Monday, 9 March 2009

Research Interests

Chemical behavioral and neurochemical bases of nestmate
Nestmate recognition, a mechanism that evolved in social
insects as defense against exploitation of nest
resources, is largely mediated by chemical signals. When
two individuals meet they match the label, the chemical
signal it carries on the epicuticle and represents the
colony odor, with a neural template present in the
brain. If the label matches the template amicable
interactions between the individual ensue, otherwise
they engage in aggressive interaction.
In my laboratory we investigate the chemical nature of
recognition signals in ants and the mode by which the
genetically based individual odors blend into a uniform
colony odor. Through chemical extraction and
identification and behavioral assays we demonstrated
that cuticular hydrocarbons comprise at least part of
the label in several ant species. Using radioactive
tracers we further demonstrated that individual ants
share their label with other nest members, thus
achieving a uniform colony odor and is distinguished
from that of other homospecific colonies. The rate and
magnitude of transfer depend on the modality used;
Trophallaxis is by far the most efficient mode of
transfer followed by allogrooming and to a minor extent
other body-to-body contacts. In all of these case we
discovered that the postpharyngeal gland, a head
exocrine gland that is idiosyncratic to ants, act as a
“gestalt organ” where individual admix their proper
hydrocarbon pool with that they acquire from their
The queen is a prime motivator for worker aggression and
territoriality. Under queenless conditions worker become
gradually less aggressive to the point where two alien
colonies can merge to a single colony. It is assumed
that the queen emits a primer pheromone that affects the
discrimination threshold of workers and renders them
intolerant to even slight deviation in recognition
pheromone composition. These social interactions are
apparently mediated by octopamine. Social isolation
seems to create a deficiency in this biogenic amine and
augment the intensity of social activity including
trophallaxis. By treating the ants with either
octopamine or an octopamine-antagonist we can modulate
this effect.
In the future we aim at understanding the mode of action
of octopamine and other biogenic amine on social
cohesion on the one hand and aggressive behavior on the
other hand.

Caste specific pheromones and queen-worker conflict in
the honeybee.
Social insects are endowed with pheromones that regulate
a multitude of social behaviors, many of which exhibit
caste specific chemistry. Queens of the honeybee Apis
mellifera, for example, possess multiple exocrine glands
that produce complex caste specific pheromones. Among
these the best researched are the mandibular and
Dufour’s gland. Caste specificity however is not due to
“fixed caste specific biosynthetic pathways”, but rather
show plasticity in workers according to their
physiological and social state. Queenless workers that
have developed ovaries exhibit the typical queen
secretion, both in the mandibular and Dufour’s glands.
Thus, the queen, probably via a queen signal, regulates
the glandular expression of workers. A series of
biosynthesis studies with Dufour’s gland have shown that
when incubated in vivo, glandular expression match the
social of the worker investigated. Glands of queenright
workers show only newly synthesized hydrocarbons
(typical worker compounds), whereas glands of queenless
workers produce also de-novo esters (typical queen
compounds). In contrast, glands incubated in vitro
produced the queen-like esters irrespective of the
social status of the workers utilized.
The close association between ovarian development and
the occurrence of queen-like pheromones suggest that
these provide a reliable fertility signal. Producing a
chemical signal by the queen denoting her fertility is a
rapid way to transmit the information. Since it is
coupled with egg laying it become immune to cheating.
Producing the signal by workers under queenless hopeless
situation may give then an edge in worker-worker
competition over reproduction and help recruiting helper
In the future we wish to unravel the queen signal that
is responsible for the regulation of mandibular and
Dufour’s gland expression in workers, and elucidate by
which mechanism the queen compounds production in is
turned on and off. We also aim at understanding better
the role of the gland in queen-worker social
interactions, in particular regarding queen-worker and
worker-worker conflicts over reproduction.

Queen-worker conflict over male production in bumblebees
Bumblebees provide an excellent model for studying
queen-worker conflict over reproduction. The constitute
monogyne colony in which the queen is singly
inseminated. Kin selection therefore predicts that
worker will gain more fitness by rearing either sons or
nephews (worker derived males) than brothers (queen
derived males). Since this species construct annual
colonies there is a narrow window for worker
reproduction and thus overt conflict is predicted to
occur towards the end of colony cycle.
The conflict over male production in Bombus terrestris
is characterized by workers oviposition on the one hand
and mutual oophagy on the other hand. This so-called
competition phase is also tightly correlated with new
queen production and marks the end of the colony life
cycle. Despite the great reproductive efforts made by
workers, molecular data indicate that the overwhelming
majority of the males are queen-derived. However, in
many cases queen death occurs during the competition
phase, leaving the stage open for worker reproduction.
It is hypothesized that queen death is cause by
matricide that has evolved as a countermeasure for queen
dominance in reproduction.
Our research in the near future centers on deciphering
the mechanisms underlying this behavioral arms race. We
wish to elucidate the signals that trigger the
competition phase and how this is related both to worker
reproduction and gyne formation.
Contrasting bumblebee and honeybee queen-worker
interactions paves the way to a better understanding of
the evolution of sociality in terms of genetic gain vs.
genetic conflict.

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