The genetic structure of the rare lagoonal sea anemone, Nematostella vectensis Stephenson (Cnidaria; Anthozoa) in the United Kingdom based on RAPD analysis

Genotype-environment interactions determine microbiota plasticity in the sea anemone Nematostella vectensis

Most multicellular organisms harbor microbial colonizers that provide various benefits to their hosts. Although these microbial communities may be host species- or even genotype-specific, the associated bacterial communities can respond plastically to environmental changes. In this study, we estimated the relative contribution of environment and host genotype to bacterial community composition in Nematostella vectensis, an estuarine cnidarian. We sampled N. vectensis polyps from 5 different populations along a north-south gradient on the Atlantic coast of the United States and Canada. In addition, we sampled 3 populations at 3 different times of the year. While half of the polyps were immediately analyzed for their bacterial composition by 16S rRNA gene sequencing, the remaining polyps were cultured under laboratory conditions for 1 month. Bacterial community comparison analyses revealed that laboratory maintenance reduced bacterial diversity by 4-fold, but maintained a population-specific bacterial colonization. Interestingly, the differences between bacterial communities correlated strongly with seasonal variations, especially with ambient water temperature. To decipher the contribution of both ambient temperature and host genotype to bacterial colonization, we generated 12 clonal lines from 6 different populations in order to maintain each genotype at 3 different temperatures for 3 months. The bacterial community composition of the same N. vectensis clone differed greatly between the 3 different temperatures, highlighting the contribution of ambient temperature to bacterial community composition. To a lesser extent, bacterial community composition varied between different genotypes under identical conditions, indicating the influence of host genotype. In addition, we identified a significant genotype x environment interaction determining microbiota plasticity in N. vectensis. From our results we can conclude that N. vectensis-associated bacterial communities respond plastically to changes in ambient temperature, with the association of different bacterial taxa depending in part on the host genotype. Future research will reveal how this genotype-specific microbiota plasticity affects the ability to cope with changing environmental conditions.

Microbiota mediated plasticity promotes thermal adaptation in the sea anemone Nematostella vectensis

At the current rate of climate change, it is unlikely that multicellular organisms will be able to adapt to changing environmental conditions through genetic recombination and natural selection alone. Thus, it is critical to understand alternative mechanisms that allow organisms to cope with rapid environmental changes. Here, we use the sea anemone Nematostella vectensis, which has evolved the capability of surviving in a wide range of temperatures and salinities, as a model to investigate the microbiota as a source of rapid adaptation. We long-term acclimate polyps of Nematostella to low, medium, and high temperatures, to test the impact of microbiota-mediated plasticity on animal acclimation. Using the same animal clonal line, propagated from a single polyp, allows us to eliminate the effects of the host genotype. The higher thermal tolerance of animals acclimated to high temperature can be transferred to non-acclimated animals through microbiota transplantation. The offspring fitness is highest from F0 females acclimated to high temperature and specific members of the acclimated microbiota are transmitted to the next generation. These results indicate that microbiota plasticity can contribute to animal thermal acclimation and its transmission to the next generation may represent a rapid mechanism for thermal adaptation.

This study shows that sea anemones acclimated to high temperatures exhibit increased resistance to thermal stress and that this improved fitness can be transferred by microbiome transplantation. These results indicate that plasticity mediated by the microbiota might be an important factor facilitating thermal adaptations in animals.

Mediators of invasions in the sea: life history strategies and dispersal vectors facilitating global sea anemone introductions

Widespread non-native species tend to demonstrate an apparent lack of selectivity in habitat requirements, feeding regimes, and reproductive needs, while displaying a tendency to thrive in human-modified habitats. The high phenotypic plasticity typical of sessile, substrate-attached marine species may enhance their chances of survival and spread in a new region. Anthropogenic activities have changed marine habitats over a wide range of phenomena, including water temperature, community species composition, and the types of available substrates, creating new physical and biotic regimes that may contribute to the potential for successful species introduction. Here we examine ten species of sea anemones that have been introduced outside of their native range, and elucidate specific characteristics that are common among globally introduced sea anemones. Various life history strategies enable these species to survive and flourish through transport, introduction, establishment and spread, leading to the successful colonization of a new geographic area. Considering life history strategies and weighing of vector potential, we suggest conditions that facilitate introduction of these species, and identify species of sea anemones that may be introduced in the future in the face of changing climate and increased anthropogenic activities.

Analysis of genetic diversity and phylogeny of Philosamia ricini (Lepidoptera: Saturniidae) by using RAPD and internal transcribed spacer DNA1

The Indian Eri silkworm, Philosamia ricini Hutt, a commercial silk producing insect, is believed to have originated in the Brahmaputra valley of Assam. In this study, the genetic diversity and phylogenetic relationships of six morphs of Eri silkworm viz. white plain, white zebra, white spotted, blue plain, blue zebra and blue spotted collected from different geographical locations of North-East India were investigated by using random amplified polymorphic DNA (RAPD) and the first internal transcribed spacer region (ITS1). This study revealed a low genetic diversity among the morphs of Eri silkworm. Twenty-eight random primers generated 199 bands. Out of these, 112 were polymorphic (56.28%) with an average of 7.1 bands per primer. The genetic similarity matrix ranged from 0.56 to 0.99. The morphs collected from same geographical area shared the same cluster in the dendrogram. The genetic diversity in case of ITS1 sequences (2.19%) was found to be less as compared to RAPD. The ITS1 sequences of the morphs collected from same geographical area were found to be identical. The information generated in this study will help in conservation and effective breeding program to improve its productivity.

Collecting, rearing, spawning and inducing regeneration of the starlet sea anemone, Nematostella vectensis

Over the past 20 years, the starlet sea anemone, Nematostella vectensis, a small estuarine animal, has emerged as a powerful model system for field and laboratory studies of development, evolution, genomics, molecular biology and toxicology. Here we describe how to collect Nematostella, culture it through its entire sexual life cycle and induce regeneration for the production of clonal stocks. In less than 1 h at a suitable field site, a researcher on foot can collect hundreds of individual anemones. In a few months, it is possible to establish a laboratory colony that will be reliable in generating hundreds or thousands of fertilized eggs on a roughly weekly schedule. By inducing regeneration roughly every 2 weeks, in less than 6 months, one can establish a clonal stock consisting of hundreds of genetically identical anemones. These results can be achieved very inexpensively and without specialized equipment.

Going where traditional markers have not gone before: utility of and promise for RAD sequencing in marine invertebrate phylogeography and population genomics

Characterization of large numbers of single-nucleotide polymorphisms (SNPs) throughout a genome has the power to refine the understanding of population demographic history and to identify genomic regions under selection in natural populations. To this end, population genomic approaches that harness the power of next-generation sequencing to understand the ecology and evolution of marine invertebrates represent a boon to test long-standing questions in marine biology and conservation. We employed restriction-site-associated DNA sequencing (RAD-seq) to identify SNPs in natural populations of the sea anemone Nematostella vectensis, an emerging cnidarian model with a broad geographic range in estuarine habitats in North and South America, and portions of England. We identified hundreds of SNP-containing tags in thousands of RAD loci from 30 barcoded individuals inhabiting four locations from Nova Scotia to South Carolina. Population genomic analyses using high-confidence SNPs resulted in a highly-resolved phylogeography, a result not achieved in previous studies using traditional markers. Plots of locus-specific FST against heterozygosity suggest that a majority of polymorphic sites are neutral, with a smaller proportion suggesting evidence for balancing selection. Loci inferred to be under balancing selection were mapped to the genome, where 90% were located in gene bodies, indicating potential targets of selection. The results from analyses with and without a reference genome supported similar conclusions, further highlighting RAD-seq as a method that can be efficiently applied to species lacking existing genomic resources. We discuss the utility of RAD-seq approaches in burgeoning Nematostella research as well as in other cnidarian species, particularly corals and jellyfishes, to determine phylogeographic relationships of populations and identify regions of the genome undergoing selection.

Evolutionary crossroads in developmental biology: Cnidaria

There is growing interest in the use of cnidarians (corals, sea anemones, jellyfish and hydroids) to investigate the evolution of key aspects of animal development, such as the formation of the third germ layer (mesoderm), the nervous system and the generation of bilaterality. The recent sequencing of the Nematostella and Hydra genomes, and the establishment of methods for manipulating gene expression, have inspired new research efforts using cnidarians. Here, we present the main features of cnidarian models and their advantages for research, and summarize key recent findings using these models that have informed our understanding of the evolution of the developmental processes underlying metazoan body plan formation.

Two alleles of NF-kappaB in the sea anemone Nematostella vectensis are widely dispersed in nature and encode proteins with distinct activities

Background

NF-κB is an evolutionarily conserved transcription factor that controls the expression of genes involved in many key organismal processes, including innate immunity, development, and stress responses. NF-κB proteins contain a highly conserved DNA-binding/dimerization domain called the Rel homology domain.

Methods/Principal Findings

We characterized two NF-κB alleles in the sea anemone Nematostella vectensis that differ at nineteen single-nucleotide polymorphisms (SNPs). Ten of these SNPs result in amino acid substitutions, including six within the Rel homology domain. Both alleles are found in natural populations of Nematostella. The relative abundance of the two NF-κB alleles differs between populations, and departures from Hardy-Weinberg equilibrium within populations indicate that the locus may be under selection. The proteins encoded by the two Nv-NF-κB alleles have different molecular properties, in part due to a Cys/Ser polymorphism at residue 67, which resides within the DNA recognition loop. In nearly all previously characterized NF-κB proteins, the analogous residue is fixed for Cys, and conversion of human RHD proteins from Cys to Ser at this site has been shown to increase DNA-binding ability and increase resistance to inhibition by thiol-reactive compounds. However, the naturally-occurring Nematostella variant with Cys at position 67 binds DNA with a higher affinity than the Ser variant. On the other hand, the Ser variant activates transcription in reporter gene assays more effectively, and it is more resistant to inhibition by a thiol-reactive compound. Reciprocal Cys<->Ser mutations at residue 67 of the native Nv-NF-κB proteins affect DNA binding as in human NF-κB proteins, e.g., a Cys->Ser mutation increases DNA binding of the native Cys variant.

Conclusions/Significance

These results are the first demonstration of a naturally occurring and functionally significant polymorphism in NF-κB in any species. The functional differences between these alleles and their uneven distribution in the wild suggest that different genotypes could be favored in different environments, perhaps environments that vary in their levels of peroxides or thiol-reactive compounds.

Molecular and morphometric variation in chromosomally differentiated populations of the grasshopper Sinipta dalmani (Orthopthera: Acrididae)

Sinipta dalmani is an Argentine grasshopper whose chromosome polymorphisms have been widely studied through cytogenetic, morphometric, and fitness component analyses. The present work analysed molecular and morphometric variation in seven chromosomally differentiated populations from Entre Rios and Buenos Aires provinces to analyse population structure. Molecular studies were performed studying RAPD loci and morphometric analyses were carried out measuring five morphometric traits. Genetic variability was high in all studied populations and was characterized by a decrease in H as a function of latitude and temperature. Both conventional F(ST) analysis and Bayesian approach for dominant marker showed that there were significant genetic differences among all populations, between provinces, and among populations within provinces. Entre Rios populations showed higher mean numbers of migrants per generation as well as low genetic differentiation and high gene flow with almost all populations whereas Buenos Aires populations may be considered as a result of a more recently colonization. There is considerable morphometric variation between populations and this variation correlates with latitude and temperature. Our results suggest that selection contributes to phenotypic differentiation among populations by moulding the differences in trait means whereas genetic drift is responsible for differences in the matrix of variance-covariance. The gene flow detected is insufficient to prevent phenotypic and chromosome divergences.

Rising starlet: the starlet sea anemone, Nematostella vectensis

In recent years, a handful of model systems from the basal metazoan phylum Cnidaria have emerged to challenge long-held views on the evolution of animal complexity. The most-recent, and in many ways most-promising addition to this group is the starlet sea anemone, Nematostella vectensis. The remarkable amenability of this species to laboratory manipulation has already made it a productive system for exploring cnidarian development, and a proliferation of molecular and genomic tools, including the currently ongoing Nematostella genome project, further enhances the promise of this species. In addition, the facility with which Nematostella populations can be investigated within their natural ecological context suggests that this model may be profitably expanded to address important questions in molecular and evolutionary ecology. In this review, we explore the traits that make Nematostella exceptionally attractive as a model organism, summarize recent research demonstrating the utility of Nematostella in several different contexts, and highlight a number of developments likely to further increase that utility in the near future.

Regional population structure of a widely introduced estuarine invertebrate: Nematostella vectensis Stephenson in New England

Nematostella vectensis is an infaunal anemone occurring in salt marshes, lagoons and other estuarine habitats in North America and the United Kingdom. Although it is considered rare and receives protection in England, it is widely distributed and abundant in the United States, particularly along the Atlantic coast. Recent studies suggest that both anthropogenic dispersal and reproductive plasticity may significantly influence the genetic structure of N. vectensis populations. Amplified fragment length polymorphism (AFLP) fingerprinting of individuals from nine populations in the northeastern United States indicates that stable populations are maintained by both asexual and sexual reproduction; in some cases asexually reproducing lineages exist within sexually reproducing populations. F statistics reveal extraordinarily high degrees of genetic differentiation between populations, even those separated by very short distances (less than 100 m). Genetic distances show little to no correlation with geographical distances, consistent with a role for sporadic, geographically discontinuous dispersal coupled with limited gene flow. No single genotype was found at more than one site, despite apparent homogeneity of habitat. In contrast with reported genotypic distributions for Nematostella in the United Kingdom, where a single clonal genotype dominates at multiple sites through southern England, our data thus fail to support the hypothesis of a general-purpose genotype in the northeastern United States. However, they are consistent with important roles for reproductive plasticity, sporadic introductions and complex local population dynamics in determining the global and regional distribution of this species.

Genetic structuring of boll weevil populations in the US based on RAPD markers

Abstract Randomly amplified polymorphic DNA (RAPD) analysis was performed to infer the magnitude and pattern of genetic differentiation among boll weevil populations from eighteen locations across eight US states and north-east Mexico. Sixty-seven reproducible bands from six random primers were analysed for genetic variation within and between weevil populations. Genetic and geographical distances among all populations were positively correlated, reflecting a pattern of isolation by distance within a larger metapopulation. Gene flow between south-central, western and eastern regions is limited, but migration between locations within regions appears to be relatively frequent up to distances of approximately 300-400 km. However, estimates of effective migration were much lower than those estimated from mtDNA-RFLP data reported previously.