In the last decade, phylogeographic analyses have uncovered a high level of cryptic diversity in subterranean taxa. In most cases, closely related cryptic species are geographically defined and allopatric. Recent extensive phylogeographic studies of the cave shrimp Troglocaris s. str. and the cave tube worm Marifugia cavatica in the Dinaric Karst using mitochondrial and nuclear genes, showed substantial level of cryptic diversity in both taxa. Most recovered cryptic lineages and phylogroups seem to be allopatric. By more detailed sampling and analyses (adding more specimens and populations), areas of sympatric occurrence of morphologically indistinguishable lineages were discovered in both taxa. We found them occurring syntopically in two areas: in the Italian Carso (cave shrimps and tube worms) and on Istra Peninsula (cave shrimps). Following the principle of competitive exclusion, two closely related species should not coexist in a stable environment; they must differ in their ecological niche, because without differentiation one species will exclude the other trough competition. At least three possible hypotheses can be put forward to explain this apparent paradox. First, as there are only few sites of syntopic occurrence, we might not be observing a long-term stable coexistence but rather the transient result of accidental immigration of one species into the range of another. Second, if co-occurring cryptic species indeed form real ecological communities, they could avoid competition through differentiation of niches by traits other than morphology. The problem with these two hypotheses is that we have yet to explain the nature of the putative reproductive barrier that both of them imply. The third hypothesis circumvents this problem by conjecturing that syntopic lineages are not species, but clones that reproduce asexually. That way, no reproductive barrier is needed to account for the occurrence of unique and stable mitochondrial and nuclear allelic combinations. Asexual reproduction has been described for decapods as well as serpulid tube worms. This mode of reproduction could represent an alternative evolutionary strategy for subterranean species.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 30216153