Tiny wasp brains show ability to alter their architecture

For an animal that has a brain about the size of two grains of sand, a lot of plasticity seems to be packed into the head of the tropical paper wasp Polybia aequatorialis.

Researchers from the universities of Washington and Texas have found that the brain architecture of these wasps undergoes dramatic changes as they cycle through a sequence of specialised jobs during their lives. The scientists previously had discovered that parts of the brains of this wasp species enlarged as the animal engage in more complex tasks.

The new work describes how this happens as dendrites, or extensions from individual neurons, reach out to receive information from other brain cells and form a dense network of connections. These networks help the wasps integrate information from visual, olfactory and touch sensory systems.

"I was astounded when we found that some of the individual neurons had dendrites that were seven to eight millimetres long in a brain that is roughly the size of two grains of sand. That's packing a huge amount of computing power in a small amount of space," said Sean O'Donnell, a UW associate professor of psychology and co-author of the new study. "These animals live in a complicated world and individuals face challenges that require a lot of brain power."

Co-authors of the paper are Theresa Jones, a UT associate professor of psychology, and Nicole Donlan, a UT research associate. "The architecture of the wasp brain is different from that in humans," said O'Donnell. "They evolved independently from us, but some of the problems they face are similar to ours because both of us are social animals. This gives researchers the opportunity to ask if there are similarities or differences in brain plasticity for social animals." P. aequatorialis wasps live in colonies of 2,000 or more adults.

The adult workers perform different jobs for the colony in a developmental sequence that is accompanied by behavioural changes as they age. They begin by performing tasks in the dim interior of the nest before moving outside where they work on the exterior of the nest. Finally, they leave the nest to forage for food and building materials for the colony and then find their way back to the nest. Each job change is accompanied by an increase in the complexity of the tasks.

The researchers found the biggest changes in brain neuron architecture occurred when the wasps shifted from working on the nest exterior to foraging.

"The forager brain is quite different. The neuron dendrite network is more complex and dense than for other job classes," said O'Donnell. "These brain changes seem to be a semi permanent way for the animals to deal with the cognitive challenges they are facing. Our earlier work showed that once workers change jobs they don't go back to previous tasks. It is plausible that they do not have the cognitive ability to do the old tasks."

He said the change in environment encountered by wasps as they develop is comparable to what people face over the course of a day. People wake up in the familiar environment of the home and family, but once they leave for home or school they face the tasks of driving a car or taking the bus in more complex environments where there are many unfamiliar people, traffic and a lot more stimulation.

Exactly what spurs the changes of the dendrite branches isn't known yet, but the researchers suspect increasing light levels outside the nest may trigger the sum of changes in brain architecture. In a part of the brain that processes visual input, the neuron branches actually shrank during the on-nest phase of life, only to rebound to even greater size during the foraging phase. This shrinkage or "pruning" of neuron branches may prepare the brain for later neuron growth to even larger sizes, perhaps also allowing new connections to form. These changes allow the wasps to function in a new environment that has different cognitive challenges.

A million to address honeybee decline

Photo:Rothamsted ResearchScientists at Rothamsted Research and Warwick University have been awarded GBP1 million by the Biotechnology and Biological Sciences Research Council (BBSRC) in partnership with Syngenta, to research the decline of honeybees.

UK government figures suggest bee numbers have fallen by 10-15 per cent over the last 2 years; the British Beekeepers’ Association (BBKA) quotes a figure nearer 30 per cent for 2008. Since the declines were first reported a number of factors have been suggested. Most scientists now believe that a complex of interacting factors is the most likely cause.

Lead researcher, Dr Juliet Osborne said, “Bees living on agricultural landscapes have a lot to deal with! They must respond to sudden changes in availability of food – pollen and nectar – whist dealing with a variety of diseases, parasites and other stresses. This project will provide us with a unique insight into how disease and food supply affect the survival of bees in farmed landscapes.”

The team will use a combination of field work and computer modelling to look at how the bees’ behaviour outside the hive, while looking for food, interacts with what is affecting bees in the hive – factors that have historically been studied separately. The ultimate aim of the project is to build a model that will allow us to understand how bees may respond to diseases in a changing farmed landscape.

Dr Peter Campbell, Syngenta said, “Honeybees are important pollinators for many crops, garden and wild flowers. They are essential both for food security and sustainable agriculture and horticulture. This work will substantially improve our understanding of the many factors affecting honeybee health. A main outcome of the project will be a predictive tool that can help beekeepers, farmers and other landscape managers to improve honeybee health.”

Professor Janet Allen, Director of Research, BBSRC said, “We are all concerned about the decline in honeybee numbers and the effect this could have on our food supplies. It is highly likely that there is no one cause of the drop in numbers which makes this project absolutely critical.”

As funders, the research councils and Syngenta are stepping up to the plate in the fight against declining honeybee populations. In addition to this project, Syngenta have also launched Operation Pollinator, a 5-year Euro1M programme in seven European countries (and the USA) to boost pollinating insects by providing wildflower strips. Dr Osborne’s project is one of four honey bee-related projects funded by the research councils in recent months, with a total investment of GBP2.1M.

For example, BBSRC is also funding a project led by Professor Ian Jones at Reading University, who is researching Israel Acute Paralysis Virus (IAPV), which is associated with colony collapse disorder and exacerbated by varroa mite infection.

Natural Environment Research Council (NERC) is funding two projects: Dr William Hughes of the University of Leeds is investigating the effects of genetic diversity on transmission and evolution of infection of honeybees by the fungal parasite, chalkbrood and Professor Mike Boots of the University of Sheffield is looking at the evolution of virulence in viral diseases that infect honeybees via varroa mite.

BBSRC also manages the Insect Pollinators Initiative – a GBP10M joint funding source under the Living with Environmental Change (LWEC) partnership. This is a joint initiative from BBSRC, Defra, the Natural Environment Research Council (NERC), the Wellcome Trust and the Scottish Government. Projects funded under the initiative are due to be announced in July 2010.

Killer bees may increase food supplies for native bees

Adult African honey bees, Apis mellifera scutelatta Lepeletier, on comb in colony. Photo: Sean McCann, University of FloridaA long-term, before and after study of Africanised bee invasion of Mexico's Yucatan shows that 'killer bees' may actually increase food resources for native bees

Aggressive African bees were accidentally released in Brazil in 1957. As "killer bees" spread northward, David Roubik, staff scientist at the Smithsonian Tropical Research Institute, began a 17-year study that revealed that Africanised bees caused less damage to native bees than changes in the weather and may have increased the availability of their food plants.

Scientists feared that dangerous swarms of Africanised bees would compete with native bees. Roubik took on the daunting task of sorting out the role of invading pollinators in tropical forests. In 1988, he set up bee traps in Sian Ka'an Biosphere Reserve – a vast area of mature tropical rainforest in Quintana Roo state on the Mexican Yucatan – with Rogel Villanueva-Gutiérrez, professor at the Colegio de la Frontera del Sur in Mexico. Africanised bees arrived in 1989.

"Our long view of the invasion shows that bees maintain higher-order evolutionary relationships with plants despite ups and downs in bee species within families," said Roubik. "Evolutionary relationships between bees and flowers, along with their flowering schedules, may be the fundamental currency that maintains this community."

Pollen from each plant species has a unique shape. Researchers compared pollen on bees in traps to pollen from flowers in the forest to determine which plants the bees were visiting.

Over the next 17 years, a severe drought and three hurricanes devastated native bees, but their populations rebounded each time. Africanised bees took over pollination of two plant families that had been important food sources for native bees: the cashew family and the spurge family. However, Pouteria, one of the plants native bees prefer, became more common. A few rare species of bees disappeared from traps later in the study.

Roubik cautions that native populations in less diverse areas might be less resilient to invasions. "Basically we're seeing 'scramble competition' as bees replace a lost source of pollen with pollen from a related plant species that has a similar flowering peak—in less-biodiverse, unprotected areas, bees would not have the same range of options to turn to."