Behavioral sequences are chronologically ordered sets of behaviors that animals show in an event. When an interindividual interaction, such as a contest, includes a behavioral sequence, it is highly complex because the players must choose one behavior from multiple options in sequence. Animals are well known to take the most cost-effective option, but such decision-making may require high cognitive ability about the opponent and the surrounding environment. Here, we proposed an extensive-form game as an optimality model based on observed behavioral sequences and tested the model in male–male contests of Pagurus nigrofascia. These contests occur between an initial male (owner) guarding a female and a solitary male (challenger). We first modeled the observed behavioral sequences as an extensive-form game. The analysis indicated that size difference was the main predictor of the first decision of the owner. Then we evaluated this prediction using different variables extracted from the same observational data, which supported the model prediction. Behavioral sequences differ in length, complexity, or both, but extensive-form game models can be used to analyze them by adjusting the model structure and analytical method. This methodology is expected to be utilized in many fields related to ethology.
Investment in antipredator behavior and foraging both directly influence fitness, yet these investments are often subject to trade-offs. In income-breeding species, individuals may initially prioritize foraging after adult emergence and subsequently increase investment in antipredator behavior as their nutritional condition improves. In this study, we investigated temporal changes in death-feigning behavior, an antipredator response, in the red flour beetle Tribolium castaneum from immediately after adult emergence. Both fed and starved individuals exhibited an increase in death-feigning duration with time after emergence. However, in starved individuals, this trend reversed after approximately 15 days, with a marked decline in duration. These results suggest that the increase in investment in death-feigning behavior early in adulthood is relatively inflexible, whereas behavioral responses become highly plastic in response to environmental conditions around day 15. Furthermore, individuals that were fed until day 18 before starvation showed a less pronounced behavioral change than those subjected to starvation from the beginning of the experimental period, suggesting that the timing of environmental exposure may influence subsequent behavioral responses. Together, these findings suggest that behavioral plasticity is not constant over time but is instead structured across developmental stages. We propose a novel conceptual framework, termed temporally structured plasticity (TSP), to describe this pattern.
The plasmodium of Myxogastria (a group of amoeboid protists) species often crawls around the forest floor to feed while searching for places to form fruiting bodies for reproduction (sporulation). Certain environmental factors that trigger sporulation have been reported; however, other unknown factors are also expected. In this study, we reported field observations of Physarum rigidum and Fuligo septica. Inspired by the field observation, we examined the effects of multiple factors on sporulation in laboratory experiments using Physarum polycephalum. We found that: (1) there was a critical body size below which sporulation did not occur under our experimental conditions and (2) the plasmodium selected its sporulation sites from the available landscape of the experimental arena: dry and low sites for the majority and dry and high sites for the minority. Further analysis revealed that they preferred the edge area at the high site. We discuss the possible ecological importance of the threshold and location preference.
The diel activity patterns of animals vary in response to environmental conditions. The Japanese mitten crab (Eriocheir japonica) is generally considered nocturnal, but its field activity remains poorly quantified. In this study, I examined appearance patterns of this species in fixed weirs in a small river, and analyzed the relationship between their occurrence patterns and environmental factors. Feeding behavior was also frequently observed among individuals at the weirs. Crab occurrence peaked during the day, declined at twilight, and was lowest at night. Water temperature, light conditions, and the presence of the nocturnal predator American bullfrog (Lithobates catesbeianus) significantly influenced crab abundance. Reduced nocturnal activity likely reflects increased predation risk and constraints associated with lower temperature and light levels. Fixed weirs may also function as habitats that modify activity patterns. These results strongly suggest that diel activity in this species is flexible and shaped by interacting environmental factors.
Behavioural consistency in fishes reflects stable individual differences in traits such as boldness, activity, and exploration across ontogeny, while social interactions play a key role in modulating behavioural and physiological responses. This study evaluated the ontogenetic repeatability of air-breathing frequency (fAB) and the social modulation of air-breathing and antipredatory behaviour in the African catfish, Clarias gariepinus. Repeatability of fAB was quantified across 115 days spanning the fry ( 0.4 g) to sub-adult ( 175 g) developmental stages in 29 individually-housed fish. Variance-component estimation yielded a statistically significant repeatability estimate of R = 0.106, indicating that individuals differed consistently in their average air-breathing frequency across repeated observations. In a separate trial, air-breathing and antipredator responses were assessed in individually- and communally-housed fish following a simulated aerial bird strike. Isolated fish exhibited significantly higher overall fAB and also resumed air-breathing significantly faster following the strike (99.3 ± 27.1 s) than grouped conspecifics (537.5 ± 42.6 s), with 87
