摘要:

Data on the frequencies of the main colour morphs (lineata, redimitaandovata) ofEnoplognatha ovatahave been collected from a total of 454 Ordnance Survey 10 km squares distributed throughout Great Britain. Onlyc.0.5% of samples were monomorphic, forlineatain each case. Multiple regression analysis has been used to assess possible associations between morph frequencies and principal components derived from nine environmental variables. The distribution of morph frequencies is not random but shows weak clines associated with certain climatic factors. These large scale clines indicate the action of natural selection although very local variations in morph frequencies may result from selection and/or drift.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1985.tb00165.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Three distantly related genera of land snails,AmplirhagadaIredale, 1933,QuistrachiaIredale, 1939, andWestraltrachiaIredale, 1933, overlap in distributions only in the Napier and Oscar Ranges, east of Derby, Western Australia. The first two remain allopatric,Quistrachiahaving a more eastern range, whileWestraltrachiaoverlaps both ranges. In the zone of sympatry, with changes proceeding from east to west,Westraltrachiadiverges in feeding, and there is massive, gradual convergence in shell size, shape and colour betweenAmplirhagadaandWestraltrachia.Shells of both genera depart markedly from their distinctive allopatric appearances to form a new morphotype in the north‐west Napier Ranges. The species there are so similar in appearance that the two genera cannot be identified at a distance of 0.5 m. Thirteen species‐level taxa are involved in these changes, four allopatricAmplirhagada, seven allopatricWestraltrachia, Quistrachia monogrammaandRhagada basedowana.Westraltrachiaspecies, the only large land snails in their main area of distribution (south‐east Kimberlcy), are pre‐adapted to graze on an occasionally present food resource, algal‐fungal blooms on limestone seepage faces. They entered the Oscar and Napier Ranges, where this food resource is more abundant, and large land snails that are generalized feeders,AmplirhagadaorQuistrachia, were already present and abundant. Hence feeding divergence occurred. Such specialization byWestraltrachiato minimize competition is readily understandable.The selective pressures that led to the striking convergence in shell features in north‐west Napier taxa

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1985.tb00166.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A model is used to show how changes in the amount of overlap between successive whorls alters the ratio of the area of shell material to the volume enclosed. An optimum amount of overlap which minimizes this ratio is shown to exist.Measurements on the shells of a number of British gastropods show that the actual amount of overlap is always greater than the optimum. It is concluded that selection for economy is being opposed by some other factor such as shell strength, shape or aperture size.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1985.tb00167.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Mature, mated femaleDrosophila buzzatiiwere given a choice of nine microbial communities actively growing on cactus homogenate in laboratory population cages. All communities contained identical naturally occurring bacteria, and comprised bacteria only and bacteria plus one of eight yeast species. Relative frequency of each yeast species ingested and number of eggs laid on each community were measured daily for three successive days. Flies generally preferred to feed and oviposit on those yeast species which are most abundant in rots ofOpuntiacactus, andPichia caclophilawas the most preferred yeast. Light intensity, position of the yeast in the cage, and probably aggregation behaviour affected preference. Direct observation of adults was found to be inadequate for determining feeding preference. The ability of the flies to discriminate between yeasts developed with time. By day three, there was a significant correlation (r= 0.96) between the yeasts preferred for feeding and those preferred for oviposition. Feeding preference may be determined in part by oviposition preference; and the latter appears to be the most fruitful avenue for future research into habitat selection byD. buzzatii

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1985.tb00168.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Seasonal selection acting on the melanic polymorphism in the two‐spot ladybirdAdalia bipunctatawas investigated in The Netherlands. An increase in melanic frequency over the spring‐summer reproductive period was quantified. The selective advantage gained by melanics averaged 9%, but significant heterogeneity occurred between populations. Adult hibernation behaviour is described. The beetles when outdoors show a highly clumped distribution both between and within trees. The distribution of the morph classes between aggregations is random. Survivorship in a hibernating cohort (initialn= 1898) on a grid of 70 lime trees near Utrecht was monitored by making three counts over the winter of 1981–1982. Intense selection favouring each melanic morph occurred during December and January. The relative fitness of non‐melanics was 0.55 (melanics =1). The discovery of dead beetles in late January (about 5% of total losses) and the absence of spatially density‐dependent mortality were consistent with a climatic stress rather than selective predation. The period of selection was associated with very cold temperatures averaging up to 4°C below normal and an overall mortality of nearly 75%. There was no change in morph frequency, near normal temperatures and a lower mortality from February to early April. Examination of groups of nearby trees in late January strongly suggested that similar differential mortality had occurred except on some willows. This difference was probably due to the more protected hibernation sites available on these trees. Samples of hibernating cohorts at three other sites showed no evidence of differential mortality. Laboratory experiments with hibernating beetles found no difference in survivorship or rate of weight loss between starved non‐melanics and melanics in temperature regimes with and without periods of adult activity. It is concluded that the intense winter selection on the study limes is probably exceptional. Examination of changes in morph frequency through the annual cycle suggests that at some sites the selection favouring melanics during reproduction is counterbalanced by selection against melanics in late summer or early autumn. The results are discussed in relation to mathematical models of cyclical selection and to other field studies including that of Timoféeff‐Ressovsky (1940), who found large decreases in melanic frequency during hibern

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1985.tb00169.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY