Evolution of switchable aposematism: insights from individual-based simulations

Abstract

Some defended prey animals can switch on their normally hidden aposematic signals. This switching may occur in reaction to predators’ approach (pre-attack signals) or attack (post-attack signals). Switchable aposematism has been relatively poorly studied, but we can expect that it might bring a variety of benefits to an aposmetic organism. First, the switching could startle the predators (deimatism). Second, it could facilitate aversive learning. Third, it could minimize exposure or energetic expense, as the signal can be switched off. These potential benefits might offset costs of developing, maintaining and utilizing the switchable traits. Here we focused on the third benefit of switchability, the cost-saving aspect, and developed an individual-based computer simulation of predators and prey. In 88,128 model runs, we observed evolution of permanent, pre-attack, or post-attack aposematic signals of varying strength. We found that, in general, the pre-attack switchable aposematism may require moderate predator learning speed, high basal detectability, and moderate to high signal cost. On the other hand, the post-attack signals may arise under slow predator learning, low basal detectability and high signal cost. When predator population turnover is fast, it may lead to evolution of post-attack aposematic signals that are not conforming to the above tendency. We also suggest that a high switching cost may exert different selection pressure on the pre-attack than the post-attack switchable strategies. To our knowledge, these are the first theoretical attempts to systematically explore the evolution of switchable aposematism relative to permanent aposematism in defended prey. Our simulation model is capable of addressing additional questions beyond the scope of this article, and we open the simulation software, program manual and source code for free public use.

Multimodal Aposematic Defenses Through the Predation Sequence

“…Such warning signals may act as a primary defense if the predator has an innate color bias (Smith, 1975;Roper, 1990;Schuler and Roper, 1992;Mastrota and Mench, 1995;Lindström et al, 1999) or has learned to avoid the warning signal through prior experience (Gittleman and Harvey, 1980;Roper and Wistow, 1986;Alatalo and Mappes, 1996;Ham et al, 2006;Green et al, 2018). Conversely, warning signals may act as a secondary defense if increased predator wariness improves the chance that prey will escape or reduces harm to prey after subjugation (Halpin et al, 2008;Ruxton et al, 2018) or if the warning signal is "switchable" and only becomes apparent after the predator has engaged with the prey (Blest, 1964;Sivinski, 1981;Grober, 1988;Broom et al, 2010;Umbers and Mappes, 2015;Kang et al, 2016;Umbers et al, 2017;Song and Jablonski, 2020). Often, visual or auditory warning signals are combined with chemical defenses, which deter predators through some combination of taste (Marples et al, 1994;Rowe, 2006, 2010), smell Guilford, 1996, 1999;Lindström et al, 2001;Jetz et al, 2001;Kelly and Marples, 2004;Rojas et al, 2019), or toxicity (Cortesi and Cheney, 2010;Arenas et al, 2015).…”

Music as aposematic signal: predator defense strategies in early human evolution

“…Any animal species may display warning signals when cornered or frightened, or when they must face the attacker. A cornered rat against a cat or a cornered cat against a dog does not become an aposematic species although they display warning signals (they try to seem bigger, make loud sounds, display canines, and behave aggressively; e.g., Song et al, 2020 ). This is not an aposematic display, but a startle , or deimatic display ( Rowe and Guilford, 1999 ).…”