Phenotypic plasticity is the ability of a genotype to express different phenotypes in different environments. Despite its common occurrence, few have investigated differences in plasticity between populations, the selection pressures responsible for it, and costs and constraints associated with it. In this thesis, I investigated this by studying local adaptation and phenotypic plasticity in populations of the common frog Rana temporaria, inhibiting islands with different pool types (temporary, permanent or both). The tadpoles develop in these pools, and have to finish metamorphosis before the pool dries out. I found that the tadpoles were locally adapted both in development time and in phenotypic plasticity of development time. Tadpoles from islands with temporary pools had a genetically shorter development time than tadpoles from islands with permanent pools. The population differentiation in development time, estimated as QST, was larger than the population differentiation in neutral molecular markers (FST), which suggest that divergent selection among the populations is responsible for the differentiation. Moreover, tadpoles from islands with more variation in pool drying regimes had higher phenotypic plasticity in development time than tadpoles from islands with only one pool type present. Interestingly, increased migration among populations did not select for increased plasticity, rather it was the local environmental variation that was important. This adaptation has occurred over a short time scale, as the islands are less than 300 generations old. In temporary pools, it is adaptive to finish development before the pool dries out. This could be achieved by entering the metamorphosis at a smaller size, as a smaller size takes shorter time to reach. However, I found that there is a minimum threshold size below which tadpoles’ cannot enter metamorphosis, and that there had been no evolution of this threshold size in populations living in temporary environments. That suggests that this developmental threshold is tightly linked to physiological constraints in the developmental process. Despite their expected importance as constrains on the evolution of plasticity, costs of plasticity are often not found in nature.  However, theories of why they are absent have not been tested empirically. In this thesis, I show that fitness costs of phenotypic plasticity are only found in populations with genotypes expressing high levels of phenotypic plasticity, while in populations with low-plastic genotypes, I find costs of not being plastic. This suggests that costs of plasticity increase with increased level of plasticity in the population, and that might be a reason why costs of plasticity are hard to detect.

Understanding the diversity of life is one of the main aims of evolutionary biology, and requires knowledge of the occurrence and causes of adaptive genetic differentiation among geographically distinct populations. Environmental stress caused by acidity may cause strong directional selection in natural populations, but is little explored from an evolutionary perspective. In this thesis, a series of laboratory experiments and field data was used to study evolutionary and ecological responses of amphibians to environmental acidity. Local adaptation to acid stress was studied in the moor frog (Rana arvalis).The results show that acid origin populations have higher acid stress tolerance during the embryonic stages than neutral origin populations, and that acid and neutral origin populations have diverged in embryonic and larval life-histories. The mechanisms underlying adaptive differentiation are partially mediated by maternal effects related to extra-embryonic membranes and egg size. Acid origin females invest in larger eggs and have a stronger egg size-fecundity trade-off than females from neutral areas, likely reflecting adaptive differentiation in maternal investment patterns. Potential carry-over effects of low pH, and the effects of UV-b/pH interaction were investigated in the common frog (R. temporaria). The results suggest that amphibian larvae are able to compensate for the negative effects of acidity experienced early in life, if conditions later turn beneficial. R. temporaria populations differed in their sensitivity to synergistic effects of low pH/UV-B, indicating variation in population responses to environmental stress. In conclusion, these results suggest rapid evolution in response to human induced environmental change, much of which may be mediated via adaptive maternal effects. Acidification may be a powerful selective force shaping life-history evolution.

This thesis is an attempt to describe how different environmental factors influence life history traits in different populations, sexes and developmental stages in the moor frog, Rana arvalis. The studied populations are located along 1100 km latitudinal gradient, with pH varying between 4.0 and 8.5. I have used data from both natural populations and common garden experiments. Reproducing moor frogs were larger and older at high latitudes, indicating a selective advantage of large size at high latitudes and/or earlier reproduction at low latitudes. When controlling for age I found that frogs were older and smaller at low pH, which may be a result of a reduced growth rate due to acid stress. The both sexes respond differently to different environments, with the lowest sexual dimorphism in body size found in the acid environments. This is possibly caused by a trade-off between growth and reproduction. Being large is considered to be advantageous, in females due to increased fecundity, and in males due to higher ability to compete for mates, while the cost of high growth is a reduced possibility to survive until the next mating season. Moor frog embryos originating from an acid population survived better under acid stress than embryos from a neutral population. Using quantitative genetic techniques I found strong maternal effects and small additive genetic variation for the traits in acid and non acid populations. The variation in acid stress tolerance owed largely to non-genetic effects. Females from acid localities lay larger eggs, which probably improves the performance of tadpoles under acid conditions. The trade-off between egg size and fecundity was stronger in acid populations indicating that females in acid populations reduced fecundity to increase offspring size. Finally, frogs from acidified environments were more asymmetric in skeletal traits further indicating the developmental stress created by acidification.

The identification of processes governing genetic structure at different spatial scales remains a major challenge in evolutionary biology and is of considerable applied interest in conservation biology. In Euphrasia stricta five varieties have been identified (brevipila, gotlandica, stricta, suecica and tenuis) based on differences in habitat, phenology and morphology. In this thesis, I examined genetic variation at AFLP and microsatellite marker loci in relation to variation in habitat and morphology within and among varieties of E. stricta on the island Gotland in the Baltic Sea. The results are discussed in relation to evolutionary processes acting within this species complex. In a study conducted at the regional scale, the two early-flowering varieties suecica and tenuis each formed a genetically distinct group, while the three late-flowering varieties brevipila, gotlandica and stricta formed a third group. The results suggest that suecica and tenuis have ancient origins since they are genetically different both from the brevipila/gotlandica/stricta group and from each other despite their similar habitat preferences. This pattern was obtained using both marker systems. Discrepancies between AFLP and microsatellites were found in patterns of isolation by distance and in estimates of expected heterozygosity, He. Focusing on the mixed genetic group brevipila/gotlandica/stricta and the causes behind their clustering together despite differences in morphology and habitat preferences, I performed a study at a smaller geographic scale. Studying a population of E. stricta I found that, although gene flow within the population was strong, it had not prevented the formation of genetic groups associated with micro-habitat properties. An important result for conservation of the rare variety suecica is its distinct genetic separation from variety tenuis. If the aim of conservation is to preserve the uniqueness of suecica, the two varieties should be treated as separated entities.

Growth rate is an important life history trait, which impacts fitness indirectly through its effect on the age and size at maturity, as well as directly through costs associated with accelerated growth such as increased predation risk. Genetic variation and plasticity in growth are widespread in nature, and local adaptation of growth rate may evolve due to divergent selection in different environments, for example related to predation risk, temperature or time constraints. I studied local adaptation of larval life history in the moor frog Rana arvalis, in a local network of ponds close to Uppsala. Local adaptation of growth rate and survival was studied in a reciprocal transplant experiment between ponds with different habitat characteristics. Meanwhile, differences among the populations in intrinsic growth, activity and response to predation were studied in a common garden experiment in the laboratory, where tadpoles were raised in the presence or absence of a predator and tested in direct predation trials. In the field, differences in growth among populations were found, independent of which pond the tadpoles were raised in, indicating that the ponds were similar growth environments. Survival differences among the populations depended on the pond, but local populations did not do better than foreign ones. In the laboratory, similar patterns in growth rate were found. All populations were highly plastic in their response to predation, having lower growth and activity in the predator-induced treatment and decreased mortality in the predation trials. Tadpole size was an important factor in escaping predation. One population clearly grew faster than the others in the field and in the lab, which could be explained in terms of its habitat of origin but was most likely related to the relatively late hatching of this population. Future studies are necessary concerning the possible costs of this accelerated growth and the importance of breeding phenology. Apart from the one differential population, I did not find evidence of local adaptation in the field or in the laboratory. The influence of habitat characteristics on tadpole life history was difficult to study, due to the limited number of ponds and many environmental differences among them. However, this thesis was a valuable pilot study concerning the design of experiments to study factors promoting and constraining local adaptation in landscape mosaics. An understanding of local adaptation at the scale at which gene flow occurs is important for the conservation of populations in fragmented landscapes as well as for the study of ecological speciation.

To understand the evolutionary and ecological significance of geographic variation in life history traits, we must understand whether the patterns are induced through plastic or adaptive responses. The Eastern Fence Lizard, Sceloporus undulatus , exhibits countergradient variation (larger body sizes, et cetera, in northern, cooler environments; presumed adaptive) in life history traits across its large geographic range. However, cogradient variation (the expected result from a plastic response, although not necessarily inconsistent with adaptation) has been suggested as a null hypothesis, especially on fine geographic scales because of relatively small environmental changes. Here we focus on life history variation on a fine geographic scale to test whether cogradient variation is exhibited even though countergradient variation is exhibited at larger scales, and if so, what mechanisms are involved in the switch. We examined north and south populations (~2° latitude between) of the S. undulatus, and the Florida Scrub Lizard, S. woodi , by measuring adult body sizes, reproduction, and hatchling body sizes over a two year period and conducting reciprocal transplants of juvenile lizards each year. Our results indicate cogradient variation (larger body size in the southern population experiencing a warmer environment) in life history traits of S. undulatus and countergradient variation, a lack of variation in adult body size, in S. woodi along the Florida peninsula. Thus, S. undulatus exhibits cogradient variation at fine geographic scales and countergradient variation at larger scales. Reciprocal transplants revealed that the larger adult body sizes in the southern population of S. undulatus could be explained by longer growth periods allowed by greater intrinsic survival. In S. woodi, the larger than expected adult body sizes in the north could be explained by faster intrinsic and extrinsic juvenile growth rates in the northern population. Because S. undulatus and S. woodi remain distinct species associated with distinct, though adjacent, habitats, we also looked for habitat-specific adaptations. The second reciprocal transplant (between species and habitats) revealed habitatspecific adaptations in juvenile growth rates, but not juvenile survival. Each native species grew faster and had a higher average probability of reaching size at maturity in their native environment than did the foreign species.

The environment can exert strong selective pressures on an organism. When selective pressures on traits differ between environments local adaptation may occur. If there is gene flow between the environments, local adaptation may be slowed or prevented. In plants, particularly weedy ephemerals, germination is a life-history trait that can be a strong determinant on fitness. In this dissertation, I explore the germination traits of two weedy Brassicaceae species, Arabidopsis thaliana and Sinapis arvensis, having populations in different habitats to determine whether germination traits within and between populations vary based on environmental conditions and to assess the extent of local adaptation. In Chapter 1, I assessed which genomic regions of A. thaliana were associated with differences in germination traits due to genotype-by-environment interactions. I performed a genome-wide association study using 100 natural accessions of A. thaliana under four light and nutrient combinations. I found 20 single nucleotide polymorphisms significantly associated with different environments, but none associated specifically with genotype-by-environment interactions. In Chapter 2, I assessed germination traits of S. arvensis collected from agricultural and non-agricultural habitats in the Bitterroot Valley of Montana. I discovered that the agricultural collection studied exhibited significantly different germination timing and amounts than the non-agricultural collections, which were statistically indistinguishable from each other. I also found evidence of a strong maternal effect on germination traits. In Chapter 3, I tested whether patterns of genetic variation between agricultural and non-agricultural collections of S. arvensis supported local adaptation to the two habitats even in the face of gene flow. While I expected to see some genetic differentiation between habitats, as seen in Chapter 2, no genetic differentiation was detected and markers putatively under selection were not associated with a particular habitat. I discuss why this might have occurred even though I have evidence for genetically-based phenotypic differentiation between agricultural and non-agricultural populations of S. arvensis. / text

Between individual behavioral variation has been described in nearly every animal taxa where it has been measured. Often, these behavioral variations correlate across contexts, forming a behavioral syndrome. Despite a recent push to better understand the origins and consequences of behavioral syndromes, there still is no cohesive framework that describes this phenomenon. Here, I develop a social insect species into a model for measuring and testing behavioral syndromes at a new level of biological organization; the colony. This builds upon the rich literature describing between-colony variation in behavior and provides novel insights into the evolution of behavioral syndromes. In my first chapter I show that colonies do not vary from one another in foraging distance, nor is foraging distance directly associated with colony size. This was my first step in demonstrating that colony behavioral variation is not simply a byproduct of colony size. In chapter two, I expanded upon this finding by testing colonies both in the lab and in the field for a variety of ecologically relevant behaviors. Here, I found that there was a behavioral syndrome that reflected foraging distance, foraging effort to novel and familiar resources, response to threat and aggression. While there is a gradient of phenotypes, some colonies either travel farther to forage for food and respond more aggressively when confronted with a conspecific invader, but appear to invest less in each given incident or food source. I consider this to be more risk-tolerant; they increase their risk of external mortality for potentially larger pay-offs. On the other hand, risk-averse colonies deploy more foragers to exploit closer resources, increase their overall activity in the response to threat, but avoid travelling farther distances or aggressively engaging invaders. Additionally, there is between population variations in risk-taking phenotype. Across the western United States, colonies at more northern latitudes are more risk-tolerant than colonies at more southern latitudes. In chapter 3, I expand upon this latitudinal gradient in behavioral phenotype by investigating what ecological factors predict a colonies level of risk-tolerance. Specifically, I focused on ecological traits that reflected predation, competition, food resource availability and abiotic stress. I found that competition for nest sites and spatial clustering predicted behavioral type; colonies at high levels of nest site competition or spatial clustering were more risk-tolerant than colonies at lower levels of competition or were more spatially dispersed. In chapter 4, I used a common garden and brood transfer experiment to investigate if the relationship between the ecological environment and behavior was the result of phenotypic plasticity or local adaptation. I show that local adaptation is the most likely explanation, as colonies with more workers from the donor colony are more, behaviorally, like the donor colony than colonies with fewer donor workers. In chapter 5 I test if the risk-taking behavioral syndrome is the result of life history strategy variation. I test the growth rate and energy allocation towards either somatic effort or reproductive effort. I found that colonies which are risk-tolerant also grow faster and dedicate more energy towards reproductive effort, which is consistent with predictions built from life history theory. This body of work shows that behavioral syndromes can exist at a new level of organization, the colony, and that variation in behavioral type is the result of differential selection pressure between populations. This directly connects behavioral syndrome research to life history strategy research. As life history strategy theory is a well-understood field, this represents a true advancement in the field of behavioral syndromes.

The persistence of a species in the face of environmental change is a function of the extent to which populations respond differently to changes in their environment and the spatial correspondence between the scale of disturbance and the scale of adaptation. The pattern by which a population, or genotype, expresses a range of phenotypes across an environmental gradient is called a norm of reaction. The level of phenotypic plasticity displayed within a population (i.e. the slope of the reaction norm) reflects the short-term response of a population to environmental change while variation in reaction norm slopes among populations reflects the spatial scale of variation in these responses. Using a reaction norm framework, I examined the spatial scale of genetic variation in plasticity for life-history traits in Atlantic cod (Gadus morhua), a marine fish of global biological and socioeconomic importance. Through common-garden experiments, I found evidence of both adaptive and non-adaptive plasticity for larval growth rate and survival in two cod populations that experience contrasting thermal environments in nature. A comparison of these reaction norms with those of four cod populations studied previously revealed significant genetic divergence in adaptive traits at a smaller spatial scale than has previously been shown for a marine fish with no apparent physical barriers to gene flow (<250 km). This fine-scale genetic structure is likely the result of populations being locally adapted to seasonal changes in temperature during the larval stage caused by differences in spawning times and may be maintained by behavioural barriers to gene flow. Implications of variation in life-history trait plasticity to fisheries management in the face of predicted changes in climate are discussed.

Phenotypic traits that vary geographically within species are commonly assumed to represent local adaptations to different environments. In order for local adaptation to evolve by natural selection, three conditions must be met: (1) traits must vary geographically, (2) local variants of traits must provide a fitness advantage (increased survival or reproductive success) within the local environment, and (3) local variants of traits must be heritable. In chapter two, we review evidence for local adaptation in birds. Geographic variation among populations is nearly ubiquitous, yet experimental tests of the fitness advantages of local trait variants are rare among populations of birds, presumably because of the difficulties in transporting individuals between populations. Thirty-seven studies have tested the heritability of among population variation in traits. Thirty-three of the 37 studies found some degree of heritability of variation among populations, consistent with traits diverging in response to natural selection. In chapter three, we experimentally test the fitness consequences of divergent nest morphologies of Yellow Warblers (Dendroica petechia) using reciprocal nest transplant experiments between a temperate and subarctic site in Canada. Yellow Warblers breeding at our subarctic site build larger nests constructed with more insulative materials than Yellow Warblers breeding at our temperate site, and these differences are the result of different nest building behaviours. Temperate nests transplanted to subarctic sites experienced significantly colder temperatures, and tended to suffer higher egg and nestling mortality due to climatic conditions (cold temperatures), than locally transplanted subarctic nests. Adult females breeding in subarctic sites that received temperate nests changed their incubation behaviours by taking shorter recesses than females who received locally transplanted subarctic nests. In contrast, subarctic nests transplanted to our temperate site showed no changes in nest temperature, fledgling success, or parental behaviour during incubation. We suggest that divergent selective pressures acting on Yellow Warblers in subarctic and temperate environments results in different nest building behaviours. Cold temperatures in our subarctic site likely favour increased investment in larger, insulative nests, whereas warmer temperatures at our temperate sites likely favour reduced investment in nest building, and consequently smaller nests. / Thesis (Master, Biology) -- Queen's University, 2010-09-28 13:16:38.686