Thomas Jankowski

Medusozoan Phylogeny and Character Evolution Clarified by New Large and Small Subunit rDNA Data and an Assessment of the Utility of Phylogenetic Mixture Models

A newly compiled data set of nearly complete sequences of the large subunit of the nuclear ribosome (LSU or 28S) sampled from 31 diverse medusozoans greatly clarifies the phylogenetic history of Cnidaria. These data have substantial power to discern among many of the competing hypotheses of relationship derived from prior work. Moreover, LSU data provide strong support at key nodes that were equivocal based on other molecular markers. Combining LSU sequences with those of the small subunit of the nuclear ribosome (SSU or 18S), we present a detailed working hypothesis of medusozoan relationships and discuss character evolution within this diverse clade. Stauromedusae, comprising the benthic, so-called stalked jellyfish, appears to be the sister group of all other medusozoans, implying that the free-swimming medusa stage, the motor nerve net, and statocysts of ecto-endodermal origin are features derived within Medusozoa. Cubozoans, which have had uncertain phylogenetic affinities since the elucidation of their life cycles, form a clade-named Acraspeda-with the scyphozoan groups Coronatae, Rhizostomeae, and Semaeostomeae. The polyps of both cubozoans and hydrozoans appear to be secondarily simplified. Hydrozoa is comprised by two well-supported clades, Trachylina and Hydroidolina. The position of Limnomedusae within Trachylina indicates that the ancestral hydrozoan had a biphasic life cycle and that the medusa was formed via an entocodon. Recently hypothesized homologies between the entocodon and bilaterian mesoderm are therefore suspect. Laingiomedusae, which has often been viewed as a close ally of the trachyline group Narcomedusae, is instead shown to be unambiguously a member of Hydroidolina. The important model organisms of the Hydra species complex are part of a clade, Aplanulata, with other hydrozoans possessing direct development not involving a ciliated planula stage. Finally, applying phylogenetic mixture models to our data proved to be of little additional value over a more traditional phylogenetic approach involving explicit hypothesis testing and bootstrap analyses under multiple optimality criteria. [18S; 28S; Cubozoa; Hydrozoa; medusa; molecular systematics; polyp; Scyphozoa; Staurozoa.].

The impact of human-made ecological changes on the genetic architecture of Daphnia species

The overenrichment (eutrophication) of aquatic ecosystems with nutrients leading to algal blooms and anoxic conditions has been a persistent and widespread environmental problem. Although there are many studies on the ecological impact of elevated phosphorus (P) levels (e.g., decrease in biodiversity and water quality), little is known about the evolutionary consequences for animal species. We reconstructed the genetic architecture of a Daphnia species complex in 2 European lakes using diapausing eggs that were isolated from sediment layers covering the past 100 years. Changes in total P were clearly associated with a shift in species composition and the population structure of evolutionary lineages. Although environmental conditions were largely re-established after peak eutrophication during the 1970s and 1980s, original species composition and the genetic architecture of species were not restored but evolved along new evolutionary trajectories. Our data demonstrate that anthropogenically induced temporal alterations of habitats are associated with long-lasting changes in communities and species via interspecific hybridization and introgression.

Phylogenetics of Trachylina (Cnidaria: Hydrozoa) with new insights on the evolution of some problematical taxa

Some of the most interesting and enigmatic cnidarians are classified within the hydrozoan subclass Trachylina. Despite being relatively depauperate in species richness, the clade contains four taxa typically accorded ordinal status: Actinulida, Limnomedusae, Narcomedusae and Trachymedusae. We bring molecular data (mitochondrial 16S and nuclear small and large subunit ribosomal genes) to bear on the question of phylogenetic relationships within Trachylina. Surprisingly, we find that a diminutive polyp form, Microhydrula limopsicola (classified within Limnomedusae) is actually a previously unknown life stage of a species of Stauromedusae. Our data confirm that the interstitial form Halammohydra sp. (Actinulida) is derived from holopelagic direct developing ancestors, likely within the trachymedusan family Rhopalonematidae. Trachymedusae is shown to be diphyletic, suggesting that the polyp stage has been lost independently at least two times within trachyline evolution. Narcomedusae is supported as a monophyletic group likely also arising from trachymedusan ancestors. Finally, some data, albeit limited, suggest that some trachyline species names refer to cryptic species that have yet to be sorted taxonomically.

The freshwater medusae of the world - a taxonomic and systematic literature study with some remarks on other inland water jellyfish

Several medusa species have been described from inland waters in Australia, Eurasia, Africa and America. The chief objective of this study is to summarize all species described from freshwater and from saline lakes, because the knowledge about this group is sparse and scattered in the literature. I summarize all accessible literature to deduct how many species of freshwater medusae exist and to show their distribution, relation and their phylogenetic origin.All medusae described from freshwater except Halmomises are Olindiidae (Limnomedusae). More than 20 Olindiidae species (in 6 genera) have been recorded from freshwater. However, about half of them may not be valid species or have been described insufficiently or improperly. Within the genera Craspedacusta only 3 (or 5) species are certain (C. sowerbii, C. iseanum, C. sinensis (and maybe C. sichuanensis and C. ziguiensis)). The genera Limnocnida may consist of 6 species, three from Africa (L. tanganjicae, L. victoriae, L. congoensis) and 3 from India (L. indica, L. biharensis, L. nepalensis). The status of Astrohydra (from Japan), Mansariella and Keralika (both from India) is uncertain. Additionally, the present study suggests that Craspedacusta and at least one type of Calpasoma hydrants are identical and Astrohydra may be closely related to Craspedacusta and/or Calpasoma.A comparison of the freshwater medusae with species described from saline lakes and brackish sites (Australomedusae from Australia and Moerisia from Egypt, Black Sea, Caspian Sea and Ganges Estuary) shows that these two groups are not closely related.

The Impact of Climate Change on Lakes in Central Europe

◦by 2071‐2100. The associated projections for the rainfall give even more cause for concern with the reductions in some areas approaching 50% in summer. In this chapter we analyse impacts of changing weather conditions on lakes in Central Europe. Long-term data sets from a number of lakes are used to link measured variables to climate signals. Particular attention is paid to the lakes in the perialpine region which are known to be very sensitive to short-term changes in the weather (Psenner, 2003; Thompson et al., 2005). Here, the topography and the steep orography enhance the water cycle, and result in flooding, debris flows, avalanches, vertical plant migration etc. The Alps also form a barrier to the mass movement of air and are responsible for the sharp climatic divide between Atlantic, Continental and Mediterranean influences. Central Europe is a variously and vaguely defined region. Rather than a physical entity, it is more a reflection of a shared history. The results summarized here are based on the analysis of long-term climatological and limnological data from the countries shown in Fig. 20.1. These include Germany (DE), Poland (PL), the Czech Republic (CZ), Slovakia (SK), Switzerland (CH), Lichtenstein (LI), Austria (AT) and Hungary (HU). The Central European countries are geographically diverse with landforms ranging from the North-German Lowlands, through the Alps to the Hungarian plain. The pannonian plain in the eastern part is also a major climatic ‘crossing point’ and is affected by the Eastern-European continental, the WesternEuropean oceanic and the Mediterranean influence.

The Impact of Variations in the Climate on Seasonal Dynamics of Phytoplankton

Phytoplankton, an assemblage of suspended, primarily autotrophic single cells and colonies, forms part of the base of the pelagic food chain in lakes. The responses of phytoplankton to anthropogenic pressures frequently provide the most visible indication of a long-term change in water quality. Several attributes related to the growth and composition of phytoplankton, such as their community structure, abundance as well as the frequency and the intensity of blooms, are included as indicators of water quality in the Water Framework Directive. The growth and seasonal succession of phytoplankton is regulated by a variety of external as well as internal factors (Reynolds et al., 1993; Reynolds, 2006). Among the most important external factors are light, temperature, and those associated with the supply of nutrients from point and diffuse sources in the catchment. The internal factors include the residence time of the lakes, the underwater light regime and the mixing characteristics of the water column. The schematic diagram (Fig. 14.1) shows some of the ways in which systematic changes in the climate can modulate these seasonal and inter-annual variations. The effects associated with the projected changes in the rainfall are likely to be most pronounced in small lakes with short residence times (see George et al., 2004 for some examples). In contrast, those connected with the projected changes in irradiance and wind mixing, are likely to be most important in deep, thermally stratified lakes.

Regional and Supra-Regional Coherence in Limnological Variables

Limnologists and water resources managers have traditionally perceived lakes as discrete geographical entities. This has resulted in a tendency for scientific lake studies to concentrate on lakes as individuals, with little connection either to each other or to large-scale driving forces. Since the 1990s, however, a shift in the prevailing paradigm has occurred, with lakes increasingly being seen as responding to regional, rather than local, driving forces. The seminal work on regional coherence in lake behaviour was that of Magnuson et al. (1990), who showed that many features of lakes within the same region respond coherently to drivers such as climate forcing and catchment processes. From this study it emerged that the degree of coherence among lakes is greatest for those properties most directly affected by climate forcing. Specifically, the physical properties of lakes tend to vary in a more coherent way than their chemical and biological properties (see also Kratz et al., 1998). Further overviews of the topics of coherence and climate-driven variability, focusing

On the influence of the freshwater jellyfish Craspedacusta sowerbii on the zooplankton community

Craspedacusta sowerbii was described for the first time in 1880 (LANKESTER 1880). Since then, the medusae have been found in many places sometimes at considerable densities (DEJDAR 1934, STADEL 1961, DVMONT 1994). Occasionally, an increase in the jellyfish population is accompanied by a decrease in some zooplankton species (DVNHAM 1941, AcKER & MuscAT 1976, STRAVIS 1996). However, hardly anything is known about the quantitative impact of Craspedacusta on the zooplankton community (DoosoN & CoorER 1983, DEVRIES 1992, DuMONT 1994). In 1995 we studied a large population of Craspedacusta (1,000 ind./m2) in a small shallow hypertrophic lake near Aachen (Germany). Here, wirh rhe increase in jellyfish numbers, a decrease o f bosminids and cyclopoid copepods to very low densities was observed. At rhe same rime, the lake was dominared by whirefish (Rutilus rutilus). In order ro invesrigate wherher Craspedacusta was a major reason for the zooplankton decline, we conducted an enclosure experiment in 1996.

Predation of freshwater jellyfish on Bosmina: the consequences for population dynamics, body size, and morphology

Invertebrate predators may cause strong changes in behaviour, life-history, and morphology of prey species. However, little is known about the influence of jellyfish on such characteristics of their prey. This study analyses the impacts of the freshwater jellyfish Craspedacusta sowerbii on life history and morphological defenses in a population of the cladoceran Bosmina longirostris. Length of mucro and antennule, sizedependent number of eggs, size at maturity, and size of juveniles, adults, and egg-carrying females were investigated during a 23 days experiment using medusae-enriched and control enclosures filled with natural plankton populations. Significant differences in parameters investigated were found not only between treatments, but also within treatments over time. Changes in Bosmina life-history parameters and morphology in controls were probably due to predation by cyclopoid copepods. The significant increase in the size of adults and egg-carrying females as well as the increase in mucro and antennule length in medusaeenriched enclosures are discussed as defense strategies against the freshwater jellyfish.

Long-term nitrate concentrations in four perialpine lakes: regional coherence and the effects of climate change

Climate change is expected to result in increasing stress on aquatic ecosystems (STRAILE et al. 2003). Observations over the last few decades indicate the climate in much of Europe, especially in winter, has been undergoing change, with an increase in the frequency of unusually mild winters. These mild winters are thought to be associated with positive anomalies of the North Atlantic Oscillation (NAO; HuRRELL 1995). The NAO, which represents a 1arge-scale fluctuation in the air pressure difference between the subtropical Azores High and the subpo1ar Iceland Low, is commonly quantified in terms of an index based on meridional surface air pressure differences over the North Atlantic (HURRELL 1995). Strong positive va1ues o f this index are associated with westerly winds and mild, wet winters over most of Europe, whereas negative va1ues are associated with weak westerlies and cold, dry winters in Europe. Research on the influence o f the NAO on aquatic ecosystems is still at an early stage, but pronounced effects have already been reported from a number of European lakes (STRAILE et al. 2003 ). Here we concentrate on the influence of climate variability on winter/spring nitrate concentrations. Some evidence aiready exists showing that climate variability may affect nitrate concentrations in 1akes. In the U.K., where winters are usually mild, winter nitrate concentrations have been found to be negative1y correlated with mean winter air temperature and with the winter NAO index (MONTEITH et al. 2000, GEORGE et al. 2004). In contrast, in Sweden, where winters are usually harsh, the correlations are positive (WEYHENMEYER 2004). Additionally, there seem to be differences in the response o f nutrients ( e.g. phosphate, nitrate) to climate variability amo n g lakes o f different size (STRAILE et al. 2003), with smaller lakes apparently reacting more sensitively than larger ones. However, until now no study has been conducted on the impact o f climate on nitrate concentrations in the lakes of central Europe. As the influence ofthe NAO on mean winter air temperature in central Europe is comparable to that in north-western Europe (see fig. 6 o f HURRELL & VAN LOON 1997), we might expect to find a similar relationship between nitrate-N and the winter NAO in central Europe as that found by GEORGE et al. (2004) for the U.K.