Mitogenomic phylogeny of mud snails of the mostly Atlantic/Mediterranean genus Tritia (Gastropoda: Nassariidae)

Abstract

The mud snails endemic to the East Atlantic/Mediterranean region (genus Tritia; subfamily Nassariinae) account for the second highest diversity within the family Nassariidae (Gastropoda: Buccinoidea). In order to understand how the diversity of species, shell morphologies, and ecological traits evolved within this genus, a robust phylogenetic framework is needed, yet still unavailable due to high levels of homoplasy in shell morphology, the main trait used for their taxonomic classification. Here, the near-complete mitogenomes of 20 species representing more than half of the diversity of Tritia were sequenced. All mitogenomes of Tritia shared the same gene order, which is identical to the consensus reported for caenogastropods. The reconstructed phylogeny indicates that all analyzed Tritia species formed a natural group except Tritia vaucheri, which was sister to an early diverging clade within subfamily Nassariinae that includes species of genus Reticunassa sister to Nassarius jacksonianus and Nassarius sp. Within Tritia, the Northwest Atlantic species Tritia obsoleta was placed as the sister group of three mostly East Atlantic/Mediterranean clades (I-III), prompting the reinstatement of the genus Ilyanassa. The latter three clades corresponded to different shell features (I, shell mostly with marked sculpture; II, shell with strong nodules and small size; and III, smooth shell). For Tritia incrassata, the analyzed specimens from Norway and from the Spanish Mediterranean coasts showed notable genetic divergence, which may indicate the existence of cryptic species. The ancestral character state reconstruction of protoconch inferred that the ancestor of Tritia had planktotrophic larvae, and that a transition to lecithotrophy occurred independently at least three times within Nassariinae. The reconstructed chronogram dated the origin of Tritia in the Oligocene and main diversification events during the Miocene to Pleistocene, correlated with drastic shifts in local paleoecosystems caused by cooling events, eustatic sea level changes, and the Messinian Salinity Crisis that favored temperate taxa.

Phylogeny of Strombidae (Gastropoda) Based on Mitochondrial Genomes

“…This result supported the hypothesis that the present-day levels of strombid diversity were achieved by the Miocene (Roy, 1996). The divergence between the Eastern Pacific/Atlantic A. gigas + S. pugilis and the Indo-Pacific E. aratrum was dated to 26 Mya (Figure 6), similar to the divergence time (about 24 Mya) between the corresponding geographical groups of marine gastropod nassariids (Caenogastropoda: Nassariidae) (Yang et al, 2021). It was inferred that the ancestor of Eastern Pacific/Atlantic strombids originated from the European Tethys (Maxwell et al, (Roy, 1996), this global cooling event is likely to have favored species that could be adapted to a subtropical environment.…”

Estuarine retention of larvae: Contrasting effects of behavioral responses to turbulence and waves

“…In the lab, inlet snail larvae responded weakly to acceleration signals in early stages but lost this response at competency (Fuchs et al 2018). The taxonomic relationship between the inlet and shelf species is unresolved (Yang et al 2021), but given that the inlet larvae's acceleration response disappears ontogenetically, we speculate that both species originated on the shelf. Inlet snails may have diverged from their congeneric counterpart as larvae developed an ability to ignore accelerations and were more easily transported into and retained in coastal embayments.…”

Acclimation of intertidally reproducing sea‐snails protects embryos from lethal effects of transient hyperthermia

“…Nonetheless, it is worth emphasizing that P. vibex does not arrest cleavage for hours at embryo‐lethal threshold temperatures as does Ilyanassa . The strong arrest mechanism in Ilyanassa could be an evolutionary novelty arising within the Tritia clade of Nassariidae, possibly associated with a transition to living in the intertidal zone (Galindo et al, 2016; Yang et al, 2021). Alternatively, the lineage of Gulf coast P. vibex may have allowed an ancestral thermoprotective mechanism to weaken in response to relaxed selection connected with the small tidal range of the Caribbean basin.…”

“…Ilyanassa obsoleta and Phrontis vibex are distant relatives in the neogastropod clade Nassariidae (Galindo et al, 2016; Yang et al, 2021). Both species are common along the coastline from Maine to the Caribbean (and much farther south, in the case of P. vibex ).…”