DIFFERENCE TASTE THRESHOLDS FOR SUCROSE IN WATER AND IN ORANGE JUICE: AN INTERLABORATORY STUDY

Difference taste thresholds, expressed as jnd values or Weberratios, were determined for sucrose in water and in orange juiceat laboratories in Sweden, U.S.A., Poland and Switzerland usinga method of constant stimuli. The following total arithmeticmean values of all 172 individual jnd values were obtained:0.266 and 0.400% sucrose at 2 and 5% sucrose in water, respectively;0.977 and 1.19% sucrose at 1.5 and 3.75% sucrose in orange juice,respectively. The frequency distributions of the individualvalues were asymetrical and showed a large variation among subjects.The results of some additional experiments at 2 and 5% sucrosein orange juice, performed only by the Polish laboratory, arereported also. Significance analyses performed according to one parametricmethod (t-test), using pooled data of groups of subjects, andone non-parametric method (Mann-Whitney's U-test), using individualthreshold values, gave the same conclusion in practically allcases. The data indicated that females had slightly lower average discriminationthresholds than males. There was a significant degree of correlationbetween subjects' discriminatory ability at different concentrationsof sucrose in each of the two media. Few significant differences between the laboratories were foundfor sucrose in water, whereas for sucrose in orange juice thefollowing rank order, from lowest to highest average jnd value,among the laboratories was obtained for both concentrationstested: Poland < U.S.A. < Sweden = Switzerland. Some speculationswere advanced as partial explanation for the differences amongthe laboratories. ^*Formerly Johansson     

The Control of the Reptilian Gonad

In reptiles, there is adequate evidence to indicate environmentalcontrol of the ovarian cycle through hvpothalamic pathways andthe subsequent release of tropic hormone (s) from the anteriorpituitary. The role of the pineal-parietal complex still remainsto be elucidated. In the hypothalamus there appear to be steroidsensitive areas and both progesterone and estrogen appear tohave important feedback influences upon gonadal growth ovulation,and ovarian steroid production. Cytological studies of the reptilianpituitary indicate similar cell types to those observed in mammalianpituitaries, but thus far, two gonadotrophs cannot be identifiedwith any certainty. Chemical and biological studies of the actionof mammalian gonadotropuis suggest that in reptiles hormoneswhich are FSH-like in mammals are able to stimulate gonadaldevelopment, ovulation, and steroid biosynthesis under certainconditions. Preliminary studies of the chemistry of turtle gonadotropuishave so far demonstrated only one active principle, which ischemically similar to mammalian LH, but is far more active thanthe latter hormone in reptilian systems. Further, the hormonealso has FSH-like activity in the reptile. Thus reptilian gonadaldevelopment can be stimulated by treatment with a variety ofmammalian gonadotropins. Recent studies have indicited an importantrole for growth hormone, acting in concert with gonadotropinand estrogen in the regulation of vitellogenesis and ovariangrowth. Piolactin appears to be an antigonadal agent in reptiles,as does progesterone. The exact manner in which these hormonesexert their antigonadal action remains to be clarified, butat least one site of action is the central nervous system; othersites maybe the liver and the fat depot. Ovarian tissue from reptiles is able to synthesize and secretesteioid hormones by pathways similar to those present in mammalianovaries. Circulating levels of estrogen have not been measured,but progesterone levels in the blood show distinct changes assocntedwith pregnancy and the presence of corpora lutea in the ovary.     

Nuclear insertions and heteroplasmy of mitochondrial DNA as two sources of intra‐individual genomic variation in grasshoppers

We examined the level of intra‐individual variation in a region of the mitochondrial genome coding for cytochrome oxydase 1 (COI) in two grasshopper species using a clone‐and‐sequence analysis of hundreds of sequences. In both Locusta migratoria and Chortoicetes terminifera, we found that 60–65% of the clones were unique COI‐like sequences. Among these COI‐like sequences, 70–75% diverged by less than 1% from the real mitochondrial haplotypes, and were likely to represent microheteroplasmic molecules. About 20% of the COI‐like sequences diverged by more than 9% from the mitochondrial haplotypes, and generally included stop codons, suggesting that these sequences were nuclear mitochondrial pseudogenes (NUMTs). Only six sequences, diverging by 2–6% from the mitochondrial haplotypes, were identified as potentially misleading in phylogenetic studies. In addition, we found that five sequences from C. terminifera were associated with mobile elements or repetitive DNA families.     

Degradation of native and exotic riparian plant leaf litter in a floodplain pond

1. A litter‐bag experiment was undertaken in a pond on the margins of a large temperate floodplain in south‐western France to assess the potential influence of the replacement of native by exotic riparian species on organic matter degradation. We determined initial litter chemical composition, breakdown rates and the invertebrate assemblages associated with the litter for five pairs of native dominant and exotic invasive species co‐occurring at different stages along a successional gradient. 2. Litter chemical composition, breakdown rates and abundance and diversity of detritivorous invertebrates were similar for the exotic and native species overall. No overall changes in organic matter degradation can thus be predicted from the replacement of dominant natives by exotic invasives. Breakdown rates were primarily driven by the C/N ratio. 3. One invasive species (Buddleja davidii) showed significantly higher breakdown rates than its native counterpart (Populus nigra), resulting in the disappearance of leaf litter 6 months prior to the next litterfall. In some cases, therefore, invasion by exotic species may result in discontinuity of resource supply for decomposers.     

Subspecific taxonomy of the desert locust,Schistocerca gregaria (Orthoptera: Acrididae), based on molecular and morphological characters

We evaluated the validity of the subspecific designation for Schistocerca gregaria gregaria (Forskål) and Schistocerca gregaria flaviventris (Burmeister), isolated in distinct regions along the north–south axis of Africa. Towards this goal, we assessed the variation of multiple morphological and molecular traits within species. We first used elliptic Fourier and landmark‐based relative warps analyses to compare the size and shape of two internal and two external structures of male genitalia. We provide a discriminant function which classified the specimens with 100% accuracy and selected shape elements of the external structures only (cercus and epiproct). We also tested eight molecular markers, and because of either absence of variation or contamination by mitochondrial DNA (mtDNA)‐like sequences, we used a clone‐and‐sequence analysis of the standard cytochrome c oxidase subunit I mitochondrial DNA barcode only. We differentiated 185 true mitochondrial sequences from 66 mitochondrial DNA‐like sequences, most of which were from S. g. gregaria specimens. On the dataset of mitochondrial origin, we identified three characteristic point mutations that diagnosed the two allopatric subspecies with 94% accuracy. Minimum spanning network and parsimony tree analyses identified S. g. flaviventris as a monophyletic lineage distinct from the nominate subspecies. Accordingly, microsatellite data indicate rarely occurring admixture events only, showing that independent evolutionary history is the norm.