摘要:

In spite of abundant evidence that intra‐ and inter‐specific competition occurs in natural communities, there is surprisingly little to suggest it is a major force promoting genetic change. This report assesses the genetic effects of competition in two species of seaweed fly,Coelopa frigidaandC. pilipes.In laboratory cultures ofC. frigidathe relative survival of heterozygotes at theAdhlocus, which was being used as a marker for the large αβ chromosomal inversion, was greater than that of homozygotes. In monocultures ofC. frigidathis competitive superiority was dependent on larval density. At low densities facilitation was seen, whereas at high larval densities there was competition. In mixed cultures of the two species, interspecific competition contributed to the differential mortality ofC. frigida, and observations of natural populations suggested that competition may have similar effects to those described in laboratory culture. A possible mechanism involving the supply of nutritive microorganisms is proposed to underly both intra‐ and inter‐specific competition. In seaweed flies, competition and the consequent differential mortality appear to be forces maintaining rather than reducing genetic

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01692.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The origin and differentiation of major clades is often assumed to have occurred in tandem with the ‘explosion’ of fossil evidence of diverse morphologies (‘disparity’) at the base of the Cambrian. Evidence is presented that this was not the case. Biogeographical and morphological differentiation among the earliest trilobites reveals incompleteness in the known early Cambrian record; similar evidence can be accrued for other major groups. Phylogenetic analysis proves the likelihood of ‘ghost’ lineages extending into the Precambrian. The important events in the generation of clades were earlier than the Cambrian ‘explosion’, at which time the groups become manifest in the fossil record. It is likely that the important phylogenetic changes happened in animals of small size; sister taxa of major groups are shown to be small animals. Decoupling cladogenesis from the Cambrian ‘explosion’ removes the necessity of invoking unknown evolutionary mechanisms at the base of the Phanerozoic. Genes controlling development may have played a role in generating new morphologies, through heterochrony for example, in the early differentiation of

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01693.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Host relations among the Aphelinidae (Hymenoptera: Chalcidoidea) are highly intriguing from an evolutionary view. Females are usually primary endoparasitoids of whiteflies or scale insects, whereas the development of the male is different and has been used for classification. In heteronomous hyperparasitoids (adelphoparasitoids or autoparasitoids) the male develops as a hyperparasitoid of conspecific females or other endoparasitoid species. We review the consequences of this mode of development which is unique because decisions concerning host selection are inextricably linked with progeny sex ratio. Autoparasitoid field sex ratios can fluctuate dramatically concurrent with changes in the relative availability of male and female hosts. A recent adaptive explanation for these sex ratios involves understanding the reproductive constraints acting on heteronomous parasitoids. Host relations in these parasitoids can show a degree of plasticity. We argue that in many instances autoparasitism may be facultative in nature and should not be used for classification. Heterotrophic parasitism, wherein the male develops as a primary parasitoid of lepidopterous eggs, has been poorly understood in the past due to uncertainties in reports of the biology and taxonomy of heterotrophic parasitoids. The host relations of this group are clarified.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01694.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Slave‐making ants raid nests of other ant species, capture the developing offspring and rear them to slave workers. Here we compare slave‐making of three formicine slave‐making ants: the facultative Formica subnuda, the obligate Polyergus breviceps, and F. subintegra which previously has been considered facultative but appears to be an obligate slave‐making ant. If F. subintegra is an obligate slavemaker, slave‐making of F. subintegra should differ from that of F. subnuda but closely resemble slave‐making of P. breviceps in the following aspects: (1) Obligate slavemakers are rarer than facultative slavemakers. (2) Slaveless colonies of facultative slavemakers are found, but obligate slavemakers always have slaves. (3) Because obligate slavemakers depend on their slaves, they should have a higher proportion of slaves than facultative slavemakers. (4) Owing to special adaptations obligate slavemakers are able to raid bigger colonies, and hence have bigger slaves than facultative slavemakers. (5) Dufour's gland of F. subintegra should be larger than that of F. subnuda. Per 100 free F. podzolica colonies, the number of P. breviceps and F. subintegra colonies with F. podzolica slaves were 1.3% and 3.9%, respectively, and the number of F. subnuda colonies with F. podzolica 3.7%, and without F. podzolica 7.5%. The proportion of slaves, when present, varied between 1–30% in the colonies of F. subnuda, and between 70–90% in the colonies of the other species. The slaves of F. subnuda were significantly smaller than those of F. subintegra and P. breviceps. The length of F. subnuda's Dufour's gland was one third of the length of F. subintegra's gland. The results show that slave‐making of F. subintegra parallels that of P. breviceps, and contrary to the earlier notion, F. subintegra is an obligate slave‐making ant. We suggest that F. subnuda and F. subintegra represent extreme modes of slave‐making behaviour in the Fo

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01695.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The present investigation ofCrepis tectorumexamines the extent to which tradeoffs and patterns of dominance contribute to the association between flower size (head width) and degree of self‐fertility among populations adapted to rock outcrops. Partial correlation analyses of phenotypic data from a F2 generation derived from a cross between two outcrop plants and of family means representing one of the parent populations indicate that small‐flowered plants fail to reallocate resources to flower and fruit production, that small flower size offers little or no advantage in terms of autofertility, and that floral reduction has little influence on the rate of flower development. Hence, it may be necessary to invoke factors other than tradeoffs to explain the decline in flower size associated with the evolution of autogamy inC. tectorum.Comparison of parent and Fl hybrid means in the crossing experiment suggests incomplete dominance in the alleles for large flower size. Under the assumption that Fl hybrid means reflect the average degree of dominance across loci, I propose inbreeding depression as the basis for some of the reduction in floral morphol

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01696.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Like other amphibians native to Britain, the natterjack toadBufo calamitamust have colonized the islands during the relatively short period between the end of the last glaciation and the separation of Britain from mainland Europe by rising sea levels. Unlike the other native amphibians, however,B. calamitais a habitat specialist at the north‐westerly edge of its biogeographical range and for most of the 8000–10000 years since its colonization has probably been restricted to open dunes, heathlands and upper saltmarshes, as isolated populations in a few discrete areas of the country. We have investigated the genetic diversity and relatedness of six widely separated British natterjack populations by allozyme analysis, and shown that all have very low diversity (OverallP95%= 2.7%, H = 0.004) by comparison with other anurans, including natterjack populations in mainland Europe and common frogs (Rana temporaria, L) in Britain. Eighty percent of loci were fixed for the same allele in all six British natterjack populations and genetic differentiation between colonies was extremely low. The possible significance of these findings to the persistence of small isolated populations at range edges is discus

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01697.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Environmentally cued polymorphisms are hypothesized to evolve when the environment is coarsegrained and different genotypes are unable to choose the habitats in which they are most fit. In Papiliopolyxenes, which has an environmentally cued pupal colour dimorphism, there is genetic variation in both tendency to produce brown or green pupae and preference for green‐ or brown‐inducing pupation sites, but the two traits are not correla

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01698.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1996.tb01692a.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY