Art Weis

University of Toronto | U of T · Department of Ecology and Evolutionary Biology

Premise: The evolutionary response of a trait to environmental change depends upon the level of additive genetic variance. It has been long argued that sustained selection will tend to deplete additive genetic variance as favoured alleles approach fixation. Non-additive genetic variance, due to interactions among alleles within and between loci, d...

The persistence of a declining population in the face of environmental change may depend on how fast natural selection restores fitness, a process called "evolutionary rescue". In turn, evolutionary rescue depends on a population's adaptive potential. Fisher's theorem states that a population's adaptive potential equals the additive genetic varianc...

Premise: Precise pollen collection methods are necessary for crop breeding, but anemophilous pollen is notoriously difficult to capture and control. Here we compared a variety of methods for the controlled capture of cannabis pollen, intended to ease the process of cross-fertilization for breeding this wind-pollinated plant, and measured the utili...

Urbanization alters the landscape, degrades and fragments habitats, and can have a profound effect on species interactions. Plant–pollinator networks may be particularly sensitive to urbanization, because plants and their insect pollinators have been shown to respond to urbanization both positively and negatively. To better understand the relations...

Non-random mortality is a key driver of evolution, but mortality that occurs early in life leaves adult traits of individuals that died unknown. This can lead to the invisible fraction problem, which causes difficulty in measuring selection and evolution in natural and experimental populations. Furthermore, seeds or other propagules that are stored...

The distribution of biodiversity depends on the combined and interactive effects of ecological and evolutionary processes. The joint contribution of these processes has focused almost exclusively on deterministic effects, even though mechanisms that increase the importance of random ecological processes are expected to also increase the importance...

Pollen is generally dispersed over short distances, which promotes population genetic structure across continuous two‐dimensional space. Quantitative genetic variance in flowering time structures mating pools in the temporal dimension, at least with respect to the phenology loci. We asked if these two phenomena, isolation by distance (IBD) and isol...

Gene flow between populations can allow the spread of beneficial alleles and genetic diversity between populations, with importance to conservation, invasion biology, and agriculture. Levels of gene flow between populations vary not only with distance, but also with divergence in reproductive phenology. Since phenology is often locally adapted, arr...

Species do not live, interact, or evolve in isolation but are instead members of complex ecological communities. In ecological terms, complex multispecies interactions can be understood by considering indirect effects that are mediated by changes in traits and abundances of intermediate species. Interestingly, traits and abundances are also central...

As climate changes at unprecedented rates, understanding population responses is a major challenge. Resurrection studies can provide crucial insights into the contemporary evolution of species to climate change. We used a seed collection of two Californian populations of the annual plant Brassica rapa made over two decades of dramatic precipitation...

Co‐expression of genes in plant sporophytes and gametophytes allows correlated gametic and sporophytic selection. Theory predicts that, under outcrossing, an allele conferring greater pollen competitive ability should fix within a population unless antagonistic pleiotropy with the sporophyte stage is strong. However, under strong selfing, pollen co...

A recent study reveals a novel type of trophic interaction: galls induced on a native Florida oak by cynipid wasps are attacked by love vine, a subtropical parasitic plant. Attack is fatal to the wasp, and thus there is the opportunity for the vine to exert selection on the wasp to alter gall structure. A recent study reveals a novel type of trophi...

Urbanization is an important component of global change. Urbanization affects species interactions, but the evolutionary implications are rarely studied. We investigate the evolutionary consequences of a common pattern: the loss of high trophic‐level species in urban areas. Using a gall‐forming fly, Eurosta solidaginis, and its natural enemies that...

Climate change has induced pronounced shifts in the reproductive phenology of plants, yet we know little about which environmental factors contribute to interspecific variation in responses and their effects on fitness. We integrate data from a 43 yr record of first flowering for six species in subalpine Colorado meadows with a 3 yr snow manipulati...

PREMISE OF THE STUDY Assortative mating by flowering time can cause temporal genetic structure in species with heritable flowering times. A strong temporal structure, when coupled with a seasonal shift in selection, may lead to adaptive temporal clines. We implemented a prospective and retrospective method to estimate the temporal genetic structure...

Climate change has induced pronounced shifts in the reproductive phenology of plants, with the timing of first flowering advancing in most species. Indeed, population persistence may be threatened by the inability to track climate change phenologically. Nevertheless, substantial variation exists in biological responses to climate change across taxa...

The resurrection approach is a powerful tool for estimating phenotypic evolution in response to global change. Ancestral generations, revived from dormant propagules, are grown side-by-side with descendent generations in the same environment. Phenotypic differences between the generations can be attributed to genetic change over time. Project Basel...

The resurrection approach of reviving ancestors from stored propagules and comparing them with descendants under common conditions has emerged as a powerful method of detecting and characterizing contemporary evolution. As climatic and other environmental conditions continue to change at a rapid pace, this approach is becoming particularly useful f...

The persistence of narrowly adapted species faced with climate change will depend on their ability to migrate apace with their historical climatic envelope or to adapt in place to maintain fitness. This second path to persistence can only occur if there is sufficient genetic variance for response to new selection regimes. Inadequate levels of genet...

Our understanding of selection through male fitness is limited by the resource demands and indirect nature of the best available genetic techniques. Applying complementary, independent approaches to this problem can help clarify evolution through male function. We applied three methods to estimate selection on flowering time through male fitness in...

Premise of the study: Project Baseline is a seed bank that offers an unprecedented opportunity to examine spatial and temporal dimensions of microevolution during an era of rapid environmental change. Over the upcoming 50 years, biologists will withdraw genetically representative samples of past populations from this time capsule of seeds and grow...

Flowering is a key life history event whose timing almost certainly affects both male and female fitness, but tests of selection on flowering time through male fitness are few. Such selection may arise from direct effects of flowering time, and indirect effects through covariance between flowering time and the environment experienced during reprodu...

Premise of research. The Wisconsin Fast Plants lines of Brassica rapa (RCBr) have been a useful model system for plant ecology, evolution, physiology, and development. However, inheritance of flowering time in the B. rapa Fast Plants has not been explored. Methodology. I used quantitative genetics to explore additive, dominant, and epistatic geneti...

The optimal timing of the seasonal switch from somatic growth to reproduction can depend on an individual's condition at reproduction, the quality of the environment in which it will reproduce, or both. In annual plants, vegetative size (a function of age at flowering) affects resources available for seed production, while exposure to mutualists, a...

The timing of transition out of one life history phase determines where in the seasonal succession of environments the next phase is spent. Shifts in the general environment (e.g., seasonal climate) affect the expected fitness for particular transition dates. Variation in transition date also leads to temporal variation in the social environment. F...

Global warming will jeopardize the persistence and genetic diversity of many species. Assisted colonization, or the movement of species beyond their current range boundary, is a conservation strategy proposed for species with limited dispersal abilities or adaptive potential. However, species that rely on photoperiodic and thermal cues for developm...

Phytophagous insects from different feeding guilds may compete indirectly via altering the chemical defenses or nutritional quality of their shared host plants. Gall-formers are understudied in this context but may be susceptible to this mode of competition early in their life history, when they may be particularly sensitive to changes to the speci...

Female bees store scattered pollens grains from their bodies for transport by different modes of grooming and pollen packing. Species with corbiculae, such as honey or bumble bees, compress grains into dense pellets borne on the hind tibiae. Other species sweep grains into local concentrations of hairs (scopae), typically around the legs (in Halict...

Gene flow is generally considered a random process, that is the loci under consideration have no effect on dispersal success. Edelaar and Bolnick (Trends Ecol Evol, 27, 2012 659) recently argued that nonrandom gene flow could exert a significant evolutionary force. It can, for instance, ameliorate the maladaptive effects of immigration into locally...

In plants, the temporal pattern of floral displays, or display schedules, delimits an individual's mating opportunities. Thus, variation in the shape of display schedules can affect the degree of population synchrony and the strength of phenological assortative mating by flowering onset date. A good understanding of the mechanisms regulating the ti...

Variation among the leaves, flowers, or fruit produced by a plant is often regarded as a nuisance to the experimenter and an impediment to selection. Here, we suggest that within-plant variation can drive selection on other plant-level traits. We examine within-plant variation in floral sex allocation and in fruit set, and predict that such variati...

Although it has been widely asserted that plants mate assortatively by flowering time, there is virtually no published information on the strength or causes of phenological assortment in natural populations. When strong, assortative mating can accelerate the evolution of plant reproductive phenology through its inflationary effect on genetic varian...

Selection gradient analysis examines the strength and direction of phenotypic selection as well as the curvature of fitness functions, allowing predictions on and insights into the process of evolution in natural populations. However, traditional linear and quadratic selection analyses are not capable of detecting other features of fitness function...

Gall insects select vigorously growing plants and plant parts when initiating gall formation. Vigor is associated with rapid growth rate, and in turn, rapid growth confers competitiveness. Are there conditions under which the cost of vigor, in the form of increased susceptibility to attack, outweighs the benefit of competitive success? I present a...

Background and aims: Adaptive explanations for variation in sex allocation centre on variation in resource status and variation in the mating environment. The latter can occur when dichogamy causes siring opportunity to vary across the flowering season. In this study, it is hypothesized that the widespread tendency towards declining fruit-set from...

Premise of research. Variation in the overall shape (e.g., skew, modality) of the flowering schedule can affect intra- and interspecific interactions, but full appreciation of these effects is hindered by the difficulty of describing and comparing schedule shapes. We propose a novel approach to schedule description and comparison based on multivari...

Background/Question/Methods Human activities such as development, pollution, and climate change have led to an increased rate of environmental change that is challenging the capacity of many plant species to adapt, disperse, and survive. Studying how plant populations respond to changing conditions is difficult and time consuming, requiring sever...

Patterns of snow cover across the Arctic are expected to change as a result of shrub encroachment and climate change. As snow cover impacts both the subnivean environment and the date of spring melt, these changes could impact Arctic food webs by altering the phenology and survival of overwintering arthropods, such as spiders (Araneae). In this fie...

Like conventional crops, some GM cultivars may readily hybridize with their wild or weedy relatives. The progressive introgression of transgenes into wild or weedy populations thus appears inevitable, and we are now faced with the challenge of determining the possible evolutionary effects of these transgenes. The aim of this study was to gain insig...

Climate change will likely cause evolution due not only to selection but also to changes in reproductive isolation within and among populations. We examined the effects of a natural drought on the timing of flowering in two populations of Brassica rapa and the consequences for predicted reproductive isolation and potential gene flow. Seeds were col...

In rare circumstances, scientists have been able to revive dormant propagules from ancestral populations and rear them with their descendants to make inferences about evolutionary responses to environmental change. Although this is a powerful approach to directly assess microevolution, it has previously depended entirely upon fortuitous conditions...

Climate change is likely to spur rapid evolution, potentially altering integrated suites of life-history traits. We examined evolutionary change in multiple life-history traits of the annual plant Brassica rapa collected before and after a recent 5-year drought in southern California. We used a direct approach to examining evolutionary change by co...

1. The gall-midge Rhabdophaga strobiloides (O.S.) forms a gall in the apical bud of actively growing willow twigs. 2. Galls were not randomly distributed among twigs. Twigs that arose towards the distal end of the branch were much more likely to be galled. Distally located twigs also grew to greater girth than more proximally located twigs. 3. Comp...

The role of biotic interactions in shaping plant flowering phenology has long been controversial; plastic responses to the abiotic environment, limited precision of biological clocks and inconsistency of selection pressures have generally been emphasized to explain phenological variation. However, part of this variation is heritable and selection a...

Explicit understanding of the spatial scale of evolutionary processes is required in order to set targets for their effective conservation. Here, we explore the spatial context of neutral and adaptive divergence in the species-rich Knersvlakte region of South Africa. Specifically, we aimed to assess the importance of erosional drainage basins as sp...

Ongoing climate change has affected the ecological dynamics of many species and is expected to impose natural selection on ecologically important traits. Droughts and other anticipated changes in precipitation may be particularly potent selective factors, especially in arid regions. Here we demonstrate the evolutionary response of an annual plant,...

Recent phylogenetic evidence suggests that the extraordinary diversity of the Cape Floristic Kingdom in South Africa may be the result of widespread evolutionary radiation. Our understanding of the role of adaptive versus neutral processes in these radiations remains largely speculative. In this study we investigated factors involved in the diversi...

We examined clinal variation in flowering time in a series of Brassica rapa populations occupying a 4-km-long urban greenbelt in southern California. Field studies on two populations showed that mean flowering date for populations of this winter annual differed by up to 3 wk during the 1998–1999 season, when an El Niñ o event elevated precipitation...

The mid-domain effect (MDE) has been proposed as a null model for diversity gradients and an explanation for observed patterns. Here we respond to a recent defense of the concept, explaining that it cannot represent a viable model in either real or null worlds. First, the MDE misrepresents the nature of species ranges. There is also an internal log...

Summary • In most documented examples of adaptive radiation, the processes driving divergence of phenotypes and, ultimately, speciation remain speculative. The remarkable radiation of the Aizoaceae in the southern African winter-rainfall deserts is no exception. • We examined the role of specialization to soil microenvironments in the coexistence a...

This paper develops methods to partition the phenotypic correlation between mates for a focal trait--the standard measure for assortative mating--into a direct component and additional indirect components. Indirect assortative mating occurs when a nonassorting trait is correlated within individuals to a directly assorting trait. Direct and indirect...

It has long been supposed that variation in mating phenology leads to assortative mating, but its inherent frequency dependence has not been examined. When plants in a population vary in their flowering schedule, the phenotypic (and genetic) composition of the mating pool changes over the season; this causes phenological assortative mating even if...

It has long been supposed that variation in mating phenology leads to assortative mating, but its inherent frequency-dependence has not been examined. When plants in a population vary in their flowering schedule, the phenotypic (and genetic) composition of the mating pool changes over the season; this causes phenological assortative mating even if...

We show with a model that variation in environmental stress between generations facilitates the evolution of stress resistance through assortative mating. Stress induces delayed maturation of susceptible phenotypes, segregating their fertile period from resistant phenotypes. Assortment of mates enhances the responsiveness of populations to natural...

The inevitable escape of transgenic pollen from cultivated fields will lead to the emergence of transgenic crop-wild plant hybrids in natural patches of wild plants. The fate of these hybrids and that of the transgene depend on their ability to compete with their wild relatives. Here we study ecological factors that may enhance the fitness of genet...

It has been argued from first principles that plants mate assortatively by flowering time. However, there have been very few studies of phenological assortative mating, perhaps because current methods to infer paternal phenotype are difficult to apply to natural populations. Two methods are presented to estimate the phenotypic correlation between m...

The evolution of the plant-gall maker interaction is complicated by the fact that galls are phenotypic entities that develop under the influence of both plant and insect genotypes. From the plant's perspective, the gall is a developmental abnormality, induced by an environmental stimulus, ie the insect. From the insect's viewpoint, the gall is a ph...

Standard quantitative genetic theory predicts that when a trait is exposed to selection, the between-generation change in the phenotypic mean, Δz̄i, will be equal to the product of the trait's heritability and the selection differential, h2S. By extension, this theory implies that if a number of replicate populations are exposed to varying intensit...

Unlike most pollinators, yucca moths are active pollinators of their host plants. Females lay their eggs in the flowers they pollinate, and their larvae feed solely on the resulting seeds. Previous evidence suggests that the yucca moth Tegeticula maculata avoids self-pollinating their host Yucca whipplei. Other yucca moths may self-pollinate more f...

New techniques for analysing the dynamics of moth populations in captivity could have broad implications for biodiversity and conservation research in general.

We constructed a model to investigate conditions under which intraspecific competition amplifies or diminishes the selective advantage to resistance. The growth trajectories of competing individual plants were depicted by logistic difference equations that incorporated basic costs (lowered growth rate) and benefits (lowered damage) of defense. Anal...

We constructed a model to investigate conditions under which intraspecific competition amplifies or diminishes the selective advantage to resistance. The growth trajectories of competing individual plants were depicted by logistic difference equations that incorporated basic costs (lowered growth rate) and benefits (lowered damage) of defense. Anal...

Plants are known to maintain fitness despite herbivore attack by a variety of damage-induced mechanisms. These mechanisms are said to confer tolerance, which can be measured as the slope of fitness over the proportion of plant biomass removed by herbivore damage. It was recently supposed by Stowe et al. (2000) that another plant property, general v...

Environmental catastrophes, such as severe drought, can reduce host-plant quality and/or abundance, which in turn decrease levels of herbivore populations. Such changes in herbivore populations affect populations of their natural enemies. As part of a long-term field experiment (1983–1991), galls of Eurosta solidaginis from 16 fields in central Pen...

Many plant traits that affect susceptibility to insect attack may have other functions important to the plant. If so, susceptibility could evolve as a correlated response to selection imposed through these other functions. We studied two populations of coyote brush, Baccharis pilularis, from contrasting habitats to see if plant adaptations to local...

Flower-feeding herbivores can directly reduce plant reproduction by con- suming gametes. They may have additional indirect effects if their damage disrupts pol- linator service and causes uneaten gametes to go unused. In a two-year study we investigated direct and indirect effects of florivory by a pollen beetle, Meligethes rufimanus, on the male a...

Flower-feeding insects may reduce the reproductive success of their host plant in subtle ways that go beyond a direct reduction in gametes. Pollinators may respond to floral damage by visiting damaged plants at lower rates. Fewer visitations to the plant may result in fewer flowers that receive pollinator service and as a consequence lead to lower...

Flower-feeding insects may influence the reproductive behavior of their host plant. In plants with labile sex expression, the ratio of maternal to paternal investment may change in response to damage, an effect that goes beyond the direct reduction of plant gametes. We examined the effects of floral herbivory by the beetle Meligethes rufimanus (Nit...

This book details 20 yr of research into a single natural enemy system, specifically the subjects of research are the host plant goldenrod (Solidago), the parasitic insect Eurosta solidaginis (Diptera: Tephritidae), and a number of natural enemies of the gallfly. Furthermore this detailed examination of the ecology and evolution of interactions amo...

A plant's grazing history can influence the nutritional quality of its leaves and directly affect herbivore performance. In addition, leaf nutritional quality can indirectly affect herbivore performance by influencing food consumption. We examined the direct and indirect influences of prior grazing of Solidago missouriensis upon leaf nutritional qu...

We examined phenotypic selection exerted by natural enemies on the gall-making fly Eurosta solidaginis in an extensive field study of 16 populations, spanning four generations. Gallmakers that induce small galls are vulnerable to the attack of Eurytoma gigantea. This imposes upward directional selection on gall size. Insectivorous birds, predominan...

We examined phenotypic selection exerted by natural enemies on the gall-making fly Eurosta solidaginis in an extensive field study of 16 populations, spanning four generations. Gall-makers that induce small galls are vulnerable to the attack of Eurytoma gigantea. This imposes upward directional selection on gall size. Insectivorous birds, predomina...

The larvae of Asphondylia rudbeckiaeconspicua Osten Sacken develop in ovoid chambers in polythalamous summer galls on the flower heads and apical meristems of Rudbeckia laciniata L. (Asteraceae). Three wasps are known to parasitize the gallmaker; Rileya americana Girault, Torymus sp. near asteridis, and T. advenus O.S. In the current study we addre...

Simulation models presented here show that gall size of Eurosta solidaginisFitch (Diptera: Tephritidae) is a reliable predictor of its quality as a host to the parasitoid Eurytoma giganteaWalsh (Hymenoptera; Eurytomidae). The nutritional value of a gall to a parasitoid increases with diameter, but so does the likelihood that ovipositing parasitoids...

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in p...

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in p...

Life history characteristics of the goldenrod gallmaker, Eurosta solidaginis Fitch (Diptera: Tephritidae), were compared between individuals using separate host species. Infestation rate, gall size, gallmaker larval weight, gallmaker mortality, and parasitoid/predator attack frequencies were examined. Galls from Solidago altissima L. (Compositae) a...

The sensitivity of genotypic expression to the environment can be depicted as the reaction norm, which is defined as the array of phenotypes produced by a single genotype over a range of environments. The authors studied selection on reaction norms of the gall-inducing Eurosta solidaginis (Diptera, Tephritidae), which attacks tall goldenrod Solidag...

The sensitivity of genotypic expression to the environment can be depicted as the reaction norm, which is defined as the array of phenotypes produced by a single genotype over a range of environments. We studied selection on reaction norms of the gall-inducing insect Eurosta solidaginis (Diptera; Tephritidae), which attacks tall goldenrod Solidago...

Females of the gallmaker, Eurosta solidaginis (Fitch) (Diptera: Tephritidae), were allowed to oviposit on genetically identical host plants (Solidago altissima L.) (Compositae) maintained in a greenhouse to investigate the flies' searching and oviposition behavior. We used focal animal and scan sampling to document activity patterns. Oviposition it...

Morphological data show three phenotypically distinct gall morphs produced by what was previously thought to be a single gallmaker, Asteromyia carbonifera (Osten Sacken). Protein gel electrophoresis was used to determine if the variants were produced by a single polymorphic species or by distinct races or species of gallmakers. Electrophoretic data...

Under a restricted set of conditions, predator-prey or parasite-host systems may exhibit an escalating arms race over several generations that is not coevolutionary. Preconditions for such a process include high correlation between prey/host quality and defensive capability, and phenotypic plasticity in predator/parasite-counter defenses that respo...

The herb Solidago altissima (Compositae) forms a gall when attacked by the fly Eurosta solidaginis (Diptera: Tephritidae). We performed an experiment to determine how histological features of gall morphology contribute to previously observed genetic variation in gall diameter. Galls induced on 10 replicated plant clones were sectioned, and their in...

Larvae of the tephritid fly Eurosta solidaginis induce ball-shaped galls on the stem of tall goldenrod, Solidago altissima. Survival probability depends on gall size; in small galls the larva is vulnerable to parasitoid oviposition, whereas larvae in large galls are more frequently eaten by avian predators. Fly populations from 20 natural old field...

The relative contributions of genetic and maternal factors to phenotypic variation were studied in seedlings of the clonal herb Solidago altissima L. Pairwise crosses were made to establish 19 full‐sibships. Because crosses were reciprocal, each parent served as seed parent to half its offspring and as pollen parent to the other half. For 18 charac...