Practical Basis of the Geometric Mean Fitness and its Application to Risk-Spreading Behavior.

Temporal variations in population size under unpredictable environments are of primary concern in evolutionary ecology, where time scale enters as an important factor while setting up an optimization problem. Thus, short-term optimization with traditional (arithmetic) mean fitness may give a different result from long-term optimization. In the long-term optimization, the concept of geometric mean fitness has been received well by researchers and applied to various problems in ecology and evolution. However, the limit of applicability of geometric mean has not been addressed so far. Here we investigate this problem by analyzing numerically the probability distribution of a random variable obeying stochastic multiplicative growth. According to the law of large number, the expected value (i.e., arithmetic mean) manifests itself as a proper measure of optimization as the number of random processes increases to infinity. We show that the finiteness of this number plays a crucial role in arguing for the relevance of geometric mean. The geometric mean provides a satisfactory picture of the random variation in a long term above a crossover time scale that is determined by this number and the standard deviation of the randomly varying growth rates. We thus derive the applicability condition under which the geometric mean fitness is valid. We explore this condition in some examples of risk-spreading behavior.

Tree hazards compounded by successive climate extremes after masting in a small endemic tree, Distylium lepidotum, on subtropical islands in Japan.

Ongoing global warming increases the frequency and severity of tropical typhoons and prolonged drought, leading to forest degradation. Simultaneous and/or successive masting events and climatic extremes may thus occur frequently in the near future. If these climatic extremes occur immediately after mass seed reproduction, their effects on individual trees are expected to be very severe because mass reproduction decreases carbohydrate reserves. While the effects of either a single climate extreme or masting alone on tree resilience/growth have received past research attention, understanding the cumulative effects of such multiple events remains challenging and is crucial for predicting future forest changes. Here, we report tree hazards compound by two successive climate extremes, a tropical typhoon and prolonged drought, after mass reproduction in an endemic tree species (Distylium lepidotum Nakai) on oceanic islands. Across individual trees, the starch stored within the sapwood of branchlets significantly decreased with reproductive efforts (fruit mass/shoot mass ratio). Typhoon damage significantly decreased not only the total leaf area of apical shoots but also the maximum photosynthetic rates. During the 5-month period after the typhoon, the mortality of large branchlets (8-10-mm diameter) increased with decreasing stored starch when the typhoon hit. During the prolonged summer drought in the next year, the recovery of total leaf area, stored starch, and hydraulic conductivity was negatively correlated with the stored starch at the typhoon. These data indicate that the level of stored starch within branchlets is the driving factor determining tree regrowth or dieback, and the restoration of carbohydrates after mass reproduction is synergistically delayed by such climate extremes. Stored carbohydrates are the major cumulative factor affecting individual tree resilience, resulting in their historical effects. Because of highly variable carbohydrate levels among individual trees, the resultant impacts of such successive events on forest dieback will be fundamentally different among trees.

Two-step mechanism of spiral phyllotaxis.

Fibonacci numbers such as 5, 8, and 13 occur in the spiral arrangement of lateral organs at shoot tips in plants. While the cone scales of conifers are normally arranged in 5 and 8 (or 8 and 13) curved rows in opposite directions, other numbers such as 4 and 7 (or 7 and 11) are found anomalously. The observed numbers still obey the Fibonacci rule, with the next number being the sum of the preceding two. Although these observations have been made for centuries, the underlying mechanisms of the numerical relationship have not been investigated. Here, we show that this phenomenon is caused by a two-step mechanism: (1) maintenance of a constant angle between consecutive lateral organs and (2) strong canalization of this angle to a specific value. The first step of the mechanism precedes the second step of the mechanism because the Fibonacci-rule pattern is due to the first step, while the second step distinguishes normal, anomalous and unobserved types. The current dominance of the normal type is a result of the evolutionary process of the second step.

Analysis of molecular mechanism for acceleration of polyembryony using gene functional annotation pipeline in Copidosoma floridanum.

BACKGROUND: Polyembryony is defined as the formation of several embryos from a single egg. This phenomenon can occur in humans, armadillo, and some endoparasitoid insects. However, the mechanism underlying polyembryogenesis in animals remains to be elucidated. The polyembryonic parasitoid wasp Copidosoma floridanum oviposits its egg into an egg of the host insect; eventually, over 2000 individuals will arise from one egg. Previously, we reported that polyembryogenesis is enhanced when the juvenile hormone (JH) added to the culture medium in the embryo culture. Hence, in the present study, we performed RNA sequencing (RNA-Seq) analysis to investigate the molecular mechanisms controlling polyembryogenesis of C. floridanum. Functional annotation of genes is not fully available for C.floridanum; however, whole genome assembly has been archived. Hence, we constructed a pipeline for gene functional annotation in C. floridanum and performed molecular network analysis. We analyzed differentially expressed genes between control and JH-treated molura after 48 h of culture, then used the tblastx program to assign whole C. floridanum transcripts to human gene. RESULTS: We obtained 11,117 transcripts in the JH treatment group and identified 217 differentially expressed genes compared with the control group. As a result, 76% of C. floridanum transcripts were assigned to human genes. Gene enrichment analysis revealed genes associated with platelet degranulation, fatty acid biosynthesis, cell morphogenesis in the differentiation and integrin signaling pathways were fluctuated following JH treatment. Furthermore, Cytoscape analysis revealed a molecular interaction that was possibly associated with polyembryogenesis . CONCLUSIONS: We have constructed a pipeline for gene functional annotation of C. floridanum, and identified transcripts with high similarity to human genes during early embryo developmental. Additionally, this study reveals new molecular interactions associated with polyembryogenesis; these interactions could indicate the molecular mechanisms underlying polyembryony. Our results highlight the potential utility of molecular interaction analysis in human twins.

Mitochondrial Genomics Reveals Shared Phylogeographic Patterns and Demographic History among Three Periodical Cicada Species Groups.

The mass application of whole mitogenome (MG) sequencing has great potential for resolving complex phylogeographic patterns that cannot be resolved by partial mitogenomic sequences or nuclear markers. North American periodical cicadas (Magicicada) are well known for their periodical mass emergence at 17- and 13-year intervals in the north and south, respectively. Magicicada comprises three species groups, each containing one 17-year species and one or two 13-year species. Within each life cycle, single-aged cohorts, called broods, of periodical cicadas emerge in different years, and most broods contain members of all three species groups. There are 12 and three extant broods of 17- and 13-year cicadas, respectively. The phylogeographic relationships among the populations and broods within the species groups have not been clearly resolved. We analyzed 125 whole MG sequences from all broods and seven species within three species groups to ascertain the divergence history of the geographic and allochronic populations and their life cycles. Our mitogenomic phylogeny analysis clearly revealed that each of the three species groups had largely similar phylogeographic subdivisions (east, middle, and west) and demographic histories (rapid population expansion after the last glacial period). The mitogenomic phylogeny also partly resolved the brood diversification process, which could be explained by hypothetical temporary life cycle shifts, and showed that none of the 13- and 17-year species within the species groups was monophyletic, possibly due to gene flow between them. Our findings clearly reveal phylogeographic structures in the three Magicicada species groups, demonstrating the advantage of whole MG sequence data in phylogeographic studies.

Bet-hedging against male-caused reproductive failures may explain ubiquitous cuckoldry in female birds.

The origin and maintenance of polyandry is one of the key unresolved questions in evolutionary biology. In particular, extra-pair paternity (EPP) due to polyandry is observed in most (socially-) monogamous female birds and the frequency of EPP is surprisingly high (up to 72% in a clutch on average in some species). Many case-by-case hypotheses have been presented to explain this phenomenon but a ubiquitous explanation is still lacking. One possible general explanation is bet-hedging, which is a strategy to avoid the risk associated to mating with a single unsuitable male and thus to minimize the chances of complete reproductive failure by the female. Here, we present a mathematical solution to demonstrate that bet-hedging polyandry becomes highly effective if the risk of extinction of a female lineage attributable to male deficiencies is high in small subpopulation or under limited mate availability. Therefore, cuckoldry or polyandry may be a female strategy to spread the risk of extinction of her genotype over multiple males. The results agree well with the observed EPP frequencies in natural populations and the results of a meta-population simulation model. Our theory contributes new insights applicable not only to birds but also to a broad taxonomic range of animals.

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.

Independent divergence of 13- and 17-y life cycles among three periodical cicada lineages.

The evolution of 13- and 17-y periodical cicadas (Magicicada) is enigmatic because at any given location, up to three distinct species groups (Decim, Cassini, Decula) with synchronized life cycles are involved. Each species group is divided into one 13- and one 17-y species with the exception of the Decim group, which contains two 13-y species-13-y species are Magicicada tredecim, Magicicada neotredecim, Magicicada tredecassini, and Magicicada tredecula; and 17-y species are Magicicada septendecim, Magicicada cassini, and Magicicada septendecula. Here we show that the divergence leading to the present 13- and 17-y populations differs considerably among the species groups despite the fact that each group exhibits strikingly similar phylogeographic patterning. The earliest divergence of extant lineages occurred ∼4 Mya with one branch forming the Decim species group and the other subsequently splitting 2.5 Mya to form the Cassini and Decula species groups. The earliest split of extant lineages into 13- and 17-y life cycles occurred in the Decim lineage 0.5 Mya. All three species groups experienced at least one episode of life cycle divergence since the last glacial maximum. We hypothesize that despite independent origins, the three species groups achieved their current overlapping distributions because life-cycle synchronization of invading congeners to a dominant resident population enabled escape from predation and population persistence. The repeated life-cycle divergences supported by our data suggest the presence of a common genetic basis for the two life cycles in the three species groups.

Evolutionary trajectories explain the diversified evolution of isogamy and anisogamy in marine green algae.

The evolution of anisogamy (the production of gametes of different size) is the first step in the establishment of sexual dimorphism, and it is a fundamental phenomenon underlying sexual selection. It is believed that anisogamy originated from isogamy (production of gametes of equal size), which is considered by most theorists to be the ancestral condition. Although nearly all plant and animal species are anisogamous, extant species of marine green algae exhibit a diversity of mating systems including both isogamy and anisogamy. Isogamy in marine green algae is of two forms: isogamy with extremely small gametes and isogamy with larger gametes. Based on disruptive selection for fertilization success and zygote survival (theory of Parker, Baker, and Smith), we explored how environmental changes can contribute to the evolution of such complex mating systems by analyzing the stochastic process in the invasion simulations of populations of differing gamete sizes. We find that both forms of isogamy can evolve from other isogamous ancestors through anisogamy. The resulting dimensionless analysis accounts for the evolutionary stability of all types of mating systems in marine green algae, even in the same environment. These results imply that evolutionary trajectories as well as the optimality of gametes/zygotes played an important role in the evolution of gamete size.

Sex differences in the protection of host immune systems by a polyembryonic parasitoid.

Endoparasitoids have the ability to evade the cellular immune responses of a host and to create an environment suitable for survival of their progeny within a host. Generally, the host immune system is suppressed by endoparasitoids. However, polyembryonic endoparasitoids appear to invade their hosts using molecular mimicry rather than immune system suppression. It is not known how the host immune system is modified by polyembryonic endoparasitoids. Using haemocyte counts and measurement of cellular immune responses, we evaluated modification of the host immune system after separate infestations by a polyembryonic parasitoid (Copidosoma floridanum) and another parasitoid (Glyptapanteles pallipes) and by both together (multi-parasitism). We found that the polyembryonic parasitoid maintains and enhances the host immune system, whereas the other parasitoid strongly suppresses the immune system. Multi-parasitization analysis revealed that C. floridanum cancelled the immune suppression by G. pallipes and strengthened the host immunity. This enhancement was much stronger with male than with female C. floridanum.

Comparative physiology of canopy tree leaves in evergreen and deciduous forests in lowland Thailand.

The typical seasonally dry forests in Southeast Asia are the mixed deciduous forest (MDF), dry dipterocarp (deciduous) forest (DDF), and dry evergreen forest (DEF). We obtained 21 physiological traits in the top/sunlit leaves of 107, 65 and 51 tree species in MDF, DEF and DDF, respectively. Approximately 70%, 95% and 95% of canopy tree species which consist of MDF, DEF and DDF are sampled, respectively. Light-saturated photosynthetic rates (Asat) exhibit a positive correlation with foliar nitrogen (N) and phosphorus (P) on leaf mass and area bases across tree species. Decreased leaf mass-based P reduces the positive slope of the mass-based N and Asat relationship across species and habitats. The differences in nutrient and water use and leaf habits are well matched to the variation in soil properties among the forest types, highlighting the reliability of this comprehensive database for revealing the mechanism of niche segregation based on edaphic factors.

Allee effect in the selection for prime-numbered cycles in periodical cicadas.

Periodical cicadas are well known for their prime-numbered life cycles (17 and 13 years) and their mass periodical emergences. The origination and persistence of prime-numbered cycles are explained by the hybridization hypothesis on the basis of their lower likelihood of hybridization with other cycles. Recently, we showed by using an integer-based numerical model that prime-numbered cycles are indeed selected for among 10- to 20-year cycles. Here, we develop a real-number-based model to investigate the factors affecting the selection of prime-numbered cycles. We include an Allee effect in our model, such that a critical population size is set as an extinction threshold. We compare the real-number models with and without the Allee effect. The results show that in the presence of an Allee effect, prime-numbered life cycles are most likely to persist and to be selected under a wide range of extinction thresholds.

A new long-term measure of sustainable growth under uncertainty.

The trade-off between short-term success and long-term sustainability is a common subject of great importance both in the biological evolution of organisms and in the economic activities of human beings. In evolutionary biology, bet-hedging theories have described it as the trade-off between the (within-generation) arithmetic mean fitness and the (between-generation) geometric mean fitness of a genotype. Accordingly, bet-hedging strategies observed in various organisms are regarded as optimizing the geometric mean fitness. To increase the geometric mean fitness signifies to suppress the between-generation variance in the mean fitness. Thus, this view is consistent with mean-variance portfolio analysis in which the standard deviation of a portfolio is regarded as a measure of risk. In the present study, we provide yet another measure of long-term sustainability, which is based on minimization of the probability of extinction/bankruptcy that randomly varying population/asset size after a long time becomes less than a certain small value. We present results for representative examples to show that the present criterion gives a qualitatively similar but quantitatively different prediction from the traditional ones. In particular, we emphasize that maximizing survival probability (i.e. minimizing extinction probability) is equivalent neither to maximizing geometric mean fitness nor to minimizing variance in mean fitness, while these three are consistently related to each other.

Fresh-marketable tomato yields enhanced by moderate weed control and suppressed fruit dehiscence with woodchip mulching.

The use of plastic film imposes various environmental risks in agroecosystems. The replacement of plastics with organic materials for mulching has been suggested to enhance the sustainability of agroecosystems. However, whether woodchip mulch can be used for annual crops needs to be verified. We examined the effects of mulberry woodchip mulches on tomato-fruit yields over two successive years. Mulberry is the unique food plant of silkworms, and it will be better if its pruned shoots can be recycled rather than incinerated as waste. Setting three treatments, including woodchip mulch, weed-free and weedy (i.e., unweeded) treatments, we compared the amounts of fresh-marketable and unmarketable tomato fruits. The yields of fresh-marketable tomato fruits in the woodchip mulch treatment were significantly 16-57% higher than those in the weed-free treatment and comparable to those in the weedy treatment. The yields of unmarketable dehiscent tomato fruits in the weed-free treatment were significantly 46-86% higher than those of the other two treatments. The woodchip mulches extensively suppressed the weed density, while the grown weeds became large, preventing strong sunlight exposure and dehiscence of tomato fruits. Current results suggest that woodchips could be a possible alternative to plastics, facilitating climate change mitigation with agroforestry practices.

Social dilemma in the excess use of antimicrobials incurring antimicrobial resistance.

The emergence of antimicrobial resistance (AMR) caused by the excess use of antimicrobials has come to be recognized as a global threat to public health. There is a 'tragedy of the commons' type social dilemma behind this excess use of antimicrobials, which should be recognized by all stakeholders. To address this global threat, we thus surveyed eight countries/areas to determine whether people recognize this dilemma and showed that although more than half of the population pays little, if any, attention to it, almost 20% recognize this social dilemma, and 15-30% of those have a positive attitude toward solving that dilemma. We suspect that increasing individual awareness of this social dilemma contributes to decreasing the frequency of AMR emergencies.

Optimal strategies and cost-benefit analysis of the [Formula: see text]-player weightlifting game.

The study of cooperation has been extensively studied in game theory. Especially, two-player two-strategy games have been categorized according to their equilibrium strategies and fully analysed. Recently, a grand unified game covering all types of two-player two-strategy games, i.e., the weightlifting game, was proposed. In the present study, we extend this two-player weightlifting game into an [Formula: see text]-player game. We investigate the conditions for pure strategy Nash equilibria and for Pareto optimal strategies, expressed in terms of the success probability and benefit-to-cost ratio of the weightlifting game. We also present a general characterization of [Formula: see text]-player games in terms of the proposed game. In terms of a concrete example, we present diagrams showing how the game category varies depending on the benefit-to-cost ratio. As a general rule, cooperation becomes difficult to achieve as group size increases because the success probability of weightlifting saturates towards unity. The present study provides insights into achieving behavioural cooperation in a large group by means of a cost-benefit analysis.

A geographic cline induced by negative frequency-dependent selection.

BACKGROUND: Establishment of geographic morph frequency clines is difficult to explain in organisms with limited gene flow. Balancing selection, such as negative frequency-dependent selection (NFDS), is instead suggested to establish a morph frequency cline on a geographic scale at least theoretically. Here we tested whether a large-scale smooth cline in morph frequency is established by NFDS in the female-dimorphic damselfly, Ischnura senegalensis, where andromorphs and gynomorphs are maintained by NFDS. RESULTS: We found a large-scale latitudinal cline in the morph frequency: andromorph frequency ranged from 0.05 (South) to 0.79 (North). Based on the empirical data on the numbers of eggs, the number of ovariole, abdomen length and latitude, the potential fitness of andromorphs was estimated to be lower than that of gynomorphs in the south, and higher in the north, suggesting the gene-by-environment interaction. From the morph-specific latitudinal cline in potential fitness, the frequency of andromorphs was expected to shift from 0 to 1 without NFDS, because a morph with higher potential fitness wins completely and the two morphs will switch at some point. In contrast, NFDS led to the coexistence of two morphs with different potential fitness in a certain geographic range along latitude due to rare morph advantage, and resulted in a smooth geographic cline of morph frequency. CONCLUSION: Our results provide suggestive evidence that the combination of NFDS and gene-by-environment interaction, i.e., multi-selection pressure on color morphs, can explain the geographic cline in morph frequency in the current system.

Historical effect in the territoriality of ayu fish.

Ayu fish form algae-feeding territories in a river during a non-breeding (growing) season. We build a cost-benefit theory to describe the breakdown and formation of territory. In the early stage of a growing season, all fish hold territories at low densities. Once all territory sites are occupied, excess fish become floaters. When fish density further increases, a phase transition occurs: all the territories suddenly break down and fish form a school. In contrast, when the fish density is decreased, territories are suddenly formed from the school. Both theory and experiments demonstrate that ayu should exhibit a historical effect: the breakdown and formation processes of territory are largely different. In particular, the theory in formation process predicts a specific fish behavior: an "attempted territory holder" that tries to have a small territory emerges just before the formation of territory.

Eight-year periodical outbreaks of the train millipede.

Periodical cicadas are the only confirmed periodical animals with long life cycles. In Japan, however, 8-year periodicity had been suggested in a species of train millipedes that had frequently obstructed trains in the central mountainous region of Honshu, Japan. This species was identified as Parafontaria laminata armigera Verhoeff (Diplopoda: Xystodesmidae), which is endemic to Japan. We finally confirmed the 8-year periodicity of this millipede using detailed surveys of life histories over 8 years. Seven broods were recognized, with almost no overlaps in their distributions. We also report the historical outbreaks and train obstructions of this millipede during 1920-2016. This is the first confirmed case of periodical non-insect arthropods.

Life history and nesting ecology of a Japanese tube-nesting spider wasp Dipogon sperconsus (Hymenoptera: Pompilidae).

To clarify the life history of the Japanese spider wasp Dipogon sperconsus, bionomical studies using bamboo-cane trap nests were carried out in Japan. Based on weekly and consecutive daily surveys of trap nests and rearing of broods from collected nests, we evaluated the production of cells and eggs per day, prey spiders, and seasonal patterns of nesting activities. We found a relatively short critical period of switching from the summer generation into the overwintering generation. We also found that the voltinism is affected by the timing of egg production of the second generation in relation to this critical period. The developmental period for each generation and sex, voltinism and cell production per day were determined based on data for a large number of individuals for the first time.