Sex identification in female crayfish is bimodal

Experience shapes accuracy in territorial decision-making in a poison frog

The trade-off between speed and accuracy affects many behavioural processes like predator avoidance, foraging and nest-site selection, but little is known about this trade-off relative to territorial behaviour. Some poison frogs are highly territorial and fiercely repel calling male intruders. However, attacks need to be conducted cautiously, as they are energetically costly and bear the risk of own injury or accidentally targeting the wrong individual. In this study, we investigated the speed–accuracy trade-off in the context of male territoriality during the breeding season in the brilliant-thighed poison frog, Allobates femoralis. In our experiment, we presented the call of an invisible ‘threatening’ intruder together with a visible ‘non-threatening’ intruder, using acoustic playback and a frog model, respectively. Contrary to our prediction, neither reaction time nor approach speed of the tested frogs determined the likelihood of erroneous attacks. However, younger individuals were more likely to attack the non-threatening model than older ones, suggesting that experience plays an essential role in identifying and distinguishing rivalling individuals in a territorial context.

The complexity of mating decisions in stalk-eyed flies

All too often, studies of sexual selection focus exclusively on the responses in one sex, on single traits, typically those that are exaggerated and strongly sexually dimorphic. They ignore a range of less obvious traits and behavior, in both sexes, involved in the interactions leading to mate choice. To remedy this imbalance, we analyze a textbook example of sexual selection in the stalk-eyed fly (Diasemopsis meigenii). We studied several traits in a novel, insightful, and efficient experimental design, examining 2,400 male-female pairs in a "round-robin" array, where each female was tested against multiple males and vice versa. In D. meigenii, females exhibit strong mate preference for males with highly exaggerated eyespan, and so we deliberately constrained variation in male eyespan to reveal the importance of other traits. Males performing more precopulatory behavior were more likely to attempt to mate with females and be accepted by them. However, behavior was not a necessary part of courtship, as it was absent from over almost half the interactions. Males with larger reproductive organs (testes and accessory glands) did not make more mating attempts, but there was a strong tendency for females to accept mating attempts from such males. How females detect differences in male reproductive organ size remains unclear. In addition, females with larger eyespan, an indicator of size and fecundity, attracted more mating attempts from males, but this trait did not alter female acceptance. Genetic variation among males had a strong influence on male mating attempts and female acceptance, both via the traits we studied and other unmeasured attributes. These findings demonstrate the importance of assaying multiple traits in males and females, rather than focusing solely on prominent and exaggerated sexually dimorphic traits. The approach allows a more complete understanding of the complex mating decisions made by both males and females.

Aggressive Bimodal Communication in Domestic Dogs, Canis familiaris

Evidence of animal multimodal signalling is widespread and compelling. Dogs’ aggressive vocalisations (growls and barks) have been extensively studied, but without any consideration of the simultaneously produced visual displays. In this study we aimed to categorize dogs’ bimodal aggressive signals according to the redundant/non-redundant classification framework. We presented dogs with unimodal (audio or visual) or bimodal (audio-visual) stimuli and measured their gazing and motor behaviours. Responses did not qualitatively differ between the bimodal and two unimodal contexts, indicating that acoustic and visual signals provide redundant information. We could not further classify the signal as ‘equivalent’ or ‘enhancing’ as we found evidence for both subcategories. We discuss our findings in relation to the complex signal framework, and propose several hypotheses for this signal’s function.

Glyphosate-based herbicide has contrasting effects on prey capture by two co-occurring wolf spider species

Anthropogenic substances have the potential to affect animal behavior either because they present a novel stimulus or because they interfere with natural chemical communication pathways. Such shifts can alter the dynamic between predators and potential prey, which might affect population success as well as the strength of food web linkages. We examined the foraging of two wolf spiders, Tigrosa helluo and Pardosa milvina (Araneae, Lycosidae), that are abundant in agroecosystems where they are routinely exposed to herbicides. We tested the hypothesis that the presence of a commercial formulation of a glyphosate-based herbicide would affect the prey capture behavior of these two wolf spiders. We tested the larger Tigrosa foraging on Pardosa or crickets (Acheta domesticus) and the smaller Pardosa foraging on crickets. Tigrosa subdued crickets more quickly and with fewer lunges than it took them to capture Pardosa. The presence of herbicide allowed Tigrosa to orient toward and capture both prey species more quickly but it did not affect the number of lunges required to subdue either prey. Herbicide did not affect the timing of prey capture for Pardosa but it did cause them to use more lunges in the process. Thus, herbicide had contrasting effects on foraging behavior of these two agrobiont predators, which means that it could shift the direction and strength of food web linkages in complex ways.

Revisiting social recognition systems in invertebrates

Since the 1970s, the ability of some invertebrate species to recognize individual conspecifics has attracted increased scientific interest. However, there is still confusion in the literature, possibly due to the lack of unambiguous criteria for classifying social recognition in its different forms. Here, we synthesize the results of studies on invertebrates and provide a framework with the purpose of identifying research needs and directions for future investigations. Following in part Sherman et al.'s (Behavioural ecology: an evolutionary approach. Blackwell Science, Oxford, pp 69-96, 1997) definition of 'recognition systems' and Tibbetts and Dale's (Trends Ecol Evol 22:529-537, 2007) classification of 'individual recognition,' we first discuss different case studies that exemplify the categories of 'familiar recognition' and 'class-level recognition.' Then, through the analysis of the invertebrate literature, we illustrate eight key properties that characterize 'true individual recognition' systems. We are confident that the proposed framework will provide opportunities for exciting discoveries of the cognitive abilities in invertebrates.

I know my neighbour: individual recognition in Octopus vulgaris

Background

Little is known about individual recognition (IR) in octopuses, although they have been abundantly studied for their sophisticated behaviour and learning capacities. Indeed, the ability of octopuses to recognise conspecifics is suggested by a number of clues emerging from both laboratory studies (where they appear to form and maintain dominance hierarchies) and field observations (octopuses of neighbouring dens display little agonism between each other). To fill this gap in knowledge, we investigated the behaviour of 24 size-matched pairs of Octopus vulgaris in laboratory conditions.

Methodology/Principal Findings

The experimental design was composed of 3 phases: Phase 1 (acclimatization): 12 “sight-allowed” (and 12 “isolated”) pairs were maintained for 3 days in contiguous tanks separated by a transparent (and opaque) partition to allow (and block) the vision of the conspecific; Phase 2 (cohabitation): members of each pair (both sight-allowed and isolated) were transferred into an experimental tank and were allowed to interact for 15 min every day for 3 consecutive days; Phase 3 (test): each pair (both sight-allowed and isolated) was subject to a switch of an octopus to form pairs composed of either familiar (“sham switches”) or unfamiliar conspecifics (“real switches”). Longer latencies (i.e. the time elapsed from the first interaction) and fewer physical contacts in the familiar pairs as opposed to the unfamiliar pairs were used as proxies for recognition.

Conclusions

Octopuses appear able to recognise conspecifics and to remember the individual previously met for at least one day. To the best of our knowledge, this is the first experimental study showing the occurrence of a form of IR in cephalopods. Future studies should clarify whether this is a “true” IR.

Intra-sex dimorphism in crayfish females

A unique cycle of female form alternation has been revealed in an experimental population of Orconectes limosus during a year-long observation. Significant cyclic changes observed in chelae length, width, and robustness, as well as in abdomen width, demonstrated a form alternation similar to that in conspecific males. Small females alternate between sexually active and sexually inactive forms with a short time interval between successive molts as well as different growth patterns of some body parts. Form alternation efficiently produces larger chelae, abdomen, and body dimensions, especially the molt to form I (sexually active). Larger females that undergo only a single annual molt do not alter between forms and are sexually active. They grow slowly and lose chelae robustness. The cycle of form alternation, consisting of two molts per year, may facilitate the effective utilization of resources to increase the size of body parts important to survival and reproduction.

To signal or not to signal? Chemical communication by urine-borne signals mirrors sexual conflict in crayfish

BACKGROUND

Sexual selection theory predicts that females, being the limiting sex, invest less in courtship signals than males. However, when chemical signals are involved it is often the female that initiates mating by producing stimuli that inform about sex and/or receptivity. This apparent contradiction has been discussed in the literature as 'the female pheromone fallacy'. Because the release of chemical stimuli may not have evolved to elicit the male's courtship response, whether these female stimuli represent signals remains an open question. Using techniques to visualise and block release of urine, we studied the role of urine signals during fighting and mating interactions of crayfish (Pacifastacus leniusculus). Test individuals were blindfolded to exclude visual disturbance from dye release and artificial urine introduction.

RESULTS

Staged female-male pairings during the reproductive season often resulted in male mating attempts. Blocking female urine release in such pairings prevented any male courtship behaviour. Artificial introduction of female urine re-established male mating attempts. Urine visualisation showed that female urine release coincides with aggressive behaviours but not with female submissive behaviour in reproductive interactions as well as in intersexual and intrasexual fights. In reproductive interactions, females predominately released urine during precopulatory aggression; males subsequently released significantly less urine during mating than in fights.

CONCLUSIONS

Urine-blocking experiments demonstrate that female urine contains sex-specific components that elicit male mating behaviour. The coincidence of chemical signalling and aggressive behaviour in both females and males suggests that urine release has evolved as an aggressive signal in both sexes of crayfish. By limiting urine release to aggressive behaviours in reproductive interactions females challenge their potential mating partners at the same time as they trigger a sexual response. These double messages should favour stronger males that are able to overcome the resistance of the female. We conclude that the difference between the sexes in disclosing urine-borne information reflects their conflicting interests in reproduction. Males discontinue aggressive urine signalling in order to increase their chances of mating. Females resume urine signalling in connection with aggressive behaviour, potentially repelling low quality or sexually inactive males while favouring reproduction with high quality males.