History and evolution of the afroalpine flora: in the footsteps of Olov Hedberg

The monumental work of Olov Hedberg provided deep insights into the spectacular and fragmented tropical alpine flora of the African sky islands. Here we review recent molecular and niche modelling studies and re-examine Hedberg’s hypotheses and conclusions. Colonisation started when mountain uplift established the harsh diurnal climate with nightly frosts, accelerated throughout the last 5 Myr (Plio-Pleistocene), and resulted in a flora rich in local endemics. Recruitment was dominated by long-distance dispersals (LDDs) from seasonally cold, remote areas, mainly in Eurasia. Colonisation was only rarely followed by substantial diversification. Instead, most of the larger genera and even species colonised the afroalpine habitat multiple times independently. Conspicuous parallel evolution occurred among mountains, e.g., of gigantism in Lobelia and Dendrosenecio and dwarf shrubs in Alchemilla. Although the alpine habitat was ~ 8 times larger and the treeline was ~ 1000 m lower than today during the Last Glacial Maximum, genetic data suggest that the flora was shaped by strong intermountain isolation interrupted by rare LDDs rather than ecological connectivity. The new evidence points to a much younger and more dynamic island scenario than envisioned by Hedberg: the afroalpine flora is unsaturated and fragile, it was repeatedly disrupted by the Pleistocene climate oscillations, and it harbours taxonomic and genetic diversity that is unique but severely depauperated by frequent bottlenecks and cycles of colonisation, extinction, and recolonisation. The level of intrapopulation genetic variation is alarmingly low, and many afroalpine species may be vulnerable to extinction because of climate warming and increasing human impact.

System drift and speciation

Even if a species’ phenotype does not change over evolutionary time, the underlying mechanism may change, as distinct molecular pathways can realize identical phenotypes. Here we use quantitative genetics and linear system theory to study how a gene network underlying a conserved phenotype evolves, as the genetic drift of small changes to these molecular pathways cause a population to explore the set of mechanisms with identical phenotypes. To do this, we model an organism’s internal state as a linear system of differential equations for which the environment provides input and the phenotype is the output, in which context there exists an exact characterization of the set of all mechanisms that give the same input–output relationship. This characterization implies that selectively neutral directions in genotype space should be common and that the evolutionary exploration of these distinct but equivalent mechanisms can lead to the reproductive incompatibility of independently evolving populations. This evolutionary exploration, or system drift, proceeds at a rate proportional to the amount of intrapopulation genetic variation divided by the effective population size (Ne). At biologically reasonable parameter values this process can lead to substantial interpopulation incompatibility, and thus speciation, in fewer than Ne generations. This model also naturally predicts Haldane’s rule, thus providing another possible explanation of why heterogametic hybrids tend to be disrupted more often than homogametes during the early stages of speciation.

Variation and genetic structure of Serratula lycopifolia populations (Vill.) Kern. (Asteraceae) in Poland and adjacent regions

AFLPs were used to analyze the genetic variability of <em>Serratula lycopifolia</em>, one of the rarest plant species in Central and Western Europe, in six populations from the Wyżyna Małopolska upland (Poland), White Carpathian Mts (Slovakia and Czech Republic) and Podolian Upland (Ukraine). The results of polymorphism, PCoA and neighbor-net analyzes showed similar and relatively low genetic variation and high genetic similarity of individuals within each Polish population but there were differences between those populations. The population from Slovakia also showed comparatively high intrapopulation homogeneity and evident genetic separation from the other studied populations. Intrapopulation genetic variation was higher in the Czech and Ukrainian populations. However, AMOVA analyses revealed no significant differentiation at population and regional levels. The estimated low genetic diversity in the populations from Poland and Slovakia may be due to genetic processes such as genetic drift and inbreeding in local populations resulting from their low abundance, and does not seem characteristic of the species as a whole. These genetic analyzes make it clear that the Polish and Slovakian populations need support programmes to maintain their genetic variation. Measures should focus on increasing the number of individuals in the populations and on protecting their habitat.

The reasons for low intrapopulation genetic variation in Lamium incisum Willd

The reasons for low intrapopulation genetic variation in Lamium incisum Willd The paper presents results of a study which aim was preliminary screening of intrapopulation genetic variability in Lamium incisum Willd. This weed species is rarely distributed in Poland and lessening its count during the last years. As a plant inhabiting anthropogenic sites it is exposed to extreme conditions and disturbances caused mostly by the progressive intensification of agriculture. In order to investigate the genetic variability of the selected population markers of ISSR category were used. The analysis of chosen individuals with use of three ISSR primers revealed total of 49 loci, of which only 15 were polymorphic. Nei's gene diversity index (HE=0.099) and the mean number of alleles per locus (AE=1.160) indicated low genetic diversity within the examined population. The research presented in this paper allows for a better learning of the genetic variability of the investigated species and considers probable factors influencing its level.

Genetic variation in North American leafy spurge (Euphorbia esula) determined by DNA markers

Levels of inter- and intrapopulation genetic variation were determined in five North American populations of leafy spurge using chloroplast DNA (cpDNA) RFLPs and RAPD markers. Thirteen plastome types were identified among 123 individuals collected from five geographically separated populations. Number of plastomes within a population ranged from one to seven, with four of the populations having a predominate type plus one or more rarer types. Some plastome types were shared by populations, but plastome distribution among populations was nonrandom. RAPD markers indicated greatest relatedness among individuals within a population. Relatedness among populations as established through RAPDs was greater for geographically closer populations; this relationship was not observed for cpDNA markers. Differences in the range of movement for pollen and seed may account for differences between results of the cpDNA and RAPD analyses. The high degree of genetic variability among North American leafy spurge suggests possible multiple introductions or a high degree of variability within leafy spurge populations in its native range.

INTRAPOPULATION SIZE VARIATION OF FREE-LIVING AND TREE-BORING COLEOPTERA

Intrapopulation size variation was studied by means of length measurements quoted in taxonomic literature and from material of various groups of Coleoptera collected in the field. The degree of variation was significantly different among groups, and generally the free-living groups had lower intrapopulation size variation than most of the tree-boring and the parasitoid groups. Several tree-boring groups (e.g. Scolytidae, Curculionidae), however, had a comparatively low variation. A high intrapopulation size variation is common in species whose larvae are unable to choose and determine their own nutritional situation. Such larvae have a restricted mobility and the quality of their food is unpredictable. This is characteristic for most of the tree-boring groups. A high size variation increases the niche width of the species and probably has a buffering effect in unpredictable environments. Those tree-borers that are able to reduce the degree of unpredictability (i. e. by parental care, specialization in choice of microhabitat and in larval morphology, as in Scolytidae) have a rather low intrapopulation size variation. There are two possibilities regarding the genetic nature of the high size variation: (1) The population contains a variety of phenotypes with genetically fixed size, and (2) each individual is flexible with the possibility of becoming large or small depending upon the nutritional conditions. Possibility (1) is in agreement with the theories of a correlation between environmental heterogeneity and a high intrapopulation genetic variation. Free-living species and those tree-borers with less intrapopulation size variation are usually subject to more uniform conditions, and if adverse conditions do arise, these species usually fail to complete their development rather than produce smaller adults.