The effect of herbivores on genotypic diversity in a clonal aquatic plant

In clonal plants, vegetative parts may outcompete seeds in the absence of disturbance, limiting the build‐up of genotypic diversity through repeated seedling recruitment (RSR). Herbivory may provide disturbance and trigger establishment of strong colonizers (seeds) at the expense of strong competitors (clonal propagules). In the clonal aquatic fennel pondweed Potamogeton pectinatus, two distinct herbivore guilds may modify the dynamics of propagation. In winter, Bewick's swans may deplete patches of tubers, promoting seedling establishment in spring. In summer, seed consumption by waterfowl can reduce the density of viable seeds but grazing may also reduce tuber production and hence facilitate seedling establishment. This study is among the first to experimentally test herbivore impact on plant genotypic diversity. We assess the separate and combined effects of both herbivore guilds on genotypic diversity and structure of fennel pondweed beds. Using microsatellites, we genotyped P. pectinatus from an exclosure experiment and assessed the contribution of herbivory, dispersal and sexual reproduction to the population genetic structure. Despite the predominance of clonal propagation in P. pectinatus, we found considerable genotypic diversity. Within the experimental blocks, kinship among genets decreased with geographic distance, clearly identifying a role for RSR in the maintenance of genotypic diversity within the fennel pondweed beds. However, over a period of five years, none of the herbivory treatments affected genotypic diversity. Hence, sexual reproduction on a local scale is important in this putatively clonal plant and possibly sufficient to ensure a relatively high genotypic diversity even in the absence of herbivores. Although we cannot preclude a role of herbivory in shaping genotypic diversity of a clonal plant, after five years of exclusion of the two investigated herbivore guilds no measurable effect on genotypic diversity was detected.     

Intraspecific genotypic diversity in plants

Variations in the nuclear DNA, mainly as a result of quantitative modulations of DNA repeats belonging to different sequence families of satellite DNA and to the activity of transposable elements, have been assessed within several angiosperm species. These variations alter the amount and organization of the DNA and therefore the genotype, rather than the genome proper. They take place on an evolutionary time scale as the result of selection processes after the occurrence of uncontrolled events in the genome or may be due to direct responses of plant genomes to environmental stimuli that occur under plant-level control within a short developmental period of a single generation. These DNA changes are correlated to changes in the developmental dynamics and phenotypic characteristics of the plants, and the capability to carry out genotypic variation is an evolutionary trait that allows plant species to adapt to different environmental conditions, as well as to the variability of conditions in a given environment. The link between developmental and environmental stimuli and repetitive DNA that elicits the intraspecific diversity of plant genotypes may provide models of evolutionary change that extend beyond the conventional view of evolution by allelic substitution and take into account epigenetic effects of the genome structure.     

Genetic ecotoxicology: The genotypic diversity approach

Organismal responses at the genetic level to exposure to environmental genotoxicants have been well documented. An elucidation of the molecular mechanisms involved with these responses, as well as an assessment of the changes that may occur to the genetic material, will provide an understanding of the potential for deleterious consequences at higher levels of biological organization. Moreover, modern procedures of molecular biology offer the hope that alterations and changes to genetic material can be readily detected.     

Genetic diversity in parthenogenetic triploid Paragonimus westermani

Paragonimus westermani is a medically important foodborne trematode occurring throughout southeast Asia. We have used molecular techniques to test the hypothesis that the parthenogenetic triploid form of P. westermani has arisen only once. Sources of data for comparison were: (a) restriction fragment length polymorphisms (RFLPs) of ribosomal internal transcribed spacers (ITS); and (b) 'fingerprint' patterns observed when genomic digests were probed with simple sequence repeats (ATT)10 and (ATGT)7. In all cases there were distinct differences among triploid isolates from southwest Japan, northeast China and Korea. These findings are considered in the context of previous cytogenetic, allozyme, mitochondrial-RFLP and partial cytochrome c-oxidase subunit I (COI) sequence studies and indicate that triploid lineages may have arisen independently on more than one occasion. We favour this view. An alternative explanation is that the triploids did have a single origin, but that different clonal lineages have undergone subsequent mutations.     

Population genetics of a successful invader: the marsh frog Rana ridibunda in Britain

We investigated the genetic outcome of successful invasion by an alien species, the marsh frog Rana ridibunda, in Britain. Twelve adults translocated from Hungary into Kent (Romney) in 1935 resulted rapidly in a large localized population. A further successful translocation in 1973 from Romney to Sussex (Lewes), together with other range extensions, provided an opportunity to test bottleneck effects during colonization events. Romney and Lewes frogs had similar genetic diversities to those in Hungary at 14 random amplified polymorphic DNA marker (RAPD) and five microsatellite loci. The introduced populations were, however, differentiated genetically from each other and from a reference population in Hungary. Fitness assessments (larval growth and survival) revealed no differences between the Lewes and Romney populations. Despite starting with few founders, significant bottleneck effects on R. ridibunda in Britain were therefore undetectable, presumably because population expansions were rapid immediately after the translocations.     

Old world versus new world: life-history alterations in a successful invader introduced across Europe

We examined differences in pumpkinseed (Lepomis gibbosus) life-history traits between native North American and introduced European populations, and tested three life-history predictions related to the effect of temperature, growth, waterbody size, and the presence/absence of predators on native and non-native populations. Pumpkinseed populations exhibit more ‘opportunistic’ traits (earlier maturity, smaller size at maturity, and higher reproductive allocation) in their introduced European range than those in their native range. Predictions of life-history traits were improved when indicators of juvenile growth rate (mean length at age 2), waterbody size (surface area), and thermal regime (air temperature degree-days above 10 °C) were incorporated into models along with continental location, but European pumpkinseed populations exhibit more opportunistic life-history traits than North American populations even when these factors are accounted for. Native pumpkinseed in waterbodies containing piscivores mature later and at a larger size, and have lower gonadosomatic indices than those in waterbodies lacking piscivores, whereas there is no significant difference in the same three life-history traits between European waterbodies containing or lacking piscivores. Because congeneric competitors of the pumpkinseed are absent from Europe, the apparent absence of a predator life-history effect there could also be due to the absence of the major sunfish competitors. In either case, the evolution and maintenance of more opportunistic traits in European pumpkinseed can likely be attributed to enemy release, and this may explain the successful establishment and spread of pumpkinseed in many parts of Europe.     

Plant genotypic diversity increases population size of a herbivorous insect

It is critical to incorporate the process of population dynamics into community genetics studies to identify the mechanisms of the linkage between host plant genetics and associated communities. We studied the effects of plant genotypic diversity of tall goldenrod Solidago altissima on the population dynamics of the aphid Uroleucon nigrotuberculatum. We found genotypic variation in plant resistance to the aphid in our experiments. To determine the impact of plant genotypic diversity on aphid population dynamics, we compared aphid densities under conditions of three treatments: single-genotype plots, mixed-genotype plots and mixed-genotype-with-cages plots. In the latter treatment plants were individually caged to prevent natural enemy attack and aphid movement among plants. The synergistic effects of genotypes on population size were demonstrated by the greater aphid population size in the mixed-genotype treatment than expected from additive effects alone. Two non-exclusive hypotheses are proposed to explain this pattern. First, there is a source-sink relationship among plant genotypes: aphids move from plant genotypes where their reproduction is high to genotypes where their reproduction is low. Second, natural enemy mortality is reduced in mixed plots in a matrix of diverse plant genotypes.     

Species versus genotypic diversity of a nitrogen-fixing plant functional group in a metacommunity

Exploring species and genetic diversity interactions provides new opportunities for furthering our understanding of the ecology and evolution of population and community dynamics, and for predicting responses of ecosystems to environmental change. Theory predicts that species diversity within communities and genetic diversity within populations will covary positively, because either species and genetic diversity interact synergistically or they respond in parallel fashion to common habitat conditions. We tested the hypothesis of positive covariation between species and genotypic diversity in a metacommunity of the species-rich southwest Australian flora. We hypothesised that the connection between genotypic diversity and species diversity is strong within functional groups, but weak or non-existent if the species considered extend beyond the functional group. We show that allelic richness of Daviesia triflora, an ant-dispersed pea, covaries positively with the species richness of six co-occurring nitrogen-fixing legume species. No pattern can be detected between allelic richness of D. triflora and species richness of ant-dispersed species when four non-legumes are added. We also show that genetic diversity of D. triflora is not governed by the same environmental factors that determine the presence of a group of large-shrub/small-tree species in the same metacommunity. This study shows that species and genetic diversity covariation are more likely to be confined to within, rather than between, plant functional groups.     

Dispersal and clonal diversity of North-European parthenogenetic earthworms

At least 15 earthworm species are known to reproduce parthenogenetically. Most of these retain meiosis but the chromosome set is duplicated before meiosis; alternatively there is mitosis instead of meiosis. In both cases the offspring are genetic copies of the parent worm. Parthenogens are always polyploid. Parthenogenesis is associated with a dispersal advantage: a single propagule suffices to establish a new population. We have studied the clone pool structure and dispersal of ecologically dissimilar polyploid parthenogenetic lumbricids in northern Europe using enzyme electrophoresis. The anthropochorous Octolasion cyaneum has a very low number of clones in populations that are located far away from each other. The opposite is the eurytopic Dendrobaena octaedra that has a wide array of clones in each population. The ripicolous Eiseniella tetraedra disperses with flowing water and possibly also through zoochory. On subarctic North-European mountains its clone pool decreases with increasing elevation. At the top there are a few but persistent clones. Small brooks carry propagules downstream, so that at the mouths of brooks clone pools are more diverse than higher up; again larger rivers carry clones downstream. Clone dispersal is relatively free in a freely flowing river, while dams stop propagules in harnessed rivers. The mouths of rivers have high E. tetraedra clone diversity. Clones disperse from these clone centers to islands formed through land uplift along the northern Baltic Sea. The annual turnover of clones is high on these islands. A survey of epigeic and endogeic parthenogens on the Åland islands which serve as stepping stones between Estonia, Finland and Sweden shows an invasion route of clones across the Baltic Sea. Anthropochory (Aporrectodea rosea and Octolasion cyaneum) and hydrochory (E.tetraedra and Dendrobaena octaedra) seem to play important roles in the clone pool formation on the Åland islands. Quite recently an exotic parthenogen Dichogaster bolaui has found a curious habitat in human settlements viz., the sewer pipe system. Many clonal earthworms show significant morphological and morphometric diversity in and between sample localities but we have failed to associate this variation with the clonal variability. It seems that local factors modify the morphometrics and morphology ultimately determined by the genotype of parthenogenetic earthworms.     

Competitive naïveté between a highly successful invader and a functionally similar native species

Naïveté can occur within any novel antagonistic interaction, and competitive forces play a fundamental role in shaping community structure, yet competitive naïveté has received very little attention in the literature to date. Naïveté towards a novel competitor is unlikely to result in immediate mortality, but could potentially affect access to resources and hence population growth and survival. In cases where only one species (either native or alien) remains naïve to the other, the species that recognizes the other will gain advantage, with implications for both the persistence of the native species and the establishment and spread of the invasive. The invasive black rat (Rattus rattus) has spread throughout many coastal areas of Australia, and competes with the native bush rat (Rattus fuscipes) wherever they coexist. As these rats have now been interacting for approximately 200 years, and multi-species rodent communities generally maintain their structure through olfactory communication, our aim was to determine whether these two very closely related species recognize one another’s odors and use them to mediate their interactions. We used remote-sensing cameras deployed in single- and mixed-species sites to record the behavioral responses of each species to conspecific, heterospecific and control odors. Black rats investigated bush rat odors but not vice versa, suggesting that bush rats may remain naïve towards their new competitor. Highly successful invaders such as black rats may possess traits such as broad recognition templates and rapid learning capabilities that contribute to their ongoing success in invading new environments.     

A successful crayfish invader is capable of facultative parthenogenesis: a novel reproductive mode in decapod crustaceans

Biological invasions are impacting biota worldwide, and explaining why some taxa tend to become invasive is of major scientific interest. North American crayfish species, particularly of the family Cambaridae, are prominent invaders in freshwaters, defying the "tens rule" which states that only a minority of species introduced to new regions become established, and only a minority of those become invasive and pests. So far, success of cambarid invaders has largely been attributed to rapid maturation, high reproductive output, aggressiveness, and tolerance to pollution. We provide experimental evidence that females of one cambarid species particularly widespread in Europe, the spiny-cheek crayfish Orconectes limosus, are capable of facultative parthenogenesis. Such reproductive mode has never before been recognized in decapods, the most diverse crustacean order. As shown by analysis of seven microsatellite loci, crayfish females kept physically separated from males produced genetically homogeneous offspring identical with maternal individuals; this suggests they reproduced by apomixis, unlike those females which mated with males and had a diverse offspring. Further research is needed to clarify what environmental conditions are necessary for a switch to parthenogenesis in O. limosus, and what role it plays in natural crayfish populations. However, if such reproductive plasticity is present in other cambarid crayfish species, it may contribute to the overwhelming invasive success of this group.     

Species diversity of grasses promotes genotypic diversity of clover populations in simulated communities

Recent studies in community genetics have demonstrated strong effects of intraspecific genetic variation on the diversity of interacting species but largely ignored the potential for effects of species diversity on genetic diversity, which could also create a positive correlation between these two levels of biodiversity. Here we investigated the role that species diversity of competitors could play in shaping the genotypic diversity of a focal species, using a modified version of an existing model of grass–clover dynamics. We simulated communities in which clover genotypes varied in their relative competitive ability when growing adjacent to different grass species. Under many parameter combinations, communities with greater species richness of grasses retained greater genotypic richness within the clover population. Increasing grass species richness effectively increased biotic environmental heterogeneity with respect to clover growth, thereby promoting the maintenance of genotypic diversity. This result depended on three conditions being met: (1) a sufficiently strong tradeoff among genotypes in their fitness when growing with different grass species, (2) partial de‐coupling of competition and facilitation, with grass and clover capable of sharing microsites rather than strictly excluding one another, and (3) sufficiently high rates of clover growth and clonal spread, which allowed clover genotypes to ‘track’ the shifting mosaic of grass species. Our results demonstrate that species diversity can act as an important promoter of genotypic diversity, and they provide testable predictions concerning the conditions that promote this outcome in nature.     

Effects of tree species diversity and genotypic diversity on leafminers and parasitoids in a tropical forest plantation

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Tasting novel foods and selecting nutrient content in a highly successful ecological invader,the common myna

Invasion success is dependent on the ability of a species to discover and exploit novel food resources. Within this context, individuals must be willing to taste novel foods. They must also be capable of evaluating the nutritional content of new foods, and selecting their relative intake in order to fulfil their nutritional needs. Whereas the former capacity is well studied, little is known about the latter capacity. First, using the common myna as a model avian invader species, we quantified the willingness of mynas to taste novel foods relative to familiar ones. Mynas readily tasted high protein (HP) novel foods and consumed them in higher quantities compared to a familiar food. Data showed that at three different levels – mixes, ingredients and macronutrients – intake could not be explained by a random model. In experiment 2, we confirmed that mynas were making their selection based on protein (P) content rather than a selection for novelty per se. When given the choice of three equally unfamiliar foods, mynas again ate disproportionately from the high protein relative to high lipid and high carbohydrate foods. Analysis revealed that mynas consumed amounts of protein that were closer to the ones in their natural diet. Finally, in experiment 3, we measured inter‐individual variation in innovation and exploration propensities, and examined associations with inter‐individual variation in consumption of specific macronutrients. This analysis revealed that individuals that selected HP pellets were more exploratory and individuals that selected HC pellets were quicker to solve the innovative foraging task. These findings indicate that not only the willingness to taste novel foods, but also the capacity to evaluate their nutritional content, might be central to the myna's substantial ecological success.     

Differentiation diversity of mouse parthenogenetic embryonic stem cells in chimeric mice

Recent studies have illustrated multiple differentiation potentials of embryonic stem cells (ESCs), derived from parthenogenetic embryos, to various kinds of cells (all three embryonic germ layers). However, differentiation diversity of the parthenogenetic ESCs (PgESCs) in vivo remains to be elucidated. In the present study, we established mouse PgESC-lines and observed their contribution diversity in vivo by producing chimeric mice using embryos possessing single nucleotide polymorphisms of mitochondrial DNA (mtDNA) as hosts. Based on southern blot analysis using specific probes to detect the SNPs on mtDNA, PgESC-derived mtDNA were contained in many organs such as brain, lung, and heart of the chimeric mouse. We concluded that PgESCs contributed to various internal organs in vivo, and that they were also stably maintained in adult animals.     

DNA fingerprints of Bombyx mori L. Testing of genotypic variability of parthenogenetic strains.

A comparative analysis of the total cellular DNA in certain parthenogenetic specimens of the silkworm (Bombyx mori), produced from the females of the parthenogenetic strains by two types of parthenogenesis, has been performed through the application of the DNA fingerprinting method based on M13 phage DNA as a hybridization probe. It has been shown that parental specimens and their genetically identical off-springs produced through ameiotic parthenogenesis have identical patterns of hybridization with the hypervariable DNA fragments. The off-springs produced through the meiotic type of parthenogenesis have individual-specific patterns of hybridization, revealing a high level of polymorphism of individual genotypes. The results obtained testify to the effectiveness and reliability of this promising method for identification of genotypic variability, marking and genomic characterization of parthenogenetic clones in the silkworm.     

Effects of native species diversity and resource additions on invader impact

Theory and empirical work have demonstrated that diverse communities can inhibit invasion. Yet, it is unclear how diversity influences invader impact, how impact varies among exotics, and what the relative importance of diversity is versus extrinsic factors that themselves can influence invasion. To address these issues, we established plant assemblages that varied in native species and functional richness and crossed this gradient in diversity with resource (water) addition. Identical assemblages were either uninvaded or invaded with one of three exotic forbs: spotted knapweed (Centaurea maculosa), dalmatian toadflax (Linaria dalmatica), or sulfur cinquefoil (Potentilla recta). To determine impacts, we measured the effects of exotics on native biomass and, for spotted knapweed, on soil moisture and nitrogen levels. Assemblages with high species richness were less invaded and less impacted than less diverse assemblages. Impact scaled with exotic biomass; spotted knapweed had the largest impact on native biomass compared with the other exotics. Although invasion depressed native biomass, the net result was to increase total community yield. Water addition increased invasibility (for knapweed only) but had no effect on invader impact. Together, these results suggest that diversity inhibits invasion and reduces impact more than resource additions facilitate invasion or impact.     

The making of a rapid plant invader: genetic diversity and differentiation in the native and invaded range of Senecio inaequidens

To become invasive, exotic species have to succeed in the consecutive phases of introduction, naturalization, and invasion. Each of these phases leaves traces in genetic structure, which may affect the species’ success in subsequent phases. We examined this interplay of genetic structure and invasion dynamics in the South African Ragwort (Senecio inaequidens), one of Europe’s fastest plant invaders. We used AFLP and microsatellite markers to analyze 19 native African and 32 invasive European populations. In combination with historic data, we distinguished invasion routes and traced them back to the native source areas. This revealed that different introduction sites had markedly different success in the three invasion phases. Notably, an observed lag‐phase in Northern Germany was evidently not terminated by factors increasing the invasiveness of the resident population but by invasive spread from another introduction centre. The lineage invading Central Europe was introduced to sites in which winters are more benign than in the native source region. Subsequently, this lineage spread into areas in which winter temperatures match the native climate more closely. Genetic diversity clearly increases with population age in Europe and less clearly decreases with spread rate up to population establishment. This indicates that gene flow along well‐connected invasion routes counteracted losses of genetic diversity during rapid spread. In summary, this study suggests that multiple introductions, environmental preadaptation and high gene flow along invasion routes contributed to the success of this rapid invader. More generally, it demonstrates the benefit of combining genetic, historical, and climatic data for understanding biological invasions.     

Pollution reduces native diversity and increases invader dominance in marine hard-substrate communities

Anthropogenic disturbance is considered a risk factor in the establishment of non‐indigenous species (NIS); however, few studies have investigated the role of anthropogenic disturbance in facilitating the establishment and spread of NIS in marine environments. A baseline survey of native and NIS was undertaken in conjunction with a manipulative experiment to determine the effect that heavy metal pollution had on the diversity and invasibility of marine hard‐substrate assemblages. The study was repeated at two sites in each of two harbours in New South Wales, Australia. The survey sampled a total of 47 sessile invertebrate taxa, of which 15 (32%) were identified as native, 19 (40%) as NIS, and 13 (28%) as cryptogenic. Increasing pollution exposure decreased native species diversity at all study sites by between 33% and 50%. In contrast, there was no significant change in the numbers of NIS. Percentage cover was used as a measure of spatial dominance, with increased pollution exposure leading to increased NIS dominance across all sites. At three of the four study sites, assemblages that had previously been dominated by natives changed to become either extensively dominated by NIS or equally occupied by native and NIS alike. No single native or NIS was repeatedly responsible for the observed changes in native species diversity or NIS dominance at all sites. Rather, the observed effects of pollution were driven by a diverse range of taxa and species. These findings have important implications for both the way we assess pollution impacts, and for the management of NIS. When monitoring the response of assemblages to pollution, it is not sufficient to simply assess changes in community diversity. Rather, it is important to distinguish native from NIS components since both are expected to respond differently. In order to successfully manage current NIS, we first need to address levels of pollution within recipient systems in an effort to bolster the resilience of native communities to invasion.