A Slovenian-led expedition has discovered four new spider species in a tropical forest in Madagascar, an island known for its rich biodiversity. All four raft spiders belong to the Dolomedes genus.

Biologist Matjaž Kuntner from the National Institute of Biology (NIB) and Kuang-Ping Yu, a doctoral candidate at NIB and the University of Ljubljana, described the new spiders in the paper Discovering Unknown Madagascar Biodiversity: Integrative Taxonomy of Raft Spiders (Pisauridae: Dolomedes), published in the scientific journal PeerJ in February.

They named them after fellow researchers Matjaž Bedjanič from NIB and Matjaž Gregorič from the Research Centre of the Slovenian Academy of Sciences and Arts (ZRC SAZU), two key persons for the expedition to succeed.

The new species are called Dolomedes gregoric, Dolomedes bedjanic, Dolomedes hydatostella and Dolomedes rotundus.

Kuntner told the Slovenian Press Agency that he and Gregorič had been to Madagascar several times in the past to explore and discover new species.

"Gregorič knew these environments very well. Together with Bedjanič, they co-organised this expedition and were key to its success on the ground and in the preparation stage."

NIB has been actively involved in spider research for some time, while Madagascar is one of the biodiversity hotspots where new species are regularly discovered.

Expedition members Kuang-Ping Yu, Matjaž Gregorič, Matjaž Bedjanič and Matjaž Kuntner. Photo: Matjaž Kuntner

Describing the new spiders, Kuntner said they are relatively large and charismatic, and unlike the majority of spiders live in freshwater habitats.

Such spiders are quite well known in our region, but less is known about their diversity in some other parts of the world, especially in tropical areas, he explained.

Still, Kuntner said that the discovery of four new species in Madagascar was quite unexpected.

"If we were to judge by localities in Slovenia, we would not expect so many new species. But in Madagascar we were exploring an area that we don't know much about the fauna and flora, and in such cases we do discover more of them."

Yu and Kuntner have developed a model of integrative taxonomy that takes into account morphological, molecular and ecological variation within and between species.

Using it, they confirmed their initial findings identifying four unknown species of Madagascar raft spiders in addition to the one already known.

According to NIB, the scientific results of the research are important in terms of discovering the biodiversity of the planet's hotspots and raising awareness of the importance of preserving Madagascar's unique nature, which is severely threatened by deforestation and other human activities.