Grzegorz Iszkuło

Do secondary sexual dimorphism and female intolerance to drought influence the sex ratio and extinction risk of Taxus baccata

Sex ratio and sexual dimorphism were studied in the dioecious tree Taxus baccata. We examined five populations of T. baccata in Poland and Ukraine to identify the differences between male and female individuals. The sex of all individuals, height and diameter, needle length and area, specific leaf area (SLA), the number of stomata rows, stomatal density, and content of carbon and nitrogen were measured to identify the differences between male and female individuals. The relationship between sex ratio and climatic conditions, age and population size were analysed using data collected from the field and the literature. Female trees were shorter than males, but needles of females were longer and had larger area. Although there were no differences among sexes in SLA, nitrogen and carbon concentration, we found a positive correlation between nitrogen concentration and SLA among females. The sex ratio changed with tree height within populations, and taller height classes were biased in favour of males. Regardless of population age, the percentage of females within populations was positively correlated with precipitation. Probably high reproductive effort caused female trees to lose in competition with males, and this loss may also be enhanced by lower drought tolerance in females and could contribute to risk of extinction for T. baccata. The continental geographic range of T. baccata may be restricted by limited occurrence of females, which demand higher water resources than males.

Do Females Differ from Males of European Yew (Taxus baccata L.) in Dendrochronological Analysis

Abstract Female and male plants often differ in reproductive effort and habitat requirements. The aim of this study was to analyze these differences between the sexes and the effect of climate on tree-ring width in European yew (Taxus baccata). The study was conducted in five yew populations in western Poland. Wood samples were taken from 196 trees (98 females and 98 males) and subjected to the standard procedure of dendrochronological dating. Mean tree-ring width was significantly higher in males since about the beginning of sexual maturity. No such relationship was observed in the youngest population, which is the most distant from the current geographic limit for this species. In most of the analyzed populations, width of tree rings in female individuals, in contrast to males, was negatively correlated with high temperatures in August and September in the year prior to the formation of the tree ring, and correlated positively with precipitation in June and July in the current year. The differentiation of tree-ring width between males and females likely began when the yew trees reached sexual maturity, probably because of the assumed greater reproductive effort of females in comparison with males. The lack of difference in the youngest population may result from a short time since the beginning of sexual maturity or from a milder climate in that region. Different reactions of the two sexes to climate indicate that this may affect the range and viability of populations at the limits of the range.

Morphological differentiation supports the genetic pattern of the geographic structure of Juniperus thurifera (Cupressaceae)

Juniperus thurifera is an important component of woodland communities of dry sites within the West Mediterranean region and is characterised by a strongly disjunctive geographic range. Two subspecies were recognised, subsp. thurifera in Europe and subsp. africana in Africa. The aim of the study was the comparison of phenetic diversity to the pattern of AFLP geographic differentiation of the species described in the literature. The examination of phenetic diversity was based on the biometrical analysis of 17 populations using 12 morphological characters of cone and seed. The differences among populations were analysed using Student’s t test, analysis of discrimination, UPGMA agglomeration and hierarchical analysis of variance. The majority of morphological characters differentiated at a statistically significant level between populations and between J. thurifera subsp. thurifera and subsp. africana. Three groups of populations were detected using multivariate statistical analyses. The first, well separated, is subsp. africana, while the following two concern subsp. thurifera. The morphological differentiation of populations appeared similar to that described on the AFLP. The Gibraltar Straight appeared to be the most important barrier.

Morphological diversity and structure of West Mediterranean Abies species

The aim of this study was the biometrical comparison of Abies pinsapo Boiss., Abies maroccana Trab. and Abies tazaotana Côzar ex Villar from Spain and Morocco. The morphological and anatomical analysis of the needle characters of these firs revealed significant taxonomic differences. The results showed considerable distances between regions and very small differences among the Moroccan fir taxa. The examination of the needles and earlier genetic analysis did not provide evidence for distinguishing A. tazaotana at the species level.

Effect of geographic range discontinuity on species differentiation—East-Mediterranean Abies cilicica: a case study

In the present study, a genetic analysis of nuclear microsatellites was conducted in Abies cilicica populations growing in West Taurus, East Taurus, and Lebanon mountains to obtain evidence for significant genetic differentiation. Despite range fragmentation, all examined populations tended to maintain a relatively high level of genetic diversity (HE = 0.724) and showed moderate genetic differentiation (FST = 0.134) that is frequently noted in Mediterranean tree species. However, significant inbreeding, bottleneck effect, and low effective population sizes were detected, that may negatively affect species genetic resources. Bayesian clustering revealed three distinct groups, “West Taurus”, “East Taurus,” and “Lebanon”, which reflect geographic structure of the species natural range. Minor genetic admixture between Lebanese and East Taurus populations of A. cilicica was found, but no genetic admixture between Lebanese populations and West Taurus. We argue that significant genetic differentiation discovered among areas of species occurrence is probably due to the effect of long-lasting genetic isolation that started in that region along with the Pleistocene climatic alternation and was further enhanced with human-induced deforestations.

Sex influences the taxanes content in Taxus baccata

Like other species of the genus Taxus, European yew trees contain taxanes, including paclitaxel (T) and its precursor 10-deacetylbaccatin III (10-DAB). Taxanes are one of the most effective anticancer drugs. This study was undertaken to describe the levels and patterns of taxane variation in the Sudetian region (SW Poland). Paclitaxel (T) and 10-deacetylbaccatin III (10-DAB) concentrations were analysed in five populations. Needles and twigs were analysed from 60 individuals (30 males and 30 females) in each population. In addition, morphometric measurements were taken in the populations to obtain light intensity coefficients (specific leaf area, SLA). High variability in the taxane contents at both intra and interpopulational levels was found. Nevertheless, females had a significantly higher taxane content compared to males. Because taxanes are carbon-based secondary metabolites, females have higher rate of gas exchange of females compared to males. This was probably an adaptation to greater reproductive effort incurred by females. In this regard, female individuals seem to be better for selecting elite cultivars with a higher taxane production. The relationship between light intensity and taxane content was not significant. Shading, important for optimizing crop production, should not reduce the concentration of taxanes.

Relative strength of fine-scale spatial genetic structure in paternally vs biparentally inherited DNA in a dioecious plant depends on both sex proportions and pollen-to-seed dispersal ratio

In plants, the spatial genetic structure (SGS) is shaped mainly by gene dispersal and effective population density. Among additional factors, the mode of DNA inheritance and dioecy influence SGS. However, their joint impact on SGS remains unclear, especially in the case of paternally inherited DNA. Using theoretical approximations and computer simulations, here we showed that the relative intensity of SGS measured in paternally and biparentally inherited DNA in a dioecious plant population depends on both the proportion of males and the pollen-to-seed dispersal ratio. As long as males do not prevail in a population, SGS is more intense in paternally than biparentally inherited DNA. When males prevail, the intensity of SGS in paternally vs biparentally inherited DNA depends on the compound effect of sex proportions and the pollen-to-seed dispersal ratio. To empirically validate our predictions, we used the case of Taxus baccata, a dioecious European tree. First, we showed that mitochondrial DNA (mtDNA) in T. baccata is predominantly (98%) paternally inherited. Subsequently, using nuclear DNA (nuDNA) and mitochondrial microsatellite data, we compared the fine-scale SGS intensity at both marker types in two natural populations. The population with equal sex proportions showed stronger SGS in mtDNA than in nuDNA. On the other hand, we found lower SGS intensity in mtDNA than in nuDNA in the population with 67% males. Thus, the empirical results provided good support for the theoretical predictions, suggesting that knowledge about SGS in paternally vs biparentally inherited DNA may provide insight into effective sex proportions within dioecious populations.

Influence of biotic and abiotic factors on natural regeneration of European yew (Taxus baccata L.): A review

This study examines the factors affecting the lack of success in regeneration of natural populations of European yew. Among the numerous local factors that can be important in the existing populations, the lack of reproductive success is most probably due primarily to shading, combined with low temperatures in winter, impact of herbivores, and limitations associated with dioecy. In many cases it seems necessary to apply active protection measures supporting this species within its natural range of distribution. The major recommended actions include fencing of yew populations and thinning of the canopy.

Impact of Cameraria ohridella on Aesculus hippocastanum growth and long-term effects of trunk injection with pesticides

ABSTRACT Defoliation caused annually by Cameraria ohridella has a considerable impact on the general condition of horse chestnut trees. We investigated the consequences of tree endotherapy against this insect. Wood samples, leaves and insect specimens were collected ten years after the treatment (injection) with pesticides. Insect invasion was manifested in all investigated trees by distinct radial growth depression. Treatment resulted in a growth upturn, while non-treated trees maintained decreased growth. The overall foliage infestation level was lower in treated trees, but pupal mass and potential fecundity of insect females were not affected. Our study revealed a long-lasting, positive effect of endotherapy on trees’ appearance and growth.

Males and females of Juniperus communis L. and Taxus baccata L. show different seasonal patterns of nitrogen and carbon content in needles

Genders of dioecious species often show secondary sexual dimorphisms (not directly related to the sex organs), which may be related to reproductive demand for resources during the year. Our working hypothesis stated that phenology influences yearly sex-specific pattern of foliar nitrogen concentration in dioecious species. The concentration of carbon (C) and nitrogen (N) of last year’s needles (on part of twigs where strobili are bearing) was measured in 1-month intervals from March to November in Taxus baccata L. and Juniperus communis L. separately for males and females. Seasonal C concentration of needles was unrelated to gender, probably due to storage elsewhere in the plants. Needles of J. communis females had higher N concentration in March and April but this dropped to the same level as males after flowering and vegetative growth began. This suggests that females of J. communis, a species of N-poor habitats, have a long-term strategy of N storage. Nitrogen concentration was not different between the sexes during the rest of the growing season. In T. baccata, N concentration was higher in males throughout the analysed period, but the highest differences were in the period of intensive shoot elongation and radial growth. The high demand for N in the period of intensive growth and female cone maturation may result in restrictions in the vegetative growth of females. The results indicate that the time (phenology) and species-specific strategy significantly affect the concentration of N in females and males.