Jayme Magalhães Santangelo

Rhodnius prolixus interaction with Trypanosoma rangeli: modulation of the immune system and microbiota population

BackgroundTrypanosoma rangeli is a protozoan that infects a variety of mammalian hosts, including humans. Its main insect vector is Rhodnius prolixus and is found in several Latin American countries. The R. prolixus vector competence depends on the T. rangeli strain and the molecular interactions, as well as the insect’s immune responses in the gut and haemocoel. This work focuses on the modulation of the humoral immune responses of the midgut of R. prolixus infected with T. rangeli Macias strain, considering the influence of the parasite on the intestinal microbiota.MethodsThe population density of T. rangeli Macias strain was analysed in different R. prolixus midgut compartments in long and short-term experiments. Cultivable and non-cultivable midgut bacteria were investigated by colony forming unit (CFU) assays and by 454 pyrosequencing of the 16S rRNA gene, respectively. The modulation of R. prolixus immune responses was studied by analysis of the antimicrobial activity in vitro against different bacteria using turbidimetric tests, the abundance of mRNAs encoding antimicrobial peptides (AMPs) defensin (DefA, DefB, DefC), prolixicin (Prol) and lysozymes (LysA, LysB) by RT-PCR and analysis of the phenoloxidase (PO) activity.ResultsOur results showed that T. rangeli successfully colonized R. prolixus midgut altering the microbiota population and the immune responses as follows: 1 - reduced cultivable midgut bacteria; 2 - decreased the number of sequences of the Enterococcaceae but increased those of the Burkholderiaceae family; the families Nocardiaceae, Enterobacteriaceae and Mycobacteriaceae encountered in control and infected insects remained the same; 3 - enhanced midgut antibacterial activities against Serratia marcescens and Staphylococcus aureus; 4 - down-regulated LysB and Prol mRNA levels; altered DefB, DefC and LysA depending on the infection (short and long-term); 5 - decreased PO activity.ConclusionOur findings suggest that T. rangeli Macias strain modulates R. prolixus immune system and modifies the natural microbiota composition.

Abundance, composition and spatial variation in the egg bank of a tropical zooplankton community

Resting eggs have important ecological roles in zooplankton communities, but characterizations of egg banks in tropical systems remain scarce. Here, we describe the abundance, composition and spatial variation in the egg bank of a tropical zooplankton community in a shallow aquatic system (Imboassica lagoon, Brazil). Due to sporadic disturbances by sandbar openings at this system, we hypothesized that the abundance and species richness close to the sandbar is lower when compared to other sites. Sediment samples were collected at four sampling stations, and the egg bank was analyzed using ex situ hatching experiments. Hatchlings from 21 rotifer and five cladoceran species were identified considering all sampling stations. The number of hatchlings at the sampling stations ranged from 14.2 (± 3.8 SE) to 192.8 (± 37.1), whereas species richness ranged from 3.6 (± 0.7) to 12.2 (± 0.5) in 100 g of wet sediment. Abundance and species richness were similar at three of the sampling stations, suggesting low spatial variations in the egg bank of shallow systems. Significantly lower values for abundance and species richness were found close to the sandbar when compared to the other sampling stations, probably as a result of local and recurrent disturbances due to artificial sandbar openings. The presence of an egg bank is a possible mechanism for facilitating the reestablishment of active populations after disturbances by sandbar openings and consequent increases in salinity at Imboassica lagoon. Os ovos de resistência apresentam importantes funções ecológicas para as comunidades zooplanctônicas, mas a caracterização do banco de ovos de sistemas tropicais permanece escassa. Nesse estudo nós descrevemos a abundância, a composição e a variação espacial do banco de ovos de uma comunidade zooplanctônica tropical oriunda de um sistema aquático raso (lagoa Imboassica, Brasil). Devido a eventuais distúrbios ocasionados por aberturas de barra nesse sistema, nós hipotetizamos que a abundância e a riqueza de espécies próximo à barra de areia são menores quando comparadas a outros locais. Amostras de sedimento foram coletadas em quatro estações amostrais, e o banco de ovos foi analisado através de experimentos de eclosão ex situ. Através dos organismos eclodidos dos ovos foram identificadas 21 espécies de rotíferos e cinco de cladóceros, considerando todas as estações amostrais. O número de organismos eclodidos nas estações amostrais variou de 14.2 (± 3.8 EP) a 192.8 (± 37.1), enquanto a riqueza de espécies variou de 3.6 (± 0.7) a 12.2 (± 0.5) em 100 g de sedimento úmido. A abundância e a riqueza de espécies foram similares em três das estações amostrais, sugerindo uma baixa variação espacial no banco de ovos de sistemas rasos. Valores significativamente menores de abundância e riqueza de espécies foram encontrados próximo à barra de areia, quando comparados com as outras estações, provavelmente como resultado de distúrbios locais e recorrentes devido às aberturas artificiais da barra de areia. A presença de um banco de ovos é um possível mecanismo facilitador do restabelecimento das populações ativas após distúrbios ocasionados por aberturas de barra e consequentes aumentos da salinidade na lagoa Imboassica.

An overview of the contribution of studies with cladocerans to environmental stress research

Cladocerans are microcrustaceans component of the zooplankton in a wide array of aquatic ecosystems. These organisms, in particular the genus Daphnia, have been widely used model organisms in studies ranging from biomedical sciences to ecology. Here, we present an overview of the contribution of studies with cladocerans to understanding the consequences at different levels of biological organization of stress induced by environmental factors. We discuss how some characteristics of cladocerans (e.g., small body size, short life cycles, cyclic parthenogenesis) make them convenient models for such studies, with a particular comparison with other major zooplanktonic taxa. Then we illustrate the contribution of cladocerans to stress research with examples encompassing stress responses spanning from the molecular to the populational level. Most worth of note are recent studies that presented evidence of beneficial consequences of mild stress caused by natural stressors (cross-tolerance), which may be passed along across generations, favoring individual survival and species persistence in fluctuating environments. This would be particularly relevant for environments prone to frequent natural environmental fluctuations, such as coastal lagoons and other shallow aquatic ecosystems. Based on reviewed studies, a conceptual model is presented summarizing the potential effects of a first stressor on the organisms resistance to a second one. We finish by highlighting some gaps on environmental stress research that could benefit from further studies using cladocerans as model organisms.

Zooplankton resting egg banks in permanent and temporary tropical aquatic systems

AIM: We evaluated zooplankton resting egg banks and active communities in five coastal lagoons and in five temporary pools, aiming to compare the active and the dormant communities in such environments. As they differ in hydroperiod, we expected that pools present richer resting egg banks in comparison to those found in lagoons. METHODS: Zooplankton community was sampled twice in 2006 (lagoons) and in 2010 (pools) and resting egg banks were sampled once in December 2007 (lagoons) and in May 2010 (pools). Resting eggs were isolated from the sediment by applying the sugar flotation method. RESULTS: In opposition to our expectation, species richness in the resting egg banks of pools did not differ from those of lagoons. Additionally, no difference was found between the active and the dormant zooplankton communities in each water body for both temporary and permanent environments. However, similarity between active and dormant communities was greater in permanent environments than it was in temporary environments. CONCLUSIONS: It seems that the diapause strategy observed in certain tropical zooplankton populations cannot be predicted based on the awareness of the environment type (permanent or temporary), since hatching cues may be species-specific.

Lethal and sublethal effects of essential oil of Lippia sidoides (Verbenaceae) and monoterpenes on Chagas’ disease vector Rhodnius prolixus

The aim of this study was to identify the composition of the essential oil from leaves of Lippia sidoides (EOLS), a typical shrub commonly found in the dry northeast of Brazil, popularly known as “alecrim-pimenta”. Additionally, we investigated the nymphicidal, ovicidal, phagoinhibitory and excretion effects of EOLS, its major constituent thymol and its isomer carvacrol, on fourth instar nymphs and eggs of Rhodnius prolixus, the Chagas’ disease vector. The nymphicidal and ovicidal activity of thymol, carvacrol, and EOLS was assessed by tests using impregnated Petri dishes. The lethal concentration values (LC50) for EOLS, carvacrol, and thymol were 54.48, 32.98, and 9.38 mg/cm2, respectively. The ovicidal test showed that both carvacrol and thymol (50 mg/cm2) inhibited hatching (50% and 23.3%, respectively), while treatments with 10 mg/cm2 or 50 mg/cm2 EOLS did not affect the hatching rate at all (80% and 90%, respectively). We observed an anti-feeding effect in insects fed with blood containing natural products at the higher concentrations (100 µg/mL). Finally, excretion rate was affected by EOLS and carvacrol, but not by thymol. These findings offer novel insights into basic physiological processes that make the tested natural compounds interesting candidates for new types of insecticides.

Effects of sandbar openings on the zooplankton community of coastal lagoons with different conservation status

OBJETIVO: Aberturas artificiais da barra de areia sao praticas de manejo comuns em lagoas costeiras, mas podem ser uma ameaca se provocarem efeitos negativos a qualidade de agua e para a biota aquatica. Nesse estudo foram comparados os efeitos de aberturas de barra em duas lagoas costeiras proximas, que diferem no estado trofico e no historico de aberturas de barra. METODOS: Variaveis limnologicas e a comunidade zooplanctonica foram analisadas mensalmente durante um ano antes e um ano depois de aberturas de barra ocorridas no mesmo mes para ambas as lagoas, totalizando 24 amostras. Foram comparados os efeitos da abertura de barra nas variaveis-resposta em funcao dos dois tipos de sistema. RESULTADOS: As aberturas de barra determinaram alteracoes em algumas variaveis limnologicas (profundidade e salinidade), mas estes efeitos ocorreram de forma diferenciada nos dois tipos de sistema. A estrutura da comunidade zooplanctonica mudou mais fortemente na lagoa eutrofica e mais comumente conectada ao mar. A ocorrencia e abundância de algumas especies foram fortemente ligadas as mudancas nas variaveis limnologicas. CONCLUSOES: Os dados indicam que as comunidades zooplanctonicas sao mais resistentes as aberturas de barra em lagoas costeiras historicamente menos impactadas. A direcao e a intensidade das mudancas provocadas pelas aberturas de barra podem ser especificas para cada lagoa, devido a diferencas no historico de impactos que, em longo prazo, modificam a qualidade da agua e a estrutura da comunidade zooplanctonica nestes sistemas e, consequentemente, sua resistencia e resiliencia.

Species and clone-dependent effects of tilapia fish (Cichlidae) on the morphology and life-history of temperate and tropical Daphnia

In aquatic systems, tilapia introductions may result in marked changes in the structure of prey communities. In this study, we experimentally examined the effects of tilapia-mediated water at the individual and population levels of prey by exposing three Daphnia species to predation cues. We hypothesized that tilapia-mediated water determines reduced age and size at primipara, greater and faster reproduction, enhanced intrinsic rates of population increase (r), and longer tail spines in Daphnia; but that the magnitude of these changes would be species and clone-dependent. When three tropical D. laevis and one temperate D. similis clones were exposed to predation cues, adaptive changes were observed in some of the aforementioned parameters for each clone. The three D. laevis clones exhibited changes in all life-history and morphological measures. Temperate Daphnia spinulata displayed no changes but decreased r values in the presence of predators. The observed changes in the species and clones tested here suggest that, overall, both temperate and tropical Daphnia can detect and adaptively react to the risk of tilapia predation. However, only a fraction of the possible defenses may be displayed by individual clones. In contrast, D. spinulata seems more vulnerable to tilapia predation, given its long body length and absence of adaptive changes. Our study indicates that Daphnia can respond to tilapia-mediated water, and that interspecific and clonal variation exists between temperate and tropical species.

Long-term dynamics of the zooplankton community during large salinity fluctuations in a coastal lagoon

Aquatic coastal systems are affected by high fluctuations in salinity and the zooplankton may rely on dispersal or dormancy to recolonise these environments. Here, we analysed the long-term dynamics of the zooplankton community over 6 years during large salinity fluctuations in a coastal lagoon (Garcas Lagoon, Brazil) and the effect of salinity on the hatching patterns of the resting egg bank. We hypothesised that salinity is the main driving factor of the zooplankton community structure, and that increases in salinity reduce the species richness and the abundance of hatchlings. Multiple regression analysis showed that salinity was associated negatively with species richness in the open water, whereas total phosphorus and chlorophyll-a concentrations were negatively and positively related to abundance respectively. Redundancy analysis demonstrated that temporally structured environmental variables (total phosphorus and salinity) were important for zooplankton composition. Periods of low salinity allowed the presence of freshwater organisms, changing the zooplankton composition over the years. However, our hatchling experiment showed a depauperate resting egg bank. Overall, our results showed a strong influence of salinity on the structure and dynamics of the zooplankton at Garcas Lagoon, and that the resting egg bank likely plays a minor role in the zooplankton colonisation during low-salinity periods.