Mediterranean Lithophyllum stictiforme (Corallinales, Rhodophyta) is a genetically diverse species complex: implications for species circumscription, biogeography and conservation of coralligenous habitats

Abstract

Lithophyllum species in the Mediterranean Sea function as algal bioconstructors, contributing to the formation of biogenic habitats such as coralligenous concretions. In such habitats, thalli of Lithophyllum, consisting of crusts or lamellae with entire or lobed margins, have been variously referred to as either one species, L. stictiforme, or two species, L. stictiforme and L. cabiochiae, in the recent literature. We investigated species diversity and phylogenetic relationships in these algae by sequencing three markers (psbA and rbcL genes, cox2,3 spacer), in conjunction with methods for algorithmic delimitation of species (ABGD and GMYC). Mediterranean subtidal Lithophyllum belong to a well‐supported lineage, hereby called the L. stictiforme complex, which also includes two species described from the Atlantic, L. lobatum and L. searlesii. Our results indicate that the L. stictiforme complex consists of at least 13 species. Among the Mediterranean species, some are widely distributed and span most of the western and central Mediterranean, whereas others appear to be restricted to specific localities. These patterns are interpreted as possibly resulting from allopatric speciation events that took place during the Messinian Salinity Crisis and subsequent glacial periods. A partial rbcL sequence from the lectotype of L. stictiforme unambiguously indicates that this name applies to the most common subtidal Lithophyllum in the central Mediterranean. We agree with recent treatments that considered L. cabiochiae and L. stictiforme conspecific. The diversity of Lithophyllum in Mediterranean coralligenous habitats has been substantially underestimated, and future work on these and other Mediterranean corallines should use identifications based on DNA sequences.

Coralline Algae in a Changing Mediterranean Sea: How Can We Predict Their Future, if We Do Not Know Their Present?

“…The two recent studies of Pezzolesi et al (2019) and De Jode et al (2019) unraveled a striking case of cryptic diversity: the Lithophyllum stictiforme complex. Lithophyllum stictiforme and Lithophyllum cabiochiae have been long known as common species in the Mediterranean subtidal, where they are major contributors to the formation of coralligenous concretions (Athanasiadis, 1999a; see also Boudouresque and Verlaque, 1978;Furnari et al, 1996).…”

“…The genetic diversity of these organisms unraveled by DNA sequence data is much higher than indicated by morpho-anatomical data, both in geniculate and non-geniculate species. Cryptic diversity has been shown to abound in marine macroalgae (De Clerck et al, 2013;Verbruggen, 2014); although corallines have a morpho-anatomical structure that offers more characters for species discrimination compared to other red seaweeds, they are perhaps the group of rhodophytes in which this situation is most pervasive (Pezzolesi et al, 2019). Second, many morphoanatomical features traditionally used to identify corallines are not reliable for identification purposes.…”

“…This may create great confusion when different cryptic species have different geographical distributions. Considering this problem, in absence of molecular data the practice of identifying specimens from a certain geographical region with names of species described from widely separated regions should be abandoned (Pezzolesi et al, 2019).…”

“…Whereas some authors have separated these species, others (Cormaci et al, 2017;Guiry and Guiry, 2019) consider L. cabiochiae and L. stictiforme conspecific. Pezzolesi et al (2019), sequencing three markers (cox2,3, psbA, rbcL) in samples collected from many sites in the western and central Mediterranean, concluded that Lithophyllum stictiforme represents a complex of at minimum 13 cryptic species. De Jode et al (2019), combining Sanger sequencing (COI, psbA, LSU) and transcriptomics, reached very similar conclusions, showing that on the French coasts specimens with the L. stictiforme/L.…”

The Minute Alga Schizocladia ischiensis (Schizocladiophyceae, Ochrophyta) Isolated by Germling Emergence from 24 m Depth off Rhodes (Greece)

“…Significant gaps remain in the knowledge of the seaweed flora of the Mediterranean, which is regarded as a species-rich region, with 190 green, 277 brown, and 657 red macroalgae recorded so far [1,2]. However, there are a large number of taxa in need of taxonomic reassessment, and recently revealed cases of cryptic diversity [3,4] suggest that molecular-assisted identification will be useful to improve our knowledge of this flora [2]. In general, there are more macroalgal records in the Western than in the Eastern Mediterranean [5]; however, it is unclear whether this is due to a lower macroalgal diversity in this part of the Mediterranean Sea or reflects a general trend of fewer biodiversity studies in the Eastern in comparison to the Western basin.…”