ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00872.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The rotation of insecticides used by the Onchocerciasis Control Programme in West Africa is reviewed and the motives for this rotation are shown to be not only management of temephos resistance in theSimuliumvectors but also constraints on what compounds are usable at particular seasons. A computer model indicates that without these seasonal constraints there is unlikely to be an advantage in a pre‐planned rotation of insecticides, as compared with the prompt switching of compounds as dictated by detection of build up of resistance and switching back to the original compound if the regression of resistance is found to give the opportunity to do so. The latter sequence of events can hardly be called a ‘strategy’ for resistance management, but is what any well‐managed pest control programme would be expected to do.The use of an insecticide mixture is different in principle from the use of rotation and depends on the idea that if the mixture is used from the outset, when resistance to both components of the mixture is likely to be rare, the double resistance combination would be so rare as to be dwarfed in numbers by those insects which avoid exposure altogether. The prospects for successful use of a mixture depend on each component killing a very high percentage of the exposed insects which are genetically susceptible to it. Whether this condition is met could be tested, for example, in the case of exposure of mosquitoes to insecticide‐treate

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00873.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The functional significance of hermaphroditism is, as yet, not well understood. This study attempts to examine the relevance of some theories on this topic to reality, by reviewing the literature on hermaphroditism among molluscs. The study reveals that about 40% of the 5600 mollusc genera are either simultaneous or sequential hermaphrodites. Hermaphroditism occurs in 100% of the Solenogastres, 99% of the Opisthobranchia, 100% of the Pulmonata, 3% of the Prosobranchia and 9% of the Bivalvia.Sequential hermaphroditism, whatever its theoretical advantages over gonochorism, is not common among molluscs.Simultaneous hermaphroditism is common among the Euthyneura. Over 80% of the hermaphroditic genera belong to the Euthyneura (about 2000 recent genera), and over 99% of the Euthyneura are hermaphrodites. The almost ubiquitous occurrence of hermaphroditism throughout the Euthyneurans, coupled with this group's very widespread dispersal in marine, terrestrial and freshwater habitats (and corresponding exposure to a very wide range of predators, competitors or parasites); and also its wide range of population densities, suggests that in this group hermaphroditism is not an adaptive response to selective forces of the environment and it may well be a phylogenetic constraint.A few stylommatophorans have broken this constraint by possessing genitalia in which the male system is absent (aphally) or extremely reduced (hemiphally). They reproduce by self‐fertilization. In theory this is advantageous in that these species save the cost of developing two sets of reproductive apparatus. In reality there is no record of aphally occurring throughout an entire species, as one may expect if this saving of cost were so overwhelmingly advantageous. There is also no record of stylommatophoran individuals developing only the male system, as one may expect if there was any evolutionary trend from hermaphroditism towards gonochorism.Simultaneous hermaphroditism offers a (theoretical) option to selling. Selfing by self‐fertilization is widespread among freshwater basommatophorans, amphibious stylommatophorans and freshwater bivalves. Selfing by parthenogenesis is widespread among freshwater prosobranchs. Altogether, of 48 genera which self, 60% are dwellers of freshwater. Certain freshwater habitats may perhaps be less stable than most marine or terrestrial ones are.Beyond the Euthyneura, hermaphroditism is common among parasitic, deep sea and Cnidaria‐eating molluscs. Perhaps these three associations should be slightly rearranged and combined into a single generalization: that hermaphroditism (beyond the Euthyneura) is widespread among molluscs that live in a close and permanent intimacy with live marine invertebrates, whether as parasites, commensals or predators.Gonochorism but with dwarf males is common among the Eulimoidea, which are parasites, and Galeommatoidea, which are commensals. This situation of gonochorism, in which there is a very close association between members of the two sexes, is functionally a hermaphroditic type. Animals that can manipulate the physiology and endocrinology of their hosts may also have the tendency and ability to manipulate the size of their own males. It may well be that the female not only determines the size of the male but also his sex, in which case dwarf males should be considered as a case of environmental sex determination.The theoretical possibility that hermaphroditism may evolve in brooding animals was examined in gastropods. Among the (predominantly gonochoric) prosobranchs brooding is recorded in 85 genera (4%), only two of which are hermaphrodites. Among the (predominantly hermaphrodite) heterobranchs it is recorded in only 95 odd genera (4%). When all gastropod genera are considered together, the frequency of hermaphroditism among the brooders is only very slightly and insignificantly higher than in the non‐brooders. When only the prosobranchs are considered, the frequency of hermaphroditism among the brooders is actually lower than among non‐brooders. The theory that hermaphroditism evolves in brooding animals thus appears not to be relevant to the vast majority of gastropods.Brooding is widespread among freshwater prosobranchs (48% of the brooding genera). In this habitat, brooding may perhaps be an adaptation to protect the developing embryo against osmotic

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00874.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In previous experiments we found thatDrosophila melanogasterlines selected for increased adult desiccation resistance had increased resistance to other environmental stresses at the adult stage including starvation, intense60Co‐γ radiation and a toxic ethanol level. In further studies on these lines, we now show that selection did not alter resistance to desiccation and ethanol at the larval stage. As well as having a lower early fecundity, selected lines showed increased adult male longevity and increased viability at high larval densities compared with control lines. There were no changes in development time or mating success. The increased male longevity is consistent with the reduced metabolic rate of the selected lines.A genetic correlation between resistance to different stresses was confirmed by an analysis of isofemale lines derived from a population founded by flies from a stress‐resistant line and an unselected line. The results are consistent with the existence of genes segregating in natural populations conferring increased general stress resist

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00875.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

We studied the genetic structure of a population of the clonal grassSetaria incrassatausing isozyme electrophoresis to determine the extent of clone and gene diversity within and between three spatially isolatedSetariapatches. High clone diversity and an even distribution of genets, which covered less than 0.25 m2on average, indicated that patch formation was dominated by propagation from seed. Gene diversity was high within the population and there was little genetic differentiation between patches. High levels of heterozygosity and polymorphism and strongly negative fixation indices indicated extensive recombination through outbreeding, despite the low number of alleles per locus. The synergistic effects of vegetative and sexual propagation may have contributed towards the unexpectedly high genetic diversity of this population. Genetic diversity in clonal populations may be preserved in the genotypes of clones and may therefore be increased by even rare recombination events.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00876.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Arctic charr,Salvelinus alpinus(L.), commonly exhibits two coexisting morphotypes, dwarf and normal charr, which are characterized by differences in adult body size and colouration. We tested whether or not the morphotypic differences were genetically determined in rearing experiments with offspring of the two morphs and of their crosses. The experiments suggest that this ecological polymorphism in Arctic charr is largely environmentally determined. When reared under similar conditions, offspring of each of the two morphs differed little in size at the same age, and they had the same early developmental rate and maturation pattern. Moreover, the presence of parr marks along the flanks of the fish, one characteristic of dwarf charr, depended on body size and not on parental morph. Genetic differences between the morphs were suggested for growth rate during the second year of life, and for jaw morphology. Comparisons between charr life histories in captivity and in the wild suggest that ecological polymorphism in Arctic charr is chiefly a result of variation in growth conditions between different habitats.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00877.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The lacertid lizard (Gallotia stehlini), an endemic of Gran Canaria, shows no visually obvious geographic variation, yet all seven scalation characters that were examined exhibit significant geographic variation. The number of collar scales, scales along the ventral trunk and femoral pores are correlated with habitat type, while the number of femoral pores is correlated negatively with altitude. Mantel tests were used to compare simultaneously an observed pattern with three hypothesized patterns (habitat type, altitude and proximity). They indicate that, while several individual characters are significantly associated with the putative causal factors of habitat type and altitude, there is no association between an overall scalation distance matrix and habitat type, or altitude when the effect of proximity is removed. Consequently, one should consider the individual characters as well as the multivariate generalized distances. Some of the observed patterns of geographic variation in scalation are very similar to those of the small scincid lizardChalcides sexlineatuson Gran Canaria and also parallel the altitudinal and latitudinal variation in the scalation of the Tenerife lacertid (Galotia galloti). The low level of congruence in patterns of geographic variation in individual characters (i.e. some vary with latitude, some with altitude and one varies with longitude) is consistent with the hypothesis that ecogenetically caused geographic variation may result in lower inter‐character congruence than phylogenetically caused geographic variatio

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00878.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Book reviewed in this article:The Individual in Darwin's World, by S. J. Gould.The Units of Evolution. Essays on the Nature of Species, edited by M; Ereshefsky.Evolutionary Biology of Aging, by M. R. RoseGenetic and Ecological Diversity, by L. M. Cook.Evolutionary Genetics and Environmental Stress, by A. A. Hoffmann and P. A. Parsons.Sodium Hunger, by J. Schulkin.Practical Taxonomic Computing, by R. J. Pankhurst.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00879.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00872a.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY