Girardia, Ball, 1974

Catalá, Alejandro, Benítez-Álvarez, Lisandra, Diez, Yander L., Blasco, Gema & Riutort, Marta, 2024, Treasure island: DNA data reveals unknown diversity in Cuban freshwater planarians (Platyhelminthes: Tricladida), Zoologia (e 23101) 41, pp. 1-13 : 9

Cuban Girardia evolutionary relationships

The phylogenetic trees of Girardia obtained from the concatenated dataset show similar major phylogenetic relationships as those estimated by BenÍtez-Álvarez et al. (2023b). Nonetheless, the South American clade was already defined as an unsupported and unresolved group in BenÍtez-Álvarez et al. (2023b). Thus, more data and a focused study are necessary to resolve its relationships. As for the two newly sequenced Cuban putative species, they show an ancient relationship to the rest of the Girardia ingroup. The two Cuban lineages and a Mexican species constitute the first lineages to diverge before the South American clade diversifies, although the order of divergences among these three groups is not supported and they form a trichotomy ( Fig. 4 ).

Sluys (1992) suggested that species of Girardia from The Antilles are related to those of South America by comparing the morphology of their copulatory apparatus. However, excluding G. sinensis , in the present molecular analyses the Cuban species do not group within the South American or the North American + South American clades but, otherwise, are rather related to a species from Mexico ( Fig. 4 ). The Cuban biota had three major sources of colonization (North, Central, and South America) related to the geological history of the island ( Hedges 2001). Our results suggest that the colonization of the Cuban archipelago by representatives of Girardia could originate from Central America, probably in a quite ancient event considering the basal branches leading to the two Cuban lineages in our trees. On the other hand, a previous biogeographic hypothesis suggested a single-species island endemism for the freshwater planarians on The Antilles ( Ball 1983). However, our results show a different scenario for the Cuban archipelago indicating that each island may harbor more than one species, suggesting an ancient colonization and posterior speciation occurring on the islands. As proposed by Sluys (1992), the previously observed pattern is the result of sampling biases rather than the real biogeographic history of the group in the region. To have a better understanding of the distribution pattern of planarians in The Antilles, sampling unexplored areas not only in Cuba but also in the other Antillean islands and the continental regions surrounding them is necessary.

Figures

Figure 4. Phylogenetic relationships within Girardia based on dataset 3 (COI+EF) including Cuban specimens. Groups indicated by letters and colours highlight the clades delimited in Benítez-Álvarez et al. (2023b). (A) Consensus of Bayesian and Maximum Likelihood analyses with collapsed clades (triangles) and singletons (rectangles) showing species identifications, when available, and countries of origin of the various terminals. The nodes with a support below 0.5 or 50 have been collapsed. Symbols above branches: posterior probability values. Symbols below branches: ultrafast bootstrap and SH-aLRT support. (B) Bayesian circular tree with all terminals; values at nodes correspond to posterior probability support. The colours in the terminals indicate Cuban specimens. Scale bar represents substitutions per nucleotide.