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Species distributions are shifting in response to increased habitat temperatures as a result of ongoing climate change. Understanding variation in physiological plasticity among species and populations is important for predicting these distribution shifts. Interspecific variation in intertidal ectotherms’ short-term thermal plasticity has been well established. However, intraspecific variation among populations from differing thermal habitats remains a question pertinent to understanding the effects of climate change on species’ ranges. In this study, we explored upper thermal tolerance limits and plasticity of those limits using a foot muscle metric and 2 cardiac metrics (Arrhenius breakpoint temperature, ABT, and flatline temperature, FLT) in adult file limpets Lottia limatula. Limpets were collected from thermally different coastal and inland-estuarine habitats and held for 2 wk at 13, 17 or 21°C prior to thermal performance assays. Compared to limpets from the warm estuary site, limpets from the cold outer coast site had similar foot muscle critical thermal maxima (CTmax; 35.2 vs. 35.6°C) but lower cardiac thermal tolerances (ABT: 30.5 vs. 35.1°C). Limpets from the cold coast site had higher acclimation responses in foot muscle CTmax (0.22°C per 1°C rise in acclimation) than those of the warm estuary site (0.07°C per 1°C rise in acclimation), but lower acclimation responses in cardiac thermal tolerance (ABT: -0.85°C per 1°C rise in acclimation) than those of the estuary site (ABT: 0.10°C per 1°C rise in acclimation). Since outer coast populations had lower cardiac plasticity and higher mortalities in the warm acclimation, we predict L. limatula from colder habitats will be more susceptible to rising temperatures. Our findings illustrate the importance of population-specific variation in short-term thermal plasticity when considering the effects of climate change on ectotherms.

Organismal metabolic rates reflect the interaction of environmental and physiological factors. Thus, calcifying organisms that record growth history can provide insight into both the ancient environments in which they lived and their own physiology and life history. However, interpreting them requires understanding which environmental factors have the greatest influence on growth rate and the extent to which evolutionary history constrains growth rates across lineages. We integrated satellite measurements of sea-surface temperature and chlorophyll-a concentration with a database of growth coefficients, body sizes, and life spans for 692 populations of living marine bivalves in 195 species, set within the context of a new maximum-likelihood phylogeny of bivalves. We find that environmental predictors overall explain only a small proportion of variation in growth coefficient across all species; temperature is a better predictor of growth coefficient than food supply, and growth coefficient is somewhat more variable at higher summer temperatures. Growth coefficients exhibit moderate phylogenetic signal, and taxonomic membership is a stronger predictor of growth coefficient than any environmental predictor, but phylogenetic inertia cannot fully explain the disjunction between our findings and the extensive body of work demonstrating strong environmental control on growth rates within taxa. Accounting for evolutionary history is critical when considering shells as historical archives. The weak relationship between variation in food supply and variation in growth coefficient in our data set is inconsistent with the hypothesis that the increase in mean body size through the Phanerozoic was driven by increasing productivity enabling faster growth rates.

The extraordinary diversity in molluscan body plans, and the genomic mechanisms that enable it, remains one of the great questions of evolution. The eight distinct living taxonomic classes of molluscs are each unambiguously monophyletic; however, significant controversy remains about the phylogenetic relationships among those eight branches. Molluscs are the second-largest animal phylum, with over 100 000 living species with broad biological, economic and medical interest. To date, only around 53 genome assemblies have been accessioned to NCBI GenBank covering only four of the eight living molluscan classes. Furthermore, the molluscan taxa where partial or whole-genome assemblies are available are often aberrantly fast evolving or recently derived lineages. Characteristic adaptations provide interesting targets for whole-genome projects, in animals like the scaly-foot snail or octopus, but without basal-branching lineages for comparison, the context of recently derived features cannot be assessed. The currently available genomes also create a non-optimal set of taxa for resolving deeper phylogenetic branches: they are a small sample representing a large group, and those that are available come primarily from a rarefied pool. Thoughtful selection of taxa for future projects should focus on the blank areas of the molluscan tree, which are ripe with opportunities to delve into peculiarities of genome evolution, and reveal the biology and evolutionary history of molluscs. This article is part of the Theo Murphy meeting issue ‘Molluscan genomics: broad insights and future directions for a neglected phylum’.

Background The processes through which populations originate and diversify ecologically in the initial stages of adaptive radiation are little understood because we lack information on critical steps of early divergence. A key question is, at what point do closely related species interact, setting the stage for competition and ecological specialization? The Hawaiian Islands provide an ideal system to explore the early stages of adaptive radiation because the islands span ages from 0.5–5 Mya. Hawaiian spiders in the genus Tetragnatha have undergone adaptive radiation, with one lineage (“spiny legs”) showing four different ecomorphs (green, maroon, large brown, small brown); one representative of each ecomorph is generally found at any site on the older islands. Given that the early stages of adaptive radiation are characterized by allopatric divergence between populations of the same ecomorph, the question is, what are the steps towards subsequent co-occurrence of different ecomorphs? Using a transcriptome-based exon capture approach, we focus on early divergence among close relatives of the green ecomorph to understand processes associated with co-occurrence within the same ecomorph at the early stages of adaptive radiation. Results The major outcomes from the current study are first that closely related species within the same green ecomorph of spiny leg Tetragnatha co-occur on the same single volcano on East Maui, and second that there is no evidence of genetic admixture between these ecologically equivalent species. Further, that multiple genetic lineages exist on a single volcano on Maui suggests that there are no inherent dispersal barriers and that the observed limited distribution of taxa reflects competitive exclusion. Conclusions The observation of co-occurrence of ecologically equivalent species on the young volcano of Maui provides a missing link in the process of adaptive radiation between the point when recently divergent species of the same ecomorph occur in allopatry, to the point where different ecomorphs co-occur at a site, as found throughout the older islands. More importantly, the ability of close relatives of the same ecomorph to interact, without admixture, may provide the conditions necessary for ecological divergence and independent evolution of ecomorphs associated with adaptive radiation. Electronic supplementary material The online version of this article (10.1186/s12862-018-1209-y) contains supplementary material, which is available to authorized users.

Many of the morphological and physiological adaptations that marine mammals exhibit for an aquatic life enhance their ability to feed. Mysticeti use baleen to filter large numbers (e.g., swarms of krill or schools of fish) of smaller prey, while Odontoceti generally use raptorial biting and/or suction to capture larger, individual prey, often after pursuit. Some species of Phocidae and walruses rely primarily on suction feeding while most use raptorial biting. Sea otters use their fore paws to capture sessile invertebrates. Dugongs feed by scouring the seafloor, cropping leaves of seagrasses or uprooting the rhizomess. Manatees also have large facial muscles used for grazing and browsing. The mammary glands of marine mammals are relatively flat and lie beneath the blubber or skin. The availability of food is often unpredictable and episodic, so animals will often eat as much as possible and build body fat reserves when food is available. This behavior insures that they have sufficient energy for periods of anticipated or unanticipated fasting.

The position of scaphopods in molluscan phylogeny remains singularly contentious, with several sister relationships supported by morphological and phylogenomic data: Scaphopoda + Bivalvia (Diasoma), Scaphopoda + Cephalopoda (Variopoda), and Scaphopoda + Gastropoda. Nervous system architecture has contributed significant insights to reconstructing phylogeny in the Mollusca and other invertebrate groups, but a modern neurophylogenetic approach has not been applied to molluscs, hampered by a lack of clearly defined homologous characters that can be unequivocally compared across the radical body plan disparity among the living clades. We present the first three-dimensional reconstruction of the anterior nervous system of a scaphopod, Rhabdus rectius, using histological tomography. We also describe a new putative sensory organ, a paired and pigmented sensory mantle slit. This structure is restricted to our study species and not a general feature of scaphopods, but it forms an integral part of the description of the nervous system in R. rectius. It also highlights the potential utility of neuro-anatomical characters for multiple levels of phylogenetic inference beyond this study. This potential has not previously been exploited for the thorny problem of molluscan phylogeny. The neuroanatomy of scaphopods demonstrates a highly derived architecture that shares a number of key characters with the cephalopod nervous system, and supports a Scaphopoda + Cephalopoda grouping.

Recognizing the threat of additive risk Humans are accelerating the extinction rates of species in both terrestrial and marine environments. However, species extinctions have occurred across time for a variety of other reasons. Finnegan et al. looked at the extinction rates across marine genera (groups of species) over the past 23 million years to determine intrinsic extinction rates and what traits or regions correspond to the highest rates. Combining patterns of intrinsic extinction with regions of high anthropogenic threat revealed taxa and areas, particularly in the tropics, where the risk of extinction will be especially high. Science , this issue p. 567

The relationships among the living classes of molluscs have remained contentious, in part because of a lack of consistent morphological characters that unequivocally unite clusters of taxa within this extremely disparate phylum. The osphradium, a chemosensory organ on or near the gills, is a putative potential synapomorphy of Mollusca. Although the osphradium regularly appears on illustrations of hypothetical unifying molluscan bauplans, the homology of these putative sensory structures has been debated in most classes. Considered examination of the evidence for homology based on development, ultrastructure, neural architecture, and function, demonstrates a lack of support for inferred homology among the varied structures described as ‘osphradia’. Neuroanatomical features are increasingly recognized as important for resolving deep phylogenetic divergences. The construction of morphological character sets for phylogenetic inference is dependent on robust determination of homology. Naming a structure does not underwrite its relationship to any other sensory organ. A fundamental assumption that one clade is ‘primitive’ may have biased the interpretation of anatomical results by early, and even some contemporary researchers, leaving the equality among important characters in doubt. Although these various sensory structures are no doubt real anatomical features, we question the assumption that there is a single molluscan osphradium and propose that at least two distinct classes of epithelial sensory structures have been identified as the molluscan osphradium. The complex suite of characters that describe the many varied sense organs in the mantle cavities of molluscs, may yet provide a foundation for neurophylogenetic insights to molluscan evolution.

Mollusks are the most morphologically disparate living animal phylum, they have diversified into all habitats, and have a deep fossil record. Monophyly and identity of their eight living classes is undisputed, but relationships between these groups and patterns of their early radiation have remained elusive. Arguments about traditional morphological phylogeny focus on a small number of topological concepts but often without regard to proximity of the individual classes. In contrast, molecular studies have proposed a number of radically different, inherently contradictory, and controversial sister relationships. Here, we assembled a data set of 42 unique published trees describing molluscan interrelationships. We used these data to ask several questions about the state of resolution of molluscan phylogeny compared with a null model of the variation possible in random trees constructed from a monophyletic assemblage of eight terminals. Although 27 different unique trees have been proposed from morphological inference, the majority of these are not statistically different from each other. Within the available molecular topologies, only four studies to date have included the deep sea class Monoplacophora; but 36.4% of all trees are not significantly different. We also present supertrees derived from two data partitions and three methods, including all available molecular molluscan phylogenies, which will form the basis for future hypothesis testing. The supertrees presented here were not constructed to provide yet another hypothesis of molluscan relationships, but rather to algorithmically evaluate the relationships present in the disparate published topologies. Based on the totality of available evidence, certain patterns of relatedness among constituent taxa become clear. The internodal distance is consistently short between a few taxon pairs, particularly supporting the relatedness of Monoplacophora and the chitons, Polyplacophora. Other taxon pairs are rarely or never found in close proximity, such as the vermiform Caudofoveata and Bivalvia. Our results have specific utility for guiding constructive research planning to better test relationships in Mollusca as well as other problematic groups. Taxa with consistently proximate relationships should be the focus of a combined approach in a concerted assessment of potential genetic and anatomical homology, whereas unequivocally distant taxa will make the most constructive choices for exemplar selection in higher level phylogenomic analyses. (Aculifera; Conchifera; Mollusca; Serialia; supertree; Testaria.)

Sea level change influences biodiversity of endemic cave fauna to varying degrees. In anchialine systems, a marine layer flows under less saline layers, each with differing associated fauna. We assess the role of present and historic (last glacial maximum – 18,000 years ago) distance from the ocean in determining species richness and phylogenetic diversity patterns for two groups of anchialine crustaceans: the marine-restricted Remipedia and a subset of groundwater-inhabiting atyid shrimp with greater tolerance for salinity variation. We calculated species richness and phylogenetic diversity per cave based on records of remipede and atyid diversity at 137 locations in the Yucatan Peninsula, Caribbean, Australia, and the Canary Islands. After calculating the distance of each cave’s surface opening from the past and present shoreline, we evaluated how species richness and phylogenetic diversity change with distance from the present and historic ocean. Remipede species richness and phylogenetic diversity declined rapidly with distance from the ocean. Ninety-five percent of the remipedes surveyed were located within 7 km of the present ocean and 18 km of the historic ocean. Atyid species richness and phylogenetic diversity declined more slowly with distance from the ocean than that of remipedes. Atyid shrimp were also distributed over a broader range: 95 % were located within 100 km of the present ocean and 240 km of the historic ocean. Our findings indicate that coastal geomorphology and salinity tolerance influence a clade’s distribution with respect to its distance from the ocean. We also report a possible latent response to sea level change.

We provide a size-based ontogenetic sequence of the development and differentiation of the lower reproductive tract of the heterobranch gastropod Helix aspersa (Muller 1774). Twelve development stages distributed among nine size classes were recognized based on readily visible changes in morphology and changes in tissue density. Geometric morphometrics was used to calculate the deformation between stages as represented by thin-plate spline bending energies. The developmental stages and sequence of developmental events are also compared to previously published scenarios for the evolution of stylommatophoran and other pulmonate reproductive tracts. These comparisons suggest that heterochronies, which include both acceleration and retardation, are operating in the morphological evolution of the pulmonate lower reproductive tract. This supports previous observations that largest number of developmental changes coincides with the transition to sexual maturity, which is also seen in the exponential curve of bending energies we observed in Helix aspersa. The belated organogenesis makes the ontogeny of the complex hermaphroditic reproductive system of pulmonates readily observable in size-friendly juveniles. This observation, coupled with the ease of raising individuals in the laboratory, recommends Helix aspersa as a potential model laboratory system for investigating molluscan evolutionary development.

Species interactions are best seen and understood through perturbations of the species themselves. These perturbations can be accomplished on small scales through controlled manipulations, but they sometimes happen on larger scales through more fortuitous contrasts over space or time. We used similarities and differences between the North Atlantic and Pacific oceans in an effort to improve understanding of the key dynamic processes that regulate the abundance and distribution of species. The North Atlantic biota is impoverished; many of its recent elements are derived from the North Pacific through transarctic biotic interchange. Sea otters, absent from the North Atlantic, drive a trophic cascade in the North Pacific by limiting herbivorous sea urchins, in turn allowing kelp and other macroalgae to flourish. Otariid pinnipeds are also absent from the North Atlantic. We suggest that the absence of sea otters as competitors and of otariid pinnipeds as predators favored the evolution of large body size in Atlantic cod. Cod therefore assumed the ecological role of sea otters in the North Atlantic, creating a functionally analogous ecosystem in which the collapse of cod has led to a kelp-to-urchin phase shift. The decline of cod and other finfish has also been instrumental in driving neritic/oceanic habitats in the North Atlantic from domination by fishes to domination by shrimps and other crustaceans. We hypothesize that the recent collapse of North Pacific pinnipeds helped drive that ecosystem in the opposite direction-from domination by shrimp and other crustaceans before the collapse to domination by fish today.

Convergent evolution tends to lead to similar phenotypic responses to the same selective pressures. However, when the phenotypic response is polymorphic, it is less clear how evolutionary convergence can lead to parallel diversity across species and populations. The present study focuses on South American spiders in the genus Selkirkiella (Theridiidae), which are shown to be polymorphic for colour. We (1) examine the number of morphs and their correspondence across taxa and (2) place the phenomenon in a phylogenetic context to determine whether the colour polymorphism in Selkirkiella albogutatta from the Juan Fernandez archipelago represents a case of independent evolution and convergence, or whether there is common ancestry with other colour-polymorphic theridiids. Regarding the latter question, we also examine colour morphs in a related species (Selkirkiella luisi) from continental areas. We show that S. alboguttata and S. luisi have six and two morphs, respectively. The rank-order of morph frequencies in both species is approximately similar to that reported in other polymorphic theridiids. A molecular phylogeny supports previous work and shows that the colour polymorphism in Selkirkiella species appears to be a case of convergent evolution of a diverse colour polymorphism at the family level.

It is a great pleasure to award Judy Scotchmoor, former Assistant Director for Outreach and Education at the University of California’s Museum of Paleontology (UCMP), the Paleontological Society’s Pojeta Award. Judy is perhaps best known as a science educator and many of her most significant accomplishments have been in that context. However, Judy’s association and involvement in paleontology has included much more than this. Judy was a renowned middle school science teacher at Marin Country Day School when she first came into contact with paleontology. Her love of science was enormous and she dedicated herself to sharing that love and excitement with her students. This also meant experiencing science herself, not just teaching it, and this led her to seek out opportunities to participate first hand. Paleontology had been of interest since her undergraduate days and she sought out opportunities to participate, including a Museum of the Rockies course in Bozeman, Montana followed by volunteer work as a field assistant in the Precambrian of the White Sea in Russia, and in the Cretaceous of the North Slope of Alaska. Those experiences, followed by a weekend teachers’ workshop, convinced her that paleontology was both her first love as well as an exciting source of topics for her teaching. Her passion and commitment to paleontology was so strong that she spent her next sabbatical year volunteering in UCMP’s preparation lab where she learned fossil preparation and worked in the field at …

Echolocation has evolved independently in several vertebrate groups, and hypotheses about the origin of echolocation in these groups often invoke abiotic mechanisms driving morphological evolution. In bats, for example, the ecological setting associated with the origin of echolocation has been linked to global warming during the Palaeocene–Eocene; similarly, the origin of toothed whales (odontocetes) has been broadly correlated with the establishment of the circum-Antarctic current. These scenarios, and the adaptational hypotheses for the evolution of echolocation with which they are associated, neglect a consideration of possible biotic mechanisms. Here we propose that the origin of echolocation in odontocetes was initially an adaptation for nocturnal epipelagic feeding – primarily on diel migrating cephalopods. We test this hypothesis using data on the temporal, geographical, and water column distributions of odontocetes and cephalopods, and other global events from their respective tertiary histories. From this analysis, we suggest that echolocation in early odontocetes aided nocturnal feeding on cephalopods and other prey items, and that this early system was exapted for deep diving and hunting at depths below the photic zone where abundant cephalopod resources were available 24 h a day. This scenario extends to the evolution of other cephalopod feeding (teuthophagous) marine vertebrates such as pinnipeds and Mesozoic marine reptiles.

The position of scaphopods in molluscan phylogeny remains singularly contentious, with several sister relationships supported by morphological and phylogenomic data: Scaphopoda + Bivalvia (Diasoma), Scaphopoda + Cephalopoda (Variopoda), and Scaphopoda + Gastropoda. Nervous system architecture has contributed significant insights to reconstructing phylogeny in the Mollusca and other invertebrate groups, but a modern neurophylogenetic approach has not been applied to molluscs, hampered by a lack of clearly defined homologous characters that can be unequivocally compared across the radical body plan disparity among the living clades. We present the first three-dimensional reconstruction of the anterior nervous system of a scaphopod, Rhabdus rectius, using histological tomography. We also describe a new putative sensory organ, a paired and pigmented sensory mantle slit. This structure is restricted to our study species and not a general feature of scaphopods, but it forms an integral part of the description of the nervous system in R. rectius. It also highlights the potential utility of neuro-anatomical characters for multiple levels of phylogenetic inference beyond this study. This potential has not previously been exploited for the thorny problem of molluscan phylogeny. The neuroanatomy of scaphopods demonstrates a highly derived architecture that shares a number of key characters with the cephalopod nervous system, and supports a Scaphopoda + Cephalopoda grouping.

Marine taxa are threatened by anthropogenic impacts, but knowledge of their extinction vulnerabilities is limited. The fossil record provides rich information on past extinctions that can help predict biotic responses. We show that over 23 million years, taxonomic membership and geographic range size consistently explain a large proportion of extinction risk variation in six major taxonomic groups. We assess intrinsic risk-extinction risk predicted by paleontologically calibrated models-for modern genera in these groups. Mapping the geographic distribution of these genera identifies coastal biogeographic provinces where fauna with high intrinsic risk are strongly affected by human activity or climate change. Such regions are disproportionately in the tropics, raising the possibility that these ecosystems may be particularly vulnerable to future extinctions. Intrinsic risk provides a prehuman baseline for considering current threats to marine biodiversity.

Here we report the successful use of rolling circle amplification (RCA) for the amplification of complete metazoan mt genomes to make a product that is amenable to high-throughput genome sequencing techniques. The benefits of RCA over PCR are many and with further development and refinement of RCA, the sequencing of organellar genomics will require far less time and effort than current long PCR approaches.

Kelps and other fleshy macroalgae—dominant reef-inhabiting organisms in cool seas— may have radiated extensively following late Cenozoic polar cooling, thus triggering a chain of evolutionary change in the trophic ecology of nearshore temperate ecosystems. We explore this hypothesis through an analysis of body size in the abalones (Gastropoda; Haliotidae), a widely distributed group in modern oceans that displays a broad range of body sizes and contains fossil representatives from the late Cretaceous (60-75 Ma). Geographic analysis of maximum shell length in living abalones showed that small-bodied species, while most common in the Tropics, have a cosmopolitan distribution, whereas large-bodied species occur exclusively in cold-water ecosys- tems dominated by kelps and other macroalgae. The phylogeography of body size evolution in extant abalones was assessed by constructing a molecular phylogeny in a mix of large and small species obtained from different regions of the world. This analysis demonstrates that small body size is the plesiomorphic state and largeness has likely arisen at least twice. Finally, we compiled data on shell length from the fossil record to determine how (slowly or suddenly) and when large body size arose in the abalones. These data indicate that large body size appears suddenly at the Miocene/Pliocene boundary. Our findings support the view that fleshy-algal dominated ecosys- tems radiated rapidly in the coastal oceans with the onset of the most recent glacial age. We con- clude with a discussion of the broader implications of this change.