Marcelo M. Dalosto

Differences in oxygen consumption and diel activity as adaptations related to microhabitat in Neotropical freshwater decapods (Crustacea).

This study evaluated oxygen consumption (MO(2)) and diel activity in Aegla longirostri, Trichodactylus panoplus and Parastacus brasiliensis (three species of freshwater decapods that occur in sympatry), under two different conditions of O(2) availability, limited and constant; and searched for the existence of a relationship between these two variables. The Kruskal-Wallis test showed that in all the species, MO(2) was higher under constant O(2) availability; T. panoplus and P. brasiliensis showed an oxygen-dependent pattern, while A. longirostri showed higher MO(2) values and less variation in the values between the treatments, indicating a higher and more oxygen-independent metabolism. P. brasiliensis was more active in constant O(2). A. longirostri was more active in limited O(2) and did not show a clear diel activity in any case, showing behavioral changes when in unfavorable conditions. The Spearmans rank correlation analysis did not indicate any relationship between MO(2) and activity. These results indicate a higher metabolism in A. longirostri. The less demanding metabolisms of P. brasiliensis and T. panoplus allow these species to occupy environments that are unavailable to A. longirostri due to differences in dissolved-oxygen concentrations.

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.

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.

Effects of carbofuran and metsulfuron-methyl on the benthic macroinvertebrate community in flooded ricefields

OBJETIVO: O objetivo desse estudo foi avaliar o efeito do inseticida carbofurano e do herbicida metsulfuron-methyl na abundância e diversidade de macroinvertebrados bentonicos em campo de arroz irrigado. METODOS: Para isto, dois tratamentos com agrotoxicos [o inseticida carbofurano (IC) e o herbicida metsulfuron-methyl (HM)] e um controle (Co), tratamento sem pesticida, foram aplicados em uma area experimental no Departamento de Fitotecnia da Universidade Federal de Santa Maria. Amostras de solo foram coletadas em triplicatas em cada tratamento 30 dias antes (DBA) e 1, 10 e 51 dias apos a aplicacao dos pesticidas, posteriormente a macrofauna foi identificada. RESULTADOS: Vinte e um (21) taxa foram identificados, entre esses Trichoceridae esteve presente apenas em Co, enquanto que Hydroptilidae foi coletado apenas em IC, e Corixidae em HM. Em Co e IC, o grupo mais abundante foi Annelida, e em HM foi Diptera (Chironomidae) que prevaleceu. Diferencas significativas foram observadas entre Co e IC, na densidade de Odontoceridae (Co>IC) e Hydrophilidae (Co HM) e Hirudinea (Co<HM). CONCLUSAO: Entretanto, apesar dos possiveis efeitos negativos dos pesticidas sobre a comunidade bentonica verificados nos primeiros dias apos a aplicacao, verificou-se que de forma geral a comunidade recuperou-se rapidamente.

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.