Population and life-stage specific sensitivities to temperature and salinity stress in barnacles

Temperature and salinity shape the distribution and genetic structure of marine communities. Future warming and freshening will exert an additional stress to coastal marine systems. The extent to which organisms respond to these shifts will, however, be mediated by the tolerances of all life-stages and populations of species and their potential to adapt. We investigated nauplius and cypris larvae of the barnacle Balanus (Amphibalanus) improvisus from the Swedish west coast with respect to temperature (12, 20, and 28 °C) and salinity (5, 15, and 30) tolerances. Warming accelerated larval development and increased overall survival and subsequent settlement success. Nauplii developed and metamorphosed best at intermediate salinity. This was also observed in cypris larvae when the preceding nauplii stages had been reared at a salinity of 30. Direct comparisons of the present findings with those on a population from the more brackish Baltic Sea demonstrate contrasting patterns. We conclude that i) B. improvisus larvae within the Baltic region will be favoured by near-future seawater warming and freshening, that ii) salinity tolerances of larvae from the two different populations reflect salinities in their native habitats, but are nonetheless suboptimal and that iii) this species is generally highly plastic with regard to salinity

Sperm adaptation in relation to salinity in three goby species

In externally fertilizing species, the gametes of both males and females are exposed to the influences of the environment into which they are released. Sperm are sensitive to abiotic factors such as salinity, but they are also affected by biotic factors such as sperm competition. In this study, the authors compared the performance of sperm of three goby species, the painted goby, Pomatoschistus pictus, the two-spotted goby, Pomatoschistus flavescens, and the sand goby, Pomatoschistus minutus. These species differ in their distributions, with painted goby having the narrowest salinity range and sand goby the widest. Moreover, data from paternity show that the two-spotted goby experiences the least sperm competition, whereas in the sand goby sperm competition is ubiquitous. The authors took sperm samples from dissected males and exposed them to high salinity water (31 PSU) representing the North Sea and low salinity water (6 PSU) representing the brackish Baltic Sea Proper. They then used computer-assisted sperm analysis to measure the proportion of motile sperm and sperm swimming speed 10 min and 20 h after sperm activation. The authors found that sperm performance depended on salinity, but there seemed to be no relationship to the species' geographical distribution in relation to salinity range. The species differed in the proportion of motile sperm, but there was no significant decrease in sperm motility during 20 h. The sand goby was the only species with motile sperm after 72 h

Immigrant reproductive dysfunction facilitates ecological speciation

The distributions of species are not only determined by where they can survive – they must also be able to reproduce. Although immigrant inviability is a well-established concept, the fact that immigrants also need to be able to effectively reproduce in foreign environments has not been fully appreciated in the study of adaptive divergence and speciation. Fertilization and reproduction are sensitive life-history stages that could be detrimentally affected for immigrants in non-native habitats. We propose that “immigrant reproductive dysfunction” is a hitherto overlooked aspect of reproductive isolation caused by natural selection on immigrants. This idea is supported by results from experiments on an externally fertilizing fish (sand goby, Pomatoschistus minutus). Growth and condition of adults were not affected by non-native salinity whereas males spawning as immigrants had lower sperm motility and hatching success than residents. We interpret these results as evidence for local adaptation or acclimation of sperm, and possibly also components of paternal care. The resulting loss in fitness, which we call “immigrant reproductive dysfunction,” has the potential to reduce gene flow between populations with locally adapted reproduction, and it may play a role in species distributions and speciation

Temporal variation in ecological and evolutionary contributions to phytoplankton functional shifts

Communities and their functioning are jointly shaped by ecological and evolutionary processes that manifest in diversity shifts of their component species and genotypes. How both processes contribute to community functional change over time is rarely studied. We here repeatedly quantified eco-evolutionary contributions to CO2-driven total abundance and mean cell size changes after short-, mid-, and longer-term (80, 168, and >168d, respectively) in experimental phytoplankton communities. While the CO2-driven changes in total abundance and mean size in the short- and mid-term could be predominantly attributed to ecological shifts, the relative contribution of evolution increased. Over the longer-term, the CO2-effect and underlying eco-evolutionary changes disappeared, while total abundance increased, and mean size decreased significantly independently of CO2. The latter could be presumably attributed to CO2-independent genotype selection which fed back to species composition. In conclusion, ecological changes largely dominated the regulation of environmentally driven phytoplankton functional shifts at first. However, evolutionary changes gained importance with time, and can ultimately feedback on species composition, and thus must be considered when predicting phytoplankton change

Editorial: Influence of environmental variability on climate change impacts in marine ecosystems

multiple drivers, environmental variability, Climate change, marine heatwaves, stressmemory, Ecological memory, Thermal performance curves, acclimatio

Larval development of the barnacle Amphibalanus improvisus responds variably but robustly to near-future ocean acidification

Increasing atmospheric CO2 decreases seawater pH in a phenomenon known as ocean acidification. In two separate experiments we found that larval development of the barnacle Amphibalanus (Balanus) improvisus was not significantly affected by the level of reduced pH that has been projected for the next 150 years. After 3 and 6 days of incubation, we found no consistent effects of reduced pH on developmental speed or larval size at pH 7.8 compared with the control pH of 8.1. After 10 days of incubation, there were no net changes in survival or overall development of larvae raised at pH 7.8 or 7.6 compared with the control pH of 8.0. In all cases, however, there was significant variation in responses between replicate batches (parental genotypes) of larvae, with some batches responding positively to reduced pH. Our results suggest that the non-calcifying larval stages of A. improvisus are generally tolerant to near-future levels of ocean acidification. This result is in line with findings for other barnacle species and suggests that barnacles do not show the greater sensitivity to ocean acidification in early life history reported for other invertebrate species. Substantial genetic variability in response to low pH may confer adaptive benefits under future ocean acidification

Molecular, behavioural and morphological comparisons of sperm adaptations in a fish with alternative reproductive tactics

In species with alternative reproductive tactics, there is much empirical support that parasitically spawning males have larger testes and greater sperm numbers as an evolved response to a higher degree of sperm competition, but support for higher sperm performance (motility, longevity and speed) by such males is inconsistent. We used the sand goby (Pomatoschistus minutus) to test whether sperm performance differed between breeding-coloured males (small testes, large mucus-filled sperm-duct glands; build nests lined with sperm-containing mucus, provide care) and parasitic sneaker-morph males (no breeding colouration, large testes, rudimentary sperm-duct glands; no nest, no care). We compared motility (per cent motile sperm), velocity, longevity of sperm, gene expression of testes and sperm morphometrics between the two morphs. We also tested if sperm-duct gland contents affected sperm performance. We found a clear difference in gene expression of testes between the male morphs with 109 transcripts differentially expressed between the morphs. Notably, several mucin genes were upregulated in breeding-coloured males and two ATP-related genes were upregulated in sneaker-morph males. There was a partial evidence of higher sperm velocity in sneaker-morph males, but no difference in sperm motility. Presence of sperm-duct gland contents significantly increased sperm velocity, and nonsignificantly tended to increase sperm motility, but equally so for the two morphs. The sand goby has remarkably long-lived sperm, with only small or no decline in motility and velocity over time (5 min vs. 22 h), but again, this was equally true for both morphs. Sperm length (head, flagella, total and flagella-to-head ratio) did not differ between morphs and did not correlate with sperm velocity for either morph. Thus, other than a clear difference in testes gene expression, we found only modest differences between the two male morphs, confirming previous findings that increased sperm performance as an adaptation to sperm competition is not a primary target of evolution.</p

Toxic Algae Silence Physiological Responses to Multiple Climate Drivers in a Tropical Marine Food Chain

Research on the effects of climate change in the marine environment continues to accelerate, yet we know little about the effects of multiple climate drivers in more complex, ecologically relevant settings – especially in sub-tropical and tropical systems. In marine ecosystems, climate change (warming and freshening from land run-off) will increase water column stratification which is favorable for toxin producing dinoflagellates. This can increase the prevalence of toxic microalgal species, leading to bioaccumulation of toxins by filter feeders, such as bivalves, with resultant negative impacts on physiological performance. In this study we manipulated multiple climate drivers (warming, freshening, and acidification), and the availability of toxic microalgae, to determine their impact on the physiological health, and toxin load of the tropical filter-feeding clam, Meretrix meretrix. Using a structural equation modeling (SEM) approach, we found that exposure to projected marine climates resulted in direct negative effects on metabolic and immunological function and, that these effects were often more pronounced in clams exposed to multiple, rather than single climate drivers. Furthermore, our study showed that these physiological responses were modified by indirect effects mediated through the food chain. Specifically, we found that when bivalves were fed with a toxin-producing dinoflagellate (Alexandrium minutum) the physiological responses, and toxin load changed differently and in a non-predictable way compared to clams exposed to projected marine climates only. Specifically, oxygen consumption data revealed that these clams did not respond physiologically to climate warming or the combined effects of warming, freshening and acidification. Our results highlight the importance of quantifying both direct and, indirect food chain effects of climate drivers on a key tropical food species, and have important implications for shellfish production and food safety in tropical regions.</p

No barrier to emergence of bathyal king crabs on the Antarctic shelf

Cold-water conditions have excluded durophagous (skeleton-breaking) predators from the Antarctic seafloor for millions of years. Rapidly warming seas off the western Antarctic Peninsula could now facilitate their return to the continental shelf, with profound consequences for the endemic fauna. Among the likely first arrivals are king crabs (Lithodidae), which were discovered recently on the adjacent continental slope. During the austral summer of 2010‒2011, we used underwater imagery to survey a slope-dwelling population of the lithodid Paralomis birsteini off Marguerite Bay, western Antarctic Peninsula for environmental or trophic impediments to shoreward expansion. The population density averaged ∼4.5 individuals × 1,000 m(−2) within a depth range of 1,100‒1,500 m (overall observed depth range 841–2,266 m). Images of juveniles, discarded molts, and precopulatory behavior, as well as gravid females in a trapping study, suggested a reproductively viable population on the slope. At the time of the survey, there was no thermal barrier to prevent the lithodids from expanding upward and emerging on the outer shelf (400- to 550-m depth); however, near-surface temperatures remained too cold for them to survive in inner-shelf and coastal environments (<200 m). Ambient salinity, composition of the substrate, and the depth distribution of potential predators likewise indicated no barriers to expansion of lithodids onto the outer shelf. Primary food resources for lithodids—echinoderms and mollusks—were abundant on the upper slope (550–800 m) and outer shelf. As sea temperatures continue to rise, lithodids will likely play an increasingly important role in the trophic structure of subtidal communities closer to shore

The physiological ecology and life history strategies of the nudibranch molluscs 'Adalaria proxima' (Alder & Hancock) and 'Onchidoris muricata' (Müller) (Gastropoda: Opisthobranchia)

This study investigated the physiological ecology, larval biology and population genetics of the nudibranch molluscs Adalaria proxima (A & H) and Onchidoris muricata (Müller). These two species are annual, simultaneous hermaphrodites and are ecologically very similar with the exception that A. proxima reproduces by means of pelagic lecithotrophic larvae whereas Omuricata has long-term planktotrophic larvae. The aim of the study was therefore to determine the selective pressures which resulted in the evolution of different larval types in these two species, and to ascertain the ecological and population genetic consequences thereof. Simple energy budgets comprising the major components (consumption, growth, respiration and reproduction) were constructed for laboratory populations of each species. In both A. proxima and O. muricata, feeding rate displayed an asymptotic increase with body size. Mean feeding rates of A. proxima were greater than those of comparable O. muricata individuals, and overall assimilation efficiency was higher in A. proxima than in O. muricata. This difference was reflected in the somatic growth rates which were correspondingly greater in A. proxima than in O. muricata. Net growth efficiencies were broadly comparable between the two species, however, growth of A. proxima was approximately linear over' time whilst that of O. muricata displayed a curvilinear, almost exponential, pattern. This is interpreted as demonstrating that some form of constraint (possibly feeding rate) operated on the growth rates of A. proxima but not on those of O. muricata. Respiration rates were found to be relatively constant within given animals, but significant differences were found between individuals. The allometry of respiration rate was not constant; Omuricata demonstrated a more rapid increase in respiration rate with increasing body size than did A. proxima. Individual variations in respiration rate did not reflect variations in the energy partitioned to either growth or reproduction. Reproductive patterns in the two species were dissimilar. A. proxima laid fewer spawn masses containing fewer, larger ova than those laid by O. muricata individuals. In addition, the spawning period of A. proxima was shorter than that of O. muricata (60 days and 105 days respectively). Both species exhibited a similar (proportional) degree of somatic catabolism over these periods. The consequently more rapid "degrowth" of A. proxima is interpreted as the necessary utilization of an energy resource (i. e. the soma) caused by an inability to meet the energy demands of reproduction through feeding alone. This was not the case in Oanuricata individuals which exhibited a much smaller maximum body size and were able to feed at a sufficiently rapid rate to maintain reproduction. In the latter case, the longer reproductive period served to maximise the total reproductive output. Several different measures of "Reproductive Effort" (RE) were calculated. These generally indicated that the RE of Omuricata was considerably greater than that of A. proxima. Although such differences have been used in the literature to classify the respective costs of different larval types or "reproductive strategies", the variability of the RE's obtained from the different measures used here has led to the suggestion that the general lack of association between RE and reproductive strategy which has been reported elsewhere may (partially) be attributable to the different measures of RE employed in different studies. Studies of the embryonic and larval period showed that the egg-to-juvenile period of O. muricata was approximately 50% longer than that of A. proxima. This difference was primarily attributable to the extended pelagic development of O. muricata larvae. Estimates of the degree of dispersal, and hence gene-flow, between populations of these species were tested by investigating the biochemical genetics of such populations. No data were available for O. muricata, but A. proxima populations proved to be more genetically heterogeneous than had been expected. It is therefore concluded that actual pelagic dispersal may be considerably abbreviated over that expected on the basis of larval culture data alone. A model is developed to explain the possible consequences of different egg-to-juvenile periods (which accrue from different larval types) on both the ecology of the benthic adult, and on overall energy partitioning to reproduction. However, although (probable) proximate causes and effects of the different reproductive traits exhibited by A. proxima and Oanuricata are shown, it has not been possible to determine the exact selective pressures which caused A. proxima to diverge from the ancestral "O. muricata" stock through the evolution of a pelagic lecithotrophic larva