Up and away: ontogenic transference as a pathway for aerial dispersal of microplastics

Microplastics (MPs) are ubiquitous pollutants found in marine, freshwater and terrestrial ecosystems. With so many MPs in aquatic systems, it is inevitable that they will be ingested by aquatic organisms and be transferred up through the food chain. However, to date, no study has considered whether MPs can be transmitted by means of ontogenic transference, i.e. between life stages that use different habitats. Here, we determine whether fluorescent polystyrene beads could transfer between Culex mosquito life stages and, particularly, could move into the flying adult stage. We show for the first time that MPs can be transferred ontogenically from a feeding (larva) into a non-feeding (pupa) life stage and subsequently into the adult terrestrial life stage. However, transference is dependent on particle size, with smaller 2 µm MPs transferring readily into pupae and adult stages, while 15 µm MPs transferred at a significantly reduced rate. MPs appear to accumulate in the Malpighian tubule renal excretion system. The transfer of MPs to the adults represents a potential aerial pathway to contamination of new environments. Thus, any organism that feeds on terrestrial life phases of freshwater insects could be impacted by MPs found in aquatic ecosystems.

Changes in the Gut Microbiome of the Sea Lamprey during Metamorphosis

ABSTRACTVertebrate metamorphosis is often marked by dramatic morphological and physiological changes of the alimentary tract, along with major shifts in diet following development from larva to adult. Little is known about how these developmental changes impact the gut microbiome of the host organism. The metamorphosis of the sea lamprey (Petromyzon marinus) from a sedentary filter-feeding larva to a free-swimming sanguivorous parasite is characterized by major physiological and morphological changes to all organ systems. The transformation of the alimentary canal includes closure of the larval esophagus and the physical isolation of the pharynx from the remainder of the gut, which results in a nonfeeding period that can last up to 8 months. To determine how the gut microbiome is affected by metamorphosis, the microbial communities of feeding and nonfeeding larval and parasitic sea lamprey were surveyed using both culture-dependent and -independent methods. Our results show that the gut of the filter-feeding larva contains a greater diversity of bacteria than that of the blood-feeding parasite, with the parasite gut being dominated byAeromonasand, to a lesser extent,CitrobacterandShewanella. Phylogenetic analysis of the culturableAeromonasfrom both the larval and parasitic gut revealed that at least five distinct species were represented. Phenotypic characterization of these isolates revealed that over half were capable of sheep red blood cell hemolysis, but all were capable of trout red blood cell hemolysis. This suggests that the enrichment ofAeromonasthat accompanies metamorphosis is likely related to the sanguivorous lifestyle of the parasitic sea lamprey.

Early Life History of Fishes in the San Francisco Estuary and Watershed

<em>Abstract.</em>—Understanding how environmental factors influence first feeding success is critical for the conservation-oriented larval culture of delta smelt <em>Hypomesus transpacificus</em>, a threatened osmerid endemic to the San Francisco Estuary. We investigated the effects of light intensity, alga concentration, and prey (rotifer) density on feeding of cultured delta smelt larvae. In one experiment, first feeding larvae were exposed to three light intensities (0.01, 0.3, and 1.9 μmoles ^.s^–1.m^–2) and three alga concentrations (0, 0.5, and 2 × 10⁶cells/mL). Intestinal contents were examined to determine the incidence of feeding and gut fillness. Maximum feeding responses (92% feeding; 4.8 rotifers/feeding larva in 2 h) were observed at the highest light intensity and alga concentrations; feeding sharply declined with a reduction of either factor. A second experiment was performed to study the effect of alga concentration (0, 1.5, 3, and 6 × 10⁶cells/mL) in more detail. Feeding responses were very low without algae (13% feeding; 2.1 rotifers/feeding larva in 2 h), but dramatically increased at high concentrations (83% feeding; 5.1 rotifers/feeding larvae in 2 h). In a third experiment, the effect of prey (rotifer) density (0.1, 1, 10, and 100 rotifers/mL) was tested, which significantly enhanced feeding up to the 10/mL treatment (84% feeding; 4.2 rotifers/feeding larvae in 1 h). All three environmental factors significantly affected feeding success of larval delta smelt. Optimization of these factors has improved survival and growth during the sensitive larval period and has improved laboratory culture of delta smelt.

Physicochemical Conditions and Microbial Activities in the Highly Alkaline Gut of the Humus-Feeding Larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

ABSTRACT The soil macrofauna plays an important role in the carbon and nitrogen cycle of terrestrial ecosystems. In order to gain more insight into the role of the intestinal microbiota in transformation and mineralization of organic matter during gut passage, we characterized the physicochemical conditions, microbial activities, and community structure in the gut of our model organism, the humus-feeding larva of the cetoniid beetle Pachnoda ephippiata. Microsensor measurements revealed an extreme alkalinity in the midgut, with highest values (pH > 10) between the second and third crown of midgut ceca. Both midgut and hindgut were largely anoxic, but despite the high pH, the redox potential of the midgut content was surprisingly high even in the largest instar. However, reducing conditions prevailed in the hindgut paunch of all instars (Eh ∼ −100 mV). Both gut compartments possessed a pronounced gut microbiota, with highest numbers in the hindgut, and microbial fermentation products were present in high concentrations. The stimulation of hindgut methanogenesis by exogenous electron donors, such as H2, formate, and methanol, together with considerable concentrations of formate in midgut and hemolymph, suggests that midgut fermentations are coupled to methanogenesis in the hindgut by an intercompartmental transfer of reducing equivalents via the hemolymph. The results of a cultivation-based enumeration of the major metabolic groups in midgut and hindgut, which yielded high titers of lactogenic, propionigenic, and acetogenic bacteria, are in good agreement not only with the accumulation of microbial fermentation products in the respective compartments but also with the results of a cultivation-independent characterization of the bacterial communities reported in the companion paper (M. Egert, B. Wagner, T. Lemke, A. Brune, and M. W. Friedrich, Appl. Environ. Microbiol. 69:6659-6668, 2003).

A novel ontogenetic pathway in hybrid embryos between species with different modes of development

To investigate the bases for evolutionary changes in developmental mode, we fertilized eggs of a direct-developing sea urchin, Heliocidaris erythrogramma, with sperm from a closely related species, H. tuberculata, that undergoes indirect development via a feeding larva. The resulting hybrids completed development to form juvenile adult sea urchins. Hybrids exhibited restoration of feeding larval structures and paternal gene expression that have been lost in the evolution of the direct-developing maternal species. However, the developmental outcome of the hybrids was not a simple reversion to the paternal pluteus larval form. An unexpected result was that the ontogeny of the hybrids was distinct from either parental species. Early hybrid larvae exhibited a novel morphology similar to that of the dipleurula-type larva typical of other classes of echinoderms and considered to represent the ancestral echinoderm larval form. In the hybrid developmental program, therefore, both recent and ancient ancestral features were restored. That is, the hybrids exhibited features of the pluteus larval form that is present in both the paternal species and in the immediate common ancestor of the two species, but they also exhibited general developmental features of very distantly related echinoderms. Thus in the hybrids, the interaction of two genomes that normally encode two disparate developmental modes produces a novel but harmonious ontongeny.

Optimization of shock parameters in inducing mitotic gynogenesis in the carp Cyprinus carpio L.

The relative effects of heat-shock parameters on the induction of first-cleavage suppression of common carp (Cyprinus carpio L.) eggs were examined. Eggs of females with scattered scales were fertilized with sperm that had been irradiated with gamma-ray cobalt-60. Fertilized eggs were exposed to heat shock at different temperatures (39, 40, 41 °C) for periods of 1–3 min at 0.5-min intervals, initiated at 41, 44, or 47 min post fertilization in a factorial design. The use of three treatment factors made it possible to analyze the main effects and all possible combinations of the three factors. The highest percentage of mitotic gynogenetic diploids (mitotic-G2n) (up to 10.6% survival at the feeding larva stage relative to the total number of inseminated eggs) was obtained from the groups treated at 40 °C for 2 min at 44 min post fertilization (ambient temperature 21 °C). Optimum duration was observed to be 2.5–3 min at 39 °C and 1–1.5 min at 41 °C. The embryos were developed under hatchery condition, while larvae were reared in a flow-through system with natural feeding. Isozyme and scale pattern analysis performed on putative mitotic-G2n individuals both proved that their genome is of maternal origin.