The conspicuousness of the toxicHeliconiusbutterflies across time and habitat

Abstract

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Light environment influences mating behaviours during the early stages of divergence in tropical butterflies

“…The differences in illuminance we measured may correlate with spectral differences; under shaded conditions, the available light may be reflected from the vegetation or from outside the path of direct sunlight, and consequently lack red wavelengths (but be rich in greenish or bluish light) [16,17]. Indeed, previous work modelling Heliconius vision suggests that red patterns are more conspicuous to Heliconius when presented in bright sunlight [41] (though whether this affects Heliconius behaviours has not previously been tested).…”

“…H. melpomene are broadly separated from H. heurippa-timareta (along with closely related H. cydno) taxa across a gradient of open to closed forest and decreasing light intensity [32,40]. These contrasting sensory environments are predicted to alter how colour patterns are perceived by butterfly visual systems [41]. While H. heurippa and H. t. linaresi are not ecologically isolated in this way, their forest habitats are highly heterogenous and Heliconius are known to settle with their wings open in more brightly illuminated 'light patches' [42].…”

True UV color vision in a butterfly with two UV opsins

“…Male H. erato butterflies evidently use their duplicated UVRh2 (violet), blue, and long wavelength opsins in the context of mate choice discrimination of 3-OHK versus non-3-OHK yellow wing colors (Finkbeiner et al 2017), an advantage predicted by modeling the discrimination abilities of H. erato males in comparison with a hypothetical male H. erato visual system in which UVRh1 takes the place of UVRh2 (Table 1) (McCulloch et al 2017). Moreover, the loss of UVRh2 protein expression in H. melpomene (which use their ancestral UVRh1 opsin and not UVRh2) may contribute to increased attempts to mate with other species due to a reduction in visual ability to recognize conspecifics (Bybee et al 2012, Dell’Aglio et al 2019). Heliconius are part of a large mimicry complex that includes both unpalatable within-genus Müllerian mimics (which display 3-OHK yellow wing pigments) and palatable Batesian mimics such as Eueides isabella (which display unknown yellow wing pigments) (Srygley and Chai 1990; Bybee et al 2012).…”

“…Early visual modeling of the Heliconius visual system suggested an additional benefit to Heliconius’ displaying 3-OHK yellow pigments on the wing: with a second UV opsin in their eyes, more colors can be discriminated among Heliconius yellows than can be discriminated among the yellows of outgroup taxa (Briscoe et al 2010). More recent work suggests Heliconius species may indeed be more conspicuous to conspecifics in their preferred habitats and light environment (Dell’Aglio et al 2018, Dell’Aglio et al 2019).…”

“…This wing pigment has evolved in Heliconius along with their duplicated UV opsins (Briscoe et al 2010), and close relatives to this genus lack both the opsin duplication and the 3-OHK wing pigment (Yuan et al 2010). It has been proposed that the second UV opsin might allow for better discrimination of yellow-winged Heliconius conspecifics from yellow-winged non-Heliconius mimics (Bybee et al 2012), perhaps because these butterflies' yellows differ with respect to UV wavelengths; recent experiments lend some support to this hypothesis (Finkbeiner et al 2017, Dell'Aglio et al 2018) but more behavioral experiments examining the functional significance of the duplicate UV opsins are needed.…”