Neural activity in the brains of the Japanese worker honeybees involved in a hot defensive bee ball reflects thermal stimuli processing
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1
Graduate School of Science, The University of Tokyo, Department of Biological Sciences, Japan
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2
Japan Society for the Promotion of Science, Japan
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3
Kanazawa University, Institute of Science and Engineering, Japan
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4
Graduate School of Agriculture, Tamagawa University, Japan
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5
Tamagawa University, Honeybee Research Center, Japan
In nature, animals threatened by predators exhibit a variety of adaptive behaviors to escape or actively defend themselves against the predators. Some animals exhibit characteristic anti-predator behaviors against their natural enemies that are considered to be an evolutionary consequence of adaptation to the threat of natural enemies. The neural bases of the anti-predator behaviors, however, remain unknown.
Although honeybees commonly use their stingers to counterattack predators, the Japanese honeybee (Apis cerana japonica) uses a different strategy to fight against the giant hornet (Vespa mandarinia japonica), their most formidable natural enemy. If a foraging hornet tries to enter the beehive, a group of more than 500 workers quickly forms a spherical assemblage called a ‘hot defensive bee ball’, trapping the hornet inside the ball. In the ball formation, honeybees vibrate their flight muscles to produce heat. The temperature in the ball quickly rises to almost 47°C, which is lethal to the hornet but not to the honeybees. Finally, the hornet is killed by the heat produced. On the other hand, European honeybees (A. mellifera ligustica), which are a related but allopatric species, exhibit only stinging behavior against the hornet, and colonies of the European honeybees are often destroyed. Thus, the defensive bee ball formation is considered to result from Japanese honeybee-specific selective pressure to avoid predation by the giant hornets that inhabit East Asia, including Japan.
To elucidate the neural mechanism underlying this behavior, we used an immediate early gene (IEG), and revealed that the neural activity of one subtype of intrinsic neurons of the mushroom bodies (MBs) is preferentially increased in the brains of the Japanese honeybee workers during the formation of a hot defensive bee ball.
Furthermore, we asked what kind of sensory information induces the pattern of neural activity observed during defensive bee ball formation. In the brains of the bees exposed to high temperature (46°C), distribution pattern of IEG-positive cells well resembled that observed in the bee ball forming bees. On the other hand, scarce IEG-positive MB neurons were detected in the bees exposed to isoamyl acetate, which is the major component of honeybee alarm pheromone emitted from a hot defensive bee ball. These results suggested that the neural activity detected in the brains of worker honeybees involved in the fromation of a hot defensive bee ball mainly reflects thermal stimuli processing. In contrast to 46°C exposed-bees, there were few IEG-positive MB neurons when the bees were exposed to 42°C. This result indicated that the some MB neurons exhibit temperature selective activation and have threshold between 42°C and 46°C.
Because there is only 3-5°C difference in the lethal temperature between the Japanese honeybee and the giant hornet, accurate monitoring of temperature in a bee ball seems critical for the bees. The MB neusons activated under 46°C may play an important role in keeping of appropreate internal temperature of a hot defensive bee ball.
Keywords:
defensive behavior,
Honeybee,
Immediate early Gene,
thermal information processing
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Genes and Behavior
Citation:
Ugajin
A,
Kiya
T,
Kunieda
T,
Ono
M,
Yoshida
T and
Kubo
T
(2012). Neural activity in the brains of the Japanese worker honeybees involved in a hot defensive bee ball reflects thermal stimuli processing.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00221
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Takeo Kubo, Graduate School of Science, The University of Tokyo, Department of Biological Sciences, Tokyo, Japan, stkubo@biol.s.u-tokyo.ac.jp