Figs (Ficus spp.) and fig wasps (Chalcidoidea, Agaonidae): hypotheses for an ancient symbiosis

Figs and their pollinating fig wasps are dependent on one another for propagation of their own kinds. The wasps reproduce by ovipositing through the styles of female flowers within the closed fig receptacles (syconia). About half of the female flowers within the syconia of monoecious figs have styles which are longer than the ovipositors of the wasp, and they will therefore produce seeds rather than wasp larvae. Since a longer ovipositor would enable a wasp to reach more ovules and deposit more eggs, the question arises at to why longer ovipositors have not evolved.
In an attempt to answer this question, four seemingly plausible hypotheses are examined but each is shown to be problematical in some way. Consideration is then given to a fifth hypothesis which proposes that ovipositor length is constrained by abortion of syconia with relatively few seed embryos and many agaonid larvae. It is argued first that this pattern of abortion will be selected during a sustained period of heavy wasp infestation because seeds will then become scarce relative to pollen-carrying wasps. Increased expenditure by the fig on seed production would therefore be favoured by natural selection. A greater expenditure on seeds would occur if young syconia with exceptionally heavy wasp infestations were dropped and the saved nutrients invested in syconia of a subsequent crop containing average levels of wasp larvae and seeds. Provided that the energy and nutrient cost of dropping young syconia is small, the selective advantage to the wasp of longer ovipositors is eliminated in this way. A stable coexistence of figs and wasps is therefore possible. The paper concludes by discussing two general predictions of the abortion hypothesis, and how these may be tested.     

Kinetic parameters of nitrogen mineralization rates of leguminous crops incorporated into soil

Summary Fresh leguminous plant residues were incorporated into soil columns and incubated at 23°C for up to 20 weeks. The N released from specific fractions (foliage, stems, and roots) of each residue were monitored at specific time intervals. Relationships between organic carbon, total nitrogen, CN ratio, lipids, and lignin content of the plant materials and the cumulative amount of N mineralized in soil were investigated. Statistical analyses indicated that the rates of N mineralized were not significantly correlated with the organic C nor lipid content of the residues. However, the cumulative amount of N released was significantly correlated with the total N content of the plant material (r=0.93^***). The percentage of organic N of the legumes mineralized in soil ranged from 15.9 to 76.0%. The relationship between the percentage of N released and the CN ratio of the plant material showed an inverse cuvilinear response (r= 0.88^***). It was also evident that the composition of lignin in the residue influenced N mine-ralization rates of the leguminous organs incorporated into soil.There was a curvilinear relationship between the cumulative amount of N released from the residues and time of incubation. Nitrogen mineralization rates were described by first-order kinetics to estimate the N mineralization potential (N₀), mineralization rate constant (k), and the time of incubation required to mineralize one-half of N₀ (t_1/2). The kinetic parameters were calculated by both the linear least squares (LLS) and nonlinear least squares (NLLS) transformations. The N₀ values among the crop residues varied from –35 to 510 g Ng^–1 soil. Statistical analyses revealed that the N₀ values obtained by both LLS and NLLS methods were significantly correlated (r=0.93^***). The mineralization rate constants (k) of the residues ranged from 0.045 to 0.325 week^–1. The time of incubation required to mineralize one-half the nitrogen mineralization potential (t_1/2) of the legumes incorporated into soil ranged from 2.1 to 15.4 weeks.     

Stoichiometry of proton uptake in isolated pea chloroplasts under different light intensities

The number of protons released inside the chloroplast thylakoids per electron which is transferred through the electron transport chain (H⁺/e^– ratio) was measured in isolated pea chloroplasts at pH 6.0 under continuous illumination and with methyl viologen as an electron acceptor. At saturating light intensity (200 W · m^–2) (strong light) the H⁺/e^– ratio was 3. At low intensity (0.9 W · m^–2) (weak light) the H⁺/e^– ratio was 2 with dark-adapted chloroplasts, but it was close to 3 with chloroplasts that were preilluminated with strong light. It is shown that the presence of azide in the reaction mixture leads to errors in the determination of the H⁺/e^– ratio due to underestimation of the initial rate of H⁺ efflux on switching off the light. To explain the above data, we assume that transformation of the electron transport chain occurs during illumination with strong light, namely, the Q cycle becomes operative.     

Evolution of nesting strategies of ants: genetic evidence from different population types of Formica ants

Genetic population structure was studied in two types of populations in the ants Formica exsecta and F. pressilabris: populations consisting of single-nest colonies (monodomy) and populations consisting of multi-nest colonies (polydomy). These characteristics seem to be associated with the number of egg-laying females (gynes) in a nest, mating structure of the population, sex ratio and male size variation. The monodomous populations are characterized by single-gyne nests, the population sex ratio is either I:1 or female-biased, males are mainly large-sized, and there is slight inbreeding in the population. The polydomous populations have multi-gyne nests with gynes related to each other, sex ratio is strongly male-biased, most males are small-sized, and there is slight genetic microdifferentiation within the populations. Diploid males found in a polydomous F. pressilabris population suggest that the population is inbred and isolated. Habitat localization is presented as a plausible explanation for the evolution of the polygynous and polydomous population structure.     

Production of second generation triploid and tetraploid rainbow trout by mating tetraploid males and diploid females — Potential of tetraploid fish

Summary First generation tetraploids were produced by hydrostatic pressure treatment before the first cleavage and raised until the adult stage. Their survival and growth were severely depressed when compared to the diploid control: after two years, no ovulated females were found although males produced sperm at 1 and 2 years of age and were mated individually with diploid females. The progenies were consistently normal with high survival rates. They were found to be almost all triploids by karyology, which failed to detect a significant rate of aneuploidies. However, the fertilizing ability of tetraploid males was always low (0 to 97% of the control; average 40%). Several arguments presented here support the hypothesis that diploid spermatozoas, which are wider than haploid ones, would be frequently blocked during their penetration through the micropyle canal. Second generation tetraploids were produced after such matings by heat shocks, causing the retention of the second polar body. Their survival and growth were much more satisfactory than in the first generation, although still lower than in diploid and triploid controls issuing from diploid parents. Performances of second generation triploids were comparable to those of diploids, and slightly better than those of conventional triploids issuing from diploid parents. 94.5% of the second generation tetraploids were male.     

Effects of intravenous epinephrine on macaque platelets

Blood was obtained from three species of macaques for a study of platelets. A rapidly mobilizable platelet pool was demonstrated in rhesus macaques given intravenous epinephrine. The number of platelets/ml of blood increased about 30% 3 to 5 min after epinephrine was given. The size distributions of the platelets were similar before and after injection. Platelet aggregability was increased after injection. Basal platelet aggregabilities, as measured by platelet aggregate ratios, were similar in rhesus macaques. Celebes black macaques, and human subjects, but were significantly greater in cynomolgus macaques than in the other three species.     

Relationship between chloroplast structure and O2 evolution rate of leaf discs in plants from different biotopes in South Finland

Abstract The chloroplast ultrastructure, especially the thylakoid organization, the polypeptide composition of the thylakoid membranes and photosynthetic O₂ evolution rate, chlorophyll (Chl) content and Chi a/b ratio were studied in leaves of nine plants growing in contrasting biotopes in the wild in South Finland. All the measurements were made at the beginning of the period of main growth on leaves approaching full expansion, when the CO₂-saturated O₂ evolution rate (measured at 20°C and 1500 μmol photons m^?2s^?1) was at a maximum, ranging from 19.2 to 6.9 μmol O₂ cm^?2 h^?1. Among the species, the Chi a/b ratio varied between 3.75 and 2.71. In the mesophyll chloroplasts, the ratio of the total length of appressed to non-appressed thylakoid membranes varied between 1.07 and 1.79, the number of partitions per granum varied between 2.8 and 12.0 and the grana area between 21 and 42% of the chloroplast area. There was a significant relationship between the rate of O₂ evolution of the leaf discs and the thylakoid organization in the mesophyll chloroplasts. The higher the O₂ evolution rate, the lower was the ratio of the total length of appressed to non-appressed thylakoid membranes and also the lower the grana area. Although the relationship of the photosynthetic rate with the Chi content and the Chi a/b ratio of the leaves was not as clear, a significant negative correlation existed between the Chi a/b ratio and the ratio of appressed to non-appressed thylakoid membranes, indicating lateral heterogeneity in the distribution of different Chl- protein complexes.     

Study on growth and biomass of underground organs ofTypha angustata Bory & Chaub

Underground and aboveground biomass and their ratios at flowering time in different natural stands of Typha angustata near Jaipur, India were studied in the field and experimentally over a period of eleven months (June to April). The underground biomass was 40–50% of the aboveground biomass in both natural and experimental conditions.     

Specific photoperiodic stimulation of dry matter production in a high-latitude cultivar of Poa pratensis

Vegetative plants of Poa pratensis L. cv. Holt (origin 69°N) raised in short days gave large and significant increases in plant dry weight, plant height and leaf area upon exposure to continuous light, compared with 8-h short days, at essentially identical daily inputs of radiant energy (8-h summer daylight ± low intensity extension). For example, by the fourth harvest (after 26, 34 and 46 days at 21, 15 and 9°C, respectively), the dry weights of plants in long days were 81, 163 and 195% greater than those of the corresponding short-day controls at the respective temperatures. Plant leaf areas in long days were between two and four times as large as control values by the end of the experiment. This was mainly due to increased leaf length caused by long-day stimulation of cell extension and division. However, the photoperiod did not affect the partitioning of assimilates amongst leaves, culms and stolons. Most of these effects could also be brought about by exogenous gibberellin application to plants in short days. However, in contrast to the effect of long days, gibberellin treatment also induced stem internode elongation even in these vegetative plants. Examination by standard growth analysis procedures revealed that the observed increases in relative growth rate were due primarily to increased net assimilation rate followed, several days later, by increases in leaf area ratio when newly-emerged leaves began to constitute a significant proportion of the leaf area. It is concluded that these reactions are of great adaptive significance for growth at the marginal temperatures prevailing at high latitudes.     

Is male back space limiting? An investigation into the reproductive demography of the giant water bug,Abedus indentatus (Heteroptera: Belostomatidae)

Because male giant water bugs in the subfamily Belostomatinae provide parental care by brooding eggs on their back, an accurate assessment can be made of both the actual and potential reproductive capacity of males. Two operational sex-ratio (OSR) indices were developed and empirically measured for a population of giant water bug, Abedus indentatus,in California. One index was based on reproductive rates measured in the laboratory; the other index was based on reproductive resources observed in the field. Both OSR indices suggest that the operational sex ratio fluctuates between maleskewed ratios in the summer and femaleskewed ratios in the winter. This pattern appears to be the consequence of two factors. First, the adult sex ratio is significantly female biased. Second, although males can outreproduce females at high ambient temperatures, the reverse is true at low temperatures. Possible reasons for the female-skewed adult sex ratio are examined, including differential recruitment, differential mortality, and sampling bias.