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The early life history of the clam Macoma balthica in a high CO2 world.

ABSTRACT: This study investigated the effects of experimentally manipulated seawater carbonate chemistry on several early life history processes of the Baltic tellin (Macoma balthica), a widely distributed bivalve that plays a critical role in the functioning of many coastal habitats. We demonstrate that ocean acidification significantly depresses fertilization, embryogenesis, larval development and survival during the pelagic phase. Fertilization and the formation of a D-shaped shell during embryogenesis were severely diminished: successful fertilization was reduced by 11% at a 0.6 pH unit decrease from present (pH 8.1) conditions, while hatching success was depressed by 34 and 87%, respectively at a 0.3 and 0.6 pH unit decrease. Under acidified conditions, larvae were still able to develop a shell during the post-embryonic phase, but higher larval mortality rates indicate that fewer larvae may metamorphose and settle in an acidified ocean. The cumulative impact of decreasing seawater pH on fertilization, embryogenesis and survival to the benthic stage is estimated to reduce the number of competent settlers by 38% for a 0.3 pH unit decrease, and by 89% for a 0.6 pH unit decrease from present conditions. Additionally, slower growth rates and a delayed metamorphosis at a smaller size were indicative for larvae developed under acidified conditions. This may further decline the recruit population size due to a longer subjection to perturbations, such as predation, during the pelagic phase. In general, early life history processes were most severely compromised at ~pH 7.5, which corresponds to seawater undersaturated with respect to aragonite. Since recent models predict a comparable decrease in pH in coastal waters in the near future, this study indicates that future populations of Macoma balthica are likely to decline as a consequence of ongoing ocean acidification.

SUBMITTER: Van Colen C

PROVIDER: S-EPMC3438177 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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The early life history of the clam Macoma balthica in a high CO2 world.

Van Colen Carl C Debusschere Elisabeth E Braeckman Ulrike U Van Gansbeke Dirk D Vincx Magda M

PloS one 20120910 9

This study investigated the effects of experimentally manipulated seawater carbonate chemistry on several early life history processes of the Baltic tellin (Macoma balthica), a widely distributed bivalve that plays a critical role in the functioning of many coastal habitats. We demonstrate that ocean acidification significantly depresses fertilization, embryogenesis, larval development and survival during the pelagic phase. Fertilization and the formation of a D-shaped shell during embryogenesis ...[more]

PMID: 22970279

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Project description:BackgroundAllopatric divergence across lineages can lead to post-zygotic reproductive isolation upon secondary contact and disrupt coevolution between mitochondrial and nuclear genomes, promoting emergence of genetic incompatibilities. A previous F ST scan on the transcriptome of the Baltic clam Macoma balthica highlighted several genes potentially involved in mito-nuclear incompatibilities (MNIs). As proteins involved in the mitochondrial oxidative phosphorylation (OXPHO) chain are prone to MNIs and can contribute to the maintenance of genetic barriers, the mitochondrial genomes of six Ma. balthica individuals spanning two secondary contact zones were sequenced using the Illumina MiSeq plateform.ResultsThe mitogenome has an approximate length of 16,806 bp and encodes 13 protein-coding genes, 2 rRNAs and 22 tRNAs, all located on the same strand. atp8, a gene long reported as rare in bivalves, was detected. It encodes 42 amino acids and is putatively expressed and functional. A large unassigned region was identified between rrnS and tRNA (Met) and could likely correspond to the Control Region. Replacement and synonymous mutations were mapped on the inferred secondary structure of all protein-coding genes of the OXPHO chain. The atp6 and atp8 genes were characterized by background levels of replacement mutations, relative to synonymous mutations. However, most nad genes (notably nad2 and nad5) were characterized by an elevated proportion of replacement mutations.ConclusionsSix nearly complete mitochondrial genomes were successfully assembled and annotated, providing the necessary roadmap to study MNIs at OXPHO loci. Few replacement mutations were mapped on mitochondrial-encoded ATP synthase subunits, which is in contrast with previous data on nuclear-encoded subunits. Conversely, the high population divergence and the prevalence of non-synonymous mutations at nad genes are congruent with previous observations from the nuclear transcriptome. This further suggest that MNIs between subunits of Complex I of the OXPHO chain, coding for NADH dehydrogenase, may play a role in maintaining barriers to gene flow in Ma. balthica.

Project description:Detritivores are essential to nutrient cycling, but are often neglected in trophic networks, due to difficulties with determining their diet. DNA analysis of gut contents shows promise of trophic link discrimination, but many unknown factors limit its usefulness. For example, DNA can be rapidly broken down, especially by digestion processes, and DNA provides only a snapshot of the gut contents at a specific time. Few studies have been performed on the length of time that prey DNA can be detected in consumer guts, and none so far using benthic detritivores. Eutrophication, along with climate change, is altering the phytoplankton communities in aquatic ecosystems, on which benthic detritivores in aphotic soft sediments depend. Nutrient-poor cyanobacteria blooms are increasing in frequency, duration, and magnitude in many water bodies, while nutrient-rich diatom spring blooms are shrinking in duration and magnitude, creating potential changes in diet of benthic detritivores. We performed an experiment to identify the taxonomy and quantify the abundance of phytoplankton DNA fragments on bivalve gut contents, and how long these fragments can be detected after consumption in the Baltic Sea clam Macoma balthica. Two common species of phytoplankton (the cyanobacteria Nodularia spumigena or the diatom Skeletonema marinoi) were fed to M. balthica from two regions (from the northern and southern Stockholm archipelago). After removing the food source, M. balthica gut contents were sampled every 24 hours for seven days to determine the number of 23S rRNA phytoplankton DNA copies and when the phytoplankton DNA could no longer be detected by quantitative PCR. We found no differences in diatom 18S rRNA gene fragments of the clams by region, but the southern clams showed significantly more cyanobacteria 16S rRNA gene fragments in their guts than the northern clams. Interestingly, the cyanobacteria and diatom DNA fragments were still detectable by qPCR in the guts of M. balthica one week after removal from its food source. However, DNA metabarcoding of the 23S rRNA phytoplankton gene found in the clam guts showed that added food (i.e. N. spumigena and S. marinoi) did not make up a majority of the detected diet. Our results suggest that these detritivorous clams therefore do not react as quickly as previously thought to fresh organic matter inputs, with other phytoplankton than large diatoms and cyanobacteria constituting the majority of their diet. This experiment demonstrates the viability of using molecular methods to determine feeding of detritivores, but further studies investigating how prey DNA signals can change over time in benthic detritivores will be needed before this method can be widely applicable to both models of ecological functions and conservation policy.

Project description:Abstract Taking advantage of the unique system of doubly uniparental inheritance (DUI) of mitochondria, we developed a reliable molecular method to sex individuals of the marine bivalve Macoma balthica rubra. In species with DUI (~100 known bivalves), both sexes transmit their mitochondria: males bear both a male‐ and female‐type mitogenome, while females bear only the female type. Male and female mitotypes are sufficiently divergent to reliably PCR‐amplify them specifically. Loop‐mediated isothermal amplification (LAMP) is a precise, economical and portable alternative to PCR for molecular sexing and we demonstrate its application in this context. We used 154 individuals sampled along the Atlantic coast of France and sexed microscopically by gonad examination to test for the congruence among gamete type, PCR sexing and LAMP sexing. We show an exact match among the sexing results from these three methods using the male and female mt‐cox1 genes. DUI can be disrupted in inter‐specific hybrids, causing unexpected distribution of mitogenomes, such as homoplasmic males or heteroplasmic females. To our knowledge, DUI disruption at the intra‐specific scale has never been tested. We applied our sexing protocol to control for unexpected heteroplasmy caused by hybridization between divergent genetic lineages and found no evidence of disruption in the mode of mitochondrial inheritance in M. balthica rubra. We propose LAMP as a useful tool to accelerate eco‐evolutionary studies of DUI. It offers the opportunity to investigate the potential role of, previously unaccounted‐for, sex‐specific patterns such as sexual selection or sex‐specific dispersal bias in the evolution of free‐spawning benthic species. Our paper reports testing on the evolutionary stability of sex‐link mitochondrial heteroplasmy in males of the gonochoric bivalve Macomabalthicarubra, and the practical use of this stability to sex individuals molecularly, using loop‐mediated isothermal DNA amplification.

Dataset Information

The early life history of the clam Macoma balthica in a high CO2 world.

Publications

The early life history of the clam Macoma balthica in a high CO2 world.

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