Explore the vast range of titles available.

Many taxa around the globe are threatened by often unexplained mass mortality events (MMEs), which can decimate populations and compromise key ecosystem functions. One example of a highly threatened taxon facing frequent MMEs is freshwater mussels (Unionida). There has been a recent increase in interest in understanding the causes of freshwater mussel MMEs, but standardised methodologies for how best to respond to them to facilitate diagnoses are unavailable. When an MME is observed, swift and appropriate sample collection is imperative owing to the transient nature of these phenomena. Here we provide structured guidance that will facilitate rapid and appropriate sampling of MMEs, using freshwater mussels as an example. We set out standardised procedures for sample collection, preparation and preservation. The procedures we outline will improve our capacity for diagnostic investigations of MMEs and other mortality events, not only in freshwater mussels but also across many other taxa. This, in turn, can inform appropriate management responses.

We detail gross and histopathological changes associated with infection by the eggs, larvae, and cuticular remnants of Unionicola sp. in the mantle, gill, and visceral mass of 25 Alabama creekmussels, Strophitus connasaugaensis, collected during May 2010 through July 2012 from 2 Alabama streams. A multitude (estimated mean intensity >100) of mite eggs and larvae typically infected mantle, gill, and visceral mass integument. Pathology associated with eggs (prevalence = 0.57) and larvae (prevalence = 0.39) typically consisted of localized distension of the infection site; a host response to these infections was indeterminate. However, larval mites embedded in suprabranchial connective tissues were typically encapsulated (prevalence = 0.89). Mite remnants (prevalence = 0.5) occurred in mantle, gill, visceral mass integument, foot, heart, pericardial gland, intestinal lamina propria, and were typically encapsulated. We speculate that S. connasaugaensis clears some infections but is recolonized by autoinfection or horizontal dispersal of mites in the stream. Noteworthy is that high-intensity infections seemingly do not markedly impact the histological picture of mussel tissues, indicating that mites are relatively benign symbionts that are of little concern to mussels under normal environmental conditions.

Eggs of Huffmanela cf. carcharhini from the skin of an aquarium-held, juvenile sandbar shark, Carcharhinus plumbeus, from the Pacific Ocean were studied using light and scanning electron microscopy. Grossly, eggs imparted a scribble-like skin marking approximately 130 × 60 mm on the right side of the shark's snout adjacent to its eye and nostril. Fresh (unfixed) eggs were elliptical, 75–95 µm long (x¯  =  85 µm, SD  =  ±4.5; n  =  75), 48–63 µm wide (53 ± 3.4; 75), 8–10 µm in shell thickness (9 ± 1.3; 27), 45–68 µm in vitelline mass length (52 ± 6.9; 8); had a smooth shell surface and nonprotruding polar plugs 8–13 µm wide (10 ± 1.5; 73); lacked thin filaments, superficial envelope, and shell spines; sank in 35 ppt artificial seawater; and did not spontaneously hatch after 12 hr in 35 ppt artificial seawater. Formalin-fixed eggs measured 193 days postfixation were 75–95 µm long (84 ± 3.9; 150), 45–60 µm wide (50 ± 2.2; 150), 5–10 µm in shell thickness (8 ± 1.2; 87), 45–60 µm in vitelline mass length (51 ± 3.0; 92), and 30–40 µm in vitelline mass width (33 ± 2.0; 84), and had nonprotruding polar plugs that were 10–15 µm long (11 ± 1.4; 93) and 8–10 µm wide (9 ± 1.1; 108). Forcibly hatched first-stage larvae (unfixed) were filiform, 188–273 µm long (212 ± 25.5; 13), 8–13 µm wide (10 ± 1.2; 13), and had fine transverse striations. Eggs infected the epidermis only. Histology revealed intra-epithelial inflammation with eosinophilic granulocytes and hyperplasia, plus dermal lymphofollicular hyperplasia associated with the infection. The eggs of H. cf. carcharhini likely undergo considerable ex utero development before being sloughed (unhatched) from the host, along with epidermal cells.

The “freshwater mussels” (Mollusca: Bivalvia: Unionoida) are a species rich group of parasitic bivalves comprising an estimated 898 species in 6 families, 2 subfamilies, and 29 genera worldwide. Renown for its biodiversity, Alabama has a large proportion of this total number of species, with 180 species of Unionidae and 2 of Margaritiferidae. The total number of unionid species in Alabama also includes 24 extinct, 26 extirpated, and 74 imperiled unionids, and, because of that, the conservation status of these invertebrates is of interest to the Alabama Department of Conservation and Natural Resources. Historically, our understanding of unionid systematics was based on shell morphology and larval (glochidia) characteristics. More recently, phylogentic relationships of mussels are being revealed following the sequencing of highly conserved genes. However, scant information is available on the soft tissues of these invertebrates, and no comprehensive histological treatment of any species has been published to date. This lack of foundational information is a barrier to advancing our knowledge of mussel biology.This dissertation is a systematic, comparative anatomical study that treats morphological diversity of cells and tissues across three primary lineages (subfamilies) of unionids. I test the hypothesis that freshwater mussel lineages exhibit few morphological differences in their “soft tissues,” which contrasts to the level of morphological diversity exhibited by their shells and larvae. Representative mussel species subjected to anatomical study were selected based upon the taxonomic arrangement of Ortmann (1910) and the combined phylogenetic analysis of Graf and Cummings (2006). The Alabama rainbow (Villosa nebulosa) was selected as the representative of Lampsilinae, Unioninae was represented by the Gulf pigtoe (Fusconaia cerina), and the Alabama creekmussel (Strophitus connasaugaensis) was selected as the representative of Anodontinae. Alabama rainbows were collected from the South Fork of Terrapin Creek during May 2010 (n=36), August 2010 (n=39), and August 2011 (n=5) plus Shoal Creek in May 2011 (n=5). Gulf pigtoes were collected from the Cahaba River in May 2011 (n=10), August 2011 (n=28), and June 2012 (n=7). Alabama creekmussels were collected from Shoal Creek in May 2011 (n=5), January 2012 (n=3), and May 2012 (n=8) as well as from the South Fork of Terrapin Creek in August 2011 (n=7). Select specimens of V. nebulosa (n=45) and S. connasaugaensis (n=10) were sourced from pond and recirculating culture systems of the Alabama Aquatic Biodiversity Center (Marion, Alabama). Mussels were digitally photographed to document gross features and routinely processed for histology following standard protocols before being photographed with a digital camera mounted to a compound microscope.Herein, the null hypothesis that the level of morphological diversity in cells and tissues was qualitatively low across the studied mussel species is accepted. Major and minor anatomical differences between the studied mussels are reported in tables provided herein (totaling 12 distinctive histological features). Some of these differences are relevant to assessing mussel health and propagation efficacy. For example, I speculate that a robust, branched mantle edge with a high surface area may be linked to shell thickness, and, if not fully formed, may cause shell deformities. Workers monitoring mussel health or stream health by studying soft tissue structure should focus on structurally conserved tissues whereas histopathological changes to unionid tissues that exhibit interspecific variation may be less easily comparable.

The infection pattern of Kroeyerina elongata (Kroyeriidae, Copepoda) in the olfactory sacs of the blue shark, Prionace glauca, was investigated using 4,722 copepods from 54 olfactory sacs. Copepod prevalence and mean intensity of infection per olfactory sac were 94.0 and 91.1%, respectively, and the most intensely infected olfactory sac and shark hosted 218 and 409 copepods, respectively. There were significant linear relationships between the number of female and total copepods per left olfactory sac and shark fork length as well as between the numbers of female, male, and total copepods per shark and mean olfactory sac width and cumulative olfactory sac width. Female copepods typically outnumbered males within olfactory sacs (mean intensity  =  65.7 and 26.3, respectively), and no statistical differences were detected between the numbers of copepods inhabiting the left and right olfactory sacs. Copepods were not evenly distributed within olfactory sacs. Typically, female copepods occupied olfactory chambers located centrally along the length of the olfactory sac, while males infected lateral olfactory chambers nearest the naris. The orientation of most copepods (84.6%) suggested positive rheotaxis relative to the path of water through the olfactory sac. Within olfactory chambers, most mature females (68.2%) infected the first third of the peripheral excurrent channel and the adjacent fringe of olfactory lamellae, while most males (91.7%) infected the olfactory lamellae, and the 4 larval females collected were attached within the lamellar field and grasped by males. Based on the observed infection patterns and the pattern of water flow throughout the olfactory sac, a hypothesis regarding the life cycle of K. elongata is advanced wherein infective copepodids are swept into the olfactory sac from the surrounding sea and initially colonize the olfactory lamellae. Copepodids feed and mature among the olfactory lamellae, and adult males search for mates and copulate with young females among the olfactory lamellae. Inseminated females move to the peripheral excurrent channels to mature and produce ovisacs. Hatching ovisacs release free-swimming nauplii into the excurrent water flow to be swept into the milieu, where they can molt into infective copepodids that may infect new hosts.

Stomatal conductance ( g s) in terrestrial vegetation regulates the uptake of atmospheric carbon dioxide for photosynthesis and water loss through transpiration, closely linking the biosphere and atmosphere and influencing climate. Yet, the range and pattern of g s in plants from natural ecosystems across broad geographic, climatic, and taxonomic ranges remains poorly quantified. Furthermore, attempts to characterize g s on such scales have predominantly relied upon meta-analyses compiling data from many different studies. This approach may be inherently problematic as it combines data collected using unstandardized protocols, sometimes over decadal time spans, and from different habitat groups. Using a standardized protocol, we measured leaf-level g s using porometry in 218 C3 woody angiosperm species in natural ecosystems representing seven bioclimatic zones. The resulting dataset of 4273 g s measurements, which we call STraits (Stomatal Traits), was used to determine patterns in maximum g s ( g smax) across bioclimatic zones and whether there was similarity in the mean g smax of C3 woody angiosperms across ecosystem types. We also tested for differential g smax in two broadly defined habitat groups – open-canopy and understory-subcanopy – within and across bioclimatic zones. We found strong convergence in mean g smax of C3 woody angiosperms in the understory-subcanopy habitats across six bioclimatic zones, but not in open-canopy habitats. Mean g smax in open-canopy habitats (266 ± 100 mmol m-2 s-1) was significantly higher than in understory-subcanopy habitats (233 ± 86 mmol m-2 s-1). There was also a central tendency in the overall dataset to operate toward a g smax of ∼250 mmol m-2 s-1. We suggest that the observed convergence in mean g smax of C3 woody angiosperms in the understory-subcanopy is due to a buffering of g smax against macroclimate effects which will lead to differential response of C3 woody angiosperm vegetation in these two habitats to future global change. Therefore, it will be important for future studies of g smax to categorize vegetation according to habitat group.

Giant exoplanets orbiting close to their host stars are unlikely to have formed in their present configurations 1 . These ‘hot Jupiter’ planets are instead thought to have migrated inward from beyond the ice line and several viable migration channels have been proposed, including eccentricity excitation through angular-momentum exchange with a third body followed by tidally driven orbital circularization 2 , 3 . The discovery of the extremely eccentric ( e  = 0.93) giant exoplanet HD 80606 b (ref.  4 ) provided observational evidence that hot Jupiters may have formed through this high-eccentricity tidal-migration pathway 5 . However, no similar hot-Jupiter progenitors have been found and simulations predict that one factor affecting the efficacy of this mechanism is exoplanet mass, as low-mass planets are more likely to be tidally disrupted during periastron passage 6 – 8 . Here we present spectroscopic and photometric observations of TIC 241249530 b, a high-mass, transiting warm Jupiter with an extreme orbital eccentricity of e  = 0.94. The orbit of TIC 241249530 b is consistent with a history of eccentricity oscillations and a future tidal circularization trajectory. Our analysis of the mass and eccentricity distributions of the transiting-warm-Jupiter population further reveals a correlation between high mass and high eccentricity. The spectroscopic and photometric observations of a high-mass, transiting warm Jupiter, TIC 241249530 b, with an orbital eccentricity of 0.94, provide evidence that hot Jupiters may have formed by means of a high-eccentricity tidal-migration pathway.

Increasing anthropogenic turbidity is among the most prevalent disturbances in freshwater ecosystems, through increases in sedimentary deposition as well as the rise of nutrient-induced algal blooms. Changes to the amount and color of light underwater as a result of elevated turbidity are likely to disrupt the visual ecology of fishes that rely on vision to survive and reproduce; however, our knowledge of the mechanisms underlying visual responses to turbidity is lacking. First, we aimed to determine the visual detection threshold, a measure of visual sensitivity, of two ecologically and economically important Lake Erie fishes, the planktivorous forage fish, emerald shiner ( ), and a primary predator, the piscivorous walleye ( ), under sedimentary and algal turbidity. Secondly, we aimed to determine if these trophically distinct species are differentially impacted by increased turbidity. We used the innate optomotor response to determine the turbidity levels at which individual fish could no longer detect a difference between a stimulus and the background (i.e. visual detection threshold). Detection thresholds were significantly higher in sedimentary compared to algal turbidity for both emerald shiner (mean ± SE = 79.66 ± 5.51 NTU, mean ± SE = 34.41 ± 3.19 NTU) and walleye (mean ± SE = 99.98 ± 5.31 NTU, mean ± SE = 40.35 ± 2.44 NTU). Our results suggest that across trophic levels, the visual response of fishes will be compromised under algal compared to sedimentary turbidity. The influence of altered visual environments on the ability of fish to find food and detect predators could potentially be large, leading to population- and community-level changes within the Lake Erie ecosystem.