Does spatial variation in predation pressure modulate selection for aposematism?. Issue 18 (15th August 2017)

• Record Type: Journal Article
• Authors: Aluthwattha, S. Tharanga; Harrison, Rhett D.; Ranawana, Kithsiri B.; Xu, Cheng; Lai, Ren; Chen, Jin
• Is Part Of: Ecology and evolution. Volume 7:Issue 18(2017:Oct.)
• Page Start: 7560
• Page End: 7572
• Publication Date: 2017-08-15
• Subjects: conspicuousness -- Danainae -- fitness -- mimicry -- toxicity -- warning signals; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.3221
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: It is widely believed that aposematic signals should be conspicuous, but in nature, they vary from highly conspicuous to near cryptic. Current theory, including the honest signal or trade‐off hypotheses of the toxicity–conspicuousness relationship, cannot explain why adequately toxic species vary substantially in their conspicuousness. Through a study of similarly toxic Danainae (Nymphalidae) butterflies and their mimics that vary remarkably in their conspicuousness, we show that the benefits of conspicuousness vary along a gradient of predation pressure. Highly conspicuous butterflies experienced lower avian attack rates when background predation pressure was low, but attack rates increased rapidly as background predation pressure increased. Conversely, the least conspicuous butterflies experienced higher attack rates at low predation pressures, but at high predation pressures, they appeared to benefit from crypsis. Attack rates of intermediately conspicuous butterflies remained moderate and constant along the predation pressure gradient. Mimics had a similar pattern but higher attack rates than their models and mimics tended to imitate the signal of less attacked model species along the predation pressure gradient. Predation pressure modulated signal fitness provides a possible mechanism for the maintenance of variation in conspicuousness of aposematic signals, as well as the initial survival of conspicuous signals in cryptic populations in the process of aposematic signal evolution, and an alternative explanation for the evolutionary gain and loss of mimicry. Abstract : Toxicity independent variations of conspicuousness in aposematic signals could not be successfully explained by the available hypotheses. We used similarly toxic Danainae (Nymphalidae) butterflies and their mimics that remarkably in their conspicuousness, to test the benefits of conspicuousness along a gradient of predation pressure. Our results suggest that predation pressure modulated signal fitness provides a possible mechanism for the maintenance of the diversity in conspicuousness of aposematic signals and an alternative explanation for the evolutionary gain and loss of mimicry.