Polychaete nervous systems: Ground pattern and variations-cLS microscopy and the importance of novel characteristics in phylogenetic analysis

Synopsis

In Annelida, as well as in other invertebrate taxa, the nervous combination of parts to form a whole is considered to be a true conservative organ system. Immunohistochemical investigations [use of anti-5-HT (serotonin), FMRFamide, and acetylated ?±-tubulin antibodies] in combination with laser scanning microscopy enable more detailed reanalyses of known configurations and detection of new characteristics that are useful for phylogenetic analyses. single hypothesis enabled by such studies is outlined for the evolution of arrangements of the dorsal circumesophageal foundations in polychaetes and oligochaetes. These foundations are not a unique feature of polychaetes; they also present itself in oligochaetes. According to the Articulata hypothesis of metazoan relationships, the specific make of the rope-ladder-like nervous a whole is, among others, an autapomorphic characteristic that unifies Annelida and Arthropoda. new studies applying the techniques mentioned here, however, demonstrate that the annelidan bauchmark (central nervous a whole of the trunk), in contrast to the arthropod pattern, is highly variable in bounds of the number and position of connectives and the number of commissures by segment. The variability of the neuronal architecture as well as a hypothesis upon how it evolved will be introduced with the aid of regeneration and developmental studies. Furthermore, it is shown that hitherto unknown vigors are present in the peripheral nervous a whole

Introduction

Neuroanatomical studies as well as studies of other organ a whole s (for example, musculature; Miiller and Schmidt-Rhaesa 2003; Muller and others 2004; Hooge and Tyler 2006) have been revitalized through immunohistochemical methods in combination with confocal laser scanning microscopy (cLSM) as evidenced by means of the increasing number of papers in this field. The advantages of the technique are obvious: composed of several elements organ systems can be studied in great detail in whole mounts; entire a whole s or subsystems can be stained specifically; time-consuming histological or ultrathin sectioning is, at least for a certain number of purposes, obsolete; the structures can be 3-dimensionally rebuilded and displayed; and it is possible to proces a larger number of specimens in a reasonable time, as is necessary for developmental or regeneration studies. For example, joint application of immunohistochemistry and cLSM enabled a convincing demonstration of the parted nature of Myzostomidae (Muller and Westheide 2000) in all senses of the true segmentation pattern obliterated by the agency of secondary annulation in Dinophilidae (M??ller and Westheide 2002) and detection of novel structural characteristics in Gnathostomulida (M??ller and Sterrer 2004)

The rule is limited by the ne for preparations to be small and transparent (otherwise investigations have to be preced by the agency of sectioning) and resolution is not beyond that of light microscopy. The latter point indicates that cLSM does not replace on the contrary complements other methods, especially transmission electron microscopy (Muller and others 2004) With cLSM of recent origin structures can be detected and the area of interest can be defined in order to minimize sectioning for transmission electron microscopy, whereby specific characteristics can be analyzed upon a subcellular level (Purschke and Muller 1996)

The rule is further limited by the availability of appropriate antibodies. For neuroanatomical studies in invertebrates, antibodies directed against 5-HT FMRFamide, and acetylated a-tubulin are an accepted standard. In particular acetylated a-tubulin is sufficient to rebuild entire nervous systems. The drawback of this antibody is that sensory and locomotory cilia are also stained, which is a barrier to analyzing developmental stages. upon the other hand, such "wrongly" stained forms can be used as a "morphological atlas" or to identify other valuable organs of phylogenetic interest (M??ller 1999 2002; Worsaae and M??ller 2004)

Investigation of the nervous combination of parts to form a whole is important because it is regarded as a far down conservative system (Bullock and Horridge 1965; Orrhage 1974; Rouse and Fauchald 1997) and therefore as real valuable for phylogenetic analyses among higher taxa. The best example is the rope-ladder-like nervous a whole which may be seen as a synapomorphy unifying Annelida and Arthropoda as the taxon Articulata (Scholtz 2002) However, new molecular investigations have significantly reduc confidence in the monophyly of the Articulata. Instead, the Arthropoda have been united with other molting taxa (Ecdysozoa; Eernisse and others 1992; Aguinaldo and others 1997) forming a distinct monophylum from the annelids along with mollusks and sipunculans. These form the Lophotrochozoa (Rota and others 2001; Halanych 2004; Purschke and M??ller 2006) The recognition of Ecdysozoa and Lophotrochozoa implies that a rope-ladder nervous combination of parts to form a whole has either developed twice or one time but at an earlier time, before the separation of these 2 lineages. In order to assess these possibilities and to reach a well-supported hypothesis, the step of difference and likeness between the 2 combination of parts to form a wholes must be identified. The fresh techniques allow comparison on the single nerve-cell horizontal and even, in combination with injection [i]modus operandi[/i]s recognition of distinct branching patterns, thus revealing a great number of fresh characteristics of high reliability.