Micromoina arboricola n. gen., n. spec. (Crustacea: Cladocera), a new moinid living in a forest tree-hole in Minas Gerais, Brazil

With a maximum size of ca 0.5 mm, Micromoina arboricola is among the smallest moinids known to date. It was discovered in a flooded treehole in a forest in the Medio Rio Doce Valley, Minas Gerais, Brazil, where it mainly feeds on particulate organic matter derived from the vinhatico tree. However, it is easily cultured in the lab on a diet of green algae plus yeast and pelleted fish food. Structurally, it is a miniature version of a moinid, distinguished by characters on the antennules (both sexes) and the postabdomen. The latter is peculiar in shape, in lacking a basal spine, and in having only three lateral plumose setae. A comparative investigation of the barcoding fragment of the COI gene in a number of moinids confirms the family Moinidae as composed of several genera, as well as the status of the new taxon

A review of typhloplanid flatworm ecology, with emphasis on pelagic species

The study of microturbellaria is not popular, and hence, the taxonomy and ecology of these animals are poorly known. In temperate zone ponds and lakes, the number of species may be up to 50+ per water body. The Typhloplanidae, the subject of this review, live in the littoral-benthic zone, but pelagic occurrences have been accumulating since the first case was reported in 1952. Four species are currently known to be occasionally pelagic; all live in warm-temperate or tropical lakes. Typically, one species per lake is found, but in one lake in Brazil, 2 species co-occur. One of these feeds on the other and on zooplankton, with a preference for Cladocera. Flatworms seem to trade the littoral zone for the pelagic if predation pressure in the littoral exceeds that in the open water, and if the pelagic offers better food. Most Typhloplanidae feed on arthropods, often with a preference for cladocerans, and show parallels with the cladocerans and rotifers in that 2 types of eggs (subitaneous and resting) are produced. In some flatworms, however, resting egg formation does not require amphimixis. There is also great variation between species in both the number of clutches and their composition, and within species, latitudinal differences may be important. At the cold extreme, species produce only one clutch of resting eggs; at the tropical extreme, species produce many subitaneous clutches, although resting eggs continue to be produced as well. The factors driving the life cycles of the pelagic species are discussed and include familiar variables such as temperature (circulation patterns), food, and predation. Flatworms also produce mucus and toxins that add complexity to their ecology; toxins are used for catching prey, and possibly for defense against predators (but not fish). If they become too abundant for their food supply, flatworms also seem to switch to resting egg production or block reproduction

Arsenic toxicity to cladocerans isolated and associated with iron: implications for aquatic environments

ABSTRACT Arsenic is an ametal ubiquitous in nature and known by its high toxicity. Many studies have tried to elucidate the arsenic metabolism in the cell and its impact to plants, animals and human health. In aqueous phase, inorganic arsenic is more common and its oxidation state (As III and As V) depends on physical and chemical environmental conditions. The aim of this study was to evaluate toxicity of arsenic to Daphnia similis and Ceriodaphnia silvestrii, isolated and associated with iron. The results showed differences in toxicity of As III and As V to both species. Effective concentration (EC50) mean values were 0.45 mg L-1 (As III) and 0.54 mg L-1 (As V) for D. similis, and 0.44 mg L-1 (As III) and 0.69 mg L-1 (As V) for C. silvestrii. However, As V IC25 mean value was 0.59 mg L-1, indicating that C. silvestrii has mechanisms to reduce arsenic toxicity. On the other hand, when associated with iron at 0.02 and 2.00 mg L-1, EC50 values decreased for D. similis (0.34 and 0.38 mg L-1) as well as C. silvestrii (0.37 and 0.37 mg L-1), showing synergistic effect of these substances

High temperatures and absence of light affect the hatching of resting eggs of Daphnia in the tropics

Temperature and light are acknowledged as important factors for hatching of resting eggs. The knowledge of how they affect hatching rates of this type of egg is important for the comprehension of the consequences of warming waters in recolonization of aquatic ecosystems dependent on dormant populations. This study aimed at comparing the influence of different temperature and light conditions on hatching rates of Daphnia ambigua andDaphnia laevis resting eggs from tropical environments. The ephippia were collected in the sediment of three aquatic ecosystems, in southeastern Brazil. For each lake, the resting eggs were exposed to temperatures of 20, 24, 28 and 32 °C, under light (12 h photoperiod) and dark conditions. The results showed that the absence of light and high temperatures have a negative influence on the hatching rates. Statistical differences for hatching rates were also found when comparing the studied ecosystems (ranging from 0.6 to 31%), indicating the importance of local environmental factors for diapause and maintenance of active populations

Predation and reproductive performance in two pelagic typhloplanid turbellarians

<div><p>We investigated feeding and reproductive performance of coexisting pelagic turbellarians from experiments on predation rates of <i>Mesostoma ehrenbergii</i> and <i>M</i>. <i>craci</i> as a function of food (<i>Daphnia similis</i>, three levels) and temperature (4 levels) during 10 days. Flatworms were collected from the pelagic of a subtropical lake in Brazil. Growth was more rapid at higher temperatures: more prey were consumed, and more eggs produced. <i>M</i>. <i>craci</i> and particularly <i>M</i>. <i>ehrenbergii</i> fitted a linear mixed-effects model and showed a type II functional response. <i>M</i>. <i>craci</i> was the more stenothermic of the two. Intrageneric predation also occurred: <i>M</i>. <i>ehrenbergii</i> fed on <i>M</i>. <i>craci</i>, but not vice versa. After a first clutch of subitaneous eggs, <i>M</i>. <i>ehrenbergii</i> produced resting eggs only. In <i>M</i>. <i>craci</i> an intermediate type of eggs hatched some time after release, survived passage through the gut of <i>M</i>. <i>ehrenbergii</i>, but did not resist drying. By primarily selecting cladoceran prey, <i>M</i>. <i>ehrenbergii</i> can make coexistence of both flatworms possible. As population density of <i>M</i>. <i>ehrenbergii</i> increases, it turns to producing resting and non-viable subitaneous eggs, thus limiting its population size. In nature, these processes structure the zooplankton community, while avoiding extinction of prey and predator.</p></div

Predation and reproductive performance in two pelagic typhloplanid turbellarians - Fig 2

<p>Prey consumed as function of prey density (A₁ and B₁) and prey consumed/prey offered ratio (A₂ and B₂) for <i>Mesostoma ehrenbergii</i> and <i>Mesostoma craci</i>, respectively. Closed circle, closed square, closed triangle and closed diamond correspond to 20, 24, 28 and 32°C, respectively.</p

Toward a phylogeny and biogeography of Diaphanosoma (Crustacea : Cladocera)

Diaphanosoma s.l., with 40+ described species, is the largest genus of the Sididae and the Ctenopoda, similar in many ways to the anomopod genus Daphnia. Here, we offer a c morphological evaluation of 33 species and contrast it with an analysis of the bar coding fragment of the cytochrome c oxidase subunit (COI) gene in order to gain insight into the taxonomy and phylogeny of the group. A search for structure in the genus based on micromorphological characters identified (1) the number of setae on the endopodite of P6 and (2) the relative length of the three apical setae of the exopodite of P6 as consistent markers, recovering two clades, the hexa-clade (with six endital setae) and the hepta-group (with seven setae). A third character is the armament of the posterior zone of the ventral margin of the valves, denticulated in the hexa-group, with fine filaments between the denticles in the hepta-group. Taxonomically, the two clades are assigned the rank of genera. Valid names for both are available in the published literature (Diaphanosoma Fischer s.s. and Neodiaphanosoma Paggi and Da Rocha, amended). A COI-based phylogenetic estimate leads to the same conclusion as morphology, but reveals cryptic speciation as well. COI reveals relatively small genetic distances within and between temperate climate species (e.g., in the D. birgei group) and large differences that form a cline from Australia (the terra typica) across southeast Asia in the tropical Neodiaphanosoma species D. excisum. African populations need more study, but probably represent a separate species. The entire group shows (macro)morphological stasis in the presence of molecular evolution but Neodiaphanosoma is evolving at a much faster rate than Diaphanosoma s.s. that is either a younger group. This hypothesis needs more testing, however. A biogeographic map recovers Neodiaphanosoma (containing slightly over 10 species) as restricted to the tropics, with limited penetration of the subtropics in the southern hemisphere. The more speciose Diaphanosoma group (up to 30 species) lives in the temperate and continental climate zone, with limited extension into subpolar zones, but considerable penetration of the subtropics and tropics. The subtropics, where both groups broadly overlap, is the zone with the highest species richness