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Symbiotic
associations between different organisms are of great importance for
evolutionary and ecological processes. Bacteria are particularly
valuable symbiotic partners due to their huge diversity of biochemical
pathways that may open entirely new ecological niches for higher
organisms. Recently, we discovered a unique association between a new Streptomyces species and the European Beewolf (Philanthus triangulum, Hymenoptera, Crabronidae). Beewolf females cultivate the Streptomyces
bacteria in specialized antennal glands and apply them to the brood
cell prior to oviposition. The bacteria are taken up by the larva and
occur on the walls of the cocoon. Bioassays indicate that the
streptomycetes protect the cocoon from fungal infestation and
significantly enhance the survival probability of the larva, possibly
by producing antibiotics. Behavioral observations strongly suggest a
vertical transmission of the bacteria.
We screened 23 congeneric beewolf species for
symbiotic bacteria in the antennae and found the Streptomycetes to be
present in all Philanthus species. However, closely related genera of the subfamily Philanthinae (Aphilanthops, Clypeadon, Cerceris) did not seem to harbor symbiotic bacteria in the antennae. Thus, the symbiosis with Streptomyces
bacteria probably evolved around the origin of the genus Philanthus.
This mutualistic association is the first case of bacteria being
cultivated in insect antennae and the first example of a symbiosis
involving bacteria of the important antibiotic-producing genus Streptomyces.
We are currently investigating the phylogenetic
relationships among hosts and symbionts to test for coevolution
and cospeciation. Strictly congruent phylogenies would indicate
a long history of vertical transmission of the bacteria and cospeciation
with the hosts, whereas lack of congruence would point to horizontal
transmission events of bacteria between different host species and/or
acquisition of bacteria from the environment.
Publications
Goettler, W., Kaltenpoth, M., Herzner, G., Strohm,
E. (2007) Morphology and ultrastructure of a bacteria cultivation
organ: The antennal glands of female European beewolves, Philanthus
triangulum (Hymenoptera, Crabronidae). Arthropod
Structure and Development 36: 1-9.
Kaltenpoth, M. (2006) Symbiotische Streptomyces-Bakterien
in Grabwespen. Naturwissenschaftliche Rundschau 59 (11): 618-619.
Kaltenpoth, M., Göttler, W., Dale, C., Stubblefield,
J.W., Herzner, G., Roeser-Mueller, K., and Strohm, E. (2006) 'Candidatus
Streptomyces philanthi', an endosymbiotic streptomycete in the antennae
of Philanthus digger wasps. International
Journal of Systematic and Evolutionary Microbiology 56 (6): 1403-1411.
Kaltenpoth, M. (2005). Bakterien schützen Wespen-Nachwuchs
vor Pilzbefall. Naturwissenschaftliche
Rundschau 58: 329-330.
Kaltenpoth, M., Göttler, W., Herzner, G. and Strohm,
E. (2005). Symbiotic bacteria protect wasp larvae from fungal infestation.
Current
Biology 15: 475-479.
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