Predictive models of abundance are valuable for assessing how environmental factors influence the susceptibility of areas to colonization by non-native species. Limnoperna fortunei, native to Southeast Asia, is an invasive species in South America with potential impacts similar to those of Dreissena polymorpha in North America and Europe. In this study, we evaluated the influence of limnological factors on the structure and abundance of L. fortunei larvae across three fluvial systems in the Upper Paran & aacute; River floodplain. We addressed two main questions: (1) which limnological features are most important for the establishment of L. fortunei in a given area, and (2) how do these features influence the population dynamics of this invader? Our results revealed that L. fortunei larval densities were significantly affected by both spatial and temporal variations in limnological factors. Higher temperatures, chlorophyll-a concentrations, and turbidity were associated with increased reproduction rates and larval densities of L. fortunei. Conversely, high water velocity and water levels were linked to larger proportions of larger and damaged larvae, suggesting that these conditions may hinder successful establishment. Our findings indicate that L. fortunei thrives particularly well in warmer and more productive waters. We advocate for future research on the dispersal of L. fortunei to incorporate these environmental predictors, better forecasting the risk of successful colonization.
In this scoping review, we synthesize information available on the physiological ecology of the hard clam (Mercenaria spp.). This review builds on chapters within the Biology of the Hard Clam, summarizing research conducted in the 25 years since publication, and broadens the scope to include all physiological responses to environmental stressors. This comprehensive literature review was conducted to determine the effects of environmental stress on the physiological ecology of Mercenaria mercenaria and M. campechiensis to improve restoration efforts, our understanding of natural populations under future climate scenarios, and aquaculture. We searched Scopus, Web of Science Core Collection, ProQuest Dissertations & Theses Global, ProQuest Science & Technology Database Collection, Google Scholar and articles from the National Oceanic and Atmospheric Administration (NOAA) website based on target keywords related to physiological responses and environmental parameters of interest. Our search identified 2,406 potential studies that were then screened by title and abstract, then full text to determine eligibility based on inclusion and exclusion criteria. Ultimately, 219 papers were synthesized that evaluated the response of hard clams to temperature, food availability, pH, dissolved oxygen, salinity, nutrients, turbidity and multiple stressors. The individual response was quantified based on survival, growth, metabolism, reproduction, feeding or behaviour. Most research focused on the effects of temperature and food on the northern quahog, Mercenaria mercenaria, with an emphasis on growth and survival of larger individuals. A paucity of research exists on the southern quahog and early life stages of hard clams, as well as the impacts of environmental stress on reproduction, metabolism and behaviour. As many of these parameters contribute to the ecosystem services provided by hard clam, filling the research gaps identified in this review will improve hard clam restoration efforts, aquaculture and our understanding of the physiological capacity of these congeners in modified habitats.
This study examined spatial and temporal variation in size at maturity (L50) of the broadcast-spawning mollusc Chiton articulatus, a small-scale fishery species distributed in the Mexican Tropical Pacific. Adult specimens were collected monthly over multiple years between 2011 and 2023 at seven intertidal sites spanning a latitudinal gradient, encompassing both cold (La Ni & ntilde;a) and warm (El Ni & ntilde;o) events of the El Ni & ntilde;o-Southern Oscillation (ENSO), hereafter referred to as 'thermal phases'. Total body length (TL), body weight and gonad weight were recorded, and the gonadosomatic index (GSI) was calculated for each individual. L50 was estimated annually at the population level using pooled individuals by fitting a logistic model to TL frequency distributions of mature adults (GSI >= 4%). Across the species distribution, estimated L50 values ranged from c. 50 to 64 mm TL, with the highest L50 values observed in Sinaloa (northernmost site), whereas the lowest occurred in Oaxaca (southernmost site). Notably, Nayarit (20 degrees 45 ' N; located near the tropical-subtropical climatic transition zone) deviated from the general latitudinal pattern, exhibiting consistently smaller L50 values (50.8 mm) than expected. Central populations (Jalisco, Colima, Michoac & aacute;n and Guerrero) showed intermediate and relatively uniform L50 values ranging from 55.5 to 56.5 mm. Unexpectedly, L50 exhibited opposite responses to thermal phases at the two geographic range margins. At the northern distribution limit, warmer phases were associated with larger L50 values, whereas L50 decreased during colder phases in years (2021-2023). In contrast, at the southern distributional limit, larger L50 values were associated with cold phases. Overall, the findings indicate that spatial patterns provide an important geographic context for variation in size at maturity in C. articulatus and reflect the influence of thermal variability interacting with local ecological conditions. These results highlight the importance of spatially explicit reproductive monitoring and adaptive fishery management strategies, particularly under ongoing climate variability.
The formation of the sclerites (spicules and scales) in the girdles of five species of polyplacophorans of the order Chitonida (Acanthochitona fascicularis, Acanthochitona crinita, Lepidochitona cinerea, Ischnochiton rissoi and Rhyssoplax olivacea) has been studied at the ultrastructural level and by optical and transmission electron microscopy to analyse the relationships of the scleritome within the Aculifera. The sclerites of the studied chitons were secreted inside an invagination of the microvillous cellular membrane of a single epithelial cell located in the papillae. This invagination was initially secluded from the organic cuticle, and it represented a minute extrapallial space, favouring the saturation of ions inside. Active secretion of vesicles and organic network from the microvilli of the crystallization chamber wall was observed. These vesicles penetrated the forming sclerite. When the sclerites grew, additional secreting cells appeared at the basal zone of the crystallization chambers and the extrapallial space between the forming sclerites and the microvillous walls became nanometric. At the end of the formation of the sclerites, the crystallization chambers opened, releasing the sclerites into the cuticle. The sclerites were temporarily attached to the papillae by elongated microvilli but eventually were released and reached the cuticle surface. The pattern of secretion of the sclerites in the studied Polyplacophora was similar to that observed in most of the studied Solenogastres. This pattern, with a microvillous secreting epithelium, is similar to that of the shell-secreting mantle epithelium of conchiferan molluscs, such as the bivalves, some gastropods and the cephalopod Nautilus. It should, therefore, be considered the plesiomorphic state in Aculifera.
Siphonaria is a genus of panpulmonate marine limpets often mistaken for 'true' or patellogastropod limpets because of their remarkably convergent appearance. Among the c. 130 species of Siphonaria reported worldwide, S. japonica (Donovan, 1824) is the most commonly encountered species in the northwestern Pacific (NWP) region, including China, Japan and Korea. Siphonaria japonica shells are highly variable, leading to a prevalent view of a single species with considerable ecophenotypic variation. This study presents morphological (shell and radula) and molecular [sequence data for the mitochondrial gene cytochrome c oxidase subunit I (COI)] evidence leading to the discovery of a still undescribed species that has been previously mistaken for S. japonica in Korea and likely in other NWP localities. Our integrated analysis of shell and radula characters for selected sequenced Korean voucher specimens has revealed an overlooked species within the range of specimens considered to be S. japonica. The 'tall form' is distinguished from the 'short form' by a larger, oval shell with an elevated, posteriorly curved apex and a weakly undulated margin formed by alternating thick primary and thin secondary ribs, as well as a higher number of radula teeth per row with unicuspid and/or bicuspid mesocone in the innermost lateral teeth. In contrast, the 'short form' has a smaller, oval shell with a lower, flattened apex; a coarsely undulated margin due to strong primary ribs without secondary ribs; and fewer radula teeth per row, with a consistently bicuspid mesocone. Mitochondrial COI sequence analysis revealed a substantial genetic divergence (uncorrected p-distance 19.2-20.5%) between the two shell forms, exceeding intraspecific variation observed within each form. Phylogenetic analyses consistently recovered them as distinct, well-supported clades, indicating that they represent separate species. An extensive comparative analysis of both species across the NWP is required to investigate the distribution of the two shell forms and understand the ecological and phylogeographic factors influencing these co-occurring species.
Extreme events such as heatwaves have become more frequent, severe and long-lasting. Microbial endolithic communities, which have long been considered as parasitic and detrimental to intertidal mussels, have increasingly been considered as thermally advantageous for mussel beds through the increased albedo related to the white shell discolouration, which lowers body temperatures and increases survival rates. Despite the putative beneficial thermal effects endolith-infested mussel beds may confer to infauna using these beds as habitats, we are still critically lacking information about the ability of highly motile species to actively choose infested beds over noninfested ones. The present study was opportunistically conducted during the unprecedented mid-July 2022 atmospheric heatwave that coincided with midday low tides to investigate whether the common periwinkle Littorina littorea actively selects infested beds over noninfested ones, and whether L. littorea inhabiting infested beds had lower body temperature than those found in noninfested beds and on bare rocks. Littorina littorea is shown to consistently actively select endolith-infested Mytilus edulis patches as thermally benign microhabitats under conditions of extreme heat stress. This behaviour drastically decreased L. littorea body temperatures, which were on average 8.7 degrees C and 10.2 degrees C cooler than individuals observed in noninfested mussel patches and on bare rock, respectively. This decrease notably surpasses by far the heat-induced microhabitat choice reported in the literature and the putative beneficial effects of aggregation behaviour and evaporative cooling as thermal adaptations to heat stress. They were, however, comparable to the thermal benefits of postural behaviours reported for high-shore littorinids that experience some of the most stressful intertidal thermal conditions on a global scale. The ability of L. littorea, and eventually other motile infauna species to choose thermally benign endolith-infested mussel beds may then alleviate thermal stress through an increase in their thermal safety margin.
A common assumption within invasion biology is that successful introduced species are physiologically more competent than native species. Temperature in freshwater ecosystems is a primary factor shaping species distribution and abundance, making thermal tolerance a critical trait to predict the effects of climate change on species locally adapted to their abiotic environment. We hypothesized that introduced species would have a broader thermal tolerance range (TTR) than native species. To test this, we evaluated the thermal tolerance of four native freshwater gastropods species (Aroapyrgus clenchi, Pyrgophorus coronatus, Mexinauta impluviatus and Pomacea flagellata) and two introduced species (Tarebia granifera and Melanoides tuberculata) in the Pantanos de Centla Biosphere Reserve, Mexico. Temperature tolerance ranges were determined using progressive temperature increments of eight temperatures between 19 and 35 degrees C. All species exhibited a Gaussian distribution in their thermal tolerance and survived relatively high temperatures, as is expected for tropical species. However, species-specific analyses showed that a wider thermal capacity was not an attribute of introduced species. The results show that the native Pomacea flagellata exhibited the widest TTR (38.3 degrees C), a value that exceeded the TTRs of the introduced species. The smallest native species, Aroapyrgus clenchi and Pyrgophorus coronatus, displayed the lowest thermal capacity, positioning them as potential 'losers' under predicted climate warming. Our findings highlight the importance of taking a dynamic perspective when evaluating physiological traits in the context of biological invasions, where evaluating physiological traits of both introduced and native species is critical for predicting community responses to global change and for prioritizing conservation efforts.
Size-assortative mating is a well-documented pattern in a wide diversity of animals, including marine gastropods. In most cases, positive assortative mating by size is due to males mating with larger, more fecund females, which is often mediated by males following female mucus trails in gastropods. Fecundity selection has been invoked to explain not only size-assortative mating but also sexual size dimorphism in most taxa studied to date. To widen the generality of these hypotheses, we tested for these patterns in the intertidal, dioecious gastropod Nerita yoldii across sites and years in Hong Kong. In N. yoldii, females were larger than males in most mating pairs, and size was generally a predictor of fecundity in females. There was, however, no evidence of size-assortative mating or sex-dependent mucus trail following. There was also no clear pattern of sexual selection, measured using sexual selection intensity, which varied between sites and years. Overall, the reproductive behaviour of N. yoldii was dependent on site and year and did not conform to the common patterns found in other marine gastropods. Evidence from this tropical nerite, therefore, suggests sexual selection should be considered as only one of several potential mechanisms underlying these common patterns.
Phylogenetic trees of the slug family Limacidae were constructed using two nuclear markers-internal transcribed spacer 1 and the single-copy intron 8 of the embryonic lethality and abnormal visual system gene (ELAVI8)-and two mitochondrial ones-cytochrome c oxidase subunit I (COI) and 16S ribosomal rRNA. Two Eumilax species formed the most basal clade, supporting the distinction between subfamilies Eumilacinae and Limacinae. The next most basal clade consisted of Svanetia and a monophyletic Gigantomilax. Limax, Limacus and Turcomilax formed a clade that was the sister to the remaining genera considered. Of these, Lehmannia, Malacolimax and Weltersia formed a clade that was the sister to Ambigolimax and to Bielzia. ELAVI8 was particularly good at resolving the basal parts of the tree, but the mitochondrial markers were necessary for more distal parts. Despite their lacking a rectal caecum, Malacolimax wiktori and an undescribed North African species belong in Ambigolimax, as does A. melitensis. We argue for synonomizing Lehmannia islandica and L. janetscheki with L. marginata. Intraspecific variation in COI was often high (typically over 5%), and Malacolimax mrazeki appeared paraphyletic. We plotted the worldwide distributions of the 26 COI haplotypes of A. valentianus (based on 193 sequences) and 17 haplotypes of A. parvipenis (110 sequences). In both these invasive species, some haplotypes occur widely, but geographical restrictions are also apparent. North America is impoverished in haplotype diversity, suggesting a colonization via Europe. The low diversity of A. valentianus in Spain contradicts the assumption that it is a native there; probably Ambigolimax species derive from North Africa. Ambigolimax waterstoni and Lehmannia rupicola are newly recorded for Corsica based on reinterpretation of sequences in the BOLD database.
Recent molecular studies of the extant nautilid genera Nautilus and Allonautilus have revealed new information about the relationships among species. However, identifying relevant morphological descriptors for phylogenetic reconstruction continues to be a challenge for the species in these two genera. This study investigates the colour patterns of modern nautilids and defines new characters that can be used in phylogenetic analysis. The relevance of these characters (i.e. the likelihood that they reflect a phylogenetic signal) was assessed by mapping them onto the most recent molecular phylogeny. Ancestral character reconstructions and the retention index were employed to evaluate the strength of the phylogenetic signal and explore the evolution of the characters. Our results reveal that variation in the pattern of colour stripes, including their width, sharpness, number and distribution, as well as the presence of longitudinal bands, branching, intercalation and discontinuities in the stripes, are useful in discriminating clades. Thus, this study provides the basis for a more comprehensive phylogeny of both recent and, possibly, fossil nautilids based on morphological characters.
Numerous Quaternary and subrecent occurrences of brackish water snails (Truncatelloidea: Hydrobiidae, Cochliopidae[?]) have been recorded in northern Central Germany (Thuringia, Saxony-Anhalt). This high concentration of inland occurrences is unparalleled in Central Europe. The Holocene mass occurrences in the Mansfeld Lake region have become particularly well known. Today, brackish water snails are extinct in Central Germany. This makes the discovery of numerous mummified hydrobiid snails in the Regius Collection (Senckenberg Natural History Collections Dresden, Museum of Zoology), which Karl Regius was able to collect alive in 1948/1949 in a side ditch of the S & uuml;lze river north-east of Dodendorf, all the more significant. This is the only place in Central Germany where the snails have ever been found alive. This material provided the first opportunity to carry out a reliable identification using molecular genetic methods. Not only was Ecrobia ventrosa (Montagu, 1803) confirmed for Central Germany, but also extensive comparisons were made with 33 recent populations of this species from European and North African coasts. These showed that E. ventrosa from Dodendorf was most closely related to the populations of the Baltic Sea, the North Sea and the neighbouring Atlantic.
The Tortonian phosphatic hardground and overlying section of coquinas interbedded with bioturbated bioclastic packstones at S'Algar, Menorca, Spain, record two distinct bivalve faunas. The phosphatic hardground is dominated by infaunal, aragonitic taxa, while the overlying beds comprise epifaunal, calcitic fossils. These two distinct faunas represent m & eacute;langes from reworking of shells from different shelf environments. Hardground bivalves are preserved in four preservational forms (denoted 'A' to 'D') that are mixed together in the mineralized bed. Each taphonomic form is characterized by distinct bivalve associations, as well as by different levels of boring (Entobia isp.) and encrustation. A Glycymeris-Crassatella-Clypeaster association ('preservation A') records part of an upper ramp slope fauna that was periodically affected by high-energy and low-oxygen conditions due to upwelling waters. It represents a pre-mineralization fauna, as well as part of an opportunistic hard ground association along with Gastrochaena. A smaller sized contemporaneous fauna ('preservation B'), characterized by an arcid-carditid-venerid association, is derived from the middle ramp that was affected by storms and a persistent-westward flowing current that intermittently drove upwelling. The other two hardground preservation forms ['forms C and D' (unaltered)] suggest a multiphase mineralization mechanism. In contrast to the hardground fauna, the overlying shell beds and bioturbated bioclastic packstones contain a distinct assemblage of fossil bivalves, predominantly comprising pectinoids (spondylids, pectinids) and oysters (ostreids, gryphaeids) with varying degrees of disarticulation, fragmentation and wear. The majority of the pectinoids are unencrusted and show no sign of boring, the exceptions being spondylids. Pectinoids dominate the lowermost section with thick shell beds, while gryphaeids dominate the predominantly bioturbated uppermost sediments. These faunas are interpreted as having been derived from a middle ramp palaeoenvironment that was affected by storm activity that punctuated periods of low sedimentation on a current-swept seafloor. Changes in the frequency and directionality of storm and current activity drove environmental change through time.
Marine molluscs exhibit a wide range of developmental modes that can be explained by phylogenetic history but that can also be explained by ecological adaptation, involving trade-offs among fecundity, dispersal and offspring survival. We examined the energy apportioned to reproduction by two congeneric, co-existing species of the intertidal limpet Siphonaria that fall into different clades of the genus. Both species lay egg masses. Those of S. concinna contain thousands of eggs that hatch after a few days as planktotrophic larvae. The egg masses of S. serrata contain hundreds of eggs that develop for around 4 weeks and hatch as crawl-away juveniles. We measured each species' annual reproductive output in terms of fecundity (number of egg masses per individual and estimated total number of eggs) and egg mass dry weight, to estimate an annual reproductive energy budget for a standard animal by measuring the calorific content of egg masses. Despite major differences in fecundity and development, both species apportioned similar amounts of energy into each egg mass (c. 0.17 J), with similar annual energetic investment into spawning (c. 1.06 and 1.04 J, respectively, for S. concinna and S. serrata). The life history attributes of the two species correspond with the classic r- and K-selected traits and the results suggest an evolutionarily stable value for reproductive investment where these two species co-exist.
Microhabitat choice has been proposed as a mechanism contributing to the maintenance of colour polymorphism in marine gastropods, based on observed associations between shell colour and microhabitat in certain species (e.g. Littorina saxatilis). To examine this hypothesis, different colour morphs of L. saxatilis were studied following a mark-recapture experimental design to assess whether this species preferentially chooses those microhabitats matching its shell colour, presumably favouring crypsis. Our results revealed no significant association between shell colour and microhabitat. Furthermore, despite movement patterns being affected by habitat heterogeneity, no clear evidence supporting an active search for crypsis was found. These results suggest that microhabitat choice does not play an important role in maintaining intrapopulation shell colour polymorphism in L. saxatilis, highlighting the relevance of alternative, more plausible processes such as differential predation.
