Do yearly temperature cycles reduce species richness? Insights from calanoid copepods

The metabolic theory of ecology (MTE) has explained the taxonomic richness of ectothermic species as an inverse function of habitat mean temperature. Extending this theory, we show that yearly temperature cycles reduce metabolic rates of taxa having short generation times. This reduction is due to Jensen’s inequality, which results from a nonlinear dependency of metabolic rate of organisms on temperature. It leads to a prediction that relatively lower species richness is found in habitats with larger amplitudes of yearly temperature cycles where mean temperatures and other conditions are similar. We show that metabolically driven generation time of a taxon also relates functionally to species richness, and similarly, its yearly cycles reduce richness. We test these hypotheses on marine calanoid copepods with 46,377 records of data collected by scientific cruise surveys in Mediterranean regions, across which the temperature amplitudes vary dramatically. We test both bio-energetic and phenomenological effects of temperature cycles on richness in 86 1° × 1° latitudinal and longitudinal spatial units. The models incorporated the effect of both periodic fluctuations and mean temperature explained 21.6% more variation in the data, with lower AIC, compared to models incorporated only the mean temperature. The study also gives insight into the basis of energetic-equivalence rule in MTE determining richness, which can be governed by generation time of taxon. The results of this study lead to the proposition that amplitude of yearly temperature cycles may contribute to both the longitudinal and the latitudinal differences in species richness and show how the metabolic theory can explain macro-ecological patterns arising from yearly temperature cycles.     

Do dingoes suppress the activity of feral cats in northern Australia?

Large predators can have profound impacts on community composition. Not only do they directly affect prey abundance, they also indirectly affect prey abundance through their direct effects on smaller predators. In Australia, dingoes fill the role of a large predator and, in southern Australia, have clear impacts on introduced foxes. Their effect on introduced cats, however, is less clear. Here we present data from multiple sites across northern Australia (where foxes are absent), which reveal a negative correlation between cat and dingo activity. This relationship could arise because cats avoid areas where dingoes are active, or because cats are less abundant in areas with high dingo densities, or a combination of both. At a subset of our study sites, we experimentally reduced dingo (but not cat) abundance by poison baiting. This resulted in a 55% drop in dingo activity within 4 weeks of baiting, but without a compensatory increase in cat activity. This suggests the negative correlation between cat and dingo activity is not a simple consequence of cats reactively avoiding areas with higher dingo traffic, but rather, that there are fewer cats in areas where dingoes are more active. This study is a rare demonstration of the potential for dingoes to affect the behaviour and potentially the population size of feral cats, and therefore reduce the impact of feral cats on vulnerable native prey species.     

Are we missing half of the viruses in the ocean?

Viruses are abundant in the ocean and a major driving force in plankton ecology and evolution. It has been assumed that most of the viruses in seawater contain DNA and infect bacteria, but RNA-containing viruses in the ocean, which almost exclusively infect eukaryotes, have never been quantified. We compared the total mass of RNA and DNA in the viral fraction harvested from seawater and using data on the mass of nucleic acid per RNA- or DNA-containing virion, estimated the abundances of each. Our data suggest that the abundance of RNA viruses rivaled or exceeded that of DNA viruses in samples of coastal seawater. The dominant RNA viruses in the samples were marine picorna-like viruses, which have small genomes and are at or below the detection limit of common fluorescence-based counting methods. If our results are typical, this means that counts of viruses and the rate measurements that depend on them, such as viral production, are significantly underestimated by current practices. As these RNA viruses infect eukaryotes, our data imply that protists contribute more to marine viral dynamics than one might expect based on their relatively low abundance. This conclusion is a departure from the prevailing view of viruses in the ocean, but is consistent with earlier theoretical predictions.     

Antarctic DNA barcoding; a drop in the ocean?

Coordinated, circum-Antarctic sampling expeditions during International Polar Year 2008/09 have given access to comprehensive collections suitable for DNA barcoding. Collaborations between the Census of Antarctic Marine Life (CAML), the Marine Barcode of Life project and the Canadian Centre for DNA Barcoding have enabled the Antarctic scientific community to initiate large-scale DNA barcoding projects to record the genetic diversity of Antarctic marine fauna, coordinated by the CAML Barcoding Campaign. A total of 20,355 marine specimens from more than 2,000 morphospecies covering 18 phyla are in the processing pipeline, and to date, 11,530 sequences have been processed with the remainder due by the end of 2010. Here, we present results on the current geographic and taxonomic coverage of DNA barcode data in the Southern Ocean and identify the remaining gaps. We show how DNA barcoding in the Antarctic is answering important questions regarding marine genetic diversity and challenging current assumptions of species distribution at the poles.     

Dispersal and divergence across the greatest ocean region: Do larvae matter?

For marine, benthic animals, duration of planktonic larval stagesis expected to correlate with dispersal ability, and thus speciesranges, at least where planktonic dispersal is necessary toreach habitats. Yet past analyses of larval duration and speciesranges across the insular Pacific show at most a weak correlation.So, do larvae matter in determining species ranges in such anisland setting? We analyze an extensive dataset on cowries andfind, again, that estimated larval duration does not correlatewith species ranges. Several factors can obscure a real correlation,however, including estimation error, intraspecific variation,other factors affecting dispersal, poor taxonomy, and remoteendemics. We show that taking these into consideration greatlyimproves correlation. Further evidence for the importance oflarval duration comes from diversity and speciation patterns.Diversity of poor dispersers drops more rapidly eastward acrossthe Pacific and leads to taxonomic differences in communitycomposition across the basin. Geographic scale of differentiationis strongly influenced by larval duration and leads to the mostrapid diversification at intermediate dispersal capacities.A major lesson from the phylogenetically corrected cowrie datasetis that without accurate and appropriate taxonomy, clear andimportant distributional and diversity patterns can become obscured.Inappropriate taxonomic scale can also obscure macroecologicalpatterns: cowrie tribes/subfamilies show substantial variationin the steepness of their diversity cline across the Pacificand in their proportional local abundance, showing the importanceof ecological traits in controlling distributions. In contrastsuch variation was not evident in a study focused at the familylevel in corals and fishes.     

Carbon or nitrogen limitation in marine copepods?

The elemental limitation of copepod production can be studiedusing stoichiometric models, which balance carbon (C) and nitrogen(N) in ingested food and predator biomass, and assume that theelement in shortest supply is used as efficiently as possible.A model of this type was developed which has two important features:(i) it is assumed that a maximum N net production efficiencyof 1.0 is possible, although assimilation of N may be <1.0;and (ii) assimilation of C in the gut is handled by dividingfood into biochemical compounds. Model results suggested thatmarine copepods should commonly be limited by C, owing to theirlow C net production efficiency, and the low food C:N ratiostypical of the upper ocean. Nevertheless, the work demonstratedthat copepods might still preferentially ingest protein-richprey to maximize production because the associated C is easilyassimilated. A comparison of model predictions with two experimentalstudies, however, revealed that in the studies copepods werenot utilizing N as efficiently as would be expected by stoichiometrictheory. This finding suggests that copepod nutrition is morecomplicated than simple elemental limitation by C or N: imbalancesof specific compounds, such as essential amino acids, may becontrolling production. In addition, the nutritional requirementsof copepods may vary on a seasonal basis in a complex manner.     

How many copepods?

At present there are approximately 11500 known species of copepods. The number of species described during the past 27 years is nearly two-thirds of all those described in the previous 100 years. Approximately one-third of marine copepod species are parasites or associates, nearly equally divided between those on fishes and those on invertebrates. Individual copepods are extremely abundant, not only as free-living species or parasites of fishes, but as associates of invertebrates, especially in the tropical regions of the world.     

Marine phytoplankton: how many species in the world ocean?

Towards the end of the 1980s, living plankton flora of the worldocean amounted to 474-504 genera and 3444–4375 speciesif one neglects the increase rate of taxa during the latestyears In the above figures, the lower estimate is that of the‘reliable’ taxa (of practical value for identificationtasks), whereas the higher estimate includes the insufficientlyknown or doubtful organisms, and synonyms are excluded. Thefrequency distribution of the numbers of species per genus confirmsthe general hyperbolic law, which implies that a relativelylarge number of genera are uni- or paucispecific.     

How are the vertical migrations of copepods controlled?

Using Calanus finmarchicus (Gunnerus) as a model organism, a hypothesis is suggested to explain the diel and seasonal vertical migrations of herbivorous copepods in boreal and polar waters. The hypothesis is based on the following assumptions. Hungry copepods are assumed to react to food smell by increased swimming. High lipid content is assumed to turn the copepods upside down. Light avoidance is assumed to operate solely while the copepods are satiated. The following three major peaks in downflux of phytoplankton remains are assumed to reach 1000 m depth or more: pre- and post-spring bloom peaks and the autumn increase. A minor “afternoon peak” in short-range downflux of phytoplankton is also assumed to exist. The assumptions are used to explain the following main traits in copepod migrations. The afternoon increase in downflux of phytoplankton material induces upward swimming of hungry copepods. If satiated, light avoidance brings them down again at dawn. The late stages of many species of copepods accumulate large amounts of lipids and if the above assumptions are valid, they will be turned upside down and swim down if activated. During midsummer, the downflux does not reach deep water and the copepods are assumed to spend some time in midwater until they moult. Copepods moulting from stage V into female adults use up to half of their lipids to produce eggs, which are more anteriorly located. This is assumed to turn their bodies back into an upright position and the copepods are assumed to swim up to the surface again when they smell sinking phytoplankton remains. Fat copepods are assumed to follow the downflux of phytoplankton material down to diapause depths, especially at the end of the spring bloom and in autumn. It is assumed that enough lipids are used up during the diapause to turn the copepods into head-up position again. The smell of fast-sinking fecal pellets containing prebloom phytoplankton is assumed to bring the copepods up from diapause again in late winter. The probable implications for the survival of cod larvae are discussed.     

Do we need nasal vaccines against COVID 19 to suppress the transmission of infections?

Covid-19 vaccines have within the first year prevented about 14 million deaths but did not induce a strong mucosal immune response. Data from US, UK, Singapore and Israel showed a variable and mostly modest effects of vaccination on virus excretion during breakthrough infections. Contact studies showed decreased transmission of infection from vaccinated index cases, but the effect varied according to dominant virus type, with study type and the nature of the contact group and diminished with time after vaccination. Some researchers suspect that it is unlikely to stop the pandemic with injected vaccines alone. Promising animal experiments were conducted with mucosal vaccines. Mice nasally immunized with a chimpanzee adenovirus vector mounted a mucosal immune response, were protected against viral challenge after a single vaccine dose and suppressed nasal replication of the challenge virus. Phage T4 expressing SARS-CoV-2 spike and nucleocapsid induced a sterilizing lung immunity in nasally vaccinated mice. Also hamsters intranasally immunized with the prefusion-stabilized spike protein showed no infectious virus in nasal turbinates upon challenge. Other studies showed that intranasal vaccination with an adenovirus vaccine reduced but did not eliminated viral transmission from infected to naïve hamsters. Intranasal vaccination of rhesus macaques with adenovirus vaccines also substantially reduced or even suppressed viral replication in the upper and lower respiratory tract. Human data on mucosal SARS-CoV-2 vaccines are so far limited to safety and immunogenicity studies. Aerosolized adenovirus vaccines given either as a booster or as primary immunization were safe and induced similar or superior immune response than injected vaccines while an aerosolized influenza vectored vaccine induced only a weak humoral and cellular immune response. Overall 100 mucosal SARS-CoV-2 vaccines are in development and 20 are in clinical trials. First human trials demonstrate that this will not be an easy task.     

Are copepods important grazers of the spring phytoplankton bloom in the western Irish Sea?

The spring phytoplankton bloom and copepod grazing were studied at a coastal and offshore station in the western Irish Sea during 1997. Maximum chlorophyll standing stocks of 132.8 mg m^-2 inshore and 199.4 mg m^-2 offshore were measured in late April. At that time, mean water column temperatures were 10 and 8C at the coastal and offshore station, respectively. Spring bloom production at the coastal station was estimated as 31.2 g C m^-2 and was dominated by the diatom Guinardia delicatula. Offshore, production was 28.2 g C m^-2 and the bloom was composed of small (10 m) phytoflagellates and the silicoflagellate Dictyocha speculum. Maximum copepod abundance (189 and 544 x 10³ individuals m^-2, inshore and offshore, respectively) coincided with the spring bloom. Pseudocalanus and Temora ingestion rates were derived from measurements of gut pigment fluorescence, and were found to vary during the course of the spring bloom as a result of changes in gut content. Grazing by late copepodite and adult Pseudocalanus and Temora was variable inshore, but overall accounted for 17% of bloom production. Offshore, 22% of bloom production was grazed with maximum grazing (76% of daily production) occurring at the end of the bloom. Large copepod species were not major grazers of the spring bloom. Greater utilization of spring bloom production by copepods in the western Irish Sea compared to regions of the North Sea is attributed to differences in population size at the time of the bloom.      

Do stocked hatchery‐reared juveniles ecologically suppress wild juveniles in Salvelinus leucomaenis?

The dominancy of semi‐wild and hatchery‐reared white‐spotted charr Salvelinus leucomaenis juveniles was evaluated using pair‐wise enclosure tests and field stocking tests. The semi‐wild S. leucomaenis originated in a hatchery, being stocked into the test stream as eyed‐eggs. In the pair‐wise enclosure test, the semi‐wild S. leucomaenis dominated the hatchery S. leucomaenis that were of a similar standard length (L_S). The semi‐wild S. leucomaenis were subordinate to hatchery S. leucomaenis that were > 11% larger in L_S. In the field stocking test, the abundance and growth of semi‐wild S. leucomaenis was decreased in the presence of larger hatchery S. leucomaenis (14% larger L_S). Taken together, these results suggest that larger hatchery S. leucomaenis ecologically suppress the smaller semi‐wild S. leucomaenis. Salvelinus leucomaenis juveniles that are stocked with the intention of supplementing natural populations should be < 10% larger than their wild counterparts at the time of stocking to minimize their competitive advantage. The semi‐wild and hatchery S. leucomaenis used in both tests were genetically similar individuals, suggesting that the differences are due to the early rearing environment of either a natural stream or hatchery. The hatchery S. leucomaenis have lower levels of aggression as a result of selection in the hatchery rearing environment. Rearing in a natural stream from the eyed‐egg stage is likely to increase their lowered aggression.     

Cyclopoid copepods as bioindicators of eutrophication in reservoirs: Do patterns hold for large spatial extents?

Some species of copepods are sensitive to water quality oscillations from natural or anthropogenic causes. Information on basic ecological attributes such as abundance can be helpful in the context of hydric resources monitoring. Our study analyzed if the abundance of 22 copepod species of the second largest basin of South America was more associated with variables oscillating by natural or anthropic causes, contrasting among oligotrophic, mesotrophic, and eutrophic reservoirs. Our aim was to identify and understand the abundance of species with potential to monitor water quality in large scale assessments. Potential bioindicators would have different abundances in eutrophic, mesotrophic and oligotrophic sites and would not oscillate according to natural characteristics of reservoirs (water temperature, air temperature, and depth). Two species were sensitive to eutrophication and were not related to natural characteristics of reservoirs, that is, they were suitable for biomonitoring the La Plata Basin. Thermocyclops minutus negatively responded to eutrophication, while Acanthocyclops robustus responded positively. Additional exploratory analyses identified that Copepod abundance was related to total phosphorus, chlorophyll-a concentration, water transparency, total suspended matter, and depth. Metacyclops mendocinus, Acanthocyclops robustus, Mesocyclops meridianus, Mesocyclops ogunnus, and Thermocyclops decipiens were abundant in eutrophic reservoirs, and Thermocyclops minutus, and Thermocyclops inversus were associated with higher water transparency, typically oligo/mesotrophic reservoirs. Overall, we found that cyclopoids are highly affected by eutrophication, and species abundance could be used to monitor reservoirs and anticipate potential impacts on water quality in large-scale biomonitoring schemes.     

Flowering and fruiting phenology in the coastal shrublands of Doñana,south Spain

Flowering and fruiting phenological patterns at the individual-, population-, and community level were studied in a southern Spanish scrub community composed of 30 shrub species. Few individuals of any species produced a high number of flowers. Intrapopulation deviation in the peak time of flowering showed a strong and positive skewness. Relative flowering duration, however, displayed a virtually normal distribution. Generally, species flowering in spring have a short flowering time, while species flowering earlier or later in the year show significantly longer flowering periods. Species were in bloom throughout the year, but there was a major peak during spring and two lesser ones in autumn and early summer. Shallow rooting taxa in typically mediterranean genera displayed a strategy of spring flowering and summer fruiting. Summer and autumn flowering occurred among heath-like shrubs of relatively wet places, and forest-associated, vertebrate-dispersed species which commonly have underground storage organs. Species with ripe fruits presented two peaks, the major one during the summer including the majority of taxa with seeds dispersed by non-vertebrate agents. There was a minor fruiting peak in autumn dominated by taxa that rely on vertebrates for dispersal. The complex seasonal patterns observed are interpreted in relation to environmental conditions and physiological constraints on species living in a highly seasonal climate.     

Marine chitinolytic enzymes,a biotechnological treasure hidden in the ocean?

Applied Microbiology and Biotechnology - Chitinolytic enzymes are capable to catalyze the chitin hydrolysis. Due to their biomedical and biotechnological applications, nowadays chitinolytic enzymes...     

Have we been underestimating the effects of ocean acidification in zooplankton?

Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry. The perception that copepods are insensitive to OA is largely based on experiments with adult females. Their apparent resilience to increased carbon dioxide (pCO₂) concentrations has supported the view that copepods are ‘winners’ under OA. Here, we show that this conclusion is not robust, that sensitivity across different life stages is significantly misrepresented by studies solely using adult females. Stage‐specific responses to pCO₂ (385–6000 μatm) were studied across different life stages of a calanoid copepod, monitoring for lethal and sublethal responses. Mortality rates varied significantly across the different life stages, with nauplii showing the highest lethal effects; nauplii mortality rates increased threefold when pCO₂ concentrations reached 1000 μatm (year 2100 scenario) with LC₅₀ at 1084 μatm pCO₂. In comparison, eggs, early copepodite stages, and adult males and females were not affected lethally until pCO₂ concentrations ≥3000 μatm. Adverse effects on reproduction were found, with >35% decline in nauplii recruitment at 1000 μatm pCO₂. This suppression of reproductive scope, coupled with the decreased survival of early stage progeny at this pCO₂ concentration, has clear potential to damage population growth dynamics in this species. The disparity in responses seen across the different developmental stages emphasizes the need for a holistic life‐cycle approach to make species‐level projections to climate change. Significant misrepresentation and error propagation can develop from studies which attempt to project outcomes to future OA conditions solely based on single life history stage exposures.