There are questions that we asked or tried to answer: why is the sky blue, how many stars are in the sky, who is stronger - a white shark or a killer whale, etc. And there are questions that we did not ask, but the answer does not become less interesting from this. These questions include the following - what is so important decided to investigate scientists from Lund (Sweden), Witwatersrand (South Africa), Stockholm (Sweden) and Würzburg (Germany) universities combined? It must be something very important, very complex and incredibly useful. Well, it’s hard to say for sure about this, but it’s definitely very entertaining, namely, how dung beetles orient themselves in space. At first glance, everything is trivial here, but our world is full of things that are not as simple as they seem, and dung beetles confirm this. So, what is so unique in the navigation system of the dung beetle, how did scientists check 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.
Protagonist
First of all, it is worth getting to know the main character of this study. He is strong, hardworking, persistent, handsome and caring. He is a dung beetle from the superfamily Scaraboid.
Dung beetles got their not very attractive name due to their gastronomic preferences. On the one hand, this is a little nasty, but for the dung beetle 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 Deltochilum valgum, which loves to eat centipedes.
The prevalence of dung beetles can be the envy of most other living beings, as they live on all continents except Antarctica. The habitat ranges from cool forests to hot deserts. Obviously, a large concentration of dung beetles is easier to find in the habitats of animals that are "factories" for the production of their food. Dung beetles prefer to stock up on food for the future.
A short video about dung beetles and the complexity of their lifestyle (BBC, David Attenborough).
Different types of beetles have their own behavioral adaptive features. Some form balls of manure, which are rolled from the place of collection and buried in a hole. Others dig tunnels underground, filling them with food. And still others, who know the saying about Mohammed and grief, simply live in piles of manure.
Food supplies 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 dung beetle larvae live in what their parent collected earlier. And the more manure, that is, food for the larvae, the more likely they are to survive.
I came across this wording in the process of collecting information, and it somehow doesn’t sound very good, especially the last part:... Males fight for females, resting their feet on the walls of the tunnel, and pushing their opponent with horn-shaped outgrowths ... Some males do not have horns and therefore do not fight, but they have larger gonads and guard the female in the neighboring tunnel ...
Well, let's move from the lyrics directly to the research itself.
As I mentioned earlier, some species of dung beetles form balls and roll them in a straight line, regardless of the quality and difficulty of the chosen route, into a storage burrow. It is with this behavior of these beetles that we are best acquainted through numerous documentaries. We also know that in addition to strength (some species can lift up to 1000 times their own weight), gastronomic preferences, and caring for offspring, dung beetles have excellent spatial orientation. Moreover, they are the only insects that are able to navigate at night by the stars.
In South Africa (the place of observation), the dung beetle, having found “prey”, forms a ball and begins to roll it in a straight line in a random direction, the main thing is away from competitors who will not hesitate to take away food from it. Therefore, in order for an escape to be effective, one must move in the same direction all the time without losing one's course.
The sun is the main reference, 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 don't the beetles 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 suggested that the second guide for 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 their way.
In their work, the scientists decided to test how dung beetles use this multimodal sensory information, when they prefer to navigate by the sun, and when by the direction of the wind, and whether they use both options at the same time. Observations and measurements were carried out in the natural habitat of the subjects, as well as in simulated controlled laboratory conditions.
Results of the study
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 (А), changes in wind direction during the day (В).
Preliminary measurements of wind speed and direction were made. At night, the speed was the lowest (<0,5 m/s), but increased closer to dawn, reaching a daily peak (3 m/s) in the period from 11:00 to 13:00 (sun height ∼70°).
The velocities are remarkable in that they exceed the threshold of 0,15 m/s required for the menotactic orientation of dung beetles. At the same time, the peak of wind speed coincides in time of day with the peak of beetle activity. Scarabaeus lamarcki.
Beetles roll their prey in a straight line from the collection point for a fairly long 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 beetle activity (from 06:30 to 18:30), the average change in wind direction during a time interval of 6 minutes is no more than 27.0°.
Combining data on wind speed and direction throughout the day, scientists believe that such weather conditions are sufficient for multimodal orientation of beetles.
Image #2
It's time for observation. To test the possible influence of wind on the characteristics of the orientation of dung beetles in space, a circular "arena" was created, in the center of which was food. The beetles were able to freely roll the balls they formed in any direction from the center in the presence of a controlled stable air flow at a speed of 3 m/s. These tests were performed on clear days when the sun's altitude varied throughout the day as follows: ≥75° (high), 45–60° (medium), and 15–30° (low).
Changes in airflow and sun position can change 180° between two beetle sets (2А). It is worth considering the fact that beetles do not suffer from sclerosis, and therefore, after the first call, they remember the route they have chosen. Knowing this, scientists take into account changes in the angle of exit from the arena during the subsequent entry of the beetle as one of the indicators of the success of orienteering.
At sun height ≥75° (high), azimuth changes in response to a 180° change in wind direction between first and second sets were clustered around 180° (P < 0,001, V-test) with a mean 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 a subtle reaction of 13,7 ± 89,1° (lower circle on 2B).
Curiously, at medium and low sun altitudes, the beetles stuck to their routes despite changes in wind direction - average altitude: -15,9 ± 40,2°; P < 0,001; low elevation: 7,1 ± 37,6°, P < 0,001 (2C и 2D). But a change in the direction of the sun's rays by 180 ° had a reverse reaction, that is, a radical change in the direction of the route of the beetle - the average height: 153,9 ± 83,3 °; low altitude: −162 ± 69,4°; P<0,001 (lower circles on 2А, 2S и 2D).
Perhaps the orientation is not affected by the wind itself, but by smells. To test this, the second group of test beetles had the distal segments of the antennae responsible for smell removed. The route changes in response to the 180° change in wind direction exhibited by these beetles were still significantly clustered around 180°. In other words, there is virtually no difference in the degree of orientation in beetles with and without the sense of smell.
An intermediate conclusion is that dung beetles use the sun and wind in their orientation. At the same time, under controlled laboratory conditions, it was found that the wind compass prevails over the solar compass 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 multi-modal compass system in which the interaction between two modalities changes according to sensory information. That is, the beetle navigates at any time of the day, relying on the most reliable source of information at that particular moment (the sun is low - the sun is the landmark; the sun is high - the wind is the landmark).
Next, the scientists decided to check whether the wind helps in orienting 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 approaches at a high position of the sun: 10 with wind and 10 without wind (2F).
As expected, the presence of wind increased the accuracy of beetle orientation. It is noted that in early observations of the accuracy of the solar compass, the change in azimuth between two successive sunsets is doubled at a high position of the sun (> 75°) compared to a lower position (<60°).
So, we realized that the wind plays an important role in orienting the dung beetles, compensating for the inaccuracies of the solar compass. But how does the beetle gather 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 conducted tests indoors at a constant air flow (3 m / s) with the participation of two groups of beetles - with antennae and without them (3A).
Image #3
The main criterion for orientation accuracy was the change in azimuth between two approaches when the direction of the air flow changed by 180°.
The change in the direction of movement of beetles with antennae was clustered around 180°, in contrast to beetles without antennae. In addition, the mean 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° (plot on 3V). That is, beetles without antennae could not normally navigate in the wind. However, they still had good orientation to the sun.
On the image 3А a test setup is shown to test the ability of beetles to combine information from different sensory modalities to adjust their route. To do this, both reference points (wind + sun) were present in the test during the first run, or only one reference point (sun or wind) during the second run. Thus, multimodality and unimodality were compared.
Observations showed that changes in the direction of beetle movement after the transition from a multi- to unimodal landmark were concentrated around 0°: wind only: −8,2 ± 64,3°; sun only: 16,5 ± 51,6° (plots in the center and right of the 3C).
This orientation characteristic did not differ from that which was obtained in the presence of two (sun + wind) landmarks (the graph on the left in 3S).
This suggests that under controlled conditions, the beetle can use one landmark if the second does not provide sufficient information, that is, compensate for the inaccuracy of one landmark with the second.
If you think scientists have stopped there, they are not. Next, it was necessary to check how well the beetles store information about one of the landmarks, and whether they use it in the future as an addition. For this, 4 visits were carried out: in the first there was 1 landmark (the sun), in the second and third, an air flow was added, and during the fourth, there was only an air flow. A test was also conducted, where the landmarks were in reverse order: wind, sun + wind, sun + wind, sun.
The tentative theory is that if beetles can store information about both landmarks in the same spatial memory area in the brain, then they should maintain the same direction on the first and fourth passes, i.e. changes in direction of travel should cluster around 0°.
Image #4
The collected data on the change in azimuth during the first and fourth approaches confirmed the above assumption (4A), which was further confirmed by simulation, the results of which are depicted in plot 4C (left).
As an additional check, tests were carried out where the airflow was replaced by a UV spot (4B and 4C on the right). The results were almost identical to those of the sun and airflow tests.
For a more detailed acquaintance with the nuances of the study, I recommend looking at и to him.
Finale
The totality of the results of experiments both in the natural environment and in the controlled environment showed that in dung beetles, visual and mechanosensory information converge in a common neural network and are stored in the form of a multimodal compass image. A comparison of the effectiveness of using either the sun or the wind as a guide showed that beetles use more of the guide that provides them with more information. The second is used as a spare or supplement.
This may seem very common to us, but we should not forget that our brains are much larger than those of a small bug. But, as we have understood, even the smallest creatures are capable of complex mental processes, because in the wild, your survival depends on either strength or intelligence, and most often on a combination of both.
Friday off-top:
Even beetles fight for prey. And it doesn't matter that the prey is a ball of manure.
(BBC Earth, David Attenborough)
Thanks for watching, stay curious and have a great weekend guys! 🙂
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Source: habr.com