A biogeographic framework of octopod species diversification: the role of the Isthmus of Panama

Deep genetic divergences and few morphological changes support the cryptic speciation in Larimus breviceps (Sciaenidae, Acanthuriformes) from the western South Atlantic

We evaluate the evidence of cryptic speciation in Larimus breviceps, a species widely distributed in the western South Atlantic, from the Greater Antilles to Santa Catarina in Brazil. Mitochondrial (COI, Cyt b, and Control Region) and nuclear (IGF1 and Tmo-4C4) sequences were obtained from populations in the western South Atlantic. The analysis revealed two genetically distinct, sympatric lineages with no gene flow, with L. breviceps lineage II (LII) being closer to Larimus pacificus than to the L. breviceps lineage I (LI). The most recent common ancestor (TMRCA) for the L. breviceps LI and L. pacificus/L. breviceps LII clade dates from 12.3 Ma, whereas TMRCA for the L. pacificus and L. breviceps LII dates from 3.4 Ma, indicating that speciation processes may be related to the rise of the Isthmus of Panama. Despite these profound genetic differences, morphometric analyses found only subtle differences between lineages, with specimens of the LI being slightly larger than those of the LII, suggesting the existence of cryptic species. Within each lineage there is a pattern of panmixia within the study area. Therefore, we suggest that it is necessary a taxonomic revision of Larimus from the western Atlantic to validate the species status of such lineages.

Atlantic Oceanic Squids in the "Grey Speciation Zone"

Cryptic species complexes represent an important challenge for the adequate characterization of Earth's biodiversity. Oceanic organisms tend to have greater unrecognized cryptic biodiversity since the marine realm was often considered to lack hard barriers to genetic exchange. Here, we tested the effect of several Atlantic and Mediterranean oceanic barriers on 16 morphospecies of oceanic squids of the orders Oegopsida and Bathyteuthida using three mitochondrial and one nuclear molecular marker and five species delimitation methods. Number of species recognized within each morphospecies differed among different markers and analyses, but we found strong evidence of cryptic biodiversity in at least four of the studied species (Chtenopteryx sicula, Chtenopteryx canariensis, Ancistrocheirus lesueurii, and Galiteuthis armata). There were highly geographically structured units within Helicocranchia navossae that could either represent recently diverged species or population structure. Although the species studied here can be considered relatively passive with respect to oceanic currents, cryptic speciation patterns showed few signs of being related to oceanic currents. We hypothesize that the bathymetry of the egg masses and duration of the paralarval stage might influence the geographic distribution of oceanic squids. Because the results of different markers and different species delimitation methods are inconsistent and because molecular data encompassing broad geographic sampling areas for oceanic squids are scarce and finding morphological diagnostic characters for early life stages is difficult, it is challenging to assess the species boundaries for many of these species. Thus, we consider many to be in the "grey speciation zone." As many oceanic squids have cosmopolitan distributions, new studies combining genomic and morphological information from specimens collected worldwide are needed to correctly assess the actual oceanic squid biodiversity.

Interrelationships and biogeography of the New World pufferfish genus Sphoeroides (Tetraodontiformes: Tetraodontidae) inferred using ultra-conserved DNA elements

Colonization of the New World by marine taxa has been hypothesized to have occurred through the Tethys Sea or by crossing the East Pacific Barrier. To better understand patterns and timing of diversification, geological events can be coupled with time calibrated phylogenetic hypotheses to infer major drivers of diversification. Phylogenetic relationships among members of Sphoeroides, a genus of four toothed pufferfishes (Tetraodontiformes: Tetraodontidae) which are found nearly exclusively in the New World (eastern Pacific and western Atlantic), were reconstructed using sequences from ultra-conserved DNA elements, nuclear markers with clear homology among many vertebrate taxa. Hypotheses derived from concatenated maximum-likelihood and species tree summary methods support a paraphyletic Sphoeroides, with Colomesus deeply nested within the genus. Analyses also revealed S. pachygaster, a pelagic species with a cosmopolitan distribution, as the sister taxon to the remainder of Sphoeroides and recovered distinct lineages within S. pachygaster, indicating that this cosmopolitan species may represent a species complex. Ancestral range reconstruction may suggest the genus colonized the New World through the eastern Pacific before diversifying in the western Atlantic, though date estimates for these events are uncertain due to the lack of reliable fossil record for the genus.

Genetic confirmation of Octopus insularis (Leite and Haimovici, 2008) in South Florida, United States using physical features and de novo genome assembly

The distribution of octopuses within the Octopus vulgaris species complex remains inadequately understood. Species determination can be complex and involves characterizing a specimen's physical features and comparing its genetic makeup to other populations. In this study, we present the first genetic confirmation of Octopus insularis (Leite and Haimovici, 2008) inhabiting the coastal waters of the Florida Keys, United States. We employed visual observations to identify species-specific body patterns of three wild-caught octopuses and used de novo genome assembly to confirm their species. All three specimens exhibited a red/white reticulated pattern on their ventral arm surface. Two specimens displayed body pattern components of deimatic display (white eye encircled by a light ring, with darkening around the eye). All visual observations were consistent with distinguishing features of O. insularis. We then compared mitochondrial subunits COI, COIII, and 16S in these specimens across all available annotated octopod sequences, including Sepia apama (Hotaling et al., 2021) as a control outgroup taxon. For species exhibiting intraspecific genomic variation, we included multiple sequences from geographically distinct populations. Laboratory specimens consistently clustered into a single taxonomic node with O. insularis. These findings confirm O. insularis presence in South Florida and suggest a more extensive northern distribution than previously assumed. Whole genome Illumina sequencing of multiple specimens enabled taxonomic identification with well-established DNA barcodes while also generating the first de novo full assembly of O. insularis. Furthermore, constructing and comparing phylogenetic trees for multiple conserved genes is essential for confirming the presence and delineation of cryptic species in the Caribbean.

Morphological Description and Phylogenetic Analyses of a New Species of Callistoctopus (Cephalopoda, Octopodidae) from China

A new octopus species, Callistoctopus tenuipes sp. nov., was formally described from the southeastern coastal waters of China using morphological description and molecular analysis methods. C. tenuipes sp. nov. is a small- to moderate-sized octopus, which is characterized by very narrow and long arms. Although it was previously misidentified as the juvenile of Octopus minor (Sasaki, 1920), it can be recognised by spots, gill lamellae count, funnel organ shape, enlarged suckers, and ligula shape. C. tenuipes sp. nov. differs from the small-sized octopus Callistoctopus xiaohongxu, mainly in the gill lamellae count, funnel organ shape, and arm-length index. In the molecular analysis, sequences obtained from the cytochrome c-oxidase subunit I (COI) gene of eight specimens were 590 bp in length. The pairwise Kimura 2-parameter (K2P) genetic distances between Octopodidae species ranged from 8.58 to 23.79% based on the COI gene. The phylogenetic analyses suggested that C. tenuipes sp. nov. belonged to the Callistoctopus clade and may have a close affinity with C. xiaohongxu and O. minor. Moreover, three species delimitation methods all strongly supported C. tenuipes as a separate species.

Morphological description and mitochondrial DNA-based phylogenetic placement of a new species of Callistoctopus Taki, 1964 (Cephalopoda, Octopodidae) from the southeast waters of China

In this study, we described a new species of octopus and named it Callistoctopusxiaohongxu sp. nov. based on nine specimens captured in the waters of southeast China. Callistoctopusxiaohongxu sp. nov. is a small to moderate-sized octopus. The most characteristic and defining morphological features are the reddish-orange to reddish-brown skin, gills with 8 or 9 lamellae per demibranch, \∧/-shaped funnel organ, and small suckers. Fragments obtained from the mitochondrial cytochrome c oxidase subunit I (COI) gene of nine specimens were 593 bp in length, and the genetic distance among the specimens of C.xiaohongxu sp. nov. and the other 16 octopods ranged from 11.13 to 21.09%. Topologies resulting from ML and BI analyses of the COI gene showed a highly supported monophyletic clade (bootstrap value [BS] = 94%, posterior probability [PP] = 100%) containing all the specimens identified as C.xiaohongxu sp. nov.

Origins of Galápagos’ land-locked vertebrates: what, whence, when, how?

Based on a synthesis of new molecular phylogenetic data, a detailed review is presented for the origins of the Galápagos’ native land-locked vertebrates [42 species; 11 clades: geckos (3), lava lizards (2), giant tortoises (1), iguanas (1), racer snakes (1) and oryzomyine rodents (3)]. Nine groups have roots in coastal Ecuador and Peru and would have been transported to the archipelago on rafts, many on the Humboldt Current. Inferring the sources of the giant tortoises, which probably floated over unaided, and the iguanas is more challenging because their closest living relatives occupy ground remote from the Pacific. Acknowledging uncertainties with the age-dating of both the phylogenetic tree nodes and the landmass emergences, seven, probably eight, of the colonizations likely involved beachings on the modern-day islands within the last 4 Myr. Three, possibly four, of the earlier arrivals may have been on now-submerged landmasses that were created by the Galápagos volcanic hotspot. Alternatively, the true sister taxa of the Galápagos species could be extinct and these colonizations, too, are more recent. This is likely for the giant tortoises. The assembled data set hints at the oldest/youngest clades showing the highest/lowest levels of diversification, although other factors also exert an influence.

Octopodoidea as predators near the end of the Mesozoic Marine Revolution

Octopodoidea are a highly versatile and diverse group of marine predators comprising > 200 species today; however, their diversity and ecology in deep time are virtually unknown. Because these soft-bodied cephalopods have a low preservation potential, only a single body fossil species has been documented. Unlike other modern cephalopods, octopodoids leave behind a characteristic drill hole on their molluscan and crustacean prey. These traces provide a means to track their presence and behaviour in deep time. Although severely understudied, some of such holes have been documented from the Eocene–Pleistocene fossil record. We document the oldest recognized drill holes attributed to octopodoids, found in lucinid bivalves from the Late Cretaceous (Campanian) of South Dakota, USA. These observations demonstrate that the drilling habit of these animals evolved early in the evolutionary history of Octopodoidea, ~25 Myr earlier than was previously known. The drilled lucinids lived in cold methane seeps in the Western Interior Seaway. These predation traces have never been found in fossil seeps previously, thus adding a new predator to the food web of cold seeps. Finally, our results provide direct evidence that Octopodoidea were an integral component of the rise of shell-destroying predators during the Mesozoic Marine Revolution.