Developmental gene expression in the eyes of the pygmy squid Xipholeptos notoides.

The eyes of squids, octopuses, and cuttlefish are a textbook example for evolutionary convergence, due to their striking similarity to those of vertebrates. For this reason, studies on cephalopod photoreception and vision are of importance for a broader audience. Previous studies showed that genes such as pax6, or certain opsin-encoding genes, are evolutionarily highly conserved and play similar roles during ontogenesis in remotely related bilaterians. In this study, genes that encode photosensitive proteins and Reflectins are identified and characterized. The expression patterns of rhodopsin, xenopsin, retinochrome, and two reflectin genes have been visualized in developing embryos of the pygmy squid Xipholeptos notoides by in situ hybridization experiments. Rhodopsin is not only expressed in the retina of X. notoides but also in the olfactory organ and the dorsal parolfactory vesicles, the latter a cephalopod apomorphy. Both reflectin genes are expressed in the eyes and in the olfactory organ. These findings corroborate previous studies that found opsin genes in the transcriptomes of the eyes and several extraocular tissues of various cephalopods. Expression of rhodopsin, xenopsin, retinochrome, and the two reflectin genes in the olfactory organ is a finding that has not been described so far. In other organisms, it has been shown that Retinochrome and Rhodopsin proteins are obligatorily associated with each other as both molecules rely on each other for Retinal isomerisation. In addition, we demonstrate that retinochrome is expressed in the retina of X. notoides and in the olfactory organ. This study shows numerous new expression patterns for Opsin-encoding genes in organs that have not been associated with photoreception before, suggesting that either Opsins may not only be involved in photoreception or organs such as the olfactory organ are involved in photoreception.

Mesoscale eddies exert inverse latitudinal effects on global industrial squid fisheries.

Squid species, as a burgeoning global food source, has garnered significant concerns due to expanding fisheries and little regulation. Elucidating the dynamics of squid fisheries and their biophysical coupling mechanisms is crucial for predicting spatiotemporal variations in squid fisheries and their sustainable management. Mesoscale eddies are discrete rotating oceanographic features that dominate local environmental variations and have been shown to modulate top predators. However, given controls of both predators and environmental factors, it remains unknown how eddies impact mid-trophic level species such as squids. Using satellite-based global squid fishery datasets, we showed an inverse latitudinal pattern of eddy-induced squid fisheries, where fishing activities are aggregated in (repelled from) cyclonic (anticyclonic) eddy cores in tropical waters and anticyclonic (cyclonic) eddy cores in temperate waters, and this pattern can be significantly enhanced with increasing eddy amplitude. Regarding solely the satellite-based global squid fisheries, eddy-induced environmental variations may generate a trade-off between food intake and energy expenditure, causing these oceanic squids to prefer cool cyclonic eddies in hot but food-limited waters, and warm anticyclonic eddies in nutritious but heat-limited waters. Given that eddy activity is projected to continuously enhance under global warming, our finding of eddy-driven bottom-up control for squid fisheries highlights an increasingly important hotspot for squid stock predictions and ecosystem-based ocean management in a changing climate.

Insights on long-term ecosystem changes from stable isotopes in historical squid beaks.

BACKGROUND: Assessing the historical dynamics of key food web components is crucial to understand how climate change impacts the structure of Arctic marine ecosystems. Most retrospective stable isotopic studies to date assessed potential ecosystem shifts in the Arctic using vertebrate top predators and filter-feeding invertebrates as proxies. However, due to long life histories and specific ecologies, ecosystem shifts are not always detectable when using these taxa. Moreover, there are currently no retrospective stable isotopic studies on various other ecological and taxonomic groups of Arctic biota. To test whether climate-driven shifts in marine ecosystems are reflected in the ecology of short-living mesopredators, ontogenetic changes in stable isotope signatures in chitinous hard body structures were analysed in two abundant squids (Gonatus fabricii and Todarodes sagittatus) from the low latitude Arctic and adjacent waters, collected between 1844 and 2023. RESULTS: We detected a temporal increase in diet and habitat-use generalism (= opportunistic choice rather than specialization), trophic position and niche width in G. fabricii from the low latitude Arctic waters. These shifts in trophic ecology matched with the Atlantification of the Arctic ecosystems, which includes increased generalization of food webs and higher primary production, and the influx of boreal species from the North Atlantic as a result of climate change. The Atlantification is especially marked since the late 1990s/early 2000s. The temporal patterns we found in G. fabricii's trophic ecology were largely unreported in previous Arctic retrospective isotopic ecology studies. Accordingly, T. sagittatus that occur nowadays in the high latitude North Atlantic have a more generalist diet than in the XIXth century. CONCLUSIONS: Our results suggest that abundant opportunistic mesopredators with short life cycles (such as squids) are good candidates for retrospective ecology studies in the marine ecosystems, and to identify ecosystem shifts driven by climate change. Enhanced generalization of Arctic food webs is reflected in increased diet generalism and niche width in squids, while increased abundance of boreal piscivorous fishes is reflected in squids' increased trophic position. These findings support opportunism and adaptability in squids, which renders them as potential winners of short-term shifts in Arctic ecosystems.

Seasonal-Spatial Distribution Variations and Predictions of Loliolus beka and Loliolus uyii in the East China Sea Region: Implications from Climate Change Scenarios.

Global climate change profoundly impacts the East China Sea ecosystem and poses a major challenge to fishery management in this region. In addition, closely related species with low catches are often not distinguished in fishery production and relevant data are commonly merged in statistics and fishing logbooks, making it challenging to accurately predict their habitat distribution range. Here, merged fisheries-independent data of the closely related squid Loliolus beka (Sasaki, 1929) and Loliolus uyii (Wakiya and Ishikawa, 1921) were used to explore the construction and prediction performance of species distribution models. Data in 2018 to 2019 from the southern Yellow and East China Seas were used to identify the seasonal-spatial distribution characteristics of both species, revealing a boundary line at 29.00° N for L. uyii during the autumn, with the highest average individual weight occurring during the summer, with both larvae and juveniles occurring during the autumn. Thus, the life history of L. uyii can be divided into winter-spring nursery and summer-autumn spawning periods. L. beka showed a preference for inshore areas (15-60 m) during the summer and offshore areas (32.00-78.00 m) during the winter. High-value areas of both species included inshore areas of the southern Yellow and mid-East China Seas during the autumn, enlarging during the spring to include central areas of the survey region, before significantly decreasing during the summer. Therefore, this study provides both a novel perspective for modeling biological habitat distribution with limited data and a scientific basis for the adjustment of fishery resource management and conservation measures in the context of climate change.

Anatomy and size of Megateuthis, the largest belemnite.

Belemnite rostra are very abundant in Mesozoic marine deposits in many regions. Despite this abundance, soft-tissue specimens of belemnites informing about anatomy and proportions of these coleoid cephalopods are extremely rare and limited to a few moderately large genera like Passaloteuthis and Hibolithes. For all other genera, we can make inferences on their body proportions and body as well as mantle length by extrapolating from complete material. We collected data of the proportions of the hard parts of some Jurassic belemnites in order to learn about shared characteristics in their gross anatomy. This knowledge is then applied to the Bajocian genus Megateuthis, which is the largest known belemnite genus worldwide. Our results provide simple ratios that can be used to estimate belemnite body size, where only the rostrum is known.

A Theoretical Comparison of Alternative Male Mating Strategies in Cephalopods and Fishes.

We used computer simulations of growth, mating and death of cephalopods and fishes to explore the effect of different life-history strategies on the relative prevalence of alternative male mating strategies. Specifically, we investigated the consequences of single or multiple matings per lifetime, mating strategy switching, cannibalism, resource stochasticity, and altruism towards relatives. We found that a combination of single (semelparous) matings, cannibalism and an absence of mating strategy changes in one lifetime led to a more strictly partitioned parameter space, with a reduced region where the two mating strategies co-exist in similar numbers. Explicitly including Hamilton's rule in simulations of the social system of a Cichlid led to an increase of dominant males, at the expense of both sneakers and dwarf males ("super-sneakers"). Our predictions provide general bounds on the viable ratios of alternative male mating strategies with different life-histories, and under possibly rapidly changing ecological situations.

Orthoceratoid and coleoid cephalopods from the Middle Triassic of Switzerland with an updated taxonomic framework for Triassic Orthoceratoidea.

Orthoconic cephalopods are subordinate, but persistent, widespread and regionally abundant components of Triassic marine ecosystems. Here, we describe unpublished specimens from the Anisian (Middle Triassic) Besano Formation at Monte San Giorgio, Switzerland. They can be assigned to two major but unrelated lineages, the Coleoidea and the Orthoceratoidea. The orthoceratoids belong to Trematoceras elegans (Münster, 1841) and occur regularly within the Besano Formation, are uniform in size, and have few available morphological characters. In contrast, coleoids are more diverse and appear to be restricted to shorter intervals. A new coleoid is described as Ticinoteuthis chuchichaeschtli gen. et sp. nov. To better put the orthoceratoids of the Besano Formation into perspective, we also synthesise the current taxonomy of Triassic orthoceratoids on a global scale. The currently used scheme is largely outdated, with very little taxonomic progress in the past 100 years. Despite previous research showing the distinctness of Triassic orthoceratoids from Palaeozoic taxa, they are still commonly labelled as "Orthoceras" or "Michelinoceras", which are confined to the Palaeozoic. We show that Triassic orthoceratoids probably belong to a single lineage, the Trematoceratidae, which can be assigned to the Pseudorthocerida based on the embryonic shell and endosiphuncular deposits. Many Triassic species can probably be assigned to Trematoceras, but there are at least two additional Triassic orthoceratoid genera, Paratrematoceras and Pseudotemperoceras. Finally, we review the palaeobiogeographic and stratigraphic distribution of the group and outline possible future research directions.

Ritualized ink use during visual courtship display by males of the sexually dimorphic cuttlefish Sepia andreana.

Visual display is a crucial aspect of courtship, and their success relies on both display quality and the surrounding environment, such as the visual background. Cephalopods may release ink when attacked by predators or during aggressive interactions with conspecifics. Here, we report that ink is used as a part of the courtship display by males of the cuttlefish species Sepia andreana. Males of this species engage in a highly ritualized multimodal courtship using a pair of markedly long sexually dimorphic arms. At the climax of the courtship, the male releases a diffuse backdrop of ink near himself and then performs the specific courtship display by extending his sexually dimorphic arms and altering his body pattern to pale in front of this ink backdrop, and then proceeds to mate. This novel use of cephalopod ink could make the surroundings darker and more homogeneous, potentially serving as a temporary modification of the visual environment for courtship display.

The complete mitochondrial genome of Octopus vulgaris.

BACKGROUND: The Octopus vulgaris species complex consists of numerous morphologically similar but genetically distinct species. The current publicly available mitogenome of this species has been generated from a specimen collected from Tsukiji Fish Market, Tokyo, Japan. Octopus from the northwestern Pacific Ocean are now considered to be a separate species, Octopus sinensis. For this reason, we hypothesised that the current record of O. vulgaris was sequenced from a specimen of O. sinensis. Here, we sequenced the first complete mitogenome of a specimen of Octopus vulgaris sensu stricto that was collected from the species' confirmed distribution areas in northeastern Atlantic. METHODS AND RESULTS: The complete mitogenome was assembled de novo and annotated using 250 bp paired-end sequences. A single circular contig 15,655 bp in length with a mean read coverage of 1089 reads was reconstructed. The annotation pipeline identified 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNA) and two ribosomal RNAs. A maximum likelihood phylogenetic tree recovered the assembled mitogenome as the sister taxon of a monophyletic group comprising O. sinensis and the previously published mitogenome of "O. vulgaris" from Japan. This confirms that the latter was a Japanese specimen of O. sinensis. CONCLUSION: The mitogenome sequenced here is the first to be published for Octopus vulgaris sensu stricto. It represents an important first step in genetics-informed research on the evolution, conservation, and management of this commercially important species.

Inventory of mollusks from the estuary of the Paraíba River in northeastern Brazil / Inventário de moluscos do estuário do Rio Paraíba no nordeste do Brasil

Abstract: Coastal ecosystems of northeastern Brazil have important biodiversity with regard to marine mollusks, which are insufficiently studied. Here we provide an inventory of mollusks from two sites in the estuary of the Paraíba River. Mollusks were collected in 2014 and 2016 on the coast and sandbanks located on the properties of Treze de Maio and Costinha de Santo Antônio. The malacofaunal survey identified 12 families, 20 genera and 21 species of bivalves, 17 families, 19 genera and 20 species of gastropods and one species of cephalopod. Bivalves of the family Veneridae Rafinesque, 1815 were the most representative, with a total of five species. Gastropods of the family Littorinidae Children, 1834 had the greatest species richness. The most abundant species were: Neritina virginea (Linnaeus, 1758), Brachidontes exustus (Linnaeus, 1758), Crassostrea brasiliana (Lamarck, 1819), Cerithium atratum (Born, 1778), Anomalocardia brasiliana (Gmelin, 1791), Parvanachis obesa (C. B. Adams, 1845), Phrontis polygonata (Lamarck, 1822), Littoraria angulifera (Lamarck, 1822), L. flava (King, 1832), Tagelus plebeius (Lightfoot, 1786), Echinolittorina lineolata (d'Orbigny, 1840) and Iphigenia brasiliensis (Lamarck, 1818). The results show that the study area has considerable species richness of Mollusca, requiring environmental monitoring in the region mainly due to the economic importance of some species to the local population.

Resumo: Os ecossistemas costeiros do nordeste do Brasil têm uma importante biodiversidade de moluscos marinhos, a qual ainda é insuficientemente estudada. Este trabalho representa um inventário dos moluscos em duas localidades no estuário do Rio Paraíba. Moluscos foram coletados entre 2014 e 2016 na costa e área de restinga localizadas nas propriedades de Treze de Maio e Costinha de Santo Antônio. Este levantamento malacofaunístico identificou 12 famílias, 20 gêneros e 21 espécies de bivalves, 17 famílias, 19 gêneros e 20 espécies de gastrópodes e uma espécie de cefalópode. Os bivalves da família Veneridae Rafinesque, 1815 foram os mais representativos com um total de cinco espécies. Os gastrópodes da família Littorinidae Children, 1834 apresentaram a mais alta riqueza de espécies. As espécies mais abundantes foram: Neritina virginea (Linnaeus, 1758), Brachidontes exustus (Linnaeus, 1758), Crassostrea brasiliana (Lamarck, 1819), Cerithium atratum (Born, 1778), Anomalocardia brasiliana (Gmelin, 1791), Parvanachis obesa (C. B. Adams, 1845), Phrontis polygonata (Lamarck, 1822), Littoraria angulifera (Lamarck, 1822), L. flava (King, 1832), Tagelus plebeius (Lightfoot, 1786), Echinolittorina lineolata (d'Orbigny, 1840) e Iphigenia brasiliensis (Lamarck, 1818). Os resultados mostram que a área estudada tem uma considerável riqueza de espécies de Mollusca, necessitando de monitoramento ambiental, principalmente devido à importância econômica de algumas espécies para a população local.