Testes empíricos sobre a ocorrência diferencial de listras em duas espécies de Monodelphis (Didelphidae: Mammalia) e seu papel como coloração disruptiva e na evasão de predadores

• Ano de defesa: 2014
• Autor(a) principal: Leone, Maíra Franco
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Mestrado em Biologia Animal; UFES; Programa de Pós-Graduação em Ciências Biológicas
• Palavras-chave em Português: Camouflage; Disruptive coloration; Crypsis; Predation; Visual search; Animal coloration; Camuflagem; Coloração disruptiva; Criptismo; Predação; Busca visual; Coloração animal; Zoologia; 57
• Link de acesso: http://repositorio.ufes.br/handle/10/9419

Camouflage is a defense strategy that has been studied for over two hundred years and includes a variety of types, such as disruptive coloration, background matching, countershading and distractive markings. Although there are several works on camouflage for groups such as birds, fish and insects, studies on the influence of fur color patterns in the rate of predation of small mammals are virtually nonexistent. Monodelphis (Didelphidae) is a terrestrial small marsupial that exhibits diurnal activity, and includes a group of species with dark stripes on its back, which may be an example of disruptive camouflage. Two species in the striped group, M.americana and M.iheringi, may occur in sympatry and, when they do, we note that adult males of M.americana lose their stripes while females and juveniles of both species and males of M. iheringi keep their striped pattern. Hence, the goal of this study was to verify the effectiveness of stripes for camouflage, by testing it with the use of artificial prey models in the field and by means of an Android app. Plasticine models of the striped and nonstriped forms in two different sizes were made with similar measurements to those of each species. They were deployed in 44 stations along four transects in a forested area in the Duas Bocas Biological Reserve (Cariacica, Espírito Santo), where the two species are sympatric. At each station, four models were arranged in an equal ratio of individuals, with and without stripes, of both sizes, totaling 176 models/night. Four campaigns of 10 days each were conducted with a total effort of 6160 models-night. The models were checked for predation marks twice daily (early morning/late afternoon). Forty-one attacks were recorded, of which 13 on large models with stripes, 17 on large ones without stripes, 2 on small ones with stripes and 9 on small ones without stripes. Models without stripes represented 63% of the recorded attacks, showing a predation rate significantly higher (G = 6.8, p = 0.009). However, when only the large models were considered, the presence of stripes was not statistically significant. In the wet season (Jan/May) there was a greater difference in the capture rate between the striped and non-striped models, when striped models were significantly less preyed; the same was not observed for the dry season (Aug/Sep), when rates were similar. Another test performed used an Android app that displays pictures of striped and non-striped models on a natural litterfall background, and volunteers tried to detect the models in the picture. The app uses 20 photos in total: 10 with models with stripes and 10 without. At each round, 10 photos were randomly shown in an equal proportion of models, and the participants were asked to try to find the target in the image. The experiment was conducted with 80 participants who were not experts in the area and also were not informed about the hypothesis being tested beforehand. Four scenarios were analyzed, with distinct time limits for capture: 5 seconds, 10 seconds, 15 seconds and, aditionally, with no time limit. In all scenarios of the 800 tests with the app, there was a higher error rate of participants trying to capture striped models, particularly in the 5 seconds scenario in which the error rate was 39.5% for striped models and 24% for models without stripes. The Wilcoxon test showed that the average time taken to capture the target was statistically different (p>0.0001): in all scenarios participants took longer to find the striped models. In both tests, the presence of stripes proved relevant in camouflage, hindering the detection of individuals and contributing to the avoidance of predators. Nonetheless, stripes seem to be even more effective when combined with a reduced size, which applies to M. iheringi, the smaller species, and juveniles of M. americana. Therefore, stripes seem to be particularly important for small Monodelphis, regardless of them being adults or juveniles of different species - the latter most vulnerable and not yet sexually active. In general the stripes proved to be important, their perpetuation in adult females of M. americana could yet be related to the role played by them in the care of offspring.