Description of the Immature Stages of Three Nearctic Species of the Genus Berosus Leach (Coleoptera: Hydrophilidae)

Egg cases, larvae, and pupae of Berosus corrini Wooldridge 1964, Berosus hoplites Sharp 1887, and Berosus pugnax LeConte 1863, are described and illustrated with line drawings. Bionomic and behavioral observations of larvae and adults are included. Keys to different instars of B. hoplites and B. pugnax larvae are provided.     

Sampling multiple life stages significantly increases estimates of marine biodiversity

Biodiversity assessments are critical for setting conservation priorities, understanding ecosystem function and establishing a baseline to monitor change. Surveys of marine biodiversity that rely almost entirely on sampling adult organisms underestimate diversity because they tend to be limited to habitat types and individuals that can be easily surveyed. Many marine animals have planktonic larvae that can be sampled from the water column at shallow depths. This life stage often is overlooked in surveys but can be used to relatively rapidly document diversity, especially for the many species that are rare or live cryptically as adults. Using DNA barcode data from samples of nemertean worms collected in three biogeographical regions—Northeastern Pacific, the Caribbean Sea and Eastern Tropical Pacific—we found that most species were collected as either benthic adults or planktonic larvae but seldom in both stages. Randomization tests show that this deficit of operational taxonomic units collected as both adults and larvae is extremely unlikely if larvae and adults were drawn from the same pool of species. This effect persists even in well-studied faunas. These results suggest that sampling planktonic larvae offers access to a different subset of species and thus significantly increases estimates of biodiversity compared to sampling adults alone. Spanish abstract is available in the electronic supplementary material.     

乌苏里江洪泛湿地蜻蜓目幼虫对水文连通阻断的生态响应

大型底栖动物的群落组成完整性能够指示和预测水生态环境的健康程度和变化趋势,已经在大量研究中得到验证.然而,群落水平的全部样品采集过程的复杂性并不利于它们的便捷应用.蜻蜓目幼虫是大型底栖动物中相对易于捕捉和识别的类群,并且拥有特别的两栖生命周期,它们的多样性特征以及对水体性质变化的敏感反应,使其成为湿地生态系统中非常广泛...     

Light and electron microscopy studies of the midgut and salivary glands of second and third instars of the horse stomach bot,Gasterophilus intestinalis

A morphological study of the midgut and salivary glands of second and third instars of Gasterophilus intestinalis (De Geer) (Diptera: Oestridae) was conducted by light, scanning and transmission electron microscopy. The midgut is anteriorly delimited by a proventriculus, without caeca, and is composed of posterior foregut and anterior midgut tissue from which a double‐layered peritrophic matrix is produced. The midgut can be divided into anterior, median and posterior regions on the basis of the structural and physiological variations of the columnar cells which occur along its length. Two other types of cell were identified: regenerative cells scattered throughout the columnar cells, and, more rarely, endocrine cells of two structural types (closed and open). Different secretion mechanisms (merocrine, apocrine and microapocrine) occur along the midgut epithelium. Abundant microorganisms are observed in the endoperitrophic space of the anterior midgut. The origin and nature of these microorganisms remain unknown. No structural differences are observed between the second and third instar midguts. The salivary glands of G. intestinalis second and third instars consist of a pair of elongated tubular structures connected to efferent ducts which unite to form a single deferent duct linked dorsally to the pharynx. Several intermediate cells, without cuticle, make the junction with the salivary gland epithelium layer. Cytological characteristics of the gland epithelial cells demonstrate high cellular activity and some structural variations are noticed between the two larval stages.     

Metabolic Reconfiguration in C. elegans Suggests a Pathway for Widespread Sterol Auxotrophy in the Animal Kingdom

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Morphology and ultrastructure of spiracles in phlebotomine sandfly larvae

The morphology and ultrastructure of the larval spiracle system of three phlebotomine sandfly species, Phlebotomus perniciosus, P. perfiliewi and P. papatasi, were examined by scanning (SEM) and transmission (TEM) electron microscopy and by confocal scanning laser microscopy (CSLM). During larval development, thoracic and abdominal spiracles show considerable modifications. In fourth instar larvae, the spiracles consist of a plate with a sclerotized central portion and a peripheral circle of papillae. The latter is distinctive in the larvae of P. papatasi, which are readily distinguished from the other species. Opening clefts across the papillae communicate with an internal chamber that encircles an electrondense plug. Many cylindrical projections cross the chamber, uniting the central plug with the larval body, forming an air filter. Spiracular development in successive larval instars has both a taxonomic and adaptive value.     

Fish, Flows and Flood Plains: Links between Freshwater Fishes and their Environment in the Murray-Darling River System, Australia

Knowledge of the biology of native fishes of the Murray-Darling Basin is based largely on studies conducted under hatchery conditions and on a limited number of recreationally important species. From observations that increases in water level in aquaculture ponds initiate spawning in some species, and from limited studies of wild fishes and studies in overseas floodplain river systems, a perception has emerged of the importance of flooding and the flood plain in the life cycles of Murray-Darling fishes in general. However, there is little confirmatory evidence of the use of temporary floodplain habitats by larvae, juveniles or adults. The significance of in-channel habitats, especially for rearing, has received little attention. Murray-Darling fish species can be placed into three life history modes, based mainly on spawning style and time and developmental intervals of larvae at first feeding. Fish in each group may be able to take advantage of floods if the timing is right and prey are plentiful, however, the larvae of some species are able to recruit under non-flood conditions within the main river channel. This forms the basis of the low flow recruitment hypothesis, which attempts to explain why some species spawn during the warmest months and lowest flows and how they are able to recruit under these conditions. This hypothesis is then placed in the context of the current state of knowledge of the relationships between flow and the biology of Murray-Darling fishes, specifically cues for spawning, movement and recruitment. The lack of widespread evidence for floodplain use by any life history interval of fish may be due to a paucity of study, however, there are some fundamental factors, such as the predictability of timing and duration of high flow events as well as the lack of coincidence of high flows and high temperatures in some regions of the Basin, which may be important in determining the use of floodplain habitats by fish.     

Habitat characteristics of Anopheles gambiae s.s. larvae in a Kenyan highland

Anopheline larval habitats associated with a swamp, were examined in a highland area (1910 m elevation) of western Kenya. A significant association was found between occurrence of Anopheles gambiae Giles s.s. (Diptera: Culicidae) larvae and two factors, habitat size and vegetation type. Over 80% of An. gambiae s.s. larvae were found in small isolated pools, characterized by short plants, occurring in both swamp margins and roadside ditches. However, Anopheles gambiae s.s. was not found in habitats marked by papyrus and floating plants. The larval habitat of An. gambiae s.s. was characterized by warmer daytime temperatures of water, which were significantly affected by habitat size and plant size. The density of indoor resting An. gambiae s.s. was 0.22 per house and negatively associated with distance from the swamp. These results indicate that the practice of swamp cultivation, in populated areas of the African highlands, increases availability and enhances habitat conditions for the malaria vector.     

Optimal growth strategies of larval helminths in their intermediate hosts

We consider optimal growth of larval stages in complex parasite life cycles where there is no constraint because of host immune responses. Our model predicts an individual's asymptotic size in its intermediate host, with and without competition from conspecific larvae. We match observed variations in larval growth patterns in pseudophyllid cestodes with theoretical predictions of our model. If survival of the host is vital for transmission, larvae should reduce asymptotic size as intensity increases, to avoid killing the host. The life history strategy (LHS) model predicts a size reduction <1/intensity, thus increasing the parasite burden on the host. We discuss whether body size of competing parasites is an evolved LHS or simply reflects resource constraints (RC) on growth fixed by the host, leading to a constant total burden with intensity. Growth under competition appears comparable with "the tragedy of the commons", much analysed in social sciences. Our LHS prediction suggests that evolution generates a solution that seems cooperative but is actually selfish.     

Leucine transport in membrane vesicles from Chironomus riparius larvae displays a mélange of crown-group features

Leucine uptake into membrane vesicles from larvae of the midge Chironomus riparius was studied. The membrane preparation was highly enriched in typical brush border membrane enzymes and depleted of other membrane contaminants. In the absence of cations, there was a stereospecific uptake of l-leucine, which exhibited saturation kinetics. Parameters were determined both at neutral (Km 33 +/- 5 microM and Vmax 22.6 +/- 6.8 pmol/7s/mg protein) and alkaline (Km 46 +/- 5 microM and Vmax 15.5 +/- 2.5 pmol/7s/mg protein) pH values. At alkaline pH, external sodium increased the affinity for leucine (Km 17 +/- 1 microM) and the maximal uptake rate (Vmax 74.0 +/- 12.5 pmol/7s/mg protein). Stimulation of leucine uptake by external alkaline pH agreed with lumen pH measurements in vivo. Competition experiments indicated that at alkaline pH, the transport system readily accepts most L-amino acids, including branched, unbranched, and alpha-methylated amino acids, histidine and lysine, but has a low affinity for phenylalanine, beta-amino acids, and N-methylated amino acids. At neutral pH, the transport has a decreased affinity for lysine, glycine, and alpha-methylleucine. Taken together, these data are consistent with the presence in midges of two distinct leucine transport systems, which combine characters of the lepidopteran amino acid transport system and of the sodium-dependent system from lower neopterans.