Johan Andersson

Sexual cooperation and conflict in butterflies : a male-transferred anti-aphrodisiac reduces harassment of recently mated females

Sexual selection theory predicts that the different selection pressures on males and females result in sexual conflict. However, in some instances males and females share a common interest which could lead to sexual cooperation. In the pierid butterfly Pieris napi the male and the recently mated female share a common interest in reducing female harassment by other males soon after mating. Here we show that P. napi males transfer an anti–aphrodisiac to the female at mating, methyl–salicylate (MeS), which is a volatile substance which mated females emit when courted and which makes males quickly abandon them. A 13C–labelling experiment demonstrated that only males synthesize MeS. The effect of this antiaphrodisiac is so strong that most males will refrain from mating with virgin females to whom MeS has been artificially applied. In P. napi, males also transfer nutrients to females at mating. This increases female fecundity and longevity and so females benefit from remating. Hence, sexual cooperation gradually turns to conflict. Future research is required to reveal which sex controls the gradual decrease in the MeS titre which is necessary for allowing mated females to regain attractiveness and remate.

A variable aperture fracture network model for flow and transport in fractured rocks

A three-dimensional variable aperture fracture network model for flow and transport in fractured rocks was developed. The model generates both the network of fractures and the variable aperture distribution of individual fractures in the network. Before solving for the flow and transport of the whole network, a library of single-fracture permeabilities and particle transport residence time spectra is first established. The spatially varying aperture field within an individual fracture plane is constructed by geostatistical methods. Then the flow pattern, the fracture transmissivity, and the residence times for transport of particles through each fracture are calculated. The library of transmissivities and frequency distributions of residence times is used for all fractures in the network by a random selection procedure. The solution of flow through the fracture network and the particle-tracking calculation of solute transport for the whole network are derived from one side of the network to the other. The model thus developed can handle flow and transport from the single-fracture scale to the multiple-fracture scale. The single-fracture part of the model is consistent with earlier laboratory tests and field observations. The multiple-fracture aspect of the model was verified in the constant aperture fracture limit with an earlier code. The simulated breakthrough curves obtained from the model display dispersion on two different scales as has been reported from field experiments.

Discrete fracture network interpretation of field tracer migration in sparsely fractured rock

Field tracer migration in sparsely fractured rock is analyzed with a discrete fracture network model that has been calibrated on fracture and flow data from the Stripa-3D experiment in Sweden. Comparison between transport simulations in the flow-calibrated discrete model and tracer tests of the field experiment confirms the fracture network parameters obtained from the flow analysis except for the variance of the fracture conductivities which had to be increased. The discrete model reproduces the uneven spatial distribution of flow and tracers, the complex dispersive behavior, and channeling effects that have been observed in the field experiment. As a result of flow channeling, transport occurs along preferential paths whose transport properties may substantially deviate from the medium average properties. For example, porosity and wetted fracture surface area available to sorption may be reduced by almost 2 orders of magnitude compared to the medium average values.

Male sex pheromone release and female mate choice in a butterfly.

SUMMARY In butterflies female mate choice is influenced by both visual and olfactory cues, the latter of which are important at close range. Males of the green-veined butterfly, Pieris napi, are known to release citral (mixture of geranial and neral, 1:1), but its role(s) and conditions of release are not known. Here, we show that male P. napi release citral when interacting with conspecific males, conspecific females, heterospecific males and also when alone. The amount of citral released correlated strongly with male flight activity, which explained more than 70% of the variation. This suggests that males do not exercise control over turning release on or off, but rather that citral is emitted as a passive physical process during flight. Electroantennogram experiments showed that female antennal response was ten times more sensitive to citral than male response. Females expressed acceptance behavior when exposed to models made with freshly excised male wings or those treated with citral following chemical extraction, but not to ones with extracted wings only. Hence, these behavioral and electrophysiological tests provide strong evidence that citral is a signal from the male directed to the female during courtship, and that it functions as a male sex pheromone.

Sexual conflict and anti–aphrodisiac titre in a polyandrous butterfly: male ejaculate tailoring and absence of female control

Males of the green–veined butterfly Pieris napi synthesize and transfer the volatile methyl salicylate (MeS) to females at mating, a substance that is emitted by non–virgin females when courted by males, curtailing courtship and decreasing the likelihood of female re–mating. The volatile is released when females display the ‘mate–refusal’ posture with spread wings and elevated abdomen, when courted by conspecific males. Here, we assess how the amount of MeS released by courted females changes over time since mating, and whether it is influenced by the frequency with which females display the mate–refusal posture. We also assess whether males tailor the anti–aphrodisiac content of ejaculates with respect to the expected degree of sperm competition, by comparing how males allocate MeS proportionately to first and second ejaculates in relation to ejaculate mass. The results show that females housed for 5 days in individual cages where they were able to fly and oviposit normally, released similar amounts of MeS. However, females housed together for the same period of time, causing them to frequently display the mate–refusal posture, released significantly lower levels of MeS than the individually housed females. This indicates that female display of the mate–refusal posture depletes their anti–aphrodisiac stores, and suggests that females are unable to voluntarily control their release of the anti–aphrodisiac. A comparison of relative proportion of MeS transferred by males in their first and second ejaculates showed that proportionately more MeS was allocated to the first ejaculate, in accordance with the idea that these are tailored to delay female re–mating.

Effects of high variance of fracture transmissivity on transport and sorption at different scales in a discrete model for fractured rocks

Abstract A three-dimensional (3-D) variable-aperture fracture network model for flow and transport in fractured crystalline rocks has been applied to study the effects of large variability in fracture transmissivity on non-sorbing and sorbing tracer transport, and scale effects in transport distance. The variable-aperture character of the fractures is introduced into a 3-D network model through a library of single-fracture permeabilities and associated particle transport residence time spectra. Sorption onto the fracture walls is added by a mathematical model for linear sorption. The resulting variable-aperture fracture network model, VAPFRAC, can handle flow and transport from single-fracture scale to the multiple-fracture scale. The model produces multi-peak transport breakthrough curves even for relatively moderate values of the fracture transmissivity variance. These breakthrough curves display dispersion on two different scales in the same way as has been observed in several field experiments conducted in crystalline rocks. The multi-peak structure is due to so-called channeling. For high values of the fracture transmissivity variance the solute transport is unevenly distributed and the channeling effects are more prominent. The effect of linear sorption is not just a simple translation in mean residence time as in a homogeneous medium. The dispersion characteristics of the breakthrough curves also change when linear sorption is included. The degree of the change depends strongly on the fracture transmissivity variance, as does the translation. In particular, with a high fracture transmissivity variance the translation in mean residence time due to sorption is significantly smaller compared to the cases with a low fracture transmissivity variance. Finally, the high variability in the model output data suggests that extrapolation of results from a particular tracer experiment will be highly uncertain.

Simulation of steady-state flow in three-dimensional fracture networks using the boundary-element method

Abstract An efficient method for simulating steady-state flow in three-dimensional fracture networks is formulated with the use of the boundary-element method. The host rock is considered to be impervious, and the fractures can be of any orientation and areal extent. The fractures are treated as surfaces where fluid movement is essentially two-dimensional. Fracture intersections are regarded as one-dimensional fluid conduits. Hence, the three-dimensional geometric characteristics of the fracture geometry is retained in solutions of coupled sets of one- and two-dimentional equations. Use of the boundary-element method to evaluate the fluid responses in the fractures precludes the need to internally discretize the areal extent of the fractures.

Solute transport in heterogeneous media: A discussion of technical issues coupling site characterization and predictive assessment

Abstract Long-term predictive evaluation of solute transport and transformation in geologic media is a critical element in the performance assessment of nuclear waste geologic repositories and in the environmental restoration or control of contaminated sites that is facing many countries today. Since the geologic media are heterogeneous and their details can never be known deterministically, long-term prediction of flow and transport in such systems requires new thinking. Thus, it is no longer possible to consider site characterization and predictive modeling calculations to be separate activities; rather they are highly coupled. This paper presents a discussion of the coupling and proposes a framework of technical issues that need to be studied.

Devising scenarios for future repository evolution: A rigorous methodology

The Swedish Nuclear Power Inspectorate is developing a new methodology for the construction of scenarios for radiological consequence analysis as part of its SITE-94 performance assessment project. SITE-94 involves the incorporation of site specific data from the Aespoe site into a performance assessment (PA) of a hypothetical high-level waste repository. This paper describes a systems analysis approach that has been developed based on the concept of organizing all the events and processes which need to be taken account of in PA into a process system and a much smaller residual group which are used to generate scenarios. The methodology used for developing scenarios, producing calculation cases and addressing the various types of uncertainty involved in PA consequence analysis is described.

Implications of rock structure on the performance in the near field of a nuclear waste repository

Abstract The performance of a deep repository for nuclear waste relies heavily on its potential to retain radionuclides at source. This is achieved through a durable waste package and favourable chemical conditions under which the most dangerous nuclides are extremely difficult to dissolve in groundwater. The persistence of these favourable conditions is, however, partially controlled by the groundwater flow in the near field and its capability to transport radionuclides released from the waste form. Most source-term models used in performance assessment assume a simple conceptual model, with a deposition hole intersected by a single fracture with the release controlled by diffusion in the buffer and the chemical conditions at the source. This conceptual model is certainly a simplification of reality, where the deposition hole is intersected by an irregular network of discrete fractures with spatially varying properties and where the fractures close to the deposition hole and the tunnel are altered by excavation effects. In terms of flow modelling, spatially varying discrete fracture systems can be simulated using a number of methods including stochastic discrete fracture networks models and stochastic continuum models. This choice of models leads to uncertainty, as does incomplete knowledge of the parameters that characterize the chosen model. For modelling migration through the geosphere, the largest uncertainties are those in groundwater flow distribution and in the flow-wetted surface area. Sensitivity analyses with existing source-term models suggest that near-field release is sensitive to flow and to fracture geometry in an intermediate range only, but this result may be an artefact due to the simplifications made. The adoption of a more realistic geometrical decription of the near-field rock may lead more useful description of which near-field rock properties affect source-term release.