Solute transport in crystalline rocks at Aspö--II: blind predictions,inverse modelling and lessons learnt from test STT1

Based on the results from detailed structural and petrological characterisation and on up-scaled laboratory values for sorption and diffusion, blind predictions were made for the STT1 dipole tracer test performed in the Swedish Asp? Hard Rock Laboratory. The tracers used were nonsorbing, such as uranine and tritiated water, weakly sorbing 22Na(+), 85Sr(2+), 47Ca(2+)and more strongly sorbing 86Rb(+), 133Ba(2+), 137Cs(+). Our model consists of two parts: (1) a flow part based on a 2D-streamtube formalism accounting for the natural background flow field and with an underlying homogeneous and isotropic transmissivity field and (2) a transport part in terms of the dual porosity medium approach which is linked to the flow part by the flow porosity. The calibration of the model was done using the data from one single uranine breakthrough (PDT3). The study clearly showed that matrix diffusion into a highly porous material, fault gouge, had to be included in our model evidenced by the characteristic shape of the breakthrough curve and in line with geological observations. After the disclosure of the measurements, it turned out that, in spite of the simplicity of our model, the prediction for the nonsorbing and weakly sorbing tracers was fairly good. The blind prediction for the more strongly sorbing tracers was in general less accurate. The reason for the good predictions is deemed to be the result of the choice of a model structure strongly based on geological observation. The breakthrough curves were inversely modelled to determine in situ values for the transport parameters and to draw consequences on the model structure applied. For good fits, only one additional fracture family in contact with cataclasite had to be taken into account, but no new transport mechanisms had to be invoked. The in situ values for the effective diffusion coefficient for fault gouge are a factor of 2-15 larger than the laboratory data. For cataclasite, both data sets have values comparable to laboratory data. The extracted K(d) values for the weakly sorbing tracers are larger than Swedish laboratory data by a factor of 25-60, but agree within a factor of 3-5 for the more strongly sorbing nuclides. The reason for the inconsistency concerning K(d)s is the use of fresh granite in the laboratory studies, whereas tracers in the field experiments interact only with fracture fault gouge and to a lesser extent with cataclasite both being mineralogically very different (e.g. clay-bearing) from the intact wall rock.     

The evolution of marmot sociality: I. Why disperse late?

Summary Prolonged toleration of offspring in marmots was hypothesized to be (1) a means of preventing dispersal of undersized young (Barash 1974 a) or more generally (2) continued parental investment, increasing the probability of descendant survival and reproduction (Armitage 1981, 1987). These hypotheses are tested in this paper for one of the most social of marmot species, the alpine marmot. The animals studied lived in groups within territories defended by a dominant male and female, or as floaters lacking a well-defined home range. Offspring did not disperse before sexual maturity at age 2 (Fig. 1). Only territorial females bred, whereas territorial males were not able to monopolize reproduction likewise (Table 2). Dispersers had similar spring mass to nondispersers (Table 4). Hence, hypothesis 1 is not supported, at least not for adult-sized, > 2 years old animals. During their residency, 19% of subordinates obtained their natal territory or a neighboring one (Fig. 2). Long distance dispersal bore a high mortality risk. Thus, toleration of mature offspring could well represent parental investment. Other results, however, suggest additional influences on the timing of dispersal. (i) Males dispersed later than females (Fig. 3), possibly because of mate sharing by territorial males (see Emlen 1982). (ii) The higher mass loss of dispersers during the previous winter indicates that weak animals were forced to leave (Table 5) despite presumably lower chances of becoming territorial (Table 3). (iii) Subordinate animals which could not be the offspring of both territorials present were not more likely to disperse (Fig. 3). (iv) Lower dispersal rates when immatures lived in the group (Fig. 3) may indicate benefits from the subordinates' presence for rearing young.     

Resource allocation,brood production and cannibalism during colony founding in the fire ant,Solenopsis invicta

Summary The colony founding characteristics of newly mated fire ant queens from monogyne colonies were studied in the field and in the laboratory under haplo- and pleometrotic conditions. Initial queen weight (live) was not correlated with subsequent progeny production. During founding, queens lost a mean of 54% of their lean weight, 73% of their fat weight and 67% of their energy content. The percentage of fat decreased from 44% to 33%. Queens lost weight or energy in relation to the amount of progeny they produced (Figs. 1, 2). The efficiency of the conversion of queen to progeny increased as more progeny were produced, leading to a decline in the unit cost of progeny (Fig. 3). The more minims a queen produced, the lower the mean weight of these minims and the faster they developed (Fig. 4). In a field experiment on pleometrotic founding, total brood increased with queen number, peaked between four and seven queens and declined with 10 queens (Fig. 5). Brood developed faster at the sunny, warmer site, but total production and queen survival was higher at the shady site. As queen density increased, production per queen decreased as a negative exponential in which the exponent estimated sensitivity of brood production to queen-crowding and the constant estimated the production by solo queens (Fig. 9). These effects of queen number were confirmed in laboratory experiments. The decrease of production per queen was small and not always detectable during the egg-laying phase, but brood attrition was always strong during the larval period and increased with queen number (Figs. 8, 10). While airborne factors may have contributed to this inhibition, most of the brood reduction was due to other causes, probably cannibalism. For a given number of minims, increased queen number increased the mean weight of these minims, an effect that resulted both from a lower minim production per queen and from cannibalism of dead queens by survivors (Fig. 11). Cannibal queens lost much less weight to produce a given number of minims than unfed control queens, and these minims were heavier (Fig. 12).     

Bimodality of the combined removal and signs-of-activities estimator for sampling closed animal populations

The possibility of a bimodal log-likelihood function arises with certain data when the combined removal and signs-of-activities estimator is used. Bimodal log-likelihoods may, in turn, yield disjoint confidence intervals for certain confidence levels. The hypothesis that bimodality is caused by the violation of the equal catchability assumption of the removal model, leading to the combination of contradictory data/models in the combined estimator is set forth. Simulations exploring the effect of the violation of removal model assumptions on estimation and inference showed that the assumption of unequal capture probability influenced the frequency of bimodal likelihoods; similarly, extreme parameter values for probability of capture influenced the number of excessively large confidence intervals produced. A sex-specific combined estimator is developed as a remedial model tailored to the problem. The simulations suggest that both the signs-of-activities estimator and the sex-specific estimator perform equally well over the range of simulations presented, though the signs-of-activities estimator is easier to implement.     

Female aggression and male peace-keeping in a cichlid fish harem: conflict between and within the sexes in Lamprologus ocellatus

Summary Conflicts of interest within and between the sexes are important processes leading to variability in mating systems. The behavioral interactions mediating conflict are little documented. We studied pairs and harems of the snail-shell inhabiting cichlid fish Lamprologus ocellatus in the laboratory. Due to their larger size, males controlled the resource that limited breeding: snail shells. Males were able to choose among females ready to spawn. Females were only accepted if they produced a clutch within a few days of settling. When several females attempted to settle simultaneously the larger female settled first. Females were least aggressive when guarding eggs. Secondary females were more likely to settle when the primary female was guarding eggs. In established harems females continued to be aggressive against each other. The male intervened in about 80% of female aggressive interactions. Male intervention activity correlated with the frequency of aggression among the females in his harem. The male usually attacked the aggressor and chased her back to her own snail shell. When a male was removed from his harem, aggression between females increased immediately and usually the secondary female was expelled by the primary female within a few days. Time to harem break-up was shorter the more mobile the primary females' young were and did not correlate with the size difference between harem females. Male L. ocellatus interfere actively in female conflict and keep the harem together against female interests. Female conflict presumably relates to the cost of sharing male parental investment and to the potential of predation by another female's large juveniles on a female's own small juveniles.Correspondence to: F. Trillmich     

Oxygen bioavailability and haemoglobins in the brine shrimp Artemia franciscana

Bioavailability of oxygen for the saline-water invertebrate Artemia franciscana was studied, since both oxygen concentration and oxygen diffusion rate change with salinity. Total haemoglobin concentration and the relative contribution of each of three haemoglobins was measured in specimens acclimated to different salinities and oxygen concentrations. Both haemoglobin concentration and contribution were influenced by salinity and the group observed (males, females with and females without eggs). Multiple regression analysis showed that total haemoglobin concentration was better correlated with oxygen concentration than oxygen partial pressure. The relative proportions of haemoglobins 1, 2 and 3 were better correlated with oxygen partial pressure than oxygen concentration. These results are related to the oxygen carrying capacity and oxygen affinity of the haemolymph. Our results show that oxygen bioavailability in a saline-water environment depends on the response (relative contribution of Hb1, Hb2 and Hb3 or total haemoglobin concentration) that is studied. They also show that oxygen concentration and oxygen partial pressure have a different physiological impact on brine shrimp.     

Nectar-receiver behavior in relation to the reward rate experienced by foraging honeybees

Since forager honeybees change their food-unloading behavior according to nectar-source profitability, an experiment was performed in order to analyze whether food-receivers modify their within-hive tasks related to different reward conditions. We offered individual foragers two reward conditions at a rate feeder while an additional feeder offered a constant reward and was of free access to the rest of the hive. Both feeders were the only food sources exploited by the colony during the assays since a flight chamber was used. After receiving nectar, hive bees performed processing cycles that involved several behaviors and concluded when they returned to the delivery area to receive a new food sample. During these cycles, receivers mainly performed oral contacts offering food, or inspected cells, and often both. In the latter case, both behaviors occurred simultaneously and at the same distance from the hive entrance. When they performed a single task, either the occurrence of cell inspections increased or contact offerings decreased for the highest reward rate offered to the donor-forager. Receivers also begged for food more often after interacting with low-profit foragers. Thus, the profitability of the food source exploited by nectar-forager honeybees could affect receiver behaviors within the hives based on individual-to-individual interactions.Communicated by R.F.A. Moritz     

No reason to sneak: why males of all sizes can breed in the hole-nesting blenny, Aidablennius sphinx

Most blennioid fishes show a resource-based, promiscuous mating system with alternative 'sneaking' mating tactics. The hole-nesting species, Aidablennius sphinx, however, appears to be an exception; small males did not mimic females, most had their own nest and not once in 20 h of spawning observations did a second male enter a nest. In this field study, we ask if sneaker tactics are constrained and what factors favour independent nesting by small males. Larger males received more eggs sooner and attracted more females than smaller males. Larger males may be preferred because they released more sperm per ejaculation and fanned their eggs more often. In the long-term, however, larger males did not spawn more often than smaller males since: (1) the nests of large males filled up with eggs sooner than the nests of small males; (2) large males refused females more often than small males; and (3) a highly biased ratio of females to preferred large males meant many females had no option but to spawn with small males. Thus, small males nest independently, despite potential for female mimicry tactics (multiple females spawned simultaneously) and simultaneous parasitic spawning (males exited the nest during spawning)     

Colony growth and the ontogeny of worker polymorphism in the fire ant,Solenopsis invicta

Summary Colony size and worker polymorphism (headwidth) were determined for fire ant colonies ranging from incipient to 12 years of age. Colonies grew approximately logistically, reaching half size between 21/2 and 31/2 yr and reaching their maximum size of about 220000 workers after 4 to 6 yr. Colony size showed strong seasonal variation. There was some evidence that growth rate may vary with food density. Incipient colonies are monomorphic and consist of small workers only, but as colonies grow, production of larger workers causes the size-frequency distributions to become strongly skewed. These skewed distributions were shown to consist of two slightly overlapping normal distributions, a narrow one defined as the minor workers, and a much broader one defined as the major workers. Major workers differ from minor workers in having been subjected to a discrete, additional stimulation of body growth, resulting in a second normal subpopulation. The category of media is seen to be developmentally undefined. The mean headwidth of the workers in both of these subpopulations increased during the first 6 mo. of colony life, until colonies averaged about 4000 workers. Headwidth of minors declined somewhat in colonies older than about 5 yr, but that of majors remained stable. When the first majors appear, their weight averages about twice that of minors. This increases to about 4 times at 6 mo. and remains stable thereafter. The range of weights of majors is up to 20 times that of minors. Growth of the subpopulation of major workers is also logistic, but more rapid than the colony as a whole, causing the proportion of major workers to increase with colony size. In full sized colonies, about 35% of the workers are majors. Total biomass investment in majors increases as long as colonies grow, beginning at about 10% at 2 months and reaching about 70% in mature colonies. This suggests that major workers play an important role in colony success. The total dry biomass of workers peaked at about 106 g, that of majors at about 72 g. These values then fluctuate seasonally in parallel to number of workers. When colony growth ceases, the proportion of majors remains approximately stable. Colony size explained 98% of the variation in the number of major workers.This is paper No. 18 of the Fire Ant Research Team