The Peril of the Plankton

The pelagic environment is characterized by unevenly distributed resources and risks. Such unpredictability presents adaptive challenges to diverse planktonic organisms including the larvae of benthic marine invertebrates. Estimates of mortality during planktonic development are highly variable, ranging from 0% to 100% per day. Predation is considered a significant source of this mortality, but what explains the variability in estimates of the mortality of marine invertebrate larvae? While differential exposure of larval prey to predators may explain these widely variable estimates, adaptations that reduce vulnerability of marine larvae to predators may also be important. Although there are excellent reviews of predation upon larvae and of larval mortality and defenses, nearly 15 years have elapsed since these topics were formally reviewed. Here, we highlight recent advances in understanding the behavioral, chemical, and morphological defenses that larvae possess and assess their effectiveness in reducing the risk of predation. While recent work confirms that larval mortality is generally high, it also demonstrates that larvae can reduce their risk of predation in several ways, including: (1) temporarily escaping the benthos during vulnerable early stages, (2) producing chemical compounds that reduce palatability, (3) possessing morphological defenses such as spines and shells, and (4) exhibiting induced defensive responses whereby larvae can alter their behavior, morphology, and life histories in the presence of predators. Taken together, these studies indicate that marine invertebrate larvae possess a sophisticated suite of defensive phenotypes that have allowed them to persist in the life cycle of benthic invertebrates for eons

Integrating Weed Management Practices to Enhance Productivity of Grazed Pastures

As animal grazing has intensified within Kentucky and the surrounding region problematic weeds such as tall ironweed, spiny amaranth, horsenettle, buttercup, common cocklebur, and thistles have been increasing. These weeds become prominent in pastures because they have spines, thorns, or are unpalatable to animals. Animals selectively graze and avoid these weedy plants and with intensive grazing practices their populations are allowed to increase. Livestock producers are seeking ways to increase pasture productivity by minimizing the impact of these and other weeds on grazed lands

Understanding the Effects of Low Salinity on Fertilization Success and Early Development in the Sand Dollar Echinarachnius parma

Free-spawning marine invertebrates that live near shore or in estuaries may experience reduced fertilization success during low-salinity events. Although several studies have documented reproductive failure at reduced salinity in estuarine animals, few have looked at whether developmental failure is due to a failure of fertilization or to a failure of fertilized eggs to cleave. In this study, we examined the effects of salinities ranging from 18 to 32 psu on fertilization success and early development in the sand dollar Echinarachnius parma. In addition to decoupling the effects of low salinity on fertilization from its effects on early cleavage, we also assessed whether eggs or sperm were the weak link in accounting for reproductive failure. We found that both fertilization and cleavage failed at salinities below about 22 psu but that development could be partially rescued by returning zygotes to full-strength seawater. We also found that sperm remained active and capable of fertilizing eggs even after being exposed to low salinities for 30 min.. Taken together, these results suggest that reproductive failure at low salinities in E. parma is due more to an inability of the fertilized eggs to cleave than to an inability of sperm to fertilize eggs

Short Report: Gongylonema pulchrum Infection in a Resident of Williamsburg, Virginia, Verified by Genetic Analysis

We describe the thirteenth reported case of human infection with Gongylonema spp. in the United States and the first to be confirmed as Gongylonema pulchrum. The parasite described was isolated from the oral cavity of a resident of Williamsburg, Virginia. The identity of the parasite was verified through morphological and genetic approaches, and provided the first genetic confirmation of a Gongylonema sp. in humans

Predator-induced Plasticity in Egg Capsule Deposition in the Mud Snail, Tritia obsoleta

Most marine invertebrates develop in the plankton, where microscopic offspring can avoid abundant benthic predators until settlement. However, at least four phyla of marine invertebrates (Annelida, Mollusca, Nemertea, and Platyhelminthes) deposit benthic egg capsules or masses. Often, these animals possess additional means to protect their young, including chemical or morphological defenses or nonrandom selection of deposition sites. Egg capsule deposition is the dominant reproductive strategy among gastropod molluscs, including the mud snail, Tritia obsoleta. In intertidal and shallow subtidal habitats in New England, the mud snail preferentially deposits egg capsules on blades of eelgrass (Zostera marina), a substrate that stands upright in the water column. In a field and lab study, we examined deposition of T. obsoleta egg capsules and found that mud snails lay their egg capsules on eelgrass at 6-8 cm off the benthos or higher. When exposed to egg capsule predators, hermit crabs and periwinkles, mud snails increase the average height of deposition off the benthos by 1-3 cm. In the presence of hermit crabs, capsules deposited on a blade of eelgrass 5 cm above the benthos have survivorship as much as 4 times higher than capsules deposited directly on the benthos. We suggest that deposition of egg capsules off of the benthos is an adaptive response allowing mud snails to protect their embryos from benthic predators. We also provide evidence that snails use characteristics of the eelgrass itself to ensure capsules are laid well above the benthos

Asexual Reproduction of Marine Invertebrate Embryos and Larvae

The life histories of marine invertebrates are incredibly diverse and provide a wealth of opportunities to develop and test hypotheses about how and why modes of reproduction, development, and behavior evolve within and among lineages. With respect to the evolution of reproductive and developmental mode, phylogenetic, adaptive, and functional hypotheses presented over the past century have predominantly focused on the evolution of reproductive traits (e.g., free spawning, brooding, encapsulation; nutritional mode of larvae (e.g., planktotrophy and lecithotrophy; and developmental form (e.g., larval morphology; direct and indirect development. Frequently, but not exclusively, these hypotheses have been tied to changes in per-offspring investment and influential models of per-offspring investment often serve as a framework for studies of the evolution of developmental modes. Phylogenetic assessment of the evolution of character states within lineages has revealed frequent shifts among life histories traits.https://scholarworks.wm.edu/asbookchapters/1011/thumbnail.jp

A Novel Report of Hatching Plasticity in the Phylum Echinodermata

Hatching plasticity occurs in response to a wide range of stimuli across many animal taxa, including annelids, arthropods, mollusks, and chordates. Despite the prominence of echinoderms in developmental biology and more than 100 years of detailed examination of their development under a variety of conditions, environmentally cued hatching plasticity has never been reported in the phylum Echinodermata. Here we report plasticity in the timing and stage of hatching of embryos of the sand dollar Echinarachnius parma in response to reductions in salinity. Embryos of E. parma increased their time to hatching more than twofold in response to ecologically relevant salinity reductions, while maintaining an otherwise normal developmental schedule. Embryos that experienced the greatest delay in hatching time emerged from the fertilization envelope as fourarm pluteus larvae rather than hatching as blastulae or early gastrulae. Salinity manipulations across multiple male-female pairs indicated high variability in hatching time both within and among clutches, suggesting significant intraspecific variation in developmental responses to salinit

Tibial Tubercle Osteotomy and Medial Patellofemoral Ligament Imbrication for Patellar Instability Due to Trochlear Dysplasia.

BackgroundThe treatment of patellar instability in the setting of trochlear dysplasia is challenging.Purpose/hypothesisThe purpose of this study was to evaluate outcomes for the treatment of recurrent patellar dislocations due to trochlear dysplasia using anteromedialization tibial tubercle osteotomy combined with medial patellofemoral ligament (MPFL) imbrication. We hypothesized that the treatment of patellar instability with tibial tubercle osteotomy and MPFL imbrication would result in improved patient satisfaction and decrease patellar instability events in patients with prior instability and trochlear dysplasia.Study designCase series; Level of evidence, 4.MethodsWe performed a retrospective analysis of patients who underwent MPFL imbrication and concomitant anteromedialization tibial tubercle osteotomy for recurrent patellofemoral instability at a single institution. The minimum follow-up was 1 year. Patient demographic information including age at the time of surgery, sex, body mass index (BMI), tibial tubercle-trochlear groove (TT-TG) distance, and grade of trochlear dysplasia was collected along with relevant operative data. Postoperatively, recurrent dislocation events as well as Knee injury and Osteoarthritis Outcome Score (KOOS), Western Ontario and McMaster Universities Osteoarthritis Index, and Kujala scores were collected, and satisfaction was ascertained by asking patients whether they would undergo the procedure again.ResultsA total of 37 knees from 31 patients (23 female) with a mean follow-up of 3.8 years (range, 1-8.9 years) were included. The mean patient age was 28.8 years (range, 14-45 years), the mean BMI was 24 kg/m2 (range, 20-38 kg/m2), and the mean preoperative TT-TG distance was 18.9 mm (range, 8.4-32.4 mm). Two knees were classified as low-grade trochlear dysplasia (Dejour A) and 35 as high-grade trochlear dysplasia (Dejour B-D). At final follow-up, patients reported mean KOOS subscale scores of 86.5 (Pain), 79.8 (Symptoms), 93.9 (Activities of Daily Living), 74.3 (Sports/Recreation), and 61.9 (Quality of Life), as well as a mean Kujala score of 81.3. Mean patient satisfaction was 8.3 of 10. The majority of knees (86.5%; 32/37) remained stable without recurrent instability after this procedure, while 13.5% (5 knees) suffered a recurrent dislocation, with 2 requiring revision surgery. Eight knees (21.6%) underwent subsequent hardware removal.ConclusionAnteromedialization tibial tubercle osteotomy with MPFL imbrication can improve recurrent patellofemoral instability and provide significant clinical benefit to patients with trochlear dysplasia

Shaped nozzles for cryogenic buffer gas beam sources

Cryogenic buffer gas beams are important sources of cold molecules. In this work we explore the use of a converging-diverging nozzle with a buffer-gas beam. We find that, under appropriate circumstances, the use of a nozzle can produce a beam with improved collimation, lower transverse temperatures, and higher fluxes per solid angle