The evolution of multimodal signals: Why are there still ugly males?

Background

Sexual selection favors signals that are complex in structure, often resulting in elaborate and bizarre mating displays. However, if mates typically prefer complex and elaborate signals why is there still substantial variation within and between species in signal complexity? An important aspect of animal signals is that they are often perceived through a range of different sensory systems and are therefore multimodal. Many animals use for example sounds as their primary signal, but sound production often involves body movements that can provide additional cues to receivers. We study how these multimodal signals evolved, how they affect mate choice and how they affect the risk of predation. Do females always prefer the same signal traits? And do ugly males benefit from reduced predation?

We use the multimodal signal of the tungara frog to study these questions. Males from this species call from water to attract females, but at the same time attract predatory bats. Their calling produces a sound, but also involves inflation and deflation of a large vocal sac. This provides a movement that is used by females as well as predatory bat to locate the caller. Furthermore, the movement itself also generates a third component, namely ripples on the water surface that are picked-up by rival males and again by predatory bats. Interestingly, males, females and bats do not use the same sensory organs for these additional cues. Females assess the vocal sac with their vision, but bats rely on their echolocation. We want to understand how each of these players perceive and use the different cues and whether this changes when we alter the sensory environment. To do this we have developed robotfrogs that allow us to manipulate each signal component independently. Furthermore, by changing acoustic conditions, altering light levels, or adding vegetation we can assess whether attractiveness changes or not.

Approaches

This project involves testing frogs or bats under controlled lab conditions. It includes the use of robotics, animal care-taking, behavioural recordings and measurements.

Frog experiments are restricted to the rainy season (April – November), but experiments with bats can be carried out year-round.

Supervision

Dr. Wouter Halfwerk
Room: H142, W&N building
Email:  w.h.halfwerk@vu.nl
Phone: +31 (0)20 – 59 82737