Beetle GPS: Multimodal Orientation System

There are questions that we asked or tried to answer them: why the sky is blue, how many stars are in the sky, who is stronger - the white shark or the killer whale, etc. And there are questions that we did not ask, but the answer from this does not become less interesting. These questions include the following - what did scientists from Lund (Sweden), Witwatersrand (South Africa), Stockholm (Sweden) and Würzburg (Germany) universities decided to investigate so important? Probably, this is something very important, very complex and incredibly useful. Well, it is difficult to unequivocally say about this, but it is definitely very entertaining, namely, how beetles-beetles navigate in space. At first glance, everything is trivial, but our world is full of things that are not as simple as the dung beetles seem to confirm this. So, what is so unique in the navigation system of the dodger, as the scientists checked it and what does the competition have to do with it? We will find answers to these and other questions in the report of the research group. Go.

The main character

The first is to get acquainted with the main character of this study. He is strong, hardworking, persistent, handsome and caring. He is a dung beetle from the scarab-like superfamily.





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Dung beetles got their not very attractive name due to their gastronomic preferences. On the one hand, it is a little bit gruesome, but for a dabbler it is an excellent source of nutrients, from which most species of this family do not need other sources of food and even water. The only exception is the species Deltochilum valgum, whose representatives love to eat centipedes.



The prevalence of dung beetles may be envied by most other living creatures, as they inhabit all continents except Antarctica. Habitat ranges from cool forests to hot deserts. Obviously, a large cluster of dung beetles is easier to find in the habitats of animals that are “plants” for the production of their food. Dung beetles prefer to stock up on food for the future.





A small video about dung beetles and the complexity of their lifestyle (BBC, David Attenborough).



Different types of beetles have their own behavioral adaptation features. Some form balls of manure, which are rolled from the place of collection and buried in a hole. Others are digging tunnels underground, filling them with food. And the third, who know the saying about Mahomet and grief, just live in piles of manure.



Food stocks are important for the beetle, but not so much for reasons of self-preservation, but for reasons of concern for future offspring. The fact is that the larvae of dung beetles live in the fact that their parents collected earlier. And the more manure, that is, food for the larvae, the greater the likelihood that they will survive.





Well, from the lyrics go directly to the study itself.



As I mentioned earlier, some species of dung beetles form balls and roll them in a straight line, not paying attention to the quality and complexity of the chosen route, into the hole for storage. It is with this behavior of these beetles that we are most familiar with thanks to numerous documentaries. We also know that in addition to strength (some species can lift up to 1000 times their own weight), gastronomic preferences and care for the offspring, dung beetles are perfectly oriented in space. Moreover, they are the only insects that are able to navigate at night by the stars.



In South Africa (location of observations), the dodger, finding “prey”, forms a ball and starts to roll it in a straight line in a random direction, the main thing away from competitors who are not shy about taking away the food it has received. Therefore, in order for the escape to be effective, it is necessary to move in the same direction all the time, without losing course.



The sun is the main landmark, as we already know, but it is not the most reliable. The height of the sun changes during the day, from which the accuracy of orientation decreases. Why do not the bugs start to wind circles, get confused in the direction and check the map every 2 minutes? It is logical to assume that the sun is not the only source of information for orientation in space. And then scientists have suggested that the second guideline for the beetles is the wind, or rather its direction. This is not a unique feature, as ants and even cockroaches are able to use the wind to find a path.



In their work, the scientists decided to check how dung beetles use this multimodal sensory information, when they prefer to orient themselves by the sun, and when along the direction of the wind, and whether they use both options at the same time. Observations and measurements were made in the natural habitat of the subjects, as well as in simulated controlled laboratory conditions.

Research results

In this study, the role of the main subject was played by a beetle of the species Scarabaeus lamarcki , and observations in the natural environment were carried out on the territory of the “Stonehenge” farm, which is near Johannesburg (South Africa).





Image No. 1: changes in wind speed during the day ( A ), changes in wind direction during the day ( B ).



Preliminary measurements of wind speed and direction were taken. At night, the speed was the lowest (<0.5 m / s), but increased towards dawn, reaching a daily peak (3 m / s) in the period from 11:00 to 13:00 (sun height of ∼70 °).



Speed ​​indicators are remarkable in that they exceed the threshold of 0.15 m / s, which is necessary for the menotactic orientation of the dung beetles. At the same time, the peak of the wind speed coincides with the time of day with the peak of activity of the Scarabaeus lamarcki beetles.



Beetles roll their prey in a straight line from the collection site for a sufficiently large distance. On average, the entire route takes 6.1 ± 3.8 minutes. Therefore, during this period of time they must follow the route as accurately as possible.



If we talk about the direction of the wind, then during the period of maximum activity of the beetles (from 06:30 to 18:30) the average change in the wind direction during a time interval of 6 minutes is no more than 27.0 °.



Combining data on the speed and direction of the wind during the day, scientists believe that such weather conditions are sufficient for multimodal orientation of beetles.





Image number 2



It's time observations. To test the possible influence of wind on the orientation characteristics of dung beetles in space, a round "arena" was created, in the center of which was food. The beetles could freely roll the balls they formed in any direction from the center if there was a controlled stable air flow at a speed of 3 m / s. These tests were conducted on clear days, when the sun's height varied throughout the day as follows: ≥75 ° (high), 45–60 ° (medium), and 15–30 ° (low).



Changes in the air flow and the position of the sun can vary by 180 ° between two sets of beetle ( 2A ). It is worth considering the fact that sclerosis beetles do not suffer, and therefore after the first approach they remember the route chosen by them. Knowing this, scientists take into account changes in the angle of exit from the arena during the subsequent approach of the beetle as one of the indicators of the success of orientation.



With a sun height of ≥75 ° (high), changes in azimuth in response to a 180 ° change in wind direction between the first and second sets were grouped around 180 ° (P <0.001, V-test) with an average change of 166.9 ± 79.3 ° ( 2B ). At the same time, a change in the position of the sun (a mirror was used) by 180 ° caused an inconspicuous reaction of 13.7 ± 89.1 ° (lower circle by 2B ).



It is curious that with the average and low altitude of the sun, the beetles stuck to their routes, despite changes in the wind direction - the average height: -15.9 ± 40.2 °; P <0.001; low altitude: 7.1 ± 37.6 °, P <0.001 ( 2C and 2D ). But the change in the direction of the sun's rays by 180 ° had a backlash, that is, a radical change in the direction of the beetle's route - the average height: 153.9 ± 83.3 °; low altitude: −162 ± 69.4 °; P <0.001 (lower circles at 2A , 2C and 2D ).



Perhaps the orientation is influenced not by the wind itself, but by smells. To test this, the second group of test beetles removed the distal antennae responsible for smelling. The route changes in response to the 180 ° change in wind direction, demonstrated by these beetles, were still significantly grouped around 180 °. In other words, there is virtually no difference in the degree of orientation in beetles with and without olfactory.



The intermediate conclusion is that dung beetles use the sun and wind in their orientation. At the same time in controlled laboratory conditions, it was found that the wind compass prevails over the sun in the case of high altitudes of the sun, but the situation begins to change when the sun approaches the horizon.



This observation indicates that there is a dynamic multimodal compass system in which the interaction between the two modalities changes in accordance with sensory information. That is, the beetle is oriented at any time of the day, relying on the most reliable source of information at this particular moment (the sun is low — the reference point is the sun; the sun is high — the reference point is the wind).



Next, scientists decided to check whether the wind helps in the orientation of the beetles or not. For this, an arena with a diameter of 1 m was prepared with food in the center. In total, the beetles made 20 sunsets at a high sun position: 10 with the wind and 10 without the wind ( 2F ).



As expected, the presence of wind increased the accuracy of orientation of the beetles. It is noted that in early observations of the accuracy of the solar compass, the change in azimuth between two successive sunset increases twice when the sun is high (> 75 °) compared to a lower position (<60 °).



So, we realized that the wind plays an important role in the orientation of dung beetles, compensating for the inaccuracies of the solar compass. But how does a bug collect information about wind speed and direction? Of course, the most obvious thing is that this happens through the antennae. In order to verify this, the scientists carried out tests in a room with a constant air flow (3 m / s) with the participation of two groups of beetles - with and without antennae ( 3A ).





Image number 3



The main criterion for the accuracy of orientation was the change in azimuth between the two runs when the direction of air flow was changed by 180 °.



Changing the direction of movement of beetles with antennae was grouped around 180 °, in contrast to beetles without antennae. In addition, the average absolute change in azimuth in beetles without antennae was 104.4 ± 36.0 °, which is very different from the absolute change in beetles with antennae - 141.0 ± 45.0 ° ( 3B diagram). That is, beetles without antennae could not properly navigate the wind. However, they were still well oriented by the sun.



Figure 3A shows a test setup to test the ability of beetles to combine information from various sensory modalities to adjust their route. For this, both benchmarks (wind + sun) during the first sunset, or only one benchmark (sun or wind) during the second, were present in the test. Thus, multimodality and unimodality were compared.



Observations showed that changes in the direction of movement of the beetles after the transition from the multi- to unimodal reference point were concentrated around 0 °: only wind: −8.2 ± 64.3 °; sun only: 16.5 ± 51.6 ° (graphs in the center and to the right of 3C ).



This orientation characteristic did not differ from that obtained when there were two (sun + wind) landmarks (the graph on the left at 3C ).



This suggests that under controlled conditions the beetle can use one benchmark, if the second does not provide sufficient information, that is, compensate for the inaccuracy of one benchmark by the second.



If you think that scientists have stopped at this, then it is not. Further, it was required to check how well beetles store information about one of the landmarks, and whether they use it in the future as a supplement. For this, 4 sets were made: in the first one there was 1 landmark (the sun), in the second and third air flow was added, and during the fourth there was only air flow. A test was also conducted where the landmarks were in reverse order: wind, sun + wind, sun + wind, sun.



The preliminary theory is that if bugs can store information about both landmarks in the same area of ​​spatial memory in the brain, then they should maintain the same direction in the first and fourth approaches, i.e. Changes in the direction of travel should be grouped around 0 °.





Image number 4



The collected data on the change in azimuth during the first and fourth approaches confirmed the above-described assumption (4A), which was further confirmed by means of a simulation, the results of which are shown in graph 4C (left).



As an additional test, tests were carried out where the air flow was replaced with an ultraviolet spot (4B and 4C on the right). The results were almost identical to the results of tests using the sun and air flow.



For more detailed acquaintance with the nuances of the study I recommend to look into the report of scientists and additional materials to it.

Epilogue

The totality of the results of experiments both in the natural environment and in the controlled environment showed that in beetle beetles, visual and mechanosensory information converge in a common neural network and are stored as a snapshot of a multimodal compass. Comparison of the efficiency of using either the sun or the wind as a guideline showed that beetles use more the reference point that provides them with more information. The second is used as a spare or complementary.



This may seem quite common for us, but do not forget that our brains are much larger than those of a small bug. But, as we understand, even the smallest creatures are capable of complex mental processes, because in the wild, your survival depends either on strength or on your mind, and most often on a combination of both.





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