THE EFFECTS OF SUGARS AND ACIDS ON CONSUMER ACCEPTABILITY OF KIWIFRUIT

A kiwifruit (Actinidia deliciosa (A Chev) Liang et Ferguson cv Hayward) pulp was made using fruit harvested immature to minimize the presence of aroma volatiles. This pulp was modified by incorporating sugars and acids to simulate kiwifruit with a range of Brix and acid levels. Using sensory evaluation, flavor acceptability was found to increase with increasing Brix. As expected, perceived " sweetness intensity" increased with increasing Brix. Acidity did not influence flavor acceptability. At high Brix, sugars were able to suppress the effects of variations in acidity. Changes in Brix did not influence " flavor intensity", suggesting that aroma volatiles may be important contributors to kiwifruit flavor intensity.     

The path of photosynthate translocation into citrus fruit

Abstract The path of [¹⁴C]photosynthate translocation into citrus fruit was examined to determine which anatomical and physiological features were involved in this process. Experiments were conducted during the final pre-harvest months of 2 years grapefruit crops (Citrus paradisi Macf. cv. ‘Marsh’). A source leaf nearest the fruit was exposed to ¹⁴CO₂ for 1 h + 5 h ambient air, followed by dissection of vascular and phloem-free tissues in the fruit quarter directly aligned with the source. Radioactivity in each tissue was quantified after separation and extraction in boiling 80% ethanol. Peel (flavedo+albedo) contained an average 35% of the label in the quarter fruit, but an additional 20% was localized entirely in dorsal vascular bundles along exterior walls of juice segments. Less [¹⁴C]photosynthate was recovered from other vascular tissues and was nearly absent from adjacent mature seeds. Radioactivity in the single layer of segment epidermis, however, averaged 17% of that in the quarter fruit. Juice tissues interior to this accumulated only 17% of the total. No phloem tissue was evident in either the segment epidermis or juice tissues, but over 70% of the [¹⁴C]assimilates in the latter were localized in thread-like stalks which attach juice vesicles to dorsal vascular bundles. In addition, labelled hexose/sucrose ratios in these structures increased with distance from the vascular bundle. The majority of photosynthates, therefore, entered citrus fruit via dorsal vascular bundles and were partially hydrolysed during slow transfer through non-vascular segment epidermis and juice stalks.     

Morphometric Analysis of the Growth of Phsp70-ipt Transgenic Tobacco Plants

The effect of introducing a supplementary ipt-gene into thegenome of Nicotiona tabacum L. cv. Petit Havana SR 1 is studiedon the morphological plant development. The ipt-gene, accountingfor the biosynthesis of cytokinins, was coupled to the heat-induciblehsp70- promoter from Drosophila melanogaster. Besides the influenceof the hormonal changes involved, the effects of the experimentalconditions are examined, namely the in vitro growth conditionsfor selecting transformed plants and the heat treatment to induceipt-gene expression. The phenotype of the plants is determined by the tissue sensitivityto three factors: (1) heat treatment reduces stem elongationand diameter growth; (2) in vitro pre-cultivation also reducesstem elongation; and (3) expression of the ipt-gene stimulatesdiameter growth, induces debudding of the axillary shoots andinhibits root development. In addition, axillary bud developmentindicates that in vitro cultivation affects ipt-gene expression. Key words: Cytokinin, heat treatment, in vitro cultivation, ipt-gene, morphology     

Remodelling of Neuromuscular Systems During Insect Metamorphosis

During metamorphosis in the hawkmoth, Manduca sexta, the larvalthoracic legs are replaced by a new set of adult legs that includenew sensory neurons and muscles, and participate in new patternsof locomotor activity. Larval leg motoneurons persist to innervatethe new adult leg muscles, but undergo striking changes in dendriticmorphology that are regulated by the insect steroid, 20-hydroxyecdysone.In the periphery, the motor terminals regress as larval musclesdegenerate, and expand as new adult muscles form from myoblasts.Evidence obtained both in vivo and in vitro suggests that theproliferation of myoblasts during metamorphosis is dependentupon innervation.     

Sympatric speciation in a genus of marine reef fishes

Sympatric speciation has been contentious since its inception, yet is increasingly recognized as important based on accumulating theoretical and empirical support. Here, we present a compelling case of sympatric speciation in a taxon of marine reef fishes using a comparative and mechanistic approach. Hexagrammos otakii and H. agrammus occur in sympatry throughout their ranges. Molecular sequence data from six loci, with complete sampling of the genus, support monophyly of these sister species. Although hybridization occurrs frequently with an allopatric congener in an area of slight distributional overlap, we found no F₁ hybrids between the focal sympatric taxa throughout their coextensive ranges. We present genetic evidence for complete reproductive isolation based on SNP analysis of 382 individuals indicating fixed polymorphisms, with no shared haplotypes or genotypes, between sympatric species. To address questions of speciation, we take a mechanistic approach and directly compare aspects of reproductive isolation between allopatric and sympatric taxa both in nature and in the laboratory. We conclude that the buildup of reproductive isolation is strikingly different in sympatric vs. allopatric taxa, consistent with theoretical predictions. Lab reared hybrids from allopatric species crosses exhibit severe fitness effects in the F₁ or backcross generation. No intrinsic fitness effects are observed in F₁ hybrids from sympatric species pairs, however these treatments exhibited reduced fertilization success and complete pre‐mating isolation is implied in nature because F₁ hybrid adults do not occur. Our study addresses limitations of previous studies and supports new criteria for inferring sympatric speciation.     

The impact of kleptoparasitic invasions on the evolution of gall-size in social and solitary Australian Acacia thrips

Many species of gall-inducing Acacia thrips are attacked by kleptoparasitic thrips who enter the gall, destroy the occupants, and then use the gall for producing their own offspring. The hypothesis tested here is that pressure exerted by ldeptoparasites （genus Koptothrips） not only provoked the evolution of soldiers in the gall-inducing clade, but have also influenced the evolution of gall size and morphology. Various size dimensions of invaded galls were compared to those of uninvaded galls using data from six gall-inducing species and their kleptoparasites. For the non-social gall-inducing species （K. ellobus and K. nicholsoni） invaded galls showed no significant size differences from galls that had not been invaded. For the four social gall-inducingspecies （K. habrus, K. intermedius, K. waterhousei and K. morrisi） invaded galls were significantly narrower and/or shorter than uninvaded galls. Galls of social species that had not been invaded and contained adult soldiers were significantly larger than galls where soldiers were still at a larval stage, suggesting that gall size is related to gall age in these species. An hypothesis is proposed that links the timing of invasion by kleptoparasites to size of the host gall： induction of a smaller gall by host founders will reduce the period of vulnerability to invasion （before soldiers become adults） for social thrips by allowing foundresses in these smaller galls to begin laying soldierdestined eggs relatively sooner.     

Assessing the taxonomic status of dingoes Canis familiaris dingo for conservation

• 1 The conservation status of the dingo Canis familiaris dingo is threatened by hybridization with the domestic dog C. familiaris familiaris. A practical method that can estimate the different levels of hybridization in the field is urgently required so that animals below a specific threshold of dingo ancestry (e.g. 1/4 or 1/2 dingoes) can reliably be identified and removed from dingo populations.
• 2 Skull morphology has been traditionally used to assess dingo purity, but this method does not discriminate between the different levels of dingo ancestry in hybrids. Furthermore, measurements can only be reliably taken from the skulls of dead animals.
• 3 Methods based on the analysis of variation in DNA are able to discriminate between the different levels of hybridization, but the validity of this method has been questioned because the materials currently used as a reference for dingoes are from captive animals of unproven genetic purity. The use of pre‐European materials would improve the accuracy of this method, but suitable material has not been found in sufficient quantity to develop a reliable reference population. Furthermore, current methods based on DNA are impractical for the field‐based discrimination of hybrids because samples require laboratory analysis.
• 4 Coat colour has also been used to estimate the extent of hybridization and is possibly the most practical method to apply in the field. However, this method may not be as powerful as genetic or morphological analyses because some hybrids (e.g. Australian cattle dog × dingo) are similar to dingoes in coat colour and body form. This problem may be alleviated by using additional visual characteristics such as the presence/absence of ticking and white markings.

     

A comparison of techniques for assessing dispersal behaviour in gundis: revealing dispersal patterns in the absence of observed dispersal behaviour

Knowledge of the dispersal status of group members is important to understanding how sociality may have evolved within a species. I assessed the effectiveness of four techniques for elucidating dispersal behaviour in a rock-dwelling rodent ( Ctenodactylus gundi ) with small group sizes (2–10 animals): genetic parentage assignment, haplotype data and kinship analyses, assignment testing, and F -statistics. The first two methods provided the greatest insight into gundi dispersal behaviour. Assignment testing and F -statistics proved of limited use for elucidating fine-scale dispersal, but could detect large-scale patterns despite low sex-biased dispersal intensity (1.9 : 1) because of moderate genetic differentiation among groups ( F _ST = 0.10). Findings are discussed in light of current dispersal theory. In general, gundi dispersal is plastic, and seems to be dependent on body weight (for males), group composition, and scale of analysis (total dispersal events recorded within the population were almost twice the immigration rate into the population). Most groups were comprised of a single matriline and one immigrant male. Immigrant rather than philopatric males bred with group females. Dispersal among groups was male-biased, but dispersal or philopatry could occur by either sex. During a drought, both sexes delayed dispersal and cooperative social units formed. Whether such behaviour resulted directly from the drought or not remains unclear, however, since comparative information was not available from nondrought years. Combining fine-scale analyses with information on large-scale patterns provided substantial insight into gundi dispersal behaviour despite the limited movement of animals during a drought, and may prove useful for elucidating dispersal behaviour in other social animals.     

An elemental and stable isotope assessment of water strider feeding ecology and lipid dynamics: synthesis of laboratory and field studies

1. Despite the ubiquity and abundance of water striders (Hemiptera: Gerridae) in temperate streams and rivers and their potential usefulness as sentinels in contaminant studies, little is known about their feeding ecology and lipid dynamics. 2. In this study we used stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) and elemental carbon to nitrogen ratios (C/N) to assess dietary habits and lipid content, respectively, for water striders. 3. To determine diet‐tissue fractionation factors, nymphs of the most common species in New Brunswick, Canada, Aquarius remigis were reared in the laboratory for 73 days and exhibited rapid isotopic turnover in response to a switch in diet (C half‐life = 1.5 days, N half‐life = 7.8 days). Their lipid content increased towards the end of the growing season and resulted in lower δ¹³C values. Diet‐tissue fractionation factors were established after correction of δ¹³C data for the confounding effect of de novo lipid synthesis (strider δ¹³C_adj– diet δ¹³C_adj = 0.1‰, strider δ¹⁵N – diet δ¹⁵N = 2.7‰). 4. Water striders from the majority of 45 stream sites (83%) in New Brunswick had less than 50% contribution of aquatic carbon to their diets but showed a gradual increase in the contribution of this carbon source to their diet with increasing stream size. 5. These data indicate that striders exhibit a strong connection to terrestrial carbon sources, making them important users of energy subsidies to streams from the surrounding catchment. However, this dependence on terrestrial organic matter may limit their utility as indicators of contamination of aquatic systems by heavy metals and other pollutants.