Alexandre V. Palaoro

Modulation of male aggressiveness through different communication pathways

Communication plays a large role in resource competition, especially for potential mates, and is used by members of the competing sex to assess each other, and simultaneously to evaluate the other sex, which may be advertising its status. To assess the effects of female advertisement on male aggression, males of the decapod Aegla were paired according to body and armament size. Males were left to interact in five different treatments: with receptive females that could use both chemical and visual cues, non-receptive females that could use both types of cues, receptive females that could use only one cue, or no female in the aquarium. Fight duration, time spent in the most aggressive acts, latency period, number of antennal whips/fight duration, and time spent near the female were analyzed. The males had shorter and less intense confrontations when there was a receptive female that could signal with at least one modality. Winning males spent significantly more time near the receptive female only when both chemical and visual cues were present, when compared to the other treatments. The low level of aggression shown by the males may be related to information asymmetry due to the female’s choice: only the preferred male would receive information from the female, or males could compete for other resources that attract females. However, male aggression was modified by the presence of female chemical cues, whereas mate guarding was initiated only when both chemical and visual cues were present. Hence, male aggression can be downregulated by female receptivity.

Freshwater decapod (Aegla longirostri) uses a mixed assessment strategy to resolve contests

Howanimals decide towithdraw from a contest has puzzled researchers for years. Currently, four modelstry to explain how this decision is made: war of attrition (WOA); cumulative assessment (CAM);opponent-only assessment (OOA); and sequential mutual assessment (SAM). Although their predictionsdiffer, they must be simultaneously tested to infer which model best describes contests. Herein, weidentified the traits related to the resource-holding potential (RHP) in the decapod Aegla longirostri, andused these traits to test the predictions of each model. We identified which morphological/performancetraits affect contest outcome, related these traits to the contest duration of male dyads, and tested thedifferences in aggressive acts (claw grabs). We tested the models using pairs of random and RHP-matched opponents. Additionally, we performed contests where RHP-matched opponents couldcommunicate before the contest (‘previewed’), and contests where the focal animal would onlycommunicate with one individual and fight another unseen individual afterwards (‘unseen’). Incomparing these groups we tested whether information was being exchanged. The best predictor ofcontest outcome included a combination of cephalothorax length and claw height, and claw grabsincreased with opponent similarity. Contest duration increased with losers cephalothorax length anddecreased with winners cephalothorax length in random pairs, and winners spent more time in clawgrab than losers. These findings refute WOA and OOA. In RHP-matched pairs, no relation was found andcontests with previewed opponents were shorter than contests with unseen opponents, both resultssuggest SAM. However, the time spent in claw grab did not differ between previewed and unseen op-ponents. We argue that SAM is cognitively complex, and mutual assessment without comparison of RHPcould be a better explanation. Furthermore, claw grab is important in contest resolution. Thus, the costsinflicted may suggest a mixed assessment strategy for A. longirostris contests.© 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Mother-offspring relationship in the Neotropical burrowing crayfish Parastacus pilimanus (Von Martens, 1869) (Decapoda, Parastacidae)

This study describes the mother-offspring behaviour in the South American burrowing crayfish Parastacus pilimanus (Von Martens, 1869), by testing the mother’s offspring-recognition abilities (and vice-versa) and the tolerance of a non-parental adult to juveniles. A female carrying first-instar juveniles was collected and acclimated in the laboratory. Daily observations of 20 min were made for six months after the juveniles were released. Five juveniles were randomly chosen weekly and measured. After 106 days of observation, we observed the female’s ability to recognize her own offspring, isolating her first for two hours and then for 1, 2, 5 and 30 days. The female did not show any aggressive behaviour towards the juveniles during the observation period (182 days). The juveniles were often observed together with their mother and walking under or over her, even after the isolation. However, they were never seen returning to the female’s pleopods. No juvenile was cannibalized during the entire experiment. Together these results suggest that this species possesses adaptations that allow for the overlapping of generations, including high tolerance of the mother.

Aggressiveness and life underground: the case of burrowing crayfish

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.

Assessing the importance of burrows through behavioral observations of Parastacus brasiliensis, a Neotropical burrowing crayfish (Crustacea), in laboratory conditions

BackgroundCrayfish from the Neotropical region comprise a unique group among crustaceans. Their burrowing habits have severe consequences for many ecological, morphological, and behavioral traits. Although they are all considered true burrowers, the degree of these adaptations and their relationships to the behavioral repertoires of these crustaceans have been discussed for a long time, although with no consensus.ResultsTo address this situation, we performed behavioral observations of Parastacus brasiliensis in a laboratory environment. Animals (n = 7) were isolated and acclimated in experimental aquaria according to their size (two large and five smaller aquaria) and observed for seven days at four different times of the day (twice during the day and twice at night). Their behaviors were qualified and quantified. The time spent inside and outside the burrow was also observed and analyzed with a t test for paired samples. Their circadian activity was analyzed using Rayleighs Z test. Animals spent 54.9% of the time hiding within the burrow and also remained longer in it during the day than at night. They spent more time active outside the burrow during the night.ConclusionsThese results suggest that these crayfish are nocturnal and are definitely not a part of the lotic species group. This species appears to be closely associated with its burrow but can exhibit considerable activity outside of it and can therefore be classified as a secondary burrower. Although this is a laboratory study, the results may stimulate further studies on the importance of burrows to these animals and provide basic background information for new studies on these cryptic crustaceans.

Weaponry and defenses in fighting animals: how allometry can alter predictions from contest theory

Theoretical models have been developed to understand how animals decide to withdraw from a contest. They provide testable predictions regarding the relationship between resource holding potential (RHP) and contest duration that assume linear relationships among RHP traits. However, RHP traits might scale with body size according to power laws. Furthermore, investment across different RHP traits may vary. Herein, we provide a model that encompasses the allometric relationship between body size and other RHP traits. First, we partition RHP traits into “offensive” traits (i.e., the ability to inflict damage) and “defensive” traits (i.e., persistence in a contest). Defensive traits may in turn be subdivided into “damage endurance” (DE) or the ability to absorb damage and “stamina.” We then model scenarios where: 1) there are power relationships among RHP traits; 2) individuals invest differently in defensive and offensive traits; 3) offensive traits and DE have a positive/negative relationship with body size. We modeled sized-matched injurious contests where 1) offensive capacity (OC) increases superlinearly with body size, 2) DE increases superlinearly, and 3) OC increases superlinearly but DE increases sublinearly. Our analyses indicate that if RHP traits scale linearly current predictions are upheld for injurious contests—contest duration increases with body size. However, with power relationships we can expect nonlinear relationships. Here, contest duration increased with body size until a maximum, decreasing afterwards. Thus, considering allometric relationships between body size and RHP traits may lead to new insights in animal contest theory and may help to solve discrepancies between current theory and empirical data.

Population biology of Aegla platensis (Decapoda: Anomura: Aeglidae) in a tributary of the Uruguay River, state of Rio Grande do Sul, Brazil

Aeglids are freshwater anomurans that are endemic from southern South America. While their population biology at the species-level is relatively well understood, intraspecific variation within populations has been poorly investigated. Our goal was to investigate the population biology of Aegla platensis Schmitt, 1942 from the Uruguay River Basin, and compare our data with data from other populations. We estimated biometric data, sex ratio, population density and size-class frequencies, and frequencies of ovigerous females and juveniles, from the austral spring of 2007 until autumn 2008. Sexual dimorphism was present in adults, with males being larger than females. Furthermore, males and females were significantly larger than previously recorded for the species. The overall sex ratio was 1.33:1 (male:female), and population density ranged from 1.8 (spring) to 3.83 ind.m-² (winter). Data from this population differ from published information about A. platensis in almost all parameters quantified except for the reproductive period, which happens in the coldest months, and a population structure with two distinct cohorts. Difference among studies, however, may be in part due to methodological differences and should be further investigated in order to determine their cause. In addition to different methodologies, they may result from ecological plasticity or from the fact that the different populations actually correspond to more than one species.

One step ahead of the enemy: investigating aggressive interactions between invasive and native crayfish before the contact in nature

Abstract Biological invasions are a major cause of biodiversity loss, and early action in these cases is more cost-effective than dealing with widespread invasions. Thus, understanding possible consequences of invasions is essential for control and management actions. Given the early stage of invasion of South America by Procambarus clarkii, a potentially harmful crayfish, we investigated aggressive interactions between this invasive crayfish and the native Parastacus brasiliensis to understand potential impacts of the invader on native species before they encounter each other in nature. We paired size-matched crayfish for two experiments: one with Pr. clarkii males and females against Pa. brasiliensis; and another with Pr. clarkii intraspecific interactions. We starved the crayfish then allowed to interact in the presence of food. In interspecific fights we compared the number of attacks, time with the resource, frequency of won interactions of each species and the first species to reach the resource. Regarding the interspecific fights, Pr. clarkii attacked more often, spent more time with the resource, won more interactions and reached the resource first more often than Pa. brasiliensis. Interspecific fights escalated faster than intraspecific fights. The invasive crayfish’s ability to win might be enhanced due to ownership effects, and its impact is likely to be severe because of its life-history traits. We conclude that Pr. clarkii is definitely a threat for native crayfish, requiring that immediate actions be taken, such as dam construction and manual removal of Pr. clarkii.

How does environment influence fighting? The effects of tidal flow on resource value and fighting costs in sea anemones

An animals decision to enter into a fight depends on the interaction between perceived resource value (V) and fighting costs (C). Both could be altered by predictable environmental fluctuations. For intertidal marine animals, such as the sea anemone Actinia equina, exposure to high flow during the tidal cycle may increase V by bringing more food. It may also increase C via energy expenditure needed to attach to the substrate. We asked whether simulated tidal cycles would alter decisions in fighting A. equina. We exposed some individuals to still water and others to simulated tidal cycles. To gain insights into V, we measured their startle responses before and after exposure to the treatments, before staging dyadic fights. Individuals exposed to flow present shorter startle responses, suggesting that flowing water indicates high V compared with still water. A higher probability of winning against no-flow individuals and longer contests between flow individuals suggests that increased V increases persistence. However, encounters between flow individuals were less likely to escalate, suggesting that C is not directly related to V. Therefore, predictable environmental cycles alter V and C, but in complex ways.

Mate preference in the neotropical freshwater crab Aegla longirostri (Decapoda: Anomura): does the size matter?

This study analyzed sexual selection in Aegla longirostri through one of the mechanisms that can alter species’ evolution: mate choice. Y maze experiments were performed by placing a male or a receptive female (chooser) in the center of the maze; and two other individuals were placed each in a different corridor, according to the chooser: a receptive and an immature female, or two males that differed in size, respectively. The third corridor remained empty, and the choosers could walk among the branches of the maze. The results showed that only females spent more time in the corridors harboring a large male. Moreover, females had higher rates of movement in the corridors harboring males. Thus, female preference for larger males may be one factor that prompted the evolution of sexual dimorphism in this species.