The population genetics of the potato cyst-nematode, Heterodera rostochiensis: mathematical models to simulate the effects of growing eelworm -resistant potatoes bred from Solatium tuberosum ssp. andigena

To follow population changes when potato varieties with resistance to Heterodera rostochiensis derived from Solanum tuberosum ssp. andigena were grown on infested land, a computer programme was written including three mathematical relationships: (1) a law relating multiplication to pre-cropping density; (2) two mathematical models of inheritance of ability to overcome resistance; (3) a law relating the proportion of larvae able to become female to pre-cropping population density. The programme also included four parameters: (1) the maximum possible reproductive rate; (2) the fraction of the population (eggs) not participating in reproduction when potatoes are grown and carried over to the following year unchanged; (3) the fraction carried over annually when other crops are grown; (4) the frequency of larvae able to become female in the population initially. Population density was measured relative to the equilibrium density and was therefore independent of the units in which density is usually measured. After supplying a range of parameters for all the above to include those likely to be encountered in practice, the changes expected (a) in the frequency of larvae able to become female in the roots of resistant varieties and (b) in population density were computed for resistant varieties grown continuously or alternately with susceptible varieties in crop rotations of different lengths. Because well established field populations are relatively dense, observed reproductive rates are small and rarely approach the maximum possible. Reproductive rate is therefore a relatively unimportant determinant of genetic change. The fraction of the population carried over to the following year is more important because it affects the length of a crop rotation necessary to make loss of potato yield acceptable, determines what the multiplication rate will be and influences the speed of genetic change by providing a reservoir of initial type males which backcross with any genetically different females that may develop on the roots of resistant plants. No experiment seems to have been done specifically to determine the parameters needed to calculate population changes. Some values can be obtained from the literature but mostly they must be guessed. When the law relating the proportion of larvae able to become female to pre-cropping population density was included in the computations, it had little effect initially but later, after several generations, it delayed genetic change. Two field experiments, one by Huijsman (1961) another by Williams (1958) and Cole & Howard (1962 a), provide some of the variables needed to compute trends in population density. Best fitting variables were computed for the data in these experiments by the method of maximum likelihood. The computed parameters for one experiment were not very realistic but those for the other were in line with what would be expected in practice and tended to favour the hypothesis that larvae able to become female in the roots of resistant plants are double recessives (aa). The computations lead us to suggest that the best policy for potato growers who have fields suitable for resistant varieties is to alternate resistant with susceptible varieties in a crop rotation containing potatoes every 3 or 4 years.     

GLOBAL HEALTH ETHICS FOR STUDENTS

As a result of increased interest in global health, more and more medical students and trainees from the 'developed world' are working and studying in the 'developing world'. However, while opportunities to do this important work increase, there has been insufficient development of ethical guidelines for students. It is often assumed that ethics training in developed world situations is applicable to health experiences globally. However, fundamental differences in both clinical and research settings necessitate an alternative paradigm of analysis. This article is intended for teachers who are responsible for preparing students prior to such experiences. A review of major ethical issues is presented, how they pertain to students, and a framework is outlined to help guide students in their work.     

Sensory and skeletal development and growth in relation to the duration of the embryonic and larval stages in damselfishes (Pomacentridae)

Several trends were found in comparisons of rates of growth and development of larvae of four coral-reef damselfishes ( Chromis atripectoralis, Pomacentrus amboinensis, Premnas biaculeatus, Acanthochromis polyacanthus ), which were reared under constant temperature conditions in the laboratory, and which varied in their early life stage durations (respectively, egg stage durations were 2, 4, 7, 16; larval stage durations were 25, 23, 14, 0). Parameters measured included standard length, muscle area, eye diameter, and selected stages of retinal development, olfactory development, and skeletal ossification. Rates of ossification and olfactory development were inversely related to growth rate (in length and muscle area) among most species. Rates of eye growth and retinal development were also negatively correlated among all species. These results are consistent with the concept of a trade-off between growth and development. We observed a positive relationship between egg stage duration and developmental rate, and a negative correlation between larval stage duration and developmental rate. Acanthochromis developed slower than predicted by the general trends, although retinal development was very rapid. Specific retinal stages correlated with settlement, regardless of ontogenetic rates. Olfactory development was especially rapid in the anemonefish Premnas biaculeatus , which imprints to olfactory cues as an embryo. Skeletal ossification was rapid in species with pelagic larvae, and much slower in the benthic brooder. Literature-derived data on size and age at hatching and settlement from > 40 species of tropical pomacentrids were transformed into growth and developmental rates; correlations of these literature-derived parameters were mostly consistent with our controlled four-species comparison.  © 2003 The Linnean Society of London, The Biological Journal of the Linnean Society , 2003, 80 , 187−206.     

Starch Synthesis During Dormancy Breakage in Oilseed of Corylus avellana

Dormancy in seed of Corylus avellana L. (hazel) is broken bya sustained period of cold stratification. During this timeboth cytological and metabolic changes occur. Starch was presentinitially at a low level but increased by 20% in the embryonicaxes of hazel seeds during stratification at 5 °C, whileit decreased rapidly and then remained constant in the embryonicaxes from seeds held at 20 °C. Histochemical study confirmedthis analytical result. A comparison of the developmental patternof starch level with bound and soluble ADP glucose-starch synthaseactivity at 5 and 20 °C showed that the accumulation ofstarch in the embryonic axes followed an enhanced activity ofthe granule-bound ADP glucose-starch synthase. Cold stratificationresulted in an increase in starch content, which was probablyas a result of gluconeogenesis from products of reserve lipidhydrolysis. Corylus avellana L., hazel, starch, ADP glucose-starch synthase, stratification     

Begging call matching between a specialist brood parasite and its host: a comparative approach to detect coevolution

Studies of avian brood parasite systems have typically investigated the mimicry of host eggs by specialist parasites. Yet, several examples of similarity between host and parasite chick appearance or begging calls suggest that the escalation of host–parasite arms races may also lead to visual or vocal mimicry at the nestling stage. Despite this, there have been no large-scale comparative studies of begging calls to test whether the similarity of host and parasite is greater than predicted by chance or phylogenetic distance within a geographically distinct species assemblage. Using a survey of the begging calls of all native forest passerines in New Zealand, we show that the begging call of the host-specialist shining cuckoo ( Chrysococcyx lucidus ) is most similar to that of its grey warbler ( Gerygone igata ) host compared to any of the other species, and that this is unlikely to have occurred by chance. Randomization tests revealed that the incorporation of the shining cuckoo's begging calls into our species-set consistently reduced the phylogenetic signal within cluster trees based on begging call similarity. By contrast, the removal of the grey warbler calls did not reduce the phylogenetic signal in the begging call similarity trees. These two results support a scenario in which coevolution of begging calls has not taken place: the begging call of the host retains its phylogenetic signal, whereas that of the parasite has changed to match that of its host.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 208–216.     

Frequency-dependent selection in hermaphrodites: the rule rather than the exception

It is shown for simple assumptions that frequency-dependent selection in seed plants may have at least three causes, namely: (a) sexual asymmetry; (b) differential genotypic selfing rates; and (c) gene-cytoplasm fertility interactions. Sexual asymmetry is defined as the situation where the ratio of pollen: ovule fertility is not the same for all genotypes or phenotypes in a population. A review of the literature suggests that all three causes of frequency-dependent selection probably occur in nature, and that at least the first cause, sexual asymmetry, is probably widespread in hermaphrodites. It is shown that resource-allocation theory leads to the expectation that sexual asymmetry and, therefore, frequency-dependent selection should be almost universal in hermaphrodite populations which are not largely selfed. A method for obtaining frequency-dependent fitness values is presented and applied to a population of Scots pine ( Pinus sylvestris ) showing strong sexual asymmetry.     

Distribution of Isoprenoid Quinones in Halophilic Bacteria

Menaquinones were the sole isoprenoid quinones found in 28 of the 34 halophilic organisms examined. Unsaturated and dihydrogenated menaquinones with eight isoprene units were found in some alkalophilic halophiles and representatives of the genera Halobacterium and Halococcus. Brevibacterium halotolerans and Micrococcus halobius possessed major amounts of unsaturated menaquinones with seven and eight isoprene units, respectively. Actinopolyspora halophila possessed complex mixtures of partially hydrogenated menaquinones with tetrahydrogenated menaquinones with nine isoprene units predominating. Vibrio costicola possessed both menaquinones and ubiquinones with eight isoprene units. Ectothiorhodospira halophila, Flavobacterium halmephilum, Paracoccus halodenitrificans and Pseudomonas beijerinkii contained ubiquinones as their sole respiratory quinones. Ectothiorhodospira halophila possessed major amounts of ubiquinones with eight isoprene units whereas ubiquinones with nine isoprene units predominated in Flavobacterium halmephilum, Paracoccus halodenitrificans and Pseudomonas beijerinkii.     

The "Lost Year" Question in Young Sea Turtles

An adequate understanding of young sea turtle dispersal patternsis necessary for effective management of threatened or endangeredspecies. Such patterns are poorly understood, and the term "lostyear" has been adopted to emphasize this gap in sea turtle lifehistory information. Tag returns from pen-reared yearling seaturtles indicate ocean current dispersal. Evidence indicateshatchlings would be similarly dispersed by ocean currents. Feedingstudies with tank-held animals suggest that food resources areavailable in ocean currents for long-term sea turtle survival.Green turtle (Chelonia mydas) growth appears slow in nature.