Diverted development of reproductive organs: A source of morphological innovation in land plants

Recent discussions of animal development, particularly at the level of molecular genetics, have emphasized modularity, dissociation and co-option as basic principles of evolutionary developmental biology. These concepts are discussed in relation to two specific structural innovations in land plant evolution: the leaves (microphylls) of lycopsids, and the interseminal scales ofBennettitales. Both structures appear to have been derived evolutionarily by the diverted development of reproductive organs. In the case of lycopsids, recent analyses of phylogenetic relationships suggest that leaves are sterilized sporangia modified for photosynthetic assimilation. In the case ofBennettitales, structural data suggest that the interseminal scales are sterilized cupules modified for protection of the ovules. In both cases, multiplication of reproductive organs seems to have accentuated functional redundancy, and together with the developmental autonomy (dissociation) already inherent in the modular construction of plants, appears to have facilitated sterilization and co-option of some of these structures for new purposes. Numerous other examples in plants illustrate the same principles.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

兰坪铅锌尾矿区豆科根瘤菌遗传多样性ARDRA分析

通过16S rDNA扩增产物限制性片段长度多态性分析(ARDRA),对兰坪铅锌尾矿区豆科植物根瘤菌的遗传多样性进行了研究。采用限制性内切酶Hae Ⅲ、Hind Ⅲ、Hinf Ⅰ和Taq Ⅰ对16S rDNA扩增产物进行了酶切分型,根据ARDRA酶切图谱的不同,进行树状聚类。结果表明:49株根瘤菌在40%的相似水平上按氮含量不同及铅锌含量的采集地不同分别聚为OTU1、OTU2和OTU33个群,说明根瘤菌的遗传多样性及分布与土壤中的氮含量和铅锌含量有关。代表菌株的16S rDNA测序结果分析表明,它们在系统发育树上属于Rhizobium sp.、Sinorhizobium sp.和Bradyrhizobium sp.3个系统发育分支,进一步说明兰坪铅锌尾矿区豆科植物根瘤菌多样性较丰富。     

Long-distance dispersal vs vicariance: the origin and genetic diversity of alpine plants in the Spanish Sierra Nevada

Here, we investigated the origin and genetic diversity of four alpine plant species co-occurring in the Spanish Sierra Nevada and other high mountains in south-western Europe by analysis of amplified fragment length polymorphisms (AFLPs). In Kernera saxatilis, Silene rupestris and Gentiana alpina we found intraspecific phylogroups corresponding to mountain regions as predicted by the vicariance hypothesis. Moreover, genetic distances between Sierra Nevada and Pyrenees populations were always higher than those between populations from the Pyrenees and the south-western Alps/Massif Central. This suggests successive disruption of gene exchange between mountain ranges as postglacial climatic warming proceeded from south to north. In Papaver alpinum, our data indicate that a central Pyrenean population arose via long-distance dispersal from the Sierra Nevada, and that vicariant separation events between the Sierra Nevada and the Pyrenees and between the Pyrenees and the south-western Alps occurred simultaneously. Overall, Sierra Nevada populations of all species investigated here preserve unexpectedly high (or not exceptionally reduced) genetic diversity. This testifies to the important influence of long-term isolation, i.e. vicariance, on genetic diversity through fostering the accumulation of new mutations and/or the fixation of ancestral ones.     

Mapping the geographical distribution of genetic variation in the genus Lens for the enhanced conservation of plant genetic diversity

Plant genetic resource conservation strategies, informed by an understanding of the geographical distribution of genetic variation within species, are likely to result in a wider representation of conserved diversity in ex situ gene banks and in situ genetic reserves. The main objective of this study was to map the geographical distribution of genetic variation, as revealed by randomly amplified polymorphic DNA (RAPDs), in four wild relatives of the cultivated lentil, namely Lens culinaris ssp. orientalis, L. odemensis, L. ervoides and L. nigricans . Areas of high diversity and unique diversity were located for each taxon, and regions where further germplasm collection was most likely to yield novel genetic variation were identified. There were centres of diversity for L. culinaris ssp. orientalis in southeast Turkey and northwest Syria, and in south Syria and Jordan. A centre of diversity was found to exist in Sweida province, south Syria, for L. odemensis , and for L. ervoides along the coastal border region between Syria and Turkey stretching down along the Syrian coast. There was a centre of diversity for L. nigricans in west Turkey. Analytical techniques previously used at the species level were found to be useful at the genotypic level to objectively target areas for future collection missions, to increase diversity in ex situ collections and to target areas for in situ conservation.     

A simulation study of mutations in the genetic regulatory hierarchy for butterfly eyespot focus determination

The color patterns on the wings of butterflies have been an important model system in evolutionary developmental biology. A recent computational model tested genetic regulatory hierarchies hypothesized to underlie the formation of butterfly eyespot foci [Evans, T.M., Marcus, J.M., 2006. A simulation study of the genetic regulatory hierarchy for butterfly eyespot focus determination. Evol. Dev. 8, 273-283]. The computational model demonstrated that one proposed hierarchy was incapable of reproducing the known patterns of gene expression associated with eyespot focus determination in wild-type butterflies, but that two slightly modified alternative hierarchies were capable of reproducing all of the known gene expressions patterns. Here we extend the computational models previously implemented in Delphi 2.0 to two mutants derived from the squinting bush brown butterfly (Bicyclus anynana). These two mutants, comet and Cyclops, have aberrantly shaped eyespot foci that are produced by different mechanisms. The comet mutation appears to produce a modified interaction between the wing margin and the eyespot focus that results in a series of comet-shaped eyespot foci. The Cyclops mutation causes the failure of wing vein formation between two adjacent wing-cells and the fusion of two adjacent eyespot foci to form a single large elongated focus in their place. The computational approach to modeling pattern formation in these mutants allows us to make predictions about patterns of gene expression, which are largely unstudied in butterfly mutants. It also suggests a critical experiment that will allow us to distinguish between two hypothesized genetic regulatory hierarchies that may underlie all butterfly eyespot foci.     

Methods for minimizing the loss of genetic diversity in conserved populations with overlapping generations

Minimization of the average coancestry in a population has been theoretically proven to be the most efficient method to preserve genetic diversity. In the present study, based on a population genetic model, two methods to minimize the average coancestry in populations with overlapping generations were developed. For a given parental coancestry structure, the first method (OG) minimizes the average coancestry in the next generation, and the second method (LT) is designed to minimize the long-term accumulation of coancestry. The efficiencies of the two methods were examined by stochastic simulation. Compared to random choice of parents, the annual effective population sizes under the two proposed methods increased 2–3 folds. The difference among the two methods was small in a population with short generation interval. For populations with long generation intervals, the OG method showed a slightly larger annual effective size in an initial few years. However, in the subsequent years, the LT method gave a 5–15% larger annual effective size than the OG method. From these results, it is suggested that the LT method would be preferred to the OG method in most practical situations.     

Mandible asymmetry and genetic diversity in island populations of the common shrew, Sorex araneus

Mandibles from 13 island and six mainland populations of common shrews from the west coast of Scotland were subjected to geometric morphometric analysis in order to investigate the relationship between genetic diversity and fluctuating asymmetry. Although population mean shape fluctuating asymmetry (FA) and size FA were significantly inversely correlated with population genetic diversity this result was substantially due to one island. Sanda, the smallest island with by far the lowest genetic diversity, also had the highest FA. When Sanda was removed from the analysis, the relationship was not significant. There was no relationship between genetic diversity and FA at the individual level, whether measured as mean locus heterozygosity or d(2). In general, if genetic variation affects FA at all, the effect is weak and may only be of biological interest in very small populations.     

The role of environment in shaping the genetic diversity of the subalpine mosquito,Aedes rusticus (Diptera,Culicidae)

The relative involvement of larval dietary tolerance to the leaf-litter toxic polyphenols in shaping population genetic structure of the subalpine mosquito Aedes rusticus was examined. This was compared with other parameters such as geographical range, type of vegetation surrounding the breeding site, and occurrence of annual larvicidal treatments. Population genetic structure was analysed at 10 presumed neutral polymorphic isoenzyme loci. Toxicological comparisons involved standard bioassays performed on larvae fed on toxic decomposed leaf litter. Significant overall genetic differentiation was observed among the 22 studied populations and within the five defined geographical groups. Analysis of molecular variance revealed an absence of relation between genetic and environmental parameters, genetic variance being essentially found within populations. This suggested that the larval dietary tolerance to the toxic leaf litter and the other studied parameters poorly influence population genetic structure. The local adaptation of subalpine mosquito populations to the surrounding vegetation thus appears as a labile trait. Such a dynamic adaptation is also suggested by the correlation between geographical and toxicological distances and the correlation between dietary tolerance to the leaf-litter toxic polyphenols and annual larvicidal treatments.     

Evidence for genetic drift in the diversification of a geographically isolated population of the hyperthermophilic archaeon Pyrococcus

Genetic drift is a mechanism of population divergence that is important in the evolution of plants and animals but is thought to be rare in free-living microorganisms because of their typically large population sizes and unrestricted means of dispersal. We used both phylogenetic and insertion sequence (IS) element analyses in hyperthermophilic archaea of the genus Pyrococcus to test the hypothesis that genetic drift played an important role in the diversification of these microorganisms. Multilocus sequence typing of a collection of 36 isolates of Pyrococcus, from different hydrothermal systems in the Pacific Ocean and the Mediterranean Sea, revealed that Pyrococcus populations from different geographic locations are genetically differentiated. Analysis of IS elements in these isolates exposed their presence in all individuals of only one geographically isolated lineage, that of Vulcano Island in the Mediterranean Sea. Detailed sequence analysis of six selected IS elements in the Vulcano population showed that these elements cause deleterious genomic alterations, including inactivation of gene function. The high frequency of IS elements in the sampled population together with their observed harmful effects in the genome of Pyrococcus provide molecular evidence that the Vulcano Island population of Pyrococcus is geographically isolated and that those genetic mobile elements have been brought up to high frequency by genetic drift. Thus, genetic drift resulting from physical isolation should be considered as a factor influencing differentiation in prokaryotes.     

The selfing syndrome: a model for studying the genetic and evolutionary basis of morphological adaptation in plants

Background

In angiosperm evolution, autogamously selfing lineages have been derived from outbreeding ancestors multiple times, and this transition is regarded as one of the most common evolutionary tendencies in flowering plants. In most cases, it is accompanied by a characteristic set of morphological and functional changes to the flowers, together termed the selfing syndrome. Two major areas that have changed during evolution of the selfing syndrome are sex allocation to male vs. female function and flower morphology, in particular flower (mainly petal) size and the distance between anthers and stigma.

Scope

A rich body of theoretical, taxonomic, ecological and genetic studies have addressed the evolutionary modification of these two trait complexes during or after the transition to selfing. Here, we review our current knowledge about the genetics and evolution of the selfing syndrome.

Conclusions

We argue that because of its frequent parallel evolution, the selfing syndrome represents an ideal model for addressing basic questions about morphological evolution and adaptation in flowering plants, but that realizing this potential will require the molecular identification of more of the causal genes underlying relevant trait variation.     

Small population size and extremely low levels of genetic diversity in island populations of the platypus, Ornithorhynchus anatinus

Genetic diversity generally underpins population resilience and persistence. Reductions in population size and absence of gene flow can lead to reductions in genetic diversity, reproductive fitness, and a limited ability to adapt to environmental change increasing the risk of extinction. Island populations are typically small and isolated, and as a result, inbreeding and reduced genetic diversity elevate their extinction risk. Two island populations of the platypus, Ornithorhynchus anatinus, exist; a naturally occurring population on King Island in Bass Strait and a recently introduced population on Kangaroo Island off the coast of South Australia. Here we assessed the genetic diversity within these two island populations and contrasted these patterns with genetic diversity estimates in areas from which the populations are likely to have been founded. On Kangaroo Island, we also modeled live capture data to determine estimates of population size. Levels of genetic diversity in King Island platypuses are perilously low, with eight of 13 microsatellite loci fixed, likely reflecting their small population size and prolonged isolation. Estimates of heterozygosity detected by microsatellites (H(E)= 0.032) are among the lowest level of genetic diversity recorded by this method in a naturally outbreeding vertebrate population. In contrast, estimates of genetic diversity on Kangaroo Island are somewhat higher. However, estimates of small population size and the limited founders combined with genetic isolation are likely to lead to further losses of genetic diversity through time for the Kangaroo Island platypus population. Implications for the future of these and similarly isolated or genetically depauperate populations are discussed.     

A survey of equid mitochondrial DNA: Implications for the evolution, genetic diversity and conservation of Equus

The evolution, taxonomy and conservation of the genus Equuswere investigated by examining the mitochondrial DNA sequences of thecontrol region and 12S rRNA gene. The phylogenetic analysis of thesesequences provides further evidence that the deepest node in thephylogeny of the extant species is a divergence between twolineages; one leading to the ancestor of modern horses (E.ferus, domestic and przewalskii) and the other to thezebra and ass ancestor, with the later speciation events of the zebrasand asses occurring either as one or more rapid radiations, or withextensive secondary contact after speciation. Examination of the geneticdiversity within species suggested that two of the E. hemionussubspecies (E. h. onager and E. h. kulan) onlyrecently diverged, and perhaps, are insufficiently different to beclassified as separate subspecies. The genetic divergence betweendomestic and wild forms of E. ferus (horse) and E.africanus (African ass) was no greater than expected within anequid species. In E. burchelli (plains zebra) there was anindication of mtDNA divergence between populations increasing withdistance. The implications of these results for equid conservation arediscussed and recommendations are made for conservation action.     

Low genetic diversity in the vulnerable Goitred Gazelle,Gazella subgutturosa (Cetartiodactyla: Bovidae), in Iran: potential genetic consequence of recent population declines

The Goitered Gazelle, Gazella subgutturosa, is the most widespread gazelle species in the Middle East and central Asia inhabiting desert and semi-desert habitats. Today it is threatened and its geographic range and population size have experienced significant decline in the last decades. In Iran, the remnant populations are confined to fragmented habitats. We aimed to characterise genetic diversity and phylogenetic status of the populations of Goitered Gazelle in Central Iran and to evaluate the potential effect of a historic population bottleneck on the genetic variation of today’s population. We used noninvasive sampling to uncover structure and level of genetic variation in a fragment of the cytochrome-b gene from 170 samples. Genealogical analyses were performed using HKY+I model and phylogenetic trees reconstructed using Bayesian inference and maximum likelihood. We found extremely low levels of genetic variation, with altogether only five haplotypes in samples from different populations. Overall haplotype diversity was 0.081 and nucleotide diversity 0.0003. The mean observed mismatch between any two sequences was 0.093 with the largest peak for small numbers. The mismatch distribution fit the model of population expansion and suggested that gazelles had experienced a sudden expansion. An unrooted median-joining network analysis of mtDNA haplotypes showed a star-like structure which few mutations steps separating the haplotypes from other regions. Our findings strengthen the urgency of preserving the species’ genetic diversity to prevent local extinction.     

Founding events in species invasions: genetic variation, adaptive evolution, and the role of multiple introductions

Invasive species are predicted to suffer from reductions in genetic diversity during founding events, reducing adaptive potential. Integrating evidence from two literature reviews and two case studies, we address the following questions: How much genetic diversity is lost in invasions? Do multiple introductions ameliorate this loss? Is there evidence for loss of diversity in quantitative traits? Do invaders that have experienced strong bottlenecks show adaptive evolution? How do multiple introductions influence adaptation on a landscape scale? We reviewed studies of 80 species of animals, plants, and fungi that quantified nuclear molecular diversity within introduced and source populations. Overall, there were significant losses of both allelic richness and heterozygosity in introduced populations, and large gains in diversity were rare. Evidence for multiple introductions was associated with increased diversity, and allelic variation appeared to increase over long timescales (~100 years), suggesting a role for gene flow in augmenting diversity over the long‐term. We then reviewed the literature on quantitative trait diversity and found that broad‐sense variation rarely declines in introductions, but direct comparisons of additive variance were lacking. Our studies of Hypericum canariense invasions illustrate how populations with diminished diversity may still evolve rapidly. Given the prevalence of genetic bottlenecks in successful invading populations and the potential for adaptive evolution in quantitative traits, we suggest that the disadvantages associated with founding events may have been overstated. However, our work on the successful invader Verbascum thapsus illustrates how multiple introductions may take time to commingle, instead persisting as a ‘mosaic of maladaptation’ where traits are not distributed in a pattern consistent with adaptation. We conclude that management limiting gene flow among introduced populations may reduce adaptive potential but is unlikely to prevent expansion or the evolution of novel invasive behaviour.     

Influence of genetic architecture on contemporary local evolution in the soapberry bug,Jadera haematoloma: artificial selection on beak length

Little is known about the influence of genetic architecture on local adaptation. We investigated the genetic architecture of the rapid contemporary evolution of mouthparts, the flight polymorphism and life history traits in the soapberry bug Jadera haematoloma (Hemiptera) using laboratory selection. The mouthparts of these seed‐feeding bugs have adapted in 40–50 years by decreasing in length following novel natural selection induced by a host switch to the seeds of an introduced tree with smaller fruits than those of the native host vine. Laboratory selection on beak length in both an ancestral population feeding on the native host and a derived population feeding on the introduced host reveals genetic variance allowing a rapid response (heritabilities of 0.51–0.87) to selection for either longer or shorter beaks. This selection resulted in reverse evolution by restoring long beaks in the derived population and forward evolution by re‐creating short beaks in the ancestral bugs. There were strong genetic correlations (0.68–0.84) in both populations between beak lengths and the frequency of flight morphs, with short beaks associated with short wings. The results reveal a genetically interrelated set of adaptive multivariate traits including both beak length and flight morph. This suite of traits reflects host plant patchiness and seeding phenology. Weaker evidence suggests that egg mass and early egg production may be elements of the same suite. Reversible or forward evolution thus may occur in a broad set of genetically correlated multivariate traits undergoing rapid contemporary adaptation to altered local environments.     

Quantifying the genetic component of phenotypic variation in unpedigreed wild plants: tailoring genomic scan for within-population use

The study of adaptive genetic variation in natural populations is central to evolutionary biology. Quantitative genetics methods, however, are hardly applicable to long-lived organisms, and current knowledge on adaptive genetic variation in wild plants mostly refers to annuals and short-lived perennials. Studies on long-lived species are essential to explore possible life-history correlates of genetic variation, selection, and trait heritability. In this paper, we propose a method based on molecular markers to quantify the genetic basis of individual phenotypic differences in wild plants under natural conditions. Rather than focusing on inferring individual relatedness to estimate the heritability of phenotypic traits, we directly estimate the proportion of observed phenotypic variance that is statistically accounted for by genotypic differences between individuals. This is achieved by (i) identifying loci that are correlated across individuals with the phenotypic trait of interest by means of an amplified fragment length polymorphism (AFLP)-based explorative genomic scan, and (ii) fitting multiple regression and linear random effect models to estimate the effects of genotype, environment and genotype × environment on phenotypes. We apply this method to estimate genotypic and environmental effects on cumulative maternal fecundity in a wild population of the long-lived Viola cazorlensis monitored for 20 years. Results show that between 56–63% (depending on estimation method) of phenotypic variance in fecundity is accounted for by genotypic differences in 11 AFLP loci that are significantly related to fecundity. Genotype × environment effects accounted for 38% of fecundity variance, which may help to explain the unexpectedly high levels of genetic variance for fecundity found.     

Chromosomes tell half of the story: the correlation between karyotype rearrangements and genetic diversity in sedges,a group with holocentric chromosomes

Chromosome rearrangements may affect the rate and patterns of gene flow within species, through reduced fitness of structural heterozygotes or by reducing recombination rates in rearranged areas of the genome. While the effects of chromosome rearrangements on gene flow have been studied in a wide range of organisms with monocentric chromosomes, the effects of rearrangements in holocentric chromosomes—chromosomes in which centromeric activity is distributed along the length of the chromosome—have not. We collected chromosome number and molecular genetic data in Carex scoparia, an eastern North American plant species with holocentric chromosomes and highly variable karyotype (2n = 56–70). There are no deep genetic breaks within C. scoparia that would suggest cryptic species differentiation. However, genetic distance between individuals is positively correlated with chromosome number difference and geographic distance. A positive correlation is also found between chromosome number and genetic distance in the western North American C. pachystachya (2n = 74–81). These findings suggest that geographic distance and the number of karyotype rearrangements separating populations affect the rate of gene flow between those populations. This is the first study to quantify the effects of holocentric chromosome rearrangements on the partitioning of intraspecific genetic variance.     

Population structure, genetic diversity and host specificity of the parasitic weedStriga hermonthica (Scrophulariaceae) in Sahel

Seed proteins of individual plants from 14 populations ofStriga hermonthica growing on sorghum, millet, maize and wild grasses in Burkina Faso, Mali and Niger were studied using gel electrophoresis in order to assess the population structure and genetic diversity of the parasitic weed. The relative intensity of the different bands within a pattern was used to depict the genotypic constitution of each sample. Genotypic frequencies conformed to Hardy-Weinberg expectations in 13 populations out of 14 for the two loci that were interpreted. Heterozygote deficiencies could be the result of the Wahlund effect. The genetic divergence between populations appears to be low for bothAdh andGot loci. Thus, the physiological specialization for a particular host could be a recent phenomenon. A low host specificity ofS. hermonthica populations could affect the efficiency of introducing new resistant cultivars as a control measure against the parasitic weed.