Shredder–collector interactions in temporary streams of western Oregon

1. Field data and results from laboratory rearing are combined to describe shredder–collector interactions in western Oregon temporary streams.
2. The composition of functional feeding groups in the temporary streams conforms to that predicted for permanent headwaters by the River Continuum Concept (RCC).
3. A distinct functional feeding group phenology was found, with shredders emerging first and collectors emerging last in the season. Scrapers were intermediate.
4. Presence of shredders enhanced collector growth in laboratory experiments ( P < 0.01; n = 12). The species reared in the study trials accounted for 67% of the shredder biomass and 76% of the collector biomass in the natural systems.
5. Field data and laboratory rearing trials both support the hypothesis of a close shredder–collector interaction in the processing of allochthonous material in the summer-dry headwaters studied.     

Estimation of survival rate and oviposition interval of Anopheles balabacensis mosquitoes from mark-recapture experiments in Sabah, Malaysia

An exophilic population of the vector mosquito Anopheles balabacensis Baisas was investigated in two mark-recapture studies (16.ix-13.x.1986 and 6-26.i.1987) at an inland, foothill village in Sabah, Malaysia. Wild female mosquitoes were intercepted as they came to feed on man or buffalo, given a bloodmeal, marked with fluorescent dust and released. The recapture rate was about 12%. A new method of analysis is proposed which uses cross-correlation and a time series model. The estimated survival per oviposition cycle was 0.48-0.54 and the oviposition cycle interval 2-3 days.     

Analysis of Two Rubisco-Deficient Tobacco Mutants, H7 and Sp25; Evidence for the Production of Rubisco Large Subunits in the Sp25 Mutant that Form Clusters and are Inactive

The basis for the lesions in the Sp25 and H7 ribulose-l,5-bisphosphatecarboxylase/oxygenase (Rubisco) mutants of tobacco was studiedin detail because these plants may be suitable hosts for transformationwith the genes for Rubisco enzymes of various origins that havedifferent substrate specificities. We show that the Sp25 mutantlacks active holoenzyme, but contains the large and small subunitpolypeptides, Rubisco activase and the chloroplast chaperonin,Cpn 60. The large subunit polypeptides were not distributeduniformly in the stroma in the Sp25 mutant as they were in thewild-type plants, but had an anomalous distribution being presentonly in aggregated clusters notably in chloroplasts with largestarch grains. Furthermore, these clusters were not uniformlydistributed throughout the photosynthetic cells but were localizedlargely in the mesophyll cells surrounding the vascular tissue.In contrast to the Sp25 mutant, the H7 mutant contained theRubisco holoenzyme, but in this case the enzyme was inactive.It is clear that in both these mutants the Rubisco holoenzymefails to assemble correctly. In the Sp25 mutant assembly islost completely while in the H7 mutant the holoenzyme is formed,but the assembly process fails to produce an active enzyme.We suggest that the flaw in assembly in the Sp25 mutant resultsfrom a defect in chloroplast encoded proteins. Key words: Rubisco, assembly, tobacco, mutants     

FACTORS AFFECTING THE SECRETION OF LUTEINIZING HORMONE IN THE EWE

(1) Luteinizing hormone (LH) is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre-pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle. Secretion is probably also pulsatile during the preovulatory surge of LH. (2) The secretion of LH is affected by the ovarian steroids, oestradiol and progesterone, both of which act principally to reduce the frequency of the pulses. During the luteal phase the two steroids act synergistically to exert this effect, and during anoestrus oestradiol acts independently of progesterone. Androstenedione secreted by the ovary apparently has no role in the control of LH secretion. (3) The amplitude of the pulses may also be affected by the steroids but there are conflicting reports on these effects, some showing that amplitude is lowered by the presence of oestrogen and others showing increases in amplitude in the presence of oestrogen and progesterone. (4) The secretion of LH pulses is affected by photoperiod, social environment and nutrition. Under the influence of decreasing day-length, oestradiol alone cannot reduce the frequency of pulses and the ewe experiences oestrous cycles. When day-length is increasing, the hypothalamus becomes more responsive to oestradiol which reduces the frequency of the pulses. (5) A hypothetical pheromone secreted by rams can increase the frequency of the LH pulses in anoestrous ewes and thereby induce ovulation, possibly by inhibiting the negative feedback exerted by oestradiol. (6) The relationships between nutrition and reproduction are poorly understood, but it seems likely that the effects of nutrition are mediated partly through the hypothalamus and its control of the secretion of LH pulses. (7) The pulses of LH secreted by the anterior pituitary gland are evoked by pulses of GnRH secreted by the hypothalamus. The location of the centre controlling the GnRH pulses and the neurotransmitter involved are not known.