Variability in broods of the seastar \u3ci\u3eLeptasterias aequalis\u3c/i\u3e

Enormous variation exists in the reproductive output of marine invertebrates (e.g., in the numbers of em¬bryos produced, the volumes of embryos, and the energy that they contain). It is not clear why there is such great variability or what the population-level consequences are. We sampled a population of the brooding seastar Leptasterias aequalis (Stimpson, 1862) to collect basic information on brood sizes, embryo volume, and embryo energy content with a goal to better understand the reproductive ecology of this species. We collected brooding females in February and again in April. We measured the size of their broods and sampled the broods to estimate volume and energy con¬tent of the embryos. There was great variability in the volume and energy content of embryos produced by individual females and among the embryos in a single female\u27s brood. Larger adults produced larger embryos, which generally had greater energy content and may be of a higher quality. The average energy content of embryos appeared to in¬crease during the brooding period. Larger females produced larger broods but lost a greater proportion of the embryos. The net result is that larger individuals may not produce any more juveniles than smaller individuals, but those that they do produce may be of a higher quality. Originally published in Canadian Journal of Zoologyand used with permission

The Potential for Ontogenetic Vertical Migration by Larvae of Bathyal Echinoderms

Planktotrophy is a relatively common developmental mode among bathyal and abyssal echinoderms, but the sources of food used by deep-sea planktotrophic larvae remain generally unknown. Very few deep-sea echinoderm larvae have been collected in plankton samples, so we do not know whether larvae migrate to the euphotic zone to feed or if they rely on bacteria or detritus at greater depths. We approached this question indirectly by investigating whether larvae of bathyal echinoids can tolerate the temperatures they would encounter in the euphotic zone and whether they possess sufficient energy stores to migrate to the euphotic zone without feeding. Twenty-four hour survival at 20 and 24 °C was always much lower than survival at colder temperatures, but there were species-specific and stage-specific differences in temperature tolerances. A numerical model of the energy consumed by migrating larvae predicted that larvae should be able to reach adequate phytoplankton concentrations before exhausting parental reserves, unless they swim very slowly and have very high metabolic rates. These results suggest that long vertical migrations are more likely to be limited by physiological tolerances than by energy stores

The role of taxonomic expertise in interpretation of metabarcoding studies

Abstract The performance of DNA metabarcoding approaches for characterizing biodiversity can be influenced by multiple factors. Here, we used morphological assessment of taxa in zooplankton samples to develop a large barcode database and to assess the congruence of taxonomic identification with metabarcoding under different conditions. We analysed taxonomic assignment of metabarcoded samples using two genetic markers (COI, 18S V1–2), two types of clustering into molecular operational taxonomic units (OTUs, ZOTUs), and three methods for taxonomic assignment (RDP Classifier, BLASTn to GenBank, BLASTn to a local barcode database). The local database includes 1042 COI and 1108 18S (SSU) barcode sequences, and we added new high-quality sequences to GenBank for both markers, including 109 contributions at the species level. The number of phyla detected and the number of taxa identified to phylum varied between a genetic marker and among the three methods used for taxonomic assignments. Blasting the metabarcodes to the local database generated multiple unique contributions to identify OTUs and ZOTUs. We argue that a multi-marker approach combined with taxonomic expertise to develop a curated, vouchered, local barcode database increases taxon detection with metabarcoding, and its potential as a tool for zooplankton biodiversity surveys

Amino Acid Uptake and Metabolism by Larvae of the Marine Worm Urechis caupo (Echiura), a New Species in Axenic Culture

Volume: 176Start Page: 317End Page: 32

Growth and Energy Imbalance During the Development of a Lecithotrophic Molluscan Larva (Haliotis rufescens)

Volume: 177Start Page: 237End Page: 24

Ontogenic Changes in the Rates of Amino Acid Transport from Seawater by Marine Invertebrate Larvae (Echinodermata, Echiura, Mollusca)

Volume: 176Start Page: 161End Page: 16

Comparison of Eggshell Porosity and Estimated Gas Flux between the Brown-Headed Cowbird and Two Common Hosts

The brown-headed cowbird Molothrus ater is a brood-parasite that lays eggs in nests of a wide range of host species, including the closely-related red-winged blackbird Agelaius phoeniceus and the dickcissel Spiza americana. Although cowbird eggs have accelerated development and hatch sooner than similar-sized host eggs, this development takes place within a thickened eggshell that could impede gas flux to the developing embryo. We tested the hypothesis that the accelerated development of the cowbird embryo relative to hosts is enabled by an increase in eggshell porosity that allows increased fluxes of respiratory gases to and from the developing embryo. We found cowbird eggshell thickness was significantly greater than the eggshells of these two common hosts. Although the number of pores per egg was similar among all three species, the total pore area per egg in cowbirds was significantly greater than that of either host, despite having a smaller eggshell surface area than the red-winged blackbird. Cowbird egg pore area was 1.9 X larger than that of the redwinged blackbird. Cowbird eggshells had a significantly greater gas flux than those of the red-winged blackbird and the dickcissel. When conductance was normalized to published values of egg mass, cowbird eggs had a higher mass-specific conductance than red-winged blackbird or dickcissel eggs. These results are consistent with the hypothesis that the rapid development of brown-headed cowbird embryos is facilitated by increased eggshell porosity, and that changes in eggshell porosity represent an adaptation that enables cowbird eggs to hatch earlier than equivalently-sized host eggs

Identification of Asteroid Genera With Species Capable of Larval Cloning

Volume: 204Start Page: 246End Page: 25