Does spatial variation in predation pressure modulate selection for aposematism?

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.

Habitat heterogeneity supports day-flying Lepidoptera in oil palm plantations

“…However, Core habitats remained valuable for some species. We found higher densities of Tetragonus lycaenoides and Leptosia nina in Core habitats, likely due to their preference for dense and shady habitats (Aluthwattha et al 2017). The relationship between host-plant biomass and butterfly density was not always consistent; while both adult and larval food sources of Leptosa nina were higher in Edge habitats (Luke et al 2019), Leptosa nina density was significantly higher in Core habitats.…”

Geographic mosaic of selection by avian predators on hindwing warning colour in a polymorphic aposematic moth

“…Our experiment is among the few experimental approaches integrating community‐level interactions into the study of selection on warning signals (Mochida, 2011; Valkonen et al ., 2012; Nokelainen et al ., 2014; Aluthwattha et al ., 2017), and the first to do so on such a large geographical scale. With a wide‐ranging field experiment spanning populations varying in their degree of polymorphism, we demonstrate that local bird predators avoid locally common morphs, but also that both the strength and direction of selection on warning colour varies geographically.…”

“…Gordon et al ., 2015; Aubier and Sherratt, 2015; Holmes et al ., 2017) and experimental work (e.g. Willink et al ., 2014; Aluthwattha et al ., 2017) have identified several mechanisms that allow multiple morphs to persist, there is no conclusive evidence from the field and the relative importance of different selective agents is not well understood (Stevens and Ruxton, 2012; Chouteau et al ., 2016). Alas, there is little empirical evidence as to the role of predator communities on local or global morph frequencies of aposematic prey.…”

Phylogeny and morphology of Lasiodiplodia species associated with Magnolia forest plants

“…Elevation ranges from 709–869 m and mean temperature and precipitation are 21.0 °C and 1532 mm respectively. The wet season is from May to October while the dry season is from November to April 34,35 .…”