Population cycles can maintain foraging polymorphism

The maintenance of genetic variability in morphological traits that affect fitness is poorly understood. We present a simple Mendelian model of genetic traits affecting foraging efficiency in grazing ungulates, based on a trade-off between rates of energy extraction at low versus high levels of plant abundance. The model suggests that variation in foraging efficiency could be maintained via lottery competition arising as a direct consequence of dynamically unstable interactions between consumers and their food resources. Lottery competition is a plausible mechanism for explaining wide variability in foraging efficiency, such as that documented in unstable Soay sheep populations on the St Kilda archipelago.     

Evaluation of LH-RH stimulation of testosterone as an index of reproductive status in rams and its application in wild antelope

In rams a positive correlation (P less than 0.001) existed between average testosterone levels from 30-min blood sampling for 18 h and average testosterone levels of samples taken 0, 1 and 2 h after injection of LH-RH administered 90 min after anaesthesia. Attempts were therefore made to assess testosterone status by LH-RH challenge and limited blood sampling in animals immobilized in their natural habitat. In impala (Aepyceros melampus) territorial males had higher plasma testosterone values than did bachelors after LH-RH challenge (8.1 compared with 2.6 ng/ml, P less than 0.05). In blesbok (Damaliscus dorcas), the relationship was less clear, but testicular volume was correlated with plasma testosterone concentration and with testicular responsiveness measured by testosterone produced per unit of LH (P less than 0.001 and P less than 0.05, respectively). The LH-RH challenge technique therefore has value as a measure of testicular function and permits study of ungulates in their natural environment.     

Billingen (Lower Arenig/Lower Ordovician) acritarchs from the East European Platform and their palaeobiogeographic significance

Billingen (Lower Arenig/Lower Ordovician) sediments of the St. Petersburg region, northwest Russia and the Leba area, northern Poland of the East European Craton yield acritarch assemblages, which are largely homogenous though displaying minor compositional differences that probably reflect a gradient from inner to outer shelf environments. Comparison with coeval acritarch microflora from the Yangtze Platform, South China, shows an overall similarity between Baltoscandian and South Chinese phytoplankton. The widespread uniformity in the fossil microphytoplankton may be related to the extensive global 'evae' sea-level transgression, which characterized the Billingen time. This suggests that during the Tremadoc through early Arenig times, acritarch assemblages displayed essentially an undifferentiated cold-water and oceanic character along the whole margin of Perigondwana in the South, as well as on the South Chinese and Baltic platforms, at middle latitudes (Mediterranean oceanic Realm). Despite this overall similarity, however, some typical taxa of the high-latitude Mediterranean Province (Arbusculidium, Coryphidium and Striatotheca) occur in South China, but are absent in Baltica. This discrepancy is explained as caused by differences in climatic and physiographic conditions that prevailed at the two palaeocontinents at this time. The inferred pattern of oceanic circulation during the Lower Ordovician is consistent with the palynological evidence of a prevailing warmer climate in Baltica than in South China, although the two palaeocontinents occupied the same palaeolatitudinal position.     

A lifetime perspective on foraging and mortality

Food intake carries many potential risks which may impair an animal's reproductive success not only in the current breeding cycle, but also for the rest of its lifetime. We examine the lifetime trade-off between the costs and benefits of food intake by presenting a simple animal foraging model, where each unit of food eaten carries with it a risk of mortality. We show that the optimal food intake rate over an animal's lifetime, for both semelparous and iteroparous animals, is not maximal. Instead, animals are required to strike a balance between the immediate reproductive benefits of gathering food and the future reproductive costs incurred by the food's mortality risk. This balance depends upon the lifespan of the animal as well as the nature of the risk. Different mortality risks are compared and it is shown that a mortality risk per unit time spent foraging is not, in general, equivalent to a mortality risk per unit of food consumed. The results suggest that a mortality risk per unit of food consumed, such as that presented by the presence of a toxin or of a parasite in the diet, has important consequences for feeding behaviour and is a possible factor involved in food intake regulation.     

Cyrtocrinids (Echinodermata,Crinoidea) from Upper Jurassic Štramberk‐type limestones in southern Poland

Abstract: A systematic account of highly diverse cyrtocrinid faunules from Upper Jurassic strata of ?tramberk type (Oxfordian–Tithonian) in southern Poland (Polish Carpathians) is presented. Fourteen taxa (Phyllocrinus malbosianus, Ph. stellaris, Ph. sp., Psalidocrinus armatus, Sclerocrinus compressus, S. polonicus sp. nov., Hemicrinus aff. kabanovi, Ancepsicrinus parvus gen. et sp. nov., Tetracrinus baumilleri sp. nov., Eugeniacrinites alexandrowiczi, E. cf. moravicus, E. sp., Eudesicrinus gluchowskii sp. nov. and Hemibrachiocrinus tithonicus sp. nov. are described and illustrated. Representatives of the genus Eudesicrinus, previously recorded only from the Lower Jurassic, are here shown to extend into the uppermost Jurassic. Other cyrtocrinids considered are common in Jurassic/Cretaceous strata across Europe. In the present faunules, isocrinid (Isocrinida), comatulid (Comatulida) and roveacrinid (Roveacrinida sensu Rasmussen, inclusive of Saccocoma) crinoids are associated.     

Having it all: historical energy intakes do not generate the anticipated trade-offs in fecundity

An axiom of life-history theory, and fundamental to our understanding of ageing, is that animals must trade-off their allocation of resources since energy and nutrients are limited. Therefore, animals cannot "have it all"--combine high rates of fecundity with extended lifespans. The idea of life-history trade-offs was recently challenged by the discovery that ageing may be governed by a small subset of molecular processes independent of fitness. We tested the "trade-off" and "having it all" theories by examining the fecundities of C57BL/6J mice placed onto four different dietary treatments that generated caloric intakes from -21 to +8.6% of controls. We predicted body fat would be deposited in relation to caloric intake. Excessive body fat is known to cause co-morbidities that shorten lifespan, while caloric restriction enhances somatic protection and increases longevity. The trade-off model predicts that increased fat would be tolerated because reproductive gain offsets shortened longevity, while animals on a restricted intake would sacrifice reproduction for lifespan extension. The responses of body fat to treatments followed our expectations, however, there was a negative relationship between reproductive performance (fecundity, litter mass) and historical intake/body fat. Our dietary restricted animals had lower protein oxidative damage and appeared able to combine life-history traits in a manner contrary to traditional expectations by having increased fecundity with the potential to have extended lifespans.     

Selective predation of the pike Esox lucius: comparison of lateral plates and some metric features of the three-spined stickleback Gasterosteus aculeatus

Selective predation of Esox lucius on Gasterosteus aculeatus in a natural assemblage of fish of a stream in Central Poland is described and analysed. The number of lateral plates, the standard length and four size-dependent traits were significantly smaller for sticklebacks from stomach samples than for those from population samples. Thc remaining three metric traits were not significantly different among the samples. The regressions of five metric features (out of seven) on the standard length were significantly different between the sample of caten sticklebacks and that from the free-living population. This supports the supposition that the selectivity of pikc predation with respect to metric traits is not attributable to selection on body size of the prey. Thus, it is reasonable to claim that the sample of caten sticklebacks is selectively taken from the natural population. It justifies the selective predation assumption of some hypotheses of the causes of the pattern of geographic variation in the three-spined stickleback.