Frogs near noisy streams have mastered the skill of "Hedong Lion Roar"

Produced by: Science Popularization China

Produced by: Zhao Longhui and Cui Jianguo (Chengdu Institute of Biology, Chinese Academy of Sciences)

Producer: Computer Network Information Center, Chinese Academy of Sciences

In the movie Kung Fu directed by Stephen Chow, the landlord and his wife used the Lion Roaring Skill to fight against the Fire Cloud Evil God. In the scene, the Lion Roaring Skill was like thunder, and the sound could be heard for miles, which was very powerful and could shock people.

Coincidentally, frogs living near noisy streams have also mastered the "Hedong Lion Roar" skill.

Image source: Screenshot from the movie Kung Fu

We all know that the environment will have an impact on human development. In fact, the same is true for animals.

The Animal Behavior and Bionics Project Group of the Chengdu Institute of Biology, Chinese Academy of Sciences, found that the calls of frogs living in noisy streams have undergone adaptive evolution!

Compared to frogs that inhabit quiet water environments (ponds, lakes, etc.), stream frogs have simpler, higher-frequency vocalizations, which helps them communicate in noisy environments.

Left: The living environment of the representative species of the still water frog, the plateau forest frog; Right: The living environment of the representative species of the stream frog, the small torrent frog (Image source: provided by the author)

In order to adapt to the environment, the frog's voice became louder

The acoustic adaptation hypothesis holds that the vocalizations of animals should evolve in a way that is conducive to efficient transmission in their environment. Although the hypothesis has been proposed for more than 40 years, existing research has mainly focused on the impact of vegetation on animal vocalizations.

Existing studies have shown that in closed forests, low-frequency and long-lasting calls can travel farther, while in open forests, calls with high repetition rates and significant frequency changes have better propagation efficiency, so these characteristics will be selected and continuously strengthened during the evolutionary process. At present, environmental influencing factors mainly focus on vegetation, while factors such as noise and desertification have received less attention.

Noise is ubiquitous in the environment. Common noises include abiotic noise (noise caused by wind, rain, flowing water, etc.) and biotic noise (chorus of the same species and other species, etc.). Animals are easily disturbed by various environmental noises during vocal communication.

Water noise (Image source: Veer Gallery)

However, the current research on the acoustic adaptation hypothesis from the perspective of noise is still very limited. For animals living near flowing water, water noise can cause serious interference to their vocal communications. Revealing the impact of flowing water noise on the evolution of animal calls will help fill the gaps in existing research in this field.

There is also a rule for "listening to the sound of frogs": the louder the noise, the higher the frequency

According to the sound adaptability hypothesis, most environmental noises are of relatively low frequency, while high-frequency chirps can easily avoid interference from environmental noise, and chirps with simple frequency characteristics help maintain the integrity of information transmission in noise.

Anurans (frogs and toads) can live in both noisy environments such as streams and waterfalls and quiet environments such as ponds and lakes, making them ideal models for studying the relationship between noise and the evolution of song. This study used species from the families Ranidae and Bufonidae to test whether the frequency of animal song has evolved in the direction predicted by the acoustic adaptation hypothesis.

In addition to environmental noise, the calls of amphibians are also affected by body size, temperature and evolutionary history, which pose challenges to studying the effects of noise on animal calls. This study collected the sound frequency characteristics of 105 species, as well as their body size, temperature at the time of recording, and molecular sequence data.

After constructing the phylogenetic relationships of these species based on the 12S, 16S, CXCR4 and RAG-1 genes, the evolutionary relationships, environmental temperature and body size were taken into account for the comprehensive analysis. Then, the differences in the frequency characteristics of the calls of amphibians in environments with high noise (flowing water environment) and low noise (still water environment) were compared.

Small torrent frog (Photographer: Zhao Longhui)

The results show that in a noisy environment, the calls of amphibians evolve towards high frequencies, and the changes in sound frequency in time and space are simpler. In contrast, in a quiet environment, the calls of amphibians have relatively low frequencies, and the changes in sound frequency in time and space are relatively complex.

Since environmental noise is mainly concentrated in the low-frequency band, high-frequency chirping helps to avoid the interference of flowing water. In addition, reducing the change of frequency in time and space helps to spread the chirping farther in the noise. Therefore, the above results are consistent with the prediction of the sound adaptation hypothesis.

Left: Spectrum of the call of the representative species of still water frog, Rana sylvatica (below); Right: Spectrum of the call of the representative species of stream frog, Rana sylvatica (Image source: provided by the author)

During the research, what innovations faced what difficulties?

This study integrates systematics, behavioral and bioacoustic methods, and explores the impact of running water noise on the evolution of animal vocalization characteristics under the premise of considering multiple influencing factors. It has certain innovations in both research form and content. The study involves data from 105 species, which requires consulting a large amount of literature and screening the information of each species using the same standards, so data collection is the biggest difficulty faced. Due to the long time and heavy workload, a cautious attitude and a calm mindset are required.

The evolution of frog croaking from gurgling water, what does this tell us about the relationship between animals and the environment?

Human activities have led to an increase in noise in the environment, and noise pollution has become a global ecological problem.

Many studies have found that anthropogenic noise not only has a negative impact on human health, but also reduces the communication efficiency of animals, and even affects their survival and reproduction. Both natural water noise and anthropogenic noise are mainly low-frequency, and revealing the adaptation and evolution of animal calls in water noise will help predict how long-term anthropogenic noise stress will shape animal calls, which will also provide a theoretical basis for the protection of animal diversity.

For example, for key species whose call frequencies are severely disturbed by noise, human construction can avoid the core areas where they live to ensure the normal reproduction of the species.

The Great Brown Thrush (Turdus fuscater) living in the city is suffering from severe noise pollution.

(Image source: Brumm and Zollinger, 2013)

When the external environment changes, animals first respond with behavior. Conducting animal behavior research helps us understand the relationship between animals and the environment. In addition, we have a natural curiosity about nature and humans ourselves. Research on animal behavior can not only discover many interesting phenomena, but also allow us to often see our own shadows in animals.

In-depth research on animal behavior can sometimes inspire us to create valuable things from a bionics perspective.

Conducting animal behavior and bionics research is a peek into the mysteries of life and also a peek into ourselves; it is fun and enjoyable.

References:

[1] Zhao, L., Santos, JC, Wang, J., Ran, J., Tang, Y., & Cui, J. (2021). Noise constrains the evolution of call frequency contours in flowing water frogs: a comparative analysis in two clades. Frontiers in zoology, 18(1), 1-10.

[2] Brumm, H., & Zollinger, SA (2013). Avian vocal production in noise. In Animal communication and noise (pp. 187-227). Springer, Berlin, Heidelberg.