International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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Why do social insect queens live so long? Workers take on the queen’s burdens

Author(s):
Karen Meusemann, Karen Meusemann , Adrian Geiler , Marco Kelkenberg , Hans Merzendorfer , Judith Korb
Institution(s):
Evolutionary Biology & Ecology, University of Freiburg, Hauptstr. 1, 79104 Freiburg (Brsg.), Germany; Evolutionary Biology & Ecology, University of Freiburg, Hauptstr. 1, 79104 Freiburg (Brsg.), Germany ; Evolutionary Biology & Ecology, University of Freiburg, Hauptstr. 1, 79104 Freiburg (Brsg.), Germany ; Institute of Biology, Molecular Biology, School of Scienes and Engeneering, University of Siegen, Adolf-Reichwein-Str. 2, 57076 Siegen, Germany ; Institute of Biology, Molecular Biology, School of Scienes and Engeneering, University of Siegen, Adolf-Reichwein-Str. 2, 57076 Siegen, Germany ; Evolutionary Biology & Ecology, University of Freiburg, Hauptstr. 1, 79104 Freiburg (Brsg.), Germany
Reproduction almost universally shortens lifespan. Why is this the case, if boosting both would increase evolutionary fitness? Social insects seem to have overcome this fundamental life history trade-off between fecundity and longevity. In colonies of honeybees, ants and termites, queens are highly fecund and have a long lifespan, much longer than that of non-reproducing workers, although both share the same genetic background. Reproduction even seems to increase the longevity of queens. Why the fecundity-longevity trade-off is remolded in social insects is still unclear. One plausible yet untested hypothesis is that the absence of the trade-off in queens comes with costs for workers. Considering social insects as superorganisms, workers may be equivalent to the “disposable soma” of a multicellular organism. They protect and support the queen but are to some extent disposable because, similar to the germline, reproduction is channeled through the queen. We tested this hypothesis in the termite Cryptotermes secundus by experimentally increasing the fecundity of queens and analyzing the short- and long-term impact on queens and workers. Combining ultimate fitness measures, proximate gene expression analyses and behavioral experiments, we found that enhanced fecundity had no obvious consequences for queens but instead negatively affected workers. Workers had reduced fitness and gene expression patterns over the long-term revealed signs of disrupted development. Thus, the fecundity-longevity trade-off seems shifted from within-an-individual (queen) to a trade-off between colony members (i.e. queens and workers), providing support for the superorganismal view of social insects.
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