Multimodal warning signals for a multiple predator world

• Published in: Nature Vol. 455; no. 7209; pp. 96 - 99
• Main Authors: Ratcliffe, John M., Nydam, Marie L.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.09.2008; Nature Publishing; Nature Publishing Group
• Subjects: Animal and plant ecology; Animal behavior; Animal Communication; Animal, plant and microbial ecology; Animals; Autoecology; Bayes Theorem; Biological and medical sciences; Birds; Birds - physiology; Chiroptera - physiology; Circadian Rhythm; Color; Comparative analysis; Cues; Data entry; Fundamental and applied biological sciences. Psychology; Human subjects; Humanities and Social Sciences; letter; Methods; Molecular Sequence Data; Moths - genetics; Moths - physiology; multidisciplinary; Ontario; Phylogeny; Pigmentation - physiology; Predation; Predators; Predatory animals; Predatory Behavior - physiology; Prey; Protozoa. Invertebrata; Science; Science (multidisciplinary); Seasons; Sound; Spring; Ultrasonics; Canada; North America; Ontario; America; Predator prey relation; Sound production; Insecta; Biological evolution; Aposematic color; Phylogeny; Prey; Vertebrata; Mammalia; Hyphantria cunea; Arthropoda; Lepidoptera; Defense mechanism; Selection pressure; Arctiidae; Invertebrata; Aves; Chiroptera
• ISSN: 0028-0836; 1476-4687; 1476-4687; 1476-4679
• DOI: 10.1038/nature07087

Anti-predatory defence: double jeopardy Toxic tiger moths are historically famous examples of warningly coloured insects; more recently it was found that ultrasonic sounds produced by these insects are associated with toxicity by bats and that non-toxic species can benefit from producing similar sounds. In a study of 26 moth species in southeastern Ontario, Canada, John Ratcliffe and Marie Nydam show that tiger moths' warning signals vary with the time of year, and therefore with the type of predator they are most likely to meet. Moth species that emerge in the spring, when birds are the biggest threat, tend to use visual signals such as bright colours to warn predators of their unpalatability. Species that emerge in summer rely more on ultrasonic clicks to ward-off echolocating bats, which pose the main threat during these later months. Similarly, species active during the day rely more on visual warning signals, and ultrasonic clicks are more useful at night. The research demonstrates how selection pressures from two distinct predators can guide the evolution of separate components of the insects' warning systems, resulting in a diverse arsenal of antipredator defences within the same species. Tiger moth multimodal warning signals vary according to the activity patterns of predators with divergent sensory capacities. It is suggested that selective pressures from multiple predator classes play distinct roles in the evolution of multimodal warning displays. Aposematism is an anti-predator defence, dependent on a predator’s ability to associate unprofitable prey with a prey-borne signal 1 . Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated 2 , 3 . Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats—predators with divergent sensory capacities. Many tiger moths advertise chemical defence 4 , 5 using conspicuous colouration and/or ultrasonic clicks 3 , 6 . During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.