Having One Eye Better Than the Other May Explain Ants’ Left Bias

Summary: A new study reveals behavioral lateralization may be hardwired during development rather than something learned from experience.

Source: University of Bristol.

Unlike Derek Zoolander, ants don’t have any difficulty turning left. New research from the University of Bristol has now found rock ants often have one eye slightly better than the other, which could help explain why most of them prefer to turn left, given the choice.

The research, published in Scientific Reports today and led by Dr Edmund Hunt and Emeritus Professor Nigel Franks, studied whether rock ants’ turning direction was associated with how well the ants can see in either eye. Previous research on honey bees found a link between lateralization to learn odours better with the right antenna, and more smell sensors on the right antenna than the left.

Behavioural lateralization is the preference to use a certain side of the body for certain tasks. For example, most humans are right-handed. While scientists used to think this was only a human trait, evidence for lateralization in animals, including insects like ants and bees, is becoming increasingly widespread. Research by Bristol in 2014 found that rock ants show a leftward turning bias in branching nest sites. While such lateralization may originate in asymmetrical brain structures, it may also relate to external shape asymmetries – such as the size of eyes or the length of legs.

Ant compound eyes are composed of small structures known as ommatidia which collect light. More ommatidia in an eye contributes to better vision. The researchers found that ants turning left tended to have slightly more ommatidia in their right eye, and vice versa. This may be because they prefer to walk with their inferior eye pointing toward the wall, so when they come to a branch they follow the wall along to the left. This is the first study to report a link between asymmetries in compound eyes and behavioural lateralization in insects.

ant

An exploring ant encounters an unknown branching nest site. NeuroscienceNews.com image is credited to Edmund Hunt.

Dr Edmund Hunt, EPSRC Doctoral Prize Fellow in the Department of Engineering Mathematics’ Collective Dynamics research group and corresponding author, said: “It is intriguing that lateralization of behaviour seems to be associated with observable external asymmetries in the body. This suggests that behavioural lateralization is something that is ‘hardwired’ into these animals as they develop rather than something learned through experience. It also shows that physical indicators of lateralization can be externally observable rather than hidden in the brain – and might be awaiting discovery in all sorts of animals.”

Theoretical models of behavioural lateralization suggest that population or colony-level alignment of behavioural biases should develop in social species that would benefit from coordinating their behaviour. In this case, more predictable behaviour would help them cooperate. On the other hand, the costs of being more predictable, such as vulnerability to predators, might outweigh this alignment of lateralization in non-social species.

The researchers suggest a comparative study should be carried out on compound eye asymmetry between social and non-social species of insects of the same family, such as honeybees vs. solitary bees, to see if it is more pronounced in social species.

About this neuroscience research article

Source: Joanne Fryer – University of Bristol
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to Edmund Hunt.
Original Research: Open access research for “Asymmetric ommatidia count and behavioural lateralization in the ant Temnothorax albipennis” by Edmund R. Hunt, Ciara Dornan, Ana B. Sendova-Franks & Nigel R. Franks in Scientific Reports. Published April 11 2018,
doi:10.1038/s41598-018-23652-4

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University of Bristol “Having One Eye Better Than the Other May Explain Ants’ Left Bias.” NeuroscienceNews. NeuroscienceNews, 11 April 2018.
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University of Bristol (2018, April 11). Having One Eye Better Than the Other May Explain Ants’ Left Bias. NeuroscienceNews. Retrieved April 11, 2018 from http://neurosciencenews.com/left-bias-ants-vision-8763/
University of Bristol “Having One Eye Better Than the Other May Explain Ants’ Left Bias.” http://neurosciencenews.com/left-bias-ants-vision-8763/ (accessed April 11, 2018).

Abstract

Asymmetric ommatidia count and behavioural lateralization in the ant Temnothorax albipennis

Workers of the house-hunting ant Temnothorax albipennis rely on visual edge following and landmark recognition to navigate their rocky environment, and they also exhibit a leftward turning bias when exploring unknown nest sites. We used electron microscopy to count the number of ommatidia composing the compound eyes of workers, males and queens, to make an approximate assessment of their relative sampling resolution; and to establish whether there is an asymmetry in the number of ommatidia composing the workers’ eyes, which might provide an observable, mechanistic explanation for the turning bias. We hypothesise that even small asymmetries in relative visual acuity between left and right eyes could be magnified by developmental experience into a symmetry-breaking turning preference that results in the inferior eye pointing toward the wall. Fifty-six workers were examined: 45% had more ommatidia in the right eye, 36% more in the left, and 20% an equal number. A tentative connection between relative ommatidia count for each eye and turning behaviour was identified, with a stronger assessment of behavioural lateralization before imaging and a larger sample suggested for further work. There was a clear sexual dimorphism in ommatidia counts between queens and males.

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