David E. V. Harter

Bulbils contra seeds: reproductive investment in two species of Gagea (Liliaceae)

The reproductive biology of the sympatric species Gagea lutea and Gagea spathacea was analyzed morphologically and by resource allocation measurements. Both taxa reproduce vegetatively by bulbils. The hexaploid G. lutea regularly forms seeds, but flowering plants cease to produce bulbils. Seed set was never observed in nonaploid G. spathacea which does not stop vegetative reproduction when flowering. In this species, the pollen contains a high proportion of non-viable grains. Already sterile plants invest more resources (per cent of total nitrogen) into bulbils than G. lutea (10.9 vs. 5.9%). For flowering plants, the respective values are 6.1% (flowers) plus 18.4% (bulbils) for G. spathacea versus 14.8% (flowers only) for G. lutea. G. spathacea lost the ability to reproduce sexually and relies solely on vegetative reproduction. This seems to require the breakdown of the switch mechanism between the bulbil and flower formation (as in G. lutea) and a higher net investment in reproduction, hampering individual growth.

A Comparison of Genetic Diversity and Phenotypic Plasticity among European Beech (Fagus sylvatica L.) Populations from Bulgaria and Germany under Drought and Temperature Manipulation

Premise of research. In the future, ecosystems will have to deal with climate warming in combination with increasing frequency and magnitude of extreme weather events such as drought. Adaptive phenotypic plasticity enables plants to respond to environmental variability and is likely to buffer impacts of climate change. Therefore, factors that influence the phenotypic plasticity of plant populations must be identified to assess climate change outcomes and support conservation measures. Genetic diversity in many temperate plant species is known to vary among regions and populations, largely as a result of their phylogeographic history during the late Pleistocene and Holocene. Here, we argue that high (neutral) genetic diversity of populations might represent increased probability of possessing alleles or allele combinations that are advantageous or more capable in terms of average response capacities to environmental change. Methodology. We test this idea for European beech (Fagus sylvatica) by investigating response patterns of plant growth and leaf phenology to drought and warming treatments in a common-garden experiment with seedlings of six populations from Bulgaria and Germany. Phenotypic plasticity of populations was assessed and correlated with allozyme diversity. Populations differed in their plasticity to warming with respect to timing of leaf unfolding and senescence as well as in their drought plasticity in terms of height increment (marginally not significant), with some populations showing consistently high plasticity among traits. Pivotal results. Measures of genetic diversity showed an interregional structure according to known phylogeographic patterns. Height increment plasticity showed a significant positive correlation with genetic variation (allelic diversity) at the population level. Conclusions. Our results suggest general differences in phenotypic plasticity among populations and a potential influence of genetic diversity on the average plasticity. Besides its evolutionary value, genetic diversity might thus be an important property of plant populations for their short-term response capability against adverse effects of climate change.

Spatial and ecological population genetic structures within two island-endemic Aeonium species of different niche width

Abstract The Crassulacean genus Aeonium is a well‐known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra‐island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of this study was to investigate intraspecific genetic structures and to identify spatial and ecological drivers of genetic population differentiation on the island scale. We analyzed inter simple sequence repeat variation within two island‐endemic Aeonium species of La Palma: one widespread generalist that covers a large variety of different habitat types (Ae. davidbramwellii) and one narrow ecological specialist (Ae. nobile), in order to assess evolutionary potentials on this island. Gene pool differentiation and genetic diversity patterns were associated with major landscape structures in both species, with phylogeographic implications. However, overall levels of genetic differentiation were low. For the generalist species, outlier loci detection and loci–environment correlation approaches indicated moderate signatures of divergent selection pressures linked to temperature and precipitation variables, while the specialist species missed such patterns. Our data point to incipient differentiation among populations, emphasizing that ecological heterogeneity and topographical structuring within the small scales of an island can foster evolutionary processes. Very likely, such processes have contributed to the radiation of Aeonium on the Canary Islands. There is also support for different evolutionary mechanisms between generalist and specialist species.