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Understanding the role of sensory ecology and species interactions during sexual signal adaptation to an urbanizing world

Periodic Reporting for period 1 - CITISEX (Understanding the role of sensory ecology and species interactions during sexual signal adaptation to an urbanizing world)

Reporting period: 2015-05-01 to 2017-04-30

Humans are rapidly transforming natural ecosystems into urban areas, leading to an alarming loss of biodiversity, in particular in the tropics. Some of this biodiversity loss could be mitigated if species are able to adapt to these evolutionary novel urban environments. An important aspect of urban success concerns adaptation to a sensory environment that is heavily affected by acoustic noise and artificial light pollution. Animals can for instance alter their sexual signals to optimally attract mates in the novel urban habitats. However, such change in sexual traits may at the same time attract more unwanted eavesdroppers, such as predators and parasites.The aim of this proposal is to understand whether and how sexual communication signals can adapt to the urban environment. The first research objective addresses how signal traits can change in response to the altered sensory environment of cities. For this objective we will record the sexual signals of frogs from forest and urban populations and relate various signal traits to variation in the sensory environment, such as anthropogenic noise and light levels. The second research objective addresses how signal change affects both attraction of mates and unwanted eavesdroppers present in urban areas. We will play urban and forest recorded signals in urban and forest environments to test their attractiveness to females as well as predatory bats and parasitic flies.
We have developed a recording setup to study multimodal signaling of male tungara frogs in the field. We have collected pilot data from the field to confirm that we can reliable record sounds as well as visual signal components under standardised conditions. In addition we developed a state-of-the art setup that allows automated playback in the field. The setup can be programmed via remote bluetooth connection and runs on a microcomputer to control starttime, duration and type of stimulus that we want to playback. We also developed a new type of speaker system that is endurable to the hard conditions of the tropical rain forest. This setup is based on a shaker system that can be connected to any structure that can vibrate, such as a water or leave surface. We are currently running pilots with this setup and the first results are very promising.

We have collected data on calling frogs, their sensory environment as well as the sexual and natural selection pressures operating on them in 20 different populations. The calls of 110 males from both urban and forest populations have been analysed and show striking differences between the two habitats. Environmental conditions have been also been analysed as well as the data on sexual and natural selection pressures
Our results seem to indicate that urban frogs have adapted to a live in the city by altering their call behaviour. Urban frogs call at higher rates and with higher complexity compared to their forest counterparts. Differences are related to environmental conditions,although we did not find any clear correlations between background sound and light levels signalling within habitat types. Differences in call behavior can also be explained by differences in selection pressures between habitat types, as we find fewer females, predators and parasites being attract to a male call in the city.
A male tungara frog calling to attract females
Cost of sexual signaling: calling can also attract unwanted predators such as fringe-lipped bats