Cape Town – A new ‘pearl white’ freshwater crab species has been discovered in the ‘forgotten’ Eastern Cape forests of South Africa.

Prof Savel Daniels, a molecular taxonomist at Stellenbosch University, says crabs are relatively well studied in South Africa but for some reason forests have been neglected in sampling efforts.

“Nobody has ever intensively sampled the forests in the Eastern Cape where we (incidentally) found the species at Mbotyi,” he told the FBIP.

The study formed part of the Eastern Cape Forest project, one of the Large Integrated Projects funded by the Foundational Biodiversity Information Programme (FBIP).

Mbotyi is a picturesque forested region northeast of Port St Johns and adjacent to the East Coast of South Africa.

‘Sympatry’

The crab, which shimmers in the presence of light, was collected from under stones found in small streams which flow towards the coast.

In a case of what phylogeographers call ‘sympatry’ the pearl white crab lives alongside a known rust brown species belonging to the African freshwater crab genus Potamonautes.

Like a divorced couple who still share the same house, the two related [but genetically distinct] populations are sympatric because they exist in the same geographic area and thus frequently encounter one another without breeding.

In a sense Daniels was lucky to have discovered the specimen with its striking colour difference compared to its counterpart, P. sidneyi.

In recent times and particularly with invertebrates, such discoveries, where the scientist has a clear morphological difference as a ‘lead’ for identifying a potential new species, are rare.

‘Colour morphs’

In Daniels’ line of work he often encounters ‘cryptic species’ where animals which are similar to the human eye are genetically very different. In other cases animals look different but show no significant genetic differences – different ‘morphs’.

Daniels set out to answer whether the two crabs were indeed different species, or less spectacularly, two superficial ‘colour morphs’ with the one being pearl white and the other rust brown.

Back in the laboratory at the Stellenbosch University Evolutionary Genomics Facility samples from both groups of animals were subjected to DNA sequencing, looking at three genes known by geneticists as ‘COI, 12S rRNA, and 16S rRNA’.

DNA sequence divergence

The DNA sequence divergence (i.e. the genetic difference) for the COI gene, usually a primary marker in animal genetic studies, was striking at 13.42%.

To gain a better perspective on divergence values molecular taxonomists need to look at which values from prior studies were used to designate something as sufficiently different to be called a ‘new species’.

Daniels’ paper, published in the Journal of Crustacean Biology, cited two prior studies with values ranging from 2.8% to 14.7% in the one, and 7.9% between two species in the other.

There could be no doubt that the shimmering pearl white specimen from Mbotyi was a new species to science.

Daniels found no morphological characteristics with which to distinguish P. sidneyi from the new Mbotyi species except for the striking colour difference. The latter was inspiration for the naming of the new species, one of the few opportunities for creativity in describing a new species.

As a tribute to the Xhosa people of the Mbotyi region Daniels decided to give the newly discovered crab the species epithet of mhlophe, meaning ‘white’ in isiXhosa.

He says the discovery is important as it highlights the biodiversity of the area, and further establishes the region as a ‘biodiversity hotspot’, a tourism draw card.

“Tourism in the region creates a lot of sustainable job opportunities,” he says.

The Foundational Biodiversity Information Programme (FBIP) is a long-term programme to generate, manage and disseminate foundational biodiversity information and knowledge to improve decision-making, service delivery and create new economic opportunities.

Examining species boundaries among two South African freshwater crabs, with the description of a new specie… by Dane McDonald on Scribd