Timing and Regulation of Nuclear and Cortical Events in the Cell Cycle of Tetrahymena pyriformis*

SYNOPSIS. Using continuous flow cultures based on the chemostat principle, we varied the cell generation times of the ciliate Tetrahymena pyriformis strain GL, from 4.9 to 22.2 hr and studied various parameters of the cell cycle at 28 C. These included: the duration of the periods required for oral morphogenesis, macronuclear division, cell division, G₁ S, and G₂. The size of individual cells was also measured. Independent of the growth rate, the period of oral morphogenesis occurred during the last 90 min of the cell cycle. In all cases macronuclear and cell divisions took place during the last part of these 90 min, and the final macronuclear separation occurred just before final cell separation. The S-period increased slightly, while the G₁ and G₂ both increased in roughly the same relative proportion to the increasing generation times. Slowly growing cells (generation time 20.5 hr) were shorter but broader and somewhat larger in volume than quickly growing cells (generation time 4.9 hr).     

Effects of various buffers, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and NaN3 on menadione mediated photophosphorylation in isolated chloroplasts

The effects of DCMU and NaN₃ were studied on menadione-mediated photophosphorylation in broken spinach chloroplasts kept in low oxygen tension in Tricine or HEPES buffers at either high or reduced irradiances. – (A) At high irradiance (131 W. m^?2) and absence of NaN₃ the ATP formation was inhibited by DCMU regardless of the type of buffer used. – (B) At high irradiance and presence of NaN₃ some concentrations of DCMU stimulated, whilst others inhibited the ATP formation in a HEPES buffer. The ATP formation was predominantly inhibited by DCMU in a Tricine buffer. – (C) At reduced irradiance (57 W. m^?2) the chloroplasts in a HEPES buffer were almost insensitive towards DCMU both in the presence and absence of NaN₃. – (D) Chloroplasts in a Tricine buffer were slightly stimulated in their ATP formation by DCMU at reduced irradiance either with or without the presence of NaN₃ in the experimental medium. When menadione acts as a terminal electron acceptor, oxygen is consumed on its reoxidation. The results indicate that this process may occur with oxygen released by the splitting of water as the main oxidant. – The data also demonstrate the importance of caution when selecting buffering substances as well as when choosing light intensities for experiments on photophosphorylation in chloroplasts.     

Effects of an invasive crayfish on trophic relationships in north‐temperate lake food webs

1. The introduction of invasive species is one of the main threats to global biodiversity, ecosystem structure and ecosystem processes. In freshwaters, invasive crayfish alter macroinvertebrate community structure and destroy macrophyte beds. There is limited knowledge on how such invasive species‐driven changes affect consumers at higher trophic levels. 2. In this study, we explore how the invasive rusty crayfish Orconectes rusticus, a benthic omnivore, affects benthic macroinvertebrates, as well as the broader consequences for ecosystem‐level trophic flows in terms of fish benthivory and trophic position (TP). We expected crayfish to decrease abundance of benthic macroinvertebrates, making most fish species less reliant on benthic resources. We expected crayfish specialists (e.g. Lepomis sp. and Micropterus sp.) to increase their benthic dependence. 3. In 10 northern Wisconsin lakes, we measured rusty crayfish relative abundance (catch per unit effort, CPUE), macroinvertebrate abundance, and C and N stable isotope ratios of 11 littoral fish species. We used stable isotope data and mixing models to characterise the trophic pathways supporting each fish species, and related trophic structure to crayfish relative abundance, fish body size and abiotic predictors using hierarchical Bayesian models. 4. Benthic invertebrate abundance was negatively correlated with rusty crayfish relative abundance. Fish benthivory increased with crayfish CPUE for all 11 fish species; posterior probabilities of a positive effect were >95%. TP also increased slightly with crayfish CPUE for some species, particularly smallmouth bass, largemouth bass, rock bass and Johnny darter. Moreover, both fish body size and lake abiotic variables explained variation in TP, while their effects on benthivory were small. 5. Rusty crayfish abundance explained relatively little of the overall variation in fish benthivory and TP. Although rusty crayfish appear to have strong effects on abundances of benthic macroinvertebrates, energy flow pathways and trophic niches of lentic fishes were not strongly influenced by invasive rusty crayfish.     

Effects of brown and turbid water on piscivore–prey fish interactions along a visibility gradient

1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predator–prey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25–200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predator–prey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free‐swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free‐swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator–prey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher‐order interactions.     

Developmental stability in brown trout: are there any effects of heterozygosity or environmental stress?

We studied the developmental stability of brown trout, Salmo trutta L., in 10 populations (five acidified, five control) in Norway, measured as fluctuating asymmetry (FA) and departure from the morphological norm. We measured four meristic and four morphometric characters, and scored the level of biochemical heterozygosity at 49 loci (20 polymorphic). We reared eggs of a single population in a hatchery using four different water qualities (three replicates of each treatment) to test the effect of acidification stress on developmental instability. There were no significant differences in the level of FA, in departure from the morphological norm between brown trout sampled from lakes with acidified or control water qualities, or in brown trout hatched at different water qualities. There was no correlation between level of heterozygosity and FA or departure from the morphological norm, either when tested within populations or among populations. There were no single-locus effects on developmental stability tested for 11 loci. We conclude that measures of developmental stability or morphological variability are not useful for detecting acidification stress in brown trout. Furthermore, we conclude that developmental stability in our material varies independently of heterozygosity.