Freya E. Goetz

Morphological features play a critical role in the ability of an organism to navigate its environment. Organisms living in rivers and streams must handle a spectrum of habitats that span from dynamic flows in headwater creeks to the regularly high flows of large rivers. Freshwater mussels (order Unionoida) are an interesting group of organisms that possess a variety of hypothesized shell morphology traits adapted to life across the stream size spectrum. Fusconaia flava (family Unionidae) is a species that exhibits a pattern of clinal variation, known as Ortmann's Law of Stream Position, where shell width increases with stream size. Although speculations have been made about the causes and consequences of Ortmann's Law of Stream Position, few experiments have been conducted to help explain why some freshwater mussel species exhibit this phenotype–environment association. We conducted a comparative morphometric study and a fluvial experiment to identify how intraspecific mussel morphology and behaviour vary along a stream size gradient. We used micro‐computed tomography scanning to digitize shells from hydrologically diverse habitats, then measured the width, size and median thickness of each shell. Multiple regression was used to test the association between shell width and thickness while accounting for shell size, and linear regression models were used to describe the relationships between shell traits and hydrology. In a corresponding flume experiment, we measured valve‐gaping activity and observed presumptive burrowing behaviour of wild‐collected F. flava that exhibited ‘compressed’ (small‐river morph) and ‘inflated’ (large‐river morph) shell morphologies found in the upper and lower reaches of the Gasconade River in central Missouri, USA. We scaled flume flows to mimic observed low and high streamflows on the Gasconade River and used Hall sensors to record valve movements. We found shell thickness and shell width were strongly associated with one another and increased with aspects of stream size (i.e., Strahler stream order, flow rate and catchment area). The flume experiment demonstrated the feasibility and mechanistic potential of using wild‐collected mussels in behaviour experiments. We successfully integrated flow scaling via Froude numbers and demonstrated the sensitivity of Hall sensors for continuous behavioural monitoring. Valve‐gaping activity of ‘compressed’ mussels did not appear to have an affinity to a specific flow regime, but visually they made significant spatial movements, whereas ‘inflated’ mussels exhibited pronounced changes in valve‐gaping activity under higher flow conditions but remained more or less stationary. However, our data were not capable of definitive behavioural comparisons and instead proved the value of this setup for future, larger‐scale experiments. Given the ongoing and projected increase of droughts and catastrophic flood events due to climate change, our results provide insight into how morphological trait variation and valve‐gaping activity together allow individuals to respond to streamflow fluctuations. Additionally, our integration of comparative morphometrics and flume experiments provides a promising proof of concept for testing phenotype–environment associations.

Open science, the practice of making research products and processes free and available to scientists and non-scientists alike, is transforming image-based studies using non-clinical computed tomography (CT). Recently, the National Science Foundation has established research coordination networks to help address principles of findability, accessibility, interoperability and reusability (FAIR) within the United States (US) scientific enterprise and in partnership with the global community. The Non-Clinical Tomography Users Research Network (NoCTURN) is one such organization, focused on CT data accessibility and reuse, helping to address significant obstacles related to bespoke hardware, proprietary software and siloed workflows. NoCTURN strives to develop and maintain linkages across CT ecosystems capable of driving cultural and technological changes. To that end, we discuss the last two decades of FAIR principles (when) and present our recommendations for CT data access by focusing on a survey of predominantly US CT users (who), the definition and role of metadata schemas (what), and the broad use of persistent identifiers (how).

The copepod family Shiinoidae Cressey, 1975 currently comprises nine species of teleost parasites with unusual morphology and a unique attachment mechanism. Female shiinoids possess greatly enlarged antennae that oppose a rostrum, an elongate outgrowth of cuticle that originates between the antennules. The antennae form a moveable clasp against the rostrum which they use to attach to their host. In this study, we use micro-computed tomography (microCT) to examine specimens of Shiinoa inauris Cressey, 1975 in situ attached to host tissue in order to characterize the functional morphology and specific muscles involved in this novel mode of attachment and to resolve uncertainty regarding the segmental composition of the regions of the body. We review the host and locality data for all reports of shiinoids, revise the generic diagnoses for both constituent genera Shiinoa Kabata, 1968 and Parashiinoa West, 1986, transfer Shiinoa rostrata Balaraman, Prabha & Pillai, 1984 to Parashiinoa as Parashiinoa rostrata (Balaraman, Prabha & Pillai, 1984) n. comb., and present keys to the females and males of both genera.

Siphonophores are a diverse group of hydrozoans (Cnidaria) that are found at all depths of the ocean - from the surface, like the familiar Portuguese man of war, to the deep sea. Siphonophores play an important role in ocean ecosystems, and are among the most abundant gelatinous predators. A previous phylogenetic study based on two ribosomal RNA genes provided insight into the internal relationships between major siphonophore groups, however there was little support for many deep relationships within the clade Codonophora. Here, we present a new siphonophore phylogeny based on new transcriptome data from 30 siphonophore species analyzed in combination with 13 publicly available genomic and transcriptomic datasets. We use this new phylogeny to reconstruct several traits that are central to siphonophore biology, including sexual system (monoecy vs. dioecy), gain and loss of zooid types, life history traits, and habitat. The phylogenetic relationships in this study are largely consistent with the previous phylogeny, but we find strong support for new clades within Codonophora that were previously unresolved. These results have important implications for trait evolution within Siphonophora, including favoring the hypothesis that monoecy arose twice.

Siphonophores (Hydrozoa) have unparalleled colony-level complexity, precision of colony organization, and functional specialization between zooids (i.e., the units that make up colonies). Previous work has shown that, unlike other colonial animals, most growth in siphonophores is restricted to one or two well-defined growth zones that are the sites of both elongation and zooid budding. It remained unknown, however, how this unique colony growth and development is realized at the cellular level. To understand the colony-level growth and development of siphonophores at the cellular level, we characterize the distribution of proliferating cells and interstitial stem cells (i-cells) in the siphonophore Nanomia bijuga. Within the colony, we find evidence that i-cells are present at the tip of the horn, the structure within the growth zone that gives rise to new zooids. Co-localized gene expression of vasa-1, pl10, piwi, nanos-1, and nanos-2 suggests that i-cells persist in the youngest zooid buds and that i-cells become progressively restricted to specific regions within the zooids until they are mostly absent from the oldest zooids. The examined genes remain expressed in gametogenic regions. No evidence for i-cells is found in the stem between maturing zooids. Domains of high cell proliferation include regions where the examined genes are expressed, but also include some areas in which the examined genes were not expressed such as the stem within the growth zones. Cell proliferation in regions devoid of vasa-1, pl10, piwi, nanos-1, and nanos-2 expression indicates the presence of mitotically active epithelial cell lineages and, potentially, progenitor cell populations. We provide the first evidence for i-cells in a siphonophore. Our findings suggest maintenance of i-cell populations at the sites of growth zones and that these sites are the main source of i-cells. This restriction of stem cells to particular regions in the colony, in combination with localized budding and spatial patterning during pro-bud subdivision, may play a major role in facilitating the precision of siphonophore growth. Spatially restricted maintenance of i-cells in mature zooids and absence of i-cells along the stem may explain the reduced developmental plasticity in older parts of the colony.

Cnidaria, the sister group to Bilateria, is a highly diverse group of animals in terms of morphology, lifecycles, ecology, and development. How this diversity originated and evolved is not well understood because phylogenetic relationships among major cnidarian lineages are unclear, and recent studies present contrasting phylogenetic hypotheses. Here, we use transcriptome data from 15 newly-sequenced species in combination with 26 publicly available genomes and transcriptomes to assess phylogenetic relationships among major cnidarian lineages. Phylogenetic analyses using different partition schemes and models of molecular evolution, as well as topology tests for alternative phylogenetic relationships, support the monophyly of Medusozoa, Anthozoa, Octocorallia, Hydrozoa, and a clade consisting of Staurozoa, Cubozoa, and Scyphozoa. Support for the monophyly of Hexacorallia is weak due to the equivocal position of Ceriantharia. Taken together, these results further resolve deep cnidarian relationships, largely support traditional phylogenetic views on relationships, and provide a historical framework for studying the evolutionary processes involved in one of the most ancient animal radiations.

Background: Siphonophores (Hydrozoa) have unparalleled colony-level complexity, precision of colony organization, and functional specialization between zooids (i.e., the units that make up colonies). Previous work has shown that, unlike other colonial animals, most growth in siphonophores is restricted to one or two well-defined growth zones that are the sites of both elongation and zooid budding. It remained unknown, however, how this unique colony growth and development is realized at the cellular level. Results: To understand the colony-level growth and development of siphonophores at the cellular level, we characterize the distribution of proliferating cells and interstitial stem cells (i-cells) in the siphonophore Nanomia bijuga. Within the colony we find that i-cells are present at the tip of the horn, the structure within the growth zone that gives rise to new zooids. They persist in the youngest zooid buds, but as each zooid matures i-cells become progressively restricted to specific regions within the zooids until they are mostly absent from the oldest zooids. I-cell marker-gene expression remained in gametogenic regions. I-cells are not found in the stem between maturing zooids. Domains of high cell proliferation include regions where i-cells can be found, but also include some areas without i-cells such as the stem within the growth zones. Cell proliferation in regions devoid of marker gene expression indicates the presence of mitotically active epithelial cell lineages and, potentially, progenitor cell populations. Conclusions: Restriction of stem cells to particular regions in the colony may play a major role in facilitating the precision of siphonophore growth, and also lead to a reduced developmental plasticity in other, typically older, parts of the colony. This helps explain why siphonophore colonies have such precise colony-level organization.