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Publisher’s note
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Aggressiveness and life underground: the case of burrowing crayfish
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This study compared aggression in two morphologically similar neotropical burrowing crayfishes, Parastacus pilimanus, a primary burrower, and Parastacus brasiliensis, a secondary burrower. Intraspecific pairs were formed, with a maximum 15% difference in carapace and chelae length within each pair. Pairs were allowed to interact for 20 min, during which they were recorded, and the agonistic behaviour was then analyzed throughout these recordings. The species were compared with respect to mean bout duration, first bout duration, number of bouts, latency period, frequency of highly aggressive behaviours, frequency of low aggressive behaviours, as well as the number of approaches, antennal whips and chelae punches. The proportion of interactions that resulted in formation of a clear hierarchy was also compared. Parastacus brasiliensis was the more aggressive species, showing statistically higher values for all parameters except latency, as well as number of bouts and antennal whips (among winners); while P. pilimanus performed more chelae punches. In general terms, both species showed low aggression (due to the absence of clearly escalated fights and other behaviours), which differs from the pattern expected for crayfish. The formation of dominance relationships was more frequent in P. pilimanus than in P. brasiliensis. Due to possible pressure for co-existence and reduced competition for resources, the burrowing habit appears to influence aggression, with the more fossorial species being less aggressive. It is assumed that these differences are related to: (i) phylogenetic distance from the open water species; (ii) the burrowing habitat and the related morphological adaptations and (iii) a reduced need to acquire and defend resources other than their burrows.
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Scramble competition by males of the velvet ant Nemka viduata (Hymenoptera: Mutillidae)
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The mating systems of mutillid wasps have rarely been studied. Here we present information on the mating system of Nemka viduata. At a site in southern Spain, many males of this species were seen flying over host (digger wasp) nest aggregations while searching for females. Male activity was greatest in the early morning and late afternoon, when females were more active searching for hosts, and on days when relatively large numbers of females were active. Males were not territorial but instead attempted to find emerging females before their competitors. As many as six males might arrive at a receptive female more or less simultaneously. Struggles to control access to females continued until one male copulated with the female on the ground or carried it off in flight to a location away from rival males. Male size seems to affect the patrolling behaviour (number of patrolled sites), but there is little evidence of an advantage for larger males, as expected in a scramble competition mating system. Scramble competition mating systems often evolve in species in which large numbers of males compete for scarce receptive females, a factor that makes male territorial defence of large areas highly costly.
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Interspecific contests between males of two Japanese stag beetle species, Lucanus maculifemoratus and Prosopocoilus inclinatus: what overcomes a body size disadvantage?
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In intra- and interspecific interactions, generally, body size differences between contestants are important, with larger animals being superior competitors. The males of two species of Japanese stag beetles, Lucanus maculifemoratus and Prosopocoilus inclinatus, have intrasexually selected large mandibles. Because these two species are sympatric and feed on the same food, winning interspecific competitions might have considerable effects on male fitness with regard to access to limited resources. If the outcome of interspecific competitions between these two species of beetles is determined by body size, the advantage would lie with the larger species, L. maculifemoratus. To test this prediction, we examined the behaviour and outcome of contests between these two species in detail. Contrary to our expectations, the larger size of the male L. maculifemoratus did not provide a competitive advantage against P. inclinatus. The higher winning rate of P. inclinatus was attributable to differences in mandible use: male L. maculifemoratus nipped the opponent’s dorsal side and threw it, whereas male P. inclinatus nipped both ventral and dorsal sides. The proximate cause of this difference was the interspecies difference in tactile stimulation to the mandible: a tactile stimulus on the underside of the mandible resulting in mandible-nipping behaviour was observed in both species, whereas a tactile stimulus to the upper side of the mandible resulting in mandible-nipping behaviour was observed only in P. inclinatus. The present study provides an important counter-example to the general belief that larger species have an advantage in interspecific contests involving physical combat.
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Peacock copulation calls attract distant females
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Males often continuously emit vocalizations during the breeding season that attract female mates. They can also emit calls that are specifically associated with copulations but the function of these copulation calls is often unknown. We explored the function of male copulation calls in wild and captive peafowl (Pavo cristatus) to test whether these calls attract female mating partners. By broadcasting male copulation calls, we assessed whether these playbacks affected female behavior. Females approached and spent more time near the speaker in response to copulation playback trials compared to control trials (no sound broadcast) in the wild and compared to control trials (American crow (Corvus brachyrhynchos) calls broadcast) in captivity. Our results, therefore, suggest that peacock copulation calls function to attract additional female mating partners. Because peafowl live in habitats with dense vegetation, loud copulation calls may help females locate potential mates.
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Dingo (Canis lupus dingo) acoustic repertoire: form and contexts
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The classification and description of a species’ acoustic repertoire is critical to our understanding of broader behavioural patterns and provides data for future cross-species comparative studies. To date, our understanding of canid auditory communication remains limited as full acoustic repertoires have been compiled for only nine of 36 extant species. Dingoes (Canis lupus dingo) are apex predators in Australia, and while their ecology and life-history patterns have been extensively studied, their communication system remains poorly understood. Early studies noted four sound types, but whether this represented the dingoes’ full range of laryngeal and nasal sounds was unknown. We aimed to quantitatively and qualitatively describe the full acoustic repertoire of dingoes. We identified nine discrete vocalisations (i.e., laryngeal sounds) and two nasal sounds. Of these nine vocalisations, five were previously identified as common to other canid species. This study also revealed that dingoes possess a graded acoustic communication system, where the gradual change in acoustic characteristics of discrete vocalisations was noted. Dingoes also uttered ‘mixed sounds’, a finding in concordance with previous studies of social canids. Additionally, we established an ethogram to further our understanding of the contexts in which dingo acoustic communication occurs.
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The effect of predation risk on spider’s decisions on web-site relocation
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Among the costs associated with animal-built structures, the cost of exposure to predators is important, because it affects the survival of builder animals. When predator risk increases, the builder may change the location of a structure or remain on the structure but modify its behaviour. The main purpose of this study was to examine whether builders leave their current structure locations and relocate to a new location upon predator attacks. To assess this, we used orb-web spiders that regularly renew their webs and occasionally relocates their web site upon web-rebuilding. Specifically, adult females of Cyclosa argenteoalba were exposed to the air-borne vibrations from a tuning fork. These vibrations simulate the vibrations from insect predators’ wings and trigger immediate anti-predator responses (jumping off the web to avoid attacks from predators and shaking webs). Spiders that received these simulated predator stimuli relocated more often on the day after treatment than did spiders that were not exposed to predator stimuli. This indicated that spiders estimated future predation risk from their predator-encounter experience and responded to perceived increase in predation risk at current site by abandoning their web site upon web-rebuilding. In addition, we examined whether the frequency of jumping behaviour and web relocation were correlated, but no significant relationship was detected. This result suggests that immediate anti-predator behaviour at the current site and the decision to relocate were independent of each other.
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