The Structure and Development of the Dorsal Bristle Complex of Oxytricha fallax and Stylonychia pustulata*

SYNOPSIS. Oxytricha fallax and Stylonychia pustulata possess 6 rows of dorsal bristle units. Each dorsal bristle unit consists of a pair of kinetosomes; the anterior kinetosome has a cilium and the posterior kinetosome a ciliary stub. The kinetosome pair, located at the bottom of a cortical pit surrounding the cilium and ciliary stub, is surrounded by an asymmetrical fibrillar mass. Future rows 1-4 are formed from 2 sets of primordia originating within mature dorsal rows 1-3. Rows 5 and 6 originate from the anterior regions of both right marginal cirral primordia. Old dorsal bristle units utilized in formation of primordia are presumably maintained in the new rows of the proter and opisthe; those outside the primordia are resorbed. The morphogenetic pattern of the Oxytrichidae is similar to those of the Urostylidae and Holostichidae, but quite different from that of the Euplotidae.     

An experimental analysis of the water relations of eggs of Blanding's turtles (Emydoidea blandingii)

Eggs of Blanding's turtles ( Emydoidea blandingii ) were incubated in the laboratory under hydric conditions eliciting different patterns of net water exchange between eggs and surrounding air and substrate. Eggs incubated on wet and intermediate substrates increased in mass during the first half of incubation and decreased in mass during the second half, and their mass just before hatching was slightly lower than at oviposition. Eggs incubated on dry substrates and on platforms above substrates declined in mass throughout incubation, with a rate of decline greater in the second half of incubation than in the first. The size of hatchlings was related to the hydric environment in which eggs were incubated and, possibly, to the net flux of water across eggshells. However, variation in size of hatchlings was not as great as has been reported for other species with flexible-shelled eggs, owing presumably to the constraints on water exchange imposed by the more complex eggshells of Blanding's turtles.     

Wintering Snowy Owls Bubo scandiacus integrate plumage colour,behaviour and their environment to maximize efficacy of visual displays

For a comprehensive understanding of the evolution of animal signals, it is necessary to understand how the performance of visual displays is maximized to get the most possible attention from receivers. We assessed whether the white plumage of Snowy Owls Bubo scandiacus functioned as a social signal and, if so, how coloration and behavioural adaptations enhance signal efficacy. Signalling theory predicts that: (1) the colour properties of plumage should vary across the body, with the brightest parts being those involved in visual display performance; (2) specific displays calling attention to or enhancing detection or conspicuousness to conspecifics should be evident; and (3) location of the signallers should be such that signal efficacy is optimized. All three predictions were supported. The brightest areas of the plumage (particularly the face, throat and upper breast) were always unspotted, and white is particularly effective in open habitats characteristic of this species. The birds displayed a specific posture and orientated toward the sun preferentially on sunny days, and Owls with the whitest (least spotted) plumage displayed more and signalled more frequently from perches on the ground, where albedo from the snow may enhance the visual display. Snowy Owls integrate coloration, behaviour and environment through habitat selection to maximize the efficacy of their visual displays.     

Impact of turbulence on riverine zooplankton: a mesocosm experiment

1. With increases in river discharge over time and space, zooplankton generally encounter increased turbulence, turbidity, hydraulic forces, downstream advection and food limitations, all of which should affect species diversity and densities. Of these factors, the role of turbulence on the distribution of zooplankton is least known along longitudinal and lateral dimensions in river networks. 2. We tested the factorial effects of turbulence and grazing level on Ohio River potamoplankton in spring and summer using twelve 1600‐L, outdoor mesocosms. Turbulence was calculated using the Froude number for equal depths but with current velocities of 0.064 and 0.32 m s^?1. Grazing levels corresponded to a high density treatment (=ambient river densities of rotifers, copepods and cladocerans) and a low density treatment (initially no zooplankton >64 μm). All tanks had the same water residence time, and hydraulic stress was minimized by circular flow patterns. 3. Zooplankton densities and population growth rates were significantly affected by turbulence level and season. In general, rotifer populations grew faster in high turbulence tanks (though Keratella and Brachionus populations flourished in both treatments in summer) and microcrustaceans thrived better in low turbulence environments. The larger, calanoid copepods handled more turbulent conditions much better than cyclopoids or nauplii. Zooplankton had no detectable effects on particulate organic carbon concentrations in either month (values were higher in spring), but rotifers reduced chlorophyll concentrations in both months. 4. The relative importance of turbulence in controlling potamoplankton is probably to vary not only on a longitudinal basis in river networks but also with both the hydrogeomorphic complexity of river reaches and the type and amount of river regulation. Plans for river rehabilitation and management should incorporate non‐turbulent habitats in large rivers as a means of enhancing zooplankton populations and providing an important food web component for planktivores.     

Molecular phylogenetic biodiversity assessment of arctic and boreal ectomycorrhizal Lactarius Pers. (Russulales; Basidiomycota) in Alaska, based on soil and sporocarp DNA

Despite the critical roles fungi play in the functioning of ecosystems, especially as symbionts of plants and recyclers of organic matter, their biodiversity is poorly known in high-latitude regions. In this paper, we discuss the molecular diversity of one of the most diverse and abundant groups of ectomycorrhizal fungi: the genus Lactarius Pers. We analysed internal transcribed spacer rDNA sequences from both curated sporocarp collections and soil polymerase chain reaction clone libraries sampled in the arctic tundra and boreal forests of Alaska. Our genetic diversity assessment, based on various phylogenetic methods and operational taxonomic unit (OTU) delimitations, suggests that the genus Lactarius is diverse in Alaska, with at least 43 putative phylogroups, and 24 and 38 distinct OTUs based on 95% and 97% internal transcribed spacer sequence similarity, respectively. Some OTUs were identified to known species, while others were novel, previously unsequenced groups. Non-asymptotic species accumulation curves, the disparity between observed and estimated richness, and the high number of singleton OTUs indicated that many Lactarius species remain to be found and identified in Alaska. Many Lactarius taxa show strong habitat preference to one of the three major vegetation types in the sampled regions (arctic tundra, black spruce forests, and mixed birch-aspen-white spruce forests), as supported by statistical tests of UniFrac distances and principal coordinates analyses (PCoA). Together, our data robustly demonstrate great diversity and nonrandom ecological partitioning in an important boreal ectomycorrhizal genus within a relatively small geographical region. The observed diversity of Lactarius was much higher in either type of boreal forest than in the arctic tundra, supporting the widely recognized pattern of decreasing species richness with increasing latitude.     

Muskrat predation on a diverse unionid mussel community: impacts of prey species composition,size and shape

1. The muskrat, Ondatra zibethicus, is a predator known to affect species composition, population size and age structure of freshwater unionid mussel communities. Muskrats leave large piles of dead shells (middens) on the edges of rivers, lakes and streams. We compared the species composition and size structure of shells collected from muskrat middens to the nearby live unionid community in the lower Licking River (Kentucky, USA). 2. Like previous studies, our results suggest that muskrats are both size‐selective and species‐specific predators; however, our results indicate that mussel shape is also an important factor. 3. We generated a shape metric (‘cubocity’) sensitive to the overall shape of the mussel. Species with relatively lower cubocity values (around 0.85) are plate‐like or spike‐like, while mussels with more cuboidal shells have higher cubocity values (near 1.0). 4. Our results suggest muskrats prefer cuboidal mussels and generally avoid spike‐shaped mussels. The endangered fanshell, Cyprogenia stegaria, was the most favoured prey; the fanshell’s relative size and shape appear to make it particularly vulnerable to muskrats. 5. We believe the predictive capabilities of this shape metric will be of benefit to those who monitor and manage threatened mussel populations.     

The Structure and Morphogenesis of the Ventral Ciliature in Paraurostyla hymenophora*

SYNOPSIS. The structure and morphogenesis of the ventral ciliature of Paraurostyla hymenophora (Stokes) are described. The oral primordium apparently originates in association with transverse cirrus #6, from which it migrates anteriorly simultaneous with kinetosomal proliferation. The primordium eventually forms an elongate ciliary field from which the future opisthe's fronto-ventro-transverse (FVT) and undulating membrane primordial fields arise. Concomitantly, the future proter's FVT primordial field is initiated by the disaggregation of frontal cirri #4, #5, and #6. Primordia then develop simultaneously within marginal and ventral cirral rows by a disaggregation of cirri within the respective rows, and do not give rise to new cirri until the FVT fields complete segregation into discrete cirri. Near the completion of cirral production from the FVT primordia, each ventral cirral primordium (VCP) forms the 2 rightmost transverse cirri. Segregation of new cirri within the marginal cirral primordia and VCP then occurs, eventually replacing all old cirri within their respective marginal and ventral cirral rows. At the end of cortical morphogenesis, all old ciliary organelles, with the exception of the adoral zone of membranelles, are either reorganized or replaced. These results suggest an evolutionary affinity between the ventral and marginal cirral rows and raise questions about the control of the developmental competence of individual primordia.     

Indirect effects of a parasite on a benthic community: an experiment with trematodes, snails and periphyton

1. Few studies have directly addressed the role played by parasites in the structure and function of ecosystems. Parasites influence the behaviour, reproduction and overall fitness of their hosts, but have been usually overlooked in community and ecosystem‐level studies. We investigated the effects of trematode parasites on snail–periphyton interactions. 2. Physa  acuta (Gastropoda: Pulmonata) snails infected with the trematode Posthodiplostomum minimum (often >30% of within‐shell biomass) grazed more rapidly than uninfected snails. Trematode effects on snail grazing indirectly affected the standing stock and community structure of periphyton. Populations of snails with 50% infected individuals reduced algal biomass by 20% more than populations with lesser (10% or 0%) infection rates. 3. The alga Cladophora glomerata dominated periphyton communities grazed by snail populations with 50% infection rates, whereas diatoms and blue–green algal taxa dominated when grazed by snail populations with lower infection rates. 4. Thus, trematodes indirectly affected periphyton communities by altering host snail behaviour, a trait‐mediated indirect effect. These results indicate that trematodes can indirectly influence benthic community structure beyond simple population fitness, with possible related effects on ecosystem function.