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
Various post-dropping behaviours have evolved in insects to mitigate risks such as desiccation, starvation, and drowning. Some insects exhibit upright landing, and its mechanisms have been clarified in previous studies. However, the adaptive significance of upright landing has rarely been tested experimentally. Previous studies have suggested that upright landing may facilitate escape from predators at the landing site. To test this prediction, I investigated the post-dropping behaviour of planthopper Laodelphax striatellus (Hemiptera: Delphacidae) nymphs on the water surface. Because aquatic predators such as water striders and spiders are important predators of planthoppers, the ability to land safely on the water surface is crucial for their survival. Live nymphs landed upright more frequently than dead nymphs, indicating that they actively control their body orientation to achieve upright landing on the water surface. Moreover, nymphs that landed upright were preyed upon less frequently by water striders than those that landed upside-down. Nymphs that landed upright escaped attacks by jumping. These results indicate that upright landing on the water surface by L. striatellus nymphs plays a crucial role in escaping aquatic predators.
Ultrasonic vocalizations (USVs) were not previously described for pikas. This study describes ultrasonic calls, produced by Daurian pikas Ochotona dauurica when disturbed by a potential threat (standing researcher or a small chair with mounted recording device) in the vicinity of the burrow entrances of their native colonies. The USVs of pikas were always produced as separate calls, followed by intervals of up to a few minutes. The USVs were never produced in regular series. Frequency range of 80
Mesocarnivores often engage in interspecific interactions due to overlapping habitats and resource use, which can influence behavioural decisions toward novel stimuli. We investigated species-specific responses to a novel resource in Japanese raccoon dogs (Nyctereutes procyonoides), Japanese badgers (Meles anakuma), and invasive raccoons (Procyon lotor) in Japan. An artificial wire-mesh aisle with a bait tray was installed, and the test area was divided into three phases: surrounding (Phase 1), entrance (Phase 2), and interior (Phase 3). Behaviour was quantified using principal component analysis (PCA) and generalized linear models (GLMs). In Phase 1, PC1 (motionless and exploration) and PC2 (vigilant approach) explained > 80
A foraging-related behavior potentially allowing killer whales (Orcinus orca) to identify fishing lines with hooked Atlantic bluefin tuna (Thunnus thynnus) is described from the Strait of Gibraltar. On two days, four whales were video-recorded swimming repeatedly along the fishline, intermittently interacting with it by placing it on their backs or pressing, holding, or pushing it with the fins, snout, melon or belly. These interactions are consistent with assessing line tension or weight to detect the presence of a hooked fish at depth. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo260512oo01a and at http://www.momo-p.com/showdetail-e.php?movieid=momo260512oo02a .
Urban environments exhibit a range of differences from natural environments in terms of various ecological and environmental factors. These environmental disparities will influence or modify the direction and/or intensity of sexual selection. Given the challenging survival conditions and thus low population density in urban environments in many species, selection may favor traits that enhance mating success during rare encounters. Although the impact of urban environments on acoustic signalling has received the most attention in crickets, chemical cues are also crucial for successful mating. We examined whether the chemical cues of urban males were more attractive to females than those of rural males in the ground cricket Dianemobius nigrofasciatus. Using a common garden experiment, we conducted a behavioral assay with filter papers bearing male chemical cues and quantified female response as the difference in time spent on treatment and control blank filter papers. Rural females showed a strong preference for the chemical cues of urban males, whereas urban females did not show a substantial preference for chemical cues of urban males. Our results suggest that chemical cues may alleviate some of the negative impacts of urban environments on acoustic communication. These findings highlight how urbanization can reshape sexual communication systems across sensory modalities.
Burton’s mouthbrooder Astatotilapia burtoni is an African cichlid fish exhibiting dramatic reversible phenotypic plasticity, used as a model species in neuroscience. Males engage in dyadic confrontations to establish and defend territory. Third-party males occasionally intervene in these conflicts. We examine the hypothesis that a winner effect could motivate especially high-ranking males to suppress other conflicts, preventing rivals from emerging. Using visual observation we recorded hierarchical interactions (aggression and fleeing behaviors) and third party disruptions. Consistent with this hypothesis, we found that relatively dominant males were most likely to engage dyadic conflict, as well as to intervene in third party interventions.
Animal species exhibit variation in the mating frequency of females. Theories suggest that the cost–benefit balance between males and females underlies the evolution of mating frequency. However, determining which sex is responsible for the differences in mating frequencies observed between species is usually difficult. Drosophila prolongata serves as a unique study system in which mating frequency once underwent a drastic decline during its evolutionary history. Behavioural analyses have suggested that physiological changes in either males or females could account for this evolutionary shift. To disentangle these mechanisms, we adopted an experimental approach examining the female response to the injection of male extract. In D. prolongata, a reduction of female receptivity was detected 7 days after the injection of male extract, whereas in D. melanogaster, receptivity recovered to a normal level within 3 days. When extracts of heterospecific males were injected, D. prolongata females showed a comparable level of response to D. melanogaster extract, whereas D. melanogaster females showed a weaker response to D. prolongata extract. Although the contribution of male-side factors cannot be excluded, these results support the mechanism in which females are involved in the evolution of mating frequency in D. prolongata.
Sperm depletion, a reduction in male fertilization capacity through successive mating, has been extensively documented across animal taxa. However, research has predominantly focused on quantitative reductions in sperm while overlooking potential qualitative changes. In the present study, we investigated whether successive mating affects sperm velocity in medaka (Oryzias latipes), a model fish used for reproductive studies. We compared the sperm velocity between males that mated once (single-mating condition: one male with one female) and those that mated repeatedly (multiple-mating condition: one male with 15 females). Males in the multiple mating condition mated an average of nine times (range: 7–12) within 4 h. After successive matings, the initial sperm velocity (0–10 s post-activation) was significantly reduced by 22
The “twofold cost of sex” is one of the greatest mysteries in evolutionary biology. In anisogamy (fertilization between egg and sperm), since half the offspring produced by the mother are male, to compete with thelytoky—which produces only females—in terms of reproductive rate, the number of daughters × juvenile survival probability must be doubled. The genetic benefits of sex (e.g., Red Queen) are too slow to suppress quickly increasing thelytoky. Here, I propose the “Double-Income Anisogamy” hypothesis. Resource defense by males is observed across many taxa, from insects to humans. To attract many females, males defend patches containing the resources necessary for offspring development. Since males only allow access to resources to females that accept mating, thelytokous females are eliminated. Thus, thelytokous females incur the “cost of being single”. Anisogamous females already achieve the same egg number (although half of which are males) and survival rates as thelytokous females using their own resources alone (single-income situation). If anisogamous females use resources from males (double income) to increase not the number of eggs but the survival rate of existing offspring, the number of surviving daughters (fitness) doubles, offsetting the twofold cost without considering genetic benefits. Simulations confirmed the model predictions.
Endoparasitic animals must penetrate their hosts to survive. When actively entering a host, they are expected to employ body movements different from those used when searching for hosts on land or in water. However, the body movements used during penetration have rarely been documented, and the mechanisms by which endoparasites accomplish host penetration remain largely unknown. In Strepsiptera (Insecta), tiny first-instar larvae both search for and penetrate their hosts, but the mechanisms of penetration are poorly understood. Here, we observed the body movements of first-instar larvae of Blissoxenos esakii during host penetration. We found that larvae penetrate the host while producing forward-propagating abdominal contraction waves, a movement not observed during walking on land. This study provides the first video-based documentation and analysis of host penetration by first-instar strepsipteran larvae and offers new insights into the mechanisms underlying host penetration in endoparasitic insects. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo251217be01a .
Host recognition and rejection of foreign eggs can be effective at combating brood parasitism, and egg patterning serves as a crucial visual cue for some hosts to recognize parasitic eggs. The mimicry of parasitic cuckoo eggs can typically match one or more host species, but the degree of mimicry varies among different hosts. Accurate host recognition of differences in egg markings (spots or lines) is therefore important for antiparasitic adaptation. This study focused on two closely related hosts of the common cuckoo (Cuculus canorus) that breed within the same area, the Godlewski’s bunting (Emberiza godlewskii) and the yellow-throated bunting (E. elegans). We examined the impact of introducing budgerigar (Melopsittacus undulatus) eggs with varying patterns into the nests of two bunting species, and the role of egg patterning in egg recognition. Results showed that both two bunting species exhibited an increasing trend in egg rejection for three types of foreign eggs (conspecific pattern, heterospecific pattern, and pure-white egg) ranging from low to high (Godlewski’s buntings: 45.45
We examined why Trimma marinae is monogamous despite high potential for polygyny. Previous work suggested males can care for up to three clutches, but four may exceed their capacity. We therefore tested whether a single female can saturate a male’s care capacity. In established pairs, 49 spawning intervals had a median interval of 2 days. Because eggs hatch on day 3, 75.5
Urbanization poses novel ecological challenges for animals, often driving morphological and behavioral changes. In this study, I investigated risk-taking behavior, measured as flight initiation distance (FID), in seven bird species inhabiting both highly urbanized areas of Tokyo and rural areas of Ibaraki Prefecture, Japan. All species exhibited significantly shorter FIDs in urban habitats, indicating increased tolerance toward human approach. Effect sizes (Hedges' g) for FID differences between urban and rural habitats were larger than those previously reported from Europe, suggesting more pronounced behavioral shifts in Tokyo, likely driven by the city's exceptionally high human population density. No clear correlation was found between the time since urban colonization and the magnitude of behavioral change, implying that reduced risk avoidance may emerge rapidly via habituation rather than long-term genetic adaptation. This study shows that birds inhabiting the megacity of Tokyo provide a valuable model for investigating change in risk-taking behavior in urban environments, and highlights the need for future studies examining a greater number of species with varying colonization histories and for long-term studies of the same species over time.
Movement is a key behavior affecting fitness in many animals, and one potentially beneficial form of movement is the dispersal of oviposition sites by females. When eggs are laid in a single patch, offspring face elevated risks of cannibalism and accidental extinction. The dispersal of eggs at multiple sites can enhance offspring survival. On the other hand, there are often individual differences in the moving activity of animals, some of which are genetically controlled. However, the relationship between the genetically regulated movement, oviposition site dispersal, and reproductive success is poorly understood. In this study, we investigated the relationship between female oviposition dispersal and the number of offspring using the red flour beetle Tribolium castaneum with genetically different moving activity. We found no association between female oviposition dispersal and moving activity on a genetic basis. These results suggest that the female oviposition dispersal is controlled by a mechanism different with the general moving activity. Our results also suggest that the extent of oviposition-site dispersal by females does not influence offspring number in the next generation.
Hydroelectric dams impose several sensorial challenges to fluvial cetaceans such as river dolphins, but echolocation behavioral patterns of these animals remain understudied. We compared echolocation patterns of dolphins of the recently proposed Inia araguaiaensis between one area under the influence of a dam (Tocantins River) and another area with a free-flowing river (Araguaia River). We used the F-POD (a Passive Acoustic Monitoring device) to measure the acoustic presence of dolphins (Minutes of Positive Detection, DPM), the time between consecutive echolocation clicks (Inter-Click Interval, ICI) - used as a proxy for sonar focal distance - and the Click Frequency (CF). DPM was higher in the Tocantins (19.5 DPM/ hour) than in the Araguaia (14.6 DPM/hour), the ICI was lower (faster clicks) in the Tocantins (2.6 ms vs. 8.6 ms, p < 0.001), and the CF of signals was higher in the Tocantins (102 kHz vs. 93 kHz, p < 0.001). Together, these results point to behavioral differences between echolocation patterns of Tocantins and Araguaia populations. Moreover, these results seem to indicate that dolphins of the Tocantins River adapt their echolocation behavioral patterns to a dammed environment with higher acoustic activity through the production of signals for greater precision.
Estuarine systems work as feeding, reproductive and shelter habitats for a number of aquatic species in the tropics, where estuarine fish follow the tidal dynamics for foraging and searching for shelter. Sympatric species sharing similar feeding habitats often show different foraging tactics, suggesting that behavioral differences have a primary importance for sympatric distribution. The feeding behaviors of juvenile banded puffer Colomesus psittacus and juvenile four-eyed-fish Anableps anableps, both sympatric estuarine resident species, were compared while observed in the Curuçá river estuary, NE-PA, Brazil, where they share the same micro-habitat, dwelling near the water surface, followed by stomach content analysis. Four main feeding-related behavioral patterns were described: Abrupt Dash (AD), Foraging at Roots (FR), Foraging at Margins (FM) and Occasional Feeding (OF); which presented distinct variances between the two species. A non-metric multidimensional scaling (nMDS) has shown distinct clusters between both species’ diets, based on stomach content data. The observed results suggest niche segregation between C. psittacus and A. anableps, both behavioral patterns and stomach content analyses have shown distinct feeding specializations for each species.
