Richard J. Gornall

PLANT PERFORMANCE ACROSS LATITUDE: THE ROLE OF PLASTICITY AND LOCAL ADAPTATION IN AN AQUATIC PLANT

Geographic variation can lead to the evolution of different local varieties within a given species, therefore influencing its distribution and genetic structure. We investigated the contribution of plasticity and local adaptation to the performance of a common aquatic plant (Potamogeton pectinatus) in contrasting climates, using reciprocal transplants at three experimental sites across a latitudinal cline in Europe. Plants from 54 genets, originally collected from 14 populations situated within four climatic regions (sub- arctic, cold temperate, mild temperate, and mediterranean) were grown in three different localities within three of these regions (cold temperate, Norway; mild temperate, The Netherlands; mediterranean, Spain). Tuber production was highest for the mild-temperate genets, irrespective of locality where the genets were grown. Selection coefficients indicated that populations at the European center of the species distribution perform better than all other populations, at all sites. However, marginal populations showed changes in life-history traits, such as compressed life cycles in the north and true perenniality in the south, that may allow them to perform better locally, at the limits of their distribution range. Our results thus suggest that local adaptation may overlap spatially with center-periphery gra- dients in performance caused by genetic factors (such as genetic drift and inbreeding in range-marginal populations).

Angiosperm Flavonoid Evolution: A Reappraisal

Critical review of the distribution of flavonoids in the angiosperms, combined with considerations of their biosynthesis has led to a reappraisal of existing dicta on the phylogenetic status of the various structural types. Caution is necessary when attempting evolutionary interpretations because there seem to be two trends operating within the angiosperms. The major one involves reduction in structural complexity, following a reverse direction down the biosynthetic pathway. Reduction in the actual number of flavonoid structures produced is also part of the trend. A secondary trend, often superimposed on the first, involves diversification whereby the flavonoid nucleus undergoes progressive elaboration (extra oxygenation, 0-methylation, etc.). The complications engendered by these two trends require the recognition of at least three evolutionary grades: primitive, advanced and highly advanced. It is very difficult to distinguish between the primitive and highly advanced conditions because in many cases the flavonoid phenotype is identical: in the first case the simplicity is primary and in the second it is secondary by reduction. Correlations in distribution of the different flavonoid structures can not only be interpreted in phylogenetic terms but also in terms of adaptive complexes. Many structures and groups of structures have never been reported from nature-are these ill-adaptive? On the other hand, there are several combinations which do appear regularly and it is suggested that they contribute to adaptive peaks. These flavonoid combinations are shown, within the limits of their definition, to characterize many orders and superorders (with increased precision of definition, the combinations can also be used to characterize families and lower taxa). The flavonoid profiles of the orders show a remarkable correlation with the occurrences of other secondary metabolites such as benzyl isoquinoline alkaloids, tannins, iridoids, sesquiterpenes and polyacetylenes. It is possible that flavonoids are not independent in their efficiency of action but rather act in functional consort not only with other metabolites and physiological processes, but also with morphological and anatomical

Evidence for spatial structure and directional gene flow in a population of an aquatic plant, Potamogeton coloratus

Six hundred and forty-seven samples of Potamogeton coloratus from 60 ditches in the Gordano Valley, Somerset were analysed for variation at two polymorphic PGM isozyme loci using starch gel electrophoresis. A total of eight genotypes was detected, and a high level of partitioning of genetic variability between ditches was observed with FST=0.575. Genetic variability was shown to increase with distance from the head of the valley. The genetic subdivision of the population and pattern of increasing diversity downstream and downwind were attributed to genetic bottlenecks, associated with ditch cleaning events, and subsequent directional gene flow mediated by the prevailing wind and water currents.

Population differentiation of Potamogeton pectinatus in the Baltic Sea with reference to waterfowl dispersal

Forty populations of Potamogeton pectinatus L. were sampled from around the Baltic Sea basin. Analysis of 62 ISSR ‘loci’ showed that the number of clones per population is very variable but shows a tendency to decrease with latitude. Analysis of molecular variance revealed that, overall, just over half the variability is stored within populations and just under half between them (φST 0.496). In pairwise comparisons, most populations are significantly differentiated. Genetic distance between populations, as measured by φST, increases with geographical distance. Levels of population differentiation, however, are lower on the southeastern Swedish coast than elsewhere, a reduction correlated with the importance of this area as a staging post for the massive migrations of waterfowl from arctic Russia and western Siberia. Cumulative plots of φST against geographical distance along this coast suggest that, although it does not prevent significant population differentiation, bird traffic reduces it over distances of 150–200 km.

GENETIC VARIABILITY IN TWO HYDROPHILOUS SPECIES OF POTAMOGETON, P. PECTINATUS AND P. FILIFORMIS (POTAMOGETONACEAE)

Genetic variability inPotamogeton pectinatus andP. filiformis was studied by means of isozymes. The overall levels of variability were similar to some other well studied hydrophilous species, and were shown to be distributed more between than within populations. This partitioning of variability was attributed to three main factors. (1) Clonal growth (as measured by the frequency of multi-enzyme phenotypes) was shown to be a major factor in both species, although more important inP. pectinatus. (2) Low levels of sexual reproduction were shown to be a likely contributor to the partitioning of variability inP. pectinatus; such reproduction is probably limited by seedling recruitment rather than by infrequent flowering. (3) Geographical isolation was indicated as a factor regulating gene flow at distances of more than about 1000 km in both species, with the data suggesting that dispersal between populations is mainly by seed rather than by vegetative means.

Isozyme evidence for the parentage and multiple origins ofPotamogeton ×suecicus (P. pectinatus ×P. filiformis, Potamogetonaceae)

Evidence from isozyme analyses indicates thatPotamogeton ×suecicus is the hybrid betweenP. pectinatus andP. filiformis. The hybrid appears to have arisen on several occasions. The isozyme profiles of this hybrid from the Rivers Wharfe and Ure in Yorkshire, south of the present limit of distribution ofP. filiformis, suggest that each population is a single clone; these clones may be relics from the Weichselian glacial period. Populations of the putative hybrid from the Rivers Tweed and Till are notP. ×suecicus but probably haveP. vaginatus andP. pectinatus as parents. If so, this is a remarkable example of a pondweed hybrid persisting vegetatively in an area outside the distributional range of one of its parents.

Genetic variability in British populations ofPotamogeton coloratus (Potamogetonaceae)

The partitioning of genetic variability within and between twelve British populations of the anemophilous aquaticPotamogeton coloratusHornem. was investigated by isozyme analysis. Low levels of variability as measured by P, A and H were found. Calculation of Wrights F statistics revealed a high mean value of the overall inbreeding coefficient, (FIT = 0.939), which was attributed both to high levels of genetic subdivision among populations (mean FST = 0.702) and to a high frequency of inbreeding or clonal growth within them (mean FIS = 0.796). Only two populations are polymorphic; both inhabit sites with a long post-glacial history as wetlands. Populations of recent origin, as well as some of older vintage, contain only a single multi-locus isozyme genotype, homozygous at all loci except for IDH. A genetic bottleneck following the Devensian glaciation is discussed as a possible cause of the pattern of variation. Evidence for a duplicated IDH locus is presented.

Euploid and aneuploid evolution in Potamogeton (Potamogetonaceae): a factual basis for interpretation

In a review of chromosome numbers in the genus Potamogeton, we highlight numerous errors that have crept into the literature. These have resulted chiefly from reliance on abstracts in chromosome number indices and compilations, rather than on the original publications, but partly also because of misleading summaries even in the primary literature. We present a list of counts that we believe are original and genuine, and a list of those that were never made but which nevertheless appear in the literature. Scrutiny of the list of accepted counts indicates that aneuploidy is widespread in the genus and that transition between the two common chromosome numbers (2n=26 and 2n=28) has occurred several times. Currently available data are insufficient to resolve the question of the ancestral base number. We also present details of the first chromosome counts from English populations of five taxa: P. polygonifolius Pourr. (2n=28), P. pectinatus L. (2n=ca. 78), P. perfoliatus L. (2n=ca. 52), P.×nitens Weber (P. gramineus×P. perfoliatus) (2n=ca. 52) and P.×salicifolius Wolfg. (P. lucens×P. perfoliatus) (2n=ca. 52).

INTRASPECIFIC MOLECULAR VARIATION IN HIERACIUM SECT. ALPINA (ASTERACEAE), AN APOMICTIC GROUP

Intraspecific variation of four agamospecies ofHieracium sect.Alpina was studied using RAPD and isozyme techniques. No variation in either multiprimer RAPD or multi-enzyme phenotypes was observed withinH. holosericeum, suggesting that this widespread species consists of only a single genotype. A low level of within-population isozyme variation was seen inH. tenuifrons andH. calenduliflorum, the origin of which appears to be consistent with somatic mutation. Most isozyme and all RAPD variation in these two species was partitioned between populations. A strong correlation with geography suggests that its cause may be due to polytopic (-polyphyletic?) origin or perhaps to mutation and dispersal. The most variable species wasH. alpinum, in which isozyme variation occurred mostly within populations rather than between them, suggesting occasional sexual events or that the parents ofH. alpinum were heterozygous. RAPD variation in this species, in contrast, was partitioned between Scottish and Swiss populations, suggesting the existence of geographical races.

The taxonomic significance of naphthoquinones in the Droseraceae

Abstract The distribution of the naphthoquinones 7-methyljuglone and plumbagin was studied among 63 species of the Droseraceae . Both compounds occur in Drosophyllum and Drosera ; only plumbagin was found in Dionaea and Aldrovanda . Within Drosera , naphthoquinones support the classifications of De Candolle and Diels to some extent, with subgenus Drosera containing sections having 7-methyljuglone, often with plumbagin and subgenus Ergaleium containing sections where plumbagin is predominant and 7-methyljuglone rare or absent. Within subgenus Drosera , however, no naphthoquinones were found in three Australasian sections.