I work mainly within three research projects concerning (I) The evolution of life histories and developmental plasticity in seasonal climates; (II) The effects of climatic variation on spatio-temporal aspects of host plant utilization in butterflies; (III). Although these are separate projects they both concern evolutionary and ecological aspects of insect adaptation to seasonally varying climates. Hence, there are strong synergies both on a conceptual and practical level between the two projects.
Within this project I explore the evolution and ecological significance of developmental switches and the resulting alternative developmental pathways in insects. In particular I will investigate to what degree the evolution of semi-independent developmental pathways allow differential optimization of life history traits in relation to seasonal variation in selective conditions. This includes the development of life history models and expriments in collaboration with post-doc. Sami Kivelš and PhD student -Inger Aalberg Haugen. The main model species for the empirical work in this project are the Speckled wood butterfly, Pararge aegeria and the Green-veined white butterly, Pieris napi.
The main research strategy is to develop and use life history theory to predict selection on life history traits in relation climatic variation in both space and time, and test if this has led to the evolution of developmental adaptations that allow expression of alternative adaptive phenotypes in response to information on seasonal change. This project has been financed by the Swedish Research Council (VR) but also by the Strategic Research Programme EkoKlim at Stockholm University
Species interactions are a major component of biodiversity and climate change is likely to influence both the strength and nature of many interactions between species. This may be due to changes in species distributions and distribution overlaps as well as changes in the phenologies of the interacting species. For instance, if an herbivore and its host plants are affected differently by changes in temperature and the herbivore life cycle is seasonally constrained a change in climate may lead to changes in host utilization patterns. Such changes in species interactions may influence both population dynamics and trait selection of the interacting species and may be an important mechanism for how climate change will influence community structure and networks of species interactions.
The aim of this project is to investigate how climate change through effects on distribution, abundance and phenology may influence host plant utilization, trait selection and population dynamics of a model system of two butterfly species and their host plants. The study system includes two common and widespread Pierid butterflies (Anthocharis cardamines and Pieris napi) and their Crucifer host plants (e.g. Cardamine ssp, Arabis ssp, Thlaspi arvense, Arabidopsis thaliana). As A. cardamine is a pre-dispersal seed predator it is expected to be under strong selection to match the flowering phenology of it host plants, while P. napi that feeds on the leaves of these hosts is less dependent on an exact match with flowering time. In collaboration with colleagues at SU, Prof. Johan Ehrlén and Prof. C. Wiklund and Ph.D students -Diana Posledovich and Tenna Toftegaard -I am studying how climatic variation may influence the development and phenology of the interacting species and how this may influence the way these species interact. We are performing fieldwork to investigate the relative host utilization of A. cardamine along a latitudinal gradient from Österlen in the south of Sweden to Umeå in the north. Simultaneously we are performing controlled experiments with live butterflies and plants from differnt localaities along this gradient.We are performing laboratory and greenhouse experiments that will quantify the relationships between climatic variables (temperature, photoperiod) and reproductive phenology of both butterflies and plants. We also use common garden experiments to estimate the thermal reaction norms of herbivore and host plants from the full length of the climate gradient, and test to what degree changes in thermal conditions may influence the phenological match of the interaction.This project is financed by the Strategic Research Programme EkoKlim at Stockholm University.
Together with six fellow PI:s I am involved in a large scale project that aims to reveal the genetic, developmental and evolutionary basis of adaptations that allow insects to regulate their life cycles in accordance with local conditions. I am primarly involved in exploring the ecological genomics and ecophysiology of diapause in temperate butterflies, in particular Pieris napi and Pararge aegeria. By combining functonal studies of local adaptation with controlled laboratory crosses and ecological genomics we are trying to unravel the genetic basis for adaptive variation in life cycle regulation. This work is primarily done by PhD student Peter Pruisscher that I supervise together with Dr. Chris Wheat. In order to understand these adaptations fully we are also studying the physiological mechansims that allow insects to enter, maintain and terminate diapause in accordance with seasonal change, instead of developing dircetly to reproduction. This work is done primarily by post-doc Philipp Lehmann. The project is finaced by Knut & Alice Wallenberg Foundattaion as well as by the Swedish Resarch Council. The other participating PI:s include, Sören Nylin (project leader), Chris Wheat, Christer Wiklund, Olof Leimar, Dick Nässel and Uli Theopold.
My Ph.D. work was directed towards general questions of life history evolution in seasonal environments, using different species of butterflies as model systems. In particular I was interested in the evolution of growth strategies in relation to seasonal time constraints. The main findings include that individual larvae are using the photoperiod to estimate the time that remains in the favourable season and that they use this information for making decisions about their developmental schedule. These decisions may have far reaching life history consequences since they affect age and size at maturity. Moreover, the evolution of growth decision is likely to depend on a number of trade-offs and in particular how costly it is to grow faster as a juvenile in relation to how costly it is to become a smaller adult. The struggle with these issues also led me to work on general questions regarding the evolution of phenotypic plasticity and reaction norms.
After my Ph.D I did a 2.5-year post-doc with Professor Martine Rahier at the University of Neuchatel, Switzerland doing research on the evolution of host plant utilization and life histories in a group of alpine Chrysomelid beetles (genus Oreina). The work was centered around questions of local adaptation in host plant use and the evolution of larval growth strategies in relation to seasonality. We addressed these questions by a mixture of field and laboratory experiments including both quantitative and molecular genetic investigations.
From 2002 to 2006 I held a position as assistant Professor (Forskarassistent) at the Department of Zoology, Stockholm University, that was financed by the Swedish Research Council (Vetenskapsrådet). The titel of this project was "The evolution of body size in holometabolous insects" and it was based on one fundamental question: why don't insects become bigger? In 2008 David Berger finished his Ph.D working within this project. After a Post-doc with Wolf Blanckenhorn at the University of Zürich he is now on a second Post-doc with Göran Arnqvist and Alexei Maklakov at Uppsala University.
The problem of optimal age and size at maturity is based on the fundamental trade-off between the benefits of a large size and the costs of a long juvenile period. It is typically expected that organisms should be selected to maximize juvenile growth rate in order to reach the largest possible size in the shortest possible time. However, studies of a wide range of animals have shown that individuals facing a long growth season or very good food conditions often"voluntarily" reduce juvenile growth effort/rate rather than reach a greater final size at maturity. In herbivorous insects such "good condition"- larvae could theroretically end up twice or three times as large as they typically are, if they would maximize their growth rates for the whole larval period.
There is evidence for costs of becoming big (e.g. mortality costs due to a long juvenile period or fast growth) but theory suggests that there should also be costs of being big, which would challage the common assumption of an ever increasing relationship between size and fitness. In this project we have idenfied some potentially general mechansims that are likley to infer suchs costs of a large body size.
I am continuing the work on this and related questions that pertain to the evolution of growth strategies.
A larva of the butterfly Lasiommata petropolitana feeding on grass in the field
An adult Oreina elongata feeding on the thistle Cirsium spinosissimum
A speckled wood butterfly Pararge aegeria from Madeira
The bug Picromerus bidens predating on a butterfly larva during a predation experiment