Spatial and temporal variation in distribution of Gelidium canariensis (Rhodophyta) from natural populations of the Canary Islands

This study was designed to investigate spatial and temporal variation in Gelidium canariensis populations at two shores in northern Gran Canaria during two years. Spatial scales ranged from some hundred meters (distance between shores), 10 to 30 m (distance between plots) to less than 3 m (distance between quadrats). Gelidium individuals were defined as distinct Gelidium clumps. The results show a significant difference in size of clumps between shores, but not on the smaller spatial scales. No significant temporal variation was found. There was no significant temporal or spatial variation in standing crop or density (counts made in quadrats where Gelidium was present, rather than counts for the total shore). Sporophytic and gametophytic clumps were also distinguished by identifying reproductive structures in the field. The total proportion of sporophytes was larger than the proportion of gametophytes, but at a smaller scale there could be a shift in dominance. The survival rate of clumps was similar between shores with a mean survival rate of 85%, but there was a significant difference in recruitment between shores. The results indicate a stable population structure. This revised version was published online in June 2006 with corrections to the Cover Date.     

Systematics of Pseudorchis albida s.l. (Orchidaceae) in Europe and North America

In Scandinavia Pseudorchis albida (Orchidaceae)usually divided into the lowland and subalpine P. albida s.s. and the more or less alpine P. straminea. There have been some uncertainties and conflicting views concerning die taxonomic treatment of diese taxa. To address this issue, herbarium specimens of P. albida s.l. were studied for variation in morphological characters. A small-scale population study approach was used, as herbarium sheets with two or three plants were used as population samples. Canonical Variates Analysis (CVA) indicated a distinction between taxa in population means, corresponding to P. albida s.s. and P. straminea , respectively. Principal Components Analysis (PCA), however, revealed an overlap between individuals of the two taxa. The PGA analysis, furthermore, revealed that the overlap was considerably larger in material from Central Europe man in material from Fennoscandia. Student t -tests on separate characters confirmed the picture, wim more characters significantly different in Fennoscandian than in Central European material. Furthermore, a Tukey-Kramer test revealed that there were small differences between regional populations of P. albida s.s. , while there were several significant differences in single characters between the Norm American regional population of P. straminea , as compared with the Central European and Fennoscandian regional populations. In Central Europe there is no clear separation between taxa, while in Fennoscandia the taxa are more clearly separated. This probably means that there is a difference in the time of establishment in the different regions. The author suggests a distinction of taxa at the subspecies level, and argues that the clear distinction seen in Fennoscandian material is due to separate immigration histories for die two subspecies into Fennoscandia after the last period of glaciation.     

Pollen and gene flow in fragmented habitats

Abstract. Habitat fragmentation affects both plants and pollinators. Habitat fragmentation leads to changes in species richness, population number and size, density, and shape, thus to changes in the spatial arrangement of flowers. These changes influence the amount of food for flower-visiting insects and the quantity and quality of pollinations. Seed set in small populations is often reduced and genetic variation is expected but not always found to be low. The majority of studies show that low flower densities have reduced pollination success and higher inbreeding. Density effects are stronger than size effects. Most studies concluded that species richness in flower-visiting insects is directly related to richness in plant species. However, the consequences of low insect species richness for pollination are not always clear, depending on the studied pollinator-plant relationship. The effects of the presence of simultaneously flowering species are highly dependent on the circumstances and may range from competition to facilitation. Other flowering plant species may play a role as stepping stones or corridor in the connection between populations. In the absence of stepping stones even short distances between populations act as strong barriers for gene flow. We illustrate the present review paper with own data collected for three plant species, rare in The Netherlands: Phyteuma spicatum ssp. nigrum (Campanulaceae), Salvia pratensis (Labiatae) and Scabiosa columbaria (Dipsacaceae). The species differ in their breeding systems and in the assemblage of visitor species. Data are shown on the effects of population size on species richness with consequences for seed set. Effects of flower density and isolation on pollen exchange are given. Since plant reproduction depends on the behaviour of individual insects and not on the overall behaviour of the species, the examples all point to individual insects and extrapolate to effects at the species level.     

Geography of sexual dimorphism in the tooth size of the red fox Vulpes vulpes (Mammalia, Carnivora)

Geographic variation in sexual dimorphism of tooth size was assessed for the red fox Vulpes vulpes (Linnaeus, 1758) across the whole northern range of the species. Twenty-one measurements of tooth size and skull length were taken from 2849 specimens (1577 males and 1272 females) originating from 12 Nearctic and 25 Palearctic localities. The index of sexual dimorphism was calculated as a quotient of the mean measure of certain characters in males by the respective mean in females ( M _m/ M _f). In the whole range, the males were larger than females and mean dimorphism index of tooth size ranged from 1.01 to 1.06. On average, the tooth measurements in males were 3.6% larger than in females. The highest dimorphism was observed in the canines. Dimorphism of tooth size was higher in the Palearctic than Nearctic. Statistically significant differences between regions were found for lengths of C¹, C₁ and M₁. In the Palearctic, higher values of the dimorphism indices were observed particularly in the southern parts of the Eurasian range of the red fox and in Great Britain. For a few metrical traits, sexual dimorphism indices presented significant relations to some geo-climatic variables. The geographic pattern of size dimorphism in the red fox seems to be shaped by sexual selection, intraspecific and interspecific competition and population density.     

Genetic differentiation in diapause response along a latitudinal cline in European yellow dung fly populations

Abstract.  1. Seasonality is a prime selective factor expected to result in local adaptation of life cycles and dormancy. Genetic differentiation in diapause response was investigated along a European latitudinal cline in the dung fly Scathophaga stercoraria (Diptera: Scathophagidae). Such differentiation may be mediated by additive or dominance genetic and/or maternal effects, which need to be distinguished.
2. Replicate sibships from five European populations (Lugano, Switzerland: 46.00°N; Zurich, Switzerland: 47.37°N; Oxford, U.K.: 51.75°N; Lund, Sweden: 55.70°N; Reykjavik, Iceland: 64.15°N) were raised in a common laboratory environment known to induce pupal winter diapause (12 °C and 12 h light), revealing a genetic latitudinal cline in both the proportion of individuals entering diapause and diapause duration in response to winter length estimated from weather data.
3. Populations from the extremes of the cline (Lugano and Reykjavik) were further reciprocally crossed to investigate the underlying genetics. This experiment revealed evidence for diapause induction at 12 °C being dominant (i.e. not merely additive) and clearly rejected maternal effects as the primary source of this between-population variation.     

Genetic structure and essential oil composition in wild populations of Salvia multicaulis Vahl.

The phytochemical study on ten populations of Salvia multicaulis Vahl. revealed that their essential oil qualitative profiles contained a significant amount of monoterpene hydrocarbons, which were the most abundant compounds. Besides, α-Pinene was the major constituent in all studied populations' essential oils. Significant correlations were observed between edaphic parameters and some major essential oil compounds. According to clustering analyses of the chemical data, the S. multicaulis populations were divided into three chemotypes: β-caryophyllene, camphene and camphor, and limonene. The population genetics study showed significant molecular differences among the populations. The Mantel test indicated a significant positive correlation between the geographical distances and genetic diversity, exhibiting a low amount of gene flow and a considerable genetic differentiation value. We also detected four genotypes based on the Nei's genetic distance and structure analysis. The identified chemical and genetic similarities/differences among these populations were correlated with edaphic parameters and geographic distances, suggesting that environmental factors are the primary drivers of the chemical polymorphism of essential oils in S. multicaulis populations.     

Killing me slowly: Harsh environment extends plant maximum life span

Life span (the age of death for individuals that survived the establishment phase) is a key trait in plant life history. Despite its importance for understanding plant–environment relationships, there are still numerous substantial knowledge gaps about variation in plant maximum life spans and the ecological processes underlying these patterns.Based on plant age data obtained by means of herbochronology, we analysed patterns of intraspecific plant maximum life span variation in three perennial species (Campanula scheuchzeri, Helianthemun nummularium and Lotus corniculatus) along environmental gradients of mean annual temperature, soil depth and soil nutrients. This variation was compared with predictions from the ‘death-by-starvation hypothesis’ proposed by Hans Molisch in 1938, an unjustly forgotten ‘extrinsic’ theory on plant life span variation.Our study suggests that plant age variation within populations responds sensitively to growing conditions. The most important finding is that mean annual temperature or environmental conditions related to it seems to be a driving factor for intraspecific variation in plant maximum life span in all species studied. Despite large within-population variation, individuals of C. scheuchzeri, L. corniculatus and H. nummularium generally had a longer life span under colder climates (uplands in our case). In addition, soil depth (as a proxy for habitat susceptibility to drought) was found to have a significant positive effect on the age values in the case of C. scheuchzeri.These findings, therefore, are in line with Molisch’s “death-by-starvation hypothesis”: extended maximum life span results from reduced production of sink tissues and slow vegetative growth. We conclude that the analysis of plant life span adjustments along gradients of environmental factors can considerably contribute to our understanding of how plants may cope with changing environmental conditions, e.g., due to global change.     

Genetic structure and diversity of the Diachasmimorpha longicaudata species complex in Thailand: SSCP analysis of mitochondrial 16S rDNA and COI DNA sequences

Genetic variation among 20 populations of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) in Thailand was investigated using single strand conformation polymorphism (SSCP) analysis of mitochondrial DNA sequences. From a total 641 individual parasitoids, seven distinct haplotypes containing a total of 32 polymorphic sites were observed from cytochrome oxidase subunit I (COI) sequences along with five distinct haplotypes containing a total 16 polymorphic sites from 16S rDNA sequences. Values obtained through pairwise F_ST comparisons and analysis of molecular variance (AMOVA) indicated significant genetic differentiation among D. longicaudata populations in Thailand. Congruent relationships showing separation of these populations into three groups were obtained from Neighbor joining and Bayesian phylogenetic tree analyses along with the use of haplotype networks. This SSCP analysis of populations of the D. longicaudata species complex is the first report using molecular population genetic methods to analyze the structure of this parasitoid species in Thailand. This may provide useful information for release of parasitoid strains to maximize their benefit in biological control programs.