Discovering the Unknown – What do we still not know about tardigrades from tropical regions?

Water bears (Tardigrada) are microscopic invertebrates renowned for their extraordinary resilience, allowing them to survive even under the most extreme environmental conditions. Although they occur in habitats ranging from glacier-covered mountain peaks to the deep ocean, the warm and humid climate of the tropics appears to provide particularly favourable conditions for organisms dependent on periodic water availability. Africa, characterised by immense climatic, habitat and biological diversity, therefore has the potential to represent an important spot of tardigrade diversity. Yet, around 200 formally described tardigrade species are currently known from the African continent, representing less than 15% of the world's tardigrade fauna. This number likely reflects, to a large extent, the uneven level of knowledge across different regions rather than their actual diversity.
This is clearly demonstrated by research conducted in the Repuublic of South Africa, one of the best-studied regions of african continent in terms of its tardigrade fauna. Tardigrades were detected in 50% of 172 moss, lichen and soil samples. In total, nine species new to science were confirmed, including one representing a new genus. This corresponds to a 19% probability of discovering a previously unknown species and a 1.2% probability of discovering a new genus. Notably, seven of the nine newly discovered species were each found in just one sample out of total amount, indicating a high proportion of rarely detected taxa and suggesting the existence of further, previously unrecognised diversity.
As sampling intensity increases, the rate of discovery of additional new taxa is expected to gradually decline. However, the high frequency of newly discovered species and the presence of taxa found exclusively in single samples indicate that the potential for further discoveries remains very high, even in relatively well-studied regions. Compilation of data on tardigrade diversity and distribution in Africa, with particular emphasis on South Africa and Uganda, allows us to identify significant gaps in current knowledge and areas with particularly high potential for further research. Recent studies demonstrate that even in more intensively explored regions, additional sampling continues to reveal new taxa. This suggests that the current picture of tardigrade diversity in Africa may still be substantially underestimated, and that many regions of the continent remain important areas for further research on the diversity, distribution and evolution of these remarkable organisms.