Category Archives: Communication

Miles From Home: How Ants can Navigate Long Distances (and back!) to Forage

Ants are well known for their extraordinary ability to find food, and bring back enough to feed their vast social organisations. Being able to form relationships with other organisms that digest food, carry objects 50 times their weight and achieve great feats of communication and learning all help them forage… but how exactly do they find their way? Recent research from the University of Edinburgh has concluded the fascinating story of how the Formicidae navigate.

Plot a Course! Direction of Travel

Ants can decide on a direction for walking by using the position of the Sun in their visual field, as specialised cells in their compound eyes can detect the UV polarised light emitted by the Sun. Ants can maintain the correct course, whilst decoupling information where their body is an which direction they are travelling in. They also make use of visual landmarks (such as leaf litter), olfactory and tactile cues, and some species use the Earth’s magnetic field for navigation. According to the researchers at the University of Edinburgh, the ants construct a more sophisticated representation than they thought possible from the small size of their ganglia (brains), and can integrate information from different modalities (and from different areas of the brain) into the representation of direction.

How Far? Keeping track of Distance

Day-foraging ants, such as those in the genus Cataglyphis, are able to navigate exceptionally long distance (up to 200 metres and back!) by recording the distance they have travelled as well as the direction. An internal pedometer helps the ant remember the number of steps taken and this information is integrated with the ‘optical flow’ of objects moving around their visual field (which is an illusion- of course it is actually the ant that moves). Rather than each ant randomly roving away from the hive in search of food, the successful ‘pioneer’ must communicate the location to her sisters so they can make a sortie to the high quality patch of forage en masse…

neivamyrmex_army_ants_raiding_trail.jpg

Follow the Leader: Scent Trails

The long line of ants that you are bound to see in tropical forests are formed from scent trails that allow them to navigate back home, even if it is 200 metres away and in the dark! The ability to find the shortest route back is a crucial adaptation for avoiding desiccation in hot and arid environments. However, in army ant species, a group of foragers who become separated from the main marching column can turn back and form a circular ant mill, and run round constantly until they die of exhaustion! Ants have also been recorded to carry each other along a route, if an older and more experience forager notices that an internal nest worker (which are less familiar with the outdoor environment) is off the trail.

Final Word

So ants are able to backtrack to the location of their nest using their memories and the Sun as a reference point, and the way they operate is very similar to a self-driving car. This new research gives a unique insight into how brains of ants (and other insects) operate, and will inspire the next developments in robot system building to mimic their functioning, which would especially be useful for robots that need to navigate in forested areas. Modelling the neural circuits in the ant brain will also be useful to simply understanding more about the complex behaviours of the fascinating family of insects.

Further Reading

http://www.cell.com/current-biology/fulltext/S0960-9822(16)31466-X

http://jeb.biologists.org/content/209/1/26

http://science.sciencemag.org/content/353/6304/1155

Bank Holiday Special – Why insects are so colourful: The complex business of survival

Mastering Entomology

In the desperate struggle to evade predators, many insects have evolved toxic or bad-tasting skin, a camouflaged body (‘crypsis’), or a startle response to scare away predators. In this “evolutionary arms race”, adaptations on one side call forth counter adaptations on the other side. One such defensive adaptation is to appear toxic using brightly coloured (‘conspicuous’) body coloration- this is known as ‘aposematism’ (“Ay-PO-Sematism”). This idea that signals are sent by prey to predators to indicate toxicity was first suggested by Wallace to Darwin in 1861- they theorised that this evolved to stop predators attacking toxic prey to benefit both sides.

Aposematic warning coloration is a widely utilised form of defence used in all the animal kingdom (not just insects) and has evolved separately from many different evolutionary lines (convergent evolution). It can warn predators of defences such as a painful sting, repellent spray (such as a Bombardier beetle’s noxious…

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Social Wasp Hierarchy: Who becomes Queen?

home-slide-yellowjackets

Social wasps have a caste system which separates individuals into reproductive males, infertile female ‘workers’ and a single reproductive queen. Towards the end of the summer, the existing queen runs out of stored sperm to fertilise eggs with so produces eggs that will eventually develop into fertile females. As each juvenile stage (egg, larva and pupa) is spent in a brood cell, the young queens that emerge must therefore compete to become the ultimate reproductive queen. But what factors determine which young queen dominates the hierarchy?

Eusocial species of wasps usually have their hierarchy determined by morphology of individuals. In the european wasp, Vespula vulgaris, the larvae that have been fed the most nutrients (which eventually becomes the largest reproductive adult female) will become the queen. The location of each cell is directly related to the amount of food a larva can receive, so the queen cells are usually located at the bottom of the nest which encounters most of the foragers. Several candidates of queens arise, which then compete to create a hierarchy of queens for an ultimate queen to be selected. The precise reasons behind the variations in queens is unknown, but it is thought to be related to fat stores which elevate a queen’s quality.

However not all social wasps have castes with such a variation in size and structure of individuals. In polistine paper wasps and stenogastrines (hover wasps), the hierarchy of females is determined behaviourally through dominance interactions. These hover wasps do not have predetermined or rigid castes, and young females need to constantly assert dominance to climb a strict age-based inheritance queue to become the reproductive (queen). Paper wasp colonies are founded by multiple reproductive females, and one of these foundresses will acquire dominance over the others and become the sole reproducer, with the others becoming ‘helper females’.

All female wasps are potentially capable of becoming the colony’s queen, which is usually achieved by a wasp laying eggs first and constructing the nest. Multiple young females usually compete with each other by eating the eggs of rival females. The queen may simply be the female that eats the largest number of eggs whilst safeguarding her own (and laying the most). Once the eggs have hatched, the subordinate females stop laying eggs and instead forage for the new queen and feed her young. If the dominant female dies, a new hierarchy may be established with a former worker acting as the replacement queen.

Different genera of wasps have different strategies for deciding which female becomes the egg laying queen that will give rise to a new progeny. However all strategies end up with the strongest and most reproductively capable female becoming queen. One or a multitude of factors may influence how competitive a young queen is, which include morphology (size and structure), nutrition (fat stores) and behaviour (e.g. aggression). Paper wasps have been found to recognise individual faces, so more complex forms of communication (using facial cues) may be used in the competition to become queen.

How do Social Insects make Decisions?

beesmed

Using information passed on by others can greatly improve individual fitness, and has been the fundamental mechanism underlying the evolution of social insects such as bees, wasps, ants and termites. However in some situations it is better to ignore social information and for an individual to use its own prior knowledge and experience. So how do these colony-forming insects tailor their reliance on social information for the benefit of the ‘superorganism’? Scientists have recently reviewed the literature and made theories as to the nature of decision making in insects.

Social information is relatively ‘cheap’ to obtain for hymenopteran foragers, because they can bypass the costs associated with exploration and food sources obtained socially are likely to be better quality. In the truly eusocial western honeybee, Apis mellifera, generations overlap so information passed on by the ‘waggle dance’ (movements conveying location and quality of food sources) increases the fitness of that colony. Foraging choice are further refined by chemical cues (pheromone trails) and simply presence of other foragers.

Relying on social information may also incur costs and may not lend an evolutionary advantage. In the case of the ant forager, if she ignores social information she may find a novel food source that will benefit the colony as a whole, whilst a well-used food source is depleted (I.e. exploration produces more up-to-date information). Honeybees that rely on dance information may take time to find a dancer and may need multiple viewing and excursions to find the communicated food source.

A trade-off between these advantages and disadvantages will adjust how often (and what proportion of) social insects rely on social information. All animals tend to display the most profitable information they know, so relying on social information may be more profitable than exploration. For example honeybees only communicate their dance after finding high quality food sources. ‘Social learning strategies’ in animals are genetically determined in response to environmental and social cues. One such approach is the ‘copy if dissatisfied’ strategy, where animals will use social information if their current information is below a fitness ‘threshold’. These optimum social learning strategies can also be acquired (ironically) through social learning.

Grüter, C., & Leadbeater, E. (2014). Insights from insects about adaptive social information use. Trends in ecology & evolution, 29(3), 177-184.

Acoustic Defence in Bush Crickets: Sex Differences

bush crickets

Many insects produce sounds for mating, territory defence and to communicate with other conspecifics. However only insects in the order orthoptera stridulate their body parts (usually a leg and a wing) to produce sounds for defence. Insects usually protect themselves from predators using distastefulness, odours, colouration (cryptic and aposematic) or by startle and escape behaviour. Sound production has evolved in orthoptera in multiple species  (convergent evolution), and in many tettigoniid species the female has also evolved a ‘response song’.

In most tettigoniid only males have the sound-producing apparatus on their wings, which are rubbed together with a modified toothed vein on the left wing (the file) which is moved against the strong edge of the right wing (the plectrum). However both male and female bush crickets are capable of this defensive behaviour, although they evolved the stridulatory structures independently from one another. Scientists therefore wanted to discover whether there is a difference between the sexes, using the bush cricket (or katydid), Poecilimon ornatus, as a model.

It was found that females had a more varied syllable duration in their defence sound. The male sound last for significantly longer and contains more impulses, which is balanced by their increased tendency to regurgitate gut contents to repulse small predators such as ants and spiders.

It is thought that bush crickets rely on this method to defend themselves because their shorter wings (used for sound production) leave them unable to fly (escape) from predators. Another theory is that both male and female Poecilimon ornatus produce sounds to “evenly distribute” the increased predation risk among the sexes. The different exposure risk to the sexes may explain the differences in acoustic defence between the two sexes.

Kowalski, K. N., Lakes-Harlan, R., Lehmann, G. U., & Strauß, J. (2014). Acoustic defence in an insect: Characteristics of defensive stridulation and differences between the sexes in the tettigoniid< i> Poecilimon ornatus</i>(Schmidt1850). Zoology.