Sea star wasting syndrome reaches the high Antarctic: Two recent outbreaks in McMurdo Sound.

Sea star wasting syndrome (SSWS) can cause widespread mortality in starfish populations as well as long-lasting changes to benthic community structure and dynamics. SSWS symptoms have been documented in numerous species and locations around the world, but to date there is only one record of SSWS from the Antarctic and this outbreak was associated with volcanically-driven high temperature anomalies. Here we report outbreaks of SSWS-like symptoms that affected ~30% of individuals of Odontaster validus at two different sites in McMurdo Sound, Antarctica in 2019 and 2022.

Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes.

Despite significant advances in invertebrate phylogenomics over the past decade, the higher-level phylogeny of Pycnogonida (sea spiders) remains elusive. Due to the inaccessibility of some small-bodied lineages, few phylogenetic studies have sampled all sea spider families. Previous efforts based on a handful of genes have yielded unstable tree topologies.

Body Size of Temperate Sea Spiders: No Evidence of Oxygen-Temperature Limitations.

AbstractOxygen limitation has been proposed as one of the key factors that limits body size at high temperatures (the oxygen-temperature hypothesis). Geographic patterns in body size are thought to be driven in part by the effects of temperature on oxygen supply and demand, particularly when the increased oxygen demand of tissues at higher temperatures outpaces the ability of large organisms to supply internal tissues with oxygen. We tested the effects of temperature on the rate of oxygen consumption of two temperate sea spider (Pycnogonida) species, and , across a range of body sizes.

Reconsidering the Oxygen-Temperature Hypothesis of Polar Gigantism: Successes, Failures, and Nuance.

"Polar gigantism" describes a biogeographic pattern in which many ectotherms in polar seas are larger than their warmer-water relatives. Although many mechanisms have been proposed, one idea-the oxygen-temperature hypothesis-has received significant attention because it emerges from basic biophysical principles and is appealingly straightforward and testable. Low temperatures depress metabolic demand for oxygen more than supply of oxygen from the environment to the organism.

Polar gigantism and the oxygen-temperature hypothesis: a test of upper thermal limits to body size in Antarctic pycnogonids.

The extreme and constant cold of the Southern Ocean has led to many unusual features of the Antarctic fauna. One of these, polar gigantism, is thought to have arisen from a combination of cold-driven low metabolic rates and high oxygen availability in the polar oceans (the 'oxygen-temperature hypothesis'). If the oxygen-temperature hypothesis indeed underlies polar gigantism, then polar giants may be particularly susceptible to warming temperatures.

Cuticular gas exchange by Antarctic sea spiders.

Many marine organisms and life stages lack specialized respiratory structures, like gills, and rely instead on cutaneous respiration, which they facilitate by having thin integuments. This respiratory mode may limit body size, especially if the integument also functions in support or locomotion. Pycnogonids, or sea spiders, are marine arthropods that lack gills and rely on cutaneous respiration but still grow to large sizes.

Upper limits to body size imposed by respiratory-structural trade-offs in Antarctic pycnogonids.

Across metazoa, surfaces for respiratory gas exchange are diverse, and the size of those surfaces scales with body size. In vertebrates with lungs and gills, surface area and thickness of the respiratory barrier set upper limits to rates of metabolism. Conversely, some organisms and life stages rely on cutaneous respiration, where the respiratory surface (skin, cuticle, eggshell) serves two primary functions: gas exchange and structural support.

Respiratory gut peristalsis by sea spiders.

The fundamental constraint shaping animal systems for internal gas transport is the slow pace of diffusion [1]. In response, most macroscopic animals have evolved systems for driving internal flows using muscular pumps or cilia. In arthropods, aside from terrestrial lineages that exchange gases via tracheal systems, most taxa have a dorsal heart that drives O-carrying hemolymph through peripheral vessels and an open hemocoel [2], with O often bound to respiratory proteins.

Out-of-the tropics or trans-tropical dispersal? The origins of the disjunct distribution of the gooseneck barnacle Pollicipes elegans.

Background: Studying species with disjunct distributions allows biogeographers to evaluate factors controlling species ranges, limits on gene flow, and allopatric speciation. Here, we use phylogeographic and population genetic studies of the barnacle Pollicipes elegans to discriminate between two primary hypotheses about the origin of disjunct distributions of extra-tropical populations: trans-tropical stepping-stone colonization versus an out-of-the tropics origin.

Results: Nucleotide diversity peaked in the centre of the species' range in samples from El Salvador and was lower in samples from higher latitudes at Mexico and Peru.

Relationships among egg size, composition, and energy: a comparative study of geminate sea urchins.

Egg size is one of the fundamental parameters in the life histories of marine organisms. However, few studies have examined the relationships among egg size, composition, and energetic content in a phylogenetically controlled context. We investigated the associations among egg size, composition, and energy using a comparative system, geminate species formed by the closure of the Central American Seaway.

Why might they be giants? Towards an understanding of polar gigantism.

Beginning with the earliest expeditions to the poles, over 100 years ago, scientists have compiled an impressive list of polar taxa whose body sizes are unusually large. This phenomenon has become known as 'polar gigantism'. In the intervening years, biologists have proposed a multitude of hypotheses to explain polar gigantism.

Estradiol's beneficial effect on murine muscle function is independent of muscle activity.

Estradiol (E₂) deficiency decreases muscle strength and wheel running in female mice. It is not known if the muscle weakness results directly from the loss of E₂ or indirectly from mice becoming relatively inactive with presumably diminished muscle activity. The first aim of this study was to determine if cage activities of ovariectomized mice with and without E₂ treatment differ.

Limits to diffusive O2 transport: flow, form, and function in nudibranch egg masses from temperate and polar regions.

Background: Many aquatic animals enclose embryos in gelatinous masses, and these embryos rely on diffusion to supply oxygen. Mass structure plays an important role in limiting or facilitating O2 supply, but external factors such as temperature and photosynthesis can play important roles as well. Other external factors are less well understood.

Egg size as a life history character of marine invertebrates: Is it all it's cracked up to be?

Egg size is one of the most important aspects of the life history of free-spawning marine organisms, and it is correlated with larval developmental mode and many other life-history characters. Egg size is simple to measure and data are available for a wide range of taxa, but we have a limited understanding of how large and small eggs differ in composition; size is not always the best measure of the characters under selection. Large eggs are generally considered to reflect increased maternal investment, but egg size alone can be a poor predictor of energetic content within and among taxa.

Oxygen hypothesis of polar gigantism not supported by performance of Antarctic pycnogonids in hypoxia.

Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (-1.

Temperature-oxygen interactions in Antarctic nudibranch egg masses.

The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion-reaction model of O(2) distributions in egg masses, using egg masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from -1.

Oxygen profiles in egg masses predicted from a diffusion-reaction model.

We developed a novel diffusion-reaction model to describe spatial and temporal changes in oxygen concentrations in gelatinous egg masses containing live, respiring embryos. We used the model in two ways. First, we constructed artificial egg masses of known metabolic density using embryos of the Antarctic sea urchin Sterechnius neumayeri, measured radial oxygen profiles at two temperatures, and compared our measurements to simulated radial oxygen profiles generated by the model.

Voluntary run training but not estradiol deficiency alters the tibial bone-soleus muscle functional relationship in mice.

The study's objective was to investigate how estrogen deficiency and run training affect the tibial bone-soleus muscle functional relationship in mice. Female mice were assigned into one of two surgical conditions, ovariectomy (OVX) or sham ovariectomy (sham), and one of two activity conditions, voluntary wheel running (Run) or sedentary (Sed). To determine whether differences observed between OVX and sham conditions could be attributed to estradiol (E(2)), additional OVX mice were supplemented with E(2).

How does metabolic rate scale with egg size? An experimental test with sea urchin embryos.

The consequences of changes in egg size for the development of marine invertebrates have been the subject of much theoretical and experimental work. Models that explore larval developmental modes in the context of maternal investment per offspring are often couched in an energetic framework, but the relationships between egg size and the energetics of larval development are poorly understood. We used blastomere separations to examine how experimental reductions in egg size affected (1) larval metabolic rate and (2) larval resistance to starvation.

Estradiol and tamoxifen reverse ovariectomy-induced physical inactivity in mice.

Unlabelled: Decreased physical activity and increased body mass are associated with estrogen deficiency.

Purpose: To determine whether estrogen or the estrogen analog, tamoxifen, could reverse those detrimental effects after surgical ovariectomy in mice.

Methods: Ten-week-old C57BL/6 mice were sham operated (sham, N = 6) or ovariectomized (OVX, N = 9).