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Fighting is a costly behavior, consuming both time and energy. As a result, the benefits of acquiring resources must outweigh these costs. Resource value will thus influence willingness to invest in a contest through its objective (the intrinsic properties of the resource) and subjective value (context/state dependent). In burrowing crayfish, subjective resource value may vary with life stage: adults, subadults, and juveniles differ in their ability to obtain resources. As juveniles cannot dig their own burrows, we hypothesize that earlier life stages will exhibit lower aggression than later life stages. To test this, we evaluated contests between paired individuals according to their cephalothorax length (CL), encompassing different life stages of Parastacus brasiliensis. To quantify aggression levels, we recorded contest duration, the frequency of low and highly aggressive behaviors, the time to escalate to highly aggressive behaviors, the probability of initiating contests with highly aggressive behaviors, and the latency to initiate a contest. We examined the relationship between these dependent variables and CL (independent variable) using GLMs to test how aggressive behaviors develop. Contest duration increased with pair mean, winner's and loser's CL. Frequency of low aggressive behaviors increased with CL, whereas highly aggressive behaviors, latency, and time to reach highly aggressive behaviors were unrelated to CL. Smaller individuals had a higher probability of initiating contests with highly aggressive behaviors. Self-assessment explains the contest dynamics of P. brasiliensis, with smaller individuals giving up sooner, probably due to lower energy and time budgets.

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.

Species with similar niches may exhibit adaptations to diminish competitive pressure and allow sympatry; freshwater decapods are interesting models for the investigations of these strategies. We studied the behavior of two co-occurring decapod species: the anomuran Aegla longirostri and the crayfish Parastacus pilimanus, and investigated the following: (1) whether the species use the stream similarly; (2) if they present zonation within it; (3) if they have different activity levels; and (4) whether their activity patterns overlap. For this, we radio- tracked individuals of both species in their natural environment. Aeglids had larger home ranges than crayfish when considering only the stream. However, crayfish remained in burrows more than in the stream, and the total home ranges did not differ significantly from aeglids. Stream sections used by both species highly overlap, indicating no zonation. Aeglids used the stream more often and more intensively than crayfish, but their diel activity patterns were similar. Despite the lack of zonation in the stream and of temporal segregation, there seems to be some degree of spatial segregation. Differential habitat use seems to be the one of the mechanisms allowing crayfish to coexist with aeglids.

SUMMARY 1. Invasive species are one of the most severe threats to biodiversity, and an ability to predict the extent of potential invasions can help conservation strategies. Species distribution models (SDMs) have been widely used to project the potential range of invasive species. These models assume that species retain their niche properties during invasion (niche conservatism), although this assumption is seldom verified. 2. We gathered occurrence records for the crayfish Procambarus clarkii from the U.S.A. and Mexico (native + invasive ranges) and from the Iberian Peninsula (invasive) to test for niche conservatism across continents using niche overlap metrics (Schoener’s D). To test for differences in the climate space occupied by the species on the different continents, we performed two principal component analyses (PCAs) on the environmental data extracted from occurrence records: first, separately for each occurrence data set (i.e. each continent) and secondly, using the pooled data. Subsequently, we projected the model to South America, where this species has the potential to become invasive. 3. Schoener’s D showed high overlap (0.68) between the two regions (the Americas and Iberia), and there was no difference between the regions in both PCAs. The crayfish has conserved its niche across continents, and therefore, our model projection to South America may accurately demonstrate where invasion is most likely to occur. 4. Large parts of South America are apparently suitable, mainly Argentina, Chile, Paraguay, Uruguay and southern Brazil. This result is of great concern since this invasive species can spread quickly in suitable areas. Stronger laws and regulations should be made to protect native biodiversity and agricultural land. Our approach could be replicated for the study of invasions by other species where extensive data on the potentially invaded areas are available.

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.

Background Crayfish 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. Results To 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 Rayleigh's 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. Conclusions These 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.