Validation and implications of a growth model for brown trout, Salmo trutta, using long-term data from a small stream in north-west England

Summary 1. The objectives were: (i) to check the validity of a new growth model; (ii) to examine the relationship between population density and both mean mass and mean growth rate and (iii) to discover if compensatory growth occurred. First (0+) and second (1+) year‐old juvenile sea‐trout were sampled by electrofishing at the beginning and end of the summer from 1967 to 2000. Additional samples were taken in some years in winter and in the critical period for survival when the fry first emerge from the gravel. The trout left the stream as pre‐smolts in May, soon after their second birthday. 2. A growth model ( Elliott, Hurley & Fryer, 1995 ) estimated the mean mass of the trout over the 2 years spent in fresh water. The date and mean mass at the start of the growth period were defined as the median date for fry emerging from the gravel and their mean mass at emergence, both being estimated from individual‐based models ( Elliott & Hurley, 1998a, b ). 3. The variation in mean mass among year‐classes was small for newly‐emerged fry (CV = 6.2%), maximum at the start of the first summer of the life cycle (CV = 38.1%), and then decreased gradually for successive life‐stages to a low value for pre‐smolts (CV = 10.8%). Mean mass was not related to population density and, therefore, mean growth rate was density‐independent. Growth in the first, but not the second, winter of the life cycle was lower than model prediction, but when it was assumed in the model that there was no first‐winter growth, there was good agreement in most year‐classes between model estimated values and observed mean mass. Exceptions were that mean masses and growth rates for 0+ trout after four summer droughts were lower than expected, but compensatory growth followed, so that observed and expected masses were similar for 1+ trout. 4. Pre‐smolt mean mass on 30 April measured total growth achieved in the freshwater phase of the life cycle. This was significantly related to mean mass at the end of the first and second summers of the life cycle, but not to the emergence date and mean mass of emerging fry. 5. These juvenile sea‐trout were growing at their maximum potential in most year‐classes but when this was not achieved, compensatory growth soon restored their mass to values expected from the model. This ensured a low variation in the mean mass of pre‐smolts just before they migrated to the sea. However, the latter mass was higher in more recent year‐classes (1987–98) than in previous ones (1967–86), demonstrating the effect of slightly higher stream temperature. This study has shown the importance of developing realistic growth models in order to detect departure from maximum potential growth, and the more subtle effects of temperature change, possibly due to the effects of climate change.     

Xiphograptus and the evolution of virgella‐bearing graptoloids

Abstract: The virgellar spine is one of the most consistent features of the graptolite sicula. It is present in a large number of graptoloid groups, but evolved separately and independently in these as it is seen from the presence of the spine in either ventral (Axonophora) or dorsal (Phyllograptus, Xiphograptus) position. The evolution of the virgellar spine in the Pan‐Bireclinata in the Upper Dapingian to Lower Darriwilian time interval is known to follow four main steps, from a simple rutellum, through a lamelliform rutellum and a lanceolate virgella to the true virgellar spine. For the xiphograptids and in Phyllograptus, the origin and early development is less well documented, but appears to follow a similar path. However, the individual stages are condensed, and a true virgellar spine emerges already in the Floian time interval. A virgellar spine was found in Didymograptellus bifidus, necessitating a revision of the diagnosis of the genus Didymograptellus. A number of species of the virgellate genera Xiphograptus, Yutagraptus and Didymograptellus are described from isolated material for the first time. The species are useful for the biostratigraphic correlation of endemic mid‐continent North American faunas with the Pacific Type faunal realm. Xiphograptus artus sp. nov., Didymograptellus primus sp. nov. and Didymograptellus cowheadensis sp. nov. from the Cow Head Group of western Newfoundland are described as new.     

Characterization of novel microsatellite loci for red clover (Trifolium pratense L.) from enriched genomic libraries

Twenty‐seven polymorphic microsatellite markers were isolated from red clover (Trifolium pratense). Allelic variability and cross‐species amplification were assessed on 24 red clover and eight white clover (Trifolium repens) genotypes. The number of alleles detected in red clover ranged from two to 25. Observed and expected heterozygosities were high with average values of 0.71 and 0.88, respectively. Five of the 27 loci were also successfully amplified from white clover, where two to 13 alleles were detected. These highly polymorphic microsatellite loci provide powerful tools for population genetic studies as well as for marker‐assisted selection in this important forage legume species.     

Prey switching in Rhyacophila dorsalis (Trichoptera) alters with larval instar

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Previous studies have shown that the diel activity pattern and functional response differed between larval instars of the carnivorous caddis, Rhyacophila dorsalis. The present study examines switching by larvae of R. dorsalis presented with different proportions of two prey types; either small (length 2–4 mm) and large (5–8 mm) Chironomus larvae for second, third, fourth and fifth instars of R. dorsalis; or Baetis rhodani (9–12 mm) and large Chironomus larvae for fourth and fifth instars. Experiments were performed in stream tanks with one Rhyacophila larva per tank and 200 prey arranged in nine different combinations of the two prey types (20 : 180, 40 : 160, 60 : 140, 80 : 120, 100 : 100, 120 : 80, 140 : 60, 160 : 40 and 180 : 20). Prey were replaced as they were eaten. A model predicted the functional response in the absence of switching and provided a null hypothesis against which any tendency to switch could be tested. 2. There was no prey switching in the second and third instars, with both instars always showing a preference for small over large Chironomus larvae. Prey switching occurred in the fourth and fifth instars. As the relative abundance of one prey type increased in relation to the alternative, the proportion eaten of the former prey changed from less to more than expected from its availability, the relationship being described by an S‐shaped curve. In the experiments with small and large Chironomus, the two instars switched to large larvae when their percentage of the total available prey exceeded 29% and 37% for fourth and fifth instars, respectively. In the experiments with Baetis and large Chironomus, both instars switched to Baetis larvae when their percentage of the total available prey exceeded 36%. 3. Non‐switching in second and third instars was related to their feeding strategies, both instars preferring smaller prey items. When the fourth and fifth instars foraged actively at night, they preferred larger over small Chironomus larvae, but when they behaved as ambush predators at dusk, they captured the more active Baetis larvae in preference to the more sedentary large Chironomus larvae and only switched to the latter when they were >64% of the available prey.     

The critical thermal limits for the stone loach, Noemacheilus barbatulus, from three populations in north-west England

1. The chief objective was to determine the upper and lower thermal limits for feeding and survival in the stone loach, Noemacheilus barbatulus, using juveniles (total length 30–45 mm, live weight 0.25–0.80 g) from one population and adults (total length 77–100 mm, live weight 3.6–7.9 g) from three populations. 2. Fish were acclimatized to constant temperatures of 3, 7, 10, 15, 20, 25 and 27°C; then the temperature was changed at a rate of 1°C/30min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1°C/30min was the optimum value from preliminary experiments, using nine rates from 0.5°C/48h to 18°Ch^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values of 28.0 ± 0.15°C and 5.1 ± 0.55°C for adults, 25.0 ± 0.54°C and 6.1 ± 0.92°C for juveniles. Incipient lethal levels defined a tolerance zone within which stone loach survive for a considerable time; upper limits increased with acclimation temperature to reach a maximum plateau of 29.1 ± 0.18°C for adults and 29.0 ± 0.40°C for juveniles; lower limits also increased from near 0°C to 3.0 ± 0.40°C for adults and juveniles. Upper limits for the ultimate lethal level increased with acclimation temperature to a maximum plateau of 33.5°C for adults (95% CL ± 0.19) and juveniles (95% CL ± 0.40), whilst the lower limits increased from near 0°C to 2.5 ± 0.30°C. At acclimation temperatures below 20°C, upper incipient and ultimate lethal values were significantly lower for juveniles than those for adults. 4. The thermal tolerance of stone loach was higher than that of juvenile Atlantic salmon or brown trout, one or both of these species often being dominant in streams with stone loach.     

In Vitro Studies on the Biosynthesis of the Surface Glycoprotein of Trypanosoma congolense1,2

Tritiated leucine, glucosamine, mannose, and galactose were incorporated into the variant specific surface glycoprotein (VSG) of Trypanosoma congolense in vitro. The uptake of the precursors is shown by SDS-polyacrylamide electrophoresis and fluorography, by assay of the radioactivity in immunoprecipitates obtained with specific antisera, and by the isolation of the labeled antigens by affinity chromatography on concanavalin A-sepharose and isoelectric focusing. The in vitro labeled VSG exhibits the same degree of microheterogeneity as that observed in the VSG isolated from trypanosomes grown in animals. Analysis of the incorporated sugars after hydrolysis of the glycoprotein showed that glucosamine and mannose were utilized in biosynthesis of the carbohydrate moiety directly whereas galactose was converted possibly to other intermediates before being incorporated into the antigen. Tunicamycin completely prevented the incorporation of the radiolabeled sugars into the surface glycoprotein. The unglycosylated VSG with a molecular weight of 47 kDa had completely lost its size heterogeneity.     

Victorian gardeners and botanical nomenclature

ELLIOTT, B., 1992. Victorian gardeners and botanical nomenclature. A review of the debate over the relative importance of English over Latin names for plants is presented.