On the evolution and morphology of the rotiferan trophi, with a cladistic analysis of Rotifera

The phylogeny of Rotifera was examined in different computer‐generated cladistic analyses, including Seisonidea, Bdelloidea, Flosculariacea, Collothecacea and all ploimids treated on family level. The analyses were based on a character matrix solely dealing with morphological characters, primarily based on the trophi morphology. Limnognathia maerski (Micrognathozoa), Rastrognathia macrostoma and Gnathostomula paradoxa (Gnathostomulida) were used as outgroups. The cladistic analysis performed by paup produced 288 most parsimonious trees. peewee analyses produced between 140 and 432 trees, depending on the concavity value. The monophyly of Eurotatoria, Monogononta and Ploima was confirmed in all obtained trees. All analyses suggested a division of Ploima into major clades. One clade corresponded to Transversiramida while the other contained all other ploimid taxa and recognized Antrorsiramida as a monophylum. Based on the obtained results a scenario for the trophi evolution is proposed. The analyses suggested that the presence of an incus is synapomorphic for Gnathifera while mallei are synapomorphic for Micrognathozoa and Rotifera. The ancestral rotifer trophi probably resembled those in Harringia (Asplanchnidae).     

Interrelationships of the Gastrotricha and their place among the Metazoa inferred from 18S rRNA genes

The phylum Gastrotricha includes about 700 species. They are small worm‐like organisms abundant among marine and freshwater meiobenthos. In spite of their ubiquity, diversity and relative abundance, phylogenetic relationships of these animals remain enigmatic due to the conflicting results of morphological and molecular cladistic analyses. Also unclear are the alliances within the phylum. In order to best estimate the position of Gastrotricha among the Metazoa and to shed some light on the ingroup phylogenetic relationships, small subunit (SSU) ribosomal DNA (rDNA) from 15 species of Chaetonotida (eight genera) and 28 species of Macrodasyida (26 genera) were included in an alignment of 50 metazoan taxa representing 26 phyla. Of the gastrotrich SSU rDNA sequences, eight are new and, along with published sequences represent eight families, including the five marine most speciose. Gastrotricha were resolved within a monophyletic Lophotrochozoa as part of a clade including Micrognathozoa, Rotifera and Cycliophora. The Gnathostomulida were sister to this clade. Nodal support was low for all of these relationships except the grouping of the Micrognathozoa, Rotifera and Cycliophora. Bayesian inference resolved the Gastrotricha as monophyletic with weak nodal support; the Macrodasyida were resolved as paraphyletic with many basal nodes poorly supported. Within the Chaetonotida, the monotypic Multitubulatina Neodasys was found in alliance with the macrodasyidan Urodasys while all the Paucitubulatina were found to form a single, well‐supported clade, with Musellifer as the most basal member. Among the more densely sampled Macrodasyida the Lepidodasyidae and Macrodasyidae were each found to be polyphyletic while monophyly was well supported for the Turbanellidae and Thaumastodermatidae. The congruence of our results with those of the cladistic analysis based on morphological traits provides confidence about the value of each dataset, and calls for widening of the research to include additional taxa of particular phylogenetic significance such as the Dactylopodolidae, Diuronotus, Heteroxenotrichula and Draculiciteria. The study highlights the problems in working with small species, the need for voucher specimens and the confused taxonomic status and membership of various gastrotrich families.     

Micrognathozoa: a new class with complicated jaws like those of Rotifera and Gnathostomulida

A new microscopic aschelminth-like animal, Limnognathia maerski nov. gen. et sp., is described from a cold spring at Disko Island, West Greenland, and assigned to Micrognathozoa nov. class. It has a complex of jaws in its pharynx, and the ultrastructure of the main jaws is similar to that of the jaws of advanced scleroperalian gnathostomulids. However, other jaw elements appear also to have characteristics of the trophi of Rotifera. Jaw-like structures are found in other protostome taxa as well-for instance, in proboscises of kalyptorhynch platyhelminths, in dorvilleid polychaetes and aplacophoran mollusks-but studies of their ultrastructure show that none of these jaws is homologous with jaws found in Gnathostomulida, Rotifera, and Micrognathozoa. The latter three groups have recently been joined into the monophylum Gnathifera Ahlrichs, 1995, an interpretation supported by the presence of jaw elements with cuticular rods with osmiophilic cores in all three groups. Such tubular structures are found in the fulcrum of all Rotifera and in several cuticular sclerites of both Gnathostomulida and Micrognathozoa. The gross morphology of the pharyngeal apparatus is similar in the three groups. It consists of a ventral pharyngeal bulb and a dorsal pharyngeal lumen. The absence of pharyngeal ciliation cannot be used as an autapomorphy in the ground pattern of the Gnathifera because the Micrognathozoa has the plesiomorphic alternative with a ciliated pharyngeal epithelium. The body of Limnognathia maerski nov. gen. et sp. consists of a head, thorax, and abdomen. The dorsal and lateral epidermis have plates formed by an intracellular matrix, as in Rotifera and Acanthocephala; however, the epidermis is not syncytial. The ventral epidermis lacks internal plates, but has a cuticular oral plate without ciliary structures. Two ventral rows of multiciliated cells form a locomotory organ. These ciliated cells resemble the ciliophores present in some interstitial annelids. An adhesive ciliated pad is located ventrally close to a caudal plate. As in many marine interstitial animals-e.g., gnathostomulids, gastrotrichs, and polychaetes-a special form of tactile bristles or sensoria is found on the body. Two pairs of protonephridia with unicellular terminal cells are found in the trunk; this unicellular condition may be the plesiomorphic condition in Bilateria. Only specimens with the female reproductive system have been found, indicating that all adult animals are parthenogenetic females. We suggest that 1) jaws of Gnathostomulida, Rotifera, and the new taxon, Micrognathozoa, are homologous structures; 2) Rotifera (including Acanthocephala) and the new group might be sister groups, while Gnathostomulida could be the sister-group to this assemblage; and 3) the similarities to certain gastrotrichs and interstitial polychaetes are convergent.     

Cryptic diversity in Chortís Highland moss salamanders (Caudata: Plethodontidae: Nototriton) revealed using mtDNA barcodes and phylogenetics,with a new species from eastern Honduras

The systematic study of Central American moss salamanders has been a challenge to researchers due to their cryptic nature and subsequent difficulty in sampling. In an effort to elucidate relationships among moss salamanders from the Chortís Highlands, we quantified intra- and interspecific variation using data from the mitochondrial genes 16S (the amphibian barcoding gene), cytochrome b (cyt b; widely used in phylogenetic studies of neotropical salamanders), and cytochrome oxidase subunit I (COI, the universal metazoan barcoding gene). All three loci exhibit a bimodal ‘barcoding gap’ between ranges of intra- and interspecific variation, demonstrating unambiguous species boundaries with respect to the mitochondrial loci. A barcoding approach and Bayesian and maximum likelihood analyses of the mtDNA dataset revealed that the nominal species N. barbouri represents a species complex, with two of three populations assigned to this taxon being paraphyletic with respect to a sample from the type locality. These data also revealed an undescribed species from eastern Honduras, and confirmed the identity of allopatric populations of N. lignicola and N. limnospectator. Sequence data from cyt b presented an analytical challenge due to a high level of substitution saturation at the third codon position for some samples. Phylogenetic analyses of the entire dataset including and omitting the third position of cyt b resulted in conflicting results with respect to the position of the new species and N. tomamorum. Based on the molecular data, supplemented with data from external morphology and osteology, we formally describe a new species from Sierra de Agalta.     

Metazoa-level USCOs as markers in species delimitation and classification

Metazoa-level universal single-copy orthologs (mzl-USCOs) are universally applicable markers for DNA taxonomy in animals that can replace or supplement single-gene barcodes. Previously, mzl-USCOs from target enrichment data were shown to reliably distinguish species. Here, we tested whether USCOs are an evenly distributed, representative sample of a given metazoan genome and therefore able to cope with past hybridization events and incomplete lineage sorting. This is relevant for coalescent-based species delimitation approaches, which critically depend on the assumption that the investigated loci do not exhibit autocorrelation due to physical linkage. Based on 239 chromosome-level assembled genomes, we confirmed that mzl-USCOs are genetically unlinked for practical purposes and a representative sample of a genome in terms of reciprocal distances between USCOs on a chromosome and of distribution across chromosomes. We tested the suitability of mzl-USCOs extracted from genomes for species delimitation and phylogeny in four case studies: Anopheles mosquitos, Drosophila fruit flies, Heliconius butterflies and Darwin's finches. In almost all instances, USCOs allowed delineating species and yielded phylogenies that corresponded to those generated from whole genome data. Our phylogenetic analyses demonstrate that USCOs may complement single-gene DNA barcodes and provide more accurate taxonomic inferences. Combining USCOs from sources that used different versions of ortholog reference libraries to infer marker orthology may be challenging and, at times, impact taxonomic conclusions. However, we expect this problem to become less severe as the rapidly growing number of reference genomes provides a better representation of the number and diversity of organismal lineages.     

Further structures in the jaw apparatus of Limnognathia maerski (Micrognathozoa), with notes on the phylogeny of the Gnathifera

The jaws of Limnognathia maerski, Micrognathozoa, were investigated with light- and scanning electron microscopy. The study yielded several new structures and sclerites, including the ventral part of main jaw, the pharyngeal lamellae, the manus, the dorsal and ventral fibularium teeth, and a reinterpretation of the fibularium compartmentalization. Furthermore, it was shown that several jaw elements are composed of densely packed rods. Comparison with Rotifera and Gnathostomulida suggested that the micrognathozoan main jaw is homologous with the rotifer incus and the gnathostomulid articularium and that the pseudophalangids (the ventral jaws) and their associated sclerites correspond to the rotifer mallei. These results imply that Micrognathozoa is more closely related to Rotifera than to Gnathostomulida.     

Different filtering strategies of genotyping‐by‐sequencing data provide complementary resolutions of species boundaries and relationships in a clade of sexually deceptive orchids

Ongoing hybridization and retained ancestral polymorphism in rapidly radiating lineages could mask recent cladogenetic events. This presents a challenge for the application of molecular phylogenetic methods to resolve differences between closely related taxa. We reanalyzed published genotyping‐by‐sequencing (GBS) data to infer the phylogeny of four species within the Ophrys sphegodes complex, a recently radiated clade of orchids. We used different data filtering approaches to detect different signals contained in the dataset generated by GBS and estimated their effects on maximum likelihood trees, global F_ST and bootstrap support values. We obtained a maximum likelihood tree with high bootstrap support, separating the species by using a large dataset based on loci shared by at least 30% of accessions. Bootstrap and F_ST values progressively decreased when filtering for loci shared by a higher number of accessions. However, when filtering more stringently to retain homozygous and organellar loci, we identified two main clades. These clades group individuals independently from their a priori species assignment, but were associated with two organellar haplotype clusters. We infer that a less stringent filtering preferentially selects for rapidly evolving lineage‐specific loci, which might better delimit lineages. In contrast, when using homozygous/organellar DNA loci the signature of a putative hybridization event in the lineage prevails over the most recent phylogenetic signal. These results show that using differing filtering strategies on GBS data could dissect the organellar and nuclear DNA phylogenetic signal and yield novel insights into relationships between closely related species.     

<Emphasis Type="Italic">Boreogadus saida</Emphasis> (Lepechin) (Gadidae): a review of its metazoan parasite fauna from Greenland,eastern Canada,Alaska and the Russian Arctic

The metazoan parasite fauna of 50 specimens of Boreogadus saida (Lepechin) (Gadidae) from eastern Greenland is very similar to those of previous studies of the parasite fauna of B. saida from Greenland, eastern Canada, Alaska and the Russian Arctic. The digeneans Hemiurus levinseni, Derogenes varicus and Lecithaster gibbosus and cestode larvae were found at most stations. Single specimens of the nematode larvae Anisakis simplex were found at four stations. A comparison of the distribution of the larvae of Contracaecum sp. and Hysterothylacium sp. is difficult due to a possible confusion of the two genera. Most of the metazoan parasites of B. saida are generalist species found in several fish families. Boreogadus saida acquires most of its endoparasites by eating pelagic crustaceans, mainly copepods and amphipods. It plays an important role in the arctic ecosystem and its parasites are transferred to predatory fish, birds and mammals through the food web.     

Tubulin polymerization promoting protein (TPPP) ortholog from <Emphasis Type="Italic">Suberites domuncula</Emphasis> and comparative analysis of TPPP/p25 gene family

Sponges are one of the oldest metazoan phyla that are, due to their highly conservative nature, often referred to as the living fossils of multicellular animals. As such, they are a very important model for evolutionary, developmental and functional studies of Metazoa. Tubulin polymerization promoting proteins (TPPPs) are defined by the presence of p25-alpha domain (Pfam05517). Their functional characteristics resemble those of microtubule-associated proteins. Presence of TPPP homologous genes has been postulated in all eukaryotes with ciliated cells and their primary function has been proposed as some basic cilia-connected function. We present here the genomic structure and the corresponding cDNA sequence of one poriferan TPPP homolog (SdTPPP) isolated from the marine sponge Suberites domuncula; and a comparative analysis of TPPP homolog sequences and genomic structures from other Eukaryotes. Our results confirm the radiation of one TPPP homolog into three distinct genes in the Vertebrate lineage, but the origin of different sequences and their phylogenetic relationships show to be influenced by alternative protein isoforms, independent gene duplications, modularity of the p25-alpha domain and possible adaptational requirements to environmental conditions.     

Isolation and Characterization of Five Actin cDNAs from the Cestode Diphyllobothrium dendriticum: A Phylogenetic Study of the Multigene Family

Five cDNAs (pDidact2–pDidact6), representing different actin genes, were isolated from a Diphyllobothrium dendriticum cDNA library, and the DNA as well as the putative amino acid sequences were determined. The corresponding Didact2 and Didact4 genes code for peptides 376 amino acids long, with molecular weights 41,772 and 41,744 Da, respectively, while the deduced Didact3 protein is 377 amino acids long and weighs 41,912 Da. The pDidact5 and -6 cDNAs lack nucleotides corresponding to three to six amino acids at the amino-terminus. Two of the five cDNAs contain the conventional AATAAA as the putative polyadenylation signal, one has the common variant ATTAAA, whereas the hexanucleotide AATAGA is found 15 and 18 nucleotides, respectively, upstream of the poly(A) site in two of the cDNAs. Phylogenetic studies including 102 actin protein sequences revealed that there are at least four different types of cestode actins. In this study three of these types were found to be expressed in the adult D. dendriticum tapeworm. Structurally the cestode actin groupings differ from each other to an extent seen only among the metazoan actins between the vertebrate muscle and cytoplasmic isoforms. In the phylogenetic trees constructed, cestode actins were seen to map to two different regions, one on the border of the metazoan actins and the other within this group. It is, however, difficult to say whether the cestode actins branched off early in the metazoan evolution or if this position in the phylogenetic tree only reflects upon differences in evolutionary rate. Received: 19 June 1996 / Accepted: 20 August 1996     

Construction of a high-resolution genetic linkage map and comparative genome analysis for the reef-building coral Acropora millepora

Background  

Worldwide, coral reefs are in decline due to a range of anthropogenic disturbances, and are now also under threat from global climate change. Virtually nothing is currently known about the genetic factors that might determine whether corals adapt to the changing climate or continue to decline. Quantitative genetics studies aiming to identify the adaptively important genomic loci will require a high-resolution genetic linkage map. The phylogenetic position of corals also suggests important applications for a coral genetic map in studies of ancestral metazoan genome architecture.     

Gibberella fujikuroi mating population E is associated with maize and teosinte

Isolates of Fusarium subglutinans mating population E are usually found on maize. This fungus forms part of the so-called Gibberella fujikuroi species complex. Previously, F. subglutinans has been associated with two additional mating populations (B and H) and a variety of plant hosts. This was mainly due to a lack of diagnostic morphological characters, but the use of DNA sequence information showed that the strains making up mating populations B, E and H, as well as those associated with the different plant hosts, represent separate species. Recently, another putative mating population has been reported on the wild teosinte relatives of maize. Based on sexual compatibility studies, these isolates were apparently closely related to the pitch canker fungus, F. subglutinans f. sp. pini (= F. circinatum;G. fujikuroi mating population H). The aim of the current study was to determine whether the population of F. subglutinans from teosinte constitutes a new or an existing lineage within the G. fujikuroi complex. For this purpose, portions of the mitochondrial small subunit ribosomal DNA, calmodulin and β-tubulin genes from the fungi were sequenced. Phylogenetic analyses and comparison with sequences from public domain databases indicated that the F. subglutinans isolates from teosinte are most closely related to strains of G. fujikuroi mating population E. These results were confirmed using sexual compatibility studies. The putative mating population from the wild relatives of maize therefore forms part of the existing E-mating population and does not constitute a new lineage in the G. fujikuroi species complex.     

Chromosomal and molecular divergence in the Indian pygmy field mice Mus booduga-terricolor lineage of the subgenus Mus

Mus booduga and Mus terricolor both have 2n=40. Unlike M. booduga, with all acrocentric chromosomes, M. terricolor invariably has large submetacentric X and acrocentric Y due to an increase of heterochromatin. In contrast to the conservative karyotype of the co-existing sibling species booduga, three chromosome types of terricolor are found in different populations and their divergent karyotypes have autosomal heterochromatin variations established in the homozygous condition. The average genetic distance determined from electrophoretic study of 20 protein loci ranges from lowest (D=0.106) between chromosome types I & II to highest (D=0.185) between types II & III. In terricolor, booduga and M. m. tytleri high mean values of variations per locus (range A=1.604 to 1.928) and heterozygosity per individual per locus (range H=0.180 to 0.336) have been observed. Sequence divergence of 0.39 to 1.2%, calculated from restriction profiles of mtDNA, shows that the terricolor chromosome types have diverged recently. Hybridizations between type I females and type III males gave a preponderance of males in the F1 with varying degrees of sterility. The terricolor complex is an interesting system for critical probing for the role of heterochromatin in the process of speciation. MtDNA, protein loci and AT-rich musculus-related major and minor satellite DNA data indicate that progenitors of the booduga-terricolor lineage might have evolved simultaneously with the caroli-cookii-cervicolor lineage in the evolution of the subgenus Mus.     

Genetic structure among populations in the endemic Hawaiian Plantago lineage: insights from microsatellite variation

Endemic Hawaiian species in the genus Plantago show considerable morphological and ecological diversity. Despite their variation, a recent phylogenetic analysis based on DNA sequence data showed that the group is monophyletic and that sequence variation among species and morphotypes is low. This lack of sequence polymorphisms resulted in an inability to resolve species and population affinities within the most recently derived clade of this lineage. To assess species boundaries, population genetic structure and interpopulation connectivity among the morphologically and ecologically distinct populations within this clade, genetic variation was examined using eight microsatellite loci. Within‐population genetic diversity was found to be lowest in the Maunaiu, Hawai'i population of the endangered P. hawaiensis, and highest in the large P. pachyphylla population from 'Eke, West Maui. Isolation by distance across the range of populations was detected and indicated restricted dispersal. This result is likely to be attributable to few interisland dispersal events in the evolutionary history of this lineage. Genetic differentiation within islands tended to be higher among populations occurring in contrasting bog and woodland habitats, suggesting ecological barriers to gene flow and the potential role of ecological divergence in population diversification. Overall, these results are consistent with findings from phylogenetic analysis of the entire lineage. Our data bring new insights regarding patterns of dispersal and population genetic structure to this endemic and endangered group of island taxa. As island environments become increasingly fragmented, information of this type has important implications for the successful management of these fragile populations and habitats.     

A modern approach to rotiferan phylogeny: combining morphological and molecular data

The phylogeny of selected members of the phylum Rotifera is examined based on analyses under parsimony direct optimization and Bayesian inference of phylogeny. Species of the higher metazoan lineages Acanthocephala, Micrognathozoa, Cycliophora, and potential outgroups are included to test rotiferan monophyly. The data include 74 morphological characters combined with DNA sequence data from four molecular loci, including the nuclear 18S rRNA, 28S rRNA, histone H3, and the mitochondrial cytochrome c oxidase subunit I. The combined molecular and total evidence analyses support the inclusion of Acanthocephala as a rotiferan ingroup, but do not support the inclusion of Micrognathozoa and Cycliophora. Within Rotifera, the monophyletic Monogononta is sister group to a clade consisting of Acanthocephala, Seisonidea, and Bdelloidea-for which we propose the name Hemirotifera. We also formally propose the inclusion of Acanthocephala within Rotifera, but maintaining the name Rotifera for the new expanded phylum. Within Monogononta, Gnesiotrocha and Ploima are also supported by the data. The relationships within Ploima remain unstable to parameter variation or to the method of phylogeny reconstruction and poorly supported, and the analyses showed that monophyly was questionable for the families Dicranophoridae, Notommatidae, and Brachionidae, and for the genus Proales. Otherwise, monophyly was generally supported for the represented ploimid families and genera.     

Allozyme divergence among species ofWolffia (Lemnaceae)

The genusWolffia was surveyed electrophoretically at 14 allozyme loci. A total of 133 clones representing 10 of the 11 recognized species was examined. Genetic identities among most pairs of species are zero, with non-zero values ranging from 0.14 to 0.40.Wolffia angusta and the newly describedW. neglecta show the highest similarity, and the former species has an identity of 0.14 withW. australiana. The next highest similarity (0.34) occurs betweenW. globosa of Southeast Asia andW. cylindracea of southern Africa, which until recently, had generally been viewed as members of the same species. Other species showing some common alleles are members of a complex involvingW. arrhiza, W. columbiana, W. cylindracea, andW. globosa. WithinW. arrhiza, plants from South Africa and Europe are easily distinguished electrophoretically because each contains unique alleles at two loci. Strains from other parts of Africa vary at these loci and are not totally distinct from either the plants from South Africa or from Europe. Species ofWolffia are much more divergent at allozyme loci than the majority of congeners of flowering plants. This suggests that the species are quite old and that the difficulties in distinguishing taxa morphologically are the result of reduction rather than lack of divergence due to recent speciation. Because of the lack of shared alleles between the majority of species pairs inWolffia, enzyme electrophoresis provides limited resolution of species relationships in the genus.     

Is RAD‐seq suitable for phylogenetic inference? An in silico assessment and optimization

Inferring phylogenetic relationships between closely related taxa can be hindered by three factors: (1) the lack of informative molecular variation at short evolutionary timescale; (2) the lack of established markers in poorly studied taxa; and (3) the potential phylogenetic conflicts among different genomic regions due to incomplete lineage sorting or introgression. In this context, Restriction site Associated DNA sequencing (RAD‐seq) seems promising as this technique can generate sequence data from numerous DNA fragments scattered throughout the genome, from a large number of samples, and without preliminary knowledge on the taxa under study. However, divergence beyond the within‐species level will necessarily reduce the number of conserved and non‐duplicated restriction sites, and therefore the number of loci usable for phylogenetic inference. Here, we assess the suitability of RAD‐seq for phylogeny using a simulated experiment on the 12 Drosophila genomes, with divergence times ranging from 5 to 63 million years. These simulations show that RAD‐seq allows the recovery of the known Drosophila phylogeny with strong statistical support, even for relatively ancient nodes. Notably, this conclusion is robust to the potentially confounding effects of sequencing errors, heterozygosity, and low coverage. We further show that clustering RAD‐seq data using the BLASTN and SiLiX programs significantly improves the recovery of orthologous RAD loci compared with previously proposed approaches, especially for distantly related species. This study therefore validates the view that RAD sequencing is a powerful tool for phylogenetic inference.     

Molecular Evolution of the Metazoan Extracellular Matrix: Cloning and Expression of Structural Proteins from the Demosponges Suberites domuncula and Geodia cydonium

One crucial event during evolution to multicellularity was the development of either direct cell–cell contact or indirect interaction via extracellular matrix (ECM) molecules. The identification of those polypeptides provides conclusive data on the phylogenetic relationship of metazoan phyla and helps us to understand the position of the Metazoa among the other kingdoms. Recently it became evident that the ECM of sponges is amazingly complex; it is composed of fibrous molecules, e.g., collagen, and their corresponding receptors, which are highly similar to those existing in other metazoan phyla. While these data already support the view of monophyly of Metazoa, additional studies are required to understand whether these molecules, which are similar in their primary sequence, also have the same function throughout the metazoan kingdom. In the present study we identified the ligand for one of the autopomorphic characters of Metazoa, the single-transmembrane receptor protein with the receptor tyrosine kinase (RTK) from G. cydonium, as an example: the putative mucus-like protein from G. cydonium. This protein was upregulated during autograft fusion in the homologous system with kinetics similar to those of the RTK. Additionally, a cDNA was isolated from S. domuncula whose deduced polypeptide displays a high sequence similarity to dermatopontin, an ECM molecule found exclusively in Metazoa. Furthermore, it is documented that expression of the fibrous ECM molecule collagen is regulated by the characteristic metazoan morphogens myotrophin and endothelial monocyte-activating polypeptide. These data indicate that the ECM of sponges is not an unstructured ground substance but provides the basis for integrated cell communication. Received: 26 October 2000 / Accepted: 1 February 2001     

Genetic divergence in nuclear genomes between populations of <Emphasis Type="Italic">Fagus crenata</Emphasis> along the Japan Sea and Pacific sides of Japan

Genetic diversity and structure in Fagus crenata were studied by analyzing 14 nuclear microsatellite loci in 23 populations distributed throughout the species’ range. Although population differentiation was very low (F _ST = 0.027; R _ST = 0.041), both neighbor-joining tree and Bayesian clustering analyses provided clear evidence of genetic divergence between populations along the Japan Sea (Japan Sea lineage) and Pacific (Pacific lineage) sides of Japan, indicating that physical barriers to migration and gene flow, notably the mountain ranges separating the populations along the Japan Sea and Pacific sides, have promoted genetic divergence between these populations. The two lineages of the nuclear genome are generally consistent with those of the chloroplast genome detected in a previous study, with several discrepancies between the two genomes. Within-population genetic diversity was generally very high (average H _E = 0.839), but decreased in a clinal fashion from southwest to northeast, largely among populations of the Japan Sea lineage. This geographical gradient may have resulted from the late-glacial and postglacial recolonization to the northeast, which led to a loss of within-population genetic diversity due to cumulative founder effects.