摘要:

Electrophoresis and biochemical staining were used to analyse genetic variation in enzymes in nine species of terrestrial slugs of the genusArionfrom 58 localities in the British Isles. The species fall into three categories on the basis of the genetic structure of their populations and their breeding systems.Arion lusitanicus, A. hortensis, A. distinctusandA. oweniiare highly polymorphic and heterozygous, and apparently reproduce predominantly, if not completely, by outcrossing.Arion circumscriptus, A. silvaticus, andA. intermediusconsist of one or a few monogenic strains. Their monogenicity apparently results from an automictic mode of reproduction, most probably self‐fertilization.Arion aterandA. subfuscusconsist of both a polymorphic, heterozygous form and a monogenic strain, between which hybridization occurs. The monogenic strain and the polymorphic form ofA. subfuscusoccur in pure populations only in Ireland and England, respectively, but each has been introduced throughout the British Isles. In bothA. aterandA. subfuscus, hybrid populations show a marked deficiency of heterozygotes as a result of self‐fertilization. The genetic structures and breeding systems of populations of the species ofArionintroduced to North America are similar to those of native populations in Brit

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02018.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Previous studies of relative brain size in mammals have suggested an association with complex habitats and with low reproductive rate. In order to examine the causal relationships more thoroughly, a detailed examination of relative brain size variation in the genusPeromyscuswas undertaken. Endocranial volumes were used to estimate brain weight for 32 species including 161 subspecies, and relative brain size calculated as the species deviation from the allometric relationship between brain and body size. The intrageneric allometric coefficient was higher than most values previously reported from low taxonomic levels, but intraspecific coefficients were generally lower than this.Island species, and relict species isolated on mountain tops, which may be ecological ‘islands’, had consistently small relative brain sizes, but peninsular species were large brained. Among the remaining species there were significant correlations between litter size and relative brain size, and between the number of competitor species and relative brain size. Species with many competitor species have relatively large brains and small litters. It is concluded that the nature of the geographical distribution, the pattern of species formation and habitat complexity all influence relative brain size in existing fo

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02019.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The migration‐selection model for the spatial and temporal variation of morph frequencies ofBiston betulariaover England and Wales (Cook&Mani, 1980) has been extended to include effects due to non‐visual selection. The parameters for non‐visual selection were chosen from the recent determination by Mani (1980) and by Creedet al. (1980). The morph frequencies over England and Wales were obtained through computer simulation and the results were compared with data along the Manchester‐Yorkshire, Central Wales‐East Anglia and South Wales‐London transects. Best fits to the data were obtained by using the non‐visual selective values of Mani forcarbonariaand modified values of Creedet al. forinsularia. It is concluded that the observed polymorphism could be well explained through a balance of migration and visual and non‐vi

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02020.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Having argued that phenotypic variation with respect to the component of fitness involved in withstanding density stress is useful for the persistence of populations through time, the sources of such variation are described. Age differences and differences caused by the accidental encounters of dissimilar microenvironments are non‐genetic in origin. Genetic bases for phenotypic variation can either be proximate (each individual having a unique genotype) or ultimate. The latter case is one in which the genotypes of individuals are such that the progeny they produce are phenotypically variable. Selection favouring such genotypes can be shown to be Darwinian; group selection is not required. A means for revealing instances of the ultimate genetic control of phenotypic variation is suggested: measures of what should be error variance prove to be larger than those which should, under normal circumstances, include error variance. The last increment of variation that causes what might otherwise be repetitive structures to differ can be ascribed to decisions that are genetically pre‐set within developmental program

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02021.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

A series of morphometric analyses conducted on specimens ofNymphon brevirostreHodge andNymphon rubrumHodge from British waters has shown that the characteristics variously used in the past to distinguish these two species are invalid. In this material these characteristics range from the extreme of the typicalN. brevirostreform to that of the typicalN. rubrumform, with most of the specimens exhibiting an intermediate morphology. Multivariate analyses showed no significant splitting of the material into two groups which might correlate to Hodge's two species. Protonymphon larvae from males of both typical extreme forms were morphologically identical. It is concluded thatN. rubrumis a junior synonym ofN. brevirostre, a variable species whose morphology tends towards therubrumform as the animal grows.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02022.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

A new theory of plastid origins is presented in which only two symbiotic events are needed to explain the origin of the six fundamentally different types of plastid, which all probably originated in anteriorly biciliated phagotrophic cells. Four of them can be derived directly from a single endosymbiotic cyanophyte by the independent loss of different cyanophyte characters and the evolution of new characters in the immediate descendants of this primary endosymbiosis. Retention of the phagosomal membrane as well as the prokaryotic plasma and outer membrane could produce the dinozoan and euglenid plastids with three envelope membranes, whereas the loss of the phagosomal membrane could produce the two‐membraned envelopes characteristic of the Biliphyta and Verdiplantae*. The phycobilins were retained essentially unaltered in the Biliphyta, but are modified or lost in the other lines. In the ancestor of the Euglenozoa and Verdiplantae they were replaced by chlorophyll b. In the ancestor of algae possessing chlorophyll c they were modified to the cryptophyte type, concomitantly with the evolution of chlorophyll c2: one line of descent from this ancestor produced the dinozoan plastid by the complete loss of phycobilins, while the other was incorporated by endosymbiosis into another phagotrophic bibiliate to produce the cryptophyte plastid. The latter evolved into the chromophyte plastid by the loss of phycobilins and the evolution of chlorophyll c2. The conversion of the endosymbiont into a plastid depended on the evolution of a system to transport proteins into it. I argue that this occurred by the modification of the pre‐existing mitochondrial transport system, and that the major modifications needed to adjust this to plastids with more than two envelope membranes led to evolution of a new tubular or disc‐like morphology for the mitochondrial cristae of these groups. This new cristal morphology is maintained by stabilizing selection even in species that have secondarily lost pla

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02023.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Emergence records for three species ofDrosophilabreeding in the stinkhorn (Phallus impudicus) are presented. These areD. phalerata, D. subobscuraandD. cameraria. The numbers of stinkhorn present in one woodland (0.114 km2) have been estimated for a two‐year period. In 1976, the total number of these fungal breeding sites during the summer was approximately 8000 and in 1977 it was 5300. Utilizing the estimates of breeding site numbers,Drosophilaemergence data and estimates of adult survival from laboratory populations, density estimates forD. phalerataandD. subobscuraare calculate

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02024.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY