All-female broods in Hypolimnas bolina (L.) A re-survey of West Fiji after 60 years

In the Xymphalid butterfly Hypolimnas bolina (L.) H. W. Simmonds in 1921 demonstrated, by breeding experiments, the occurrence on the islands of West Fiji of all-female broods, and he compared their frequency with that of normal bisexual broods in the same localities. In two areas he found only unisexual families (14 of them in Suva and one on Vanua Levuj, in one island (Ovalau) only a single bisexual brood and in the other two islands, Taveuni and Kandavu, one bisexual and one of each type respectively. Nearly 60 years, and probably at least 150 generations later, we found that all-female broods were still present in four of the five islands re-investigated, and breeding showed that in these four (which included Suva) the proportion of the two types of female was approximately equal. In the fifth island only a bisexual family was bred. The only marked change between 1921 and 1980 was in the Suva area, where Simmonds found far more unisexual females than we did.
By carrying out spermatophore counts in many of our wild females we found that almost all of them had been mated, the majority of them on one occasion only. Though the data are scanty, they suggest that there is no wastage of females and that the population in 1980 was stable for the two types of brood.
Reasons for our findings are discussed, particularly in the light of the Heuch model, but we conclude that no entirely satisfactory explanation has yet been given for the persistence of all-female broods. Again, there is so far no explanation of the mechanism though we favour a cytoplasmic factor.
We feel that the status of H, bolina as a mimic of species of Euploea is less assured as the result of our survey.     

The Effect of Light Intensity on the Release of Ethylene from Leaves

When leaf discs of Xanthium strumarium L. a C₃ plant, or Zeamays L. a C₄ plant, are incubated in 1-aminocyclopropane-l-carboxylicacid (ACC) in closed flasks, ethylene is released. The rateof ethylene release appears to be dependent on the levels oflight and CO₂ available for photosynthesis in the tissues. In Xanthium the rate of ethylene release is lower in the lightthan in the dark regardless of the presence or absence of addedbicarbonate as a source of CO₂. The inhibition of ethylene releaseis most apparent in the absence of added bicarbonate (i.e. atthe CO₂ compensation point), and at light intensities sufficientto saturate photosynthesis (had the CO₂ level in the test flaskbeen maintained). In contrast, light dramatically promotes therate of ethylene release from Zea leaf tissue when the CO₂ levelis maintained above the CO2 compensation point. The rate ofethylene release from either Xanthium or Zea, incubated withor without added bicarbonate, does not appear to be alteredby further increasing the light intensity above the minimallevels sufficient to saturate photosynthesis. In the closed system used in these studies and at a light intensitysufficient to saturate photosynthesis, Xanthium and Zea leaftissue both appear to release comparable amounts of ethylenefrom ACC when the data is expressed on a chlorophyll basis.However, in Xanthium the rate of ethylene release is similarin light and dark, while in Zea the rate in the light is muchgreater than in the dark when the data is expressed either ona leaf area or on a chlorophyll basis. It is suggested thatthe different responses of these tissues to light/dark transientsmay reflect differences in their ability to metabolize ACC and/ordifferences in their ability to retain and metabolize ethyleneitself.     

Estimation of the carbon sequestration by a heterogeneous forest: night flux corrections, heterogeneity of the site and inter-annual variability

Continuous measurements of the net CO₂ flux exchanged in a mixed forest with the atmosphere were performed over 5 years at the Vielsalm experimental site. The carbon sequestration at the site was deduced by a summation of the measurements. Problems associated with this summation procedure were discussed. The carbon sequestration in the ecosystem was presented and its interannual variability was discussed. An estimation of the night flux correction was given. The correction was applied by replacing measurements made during quiet nights by a parameterization. The impact of the correction was shown to vary between 10 and 20% of the uncorrected flux, according to the year. The need to include the storage flux during turbulent periods was emphasized: its neglect leads to an error which will be greater than the one it tries to correct. It was also shown that the heterogeneity of the site made it necessary to split the data into separate series corresponding to the different vegetation patches and to fill the data gaps by using an algorithm that takes account of the weather conditions. Two series were defined, one corresponding to a beech subplot, the other to a conifer subplot. The uncertainty owing to the data split and the data gap‐filling was about 15–20% annually. The carbon sequestration was then analysed in both the subplots. The length of the growing season was about 210 days in the beech and 240 days in the conifer. The carbon sequestration over 5 years was 2.28 kg C m^2?2 in the beech and 3.58 kg C m^2?2 in the conifer. The main difference between the species appeared in spring, between March and May, when the beeches were leafless. Significant interannual variations were observed in both the subplots. They appeared mainly in summer and were primarily because of the variations in the radiation and air humidity regimes. In addition, an impact of the interannual variation of the vegetation area index (VAI) and of the leaf initiation date was observed in the beech. Finally, a decline of the carbon sequestration efficiency of the ecosystem during the season was observed in both the subplots. It was because of neither the variation in any climatic variables nor VAI variation.