Meiofaunal Polychaete Research Articles

On the quantitative distribution and community structure of the meio and macrofaunal communities in the coastal area of the Central Adriatic Sea (Italy)

Many coastal areas have served as repositories of different anthropogenic and naturally induced organic material and nutrients. The major sources thereof are riverine inputs which strongly influence the spatial and temporal distribution of benthic communities. In this study, the benthic foraminiferal, meiofaunal, and macrofaunal colonies in front of three rivers in a poorly known, but environmentally valuable, area of the Central Adriatic Sea have been examined concurrently. The physico-chemical parameters of bottom water and sediment characteristics were determined in order to characterize both the sediment-water interface and the benthic environments. Although changes in the biota are neither univocal nor unidirectional, a moderate influence of riverine input on the different communities' components can be inferred. The most affected taxa are foraminifera and copepods and, to a lesser extent, meiofaunal polychaetes and platyhelminthes. These results are also tested by the ABC curves, which reveal that the macrofaunal communities closest to the river mouths are moderately disturbed. This integrated investigation documents, for the first time, how benthic communities can be used as an early warning indicator with which to monitor the health quality of a coastal ecosystem.

Bathymetric distribution of the meiofaunal polychaetes in the nearshore zone of Martel Inlet, King George Island, Antarctica

Polychaetes, the dominant macrofaunal taxa of the Antarctic soft sediments, provided more than 40% of the animals found in Martel Inlet. However, little information is available on the composition of meiofaunal communities in polar areas. This study identified the meiofaunal polychaete species and described their bathymetric distribution in the nearshore zone. Sediment cores were taken by divers from 6–25 m depth in the summer of 1991 and 1994 in front of the Brazilian Antarctic Station (Martel Inlet, Admiralty Bay). Additional sampling was done at the 18 m depth in 1994 in order to study the influence of ice scouring. A total of 1895 specimens in 17 families were found. Three species (Apistobranchus glacierae, Leitoscoloplos kerguelensis and Ophryotrocha notialis), all of them belonging to the temporary meiofauna, provided more than 70% of the total polychaete fraction. This meiofaunal component showed similar distributional patterns to those of the macrofaunal polychaetes in this area.

Progenetic species in polychaetes (Annelida) and problems assessing their phylogenetic affiliation

Progenesis is defined as the retention of ancestral juvenile characters by adult stages of descendants due to an acceleration of the sexual maturation and thus is often regarded as a fast evolutionary process. Several small, meiofaunal polychaetes, such as Dinophilidae, some "Dorvilleidae" (for example, Parapodrilus), and Protodrilida, exhibit morphological simplicity in that they lack features typical of larger polychaetes, for example, parapodia and/or head appendages. Due to the general resemblance of adult meiofaunal polychaetes to juveniles of larger forms, progenesis has been invoked to explain evolutionary origins of many smaller taxa with increasing frequency over the past 4 decades. In this review, I summarize the interstitial species of polychaetes for which progenetic origin has been suggested on the basis of morphology. However, critical examination of morphological data that includes larval features reveals that autapomorphic characters uniting supposed progenetic taxa to specific annelid lineages are often missing. Typically larval and juvenile characters, which are argued to support hypotheses of progenetic origin, are often widely dispersed, homoplastic features. Because of this situation, molecular data seem to be the most reliable source for phylogenetic inference. However, other biological data, for example, from life history and morphology, are necessities to substantiate the progenetic evolution of these species.

Dinophilidae (Annelida) is most likely not a progenetic Eunicida: Evidence from 18S and 28S rDNA

Dinophilidae (e.g., Dinophilus O. Schmidt, 1848) is a typical meiofaunal polychaete taxon with a seemingly simple organisation, e.g., no parapodia, only a few segments (Rouse and Pleijel, 2001). Dinophilidae is thought to be an eunicidan taxon and is often presented as the classical example of progenetic evolution within annelids (Westheide, 1987). The retention of ancestral juvenile characters by adult stages of descendants (paedomorphosis) can arise either by a retardation of somatic development (neoteny) or by an acceleration of the sexual maturation (progenesis) (Gould, 1977). Due to convincing similarities to developmental stages of larger eunicidans and their relatively small size, the progenetic origin of Dinophilidae and other dorvilleids (e.g., Parapodrilus) within Eunicida has been repeatedly assumed (Fig. 1) (see Eibye-Jacobsen and Kristensen, 1994; Westheide, 1987). Based on the possession of a ventral pharyngeal organ with speciWc jaw elements, Eunicida is a well-deWned annelid taxon currently comprising “Dorvilleidae,” Eunicidae, Hartmanniellidae, Histriobdellidae, Lumbrineridae, Oenonidae, and Onuphidae (Rouse and Pleijel, 2001). However, some meiofaunal taxa like Parapodrilus and a parasitic genus Biborin lack jaw apparatuses. Eunicidan species comprise both some of the smallest polychaetes (e.g., Neotenotrocha, 250!m) and the largest polychaete up to 6 m in length (e.g., Eunice) (Eibye-Jacobsen and Kristensen, 1994; Rouse and Pleijel, 2001). The most convincing evidence for a close relationship between dinophilids and eunicidans is from Akesson’s (1977) experiments demonstrating reciprocal infection with coelomic coccidia of the genus Grellia, parasites that are generally thought to be host-speciWc. In contrast, deWnitive morphological synapomorphies are lacking. For example, the ventral pharyngeal organs of Dinophilidae and Eunicida are diVerent and most likely not homologous (Purschke, 1985, 1987). In a recent 18S rDNA study (Struck et al., 2002) Dinophilidae was not the sistergroup to any eunicidan taxon. However, data were not able to clearly refute Dinophilidae as derived eunicidans as judged by nodal support and statistical tests. Furthermore, in two of their analyses Dinophilidae were in close vicinity to Lumbrineridae and the dorvilleid Pettiboneia urciensis, the latter two taxa are usually closely related to each other in molecular analyses (e.g., Struck and Purschke, 2005). Thus, their possible progenetic origin within Eunicida is still controversial. To address the phylogenetic relationship of Dinophilidae relative to Eunicida, the nuclear 28S rDNA was chosen as an additional molecular marker. Based on 18S rDNA results (Bleidorn et al., 2003; Struck and Purschke, 2005) concerning other possible placements for Dinophilidae, partial sequences of 28S rDNA and 18S rDNA of sabellidan, eunicidan, and dinophilid species were determined in this study. Combined analyses of the two genes (approximately 4 kb of data) were performed.

Phylogeny of Nerillidae (Polychaeta, Annelida) as inferred from combined 18S rDNA and morphological data.

A phylogeny of the meiofaunal polychaete family Nerillidae based on morphological, molecular and combined data is presented here. The data sets comprise nearly complete sequences of 18S rDNA and 40 morphological characters of 17 taxa. Sequences were analyzed simultaneously with the morphological data by direct optimization in the program POY, with a variety of parameter sets (costs of gaps: transversions: transitions). Three outgroups were selected from the major polychaete group Aciculata and one from Scolecida. The 13 nerillid species from 11 genera were monophyletic in all analyses with very high support, and three new apomorphies for Nerillidae are identified. The topology of the ingroup varied according to the various parameter settings. Reducing the number of outgroups to one decreased the variance among the phylogenetic hypotheses. The congruence among these was tested and a parameter set, with equal weights (222) and extension gap weighted 1, yielded minimum incongruence (ILD). Several terminal clades of the combined analysis were highly supported, as well as the position of Leptonerilla prospera as sister terminal to the other nerillids. The evolution of morphological characters such as segment numbers, chaetae, appendages and ciliation are traced and discussed. A regressive pathway within Nerillidae is indicated for several characters, however, generally implying several convergent losses. Numerous genera are shown to require revision.

Phylogenetic position of Nerillidae and Aberranta (Polychaeta, Annelida), analysed by direct optimization of combined molecular and morphological data

The phylogenetic position of the most speciose meiofaunal polychaete family, Nerillidae, has remained contentious. Recent hypotheses have generally focused on the fact that Nerillidae shares with Aciculata (a major polychaete subgroup) features such as compound chaetae, ventral buccal organ and short ventrolateral palps. Here we present the first phylogenetic analysis of Aciculata, together with Nerillidae, combining morphological and molecular data. We also include Aberrantidae, previously referred to or placed near to spiomorph polychaetes, but recently referred to Aciculata, possibly close to Nerillidae. The data sets of 24 terminals contain 53 morphological characters and nearly complete sequences of 18S rRNA. The sequences were analysed simultaneously with the morphological data by direct optimization in the program POY with a variety of parameter settings (costs of gaps: transversions: transitions). The various settings resulted in markedly different phylogenetic hypotheses, but on the basis of congruence (ILD) the results of two parameter settings were chosen. In all analyses, the three included nerillid species constituted a monophyletic group. Only two analyses provided fully resolved cladograms. The morphological analysis gave poor resolution and the position of the nerillids was equivocal. The two molecular‐based cladograms (minimizing ILD) were also poorly resolved, but one provided a position for nerillids next to Eunice pennata and Nothria conchilega, from the subgroup Eunicida within Aciculata. The two cladograms of the combined analyses (minimizing ILD) were fully resolved and placed nerillids in a terminal position next to Aberranta sp., within a clade of eunicidan species. The study showed that the analytical conditions for the homology assignment of 18S rRNA strongly influenced the phylogenetic results. The various previous proposals on the phylogenetic position of the Nerillidae are reviewed, some of which are in accordance with the results of the present study.

Ctenodrilus serratus (Polychaeta: Ctenodrilidae) is a truly amphi-Atlantic meiofauna species – evidence from molecular data

Specimens of the meiofaunal polychaete Ctenodrilus serratus from six localities on both sides of the North Atlantic were examined by RAPD-PCR and sequencing of the internal transcribed spacers (ITS1, ITS2) and 5.8S DNA. None of the populations showed any monomorphic diagnostic DNA fragments, but rather had a highly polymorphic band pattern; cluster analyses revealed no site-specific clusters of the specimens investigated. Furthermore, sequences were almost identical in populations off the coasts of Europe and the eastern United States, whereas the Bermuda specimens differed to some extent in ITS2. These results indicate the existence of a common gene pool and demonstrate an amphi-Atlantic distribution pattern of the species. Trans-Atlantic dispersal of individuals, by whatever means, must be inferred.

Recent advances in the use of meiofaunal polychaetes for ecotoxicological assessments

Recent advances in the use of meiofaunal polychaetes for ecotoxicological assessments

Cosmopolitan versus cryptic meiofaunal polychaete species: an approach to a molecular taxonomy

Polychaete taxonomy is characterised by a high number of apparently cosmopolitan species. Detection of subtle but diagnostic ultrastructural differences and – in recent years – investigations at the molecular level have revealed that many of these "species" are actually complexes of morphologically identical or almost identical cryptic species. To disregard their existence would lead to an underestimation of global meiofauna diversity and undermine the value of many scientific studies. Therefore, we strongly recommend that they be given formal taxonomic recognition, beyond their published presentation as "operational taxonomic units", "types" or by alphabetic or numerical designators. Since there are neither generally accepted practical procedures nor any established consensus regarding the application of genetic data in taxonomy, we here provide examples of, and suggestions for, the treatment of meiofaunal species that are distinguished exclusively by molecular data, e.g. by genetic distance values, cluster analyses, diagnostic (= autapomorphic) DNA fragments from DNA fingerprinting procedures (RAPD) and/or DNA sequence differences (e.g. of ITS 2). Although no holotype material may be available because the molecular procedures require the preparation of entire specimens, practical taxonomic problems can be overcome and the recommendations of the Zoological Code of Nomenclature satisfied, by adopting the following procedures: (1) deposition of band-patterns of an individual obtained with the primers used to find diagnostic markers; (2) deposition of DNA in ethanol of one syntype individual; (3) deposition of fixed specimens (syntypes) from the locus typicus.

Genetic Relationships (RAPD-PCR) Between Geographically Separated Populations of the "Cosmopolitan" Interstitial Polychaete Hesionides gohari (Hesionidae) and the Evolutionary Origin of the Freshwater Species Hesionides riegerorum.

In an analysis of the population genetics of the tiny meiofaunal polychaete Hesionides gohari, the RAPD-PCR method was applied to 49 specimens from 7 collecting sites far apart on three continents: French Atlantic coast, Mediterranean (Majorca, Giglio, Crete), Red Sea, Indian Ocean (Phuket), and U.S. Atlantic coast (Florida). In the band patterns produced with 14 arbitrary decamer primers, 496 genetic characters were detected. Genetic distances between the H. gohari populations vary between 0.55 and 0.70. The data were evaluated by three cluster programs; in the almost congruent phenograms, three clades were found with high bootstrap values: (1) European Atlantic-Mediterranean-Red Sea, (2) Indian Ocean, (3) Western Atlantic. In all cluster analyses, Hesionides riegerorum from a U.S. east coast river system is shown as genetically nearest to the Florida specimens of H. gohari, making it most probable that this freshwater species of the genus originated from a Western Atlantic H. gohari population. The genetic distances detected between the H. gohari specimens from the three continents are almost identical to those found between morphologically similar interstitial polychaete species pairs. Thus, the degree of genetic consistency is considered not to be high enough to corroborate the notion of a cosmopolitan distribution pattern, but rather suggests that the three clades represent different species.

Genetic variability and relationships among geographically widely separated populations of Petitia amphophthalma (Polychaeta: Syllidae). Results from RAPD-PCR investigations

An analysis of the population genetics of the meiofaunal polychaete Petitia amphophthalma Siewing, 1956, in which the RAPD-PCR method was applied to 103 individuals from eight populations, some of them very far apart (Atlantic: Florida, Tenerife, France; Mediterranean: two Greek islands, Tunisia; Red Sea: Egypt), gave closely reproducible results. In the band patterns produced with 13 decamer primers, a total of 195 genetic characters was detected. The data were evaluated by a number of methods, including the cluster programs UPGMA, WPGMA and neighbour-joining. The detected genetic distances between the populations vary between 58.9 and 66.6, but 97% of the genetic characters, although polymorphic, are found in at least two populations and usually in all the others as well. Phenograms of the analyses find four population clusters [Florida, France (Atlantic), the Mediterranean and Tenerife]. They are, however, not completely congruent and show low bootstrap values at the junction points of the clusters (with the exception of the Tenerife cluster). Mediterranean P. amphophthalma form a cohesive population, although within it the genetic distances are graded in parallel with the geographic distances between the sites. The colonization of Tenerife, an island of relatively recent volcanic origin, can be taken as evidence that this meiofaunal species can become dispersed not only along coastlines but also across expanses of open water. However, the severely restricted variability of these populations implies that in this case a founder effect has operated, and that transport over open water is not a routine event but extremely rare. The absence of the species on the Australian coast and, for instance, on the Galapagos Islands indicates that there has been no continuous gene flow across the oceans. The idea that all the populations investigated belong to one cosmopolitan species is discussed.

Short- and long-term variation in a high marsh meiofauna community

The meiobenthos from a high Spartina alterniflora marsh was studied in North Inlet, South Carolina over a 22 month period to assess long- (seasonal, yearly) and short- (weekly, monthly) term variation in community structure. Nematodes composed a mean 73% of the meiofauna assemblage and copepods ranked second in abundance. Stenhelia (D.) bifidia, Schizopera knabeni, Microarthridion littorale and Enhydrosoma propinquum were the four dominant copepod species recorded from this site and each displayed seasonally distinct patterns of abundance and reproduction. Meiofaunal polychaetes, represented by Manayunkia aestuarina and juvenile Streblospio benedicti, were also seasonally important constituents of the community. Community structure parameters indicated that there was little similarity of the copepods assemblage within seasons or between years. These findings suggest that unpredictable events are important influences on meiofauna community structure and cause this system to fluctuate over the time scale of this study.