Difference in luteinizing hormone response to an opioid antagonist in beef heifers and cows

In three experiments, we examined endogenous opioid inhibition of luteinizing hormone (LH) secretion during the bovine estrous cycle. An increase in serum LH in response to the opioid antagonist naloxone (Na; 1 mg/kg i.v.) was the criterion for opioid inhibition. Estrous cycles were synchronized via prostaglandin administration. In Experiment 1, mean serum LH was not different during the luteal phase in yearling heifers (n = 6/group) at Hour 1 after Nal (2.1 ng/ml) compared to controls (1.8 ng/ml). However, LH peak amplitude was increased (p less than 0.05) in the Nal compared to the control group. Serum LH was increased (p less than 0.01) during the follicular phase in heifers at Hour 1 post-Nal compared to controls (4.7 and 3.5 ng/ml, respectively). Again, Nal administration was followed by increased (p less than 0.05) LH pulse amplitude compared to control. In Experiment 2, no effect of Nal upon serum LH was detected in cows (n = 9) during proestrus, metestrus, midluteal and late luteal portions of the estrous cycle. In Experiment 3, the LH response to Nal was examined simultaneously in yearling heifers and cows (n = 5/group) during the luteal and follicular phases. Serum LH increased (p less than 0.001) during Hour 1 post-Nal in heifers compared to cows during the follicular (3.4 vs. 1.7 ng/ml) but not during the luteal phase. LH pulse amplitude also increased (p less than 0.05) during Hour 1 post-Nal in heifers compared to cows during the luteal (2.5 vs. 1.1 ng/nl and follicular (2.5 vs. 1.3 ng/ml) phases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurements of larval Atlantic cod (Gadus morhua) routine metabolism: temperature effects, diel differences and individual-based modeling

In the present study, dry mass (M_D, μg) and routine respiration rate (R_R) (μl O₂ ind^?1 h^?1) were measured for larval cod, Gadus morhua (L.) that were reared and tested at 5.0, 7.5, and 10.0°C. Bi‐hourly measurements of R_R were made on groups of larvae using a closed‐circuit respirometer over a 24‐h period (14L : 10D light regime) to test temperature and body size effects and whether unfed larvae exhibited diel differences in metabolism. At 10°C, the relationship between mean R_R and mean M_D was: ln R_R = 1.16·lnM_D ? 6.57 (n = 31, r² = 0.883, P < 0.001). The exponential increase in R_R with temperature was described by a Q₁₀ of 3.00. Diel differences in unfed larvae were only apparent in groups of the largest larvae. A comparison of Q₁₀ estimates from this and other studies suggest a linear decrease in the effect of temperature on cod R_R with increasing log M_D for sizes encompassing larvae to large juveniles. The trend may explain, in part, observations of cod juveniles exploiting a wider range of in situ temperatures than larvae. Finally, the two most comprehensive data sets on larval cod R_R compare poorly (approximately five‐fold differences) and our results support the assertion that daily metabolic energy loss in many larval cod individual‐based models were based upon measurements that over‐estimated hourly metabolic rates by a factor of approximately four.     

Growth, reproduction and feeding behavior of the planktonic shrimp, Lucifer faxoni Borradaile, off the Texas coast

The planktonic shrimp, Lucifer faxoni, lives to an age of 30–40days off the Texas coast. In the laboratory, the shrimp took28.9 and 18.9 days to reach sexual maturity at 22 and 30°Crespectively. Oviposition was observed at night between 20.00and 23.00. Females attach eggs to the 3rd pereiopods and broodthem until the nauplii emerge. Multiple broods are produced,giving a maximal lifetime fecundity of >140 eggs per female.In addition, females may also be able to synchronize the timeof their hatching to occur at night, perhaps to further reducemortality due to predation and cannibalism. A rapid turnoverof generations, each with a short adult lifespan, sequentialspawnings, and protection of eggs until hatching, characterizesthe life strategy of this small shrimp. Adult L.faxoni are carnivorous.However, their feeding appendages do not exclude the possibilityof omnivory. The maximal, dry-weight-based, specific ingestionrate was 0.7 day^–1. Feeding activity was not affectedby either time of day or light regime.     

Growth of and toxin production by nonproteolytic Clostridium botulinum in cooked puréed vegetables at refrigeration temperatures.

Seven strains of nonproteolytic Clostridium botulinum (types B, E, and F) were each inoculated into a range of anaerobic cooked puréed vegetables. After incubation at 10 degrees C for 15 to 60 days, all seven strains formed toxin in mushrooms, five did so in broccoli, four did so in cauliflower, three did so in asparagus, and one did so in kale. Growth kinetics of nonproteolytic C. botulinum type B in cooked mushrooms, cauliflower, and potatoes were determined at 16, 10, 8, and 5 degrees C. Growth and toxin production occurred in cooked cauliflower and mushrooms at all temperatures and in potatoes at 16 and 8 degrees C. The C. botulinum neurotoxin was detected within 3 to 5 days at 16 degrees C, 11 to 13 days at 10 degrees C, 10 to 34 days at 8 degrees C, and 17 to 20 days at 5 degrees C.     

Recent advances in understanding of the evolution and maintenance of sex

The evolution of sex has been the focus of considerable attention during recent years. There is some consensus that the solution to the mystery is that sex either enables the creation and spread of advantageous traits (possibly parasite resistance) or helps to purge the genome of deleterious mutations. Recent experimental work has allowed testing of some of the assumptions underlying the theoretical models, most particularly whether interactions between genes are synergistic and whether the mutation rate is adequately high. However, although a variety of theories point out advantages to sex, most of them predict that a little sex and recombination can go a long way towards improving the fitness of a population, and it remains unclear why obligate sex is so common.     

DNA sequencing and expression of the formyl coenzyme A transferase gene, frc, from Oxalobacter formigenes.

Oxalic acid, a highly toxic by-product of metabolism, is catabolized by a limited number of bacterial species utilizing an activation-decarboxylation reaction which yields formate and CO2. frc, the gene encoding formyl coenzyme A transferase, an enzyme which transfers a coenzyme A moiety to activate oxalic acid, was cloned from the bacterium Oxalobacter formigenes. DNA sequencing revealed a single open reading frame of 1,284 bp capable of encoding a 428-amino-acid protein. A presumed promoter region and a rho-independent termination sequence suggest that this gene is part of a monocistronic operon. A PCR fragment containing the open reading frame, when overexpressed in Escherichia coli, produced a product exhibiting enzymatic activity similar to the purified native enzyme. With this, the two genes necessary for bacterial catabolism of oxalate, frc and oxc, have now been cloned, sequenced, and expressed.     

Imperfect Genes, Fisherian Mutation and the Evolution of Sex

In this paper we present a mathematical model of mutation and selection that allows for the coexistence of multiple alleles at a locus with very small selective differences between alleles. The model also allows for the determination of fitness by multiple loci. Models of this sort are biologically plausible. However, some previous attempts to construct similar models have assumed that all mutations produce a decrease in fitness, and this has led to a tendency for the average fitness of population members to decline when population numbers are finite. In our model we incorporate some of the ideas of R. A. FISHER, so that both deleterious and beneficial mutations are possible. As a result, average fitness tends to approach a stationary distribution. We have used computer simulation methods to apply the Fisherian mutation model to the problem of the evolution of sex and recombination. The results suggest that sex and recombination can provide very large benefits in terms of average fitness. The results also suggest that obligately sexual species will win ecological competitions with species that produce a substantial fraction of their offspring asexually, so long as the number of sites under selection within the genomes of the competing species is not too small and the population sizes are not too large. Our model focuses on fertility selection in an hermaphroditic plant. However, the results are likely to generalize to a wide variety of other situations as well.