Assessment of cophylogenetic patterns between the nematode genus Parapharyngodon spp. and their reptile hosts in the Canary Islands

Parasites affect some of the most important biological traits at the level of the host representing models of great interest to study coevolutionary patterns. Parapharyngodon is a genus of nematodes characterized by small bodies, sexual dimorphism and a direct life-cycle, depending entirely on their hosts to disperse. However, there is an ongoing discussion in the scientific world where some authors argue that Parapharyngodon species should be taxonomically classified as belonging to Thelandros, while others consider this a sister genus of Parapharyngodon. In order to assess the taxonomic status of Parapharyngodon spp. an integrative taxonomic approach, using both morphologic and genetic data, was carried. Phylogenetic analyses were performed using both 18S and 28S rRNA nuclear DNA sequences and combined with morphometric statistic tests in order to infer the relationships between Parapharyngodon species and the ones of Thelandros. Two Thelandros species and various Parapharyngodon spp. appeared as well-differentiated clades, potentially corroborating the generic status of Parapharyngodon. However, “Thelandros” galloti was estimated to be a sister species to Parapharyngodon echinatus, indicating the need of reassess the generic classification of this species. Other “Thelandros” species may also actually belong to Parapharyngodon, so the morphological characters used to delimit these groups also need to be redefined. Unexpectedly, Parapharyngodon micipsae is most likely a morphotype of P. echinatus and P. galloti rather than a distinct separate species. Again, this highlights the difficulty of delimiting species of these nematodes using only morphological characters. Although much is known about the morphological and ecological traits of Parapharyngodon spp. , little attention has been paid to the phylogeny of this group, or the potential for cospeciation within their hosts. In the Canary Islands Parapharyngodon species have been recorded to infect all three extant endemic lizard genera from this islands (Gallotia, Chalcides and Tarentola). DNA sequences from both18S and 28S rRNA nuclear markers were used to estimate the phylogeny of these parasites, which could then be compared to the well-known phylogenetic estimates of the reptile hosts. Two emerging different lineages were revealed, one from the most eastern islands of Lanzarote, Fuerteventura and Gran Canaria and the other comprising the more western islands of La Palma, La Gomera, Tenerife and El Hierro. Concerning the colonization patterns, it seems that this parasites colonized the Canary Islands in multiple independent events possibly partially related to the ones of Tarentola ancestral. FCUP Assessment of cophylogenetic patterns between the nematode genus Parapharyngodon spp. and their reptile hosts in the Canary Islands 5 Unexpectedly, since the hosts are all endemic to the islands, one sample from a gecko from Morocco forms part of one lineage, again demonstrating the complex nature of the model system. Gran Canaria harbours two sister lineages, one specific to Tarentola hosts and the other parasitizing Gallotia and Chalcides individuals. However, in general it is difficult to relate the estimates of genetic relationships with morphological differentiation, with hosts or even with geographic locations. Still, more studies using faster-evolving mitochondrial markers are needed to better understand Parapharyngodon phylogeny and then more accurately infer host-parasite interactions.