Global warming has dramatic impacts on ecological systems and can abruptly stretch the buffering capacity of ecosystems over the limits. It is this, the speed of global change that challenges the tools of present-day environmental scientists. New sensitive bioindicator and biomonitoring tools may help to better monitor, understand and eventually foresee global factors and consequences of environmental change. For marine environments the most simple animals, the placozoans, hold the promise of such a valuable and urgently needed biomonitoring system.

Trichoplax and other placozoans represent novel model organisms with tremendous potential for long-term monitoring of environmental change. These most simple metazoans are globally distributed in coastal marine waters, are highly sensitive to environmental factors (cf. Fig. 1), posses the smallest nuclear and the largest mitochondrial animal genome, and are exceptionally suited for field work and experimental studies (incl. ecophysiological and functional genomic studies). In placozoans we can use an innovative and unique mix of approaches to monitor the consequences of environmental change at the level of gene expression, development and population genetics. With whole genome sequences, single cell transcriptome sequences, and a unique repertoire of sympatric and allopatric placozoan species at hand, the time has come to firmly establish this simplest multicellular animal as a “Rosetta Stone” for environmental research on coastal marine environments. 

Fig. 1: Two closely related and sympatrically occurring species of the placozoon Trichoplax react highly differently to increasing ocean temperature and acidity. Trichoplax adhaerens (H1) reacts to this stress with increased sexual  reproduction (a large oocyte is seen in the centre of the animal), while T. spec. nov. (H2) reacts with sharp changes in vegetative propagation rates (here shown as no. of animals over time). Other placozoan species may also change development and morphology when faced with environmental “stress”.

Present and future work: Our long-term goals include the use of placozoans as a biomonitoring system for environmental studies in the world’s oceans. Quantifying changes in the placozoan genomes and transcriptomes in causal relation to ecological adaptations to changing environments has become feasible. Using field studies, high-throughput next generation sequencing, functional genomics, state-of-the art bioinformatics and new chip technologies I believe that placozoans offer unique opportunities to follow (and eventually model) the effects of global environmental change in coral reefs, mangroves and even temperate water ecosystems.

1. Schroth W, Streit B, Schierwater B (1996) Evolutionary handicap for sea turtles. Nature 384: 521-522.
2. Schroth W, Ender A, Schierwater B (2005) Molecular biomarkers and adaptation to environmental stress in the moon jelly (Aurelia spp.). Mar Biotechnol 7: 449-461. 

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