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The neuroecology of the insect central complex

Experimental setup

All animals have to constantly integrate a multitude of sensory information and decide what behavior to perform in response. To achieve this, the animal has to know where it is with respect to its environment and which aspects of this environment are relevant for behaviour (i.e. are attractive or pose a potential threat). After an animal identifies a desired direction of movement, this direction has to be compared to its actual heading. Any discrepancy would lead to a compensatory behavior that moves the animal towards or away from objects of interest. Although this general principle may be valid for all animals, each species is likely interested in only a particular subset of environmental features and might use a different set of cues to perceive its current position in space. Previous work in migratory insects (desert locust and Monarch butterfly) has shown that skylight signals like polarized light are used to compute an internal compass in a highly conserved region of the brain called the central complex. The activity of the neurons involved can tell the insect in which direction it is currently moving within the global reference frame provided by the sun. Surprisingly, these neurons and their activity patterns are largely identical in both species, despite many million years of separate evolutionary history. But is the principle of how these animals represent their current body orientation conserved in species that inhabit very different environments or differ in their behavioural strategies? Furthermore, how might such a shared principle have been adapted in detail to account for differences in a species’lifestyle?

1. How is the neural representation of skylight compass cues in the central complex organized across insects?We compare four species: the nocturnal bee Megalopta genalis (foraging in the dense rainforest of Panama), its diurnal relative Lasioglossum leucozonium (foraging in open fields of southern Sweden), the migratory Bogong moth (Agrotis infusa), and its non-migratory relative, the Turnip moth (Agrotis segetum). While the two moths are both nocturnal, but differ in their behavioral strategy, the two bees share a common behavioral strategy (they forage from a centrally located nest), but differ in their sensory environment. We are thus not only able to identify a common mechanism for encoding space across a wide range of species, but also reveal adaptations in the central-complex neural network resulting from distinct ecological strategies. Stanley Heinze and Eric Warrant

2.What is the neural basis of compass orientation in nocturnal and diurnal dung beetles? By recording from neurons of the central complex in closely related nocturnal and diurnal dung beetles, we will determine the relative importance of celestial polarized light and the disk of the sun or moon as compass cues, and thus attempt to identify a neural basis for cue hierarchies we have observed behaviourally. Basil el Jundi, Marie Dacke and Eric Warrant

3. Mechanisms of central neural coding of visual information in nocturnal insects.How do higher brain regions of nocturnal insects deal with the limited visual information available to them? Can we find differences in neural responses to visual stimulation that are shared across nocturnal species that differ from those of diurnal species? Stanley Heinze and Eric Warrant

4. Neural correlates of long-distance migration in nocturnal Bogong moths. Are there specializations present in the brain of the Bogong moth that can be linked to the spectacular, nocturnal long-distance migrations of these animals? What information is relayed to the motor planning centers at the output side of the central complex in these animals? Does this information differ between migrating Bogong moths and aestivating Bogong moths? How do homologous neurons behave in the non-migratory Turnip moth? Stanley Heinze and Eric Warrant

5. What does an insect care about? Differences in object related information represented in the central complex across diverse insect species. Not only do insects have to establish a representation of their current position in space (Where-information), but also have to correlate this information with objects/features of the environment that are relevant for their behavior (What-information). This association is essential for guiding behaviour and likely takes place in the central complex. Which features are relevant for behaviour depends on the species, but also on the motivational state of the animal. What information is relayed to particular parts of the central complex will be compared across several insect species and correlated to each species’ ecology. Stanley Heinze and Eric Warrant

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Electron microscope image of insect brain

Collaborators

  • Dr. William Wcislo, Smithsonian Tropical Research Institute, Panama
  • Dr. Ken Green, National Parks and Wildlife Service, Australia

Funding