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| 1.
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Sato, Yukuto ; Tsurui-Sato, Kaori ; Katoh, Mitsuho ; Kimura, Ryosuke ; Tatsuta, Haruki ; Tsuji, Kazuki
概要:
Batesian mimicry is a striking example of Darwinian evolution, in which a mimetic species resembles toxic or unpalatable
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model species, thereby receiving protection from predators. In some species exhibiting Batesian mimicry, nonmimetic individuals coexist as polymorphism in the same population despite the benefits of mimicry. In a previous study, we proposed that the abundance of mimics is limited by that of the models, leading to polymorphic Batesian mimicry in the swallowtail butterfly, Papilio polytes, on the Ryukyu Islands in Japan. We found that their mimic ratios (MRs), which varied among the Islands, were explained by the model abundance of each habitat, rather than isolation by distance or phylogenetic constraint based on the mitochondrial DNA (mtDNA) analysis. In the present study, this possibility was reexamined based on hundreds of nuclear single nucleotide polymorphisms (SNPs) of 93 P. polytes individuals from five Islands of the Ryukyus. We found that the population genetic and phylogenetic structures of P. polytes largely corresponded to the geographic arrangement of the habitat Islands, and the genetic distances among island populations show significant correlation with the geographic distances, which was not evident by the mtDNA‐based analysis. A partial Mantel test controlling for the present SNP‐based genetic distances revealed that the MRs of P. polytes were strongly correlated with the model abundance of each island, implying that negative frequency‐dependent selection interacting with model species shaped and maintained the mimetic polymorphism. Taken together, our results support the possibility that predation pressure, not isolation by distance or other neutral factors, is a major driving force of evolution of the Batesian mimicry in P. polytes from the Ryukyus.
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| 2.
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Tsurui, Kaori Sato ; Sato, Yukuto ; Kato, Emi ; Katoh, Mitsuho ; Kimura, Ryosuke ; Tatsuta, Haruki ; Tsuji, Kazuki
概要:
Batesian mimicry is a well-studied adaptation for predation avoidance, in which a mimetic species resembles an unpalatab
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le model species. Batesian mimicry can be under positive selection because of the protection gained against predators, due to resemblance to unpalatable model species. However, in some mimetic species, nonmimetic individuals are present in populations, despite the benefits of mimicry. The mechanism for evolution of such mimetic polymorphism remains an open question. Here, we address the hypothesis that the abundance of mimics is limited by that of the models, leading to mimetic polymorphism. In addition, other forces such as the effects of common ancestry and/or isolation by distance may explain this phenomenon. To investigate this question, we focused on the butterfly, Papilio polytes, that exhibits mimetic polymorphism on multiple islands of the Ryukyus, Japan, and performed field surveys and genetic analysis. We found that the mimic ratio of P. polytes was strongly correlated with the model abundance observed on each of the five islands, suggesting negative frequency-dependent selection is driving the evolution of polymorphism in P. polytes populations. Molecular phylogenetic analysis indicated that the southern island populations are the major source of genetic diversity, and the middle and northern island populations arose by relatively recent migration. This view was also supported by mismatch distribution and Tajima's D analyses, suggesting a recent population expansion on the middle and northern islands, and stable population persistence on the southern islands. The frequency of the mimetic forms within P. polytes populations is thus explained by variations in the model abundance rather than by population structure. Thus, we propose that predation pressure, rather than neutral forces, have shaped the Batesian mimicry polymorphism in P. polytes observed in the Ryukyus.
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Katoh, Mitsuho ; Tatsuta, Haruki ; Tsuji, Kazuki
概要:
Wing polymorphism of butterflies provides a good system in which to study adaptation. The Asian Batesian mimic butterfly
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Papilio polytes has unmelanized, putative mimetic red spots on its black hind wings. The size of those red spots is non-heritable but it is highly polymorphic, the adaptive significance of which is unknown. We hypothesized that under strong ultraviolet (UV) irradiation, butterflies develop a wider melanized black area to protect the wings from UV damage, and as a result express smaller mimetic red spots. Our field survey on Okinawa Island revealed a negative relationship between the sizes of the red spot and the black area in the wings. The size varied seasonally and was negatively correlated with the intensity of solar UV radiation at the time of capture. Laboratory experiments revealed that the size was reduced by strong UV irradiation not only of the eggs and larvae, but also of their mothers through a putative epigenetic mechanism. The flexible phenotypic expression of the red spots in P. polytes suggests a trade-off between protection against UV damage and predation avoidance, and provides a new insight into the evolution of Batesian mimicry.
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Katoh, Mitsuho ; Tatsuta, Haruki ; Tsuji, Kazuki
概要:
Batesian mimicry, a phenomenon in which harmless organisms resemble harmful or unpalatable species, has been extensively
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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.
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立田, 晴記 ; Tatsuta, Haruki
概要:
科研費番号: 19570099
2007年度～2009年度科学研究費補助金（基盤研究(Ｃ)）研究成果報告書 研究概要（和文）：染色体構造に多様な地域変異を有するフキバッタ亜科の1属であるPodisma属昆虫2種を材料に， … 染色体レースの空間分布状況の把握，地域集団が有する遺伝子型の特徴，また地域分化が生じた歴史的プロセスの解明を行った．北海道に分布するサッポロフキバッタでは，染色体レース間の交雑帯は存在したとしても非常に狭いこと（３ｋｍ以内），またクサツフキバッタの遺伝構造解析からは，地理的に近接していても遺伝子型の構成が類似していない場合があることが明らかになった． 研究概要（英文） : This study aimed to understand fine-scale spatial distributions of different chromosomal races and spatial variation of genetic structure in the two Podisma species distributed in Japan. As for the study of P. sapporensis in Hokkaido, intimate field studies have revealed that the envelope of the hybrid zone between different chromosomal races, if ever, will be so narrow (i.e. <3km). Landscape genetic studies on the populations of P. kanoi demonstrated that the degree of genetic differentiation between localities is not necessarily correlated with geographic distance. 研究報告書 続きを見る |
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Yanagisawa, Ryuhei ; Suwa, Ryuichi ; Takanashi, Takuma ; Tatsuta, Haruki
概要:
Managing pests with insecticides is probably the most conventional available control method. However, insecticide overus
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e often results in resistance and subsequent pest resurgence, and often adversely affects the ecosystem. The physical management of insect pests by utilizing substrate-borne vibrations, sounds, or both is increasingly attracting attention as an alternative, as it has modest ecosystem impacts. This method exploits vibroacoustic insect communication used for mating and the perception of approaching enemies, provoking behavioral responses in an ingenious manner. We aimed to examine whether substrate-borne vibrations effectively drive away tobacco whiteflies [Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae)], which are serious agricultural pests. To do so, B. tabaci individuals were artificially introduced into greenhouses where tomato (Solanum lycopersicum L.) plants were reared. A substantial reduction in the average density of B. tabaci nymphs and adults was achieved by transmitting vibrational stimuli to the plants. At the same time, no obvious reduction was found in the number of tomato plant flowers. Although the performance of the vibrational device and transmission procedures requires further improvement, the present results shed light on the potential of substrate-borne vibrations as a promising alternative for pest management.
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