Yuya Fukano

Understanding and monitoring the consequences of human impacts on intraspecific variation

Intraspecific variation is a major component of biodiversity, yet it has received relatively little attention from governmental and nongovernmental organizations, especially with regard to conservation plans and the management of wild species. This omission is ill‐advised because phenotypic and genetic variations within and among populations can have dramatic effects on ecological and evolutionary processes, including responses to environmental change, the maintenance of species diversity, and ecological stability and resilience. At the same time, environmental changes associated with many human activities, such as land use and climate change, have dramatic and often negative impacts on intraspecific variation. We argue for the need for local, regional, and global programs to monitor intraspecific genetic variation. We suggest that such monitoring should include two main strategies: (i) intensive monitoring of multiple types of genetic variation in selected species and (ii) broad‐brush modeling for representative species for predicting changes in variation as a function of changes in population size and range extent. Overall, we call for collaborative efforts to initiate the urgently needed monitoring of intraspecific variation.

Changes in defense of an alien plant Ambrosia artemisiifolia before and after the invasion of a native specialist enemy Ophraella communa.

The evolution of increased competitive ability hypothesis (EICA) predicts that when alien plants are free from their natural enemies they evolve lower allocation to defense in order to achieve a higher growth rate. If this hypothesis is true, the converse implication would be that the defense against herbivory could be restored if a natural enemy also becomes present in the introduced range. We tested this scenario in the case of Ambrosia artemisiifolia (common ragweed) – a species that invaded Japan from North America. We collected seeds from five North American populations, three populations in enemy free areas of Japan and four populations in Japan where the specialist herbivore Ophraella communa naturalized recently. Using plants grown in a common garden in Japan, we compared performance of O. communa with a bioassay experiment. Consistent with the EICA hypothesis, invasive Japanese populations of A. artemisiifolia exhibited a weakened defense against the specialist herbivores and higher growth rate than native populations. Conversely, in locations where the herbivore O. communa appeared during the past decade, populations of A. artemisiifolia exhibited stronger defensive capabilities. These results strengthen the case for EICA and suggest that defense levels of alien populations can be recuperated rapidly after the native specialist becomes present in the introduced range. Our study implies that the plant defense is evolutionary labile depending on plant-herbivore interactions.

Mate preference in males of the cabbage butterfly, Pieris rapae crucivora, changes seasonally with the change in female UV color

Abstract We initially investigated whether females of the cabbage butterfly, Pieris rapae crucivora, exhibit a seasonal change in ultraviolet wing color, which is a key stimulus for mate recognition by conspecific males, and whether and how a seasonal change affects the mating behavior of the males. We found that female UV wing color changes seasonally, the color being more pronounced in summer than in spring or autumn. We also demonstrated that male mate preference changes seasonally, concomitantly with the change in female UV color. Specifically, males appearing in summer exhibit a mating preference for summer-form females over spring- or autumn-form females, while those appearing in spring or autumn exhibit no seasonal preference, thereby facilitating more effective mate location. Our results suggest that this field of study will require more strictly controlled experimental investigation in which the seasonal change in UV color is considered when UV-influenced mating behaviors such as mate choice are investigated.

Geographic Variation in Ultraviolet Reflectance of the Wings of the Female Cabbage Butterfly, Pieris rapae

Abstract The British and Japanese subspecies of the cabbage butterfly, Pieris rapae, differ in terms of the UV reflectance of their wings (Obara and Majerus, 2000). We studied the biogeographical distribution of the female cabbage butterfly having wings with UV reflectance around the Eurasian continent, and between Britain and Japan. For the study, we collected specimens from various locations. A gradient in the UV reflectance of the wings appears to exist along the west-east axis; reflectance was higher toward the east and reached a peak in butterflies in Japan. The UV-reflecting Japanese subspecies Pieris rapae crucivora was found exclusively along the east coast of the Eurasian continent. This suggests that the Japanese subspecies has evolved from a continental ancestor, with females having UV-absorbing wings. We discuss the results of our study with regard to the evolution and adaptive significance of UV coloration in the Japanese subspecies.

Contemporary evolution of host plant range expansion in an introduced herbivorous beetle Ophraella communa

Host range expansion of herbivorous insects is a key event in ecological speciation and insect pest management. However, the mechanistic processes are relatively unknown because it is difficult to observe the ongoing host range expansion in natural population. In this study, we focused on the ongoing host range expansion in introduced populations of the ragweed leaf beetle, Ophraella communa, to estimate the evolutionary process of host plant range expansion of a herbivorous insect. In the native range of North America, O. communa does not utilize Ambrosia trifida, as a host plant, but this plant is extensively utilized in the beetles introduced range. Larval performance and adult preference experiments demonstrated that native O. communa beetles show better survival on host plant individuals from introduced plant populations than those from native plant populations and they also oviposit on the introduced plant, but not on the native plant. Introduced O. communa beetles showed significantly higher performance on and preference for both introduced and native A. trifida plants, when compared with native O. communa. These results indicate the contemporary evolution of host plant range expansion of introduced O. communa and suggest that the evolutionary change of both the host plant and the herbivorous insect involved in the host range expansion.

Serotonin-induced mate rejection in the female cabbage butterfly, Pieris rapae crucivora

Virgin female cabbage butterflies, Pieris rapae crucivora, accept and mate with courting males, whereas mated females reject them and assume the “mate refusal posture”. This study tested whether the biogenic amines, serotonin (5HT), dopamine (DA), and octopamine (OA), were responsible for this change in behavior. The results showed that 2–3-day-old virgin females fed with 5HT rejected courting males significantly more frequently compared with controls fed on sucrose. In contrast, the proportions of courting males rejected by virgin females fed with either DA or OA did not differ from sucrose-fed controls. Oral application of each amine resulted in significantly increased levels of the amine applied (or its metabolite) in the brain. The results strongly suggest that 5HT or a 5HT metabolite may be responsible for the post-mating change in behavioral response of 2–3-day-old virgin females to courting males. Similar effects of 5HT treatment were observed in 6–8-day-old virgin females, but in this case the results were only marginally different from the controls, suggesting that the effect may decline with increasing female age.

Self-discrimination in the tendrils of the vine Cayratia japonica is mediated by physiological connection.

Although self-discrimination has been well documented, especially in animals, self-discrimination in plants has been identified in only a few cases, such as self-incompatibility in flowers and root discrimination. Here, we report a new form of self-discrimination in plants: discrimination by vine tendrils. We found that tendrils of the perennial vine Cayratia japonica were more likely to coil around neighbouring non-self plants than neighbouring self plants in both experimental and natural settings. The higher level of coiling around a physiologically severed self plant compared with that around a physiologically connected self plant suggested that self-discrimination was mediated by physiological coordination between the tendril and the touched plant as reported for self-discrimination in roots. The results highlight the importance of self-discrimination for plant competition not only underground, but also above-ground.

Population abundance and host use pattern of Ophraella communa (Coleoptera: Chrysomelidae) in its native and introduced range

Abstract We found that the abundance of Ophraella communa, a specialist herbivore of the invasive weeds Ambrosia artemisiifolia and A. trifida, is higher in the introduced range than in its native range. We also found that the native O. communa does not feed on A. trifida, but introduced O. communa does so extensively.

Geographic expansion of the cabbage butterfly (Pieris rapae) and the evolution of highly UV-reflecting females

Abstract  Reflection of ultraviolet (UV) light by the wings of the female Eurasian cabbage butterfly, Pieris rapae, shows a large geographic variation. The wings of the female of the European subspecies, P. rapae rapae, reflect little UV light, while butterflies of the Asian subspecies, P. rapae crucivora, may reflect it strongly or at only intermediate levels. The geographic region where P. rapae originated remains to be determined. Moreover, it is not clear if females with wings that reflect little UV light are ancestral to females with wings that reflect UV strongly or vice versa. In the present study, we aimed to determine the geographic origin and ancestral UV pattern of cabbage butterflies through mitochondrial DNA (mtDNA) sequence analysis and amplified fragment length polymorphism (AFLP) analysis. The results of these investigations suggest that P. rapae is of European origin and that it has expanded its distribution eastward to Asia. It follows that the ancestral subspecies is the type with UV‐absorbing wings. Lower nucleotide diversities and haplotype network patterns of mtDNA derived from East Asian populations suggest that population expansion from Europe to East Asia probably occurred fairly recently and at a rapid rate.

Flower-Visiting Butterflies Avoid Predatory Stimuli and Larger Resident Butterflies: Testing in a Butterfly Pavilion

The flower-visiting behaviors of pollinator species are affected not only by flower traits but also by cues of predators and resident pollinators. There is extensive research into the effects of predator cues and resident pollinators on the flower-visiting behaviors of bee pollinators. However, there is relatively little research into their effects on butterfly pollinators probably because of the difficulty in observing a large number of butterfly pollination events. We conducted a dual choice experiment using artificial flowers under semi-natural conditions in the butterfly pavilion at Tama Zoological Park to examine the effects of the presence of a dead mantis and resident butterflies have on the flower-visiting behavior of several butterfly species. From 173 hours of recorded video, we observed 3235 visitations by 16 butterfly species. Statistical analysis showed that (1) butterflies avoided visiting flowers occupied by a dead mantis, (2) butterflies avoided resident butterflies that were larger than the visitor, and (3) butterflies showed greater avoidance of a predator when the predator was present together with the resident butterfly than when the predator was located on the opposite flower of the resident. Finally, we discuss the similarities and differences in behavioral responses of butterfly pollinators and bees.