Contraception, reproduction and demography of free-ranging Etosha lions (Panthera leo)

The use of long-acting contraceptives as an effective population control mechanism for free-ranging lions was investigated during a three-year study in the Etosha National Park on five lion prides. Lions were immobilized with ketamine hydrochloride and xylazine hydrochloride. Following immobilization, lionesses were weighed, measured and aged, while serum steroid hormone levels were analysed and vaginal smears were obtained. Physical condition and sexual state were assessed. Individuals were used as control animals or given melengestrol acetate (contraceptive) implants, branded and released; the animals were observed for possible changes in behaviour, birth rate and mortality. Ten treated lionesses were recaptured at irregular intervals to reassess weight and steroid hormone levels, while three lionesses had their implants removed to determine if their fertility would return. The contraceptives prevented pregnancy, were reversible when removed and did not alter lion behaviour significantly, except that sexual behaviour was not recorded in treated lionesses.     

SEMI-LUNAR AND LUNAR SPAWNING PERIODICITY IN SOME TROPICAL LITTORINID GASTROPODS

Littoraria strigata, Nodilittorina millegrana and N. pyramidalisall spawned regularly in a rock-flanked Malaysian bay in March-June1985, whereas none had spawned there in July-October 1981. N.millegrana showed the least precise timing with some irregularpreponderance during the days between 2d before and 7d afternew or full moon and their associated spring tides. Spawningof N. pyramidalis was more strictly confined to spring tideswith 90% of eggs appearing between 2d before and 5d after newor full moon. There was no apparent difference between alternatespawnings on new and on full moons. L. strigata also spawnedregularly on the spring tides with 89% of eggs appearing between1 and 5 days after new and full moon. In this case, however,full moon spawnings (when spring tides rose highest) yieldedsome 7 times more eggs on average than the weaker spring tidesat new moons. In laboratory aquaria, the three species all released eggs duringboth night and daytime and through periods of both spring andneap tides with no evidence that periodicity persisted in constantconditions. The different degrees of 2-weekly spawning periodicity, togetherwith littorinids which spawn only monthly, may represent a rangeof adaptation to life at increasing shore heights. (Received 26 November 1985;     

DEVELOPMENT OF A TEXTURE PROFILE PANEL FOR EVALUATING RESTRUCTURED BEEF STEAKS VARYING IN MEAT PARTICLE SIZE

A texture profile panel was developed for measuring textural properties of restructured beef steaks differing in meat particle size. For steaks of different particle sizes, considerable differences existed in the type of sample breakdown and shape of chewed pieces after just two chews. Panelists also found restructured steaks made from large meat particle sizes to be visually more distorted and to contain more gristle than steaks made from small meat particle sizes. Several characteristics (chunkiness after two chews, coarseness of chewed mass at 15 chews) were dropped from the profile over time, while several characteristics (type of sample breakdown and shape of chewed pieces at two chews, size of chewed pieces at 10 chews) not used initially, were added. The texture profile panel approach appears suitable for discerning the textural differences in restructured steaks that can arise from using different meat particle sizes during processing.     

Linking intronic polymorphism on the CHD1‐Z gene with fitness correlates in Black‐tailed Godwits Limosa l. limosa

We show that variation in an intronic length polymorphism in the CHD1‐Z gene in Black‐tailed Godwits Limosa l. limosa is associated with fitness correlates. This is the second example of the CHDZ‐1 gene being correlated with fitness, a previous study having established that Moorhens Gallinula chloropus carrying the rare Z* allele have reduced survival. In Godwits, however, carriers of the Z* allele (374 bp) fared better than those with the more frequent Z allele (378 bp) with respect to body mass, plumage ornamentation, reproductive parameters and habitat quality. The Z* allele was found in 14% of 251 adult birds from nature reserves, but was absent from 33 birds breeding in intensively managed agricultural lands. Males and females with the Z* allele had less extensive breeding plumage, and females had a higher body mass, bred earlier and had larger eggs. There were no significant differences in annual survival between birds with and without the Z* allele. DNA isolated from museum skins demonstrated that this polymorphism was present at low frequency in 1929. We speculate that strong asymmetrical overdominance may explain the low frequency of the Z* allele and that genetic linkage to causal genes might be an explanation for the phenotypic correlations. Our findings suggest a degree of cryptic genetic population structuring in the Dutch Godwit population.     

Parthenogenesis in Mites and Ticks (Arachnida: Acari)

SYNOPSIS. Parthenogenesis is discussed according to type (arrhenotoky,thelytoky, deuteroLoky, artificial parthenogenesis, gynogenesis)and presence in various acarine taxa. Evidence for parthenogenesisis based on rearing and/or cytological studies. Arrhenotokyoccurs in Mesostigmata, Prostigmata and Astigmata and usuallydoes not occur sporadically throughout these taxa; when presentit operates in many closely related species as the major typeof reproduction in certain genera, subfamilies or families.Thelytoky is present in Mesostigmata, Metastigmata, Prostigmata,Astigmata and Cryptostigmata, but in no case is the major modeof reproduction in higher taxa, i.e. subfamilies, families.Its sporadic occurrence may or may not be accompanied by polyploidy.Deuterotoky occurs in one acarine group (Listrophoridae) andartificial parthenogenesis is possible in ticks (Metastigmata).Gynogenesis is present in several species of haplo-diploid Mesostigmata(some Dermanyssidae, Phytoseiidae), although it is usually consideredin connection with thelytoky. Current studies of the effectsof ploidy level on morphological variation indicate greatercharacter variability in diploid females than in haploid males.In some species of ticks thelytoky is expressed differentiallyeven on an intraspecific level. One geographic strain of a speciesmay have the ability to reproduce thelytokously, but if matedproduces males and females.     

Performance of a new dynamic model for predicting diurnal time courses of stomatal conductance at the leaf level

Under natural conditions, plants are subjected to continuous changes of irradiance that drive variations of stomatal conductance to water vapour (g_s). We propose a dynamic model to predict the temporal response of g_s at the leaf level using an asymmetric sigmoid function with a unique parameter describing time constants for increasing and decreasing g_s. The model parameters were adjusted to observed data using Approximate Bayesian Computation. We tested the model performance for (1) instant changes of irradiance; or (2) continuous and controlled variations of irradiance simulating diurnal time courses. Compared with the two mostly used steady‐state models, our dynamic model described daily time courses of g_s with a higher accuracy. In particular, it was able to describe the hysteresis of g_s responses to increasing/decreasing irradiance and the resulting rapid variations of intrinsic water‐use efficiency. Compared to the mechanistic model of temporal responses of g_s by Kirschbaum, Gross & Pearcy, for which time constants were estimated with a large variance, our model estimated time constants with a higher precision. It is expected to improve predictions of water loss and water‐use efficiency in higher scale models by using a small number of parameters.