Evolution als eskalierende Individualisierung von Organismus und Umwelt

“Denn das Maß der Widerwärtigkeiten und Schlechtigkeiten wird augenblicklich wieder durch neue aufgefüllt, als glitte das eine Bein der Welt immer wieder zurück, wenn sich das andere vorschiebt. Daran müßte man die Ursache und den Geheimmechanismus erkennen!” (Robert Musil, Der Mann ohne Eigenschaften, I, 27) Die Frage, ob Evolution eine Fortschrittskomponente beinhalte, oder zumindest einen Trend zur Komplexität der Organismen oder der Ökosysteme, beschäftigt nicht nur Romanschreiber, sondern Biologen wie Philosophen (Ruse 1993). Ist Anpassung ein Schritt vorwärts? Wovon weg - worauf zu? Ist der komplexere Organismus besser an seine Umwelt angepaßt? Wenn ja, was sind die Konsequenzen und Kosten solchen Fortschritts? Ludwig von Bertalanffy wunderte sich über den Sinn eines evolutionären Dramas, in dem das Leben sich umständlich immer höher schraubt, um für jede erreichte Ebene einen neuen Preis zu zahlen: für Vielzelligkeit den Tod des Individuums, für das Nervensystem den Schmerz, für das Bewußtsein die Angst (Davidson 1983). Daß Evolution nicht, wie man lange glauben wollte, partout der Komplexität zustrebt, zeigt sich am Verlust der Flugfähigkeit bei vielen Inselvögeln in Abwesenheit terrestrischer Räuber, oder an der strukturellen Vereinfachung der meisten Parasiten, wird aber besonders deutlich in den klassischen Experimenten von Spiegelman (1967). Spiegelman inkubierte die RNA eines Virus in einer konstant gehaltenen Brühe aus freien Monomeren und Replikase. Unter artifizieller Selektion für rapide Reproduktion etablierte sich in diesem Experiment nach nur 75 Generationen eine stabile Mutante, die sich zwar fünfzehnmal so schnell vermehrte, sich aber von ursprünglich 4200 Nukleotiden auf nur mehr 220 reduziert hatte, nicht viel mehr als die Erkennungsstelle für die Replikase. Im Schlaraffenland, wo Ressourcen nie weniger werden, Abfälle sich nie anhäufen und Feinde nicht existieren, in einer Umwelt also, in welcher der Organismus weder bedroht noch von den Rückwirkungen seiner eigenen Handlungen betroffen wird, verläuft die Evolution anscheinend nicht in Richtung auf zunehmende Größe und Komplexität, wie dies Bonner (1988) für die reale Welt zu zeigen versuchte, sondern genau umgekehrt. Ich werde im folgenden eine Antwort auf dieses Paradoxon skizzieren, die aus den folgenden Thesen besteht: 1. Jeder Adaptivschritt eines evoluierenden Organismus zieht einen Komplementärschritt seiner unbelebten und seiner belebten Umwelt nach sich. Die Umwelt weicht vom sich adaptierenden Organismus zurück. Der Organismus von heute ist an die Umwelt von gestern angepaßt. 2. Während die unbelebte Umwelt lediglich in passiver Weise auf das energetische Vordringen des Organismus reagiert, sind Wechselwirkungen zwischen Organismus und belebter Umwelt, also anderen Organismen, teleonomisch. Wechselwirkungen, die im Energiefluß asymmetrisch sind (wie zum Beispiel zwischen Räuber und Beute), sind im Informationsfluß komplementär asymmetrisch. In dem Maße wie Energie zum erfolgreichen Räuber fließt, fließt Information zur erfolgreichen Beute. Der Räuber von heute erbt das Beutebild von gestern. 3. Einmalige Individualität, das Resultat sexueller Fortpflanzung, vermittelt diese asymmetrische Rückkoppelung und puffert die daraus resultierende zeitverschobene Eskalation. Der Trend zur Individualisierung ist selbstverstärkend und führt zu zunehmender räumlicher und zeitlicher Komplexität von Organismen und Umwelten. Individualität ist die stärkste Triebfeder in der Gestaltung der Biosphäre

Detailed reconstruction of the nervous and muscular system of Lobatocerebridae with an evaluation of its annelid affinity

BACKGROUND: The microscopic worm group Lobatocerebridae has been regarded a ‘problematicum’, with the systematic relationship being highly debated until a recent phylogenomic study placed them within annelids (Curr Biol 25: 2000-2006, 2015). To date, a morphological comparison with other spiralian taxa lacks detailed information on the nervous and muscular system, which is here presented for Lobatocerebrum riegeri n. sp. based on immunohistochemistry and confocal laser scanning microscopy, supported by TEM and live observations. RESULTS: The musculature is organized as a grid of longitudinal muscles and transverse muscular ring complexes in the trunk. The rostrum is supplied by longitudinal muscles and only a few transverse muscles. The intraepidermal central nervous system consists of a big, multi-lobed brain, nine major nerve bundles extending anteriorly into the rostrum and two lateral and one median cord extending posteriorly to the anus, connected by five commissures. The glandular epidermis has at least three types of mucus secreting glands and one type of adhesive unicellular glands. CONCLUSIONS: No exclusive “annelid characters” could be found in the neuromuscular system of Lobatocerebridae, except for perhaps the mid-ventral nerve. However, none of the observed structures disputes its position within this group. The neuromuscular and glandular system of L. riegeri n. sp. shows similarities to those of meiofaunal annelids such as Dinophilidae and Protodrilidae, yet likewise to Gnathostomulida and catenulid Platyhelminthes, all living in the restrictive interstitial environment among sand grains. It therefore suggests an extreme evolutionary plasticity of annelid nervous and muscular architecture, previously regarded as highly conservative organ systems throughout metazoan evolution. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12862-015-0531-x) contains supplementary material, which is available to authorized users

An Anatomical Description of a Miniaturized Acorn Worm (Hemichordata, Enteropneusta) with Asexual Reproduction by Paratomy

The interstitial environment of marine sandy bottoms is a nutrient-rich, sheltered habitat whilst at the same time also often a turbulent, space-limited, and ecologically challenging environment dominated by meiofauna. The interstitial fauna is one of the most diverse on earth and accommodates miniaturized representatives from many macrofaunal groups as well as several exclusively meiofaunal phyla. The colonization process of this environment, with the restrictions imposed by limited space and low Reynolds numbers, has selected for great morphological and behavioral changes as well as new life history strategies. Here we describe a new enteropneust species inhabiting the interstices among sand grains in shallow tropical waters of the West Atlantic. With a maximum body length of 0.6 mm, it is the first microscopic adult enteropneust known, a group otherwise ranging from 2 cm to 250 cm in adult size. Asexual reproduction by paratomy has been observed in this new species, a reproductive mode not previously reported among enteropneusts. Morphologically, Meioglossus psammophilus gen. et sp. nov. shows closest resemblance to an early juvenile stage of the acorn worm family Harrimaniidae, a result congruent with its phylogenetic placement based on molecular data. Its position, clearly nested within the larger macrofaunal hemichordates, suggests that this represents an extreme case of miniaturization. The evolutionary pathway to this simple or juvenile appearance, as chiefly demonstrated by its small size, dense ciliation, and single pair of gill pores, may be explained by progenesis. The finding of M. psammophilus gen. et sp. nov. underscores the notion that meiofauna may constitute a rich source of undiscovered metazoan diversity, possibly disguised as juveniles of other species.Organismic and Evolutionary Biolog

Microanatomy of the trophosome region of Paracatenula cf. polyhymnia (Catenulida, Platyhelminthes) and its intracellular symbionts

Marine catenulid platyhelminths of the genus Paracatenula lack mouth, pharynx and gut. They live in a symbiosis with intracellular bacteria which are restricted to the body region posterior to the brain. The symbiont-housing cells (bacteriocytes) collectively form the trophosome tissue, which functionally replaces the digestive tract. It constitutes the largest part of the body and is the most important synapomorphy of this group. While some other features of the Paracatenula anatomy have already been analyzed, an in-depth analysis of the trophosome region was missing. Here, we identify and characterize the composition of the trophosome and its surrounding tissue by analyzing series of ultra-thin cross-sections of the species Paracatenula cf. polyhymnia. For the first time, a protonephridium is detected in a Paracatenula species, but it is morphologically reduced and most likely not functional. Cells containing needle-like inclusions in the reference species Paracatenula polyhymnia Sterrer and Rieger, 1974 were thought to be sperm, and the inclusions interpreted as the sperm nucleus. Our analysis of similar cells and their inclusions by EDX and Raman microspectroscopy documents an inorganic spicule consisting of a unique magnesium–phosphate compound. Furthermore, we identify the neoblast stem cells located underneath the epidermis. Except for the modifications due to the symbiotic lifestyle and the enigmatic spicule cells, the organization of Paracatenula cf. polyhymnia conforms to that of the Catenulida in all studied aspects. Therefore, this species represents an excellent model system for further studies of host adaptation to an obligate symbiotic lifestyle

The Magnitude of Global Marine Species Diversity

Background: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. Results: There are ∼226,000 eukaryotic marine species described. More species were described in the past decade (∼20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∼170,000 synonyms, that 58,000–72,000 species are collected but not yet described, and that 482,000–741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7–1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. Conclusions: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century

Lurus minos, the first species of Luridae (Turbellaria: Rhabdocoela) from the Old World

Volume: 105Start Page: 636End Page: 63

Gnathostomulida in the Pelican Cays, Belize

Volume: 478Start Page: 265End Page: 27