in both life-history characters and their plasticities in response to small-scale environmental heterogeneity, environmental maternal effects may slow evolutionary change. Response to local-scale selective regimes suggests that environmental heterogeneity and local variation in phenotypic selection may act to maintain genetic variation.     

川西云杉天然种群表型多样性

为了揭示川西云杉(Picea balfouriana)天然种群表型变异程度和变异规律, 以四川甘孜藏族自治州天然分布的川西云杉为研究对象, 调查了12个种群360个单株的种实和针叶表型性状, 采用变异系数、巢式方差分析、相关分析和聚类分析等方法, 分析了种群间和种群内表型多样性。结果表明: 川西云杉表型性状在种群间和种群内存在极其丰富的多样性, 种群间表型分化系数均值为36.53%, 小于种群内变异(63.47%); 球果、针叶、种鳞和种翅的表型分化系数均值分别为47.15%、31.93%、21.89%和45.14%, 球果、针叶、种鳞和种翅4类表型性状的变异系数分别为12.56%、22.16%、12.61%和16.53%, 种鳞的变异系数和表型分化系数最小, 表明其性状最为稳定; 12个表型性状间多数呈显著或极显著正相关, 球果长、球果径、针叶长和种鳞长为川西云杉重要的表型性状。川西云杉表型变异在空间分布上呈现以经度(球果和针叶)和纬度(种鳞和种翅)并存的单向变异模式; 利用种群间欧氏距离进行聚类分析, 可以把川西云杉12个种群划分为3类。     

VARIABILITY OF THE HEPATOTOXIN MICROCYSTIN-LR IN HYPEREUTROPHIC DRINKING WATER LAKES1

The patterns of occurrence of the peptide hepatotoxin microcystin-LR (MC-LR) was studied in three hypereu-trophic hardwater lakes (Coal, Driedmeat, and Little Beaver) in central Alberta, Canada, over three open-water seasons. MC-LR concentration was based on high-performance liquid chromatography detection and expressed as μg.g^?1 of total plankton biomass, ng.L^?1 of lake water, and μg.g^?1 of Microcystis aeruginosa Kuetz. emend. Elenkin. MC-LR was highly variable temporally (differences up to 3 orders of magnitude) within each lake over an individual year, between years in an individual lake, and between lakes in any year. Seasonal (within-year) changes in MC-LR concentration (expressed in the preceding units) were positively correlated to the abundance and biomass Of the cyanobacterium M. aeruginosa (r =0.60–0.77), total and total dissolved phosphorus concentration (r =0.46–0.59), pH (r=0.38–0.58), and chlorophyll a (r=0.25–0.59). Surprisingly, there was no relationship between MC-LR concentration and water temperature (range: 7°-24°C, r =-0.13 to 0.02) and a negative correlation with nitrate concentration (r =–0.27 to -0.34). In two synoptic surveys examining spatial variability, MC-LR concentrations were quite variable (CV of 185 and 36% between sampling sites for Coal and Little Beaver lakes, respectively). Spatial distribution of MC-LR on any one day was correlated with the abundance and biomass of M. aeruginosa. Over a 24-h period, MC-LR concentration in M. aeruginosa decreased more than 6-fold at night relative to daytime concentrations. In general, analytical and within-site variation of MC-LR was relatively small (CV < 4 and 9%, respectively) but greatest both within and between years in a lake followed by diel and spatial variation.     

武夷山甜槠林水文学效应的研究

对武夷山甜槠林成熟林水文学效应的研究结果表明：观测期间,年大气降水量２６７８．７８ｍｍ,林内雨量２１８２．０４ｍｍ,林冠截留量为４９６．７４ｍｍ;林内雨中,穿透雨量２０８２．０８ｍｍ,树干茎流９９．９６ｍｍ;到达甜槠林地作用面的林内雨量中,被地表枯枝落叶层截留的雨量为１５９．８４ｍｍ,地表径流量１１．６ｍｍ,地下渗流量１０９．３２ｍｍ,其余林内雨量形成土壤含水量增量并由地表物理蒸发、根系吸收以及植物蒸腾所消耗;甜槠林地０～２０ｃｍ土层水分初渗率７８．６ｍｍ·ｍｉｎ－１,稳渗率１５．５ｍｍ·ｍｉｎ－１,达到稳渗历时４５ｍｉｎ,地表枯枝落叶最大持水量５．２ｍｍ,土壤蓄水量１５４．０ｍｍ。与国内其它地区不同类型的森林相比较,武夷山甜槠林具有较强的水文学效能。     

COST OF REPRODUCTION IN POLEMONIUM VISCOSUM: PHENOTYPIC AND GENETIC APPROACHES

I measured the effect of early reproduction on subsequent growth and survival in the alpine perennial wildflower, Polemonium viscosum. Measurements were made over 4 yr on 34 maternal sibships under natural conditions. A significant phenotypic cost of early reproduction characterized the study population. Plants that flowered after only one year's growth had twice as many leaves and 25% more shoots than nonflowering individuals of equal age. However, early flowering decreased leaf number by 18% in the subsequent year and survivorship by 20% after two years relative to changes in leaf number and survival of nonflowering plants. For such trade-offs to shape the further evolution of reproductive schedules, flowering probability and those age-specific components of plant size that represent the energetic currency for reproductive costs must be heritable. Although families showed significant heterogeneity in the probability of early flowering, most (62%) entirely failed to flower. Moreover, phenotypic variation in vegetative size components at ages 1 and 2 had little genetic basis. Only at ages 3 and 4, after vegetative and demographic costs of early reproduction had been incurred, did vegetative size components (leaf length and number, and shoot number) vary significantly among families. Results of this study provide little evidence of a genetically based trade-off between early reproduction and subsequent survival in P. viscosum.     

GEOGRAPHIC DIFFERENCES IN SEXUAL REASSORTMENT IN RNA PHAGE

The genetic structure of natural bacteriophage populations is poorly understood. Recent metagenomic studies suggest that phage biogeography is characterized by frequent migration. Using virus samples mostly isolated in Southern California, we recently showed that very little population structure exists in segmented RNA phage of the Cystoviridae family due to frequent segment reassortment (sexual genetic mixis) between unrelated virus individuals. Here we use a larger genetic dataset to examine the structure of Cystoviridae phage isolated from three geographic locations in Southern New England. We document extensive natural variation in the physical sizes of RNA genome segments for these viruses. In addition, consistent with earlier findings, our phylogenetic analyses and calculations of linkage disequilibrium (LD) show no evidence of within‐segment recombination in wild populations. However, in contrast to the prior study, our analysis finds that reassortment of segments between individual phage plays a lesser role among cystoviruses sampled in New England, suggesting that the evolutionary importance of genetic mixis in Cystoviridae phage may vary according to geography. We discuss possible explanations for these conflicting results across the studies, such as differing local ecology and its impact on phage growth, and geographic differences in selection against hybrid phage genotypes.