摘要:

The plethodontid salamander speciesEnsatina eschscholtziicomprises seven subspecies that are geographically distributed in a ring surrounding California's Central Valley. The subspecies are differentiated primarily on the basis of colour pattern, although there is also significant electrophoretic protein variation both within and among subspecies. The subspecies intergrade around the north end of the valley, whereas at the southern end, two morphologically distinct subspecies meet but do not interbreed. Thus, the species is believed to be at or near speciation. The present study examines osteological variation inEnsatina eschscholtziiusing x‐radiographs of 436 individuals from 19 localities around the ring‐shaped range of the species. In marked contrast to the distinct geographic differentiation in colour pattern variation, skeletal conservatism predominates and the small amounts of variation seen in the limbs and vertebral column show no correlation with geography. Thus, skeletal variation does not further elucidate the status of speciation inE. eschscholtii.Rare skeletal variants, especially in the limb, follow patterns of variation that implicate developmental processes in constraining skeletal variability. In the digits, variation in the number of phalanges inE. eschscholtziiis congruent with variation produced by mitotic inhibition experiments in the developing axolotl (Ambystoma mexicanum) limb. In the mesopodium, the sequence of mineralization (in rare large individuals where mineralization occurs) matches the sequence of prechondrogenic condensation in the developingAmbystomalimb. Although constraints on morphological variability by internal developmental mechanisms can account for the patterns of variation seen among these rare limb variants, the question remains open as to whether developmental processes are responsible for the overall skeletal conservatism seen inE. eschscholt

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00586.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Data are presented on the Hemiptera fauna of a moderately large and topographically diverse area of tropical rain forest in Sulawesi Utara, Indonesia. Insects were sampled using several methods at several sites over a 1‐year period. The numbers of described and undescribed species captured is used to predict the number of extant species of both Hemiptera and total insects in the world. The global estimates of 1.84–2.57 million species of insect are much lower than the 10–80 million predicted by Erwin and Stork from a study of tropical Coleoptera. The reasons for believing that the lower estimates are more reliable are disc

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00587.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

An extensive survey of isozyme phenotypes in British populations of the amphidiploid salt marsh grassSpartina anglicaand its putative parents has confirmed that the species arose by chromosome doubling inS. × townsendii, a sterile hybrid betweenS. maritimaandS. alterniflora.Isozyme phenotypes and seed protein profiles indicate thatS. anglicais almost totally lacking in genetic variation. Isozyme evidence also indicates that the parental species are characterized by low levels of genetic variation. The lack of variation inS. anglicais proposed as being due to a narrow genetic base resulting from a single origin, or a multiple origin from uniform parents; the fact that many populations are derived from very small founder populations; and because preferential pairing between identical homologous chromosomes prevents recombination between the divergent component genomes of the species. The low levels of isozyme variation that occur appear to be due to chromosome loss.The consequences for the future evolution ofS. anglica, given its lack of genetic variation, are discussed

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00588.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Populations of the common mussel (Mytilus edulis) from the North Sea area (Skakerrak‐Kattegat) and those from the Baltic Sea are almost diagnostically differentiated at five out of 22 studied allozyme loci; at a further seven loci, alleles predominant or common in one area are nearly absent in the other. Genetic distance was estimated at 0.28; this is similar to the distances of these populations to the Mediterranean musselM. galloprovincialis.The three mussel types obviously represent equal evolutionary divergence from one another, and should also be taxonomically equally separated; a semispecies rank within a more comprehensiveM. eduliscomplex or superspecies is suggested. The age of the Baltic mussel type (‘M. trossulus’), as an independent evolutionary lineage, is probably far greater than that of the post‐glacial Baltic Sea.Allele frequencies change gradually and in parallel when entering from the Kattegat through the Sound into the Baltic. Only a slight Wahlund effect at the strongly divergedGpiandPgmloci was found in intermediate populations, indicating that extensive hybridization of the two taxa takes place in the area. However, strong interlocus genotypic associations suggest that selection against hybrids is intense in later generations; thec.100 km wide hybrid zone is narrow relative to the dispersal distance. The genotypic structure of theLaplocus does not conform with those of the other loci studied in the hybrid zone; it cannot be viewed merely as a neutral marker of the process of hybrid

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00589.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

There is no direct evidence that predators exert apostatic selection (the systematic overpredation of commoner forms) on live, naturally polymorphic prey. This study tested whether captive song thrushes (Turdus philomelos) select apostatically when presented with dimorphic populations of yellow five‐banded and yellow unhanded morphs of the snailCepaea hortensis.Four thrushes were used. Two were presented with a 9: 1 ratio of five‐bandeds to unbandeds and two were presented with 1:9 ratios. Each thrush was given four trials in succession. In each trial 30 snails were presented and the trial was stopped when 15 had been eaten. There were no differences in shell size between morphs or between eaten and uneaten snails of each morph. Three thrushes selected apostatically and one thrush exerted virtually no selection. Overall, there was statistically significant apostatic select

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00590.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY