The influence of environmental factors on the distribution of Ephemeroptera, Plecoptera and Trichoptera (EPT) immatures was investigated in streams of the Brazilian Center-West (Serra do Pireneus, Pirenópolis, State of Goiás). The insects were sampled by lifting the stones in front of a sieve (0.5 mm mesh) and then removing the insects from both the stone and the sieve. Sampling was carried out for 1 h at 5 collection sites over a period of 14 months. Air and water temperature (°C), water velocity (m/s), discharge (m 3 /s), electric conductivity (µS/cm), pH, and rainfall (mm) were also recorded. In general, we may state that altitude, hydrologic classification (order) and vegetation cover were the most important factors explaining the distribution of Ephemeroptera, Plecoptera and Trichoptera immatures. The influence of the rainfall on the temporal variation of the abundance of insects was stronger in stream segments of medium order (3 rd , 4 th order) compared to smaller streams (first order).Keywords: Ephemeroptera, Plecoptera, Trichoptera, lotic environments, larval distribution.
RESUMO Comunidades de Ephemeroptera, Plecoptera e Trichoptera em riachos de montanha do Brasil Central: fatores ambientais influenciando a distribuição e abundânciaA influência de fatores ambientais sobre a distribuição de imaturos de Ephemeroptera, Plecoptera e Trichoptera (EPT) foi investigada em riachos do Centro Oeste Brasileiro (Serra do Pireneus, Pirenópolis, Estado de Goiás). Os insetos foram amostrados lavando pedras em frente a um rede (0,5 mm de malhas) e removendo os insetos tanto das pedras quanto das redes. A amostragem foi feita durante 1 h em cinco pontos de coleta em um período de 14 meses. Temperaturas do ar e da água (°C), velocidade da água (m/s), vazão (m 3 /s), condutividade elétrica (µS/cm), pH, e precipitação pluviométrica (mm) também foram registradas. Em geral, podemos afirmar que a altitude, a classificação hidrológica (ordem) e a cobertura vegetal foram os fatores mais importantes na distribuição de imaturos de Ephemeroptera, Plecoptera e Trichoptera. A influência da precipitação pluviométrica sobre a variação temporal da abundância foi maior em trechos de ordem média (3 a , 4 a ordem) quando comparado aos menores riachos (primeira ordem).Palavras-chave: Ephemeroptera, Plecoptera, Trichoptera, ambientes lóticos, distribuição larval. 612 BISPO, P. C. et al.
Revista Brasileira de Zoologia 24 (2): 283-293, junho 2007The structure of the fauna of aquatic insects in lotic environments is directly related to geomorphology, hydrology, quality of water, quality and availability of food resources, dominant substratum, temperature and dissolved oxygen (VANNOTE et al. 1980, RICHARDS et al. 1993, ZAMORA-MUÑOZ et al. 1993, ZAMORA-MUÑOZ & ALBA TERCEDOR 1996, BISPO et al. 2006. Those characteristics vary in time and space; therefore, it is expected that those variation determine the spatial and temporal alteration of diversity and of structure of fauna in the aquatic communities.Among the aquatic insects, Ephemeroptera, Plecoptera and Trichoptera, usually known as EPT, comprise a rich assemblage of taxa in low and medium order cobble streams. These organisms are sensitive to environmental perturbations and occur, mainly, in clean and well-oxygenated waters. Due to those characteristics, these organisms are frequently considered as good indicators of water quality (ROSENBERG & RESH 1993). According to MARCHANT et al. (1995), patterns found for EPT represent the same patterns found for the macroinvertebrate fauna as a whole; for this reason, studies could be restricted to that fauna. BISPO et al. (2006) have investigated the effect of environmental factors over the distribution of EPT and have concluded that precipitation, stream order and altitude were the main factors that determine distribution and fauna abundance. The present work aimed to evaluate the effect of spatial variation, including the effects of stream size, anthropic action, and seasonality (dry and rainy seasons) over diversity and structure of Ephemeroptera, Plecoptera and Trichoptera assemblages. Caixa Postal 131, Goiás, ABSTRACT. The diversity and structure of Ephemeroptera, Plecoptera and Trichoptera (EPT) assemblages in streams of Central Brazil (Serra dos Pireneus, Pirenópolis, State of Goiás) was investigated. Abundance data of EPT were obtained in Central-West Brazilian streams in order to evaluate the effect of spatial variability, including the effect of size of the stream and anthropic action, and seasonality (dry and rainy seasons) on faunal diversity and structure. The immatures were collected with circular sieves (0.5 mm mesh) during one hour at five collection stations over 14 months. From a spatial point of view, the data showed that anthropic action determined the patterns of diversity whereas the size of streams (1 st and 3 rd -4 th orders) determined the faunistic composition. In addition, environmental seasonality was an important factor for structuring the EPT fauna.
Wing pigmentation is a trait that predicts the outcome of male contests in some damselflies. Thus, it is reasonable to suppose that males would have the ability to assess wing pigmentation and adjust investment in a fight according to the costs that the rival may potentially impose. Males of the damselfly Mnesarete pudica exhibit red-coloured wings and complex courtship behaviour and engage in striking male-male fights. In this study, we investigated male assessment behaviour during aerial contests. Theory suggests that the relationship between male resource-holding potential (RHP) and contest duration describes the kind of assessment adopted by males: self-assessment, opponent-only assessment or mutual assessment. A recent theory also suggests that weak and strong males exhibit variations in the assessment strategies adopted. We estimated male RHP through male body size and wing colouration (i.e. pigmentation, wing reflectance spectra and transmission spectra) and studied the relationship between male RHP and contest duration from video-documented behavioural observations of naturally occurring individual contests in the field. The results showed that males with more opaque wings and larger red spots were more likely to win contests. The relationships between RHP and contest durations partly supported the self-assessment and the mutual assessment models. We then experimentally augmented the pigmented area of the wings, in order to evaluate whether strong and weak males assess rivals' RHP through wing pigmentation. Our experimental manipulation, however, clearly demonstrated that strong males assess rivals' wing pigmentation. We finally suggest that there is a variation in the assessment strategy adopted by males.
Zenithoptera dragonflies are known for their remarkable bluish colouration on their wings and unique male behaviour of folding and unfolding their wings while perching. However, nothing is known about the optical properties of such colouration and its structural and functional background. In this paper, we aimed to study the relationship between the wing membrane ultrastructure, surface microstructure and colour spectra of male wings in Zenithoptera lanei and test the hypothesis that colouration functions as a signal in territorial fights between males. The results show that the specific wing colouration derives from interference in alternating layers of melanized and unmelanized cuticle in the wing membrane, combined with diffuse scattering in two different layers of wax crystals on the dorsal wing surface, one lower layer of long filaments, and one upper layer of leaf-shaped crystals. The results also show that the thicker wax coverage of the dorsal surface of the wings results in increased brightness and reduced chroma. In the field experiments, we have demonstrated that there is a reduction of aggressive reactions of rivals towards individuals with experimentally reduced amount of blue wing colouration.
Assemblages of Ephemeroptera, Plecoptera and Trichoptera (EPT) of rocky substrates were studied in two streams of the Intervales State Park. Monthly collections with a Surber sampler (10 random sampling units, 1m²) were carried out from September 1999 to September 2000 and quarterly from December 2000 to September 2001 in the Bocaina and Água Comprida Streams. The EPT fauna in the Bocaina Stream was more diversified and more abundant than in the Água Comprida Stream. The EPT fauna was quite different in the two streams both in composition as in functional aspects. The results of this study indicate that there was not a clear seasonal pattern in the temporal variation of density.
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