Stop signals reduce dopamine levels and dancing in honeybees
IMAGE: A STOP SIGNALER IS ATTACKING WAGGLE DANCERS view more
CREDIT: DONG SHIHAO
Researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and the University of California San Diego have revealed that receiving an inhibitory signal (stop signal) associated with negative food conditions can decrease brain dopamine levels in dancing honeybees.
The study was published in Current Biology on April 13.
Dopamine is known as the feel-good neurotransmitter—a chemical that ferries information between neurons. In multiple animals, dopamine is involved in arousal, cognition, and sensitivity to stimuli. It is also associated with seeking and wanting behavior, particularly with the pleasurable experiences of reward.
Honeybees communicate to nestmates the location of resources by performing a waggle dance (i.e., a repetition of movements consisting of a waggle "run" and a return "run" that is unique to each particular resource location). Their behavior type is significantly correlated with dopamine levels in bee heads. Waggle dancers have significantly higher dopamine levels than all other bees.
Honeybees have a sophisticated mechanism for communicating peril. For example, foragers use the stop signal—an inhibitory signal targeted at waggle dancers—to warn of a dangerous or declining food source and to counteract the positive feedback generated by the waggle dance.
According to Dr. DONG Shihao of XTBG, it was unclear, however, how predators affected the honeybee food-wanting system.
"We were wondering whether a signal about danger at a food source could, by itself, decrease foraging motivation and thus reduce brain dopamine levels," said Dr. DONG.
The researchers decided to test the effects of predator threat on the waggle dance and stop signal. They observed that foragers produced no stop signals when they were not attacked. In contrast, when attacked by hornets, foragers completely ceased waggle dancing. Attacked bees also abandoned the dangerous feeder and spent more time in the hive. In both whole-colony and individual measurements, stop signaling sharply increased when bees were attacked by hornets.
"Our study provides the first evidence that receiving a signal associated with negative food conditions (the stop signal) is sufficient to decrease brain dopamine levels in waggle dancers, even when these dancers have not experienced peril," said Prof. TAN Ken from XTBG, corresponding author of the study.
Moreover, the researchers discovered that increasing bee dopamine levels reduced the aversiveness of hornet attacks. Bees that fed on dopamine sucrose solution spent significantly more time staying on the feeder after being attacked by a hornet, produced fewer stop signals when they returned to the hive, and performed more waggle dances than bees that were also attacked but fed pure sucrose solution. Therefore, the fear-inducing effects of an attack could be countered by pharmacologically increasing bee dopamine levels.
"Attacks by hornet predators can reduce brain dopamine levels and cause foragers to pass on such stressful information via stop signals that also reduce brain dopamine levels in recipients. Artificially increasing dopamine levels by feeding bees dopamine would reduce the aversive effects of hornet attacks," said Prof. TAN.
A hornet is preying on honeybees
CREDIT
DONG Shihao
JOURNAL
Current Biology
ARTICLE TITLE
An inhibitory signal associated with danger reduces honeybee dopamine levels
ARTICLE PUBLICATION DATE
13-Apr-2023
Air pollution is not just a human problem – it’s also changing the gut of British bumblebees
Research finds that exposure to air pollution changes bumblebee gut bacteria.
Reports and ProceedingsRecent research from the University of Leicester, UK, has identified that air pollution affects the intricate web of microbes that are all around us. Populations of bees are also declining worldwide, so the Leicester team are investigating whether these two factors are connected. Researchers are now looking into the effects of air pollution on the bee gut microbiome, a community of beneficial bacteria vital to maintaining bee health.
The team are researching how air pollution affects bee’s beneficial gut bacteria and microbiome composition, and the subsequent impact on bee health. Dr Hannah Sampson, first author on the study, explains “We know that pollution is a massive issue globally and we know that bee decline seems to be increasing over the last few years. Maybe they’re linked, as bees are constantly exposed to these pollution particulates in the air.”
The bumblebee has a delicate gut microbiome, that has coevolved with bee species over millions of years. The balance of the bacteria in the bee gut microbiome is vital to maintaining bee health, and any disruption to this microbiome could pose a risk not only to bee health but to pollination and global food security. Snodgrassella alvi is a beneficial member of the bee gut microbiome, that colonises bees’ large intestine in a structure called a biofilm. A biofilm is a protective matrix that promotes bacterial colonisation on surfaces (e.g. like plaque on teeth). S. alvi is especially important as it is one of the initial colonisers of the bee gut microbiome.
Dr Sampson, part of the air pollution bacteria team led by Professor Morrissey at the University of Leicester, grew S. alvi in lab conditions and exposed it to black carbon air pollution. She found that exposure to black carbon changed the behaviour of S. alvi and the structure and formation of the bacteria’s biofilm. This is worrying as any disruption to this could have knock-on effects to the overall composition and function of the bee gut microbiome.
Researchers also looked at the effects of black carbon pollution on live bumblebees. They sampled bees before and after exposure and measured the abundance of bacteria in their gut to observe any differences. The researchers found that there was a significant change in the abundance of two beneficial bacteria that are vital to the health of the bee gut microbiome.
Whilst Dr Sampson urges caution on concluding that air pollution directly contributes to bee population decline from this initial study, she is clear on the importance of understanding this interaction to learn how to better protect our planet: “More research needs to take place as air pollution is having a much greater impact than we think. Air pollution affects microbial communities. Changes to these important communities could have detrimental effects on lots of different ecosystems that affect bees and also directly affect humans.”
Why orchid bees concoct their own fragrance
IMAGE: MALE OF THE ORCHID BEE EUGLOSSA DILEMMA PERFORMING TYPICAL COURTSHIP DISPLAY AT A PERCH IN A FLIGHT CAGE IN FLORIDA. THEIR SCENT POCKETS ARE LOCATED ON THE THICKENED HIND LEGS. view more
CREDIT: THOMAS ELTZ
Male bees display a remarkable passion for collecting scents: they deposit scents from various sources in special pockets on their hind legs, thus composing their own fragrance. This behaviour has been known since the 1960s. The reason why they do it has been the subject of much speculation just as long. Researchers from Ruhr University Bochum, Germany, in collaboration with colleagues from the University of California at Davis and the University of Florida at Fort Lauderdale, have finally solved the mystery. The bee fragrance serves as a sex attractant and increases the reproductive success of the males, as the team found out after three years of experiments in flight cages. The group headed by PhD student Jonas Henske and Dr. Thomas Eltz from the Bochum Department of Animal Ecology, Evolution and Biodiversity describes their findings in the journal “Current Biology”, published online on 12 April 2023.
There’s been a lot of theorising about the purpose of the fragrance: some have suggested that it could be an attractant or a wedding gift for the females, or that the scent is used to communicate with rivals. In a previous paper, the group around Thomas Eltz had already shown that the male bees transport the fragrance out of the pockets on their hind legs during the courtship ritual. “What we didn’t know, however, was who was supposed to receive this signal,” says Eltz. “The females? Or rival males?”
The researchers pursued this question in the current project. For three years, they studied orchid bees in an experiment in Florida. In a 15 by 15 by 4 metre cage, they had two male bees each compete for a female – one with fragrance and one without. They then tracked whether the female mated and, if so, with which male.
Mating activities difficult to observe
“The mating of orchid bees is very rarely observed in the wild, and even in experiments it’s been almost impossible to get them to mate,” as Thomas Eltz describes the challenge. This is why the Bochum-based researchers and their US colleagues tried to offer the bees optimal conditions; for example, they used a particularly large cage and provided the animals with the perfect pollen plants.
For the experiment, the researchers first lured male bees to artificial scent sources, which the bees then used to create a fragrance. The scientists extracted this fragrance from the pockets on the hind legs using a microcapillary and subsequently transferred it to one of the bees that they tested in the experiment. Here, two males, which had been kept under identical conditions, competed for the favour of females.
Typical courtship behaviour with varying degrees of success
The males – with or without fragrance – displayed typical courtship behaviour. Mating occurred with 27 females, which each mated with a single mate. Male bees that had been equipped with fragrance were involved in 26 of these cases. In one case, a male reproduced that belonged to the control group, which should have been fragrance-free; however, the researchers found hints that this individual had also acquired a scent mixture – fragrance theft does occasionally occur.
In order to be able to prove beyond doubt which males had mated, Jonas Henske carried out paternity analyses. He compared the genetic make-up of the brood with that of the male bees.
“It’s become clear that the fragrance is an attractant for females and triggers mating behaviour in them,” as Thomas Eltz sums up the findings. “Our results also prove that the fragrance is probably not used as a status signal among males. Indeed, a male was not more likely to defend his courtship site when he was in possession of fragrance.”
About orchid bees
There are about 250 known species of euglossine bees that are important pollinators in the tropics of Central and South America. Many orchid species rely on male euglossine bees for pollination, which is why these insects are commonly known as orchid bees. These orchids produce specific flower scents as a reward, which are collected by the male bees. There are five different genera of orchid bees, and they can vary greatly in size and appearance. The male bees collect the scents with tufts of hair on their front legs, which they wring out into the pockets on their hind legs.
JOURNAL
Current Biology
ARTICLE TITLE
Function of environment-derived male fragrances in orchid bees
ARTICLE PUBLICATION DATE
12-Apr-2023
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