The Effect of conditioning the medium in drosophila, in relation to frequency-dependent selectionDolan, Rosemary; Robertson, Alan
doi: 10.1038/hdy.1975.102pmid: 814110
In the context of frequency-dependent selection, the effect of conditioning the medium, by the previous culture of larvae of a given strain, on the survival of subsequent larvae of the same or different strains was measured. Six strains were used, some inbred and some lines selected for low or high sternopleural bristles. The survival of larvae was not significantly less when the food had been conditioned by the same strain rather than by another strain, nor did conditioning by one strain have any special effect on the survival of another. The survival of lines on medium conditioned by the same strain was not less than on fresh medium, and in some cases was significantly greater.
The effect of gene dispersal on the dynamics and statics of gene substitution in plantsLevin, Donald A; Kerester, Harold W
doi: 10.1038/hdy.1975.103pmid: N/A
A computer model has been developed to determine the effect of pollen and seed dispersal patterns on the probability of fixation and time to near-fixation of a rare advantageous gene in a plant population composed of 225 individuals. In the model, pollen and seed dispersal are according to four schedules (i) zero distribution, (ii) stepping-stone distribution, (iii) leptokurtic distribution, (iv) or random distribution. All combinations of pollen and seed dispersal schedules are treated. Relative fitnesses are assigned to three genotypes, AA, Aa, and aa, the latter always being the superior type. Relative fitness takes the form of competitive ability among the several seedlings germinating at each of the 225 safe sites in the population.
Mitotic cycles in Triticum speciesDavies, P O L; Rees, H
doi: 10.1038/hdy.1975.104pmid: N/A
The duration of the mitotic cycle at 20°C was estimated in meristems of roots averaging 12 mm long in six species of the Triticinae. They include two diploids, Aegilops squarrosa and Triticum monococcum; two tetraploids, Triticum dicoccoides and Triticum timopheevi and two hexaploids, Triticum aestivum and Triticum spelta. The average duration of the cycle increased in the order 2x (11 to 12 hours) to 4x (15–16 hours) to 6x (19–20 hours).
Food induced esterase phenocopies in the snail Cepaea nemoralisOxford, G S
doi: 10.1038/hdy.1975.106pmid: 1061709
Hepatopancreatic extracts from the snail Cepaea nemoralis, assayed straight from the field, often contain three or four heavily staining esterase zones which migrate to the cathodal end of polyacrylamide disc gels during electrophoresis Previous breeding results showed that the heavily straining zones appeared allelic but to incorporate these multibanded phenotypes, a super gene of five closely linked loci was tentatively proposed. Further breeding work again failed to demonstrate multiple zones in parents or offspring and so experiments were conducted to see whether the multi-zoned phenotypes in the wild were produced by secondary modification of single primary products. Wild snails yielding extracts containing more than two heavily staining zones were shown to possess only two such zones after three months under laboratory conditions. Also, the ingestion of nettle (Urtica dioica L.) has been demonstrated to induce extra esterase zones in laboratory-reared animals. Some of the secondarily induced zones appear identical in physical, biochemical and electrophoretic properties to the primary products of other alleles, and thus appear to be electrophoretic phenocopies. A model is suggested which could account for this phenomenon.
A sex-chromosome hybrid zone in the grasshopper Podisma pedestris (Orthoptera: Acrididae)Hewitt, Godfrey M
doi: 10.1038/hdy.1975.108pmid: 1061710
Podisma pedestris exists as both an XO and neoXY form in the Southern French Alps These chromosome types are shown to be contiguously allopatric and hybrid populations have been located in several places. Hybridisation appears to be occurring freely, but the hybrid zones are quite narrow. In several places the two distributions are separated by geographic barriers such as high mountain ridges and lowlands. The history of this XY chromosomal race is discussed in the light of the genetic dynamics of hybrid zones and the biogeography of this situation. Its origin is probably post-glacial, and it may be extending its range as a salient in one region. A comparison of the properties of similar cases indicates that the formation of such chromosomal races may be a frequent event in relatively immobile species that are subjected to isolation and expansion by major climatic and ecological changes.