Universität Bern


NATURE COMMUNICATIONS Kinship reduces alloparental care in cooperative cichlids where helpers pay-to-stay
Zoettl M., Heg D., Chervet N. & Taborsky M. (2013)
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Social competence: an evolutionary approach
Taborsky, B. & Oliveira, R.F.
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Larval helpers and age polyethism in ambrosia beetles
Biedermann P.H.W. & Taborsky M.
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Animal personality due to social niche specialisation
Bergmueller R. & Taborsky M.
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Environmental Change Enhances Cognitive Abilities in Fish
Kotrschal, A. & Taborsky, B.
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Extended phenotypes as signals
Franziska C. Schaedelin and Michael Taborsky
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On the Origin of Species by Natural and Sexual Selection
G. Sander van Doorn, Pim Edelaar, Franz J. Weissing
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Cambridge University Press
Alternative Reproductive Tactics: An Integrative

Oliveira R., Taborsky M. & Brockmann H.J.
more information

Sociality in ambrosia beetles

Ambrosia beetles make up around 3400 of the 7500 species in the subfamily Scolytinae (Scolytidae and Platypotidae). Most of them construct tunnel systems in the heartwood of trees (typically in weakened or recently dead trees or, more rarely, in vigorous hosts), among others that colonize pith, large seeds, fruits and leaf petioles. The term ambrosia refers to the fungi cultivated by the beetles on their gallery walls, upon which they feed as an exclusive, or near exclusive food source. The beetles are obligately dependent upon the fungi from which they acquire essential vitamins, amino acids, and sterols.

DSCN6097Fig.1. by PB Full size [393 KB] gallerie_biedermann.ppt Fig.2. by PB Full size [793 KB]

(all pictures on this homepage can be downloaded and used by the media; fotografers PB = P. Biedermann, GK = Gernot Kunz; link to picture legends)

Sociality in Ambrosia beetles

Among all animals, the highest levels of sociality exist in some groups of insects: e.g. the hymenoptera, the termites, the aphids,... In the eusocial species of these groups members of sterile casts refrain from reproduction and help reproductives to raise their young. At least two of the origins of advanced social life (termites and ants) have arisen under inbreeding conditions under the bark of dead trees. Another group that may show similar levels of sociality and is still living under these conditions is the family Scolytidae, commonly known as the bark and ambrosia beetles. As in the eusocial hymenoptera, highly social representatives of this family are haplodiploid, which means that a female is more closely related to her sisters than to own offspring. This means that in inclusive fitness terms, females benefit more from the production of sisters than daughters, a feature regarded as being the driving force in the evolution of hymenopteran eusociality. Ambrosia beetles in general comprise species with different mating systems (exhibiting both inbreeding and outbreeding) as well as variation in diploidy / haplodiploidy and environmental conditions. Furthermore, sociality has hardly been a focus in Scolytid research. [1],[4]

Inbreeding and sex ratio adjustment

Haplodiploidy makes it more easy for a female to assign the sex of its offspring. In Xyleborini males develop from unfertilised eggs and resemble clones of the mother. Due to constant predispersal mating (brother-sister) in this tribe sex ratios are generally female biased. The reason is that the reproductive success of a female is determined primarily by the number of daughters she can produce. In an extreme case one male would be enough to fertilize all its sisters. However, our group found that females in Xylosandrus germanus adapt the number of males according to outbreeding conditions for their sons. Regardless of the fact, that due their long history of inbreeding even matings between members of neighbouring galleries show outbreeding depression. [2],[3]

DSCN6098 Fig.3. by PB Full size [432 KB] Xyleborinus_saxesenii_1.2klein Fig.4. by GK Full size [3.62 MB]

(all pictures on this homepage can be downloaded and used by the media; fotografers PB = P. Biedermann, GK = Gernot Kunz; link to picture legends)

The beetle - fungus mutualism

Mutualisms are widespread and ecologically important but, like within-species cooperation, their evolution represents a challenge for evolutionary theory. There is no general theory at the moment that approaches the explanatory power that Hamilton's rule appears to hold for the understanding of within-species interactions. Recently the mechanisms behind the evolutionary stability of the agricultural mutualism in termites and attine ants were proposed. In the third group of fungus gardening insects the mutualism is hardly examined. The benefit for the beetles is more or less clear - being provided with nutrients, in a nutrient-poor substrate. On the other hand the benefits are less clear: the fungus is transmitted by the beetle to a new sterile substrate, what would be hardly achievable otherwise. Additionally the beetles may provide their fungal beds with their faeces and excretes, that could be recycled by the fungi again.

Xyleborinus_saxesenii_2klein Fig.5. by GK Full size [5.07 MB]

(all pictures on this homepage can be downloaded and used by the media; fotografers PB = P. Biedermann, GK = Gernot Kunz; link to picture legends)

We will investigate:

- The beetle - fungus relationship and other involved organisms
- The possibility for the adult offspring to help its mother
- The proportion of non-sister matings

Publications of our department

[1]  Peer K. & Taborsky M. (2007): Delayed dispersal as a potential route to cooperative breeding in ambrosia beetles. Behavioral Ecology and Sociobiology 61, 729-730. [pdf, 250 KB]

[2] Peer K. & Taborsky M. (2005) Outbreeding depression, but no inbreeding depression in haplodiploid ambrosia beetles with regular sib mating. Evolution 59, 317-323. [pdf, 93 KB]

[3] Peer K., Taborsky M. (2004): Female ambrosia beetles adjust their offspring sex ratio according to outbreeding opportunities for their sons. Journal of Evolutionary Biology 17, 257-264. [pdf, 142 KB]

[4] Biedermann P.H.W. (2007): Social behaviour in sibmating fungus farmers. Master thesis at the Department of Behavioural Ecology, University Bern, Switzerland. [pdf, 5.3MB]

[5] Biedermann P.H.W., Klepzig K.R. & Taborsky, M. (2009): Fungus cultivation by ambrosia beetles:  Behavior and laboratory breeding success in three Xyleborine species. Environmental Entomology 38(4): 1096-1105. [pdf, 460 KB]

[6] Biedermann P.H.W. (2010): Observations on sex ratio and behavior of males in Xyleborinus saxesenii Ratzeburg (Scolytinae, Coleoptera). In: Sixty years of discovering scolytine and platypodine diversity: A tribute to Stephen L. Wood (eds. A.I. Cognato and M. Knížek). Zookeys 56: 253-267. doi: 10.3897/zookeys.56.530 [pdf, 1.1 MB]

[7] Grubbs K.J., Biedermann P.H.W., Suen G., Adams S.M., Moeller J.A., Klassen J.L., Goodwinm L.A., Woyke T., Munk A.C., Bruce D., Detter C., Tapia R., Han C.S. & Currie C.R. (2011): The Complete Genome Sequence of Streptomyces cf. griseus (XyelbKG-1 1), an Ambrosia Beetle-Associated Actinomycete. Journal of Bacteriology doi:10.1128/JB.00330-11 [pdf, 278 KB]

[8] Biedermann P.H.W., Klepzig K.D. & Taborsky M. (2011): Costs of delayed dispersal and alloparental care in the fungus-cultivating ambrosia beetle Xyleborus affinis Eichhoff (Scolytinae: Curculionidae). Behavioral Ecology & Sociobiology 65:1753–1761. doi 10.1007/s00265-011-1183-5 [pdf, 324 KB]

[9] Biedermann P.H.W. & Taborsky M. (2011): Larval helpers and age polyethism in ambrosia beetles. Proc Natl Acad Sci USA, EarlyEdition doi/10.1073/pnas.1107758108, [pdf, 1.12 MB]

[10] Keller L., Peer K., Bernasconi C., Taborsky M. & Shuker D.M. (2011): Inbreeding and selection on sex ratio in the bark beetle Xylosandrus germanus. BMC Evolutionary Biology 11: 359. doi:10.1186/1471-2148-11-359 [pdf, 182 KB]

[11] Biedermann PHW (2012): Evolution of Cooperation in Ambrosia Beetles. PhD thesis. Institute of Ecology & Evolution, University of Bern. link

[12] De Fine Licht HH & Biedermann PHW (2012): Patterns of functional enzyme activity in fungus farming ambrosia beetles. Frontiers in Zoology 9:13. doi:10.1186/1742-9994-9-13 [pdf, 503 KB]

[13] Biedermann PHW, Peer K & Taborsky M (2012): Female dispersal and reproduction in the ambrosia beetle Xyleborinus saxesenii Ratzeburg (Coleoptera; Scolytinae). Mitteilungen der Deutschen Gesellschaft für allgemeine und angewandte Entomologie 18: 231-235. [pdf, 721 KB] 

[14] Biedermann PHW, Klepzig KD, Taborsky M & Six DL (2012): Abundance and dynamics of filamentous fungi in the complex ambrosia gardens of the primitively eusocial beetle Xyleborinus saxesenii Ratzeburg (Coleoptera: Curculionidae, Scolytinae). FEMS Microbiology Ecology doi:10.1111/1574-6941.12026 [pdf, 811 KB]