Trine Bilde

Professor

Trine Bilde
See relations at Aarhus University

Our research group aims to investigate evolutionary ecology and genetics of group living, cooperation and mating systems using spiders as study systems. Additionally, we are interested in understanding the genomic consequences of sociality and inbreeding mating systems, and genetic and non-genetic processes involved in adaptation to different environments.

Our research focuses on the spider genus Stegodyphus (family Eresidae) that contains both social and subsocial (temporarily social) species, which makes it ideal for comparative studies. The social spiders are unique among group living animals, as the transition to permanent sociality is associated with regular inbreeding and highly female-biased sex ratios. Additionally, social spiders cooperate in all colony tasks and show allomaternal brood care including self-sacrifice.

      

Left: Colonies of the social spider Stegodyphus dumicola in South Africa, May 2012. The dense silk nests may contain several hundred spiders and are often interconnected with prey capture webs. Photo by: V. Settepani.  Right: Stegodyphus lineatus, matriphagy.Photo by: T. Bilde.

 

Our research aims to understand 1) the ecology and evolution of sociality, 2) reproductive division of labour and conflict resolution, and 3) population genomic consequences of inbreeding 4) non-genetic processes involved in adaptation.

Many of our projects are interdisciplinary and involves collaboration with colleagues with expertise in different fields e.g. zoology (Prof Yael Lubin, Ben Gurion University; Prof Gabriele Uhl, University of Greifswald; Dr. Tharina Bird, Natural ural History Museum of Windhoek (Namibia) and Botswana International University of Science and Technology), microbiology (Prof Andreas Schramm), bioinformatics (Prof Mikkel Schierup, BiRC), chemistry and metabolomics (Prof Thomas Vosegaard, inSPIN and iNANO; Prof Michael Lalk, University of Greifswald). We perform field work in South Africa, Namibia, Botswana, India and Israel.

Additionally, we study the evolution of polyandrous mating systems and the evolution of alternative male mating strategies in the nursery web spider Pisaura mirabilis*. This work is done in collaboration with Ass. Prof. Cristina Tuni, University of Munich, and field work in Germany, Italy, UK and Denmark.

1) Ecological genomics of inbreeding: comparative studies of inbreeding mating systems in non-model animal populations (funded by the European Research Council)

We are interested in integrating ecological and evolutionary research in order to expand knowledge on the evolutionary ecology of inbreeding in wild animal populations. We perform comparative population studies on the consequences of inbreeding in Stegodyphus, a genus of spiders including three independently evolved inbreeding social species as well as outcrossing sister species. We investigate the consequences of sociality and inbreeding for population genetic structure, genome-wide genetic diversity, molecular evolution and evolution of life history traits.

 

Left: The subsocial Stegodyphus lineatus eating a fly in our spider lab, Aarhus, August 2010.  Right: Individuals of the social spider Stegodyphus sarasinorum foraging on an ant. India, October 2010.  Photos by: V. Settepani 

 

2) Non-genetic processes involved in adaptation

Evolutionary models predict that response to environmental change occur by selection on standing genetic variation and new mutations, but it is becoming apparent that adaptation is more complex than so far realised, calling for integration of non-genetic mechanisms in our understanding of adaption, such as microbial symbionts or epigenetic changes.

Social spiders are have a wide ecological range characterized by very different habitat despite being highly inbred and showing extremely low species-wide genetic variation. We are therefore interested in examining mechanisms other than genetic variation involved in their adaptation:

- The influence of epigenetic modifications in the response to environmental change (funded by the Danish Council for Independent research):

Epigenetic modifications contribute to phenotypic variation by modifying gene expression without altering the underlying genetic code, and may therefore facilitate rapid adaptation to environmental change. We are interested in linking epigenetic modifications to the expression of phenotypic traits and individual performance along a temperature gradient, to identify mechanisms that provide adaptive benefits in specific environments.

- The influence of the microbiome in the response to environmental change:

All animals live in close association with complex microbial communities, which often contribute important function to the host phenotype. We will investigate the influence that bacterial symbionts have on local adaptation in populations of inbred social Stegodyphus in different environments. Bacterial symbionts often contribute important functions to the host phenotype and we aim to determine the spider microbiome, and to identify and link key symbionts that contribute to enhance host performance.

 Map of the mean annual temperature in Namibia, Botswana and South Africa, were we carry out our field works. Map made by V. Settepani with data from the AfrClim database.

 

3) Discovery and characterization of novel antimicrobials (funded by Novo Nordisk Foundation’s Interdisciplinary Synergy Programme)

Social spiders are highly inbred and show extremely low genetic variation, also in immune genes. Combined with an elevated risk of pathogen transfer among individuals living in close proximity, they should be highly susceptible to pathogens and disease transmission. Nevertheless, social spiders are evolutionarily and ecologically very successful, leading us to hypothesize that microbial symbionts must be essential in their protection against pathogens. We are investigating the potential of host symbionts for producing protective and novel antimicrobial compounds that provide protection against pathogens.

 

 

The team involved in the Novo Nordisk Foundation’s Interdisciplinary Synergy Programme. From left to right: Dr Marie Lund, Dr Jesper Bechsgaard, PhD Mette Marie Busck, Prof Thomas Vosegaard, Prof Trine Bilde, Prof Andreas Schramm, Dr Virginia Settepani, Prof Michael Lalk.

 

4) Evolution of social behaviour: social structure and task differentiation

Division of reproductive and non-reproductive tasks in cooperative societies is expected to reduce conflict and optimize group performance. Social spiders cooperate in all colony tasks, only some of the females in a colony reproduce while the non-reproducers become helpers. All females in the colony, reproducers and non-reproducers, actively provide extended maternal care including self-sacrifice (spiderlings consume adult females). This society structure is perfect for investigating task differentiation in reproductive and non-reproductive roles. We are interested in understanding the social structure of the spider’s colonies and the mechanisms underlying reproduction division of labour and differential participation in non-reproductive tasks such as foraging and web maintenance.

 

Left: A cluster of social Stegodyphus sarasinorum spiders individually marked for task differentiation studies, India, November 2012. Right: Individuals of the social spider Stegodyphus mimosarum foraging on a fly. Spiderlab Aarhus, March 2014. Photos by: V. Settepani. 

 

5) The role of sexual selection on alternative male mating strategies (funded by the Danish Council for Independent research)

The main goal of this study is to understand how sexual selection and male-female co-evolution drives the evolution of alternative male mating strategies. Our model system is the nursery web spider Pisaura mirabilis, where male spiders employ alternative mating strategies (death feigning and worthless nuptial gifts). We are investigating whether alternative strategies in natural populations are maintained by variation in prey availability, female mate choice, and the intensity of sexual selection.

 

Right: Adult female of the nursery web spider Pisaura mirabilis Germany, July 2009. Photo by: V. Settepani. Left: An adult male Pisaura mirabilis (in the bottom)offers a prey to the female as a nuptial gift to initiate mating. Photo by: Allan Lau.

* For more information on this project click here: http://bios.au.dk/om-instituttet/organisation/genetikogoekologi/trine-bilde-evolutionaer-biologi-af-parringssystemer-og-kooperation/evolutionary-stable-strategies/

 

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