Experimental manipulation ofHeliconiuswarning patterns reduces harassment of previously mated females

Abstract

9Why warning patterns are so diverse is an enduring evolutionary problem. Because predators 10 learn to associate particular patterns with unpleasant experiences, an individual's risk of 11 predation should decrease as the local density of its warning pattern increases. Heliconius 12 butterflies, however, are known for their diversity of warning patterns, and the establishment 13 of entirely new phenotypes is difficult to explain under strict frequency-dependent selection. 14 One possibility is that during periods of relaxed selection, drift may allow new variants to rise 15 above a threshold density until mimicry selection takes over. We propose an alternative 16 hypothesis where novel pattern phenotypes arise due to a conflict of interests between the 17 sexes. It is well established that male Heliconius use warning patterns as a mating cue. This 18 will likely be beneficial to males as it will increase the efficiency of finding mates. However, 19 already mated females may suffer fitness costs if these cues lead to harassment by males 20 during oviposition or foraging. When constraints imposed by predation are locally relaxed, 21 this could lead to rapid divergence in pattern phenotypes through chase-away sexual 22 selection. To begin to test this hypothesis, we experimentally manipulated the warning 23 patterns of mated Heliconius erato demaphoon females and recorded their interactions with 24 conspecific males, and the effect of male presence on laying rate. As predicted, males 25 interacted less with mated females whose red forewing band was blacked-out, as compared to 26 control females whose warning pattern remained intact. We also show that females lay less 27 eggs in the presence of males, but we were unable to detect a significant interaction between 28 warning pattern treatment and the presence of males on female fecundity. Our results suggest 29 that male attraction to conspecific warning patterns, may impose a previously unrecognized 30 cost on Heliconius females. 31 32

The Limits of Evolutionary Convergence in Sympatry: Reproductive Interference and Historical Constraints Leading to Local Diversity in Warning Traits

“…Other mechanisms may generate gradual departure from the ancestral trait value and may also contribute to the diversity of mimetic traits: the evolution of aposematic signals in defended species away from those exhibited in Batesian mimics has been theoretically shown (Franks et al, 2009), but empirical evidence of such effect of Batesian mimicry is still lacking. Artificial modification of the warning trait of mated females has also been demonstrated to reduce harassment by males in the butterfly H. erato, and would therefore allow them to lay more eggs, suggesting that evolution of slightly divergent trait could be promoted in females (Merrill et al, 2018).…”

Heterozygote advantage and pleiotropy contribute to intraspecific color trait variability

“…For instance, heavier wood tiger moth females may be more prone to actively reject males than lighter females. Although this hypothesis should be properly tested, it has been already shown that in Lepidoptera male harassment can be costly to females (Merrill et al., 2018 ) and females actively reject males to the point they can override male preference (Chouteau et al., 2017 ). This behavioral hypothesis is also in line with the lowest yy female mate acceptance toward males carrying the W allele that lacks the deleterious elements associated with the y allele when expressed in homozygote yy males (at least for the reproductive success).…”