Effects of food, kinship, and density on the longevity of spiderlings

Cannibalism is a behavioral characteristic found in a wide variety of animal groups. Although the rates of cannibalism can vary from one group to another, studies indicate that the main factors contributing to an increase in the frequency of such behavior are the availability of food, population density, the behavior and availability of victims, and environmental stress. We carried out different laboratory experiments to assess whether different factors such as the presence or absence of food among siblings and non-siblings, and at different densities among conspecific and heterospecific individuals, affect longevity of recently emerged Brazilian brown recluse (Loxosceles intermedia Mello-Leitão, 1934) and Chilean recluse (Loxosceles laeta (Nicolet, 1849)) spiderlings during periods of starvation. The results revealed that the survivorship of L. laeta during starvation was significantly higher than that of L. intermedia and that the addition of conspecific individuals increased survival rates by 1.5- and 1.6-fold, respectively. The tolerance of conspecifics differed between the two species, and generally, cannibalism was not observed, probably due to the risk of predation and limited consumption by weakened spiders, which coincided with the continued availability of endogenous vitelline reserves, thus indicating that the use of these spiderlings as a food resource may act to regulate starvation in more resistant spiders. The greater longevity and conspecific tolerance of L. laeta may be important factors contributing to the establishment of large populations of this spider in restricted areas, whereas for L. intermedia, hunger probably functions as a trigger for dispersal.

Sphingomyelinase D Activity in Sicarius tropicus Venom: Toxic Potential and Clues to the Evolution of SMases D in the Sicariidae Family

The spider family Sicariidae includes three genera, Hexophthalma, Sicarius and Loxosceles. The three genera share a common characteristic in their venoms: the presence of Sphingomyelinases D (SMase D). SMases D are considered the toxins that cause the main pathological effects of the Loxosceles venom, that is, those responsible for the development of loxoscelism. Some studies have shown that Sicarius spiders have less or undetectable SMase D activity in their venoms, when compared to Hexophthalma. In contrast, our group has shown that Sicarius ornatus, a Brazilian species, has active SMase D and toxic potential to envenomation. However, few species of Sicarius have been characterized for their toxic potential. In order to contribute to a better understanding about the toxicity of Sicarius venoms, the aim of this study was to characterize the toxic properties of male and female venoms from Sicarius tropicus and compare them with that from Loxosceles laeta, one of the most toxic Loxosceles venoms. We show here that S. tropicus venom presents active SMases D. However, regarding hemolysis development, it seems that these toxins in this species present different molecular mechanisms of action than that described for Loxosceles venoms, whereas it is similar to those present in bacteria containing SMase D. Besides, our results also suggest that, in addition to the interspecific differences, intraspecific variations in the venoms’ composition may play a role in the toxic potential of venoms from Sicarius species.

Toxicological Characterization and Phospholipase D Activity of the Venom of the Spider Sicarius thomisoides

Envenomation by Loxosceles spiders (Sicariidae family) has been thoroughly documented. However, little is known about the potential toxicity of members from the Sicarius genus. Only the venom of the Brazilian Sicarius ornatus spider has been toxicologically characterized. In Chile, the Sicarius thomisoides species is widely distributed in desert and semidesert environments, and it is not considered a dangerous spider for humans. This study aimed to characterize the potential toxicity of the Chilean S. thomisoides spider. To do so, specimens of S. thomisoides were captured in the Atacama Desert, the venom was extracted, and the protein concentration was determined. Additionally, the venoms were analyzed by electrophoresis and Western blotting using anti-recombinant L. laeta PLD1 serum. Phospholipase D enzymatic activity was assessed, and the hemolytic and cytotoxic effects were evaluated and compared with those of the L. laeta venom. The S. thomisoides venom was able to hydrolyze sphingomyelin as well as induce complement-dependent hemolysis and the loss of viability of skin fibroblasts with a dermonecrotic effect of the venom in rabbits. The venom of S. thomisoides showed intraspecific variations, with a similar protein pattern as that of L. laeta venom at 32–35 kDa, recognized by serum anti-LlPLD1. In this context, we can conclude that the venom of Sicarius thomisoides is similar to Loxosceles laeta in many aspects, and the dermonecrotic toxin present in their venom could cause severe harm to humans; thus, precautions are necessary to avoid exposure to their bite.

Diagnóstico do loxoscelismo no município de Ibirama, Santa Catarina, Brasil

Objetivou-se diagnosticar o loxoscelismo no município de Ibirama, Santa Catarina, bem como a partir do conhecimento da estrutura das populações das aranhas e da epidemiologia dos acidentes balizar medidas preventivas por meio do diálogo entre os atores envolvidos, intermediados pela bioética ambiental, na busca por soluções consensuais e estímulo para protagonismo e criticidade dos cidadãos. A amostragem de substratos naturais e antrópicos da área urbana e rural resultaram em 68 indivíduos, sendo 93,5% relativos à Loxosceles laeta e 6,5% à L. intermedia, predominando jovens solitários (54,4%), no intradomicílio (91,2%) da área urbana (69,1%). A alta taxa de incidência de loxoscelismo (50,2 casos/10 mil habitantes/2007-2010) em Ibirama representou padrão atípico quando comparado a outros municípios, assim como o padrão dos acidentes notificados pelas autoridades de saúde, demandando uma intervenção urgente e eficaz. A prevenção ao loxoscelismo necessita de comunicação sem tuídos entre a academia, órgãos gestores e comunidade, para se compreender como proceder com efetividade, ética e sustentabilidade, no intuito de prover um ambiente bom para todos.

Evaluation of Mesenchymal Cells (MSC) and Dapsone for the Treatment of Dermonecrotic Wounds Caused by Loxosceles laeta Venom in Rabbits

We studied the efficacy of mesenchymal stem cells (MSC), either alone or associated with dapsone (DAP) in the treatment of dermonecrotic wounds caused by Loxosceles laeta spider venom. Twenty-five male adult rabbits were distributed into five groups, of which four groups received an intradermal injection of 20 μg of L. laeta venom and only one received ultrapure water (negative control). After 4 hours, each group that received venom, was treated with MSC, DAP, MSC + DAP and Phosphate-buffered saline – PBS (positive control). Photographic records were made for analysis of the wound area evolution by morphometry. Twelve days after treatment, the skin samples around the lesion were removed for subsequent histological analysis. Concerning the rate of wound contraction, we observed that DAP showed the best percentage of contraction at day 3. In the treatments using MSCs, a negative value of wound contraction was observed for the isolated MSCs, as well as a lower contraction value for the association of the MSC + DAP when compared to PBS group. Histopathological analysis showed diminished tissue lesion and less intense inflammation in MSCs and DAP groups. This could indicated potential use of stem cells in regenerative therapies after loxoscelic accidents.