Isolation and characterization of microsatellite loci from the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae)

We report the isolation and development of 81 novel primers for amplifying microsatellite loci in the Rhagoletis pomonella sibling species complex, and the sequencing, characterization and analysis of basic population genetic parameters for nine of these genes. We also report the successful cross‐species amplification of several of these loci. The R. pomonella sibling species complex is a textbook example of genetic differentiation in sympatry via host‐plant shifting. Microsatellite markers can be useful for mapping host‐plant‐associated adaptations in Rhagoletis that generate reproductive isolation and facilitate speciation, as well as for resolving the genetic structure and evolutionary history of fly populations.     

Protein Body Degradation in the Starchy Endosperm of Germinating Sorghum

Taylor, J. R. N., Novellie, L. and Liebenberg, N. v. d. W. 1985.Protein body degradation in the starchy endosperm of germinatingsorghum.—J. exp. Bot. 36: 1287–1295. Transmission electron micrographs of starchy endosperms of germinatingsorghum indicate that the protein bodies are degraded predominantlyby progressive hydrolysis of prolamin from their surface. Theappearance of holes within partially degraded protein bodiesindicates that some internal hydrolysis also takes place. Chemicalanalyses of protein bodies isolated at different stages duringgermination showed that their amino acid composition and electrophoreticpattern remained relatively unchanged during hydrolysis. Theend result of protein body degradation was that the organellescompletely disappeared leaving empty starchy endosperm cells.The protein bodies did not swell prior to or during degradation.This mode of protein body degradation differs from that in germinatingdicotyledonous seeds and in the aleurone layer and embryo ofcereal seeds but was identical to the mode of prolamin proteinbody degradation in the starchy endosperm of germinating riceseeds. Key words: Sorghum bicolor, protein body degradation, prolamin     

Zooplankton in Rainbow Bay, a Carolina bay pond: population dynamics in a temporary habitat

SUMMARY.

• 1 Rainbow Bay is a temporary freshwater pond in South Carolina, U.S.A., that typically fills in winter and dries in spring or summer. We studied population dynamics of zooplankton in 1984 and 1985 when it held water for 282 and 57 days, respectively. The zooplankton were diverse, including one species of calanoid copepod, nine or more cyclopoid copepods, nineteen or more cladocerans, and twelve or more rotifers. The community was initially dominated by the copepods Diaptomus stagnalis and Acanthocyclops vernalis or Diacyclops haueri, later by cyclopoids and cladocerans including Daphnia laevis and Simocephalus spp.
• 2 Laboratory experiments with sediments from the dry pond support the inference from field data that time of emergence from resting stages was a proximate cause of the initial succession of species. The experiments also showed that eggs of the calanoid copepod, Diaptomus stagnalis, were inhibited from hatching in early November, but became ready to hatch by late November. A similar inhibition was not observed for cladocerans or cyclopoid copepods.
• 3 Food limitation appeared to influence population dynamics following emergence. For the cladocerans Daphnia laevis and Simocephalus spp., great reductions in size-specific fecundity occurred 1 month (1985) or 3 months (1984) after the pond filled and were associated with disappearance of the rotifer Conochilus hippocrepis. The cladocerans produced ephippia when their fecundities declined. Reproduction of Diaptomus occurred before cladoceran fecundities decreased in 1984, but during their decline in 1985. Broods of Diaptomus were smaller in 1985.
• 4 The impact of invertebrate predators was probably greater than that of vertebrate predators, but neither was sufficient to prevent over-exploitation of food resources. Prey consumption rates by salamander larvae were estimated from diets and population densities of the larvae in 1984 (Taylor et al., 1988). Their impact on the zooplankton was low in February, increased in March and April as the larvae grew, and then

     

A functional analysis of the shift from gill- to lung-breathing during the evolution of land crabs (Crustacea, Decapoda)

The evolution of air-breathing in land crabs is associated with a progressive shift in the primary site of respiratory gas exchange from the diffusion-limited gills used for water-breathing, via a simple 'cutaneous' lung surface to the perfusion-limited, invaginated lung described in the mountain crab, Pseudothelphusa garmani. The reduced diffusion limitation over the lungs facilitates oxygen transfer from air to the tissues at lower ventilation rates but is associated with accumulation of carbon dioxide. A potential respiratory acidosis is buffered by the respiratory pigment haemocyanin and by elevation of haemolymph bicarbonate levels. These changes parallel those described in vertebrates but air-breathing crustaceans maintain relatively low carbon dioxide levels in the haemolymph, either by retaining an aquatic route for its elimination over the reduced gills or by blowing it off across the lung. Maintenance of low carbon dioxide levels may be associated with a limited capacity to buffer against an acidosis due to low levels of circulating haemocyanin (i.e. crustaceans lack red blood cells). This may ultimately limit their survival in air as an acidosis will reduce oxygen transport due to a marked Bohr effect on haemocyanin. The primary role of an invaginated lung may be to reduce rates of water loss in air.     

Patterns of Root Respiration Associated with the Induction of Aluminium Tolerance in Phaseolus vulgaris L.

Aluminium (Al) tolerance in an Al-tolerant cultivar of Phaseolusvulgaris L. (‘Dade’) was found to be an inducibletrait. Upon exposure to 10 µM Al, the rate of root elongationwas inhibited in comparison to controls. During the following72 h, the rate of elongation returned to levels comparable tocontrols. In contrast, root elongation of an Al-sensitive cultivar(‘Romano’) did not recover after exposure to Al.In Dade, the resumption of root elongation following exposureto Al was accompanied by increased rates of root respiration,whereas respiration rates slowly declined over the 72 h treatmentperiod in Romano. When partitioned into growth and maintenanceexpenditures, a larger proportion of root respiration of Dadeexposed to Al was allocated to maintenance processes, potentiallyreflecting diversion of energy to metabolic pathways that offsetthe adverse effects of Al toxicity. Romano did not show sucha pattern and respiration associated with both growth and maintenancewas reduced after exposure to Al. Root and shoot growth of bothcultivars were also measured to determine the effects of long-term(21 d) exposure to 10 µM Al. Dade plants exposed to Alexhibited enhanced growth in comparison to controls, whereasRomano plants were characterized by reduced shoot and root growth.Modelling the time-course of root respiration and measuringthe long-term growth responses to Al is a valuable method ofelucidating respiratory costs of stress tolerance. Key words: Aluminium, differential tolerance, maintenance respiration, Phaseolus vulgaris, root respiration     

Higher‐order assemblies of oligomeric cargo receptor complexes form the membrane scaffold of the Cvt vesicle

Selective autophagy is the mechanism by which large cargos are specifically sequestered for degradation. The structural details of cargo and receptor assembly giving rise to autophagic vesicles remain to be elucidated. We utilize the yeast cytoplasm‐to‐vacuole targeting (Cvt) pathway, a prototype of selective autophagy, together with a multi‐scale analysis approach to study the molecular structure of Cvt vesicles. We report the oligomeric nature of the major Cvt cargo Ape1 with a combined 2.8 Å X‐ray and negative stain EM structure, as well as the secondary cargo Ams1 with a 6.3 Å cryo‐EM structure. We show that the major dodecameric cargo prApe1 exhibits a tendency to form higher‐order chain structures that are broken upon interaction with the receptor Atg19 in vitro. The stoichiometry of these cargo–receptor complexes is key to maintaining the size of the Cvt aggregate in vivo. Using correlative light and electron microscopy, we further visualize key stages of Cvt vesicle biogenesis. Our findings suggest that Atg19 interaction limits Ape1 aggregate size while serving as a vehicle for vacuolar delivery of tetrameric Ams1.     

Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton in relation to some biotic and abiotic variables in an Ethiopian rift-valley lake (Awassa)

SUMMARY. I. Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton was studied in a tropical freshwater lake. Variation in phytoplankton biomass and production, and several other limnological parameters, were also quantified.
2. Bacterial number and biomass fluctuated between 3.88–8.33×10⁶ ml⁻¹ and 68–125 mg C m⁻³, respectively. No spatial variation was observed in these bacterial variables, although other limnological parameters showed vertical variation.
3. Seasonal and vertical variation of heterotrophic bacterial activity were estimated from oxygen consumption, ¹⁴CO₂dark uptake and plate counts of colony forming units. All three methods showed vertical heterogeneity, with higher activity in the hypolimnion during the long stratification period (February May). Oxygen consumption rate and plate counts showed seasonality.
4. In spite of the low seasonality of climate in the tropics, several biological, chemical and physical variables were correlated with changes in bacterial variables. Wind and rainfall, and their effects on stratification and mixing, vertical distribution of nutrients and rate of primary production appeared to be the important parameters affecting heterotrophic bacterioplankton.     

Changes in the feeding behaviour of a malaria vector,Anopheles farauti Lav., following use of DDT as a residual spray in houses in the British Solomon Islands Protectorate

• 1 To investigate the failure of DDT to interrupt malaria transmission in parts of the British Solomon Islands Protectorate, regular all-night man-biting catches of malaria vectors were made before and after DDT house spraying on San Cristobal Island.
• 2 Changes were observed in the man-biting behaviour of Anopheles farauti. There was a reduction in the degree of entry into houses and a shifting of the times of peak biting. Whereas before spraying the indoor and outdoor biting cycles differed, after spraying there was no difference although both the indoor and outdoor cycles had altered.
• 3 DDT was found to have a deterrent effect on An.farauti but this effect decreased with time.
• 4 DDT also appears to eliminate a dominant indoor feeding fraction of the farauti population. Following this there can be an increase in an outdoor feeding fraction which can be responsible for a resumption of malaria transmission.
• 5 Biting cycles obtained before spraying are also shown for An.koliensis and An.punctulatus.