Phenotypic plasticity allows some animals to change their behavioural, morphological, performance, and life history traits in response to changes in environmental conditions such as the presence of predators. These changes can enhance survival, but come at a cost. Some of these phenotypic changes are predator and diet specific. I examined the effects of predator diet on the performance, life-history, and morphology of developing Northern Leopard Frog (Lithobates pipiens) tadpoles. Tadpoles were either exposed to cues from fish free water, cues from Brown Bullhead (Ameiurus nebulosus) fed a diet of trout pellets, or cues from A. nebulosus fed a L. pipiens tadpoles diet. Tadpoles exposed to predatory fish cues had smaller bodies, deeper tail fins, slower growth and development rates, and better rotational performance than tadpoles that were not exposed to predatory fish cues. Moreover, tadpoles appeared to differentiate between predatory fish diet and produced diet-specific responses in tail morphology and activity, although the latter effect was only marginally significant. Hatching, metamorphosis rates, and linear performance were not affected by the treatments. These results suggest that A. nebulosus can induce phenotypic changes in L. pipiens tadpoles, with some of these changes being diet specific.

Having multiple plastic responses to a change in the environment, such as increased temperature, can be adaptive for two major reasons: synergy (the plastic responses perform better when expressed simultaneously) or complementarity (each plastic response provides a greater net benefit in a different environmental context). We investigated these hypotheses for two forms of temperature-induced plasticity of Battus philenor caterpillars in southern Arizona populations: color change (from black to red at high temperatures) and heat avoidance behavior (movement from host to elevated refuges at high host temperatures). Field assays using aluminum models showed that the cooling effect of the red color is greatly reduced in a refuge position relative to that on a host. Field assays with live caterpillars demonstrated that refuge seeking is much more important for survival under hot conditions than coloration; however, in those assays, red coloration reduced the need to seek refuges. Our results support the complementarity hypothesis: refuge seeking facilitates survival during daily temperature peaks, while color change reduces the need to leave the host over longer warm periods. We propose that combinations of rapid but costly short-term behavioral responses and slow but efficient long-term morphological responses may be common when coping with temperature change.

Human activity is causing climates to change more rapidly than at any time in the last 10,000 years. If populations of organisms are unable to effectively respond to changing environments, they will be at risk of extinction. In plants, two of the most important mechanisms of response to environmental change are phenotypic plasticity, where the same genotype expresses different phenotypes in different environments, and adaptation, which requires changes in allele frequency in populations as exposed individuals show variable survival and reproduction. Although most researchers accept the importance of both of these mechanisms, they are most commonly considered in isolation in models of response and persistence to climate change. Here, I use the model species Arabidopsis thaliana to investigate the interaction of plasticity and selection in fitness and phenology response to simulated climate warming, the effect of artificial selection on variation for plastic response and cross-generational effects of environmentally induced variation in flowering time. I also study the effects of varying rates of environmental fluctuation on evolvability on populations of self-replicating computer programs using the artificial life platform Avida. I find that a small increase in ambient temperature, in line with predictions for the next few decades, is able to elicit significant plastic responses and that these responses have the potential to alter population genetic structure and affect future evolution. I also find that selection on flowering time can reduce variation for plastic response and that non-genetic effects on flowering time can significantly alter germination in the next generation. Lastly, I find that rapidly changing environments in the long term can select for more evolvable populations and genotypes. These results highlight the importance of considering plasticity and evolution together if we are going to make accurate predictions of climate change response.

The effects of food quantity on the morphology and development of the paper wasp Polistes metricus Say are studied, and experimental results are compared with predictions of the parental manipulation hypothesis. Food deprivation led to smaller female offspring. By hand feeding larvae we used a technique that counteracts the queen's hypothesized ability to restrict food provisioning. Hand feeding larvae did not result in larger offspring, but their abdomen was wider and heavier and the hand-fed wasps survived longer in a cold test. We infer that hand-fed colonies produced more gynes and fewer workers than did control colonies. Results of a restricted nourishment treatment do not support the differential feeding hypothesis, because in fasting colonies the emergence of all larvae was delayed by a month, and we did not detect discriminatory feeding of particular larvae for faster emergence. Although fasting colonies produced fewer offspring, the sex ratio did not show significant differences from the other groups. These data suggest that Polistes metricus colonies are partly able to respond to different nutritional conditions by allocating excess food to increase the number of gynes at the expense of workers.

No description available.

<p>Plants and mycorrhizal fungi form a mutualism in which plants donate carbon to the fungus and, in return, receive benefits such as increased nutrient uptake and water. Mycorrhizal fungi colonize plant roots, forming nutrient exchange structures. The fungi also colonize the soil by growing long strands of hyphae that forage for nutrients and attach plants, forming a common mycorrhizal network (CMN). Plants attached to a well-supported CMN will receive greater benefits than those attached to a lesser CMN because the more carbon donations the fungal partner receives, the more it can grow and colonize the soil, accessing hard to reach soil nutrients. Kin selection theory predicts that relatives should donate more carbon to the fungal partner than non-relatives because benefits gained by neighbouring relatives through the CMN lead to inclusive fitness gains. Thus, social environment, i.e. relatedness of the group, could affect the mycorrhizal mutualism. Moreover, the presence of mycorrhizal fungi in the soil could affect plant responses to their social environment.</p> <p>For my PhD thesis I have investigated whether mycorrhizal fungi respond to plant social environment and whether the presence of mycorrhizal fungi affects plant responses to relatedness. I have addressed these topics in three greenhouse studies and two field studies, using herbaceous plants and trees. I have found strong evidence that siblings have an increased association with their mycorrhizal partner compared to strangers, resulting in greater benefits for siblings. Taken together, the results from this thesis demonstrate that the ability for plants to recognize kin has implications beyond intra-specific competitive interactions and that plant social environment has important effects on a widespread inter-specific mutualism. Additionally, the recently discovered phenomenon of plant kin recognition has been put into the context of mycorrhizae, and I have shown that mycorrhizal plants respond differently to their social environment than non-mycorrhizal plants.</p> / Doctor of Philosophy (PhD)

Exotic species often invade new areas and displace native species. The problems associated with such invasions are well known, but for many exotic species, experimental work has not yet been done to predict which, and under what conditions they may become a problem. Two greenhouse experiments were devised to investigate the plasticity, shade tolerance, and phenotypic differences of full-siblings from 3 populations of Cardamine impatiens, a Eurasian species potentially invasive in North America. Potted plants were subjected to 0, 54, 76, or 91% shade created by neutral density shade cloth application. In addition, the impact of a cold pre-treatment of seedlings on the growth and reproductive output of C. impatiens plants was examined. In our first experiment, we subjected Cardamine impatiens to non-shaded cages, 54%, or 76% shade intensity. Plants died very quickly, so LD50 data were used as a relative measure of fitness, and relative growth indices were calculated over time. Other relative measures of fitness included canopy area, leaf area, number of leaves, number of leaves per canopy area, and final plant weight. Plants in cages with no shade treatment grew faster than those in cages with shade cloth and final plant weight decreased as shade treatment percentage increased. In each population, the number of leaves increased over time and the number of leaves per canopy area decreased over time under shade treatments. Our second experiment involved the application of 54%, 76%, and 91% shade intensity. The additional shade treatment of 91% was applied to determine the extent of plant tolerance and plasticity in response to light reduction. Due to high plant mortality in our first experiment, we treated Cardamine impatiens with a 4 week cold period prior to treatment, which simulates its biennial growth form in its natural western Virginia region habitat. Since this second experiment took place later in the year, day length was extended to more accurately duplicate the conditions during the first experiment. LD50 calculations were not necessary, and 7 of the 135 plants produced seed. Relative measures of fitness included canopy area, leaf area, number of leaves, number of leaves per canopy area, and final plant weights. As in experiment one, the number of leaves per plant increased over time, final plant weight decreased as shade treatment increased, and the number of leaves per canopy area decreased as shade treatment increased. From these two experiments, we determined that Cardamine impatiens is a species that exhibits phenotypic plasticity and therefore may pose a threat as an invasive species. C. impatiens is able to grow and exhibit plasticity of plant architecture under the conditions of very low light. The number of leaves per canopy area decreased as shade increased, suggesting that C. impatiens is highly adaptable to low light conditions, and therefore may be exhibiting phenotypic plasticity by reallocating its resources by producing fewer leaves while maintaining canopy area. This data along with other C. impatiens traits such as high levels needed for seed production, its persistence in seed banks, along with a lack of known major enemies, indicates that they have a great capacity to invade a wide variety of habitats. We also determined that a cold treatment is necessary in order for C. impatiens to obtain optimal growth and reproduction. / Master of Science

All species on Earth occupy limited geographic space. More than a century of observational, experimental, and theoretical work investigating the factors that drive species distributions have demonstrated the importance of the interactions between abiotic, biotic, and demographic factors in determining why species are found where they are. However, it is still unclear when and where these factors interact to set species range limits. Filling the existing knowledge gaps is imperative for the accurate predictions of how species will respond to global change, and particularly for invasive species, many of which are expected to benefit from global change. Here, I sought to investigate the mechanisms that enable, as well as limit, the range expansion of the globally invasive plant Sorghum halepense (L.) Pers. (Johnsongrass). I performed a series of field and laboratory experiments to study population and range dynamics throughout Johnsongrass's North American distribution, and test for the effects of climate, local habitat, and competition on multiple functional traits. I found Johnsongrass consistently demonstrated impressive performance across varying environments, often growing more than 3 m tall, producing hundreds of flowering culms within a single growing season, and maintaining positive population growth rates, even under intense competition with resident weeds. I also found evidence that seed germination has adapted to varying climates encountered during Johnsongrass's range expansion resulting in a shift in the germination temperature niche from warmer to cooler as Johnsongrass spread from warmer climates in the south to more temperate climates in higher latitudes. This shift in the germination temperature niche may have been an important contributing factor in the range expansion of Johnsongrass by enabling the optimization of seed germination in varying climates. On the other hand, results from a field study suggested a possible trade-off between flowering time and growth in populations originating from the range periphery (i.e., range boundary) which may be limiting, or slowing, continued range expansion of Johnsongrass. Together, the outcomes of this work contribute to our understanding of the factors involved in the distribution of species, which is a fundamental goal of Ecology, and essential to accurately predict how invasive species will respond to global change. / Doctor of Philosophy / Invasive species threaten our natural ecosystems, our agricultural systems, and even our infrastructure, and we spend billions of dollars each year attempting to control them and reduce their negative impacts. Climate change, habitat destruction, and other forms of global change, will benefit many of these species, magnifying their impacts and promoting their invasion into new territories. Because of the damaging effects of invasive species, and the costs to control them, it is imperative that we are able to predict how they will respond to global change so that we can improve plans to reduce their impact and spread. First, we need to understand the processes that promote their invasion across large swaths of land. Just as importantly, we must study the processes that prevent their invasion of certain areas. Here, I investigated some of the processes that have facilitated, as well as hampered, the spread of the invasive plant Johnsongrass. For this work, I used Johnsongrass plants originating from different habitats, including regions where Johnsongrass is highly invasive and those where Johnsongrass is very rare. I found Johnsongrass originating from regions where it is highly invasive were able to grow very large and produce thousands of seeds that were able to germinate under a range of conditions. These traits may have contributed to the invasion success of this species. However, I found a different pattern for plants that originated from regions where Johnsongrass is rare. These plants reached reproductive age earlier and grew smaller across all environmental conditions, potentially due to the less hospitable climates of these range edges. These findings allow us to project into future climate change scenarios, because it is likely that, as temperatures warm, invasive species will be able to invade new regions, where they will impact the work of conservationists, natural resource professionals, agricultural produces, and other land managers.

[Truncated abstract] In south-western Australia a rare plant community occurs on shallow soils overlaying massive ironstone rock. These 'ironstone communities' are open shrublands, which are subject to extremes in drought and solar radiation and support many rare and endemic species. The restricted distribution of many of these species may be related to their high degree of specialisation to this harsh habitat and their inability to respond plastically to different environmental conditions. Indeed, earlier work has shown that ironstone Hakea species (Proteaceae) have a specialist root-system morphology investing mainly in deep roots, thereby increasing their chance of accessing cracks in the rock surface and obtaining water before the onset of summer drought. In this thesis I further examine aspects of specialisation and its possible consequences for species rarity using two ironstone Hakea species and comparing them with two of their widely distributed congeners. In the first experiment (Chapter 2) I explore inherent drought tolerance, independent of root-system morphology, as a further specialisation to the ironstone environment. All species were grown in sand in pots in a glasshouse for 7 months and then droughted for 5 weeks. There was no evidence that the ironstone species had a greater inherent drought tolerance than their common congeners. During drought all species maintained leaf water content of mature leaves by reducing stomatal conductance and osmotically adjusting, though ironstone species tended to OA (osmotic adjustment) more than common species. ... This suboptimal investment of resources may result in a lower competitive ability in shadier environments, and thus could partially explain their restricted distribution. In Chapter 4, I investigated the plasticity of root traits in response to levels of phosphorus supply. South-western Australian soils are phosphorus impoverished and phosphorus is well known to elicit plastic responses in root allocation and architecture. Ironstone species showed less plasticity in total root length, producing similar root length across P treatments, while common species showed an increase in root length with increasing [P]. Other root characteristics were similarly plastic in response to P treatment between species. However, when supplied with increasing [P], ironstone species invested an increasing proportion of roots in the bottom of pots while common species invested more in the top. This differential response in root allocation in response to P may reflect a fundamental trade-off between nutrient and water acquisition, with the ironstone species mainly foraging for water and investing in deeper roots, while the common species invest more in superficial roots to obtain nutrients. In conclusion, the rarity and restricted distribution of the ironstone Hakea species may be related to their specialist root-system morphology as well as a lowered phenotypic plasticity of functional traits. A reduction in plasticity may reduce their competitive ability outside their ironstone habitats, and thus contribute to the restricted distribution of these species. This may also be the case for other rock-outcrop endemics and more generally, for other rare plant species restricted to particular habitats where a lowered phenotypic plasticity in traits relevant to their particular habitat may contribute to their restricted distribution.

Phenotypic plasticity is the ability of an organism to express different phenotypes in response to biotic or abiotic environmental cues. The ability of an organism to make changes during development to adjust to changes in its environment is a key to survival. Sexually reproducing organisms that have short life cycles and that are easy to raise in the laboratory are more conducive for developmental phenotypic plasticity. Considerable research has already been carried out on the brine shrimp, Artemia franciscana, regarding its morphology due to changing salinities. There is, however, little research considering subsequent generations and how there morphology might be affected by parental experiences. This study has examined: 1) the morphological effects of different rearing regimes of different salinity levels, and 2) the epigenetic transgenerational transfer of these morphological traits in A. franciscana. Measurements included rate of growth (as measured by instar), body size, body length, and other morphological traits. A gradual increase to more hyperosmotic conditions during development produced brine shrimp that were larger in size and also more developmentally advanced. Salinity stress experienced by adults had increased the growth rate in the F1 offspring of A. franciscana. Collectively, these data indicate that Artemia franciscana is a tractable model for investigating phenotypic plasticity. These findings have added to the ever-growing field of developmental phenotypic plasticity while also providing more information on the natural history and adaptive abilities of A. franciscana.