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Evolving communication systems in response to altered sensory environments

Periodic Reporting for period 2 - CITISENSE (Evolving communication systems in response to altered sensory environments)

Reporting period: 2020-07-01 to 2021-12-31

How animal communication systems evolve is a fundamental question in ecology and evolution and crucial for our understanding of adaptation and speciation. In the project CITISENSE we make use of the process of urbanisation to address how communication signals adapt to changes in the sensory environment. In the project we
focus on the impact of noise and light pollution on acoustic communication of a Neotropical species of frog, namely the tungara frog. Males of this species gather at night in small puddles that are formed after heavy rains and call to attract females. Their call does however also attract predatory bats and parasitic midges and their call behaviour therefore needs to be balanced between mate attraction and survival. Males can either alter their call behaviour directly, in response to immediate change to their environment, or indirectly, via selection, in which males that have the best match with their local sensory environment are better at attracting females or avoiding predators and parasites. In previous research we have found that males in urban areas attract fewer mates, but also no predators and few parasites and that these changes in sexual and natural selective pressures are related to changes in their calling behaviour. Urban males call for example at higher rates and with a higher level of complexity, which should increase their attractiveness to both intended and unintended receivers. Our central aim us to unravel the evolutionary and ecological processes that have led to the divergence in sexual signalling behaviour between urban and forest populations of our focal frog species.

To understand how the urban sensory environment influences animal communication we work on the following objectives:

1) How do senders, such as a male frog, adjust their signals to altered sensory environments?

2) How do signals evolve in response to direct (via sender) and indirect (via receivers) selection pressures?

3) What are the evolutionary consequences of signal divergence?

4) Can we predict how species adapt their signals to the sensory environment?

Insight into the effects of urbanisation on individual animals as well as their communities can help to understand why some species thrive in our cities whereas others go extinct. Such knowledge aids to understand urban community ecology and can inform best practices to improve biodiversity in human-impacted environments.
In the first part of the project we have exposed urban and forest male frogs to urban and forest sensory conditions, assessed selective pressures on calling males during field playbacks, setup a common garden breeding experiment and made a start with genomic analyses of urban and forest populations.

Our preliminary results so far indicate that males do adjust their signalling behaviour directly when exposed to both light or noise pollution, but not always in the direction and to the extend as we observe in the different populations in the field. Furthermore, we have found that the effects of noise and light on calling behaviour do not add up, but show complex interactions depending on which behaviour we assess. In some cases, the effect of light is enhanced by the effect of noise, whereas in other cases the two pollutants seem to cancel each other out.

Our field playbacks revealed that calling males attract fewer bats as well as females during light exposure compared to control and noise exposure. These results demonstrate that the differences in sexual and natural selection pressures between urban and forest populations are largely driven by light-pollution.

Our preliminary analyses of the common garden breeding experiment suggest that variation in call rate and signal complexity has a genetic basis, although their expression may depend on the environment, as so far we have not been able to find clear heritable differences between urban and forest frogs.

Preliminary screening of whole-genome sequences of urban and forest populations has so far not revealed clear structuring in relation to urbanisation.
Due to the global covid19 pandemic we have not been able to complete any of our planned experiments so far, but we expect to be able to carry out most of our plans in the remaining period. Based on our preliminary results we expect the mechanisms underlying urban-dependent signalling to be much more complex than anticipated. It seems for example that the development during the tadpole phase may play a crucial role in the formation and maintenance of the two different phenotypes. We are currently testing our state-of-the-art automated sender-receiver system that will allow us to run experimental evolution experiments under real field conditions. Based on our heritability estimates we plan to led artificially-created acoustic phenotypes evolve in urban and forest sensory conditions by tracking their mating success and survival. We expect this tool to allow us to shed light on the complex mechanisms underlying adaptive urban signalling.
Preparations of a field playback of frog sounds in Parque National Soberania, Panama.