Rapid evolution of a Batesian mimicry trait in a butterfly responding to arrival of a new model

Abstract

Batesian mimicry, a phenomenon in which harmless organisms resemble harmful or unpalatable species, has been extensively studied in evolutionary biology. Model species may differ from population to population of a single mimetic species, so different predation pressures might have driven micro-evolution towards better mimicry among regions. However, there is scant direct evidence of micro-evolutionary change over time in mimicry traits. Papilio polytes shows female-limited Batesian mimicry. On Okinawa, one mimicry model is Pachliopta aristolochiae, which was not present on the island until 1993. In P. polytes, the size of the hind-wing white spot, a mimetic trait, is maternally heritable. Among specimens collected between 1961 and 2016, the average white spot size was unchanged before the model’s arrival but has rapidly increased since then. However, white spot size showed greater variance after the model’s establishment than before. This suggests that before 1993, white spot size in this population was not selectively neutral but was an adaptive trait for mimicking an unpalatable native, Byasa alcinous, which looks like P. aristolochiae apart from the latter’s hind-wing white spot. Thus, some females switched their model to the new one after its arrival.

Evidence for frequency‐dependent selection maintaining polymorphism in the Batesian mimic Papilio polytes in multiple islands in the Ryukyus, Japan

“…In spite of the migration and gene flow, maintenance of a larger proportion of mimetic females is allowed by the greater local abundance of the model species (see Figures b and , Table ), and the observed MR differentiation cannot be explained by genetic, geographic, or environmental distance (see Figure , Table ). Based on these findings, we propose that the strong predation pressure on this butterfly (Katoh et al, ), rather than isolation by distance or other neutral processes, has shaped and maintained the Batesian mimicry patterns of P. polytes observed in the Ryukyu Islands.…”

“…The strength of the predation pressure can be estimated from beak marks (e.g., Ohsaki, ), and that on mimetic females of P. polytes seems to depend upon the abundance of the model species in the Ryukyu Islands (data not shown). Furthermore, Katoh et al () reported recent changes in wing coloration pattern in mimetic females of P. polytes with emergence of new variations of mimetic patterns of the same form in the Ryukyu Islands, suggesting that P. polytes appears to be under constant predation pressure. These data support our view that predation pressure combined with model species abundance determines the MR of P. polytes females.…”

“…Papilio polytes L., a swallowtail butterfly that is common throughout Southeast Asia, exhibits female‐limited Batesian mimicry (Clarke & Sheppard, ; Katoh, Tatsuta, & Tsuji, ; Kunte et al, ; Figure a). Some of the females mimic other unpalatable butterflies in the family Papilionidae , as a defense against avian predators (Ford, ).…”

“…The nonmimetic females resemble the males (Figure a). On several of the Ryukyu Islands in Japan, female P. polytes appear to mimic Pachliopta aristolochiae (Katoh et al, ; Uesugi, ). Interestingly, the MR of these P. polytes populations is higher on islands with greater abundance of the model species (Uesugi, ), implying that NFDS underlies the mimicry patterns.…”

“…In this study, we assess the possible association between the MR of P. polytes and the abundance of the model species in the Ryukyu Islands. Subsequent to a previous study of these two factors performed in 1982 (Uesugi, ), the distribution of the model species P. aristolochiae has expanded (Katoh et al, ). Therefore, the present investigation of P. polytes and P. aristolochiae in the Ryukyu Islands provides a powerful opportunity to address the microevolution of polymorphic Batesian mimicry in P. polytes populations.…”