Satoshi Kakishima

Chemical Identity of a Rotting Animal-Like Odor Emitted from the Inflorescence of the Titan Arum (Amorphophallus titanum)

The titan arum, Amorphophallus titanum, is a flowering plant with the largest inflorescence in the world. The flower emits a unique rotting animal-like odor that attracts insects for pollination. To determine the chemical identity of this characteristic odor, we performed gas chromatography-mass spectrometry-olfactometry analysis of volatiles derived from the inflorescence. The main odorant causing the smell during the flower-opening phase was identified as dimethyl trisulfide, a compound with a sulfury odor that has been found to be emitted from some vegetables, microorganisms, and cancerous wounds.

Objective Display and Discrimination of Floral Odors from Amorphophallus titanum, Bloomed on Different Dates and at Different Locations, Using an Electronic Nose

As olfactory perceptions vary from person to person, it is difficult to describe smells objectively. In contrast, electronic noses also detect smells with their sensors, but in addition describe those using electronic signals. Here we showed a virtual connection method between a human nose perceptions and electronic nose responses with the smell of standard gases. In this method, Amorphophallus titanum flowers, which emit a strong carrion smell, could objectively be described using an electronic nose, in a way resembling the skill of sommeliers. We could describe the flower smell to be close to that of a mixture of methyl mercaptan and propionic acid, by calculation of the dilution index from electronic resistances. In other words, the smell resembled that of “decayed cabbage, garlic and pungent sour” with possible descriptors. Additionally, we compared the smells of flowers which bloomed on different dates and at different locations and showed the similarity of odor intensities visually, in standard gas categories. We anticipate our assay to be a starting point for a perceptive connection between our noses and electronic noses.

Host-parasite Red Queen dynamics with phase-locked rare genotypes

Red Queen dynamics are observed in selected genotypes, whereas the rest of the genotypes remain subordinate in synchronized dynamics. Interactions between hosts and parasites have been hypothesized to cause winnerless coevolution, called Red Queen dynamics. The canonical Red Queen dynamics assume that all interacting genotypes of hosts and parasites undergo cyclic changes in abundance through negative frequency-dependent selection, which means that any genotype could become frequent at some stage. However, this prediction cannot explain why many rare genotypes stay rare in natural host-parasite systems. To investigate this, we build a mathematical model involving multihost and multiparasite genotypes. In a deterministic and controlled environment, Red Queen dynamics occur between two genotypes undergoing cyclic dominance changes, whereas the rest of the genotypes remain subordinate for long periods of time in phase-locked synchronized dynamics with low amplitude. However, introduction of stochastic noise in the model might allow the subordinate cyclic host and parasite types to replace dominant cyclic types as new players in the Red Queen dynamics. The factors that influence such evolutionary switching are interhost competition, specificity of parasitism, and degree of stochastic noise. Our model can explain, for the first time, the persistence of rare, hardly cycling genotypes in populations (for example, marine microbial communities) undergoing host-parasite coevolution.

The paradox of enrichment in phytoplankton by induced competitive interactions

The biodiversity loss of phytoplankton with eutrophication has been reported in many aquatic ecosystems, e.g., water pollution and red tides. This phenomenon seems similar, but different from the paradox of enrichment via trophic interactions, e.g., predator-prey systems. We here propose the paradox of enrichment by induced competitive interactions using multiple contact process (a lattice Lotka-Volterra competition model). Simulation results demonstrate how eutrophication invokes more competitions in a competitive ecosystem resulting in the loss of phytoplankton diversity in ecological time. The paradox is enhanced under local interactions, indicating that the limited dispersal of phytoplankton reduces interspecific competition greatly. Thus, the paradox of enrichment appears when eutrophication destroys an ecosystem either by elevated interspecific competition within a trophic level and/or destabilization by trophic interactions. Unless eutrophication due to human activities is ceased, the worlds aquatic ecosystems will be at risk.

Geographic body size variation in the periodical cicadas Magicicada: implications for life cycle divergence and local adaptation

Seven species in three species groups (Decim, Cassini and Decula) of periodical cicadas (Magicicada) occupy a wide latitudinal range in the eastern United States. To clarify how adult body size, a key trait affecting fitness, varies geographically with climate conditions and life cycle, we analysed the relationships of population mean head width to geographic variables (latitude, longitude, altitude), habitat annual mean temperature (AMT), life cycle and species differences. Within species, body size was larger in females than males and decreased with increasing latitude (and decreasing habitat AMT), following the converse Bergmanns rule. For the pair of recently diverged 13‐ and 17‐year species in each group, 13‐year cicadas were equal in size or slightly smaller on average than their 17‐year counterparts despite their shorter developmental time. This fact suggests that, under the same climatic conditions, 17‐year cicadas have lowered growth rates compared to their 13‐years counterparts, allowing 13‐year cicadas with faster growth rates to achieve body sizes equivalent to those of their 17‐year counterparts at the same locations. However, in the Decim group, which includes two 13‐year species, the more southerly, anciently diverged 13‐year species (Magicicada tredecim) was characterized by a larger body size than the other, more northerly 13‐ and 17‐year species, suggesting that local adaptation in warmer habitats may ultimately lead to evolution of larger body sizes. Our results demonstrate how geographic clines in body size may be maintained in sister species possessing different life cycles.

Infrared thermography and odour composition of the Amorphophallus gigas (Araceae) inflorescence: the cooling effect of the odorous liquid

During the second blooming of a cultivated Amorphophallus gigas Teijsm and Binnend in the Botanical Gardens of the University of Tokyo, the surface temperature of the inflorescence was measured using an infrared camera. Contrary to studies of other species in the genus Amorphophallus, the surface of the inflorescence showed only very faint thermogenesis and had a lower temperature than that of the background. This cooling effect appeared to be due to a loss of heat through evaporation, which was caused by the secretion of a very large amount of odorous liquid. Chemical analysis revealed that the major components of this liquid were acetic acid, propionic acid, butyric acid and valeric acids. The composition of the odorous liquid was slightly different between the spathe surface and the sterile appendix. The major component(s) of the odorous material from the spathe was butyric acid, and from the sterile appendix was valeric acids. These components would play dual roles of adding the characteristic smell to the inflorescence and cooling the inflorescence.

Evolutionary optimality in sex differences of longevity and athletic performances

Many sexual differences are known in human and animals. It is well known that females are superior in longevity, while males in athletic performances. Even though some sexual differences are attributed to the evolutionary tradeoff between survival and reproduction, the aforementioned sex differences are difficult to explain by this tradeoff. Here we show that the evolutionary tradeoff occurs among three components: (1) viability, (2) competitive ability and (3) reproductive effort. The sexual differences in longevity and athletic performances are attributed to the tradeoff between viability (survival) and competitive ability that belongs to the physical makeup of an individual, but not related to the tradeoff between survival and reproduction. This provides a new perspective on sex differences in human and animals: females are superior in longevity and disease recovery, while males are superior in athletic performance.

The contribution of seed dispersers to tree species diversity in tropical rainforests

Tropical rainforests are known for their extreme biodiversity, posing a challenging problem in tropical ecology. Many hypotheses have been proposed to explain the diversity of tree species, yet our understanding of this phenomenon remains incomplete. Here, we consider the contribution of animal seed dispersers to the species diversity of trees. We built a multi-layer lattice model of trees whose animal seed dispersers are allowed to move only in restricted areas to disperse the tree seeds. We incorporated the effects of seed dispersers in the traditional theory of allopatric speciation on a geological time scale. We modified the lattice model to explicitly examine the coexistence of new tree species and the resulting high biodiversity. The results indicate that both the coexistence and diversified evolution of tree species can be explained by the introduction of animal seed dispersers.

Genomic divergence and lack of introgressive hybridization between two 13-year periodical cicadas support life cycle switching in the face of climate change

Life history evolution spurred by post‐Pleistocene climatic change is hypothesized to be responsible for the present diversity in periodical cicadas (Magicicada), but the mechanism of life cycle change has been controversial. To understand the divergence process of 13‐year and 17‐year cicada life cycles, we studied genetic relationships between two synchronously emerging, parapatric 13‐year periodical cicada species in the Decim group, Magicicada tredecim and M. neotredecim. The latter was hypothesized to be of hybrid origin or to have switched from a 17‐year cycle via developmental plasticity. Phylogenetic analysis using restriction‐site‐associated DNA sequences for all Decim species and broods revealed that the 13‐year M. tredecim lineage is genomically distinct from 17‐year Magicicada septendecim but that 13‐year M. neotredecim is not. We detected no significant introgression between M. tredecim and M. neotredecim/M. septendecim thus refuting the hypothesis that M. neotredecim are products of hybridization between M. tredecim and M. septendecim. Further, we found that introgressive hybridization is very rare or absent in the contact zone between the two 13‐year species evidenced by segregation patterns in single nucleotide polymorphisms, mitochondrial lineage identity and head width and abdominal sternite colour phenotypes. Our study demonstrates that the two 13‐year Decim species are of independent origin and nearly completely reproductively isolated. Combining our data with increasing observations of occasional life cycle change in part of a cohort (e.g. 4‐year acceleration of emergence in 17‐year species), we suggest a pivotal role for developmental plasticity in Magicicada life cycle evolution.

Evolution of periodicity in periodical cicadas

Periodical cicadas (Magicicada spp.) in the USA are famous for their unique prime-numbered life cycles of 13 and 17 years and their nearly perfectly synchronized mass emergences. Because almost all known species of cicada are non-periodical, periodicity is assumed to be a derived state. A leading hypothesis for the evolution of periodicity in Magicicada implicates the decline in average temperature during glacial periods. During the evolution of periodicity, the determinant of maturation in ancestral cicadas is hypothesized to have switched from size dependence to time (period) dependence. The selection for the prime-numbered cycles should have taken place only after the fixation of periodicity. Here, we build an individual-based model of cicadas under conditions of climatic cooling to explore the fixation of periodicity. In our model, under cold environments, extremely long juvenile stages lead to extremely low adult densities, limiting mating opportunities and favouring the evolution of synchronized emergence. Our results indicate that these changes, which were triggered by glacial cooling, could have led to the fixation of periodicity in the non-periodical ancestors.