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Solitary bees are born with a functional internal clock – unlike honey bees

Social insects such as honeybees and wasps evolved from solitary bees and wasps, respectively. A common feature of many social insects is age-specific behavior: When they emerge from the pupa, workers usually specialize in round-the-clock tasks within the darkness of the nest, starting with caring for the brood. But they gradually shift toward more cyclical tasks away from the center of the nest as they get older – culminating in searching for food outside, exclusively in broad daylight, at the end of their lives. Here, the researchers found evidence that this shift from clockwork to rhythmic tasks, which does not occur in solitary insects, appears to be driven by a slower maturation of the “internal” (ie internal) hour of social honey bees compared to solitary bees.

They found that in the solitary red mason bee Osmia bicornis, where females of all ages feed to provide nourishment to the offspring, females and males appear on a mature, fully functional daily hour, as evidenced by their 24-hour movement rhythm and the activity of brain cells that produce a regulated protein-pigment dispersal factor. Heartbeat “(PDF).

“Our results indicate that the maturation of the biological clock is lagged in social honey bees compared to solitary bees. We expect that the rapid maturation of the biological clock is the ancestral state and will be found throughout solitary bees and wasps, which all need to forage and take care of the brood throughout their life. From this, delays in maturation may have evolved secondarily in social species, to enable age-related behavioral shifts from non-periodic brood rearing to daily foraging forage, ”says Dr. Katarina Bear, a postdoctoral scientist in the Department of Animal Ecology and Tropical Biology. At Julius Maximilian Universitaet Wuerzburg, Germany. Her study, with Professor Charlotte Hilfrich Forster, Head of Neuroscience and Genetics at Julius Maximilian University, has been published in the journal Open Access Frontiers in Cellular and Developmental Biology.

The red building bee is an important agricultural pollinator, occurring throughout Europe, North Africa and the Near East. Unlike social insects, no sterile working class is found: females spend their winter in their birthing nest to emerge in the spring, mate, and build new nests in hollow stems. Females feed on many different plant species for pollen and nectar, which they store inside a row of closed cells, and lay one egg per cell.

Beer and Helfrich-Foerster collected newly emerged bees – 40 workers (female) from isolated brood combs of honey bees (Apis mellifera), 56 female and 31 male pupae isolated from O. bicornis – and placed them inside separate tubes inside a moving motor Activity monitoring system It is a device for recording an individual’s activity. Infrared rays pass through the center of each tube, which are cut off as the bee moves. By recording the pattern of activity, in the dark and at a constant temperature, on the clock for 3 to 45 days after emergence, researchers can derive each bee’s rhythm.

The results showed that none of the honey bees showed spontaneous insects. The 24-hour rhythm immediately after leaving the pupa – regardless of contact with the birthing colony – while 88% of O. bicornis females and males did. 12% of O. bicornis who did not die young. But over time, at least two days old, all honeybees also developed ca. Rhythm 24 hours. Bear and Hilfrich Forster concluded that solitary O. bicornis bees, not social honeybees, exhibit a functional endogenous biological clock.

What is the neural basis for this difference? To answer this question, the researchers used immunohistochemistry to compare the maturity of the neurons that make PDF, in the two types. In the insect brain, a group of specialized cells called lateral ventral lateral neurons act as a regulator of the daily heartbeat, secreting bursts of PDF, the so-called neuromodulator that affects central nervous system activity. By staining dissected and fixed brains with two opposites, the first that recognizes the PDF and the second, labeled with a fluorescent marker, linked to the first, Beer and Helfrich-Förster can account for PDF-producing neurons in each hemisphere at different ages before appearing immediately four weeks later. So they showed that this increase in number continued with age in honey bees, but not in O. bicornis.

The authors concluded that the circadian pacemaker is fully mature in newly emerged O. bicornis, but needs to evolve to become fully active in honey bees, explaining why young honey bees do not yet display a daily rhythm. Possibly this delay in maturation is an evolutionary adaptation to society, as young bees need to be involved in caring for their immature siblings around the clock.

It would be interesting to conduct similar studies in other social insects such as ants, which have different forms of social behavior: some exhibit age-related behavior as they do in honeybees, while others do not. If we find similar differences in the subjective clock maturity associated with the different social structures of these types of ants, this would strongly support our hypothesis, “concludes Hilfrich Forster.

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