Biological Bulletin最新文献

AbstractThe abrasive, high-impact environment of rocky intertidal zones produces important abiotic stressors that many calcifying organisms are armored against. The ochre sea star (Pisaster ochraceus), a slow-moving but ecologically important predator in the wave-swept rocky intertidal of the eastern North Pacific, is covered aborally with calcium carbonate ossicles that are modified into spines. These spines may act as armor, providing lightweight protection for Pisaster against impacts and abrasion from abiotic particles in the intertidal. We used digital image analysis and scanning electron microscopy to characterize variation in the aboral armor of Pisaster across a range of sizes and intertidal habitats that vary in the joint impacts of water motion and abrasion. We found that Pisaster from different habitats exhibited distinct relationships between size and investment in aboral armor (spine density and areal spine coverage). Aboral armor was significantly higher in Pisaster from wave-exposed shores on which joint impacts of water motion and abrasion were highest, especially in smaller-sized individuals. We also identified specific aboral spine morphotypes, the proportions of which varied according to habitat. Individuals from wave-swept rock benches and boulder fields had short, blunt, and convex spines, whereas individuals from protected embayments had a higher proportion of upright, tapered, or columnar spines. Our results suggest that increased density and areal coverage of wider, convex spines in Pisaster are adaptive for more vulnerable life stages and in more abrasive and high-impact habitats. Future work should determine whether habitat-associated variation in the armor of Pisaster reflects a functional trade-off with feeding ability and whether it is primarily genetic or phenotypically plastic.

AbstractDefining the metabolic cost of specific biochemical processes is key to understanding strategies of energy (ATP) allocation. In this study, we determined the energy cost of RNA synthesis and the allocation of the ATP pool to this biosynthetic process. Rates of oxygen consumption, RNA synthesis, and protein synthesis were measured in early-stage embryos (single cell layer, 18-h-old blastula stage) of the sea urchin (Strongylocentrotus purpuratus) that have high rates of RNA synthesis. The inhibitory effects of actinomycin D on these processes were measured to calculate the energy cost of RNA synthesis. Across 15 different cohorts of embryos studied, the average rate of RNA synthesis was 0.19 ± 0.031 (SEM) ng RNA embryo^-1 h^-1. In the presence of actinomycin D, the rate of RNA synthesis decreased by 59%, and respiration decreased by 26%. As expected, actinomycin D also inhibited protein synthesis (by 28%) but had no effect on rates of uridine and alanine transport. This analysis revealed that the energy cost of RNA synthesis is 2.01 ± 0.24 (SEM) μJ (ng RNA synthesis)^-1-a value that is notably similar to the known cost of protein synthesis in this species of 2.40 ± 0.21 μJ (ng protein synthesis)^-1. In embryos, the rate of RNA synthesis was lower than that of protein synthesis, resulting in the former requiring only 11% of the total available ATP pool, compared to 67% for the latter. The significance of these findings is presented in the context of understanding the constraints and trade-offs of ATP allocation during development.

AbstractThe high Arctic is defined by an annual light regime ranging from 24-h light (Midnight Sun) to 24-h dark (Polar Night). Light acts as an important cue for marine zooplankton, influencing their orientation and vertical migration, prey detection and predator avoidance, and population dynamics and reproductive strategies. The spectrum and intensity of underwater light differ between Midnight Sun and Polar Night, and these differences are relevant to zooplankton visual processes. Here, we determine behavioral responses of the Arctic copepod Metridia longa, measured as swimming activity in a novel laboratory apparatus, to spectral- and irradiance-controlled light stimuli during times of Midnight Sun and Polar Night. Metridia longa maintains a consistent blue-green spectral response, from 400 to 550 nm, during both times of year. However, peak spectral response shifted between seasons, with Midnight Sun individuals showing increased activity at 501 nm compared to 473-490 nm during Polar Night. Additionally, Polar Night M. longa showed heightened irradiance sensitivity by an order of magnitude as compared to Midnight Sun individuals. Their irradiance response was also consistent across varying temperatures. We show that spectral and irradiance responses in M. longa are seasonally adapted and temperature compensated, suggesting that this copepod maintains a consistent light-mediated predator avoidance capacity, despite predicted seasonal light and temperature shifts in the high Arctic.

AbstractBioluminescence is a common feature of the fishes inhabiting the dimly lit waters of the deep sea and is thought to play roles in prey attraction, predator avoidance, communication, and counterillumination. Stomiiformes, the most abundant and speciose order of deep-sea fishes, have a stunning variety of bioluminescent organs and tissues. While some of these structures have been well described, others are poorly characterized and rarely discussed in literature. Here we synthesize data in the literature on the four types of photophores found among stomiiforms (complex serial, complex minute, simple pigmented, and simple unpigmented photophores) and assess the size, density, and distribution of the little-known complex minute photophores, in particular, in 31 species in 25 stomiiform genera. The predicted orientation of light emitted from complex serial and minute photophores in 14 species in the stomiid subfamily Stomiinae was inferred from the placement of the lens (through which light is transmitted). Complex minute photophores were found, in addition to complex serial photophores, in all stomiines examined (and in one gonostomatid) and were notably smaller and occurred in higher densities than the complex serial photophores. The predicted ventral orientation of the light emitted by the complex serial photophores in all species presumably functions in counterillumination. However, the predicted direction of transmission of light produced by complex minute photophores appears to vary within and among species, suggesting multiple functions (e.g., camouflage and/or communication), warranting further studies of photophores in these intriguing and ecologically critical fishes.

AbstractMany organisms may rely on microbes that seed the host body and are typically maintained as a consortial symbiosis. Marine invertebrates have highly diverse microbiomes and offer many different life history traits across which to explore the members and functions of these symbionts but are largely absent from the holobiont and microbiome literature compared to humans and vertebrates. We tracked the microbiome of Strongylocentrotus purpuratus larvae and examined the role of vertical transmission via gametes and the role of horizontal transmission via diet and seawater for seeding the developing larvae with microbes potentially critical to holobiont health and fitness. We used 16S short-read sequencing to track the composition and relative abundances of bacteria associated with diet (microalgae) and with habitat (filtered seawater), as well as with S. purpuratus gametes and larvae under standard lab rearing conditions. The larval microbiome differed across developmental stages and between filtered seawater and algae, and specific bacterial taxa were associated with those differences. In this experiment, developing larvae selected and maintained a unique microbiome compared to their diet and habitat. Eggs were a potentially significant source of vertical transmission during embryonic development (genus Psychromonas), while horizontal transmission via filtered seawater was the main contributor to larval feeding stages, suggesting that filtered seawater is likely the most important source of potential symbionts. Gaining new insights into how marine invertebrate larval microbiomes are seeded and with what taxa is important for endangered-species aquaculture and for ecosystem restoration and management to protect inoculation sources for early-life stage organisms.

AbstractMetamorphosis appears to be a particularly sensitive stage in marine invertebrate development, with potential carryover effects of larval experience on the postlarval stage. We investigated the impact of salinity exposure history (22‰-34‰) for 2-4 days on the ability of competent crown-of-thorns sea star (Acanthaster sp.; CoTS) brachiolaria larvae to form a normal five-armed juvenile. The decreased salinity levels used were commensurate with levels that these larvae may encounter in their habitat on the Great Barrier Reef (25‰-34‰), and the extreme low level (22‰) was used to assess salinity tolerance. At metamorphosis, low-salinity stress (<34‰) for a few days prior to settlement-as may be experienced by larvae during a runoff pulse-resulted in negative carryover effects, even when the larvae were placed in control salinity during settlement assays. A larval experience of ≤30‰ resulted in smaller juveniles. The low-salinity treatment (22‰) resulted in a large proportion of juveniles deviating from the normal five-armed profile of newly metamorphosed CoTS. Juvenile mortality was high if they were generated from larvae exposed to 22‰ and 25‰ salinity levels. Our findings highlight the importance of ecological developmental biology in understanding potential carryover effects beyond metamorphosis. These insights could help link the exposure of CoTS larvae to terrestrial runoff conditions with juvenile performance and the postmetamorphic processes that influence recruitment into the adult population.

AbstractPycnogonids (sea spiders) are benthic invertebrates exhibiting unique reproductive strategies including paternal brood care by the male in many species. To date, the mating systems of brooding Antarctic sea spiders have yet to be investigated via molecular methods, despite their dominance and importance in the Southern Ocean. To better understand how sea spiders reproduce and maintain their natural populations in this region, we employed 3RAD-derived single nucleotide polymorphisms to investigate genetic mating systems of the abundant, and putatively circumpolar, Antarctic sea spider Nymphon australe. By analyzing single nucleotide polymorphisms in genomes of individual larvae taken from offspring-carrying males, we inferred paternal full- and half-sibships and parentage for specimens of N. australe collected from the eastern Antarctic continental shelf. Notably, N. australe exhibits a polygynandrous mating system where both males and females engage in multiple mating events. Male brood partitioning on their ovigerous legs varied, with some males partitioning offspring into clutches by female genotypes and others carrying progeny from multiple female genotypes in a single clutch. However, we found no evidence of cuckoldry, where males inadvertently raise offspring sired by other males, indicating that this species has a high assurance of paternity for the progeny carried by each individual male. These findings provide foundational insights into the genetic mating system of Antarctic sea spiders and contrast with the cuckoldry frequently observed in other male brood care systems. This contrast highlights some of the evolutionary pressures acting on reproductive strategies in polar environments.

AbstractFecundity and egg size vary among females, depending on environmental conditions experienced by mothers, known as maternal effects. Temperature, salinity, food availability, competition, and predation can influence maternal allocation. We evaluated temporal changes in the reproductive biology of the pea crab Austinixa patagoniensis in the context of local spatial competition with the yellow clam Amarilladesma mactroides mediated by the ghost shrimp Audacallichirus mirim. We assessed physical environmental variables and compared size-dependent reproductive parameters-fecundity and egg volume-between two contrasting periods at Monte Hermoso Beach (38°59' S, 61°19' W): clam-period, characterized by the dominance of A. mactroides in the macrobenthic community, and crab-period, marked by the dominance of A. patagoniensis. Additionally, we calculated reproductive output for crab-period and examined the relationship between brood and female size. Fecundity did not differ between periods, whereas egg volume was greater during clam-period across all female sizes. Since no differences were found in physical environmental variables, larger egg volume was interpreted as increased allocation per offspring, suggesting adaptive allocation to counteract the negative effects of density-dependent exclusion of pea crabs, leading to offspring with greater dispersal potential and/or better ability to survive and perform under adverse conditions. Larger eggs without fecundity cost indicate greater reproductive allocation during clam-period, possibly reducing investment in other life history traits. While no correlation was found between brood and female weight, an isometric relationship was observed between brood weight and female size. Future studies should focus on how maternal effects influence the population dynamics of the species.

AbstractHorseshoe crabs (Carcinoscorpius rotundicauda, Limulus polyphemus, Tachypleus gigas, and Tachypleus tridentatus) are experiencing population decline. A systematic review of 326 papers was conducted to assess the state of conservation of these species and provide recommendations for horseshoe crab conservation in Long Island Sound, USA. Major present-day threats to horseshoe crabs include overharvest and bycatch, habitat loss and degradation, climate change, and insufficient management. The declining populations of horseshoe crabs impact shorebirds and marine organisms, contributing to the threats facing endangered species. Protecting and restoring spawning areas and juvenile habitat, adopting alternative sources for use in the fishing and the biomedical industry, exploring captive breeding and head-starting programs, and public education present promising conservation strategies. Urgent action will be necessary to conserve horseshoe crabs and their vital ecological role in Long Island Sound.

AbstractThe Warburg effect-aerobic glycolysis, diminished oxygen uptake, and lactate secretion-has been characterized in proliferative mammalian cells and in some cancers. Lactate formation remains puzzling, variously attributed to reoxidizing NADH or activating the cell cycle. Forming lactate provides the only anaerobic pathway available to mammalian cells but not for most eukaryotes or metazoans. With the purely mitotic polyp stage of a colonial marine hydroid, Eirene sp., differential feeding was used to create rapidly and slowly proliferating colonies of a genetically identical clone. The former were fed to excess three times per week, the latter once per week. Under aerobic conditions, assays using gas chromatography/mass spectrometry show that colonies of both treatments produce short-chain fatty acids, indicating end products of anaerobic mitochondrial metabolism and thus providing an alternative pathway to reoxidize NADH. After 1 h of incubation in fully aerated seawater, the concentration of acetate, propionate, and butyrate was higher in the medium than in the tissue of the colonies, suggesting that these are waste products. Colorimetric assays showed that colonies of both treatments nevertheless produced lactate. Further, the rapidly proliferating colonies produced significantly more. Eirene sp. thus carries out anaerobic mitochondrial metabolism, but this apparently has no effect on lactate production. Since earlier data show that the proliferative colonies exhibit diminished oxygen uptake, anaerobic mitochondrial metabolism appears to have little impact on the Warburg effect. This contrasts with the expectation from the literature that an alternative pathway to reoxidize NADH will abolish lactate production.