Floating in Hydra Littoralis

Mating behavior helps to shape the epidemiology of sexually transmitted infections (STIs) by determining the rate at which infectious and susceptible individuals make contact. To the extent that mating behavior shows spatial variation, it is expected that STI epidemics will also show spatial heterogeneity (provided that dispersal is limited). However, empirical data are lacking for natural systems. Here, therefore, we investigate the association between local mating behavior and STI epidemiology in natural populations of the two-spot ladybird, Adalia bipunctata, and dissect the causes of this variation. Variation in mating behavior was observed over local and regional spatial scales and high mating rate led to stronger local epidemics of the STI. Initial ecological observations suggested that reduced mating rate was associated largely with low food supply (and possibly to a lesser extent with local population density) and not with differences in thermal environment. We tested the potential role of food supply in fuelling STI epidemics in laboratory populations and confirmed that high food provision led to greater STI transmission. We conclude that food supply is strongly associated with mating rate in the field and that this produces heterogeneity in STI epidemiology. A consequence is that STI-induced sterility will reduce reproduction in habitat patches of high food quality.

In the column of hydra, tissues continually move away from a region located just underthe whorl of tentacles. Above this subtentacular region, tissues proceed into the hypostome and tentacles; below it tissues pass into the buds or continue down the stalk. These movements represent a steady state pattern of tissue renewal in which column growth is balanced by tissue loss at the body extremities. But the existence of a subtentacular zone in which tissue appears stationary does not necessarily indicate that growth is restrictedto this region, as is commonly stated.The body column of hydra can be viewed as an expanding cylinder whose elongation is balanced by tissue loss at the two ends. In such a body there must be one region from whichtissue appears to emanate, regardless of how growth is distributed along the cylinder. Only the rates at which tissues move will be characteristic of the underlying growthpattern. In Hydra littoralis, the measured rates of tissue movement down the gastric column are consistent with the distributions of mitotic figures, which indicate that growth is spread out along the column.

Tissue dynamics of steady state growth in Hydra littoralis: I. Patterns of cell division

Determining the age composition of a population is important when conducting ecological, taxonomic and environmental assessments. Morphometric measurements of the head capsule, especially the length and width, are widely used in the identification of insect instars, but alternative ways for determining the age of insects can expand the options for the analysis of field and laboratory populations. This study evaluated the morphometry of the antennae, mandibles, mentum and ventromental plates to discriminate among the four larval instars of Chironomus sancticaroli Strixino & Strixino, 1981. The larvae were reared in the laboratory under constant temperature (25°C) and photoperiod of 12/12 hours for 19 days, with a supply of food. Fifteen larvae were removed randomly every day, cleared in KOH, and slide-mounted, and had the antennae, mandibles, mentum and ventromental plates measured. The dimensions of the four structures studied allowed us to statistically distinguish each of the four larval instars. The data fit an exponential equation according to the Brooks-Dyar rule, which allows an estimate of the larval instar of specimens collected in the field, even when development takes place under different conditions. The duration of each instar was also obtained from our data, and showed an overlap of instars during development.

We analyzed over 20 study-years of data from populations of Daphnia and algae in a wide variety of field situations. These systems display three types of dynamic behavior: both populations stable; both populations cyclic; and Daphnia cyclic but algae stable. The last pattern occurs whether we analyze the total amount of algae or only edible algae. There is evidence that this range of dynamics arises from the interaction between Daphnia and its food supply, occurring in systems that are structurally the same; that is, differences in biological rates or time delays, alone, can explain the existence of different dynamic classes. This is particularly the case when different classes occur in the same species in the same environment in different years, or in similar and adjacent habitats at the same time. The cycles thus appear to be internally driven, rather than resulting from external, cyclic, forcing factors. These findings support a basic premise of most mathematical models in ecology. The broad dynamic patterns in cyclic field populations of Daphnia are similar to those found in laboratory populations. The two sets of cycles have very similar periods and (small) amplitudes; both are single-generation cycles (i.e., the period of a cycle is one generation); and both are caused by dominance and suppression, whereby each cohort suppresses reproduction until its density declines sufficiently to allow production of another cohort. The demographic features of laboratory and field cycles are also similar in detail. Since algae are dynamic in the field but not in the laboratory, we cannot conclude that the mechanisms driving laboratory and field cycles are identical. Our hypothesis is that the presence or absence of cycles is determined by the relationships between time delays in Daphnia and other rates in the interacting populations. There is, however, no obvious environmental factor affecting these rates and delays, thereby determining which dynamic class a particular system fits at a particular time. It does not appear that change in the average temperature is the critical factor. Similar single-generation cycles appear to occur in other systems and may be driven by similar dominance-and-suppression mechanisms.

We compared the bacterial communities in the larval midgut of field and laboratory populations of a polyphagous pest, the cotton bollworm (Helicoverpa armigera), using denaturing gradient gel electrophoresis (DGGE) of amplified 16S rDNA sequences and 16S library sequence analysis. DGGE profiles and 16S rDNA library sequence analysis indicated similar patterns of midgut microbial community structure and diversity: specific bacterial types existed in both populations, and a more diverse microbial community was observed in caterpillars obtained from the field. The laboratory population harbored a rather simple gut microflora consisting mostly of phylotypes belonging to Enterococcus (84%). For the field population, phylotypes belonging to Enterococcus (28%) and Lactococcus (11%), as well as Flavobacterium (10%), Acinetobacter (19%), and Stenotrophomonas (10%) were dominant members. These results provided the first comprehensive description of the microbial diversity of the midgut of the important pest cotton bollworm and suggested that the environment and food supply might influence the diversity of the gut bacterial community.

Hydra tissues continuously move from the growing column to the body extremities. To study the cellular basis of these movements, mosaic hydra were produced by grafting portions of isotopically labeled animals to portions of unlabeled ones. The progressions of labeled cells away from the original graft site were determined by the method of radioautography. From the data obtained, it is possible to deduce the migratory relations between different cell types and the patterns of their movement.Most cells move in the form of coherent expanding epithelia, in which cells do not individually wander relative to neighboring cells. The gastrodermal tissue sheet includes the gland and digestive cells; the epidermal tissue sheet includes the interstitial and epitheliomuscular cells. These tissues move distally and proximally from a “stationary region,” near the top of column. The two epithelia do not move at the same rate, however, and their stationary regions are at different column levels.Nematocytes migrate in an amoeboid fashion from the body column to the tentacles. They migrate along the epidermal muscular layer, and do not move through the mesolamella to the gastrodermis. These aspects of cell behavior are consistent with the histological structure of hydra.

The role and consequences of aggressive behavior in competition for food and space were studied among laboratory populations of juvenile medaka. Growth rate, used to measure the success of an individual fish in different competitive situations, was followed for 648 fish in populations of 1, 2, 4, 8, or 16 fish in 1-, 4-, or 8-liter baskets.Aggressive behavior was initiated by internal state of "hunger" and the presence of food stimuli and smaller medaka. Aggression was at a low level when food was supplied in excess and large fish had no competitive advantage over small fish. Reducing the amount of space from 1 to 1/16 liter per fish did not alter the growth consequences of competition as long as the accumulation of waste products was prevented and food was supplied in excess.When food supply was limited, large medaka were socially dominant, chased small fish away from food, and grew faster than small fish. If food was spatially localized the social hierarchical societies changed into territorial societies in which the dominant defended the food area, but aggression only dispersed the subordinates throughout the habitat when food was evenly distributed. The advantage of social dominance was less if population size was large, if food was evenly distributed, and visual isolation between competitors was great. The advantage was high if food was contagiously distributed and visual isolation between competitors was great.

Understanding the causes of population synchrony is an important issue for population management. Its study in field populations involves disentangling the effects of dispersal and correlated environmental noise. Here we report on an experimental investigation of the synchronizing effects of noise in closed laboratory populations of a soil mite, Sancassania berlesei. Mite life‐histories are highly plastic with respect to resource availability (which is a function of food supply and population density). By varying the food supply we imposed environmental variation. We show that (a) population synchrony is a function of environmental synchrony, (b) perceived population synchrony depends on the life‐history stage counted, and (c) average population synchrony tends to be lower than environmental synchrony: even when populations were supplied with food with a correlation of 1.0, the correlation between populations was 0.63 (bootstrapped 95%CI 0.54–0.71). This supports recent theoretical work suggesting that the Moran theorem (indicating that population synchrony equals environmental synchrony) generally overestimates the population synchrony of nonlinear systems.

Predicting the evolution of phenotypic traits requires an understanding of natural selection on them. Despite its indispensability in the fight against parasites, selection on host immune defense has remained understudied. Theory predicts immune traits to be under stabilizing selection due to associated trade-offs with other fitness-related traits. Empirical studies, however, report mainly positive directional selection. This discrepancy could be caused by low phenotypic variation in the examined individuals and/or variation in host resource level that confounds trade-offs in empirical studies. In a field experiment where we maintained Lymnaea stagnalis snails individually in cages in a lake, we investigated phenotypic selection on two immune defense traits, phenoloxidase (PO)-like activity and antibacterial activity, in hemolymph. We used a diverse laboratory population and manipulated snail resource level by limiting their food supply. For six weeks, we followed immune activity, growth, and two fitness components, survival and fecundity of snails. We found that PO-like activity and growth were under stabilizing selection, while antibacterial activity was under positive directional selection. Selection on immune traits was mainly driven by variation in survival. The form of selection on immune defense apparently depends on the particular trait, possibly due to its importance for countering the present parasite community.

1. Faecal counting techniques were used to census five large mammalian herbivores during 1988 and 1989 in the Parc National des Volcans in Rwanda. These five herbivores were the black-fronted duiker (Cephalophus nigrifrons), the bushbuck (Tragelaphus scriptus), the Cape buffalo (Syncerus caffer), the mountain gorilla (Gorilla gorilla beringei) and the African elephant (Loxodonta africana). 2. Population density estimations from standing crop counts of faeces usually correct the counts for the defecation rate of the animal and the decomposition rate of the dung, assuming that the decay of the dung is constant. However, this study found that the dung decay was not constant. For bushbucks, exponential decay curves were found in the wet seasons and sigmoidal decay curves in the dry seasons. Only sigmoidal curves were found for buffalos and elephants. Therefore, measures of dung decomposition throughout the year were used in a computer model which estimated iteratively the population density. 3. Ecological density estimates were obtained for eight habitat types found in the Park. Habitats at the summit of volcanos sustain the lowest biomass of large herbivores at 10-15 kg ha −1 whilst meadows sustain the highest biomass at 45-50 kg ha −1 . The biomass for the whole study area was calculated as 31 kg ha −1 , one of the highest biomasses for any forest yet studied. The bushbuck and the buffalo dominated this biomass. The implications of this for the conservation of the mountain gorilla are discussed and it is concluded that currently these animals have little impact on the gorilla's food supply

Toxicokinetics of hydrophobic organic compounds in oligochaeta: A critical review

Fructose occurs in fruits, vegetable, and sweetened drinks alongside glucose as free sugars or bound in sucrose, but may also be bought in a pure form. A link between sugar-sweetened drinks (SSD) and body mass index (BMI, kg/m2) is inferred from systematic reviews of both prospective cohort studies (PCSs) and randomized, controlled trials (RCTs) (Malik et al., 2006; Wolf and Dansinger, 2008). The link is seemingly strong because such studies rank highly among types of studies according to evidence-based principles on causality. On the other hand, the study results are heterogeneous, and more objective meta-analysis shows SSDs to have a “small” effect on BMI (Forshee et al., 2008); therefore, a focus on fructose and SSD may then serve only to divert attention from major causes of obesity (Storey, 2008). A number of complications and false claims arise when interpreting epidemiological and interventional studies on fructose or SSDs. The first is a notion that high-fructose corn syrup (HFCS) differs from suc...

The objective of our paper is to develop a mechanistic conceptual framework for how food webs recover from natural physical disturbances. We summarize our work on the effect of hurricanes on island food webs and review other studies documenting how other types of physical disturbances (including fires, floods, and volcanic eruptions) alter food-web interactions. Based on these case studies, we propose that four factors play an important role in food-web succession: (1) disturbance intensity, (2) sequential recovery/colonization of successively higher trophic levels, (3) tradeoffs between growth rate of organisms at different successional stages and susceptibility to consumers, and (4) detritus including autochthonous and allochthonous sources. Studies on river flooding and islands disturbed by hurricanes indicate that energy flow is higher and trophic cascades are stronger during recovery than when the food web is at a steady state. We suggest that as consumer species colonize during succession, they may change the species or phenotypic composition of their food supply from highly vulnerable to less vulnerable items, thereby weakening both bottom-up and top-down effects throughout the food web. High inputs of detritus caused by disturbances can amplify bottom-up effects during early succession, and subsequently alter top-down effects.

British Food Journal Volume 44 Issue 3 1942