摘要:

Bracken [Pteridium aquilinum(L.) Kuhn] is a cosmopolitan species and is a noxious weed in many areas. Because of its abundance, particularly in Britain, bracken affords an ideal system for investigating various aspects of population genetics and evolution. High mobility of dispersal units (spores) suggests that rates of gene flow among distant populations should be high. Gene flow is a major evolutionary force that influences the genetic structure of populations. To examine the effects of gene flow on population heterogeneity and population substructuring in bracken, starch gel electrophoresis of enzymes was used to provide the necessary genetic database. Allele frequency data at 21 loci were obtained for seven British populations, one Majorcan and one from the eastern United States. A model was employed to estimate the amount of gene flow (Nm) at several levels. Gene flow among British populations was extremely high (Nm= 36.51), one of the highest estimates reported for plants. Among eight European populations gene flow was lower (but still considered high) atNm= 2.47. Trans‐Atlantic gene flow was low (Nm= 0.0926).F‐statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing spec

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00572.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

A unifying theory for systematic analysis states that a number of methods should be used jointly to cope with various kinds of data; also that groups should be as consistent as possible, be made with least information loss, and where needed, be polythetic. A test of relationship, homogeneity, can use various kinds of data. It can take account of the internal variation of aggregate items such as genera. It can give due emphasis to smaller clusters that have likely important contexts of external items. It helps in analysing trends, cores and hazes in dendrograms. A proposed detector for formal groups can be based on measures of isolation, identifiability and inclusiveness. Non‐mathematical, inter‐item reaction tests such as hybridization and serology can also be used in grouping. All relationship data are used polythetically to reveal natural groups. This leads to a unified informational concept for taxa. This is more useful than the biological species concept that is restricted to inter‐breeding data. All the methods appear to be analogues of the powerful human grouping instinct. The resulting compatibility is important as precise methods are needed mainly when the data are too complex for the mind to use reliably. Cladograms can be made by self‐graded deweighting of homogeneity and agglomerative clustering. Unlike classical cladistics this can reveal any polythetic group. Finding the derived states for making cladograms is often much too hypothetical for a fully cladistic approach to be properly precise. Instead, where the evidence is weak, a milder strength of graded deweighting is used for the cladistic properties, which help to show relationships along with the others. Axiomatic failures of other classes of grouping methods are discussed. Unavoidable remnants of instinctive processing lower the precision of all the methods. The Uniter computer program, based on the theory, is tested with finely graded values of artificially ‘evolved’ items and with coarsely coded cladistic data. The results show that with natural data, the program should act as a fairly sensitive probe of past evolutionary branching. Another test shows how specimens from species complexes can be grouped and how distinctions between groups a

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00573.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Carotcnoids and chlorophylls a and b were extracted from final instar caterpillars of the poplar hawkmoth (Laothoe populi) and the eyed hawkmoth (Smerinthus ocellata), as well as from their food plants. Both species of caterpillar absorb the two chlorophylls and the carotenoids lutein,cis‐lutein and β‐carotene in the gut and deposit lutein andcis‐lutein in the integument. It is the lutein, together with pterobilin, that is largely responsible for the colour of the insect: yellow‐green poplar hawkmoth caterpillars have more lutein in the integument than dull green ones which in turn have more than white ones. Yellow‐green and dull green caterpillars both sequester lutein andcis‐lutein in the gut wall, but the yellow‐greens translocate more of these pigments to the integument than the dull greens. The white caterpillars absorb very little lutein andcis‐lutein into the gut, and so they have much less also in the integument. The mechanism by which the reflected light perceived by the caterpillar is translated into differential absorption of pigment by the gut and deposition in the integum

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Final instar caterpillars of the poplar hawkmoth (Laothoe populi) are usually yellow‐green when they have been feeding onSalix fragilisbut white when onPopulus alba.Similarly final instar caterpillars of the eyed hawkmoth(Smerinthus ocellata)vary in colour from yellow‐green when fed onSalix cinereaorS. fragilisto grey‐green when fed onSalix ripensorS. alba.Most caterpillars of these two moths are thus very cryptic to the human eye. It has already been shown that colour matching is brought about by young caterpillars changing colour depending on the colour of the substrate perceived by their eyes. Evidence is presented here for selective predation, probably by birds. Yellow‐green poplar hawk caterpillars disappeared fromP. albamore rapidly than did white caterpillars, but there was no significant difference in the survival of the two colour forms onS. fragilis.Yellow‐green caterpillars survived better onS. fragilisthan onP. alba, but there was no significant difference in the survival of white caterpillars on the two plants. Reasons why selective predation did not occur in all of the experiments are

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY