Nestmate recognition in the large carpenter bee, Xylocopa virginica /
Abstract
Abstract
Many species of social insects have the ability to recognize their nestmates. In
bees, sociality is maintained by bees that recognize which individuals should be helped
and which should be hanned in order to maximize fitness (either inclusive or individual)
(Hamilton 1964; Lin and Michener 1972). Since female bees generally lay eggs in a
single nest, it is highly likely that bees found cohabitating in the same nest are siblings.
According to the kin selection hypothesis, individuals should cooperate and avoid
aggression with same sex nestmates (Hamilton 1964). However, in opposite sex pairs that
are likely kin, aggression should increase among nestmates as an expression of
inbreeding avoidance (Lihoreau et al. 2007). Female bees often guard nest entrances,
recognizing and excluding foreign conspecific females that threaten to steal nest
resources (Breed and Page 1991). Conversely, males that aggressively guard territories
should avoid aggression towards other males that are likely kin (Shellman-Reeve and
Gamboa 1984). In order to test whether Xy/ocopa virginica can distinguish nestmates
from non-nestmates, circle tube testing arenas were used. Measures of aggression,
cooperation and tolerance were evaluated to detennine the presence of nestmate
recognition in this species.
The results of this study indicate that male and female X virginica have the
ability to distinguish nestmates from non-nestmates. Individuals in same sex pairs
demonstrated increased pushing, biting, and C-posturing when faced with non-nestmates.
Males in same sex pairs also attempted to pass (unsuccessfully) nOIl-nestmates more
often than ncstmates, suggesting that this behaviour may be an cxpression of dominancc
in males. Increased cooperation exemplified by successful passes was not observed
among nestmates. However, incrcased tolerance in the [onn of head-to-head touching
was observed for nestmates in female same sex and opposite sex pairs. These results
supported the kin selection hypothesis. Moreover, increased tolerance among opposite
sex non-nestmates suggested that X virginica do not demonstrate inbreeding avoidance
among nestmates.
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The second part of this study was conducted to establish the presence and extent
of drifting, or travelling to different nests, in a Xylocopa virgillica population. Drifting in
flying Hymenoptera is reported to be the result of navigation error and guard bees
erroneously admitting novel individuals into the nest (Michener 1966). Since bees in this
study were individually marked and captured at nest entrances, the locations where
individuals were caught allowed me to determine where and how often bees travelled
from nest to nest. Ifbees were captured near their home nests, changing nests may have
been deliberate or explained by navigational error. However, ifbees were found in nests
further away from their homes, this provides stronger evidence that flying towards a
novel nest may have been deliberate.
Female bees are often faithful to their own nests (Kasuya 1981) and no drifting
was expected in female X virginica because they raise brood and contribute to nest
maintenance activities. Contrary to females, males were not expected to remain faithful to
a single nest. Results showed that many more females drifted than expected and that they
were most often recaptured in a single nest, either their home nest or a novel nest. There
were some females that were never caught in the same nest twice. In addition, females
drifted to further nests when population density was low (in 2007), suggesting they seek
out and claim nesting spaces when they are available. Males, as expected, showed the
opposite pattern and most males drifted from nest to nest, never recaptured in the same location. This pattern indicates that males may be nesting wherever space is available, or
nesting in benches nearest to their territories. This study reveals that both female and
male X virginica are capable of nestmate recognition and use this ability in a dynamic
environment, where nest membership is not as stable as once thought.