Biological Bulletin最新文献

AbstractAnthropogenic climate change is considered to be one of the greatest threats facing marine biodiversity. The vast majority of experimental work investigating the effects of climate change stressors on marine organisms has focused on calcifying organisms, such as corals and molluscs, where cross-generational phenotypic changes can be easily quantified. Bivalves in particular have been the subject of numerous climate change studies, in part because of their economic value in the aquaculture industry and their important roles as ecosystem engineers. However, there has been little to no work investigating the effects of these stressors on the symbionts associated with these bivalves, specifically, their shell-boring polychaete parasites. This is important to understand because climate change may shift the synergistic relationship between parasite and host based on the individual responses of each. If such a shift favors proliferation of the polychaete, it may very well facilitate extinction of host bivalve populations. In this review I will (i) provide an overview of research completed thus far on the effects of climate change stressors on shell-boring polychaetes, (ii) discuss the technical challenges of studying these parasites in the laboratory, and (iii) propose a standardized framework for carrying out future in vitro and in vivo climate change experiments on shell-boring polychaetes.

AbstractIn recent years, low-salinity events characterized by high temperatures (18-23 °C) and low-salinity waters (20‰-22‰) have increased during late spring and summer, when many marine invertebrate larvae are developing. The present study examines the effects of low-salinity events on particle ingestion for larvae of two echinoderm species, the sea star Pisaster ochraceus and the sand dollar Dendraster excentricus. Larvae were exposed to high temperatures and low salinities for 24 hours, followed by feeding on the alga Isochrysis galbana in high or low salinity for another 10 minutes. Exposing Pisaster larvae to high temperatures and low salinities, followed by feeding in low salinity, did not impair ingestion rates. In fact, these larvae ingested particles at similar and sometimes higher rates than those in the controls. In sharp contrast, a 24-hour exposure to a high temperature and low salinity, followed by continued exposure to low salinity to feed, led to a decrease in the number of particles ingested by 8-arm Dendraster larvae. Larvae of both species captured very few particles when returned to 30‰ after a low-salinity event, indicating that continuous interruption of larval feeding by low-salinity events during development could be deleterious. Sand dollar larvae may have responded negatively to low-salinity events in our experiments because they are found in protected bays, where they may seldom experience these events.

AbstractNearshore foundation species in coastal and estuarine systems (e.g., salt marsh grasses, mangroves, seagrasses, corals) drive the ecological functions of ecosystems and entire biomes by creating physical structure that alters local abiotic conditions and influences species interactions and composition. The resilience of foundation species and the ecosystem functions they provide depends on their phenotypic and genetic responses to spatial and temporal shifts in environmental conditions. In this review, we explore what is known about the causes and consequences of adaptive genetic differentiation in marine foundation species over spatial scales shorter than dispersal capabilities (i.e., microgeographic scales). We describe the strength of coupling field and laboratory experiments with population genetic techniques to illuminate patterns of local adaptation, and we illustrate this approach by using several foundation species. Among the major themes that emerge from our review include (1) adaptive differentiation of marine foundation species repeatedly evolves along vertical (i.e., elevation or depth) gradients, and (2) mating system and phenology may facilitate this differentiation. Microgeographic adaptation is an understudied mechanism potentially underpinning the resilience of many sessile marine species, and this evolutionary mechanism likely has particularly important consequences for the ecosystem functions provided by foundation species.

AbstractMicrobial symbionts are a common life-history character of marine invertebrates and their developmental stages. Communities of bacteria that associate with the eggs, embryos, and larvae of coastal marine invertebrates tend to be species specific and correlate with aspects of host biology and ecology. The richness of bacteria associated with the developmental stages of coastal marine invertebrates spans four orders of magnitude, from single mutualists to thousands of unique taxa. This understanding stems predominately from the developmental stages of coastal species. If they are broadly representative of marine invertebrates, then we may expect deep-sea species to associate with bacterial communities that are similar in diversity. To test this, we used amplicon sequencing to profile the bacterial communities of invertebrate larvae from multiple taxonomic groups (annelids, molluscs, crustaceans) collected from 2500 to 3670 m in depth in near-bottom waters near hydrothermal vents in 3 different regions of the Pacific Ocean (the East Pacific Rise, the Mariana Back-Arc, and the Pescadero Basin). We find that larvae of deep-sea invertebrates associate with low-diversity bacterial communities (~30 bacterial taxa) that lack specificity between taxonomic groups. The diversity of these communities is estimated to be ~7.9 times lower than that of coastal invertebrate larvae, but this result depends on the taxonomic group. Associating with a low-diversity community may imply that deep-sea invertebrate larvae do not have a strong reliance on a microbiome and that the hypothesized lack of symbiotic contributions would differ from expectations for larvae of coastal marine invertebrates.

AbstractInsight into how coastal organisms will respond to changing temperature and salinity regimes may be derived from studies of adaptation to fluctuating estuarine environments, especially under stressful range-edge conditions. We characterized a dynamic range boundary between two estuarine sea slugs, Alderia modesta (distributed across the North Pacific and North Atlantic) and Alderia willowi, known from southern and central California. The species overlap from Bodega Bay to San Francisco Bay, where populations are dominated by A. modesta after winter rains but by A. willowi after peak summer temperatures. Laboratory assays confirmed superior tolerance to low salinity for the northern species, A. modesta: encapsulated embryos developed at 8 ppt, larvae survived at 4-6 ppt, and adults survived repeated exposure to 2 ppt, salinities that reduced development or survival for the same stages of A. willowi. Adults did not appreciably differ in their high-temperature threshold, however. Each species showed increased tolerance to either temperature or salinity stress at its range margin, indicating plasticity or local adaptation, but at the cost of reduced tolerance to the other stressor. At its northern limit, A. willowi became more tolerant of low salinity during the winter rainy season, but also less heat tolerant. Conversely, A. modesta became more heat resistant from spring to summer at its southern limit, but less tolerant of low salinity. Trade-offs in stress tolerance may generally constrain adaptation and limit biotic response to a rapidly changing environment, as well as differentiating species niches.

AbstractThe diversity and consequences of development in marine invertebrates have, for a long time, provided the opportunity to understand different evolutionary solutions to living in variable environments. However, discrete classifications of development can impede a full understanding of adaptation to variable environments when behavioral, morphological, or physiological flexibility and variation exist within traditionally defined modes of development. We report here novel behavioral variability in hatchlings of a marine gastropod, the Florida crown conch (Melongena corona), that has broad significance for understanding the correlated evolution of development, dispersal, and reproductive strategies in variable environments. All hatchlings crawl away from egg capsules after emergence as larval pediveligers. Some subsequently swim for a brief period (seconds to minutes) before crawling again. From detailed observations of 120 individuals over 30 days, we observed 28 (23.3%) hatchlings swimming at least once (8%-50% per maternal brood). The propensity to swim was unrelated to time spent encapsulated or size at hatching and lasted for 22 days. We manipulated hypothesized environmental cues and found that the proportion of hatchlings that swam was highest in the absence of cues related to habitat or juvenile food and lowest when only habitat cues were present. The relative growth rate of hatchlings was highest when habitats contained a putative juvenile food source. About 44% of hatchlings were competent to metamorphose at emergence but did not metamorphose at this time in the lab or the field. The rate of metamorphosis increased with age and depended on the presence of unknown cues in the field. Crawl-away larvae with prolonged swimming ability may be an adaptation to balance the unpredictable risks of exclusively benthic or pelagic development and to allow the option to disperse to higher-quality habitat.

AbstractUnderstanding how species may respond to climate change is of paramount importance. Species that occupy highly heterogenous environments, such as intertidal zone estuarine habitats, provide an ideal test case for examining phenotypic and genomic adaptations to different environmental conditions, which may influence their response to rapidly shifting climatic conditions. The California coast is projected to experience changes in both temperature and salinity, which currently vary seasonally and latitudinally. Using comparative transcriptomics, I documented patterns of positive selection between the northern-dwelling planktotrophic sacoglossan sea slug Alderia modesta, which is remarkably tolerant of low temperatures and low salinities, and its southern congener Alderia willowi, which exhibits a striking flexibility for larval type in response to seasonally shifting changes in temperature and salinity. Out of over 4000 1-to-1 orthologous genes, I found a signal of positive selection between A. willowi and A. modesta for genes involved in cell membrane and cell transport, particularly ion homeostasis (aquaporin), cell-cell signal transduction, and phosphorylation (reduced nicotinamide adenine dinucleotide [NADH] dehydrogenase). Positive selection for ion homeostasis in A. modesta has implications for its ability to tolerate the lower salinity of its northern range, and in A. willowi substitutions in NADH may assist in the high temperature tolerance of its southern California habitats. Identifying these candidate genes enables future studies of their functionalization as we seek to understand the relationship between phenotype and genotype in species whose phenotypes are influenced by environmental conditions.

AbstractFor animal embryos that develop externally, the physio-chemical environment can substantially affect offspring viability. In the case of the American horseshoe crab (Limulus polyphemus), sediment conditions along estuarine shorelines influence development rates and embryonic viability. Sandy beach habitats are considered to have optimal conditions for horseshoe crab embryonic development; however, spawning is often observed outside of these optimal habitats, in areas such as salt marshes, where reduced oxygen availability is thought to decrease the viability of eggs laid in these sediments. We excavated horseshoe crab eggs, embryos, and trilobites laid naturally in marsh and beach sediments in South Carolina to compare their development and viability between habitats. We found all developmental stages in both marsh and beach habitats. For two of three sampling areas, trilobites were more likely to be found at beaches than at marshes. Multivariate analyses demonstrate that the prevalence of early and middle developmental stages was similar between habitats but that beaches had a greater proportion of late-stage trilobites than marshes. The lower likelihood of finding trilobites at some marshes may reflect differences in spawning phenology between habitats or reduced rates of embryonic development in marshes compared to beaches, leading to potentially different developmental timelines rather than a true reduction in viability. Nevertheless, the substantial proportions of eggs laid in salt marshes that survive to the trilobite stage indicate that spawning in this habitat could represent a previously underappreciated source of recruitment for horseshoe crab populations that may need to be incorporated into population assessments.