New nematode is hermaphrodite: One of the smallest known earthworms found in Jaén

Around nine kilometres south of the city of Jaén (Spain), Spanish scientists have found a new species of nematode in the compost at a vegetable garden. The specimens found are extremely small, with adults measuring 0.2 mm in length. Moreover, there are no males among these roundworms, making the new nematodes a rare hermaphrodite species.

Nematodes are small worms that measure around 1 millimetre long and live freely in soil or water. They feed on bacteria, single-cell algae, fungi or other nematodes; they can also parasitise other animals or plants. But the most striking fact about them is their ability to adapt.

Scientists from the Andalusian Nematology Group at the University of Jaén focused on studying how a type of worm usually associated to damp environments has adapted to live in the dry ecosystems in the south of the Iberian Peninsula. This gave rise to the discovery of new species exclusive to extreme environments, which scientists could use to detect processes of desertification.

This is the case with Protorhabditis hortulana, a new species of nematode found in a vegetable garden nine kilometres south of Jaén, in a region known as Puente de la Sierra.

"We studied the nematofauna in a compost heap used to fertilise the plot and realised that it contained some very small nematodes," says Joaquín Abolafia of the department of Animal Biology, Plant Biology and Ecology of the University of Jaén, and the lead author of the study, published in the journal Zootaxa.

An unusual worm

The new species belongs to a genus which has been recorded in all continents except for the Americas and Antarctica. It is especially frequent in European soil and currently includes fifteen species with similar characteristics: small in size, measuring less than 1 mm; large mouths; usually both males and females exist.

However, in the case of P. hortulana, the adult specimens found measured 2 mm, an unusual size for this animal. The smallest nematodes found to date appeared in marine settings. "This is one of the smallest known edaphic [earth] nematodes, and it feeds on the bacteria of the compost," highlights the scientist.

Another characteristic that surprised the researchers is that all members of the species are female. "They reproduce by fertilising their ova with sperm that they produce themselves in part of their oviduct. This means they can be defined as a hermaphrodite species, a very rare trait in nematodes. This is considered a biological adaptation in the process of evolution, in the light of the difficulty of finding males in the medium they live in," Abolafia stresses.

The group of scientists is continuing their research to learn about the adaptability of these nematodes in areas that are similar to the southern part of the Iberian Peninsular, such as Iran and southern Africa, where there is a soil water deficit. "Preliminary analysis is promising," the researcher concludes.

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