Alarm! Alarm !: how fish warn relatives about danger

Friendship is in trouble. This phrase familiar to all of us becomes a matter of life and death when it comes to wildlife, namely socialized animals. Also here the phrase will be appropriate - forewarned means armed. You have probably seen sentinels in meerkats or other animals living in groups and fearing the attack of predators. In case of danger, meerkats make a sound and all his comrades immediately hide in minks. But what if you are dumb like a fish? Or rather, if you are a fish. Use chemical compounds secreted by the body, of course. Scientists have found that, if necessary, some species of group fish are able to secrete certain substances that warn relatives about the danger. How exactly did scientists find out how is their discovery different from the previous ones and how complicated is the communication system in fish society? For the answers now to the research group report.

Study basis

The main manifestation of sociality in any living organism is communication, that is, communication between representatives of a species within one group. Through communication, information is transmitted, which is quite obvious. It can be like a call to flee here, because there is a lot of goodies here, and a warning about danger must be run from it.


Fish hiding from danger.

Roughly speaking, the reasons for communication and the transmitted information are quite similar among different creatures, but the transmission methods differ: sound, light, gestures, allocation of chemical compounds, etc. And some of these signals cannot be perceived by another species, which is very useful if you warn the group about a predator that is nearby. Man, too, does not notice many of these signals. This is precisely what has led to the fact that many social aspects of various species have not been studied for decades.


Image No. 1

Researchers note that in any signal system there are several main components: context (a), voluntary signal (b), response of the receiving party (c) and the benefits for the transmitter and receiver (d).

First, an individual is confronted with a specific context (information / situation), which may be due to external (i) factors (finding food, finding other species or predators nearby), internal (ii) factors (hunger, fear, etc.) and the fact that the receiver (iii) has signals nearby. Thus, the signal context consists of external stimuli, the internal state of the individual, and the target “audience” of the generated signal, that is, whom it is aimed at. Scientists also note that these signals are voluntary and produced by an individual of their own free will.


The symbiotic relationship between the seabass and the shrimp. One of the shrimp antennas is constantly in contact with fish, which in case of danger hides in a hole. Having received such a signal, the shrimp also hides.

This point (voluntariness of the signal) is extremely important, because not all signals are. Some signals are randomly generated depending on the context without the conscious involvement of the signal source. For example, the smell of a wounded individual is a signal to others that there is a danger nearby, but this signal was actually created by a predator, not an individual victim. In other words, it was an involuntary signal.

The next element is the host. The signal causes the receiving side a certain response, which may include behavioral, physiological, and even genetic changes, depending on the nature of the signal.

Equally important is the benefit of the signal for the one who sends it and the one who receives. In this case, the situations can be either mutually beneficial or aimed at the benefit exclusively for the individual generating the signal. Mutually beneficial signals can be used as an important survival mechanism, and therefore pass from generation to generation through heredity and / or offspring training.

As scientists admit, in practice it is quite difficult to measure the intensity of the signal, its arbitrary or random nature of generation and the benefits of it for the generator and the receiving side. As a rule, these characteristics are determined after the fact, that is, the degree of survival of the group, the ratio of mortality and birth rate, etc. are estimated. Simply put, if a group uses signals and they are alive and well, then signals work to their advantage. But this approach is very inaccurate and cannot answer a number of questions: whether the group’s behavior is maintained outside controlled conditions, whether the behavior is transmitted to offspring, etc.

If we simplify the system of transmitting hazard signals, we can distinguish two main contextual elements: an external factor (predator) and an audience (representatives of the same species and / or group). In this case, the signal intensity may vary depending on the situation. If relatives are close enough, the signal will be stronger. If the victim of the attack is one, but the relatives are far away, the alarm signal will be weak so as not to attract too much attention from the predator.


Crows in the group are much bolder than individually, therefore they can even attack the bald eagle.

The composition of the audience, that is, those receiving the signal, also matters. Some birds and primates amplify the danger signal if there are representatives of not just the same species, but of the general group nearby (family, partners, offspring).

Turning to the discussion of the inhabitants of the seas and oceans, scientists again recall the importance of distinguishing between voluntary and involuntary signals. For example, Karl von Frisch discovered the chemical compound Schreckstoff in 1938, one of the components of which was H ₃ NO. This compound is made by a wounded or killed individual, but it can not be called a voluntary and deliberate alarm.


Carl von Frisch

The main component of the majority of fish signals is urine, which is used to isolate pheromones, to demonstrate dominance in a certain territory, to differentiate related individuals, etc. Based on this, scientists have suggested that urine can play an important role in signaling anxiety.

In this study, scientists conducted tests involving black thick-headed (Pimephales promelas). This type of fish leads a social lifestyle. In case of danger, they first begin to move quickly and randomly, then freeze, and then gather in tight groups and try to hide in a safe place.

The researchers conducted a series of tests in which a predator attacks a fat head in order to determine the voluntariness of the generated alarms, the signal intensity depending on the audience of the host individuals (friends / strangers) or on the presence / absence of a nearby audience as such.

Test results

69 individuals were selected as signal generators, 270 individuals as receiving ones. All individuals were not trained in alarms, but during the tests they were in the aquarium with familiar individuals or with strangers. There were no special physiological differences between the generators and the receivers: weight - 0.6 ± 0.2 g, body length - 40 ± 5 mm.

The grouping index before and after the signal was very different ( 2a ) depending on the type of signal and the type of individual generator (two-way interaction: LRT x ² ₂ = 9.94, p = 0.0069).


Image No. 2

By dividing the data by signal type and generator type, scientists were able to understand in more detail the relationship between these variables. Non-alarming signals (normal) did not differ between individuals of three different categories of signal generators (LRT x ² ₂ = 3.33, p = 0.19), but alarms on the contrary (LRT x ² ₂ = 10.75, p = 0.0046). Scientists also noticed that groups of individuals who are familiar with the individual signal generator respond much more actively to the alarm they generate (LRT x ² ₁ = 16.86, p <0.0001), but groups of “strangers” react sluggishly and slowly (LRT x ² ₁ = 1.28, p = 0.26).

Regarding numbness ( 2b) a relationship was also found between the type of signal and the type of its generator (chi-square test: x ² ₇ = 28.2, p = 0.0002). In the case of a normal signal, the receiving group often had one numb individual, regardless of the type of signal generator. However, with the alarm, there were differences, as with the grouping indicator. Receivers more often and in greater numbers are numb if the alarm comes from a familiar individual than from a stranger (Fisher's exact test: p = 0.002) or a single (isolated) individual (p = 0.0002). The reaction rates to the signals of strangers and isolated individuals are quite similar, which once again confirms the importance of social ties between individuals of the same group. As they say, they trust their own much better than strangers.

With an indicator of chaotic movements, the situation was even more curious ( 2s ). The group did not respond to normal signals from any type of generator (familiar individuals, strangers, and isolated individuals). The group’s reaction to alarms from familiar individuals was much stronger than to alarms and isolated individuals.

For a more detailed acquaintance with the nuances of the study, I recommend that you look into the report of the research group .

Epilogue

The researchers, having carried out the tests described above, confirmed the fact that alarms (in this case, chemical) are an important component of protection against predators for the individual that generates the signal, and for individuals that receive the signal. It was also found that these signals are generated voluntarily and deliberately, in contrast to involuntary signals from a wounded or killed individual.

In addition, the study showed that the group would be more willing to respond to alarms generated by an individual from the same group than by strangers or isolated individuals. This observation confirms the fact of the presence of stronger social ties within specific groups, rather than species in general.

This study allows you to better understand the social structure and its fundamental elements in underwater inhabitants. The wildlife world is a dangerous place, especially for small fish that have a lot of hungry enemies. By forming groups, they increase their chances of survival. But if the group is blind to the dangers surrounding it, there will be little use for mass. That is why environmental awareness of each member of the group plays such an important role in the struggle for survival.




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