Variation in Morphology vs Conservation of a Mitochondrial Gene in Montastraea cavernosa (Cnidaria, Scleractinia)

Skeletal morphology of many scleractinian corals may be influenced by environmental factors and may thus result in substantial intraspecific phenotypic plasticity and, possibly, in overlapping morphologies between species. Environmentally induced variation can also mask phenotypic variation that is genetically based. Morphological analyses and DNA sequence analyses were performed on Montastraea cavernosa from the Flower Garden Banks, Texas, and from the Florida Keys in order to assess variation within and between geographic regions. Skeletal characters, including corallite diameter, columella width, theca thickness, nearest-neighbor distance, length of first septa cycle, and width of first septa cycle, varied within colonies, among colonies, and between the Flower Garden Banks and the Florida Keys. Morphological variation may be controlled by environmental and genetic influences at different levels. If phenotype is under genetic control, it is not influenced by the mitochondrial cytochrome oxidase subunit I gene, because analysis of a 708 base pair fragment revealed identical sequences of M. cavernosa from these geographic regions. This high level of nucleotide sequence similarity may result from functional constraints, efficient DNA repair mechanisms, or other processes. This gene was not found to exhibit any variation in association with that observed in the morphology, and we suggest that it is an inappropriate genetic marker to use to assess intraspecific variation within this species and possibly other scleractinian species as well. Analysis via other molecular techniques will be necessary in order to assess the factors that influence morphological variation and that distinguish populations within this species

Gene Expression of Corals in Response to Macroalgal Competitors

<div><p>As corals decline and macroalgae proliferate on coral reefs, coral-macroalgal competition becomes more frequent and ecologically important. Whether corals are damaged by these interactions depends on susceptibility of the coral and traits of macroalgal competitors. Investigating changes in gene expression of corals and their intracellular symbiotic algae, <i>Symbiodinium,</i> in response to contact with different macroalgae provides insight into the biological processes and cellular pathways affected by competition with macroalgae. We evaluated the gene expression profiles of coral and <i>Symbiodinium</i> genes from two confamilial corals, <i>Acropora millepora</i> and <i>Montipora digitata</i>, after 6 h and 48 h of contact with four common macroalgae that differ in their allelopathic potency to corals. Contacts with macroalgae affected different biological pathways in the more susceptible (<i>A. millepora</i>) versus the more resistant (<i>M. digitata</i>) coral. Genes of coral hosts and of their associated <i>Symbiodinium</i> also responded in species-specific and time-specific ways to each macroalga. Changes in number and expression intensity of affected genes were greater after 6 h compared to 48 h of contact and were greater following contact with <i>Chlorodesmis fastigiata</i> and <i>Amphiroa crassa</i> than following contact with <i>Galaxaura filamentosa</i> or <i>Turbinaria conoides</i>. We documented a divergence in transcriptional responses between two confamilial corals and their associated <i>Symbiodinium</i>, as well as a diversity of dynamic responses within each coral species with respect to the species of macroalgal competitor and the duration of exposure to that competitor. These responses included early initiation of immune processes by <i>Montipora</i>, which is more resistant to damage after long-term macroalgal contact. Activation of the immune response by corals that better resist algal competition is consistent with the hypothesis that some macroalgal effects on corals may be mediated by microbial pathogens.</p></div

Number of differentially expressed genes (DEGs) in <i>Acropora millepora</i> and <i>Montipora digitata</i> coral (A) and <i>Symbiodinium</i> (B) genes for all treatments.

<p>Black bars indicate significantly up-regulated genes, and gray bars are significantly down-regulated genes relative to controls (adjusted <i>P</i> = 0.01). A =  <i>Amphiroa crassa</i>, C =  <i>Chlorodesmis fastigiata</i>, G =  <i>Galaxaura filamentosa</i> and T =  <i>Turbinaria conoides</i>.</p

Multivariate grouping of coral exposure treatments using principle components analysis based on 850 differentially expressed <i>Acropora millepora</i> and <i>Montipora digitata</i> genes (both coral and <i>Symbiodinium</i>) relative to controls.

<p>All genes included in this analysis are in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114525#pone.0114525.s002" target="_blank">S2 Table</a>. A =  <i>Amphiroa crassa</i>, C =  <i>Chlorodesmis fastigiata</i>, G =  <i>Galaxaura filamentosa</i> and T =  <i>Turbinaria conoides</i>.</p

Significantly over- or under-represented (Fisher's exact test; <i>P</i> = 0.01) biological processes and molecular functions of differentially expressed genes (DEGs) shared between coral species (A) and those specific to each coral (B and C).

<p>GO-ID indicates the identifier associated with the gene ontology term as defined by the Gene Ontology project (<a href="http://www.geneontology.org" target="_blank">www.geneontology.org</a>). Underlined adjusted <i>P</i>-value indicates under-represented gene ontology categories.</p><p>Significantly over- or under-represented (Fisher's exact test; <i>P</i> = 0.01) biological processes and molecular functions of differentially expressed genes (DEGs) shared between coral species (A) and those specific to each coral (B and C).</p

Hierarchical cluster analysis of 850 <i>Acropora millepora</i> and <i>Montipora digitata</i> genes (both coral and <i>Symbiodinium</i>) differentially expressed relative to controls as determined by ANOVA (adjusted <i>P</i><0.01) in response to algal treatments.

<p>Bars within each column represent fold change difference between treatment and control. Red bars indicate up-regulation relative to control, green indicates down-regulation and black indicates no difference. All genes included in this analysis are in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114525#pone.0114525.s002" target="_blank">S2 Table</a>.</p

Mean gene expression (spot intensity) of all differentially expressed coral and <i>Symbiodinium</i> genes (combined) grouped by macroalgal treatment (ANOVA; <i>P</i> = 0.0003).

<p>Letters indicate significant groupings by Tukey-Kramer HSD post-hoc test.</p

Genetic determinants of mate recognition in <it>Brachionus manjavacas </it>(Rotifera)

Abstract Background Mate choice is of central importance to most animals, influencing population structure, speciation, and ultimately the survival of a species. Mating behavior of male brachionid rotifers is triggered by the product of a chemosensory gene, a glycoprotein on the body surface of females called the mate recognition pheromone. The mate recognition pheromone has been biochemically characterized, but little was known about the gene(s). We describe the isolation and characterization of the mate recognition pheromone gene through protein purification, N-terminal amino acid sequence determination, identification of the mate recognition pheromone gene from a cDNA library, sequencing, and RNAi knockdown to confirm the functional role of the mate recognition pheromone gene in rotifer mating. Results A 29 kD protein capable of eliciting rotifer male circling was isolated by high-performance liquid chromatography. Two transcript types containing the N-terminal sequence were identified in a cDNA library; further characterization by screening a genomic library and by polymerase chain reaction revealed two genes belonging to each type. Each gene begins with a signal peptide region followed by nearly perfect repeats of an 87 to 92 codon motif with no codons between repeats and the final motif prematurely terminated by the stop codon. The two Type A genes contain four and seven repeats and the two Type B genes contain three and five repeats, respectively. Only the Type B gene with three repeats encodes a peptide with a molecular weight of 29 kD. Each repeat of the Type B gene products contains three asparagines as potential sites for N-glycosylation; there are no asparagines in the Type A genes. RNAi with Type A double-stranded RNA did not result in less circling than in the phosphate-buffered saline control, but transfection with Type B double-stranded RNA significantly reduced male circling by 17%. The very low divergence between repeat units, even at synonymous positions, suggests that the repeats are kept nearly identical through a process of concerted evolution. Information-rich molecules like surface glycoproteins are well adapted for chemical communication and aquatic animals may have evolved signaling systems based on these compounds, whereas insects use cuticular hydrocarbons. Conclusion Owing to its critical role in mating, the mate recognition pheromone gene will be a useful molecular marker for exploring the mechanisms and rates of selection and the evolution of reproductive isolation and speciation using rotifers as a model system. The phylogenetic variation in the mate recognition pheromone gene can now be studied in conjunction with the large amount of ecological and population genetic data being gathered for the Brachionus plicatilis species complex to understand better the evolutionary drivers of cryptic speciation.</p

Genetic determinants of mate recognition in Brachionus manjavacas (Rotifera)

© 2009 Snell et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1741-7007/7/60.DOI:10.1186/1741-7007-7-60Background: Mate choice is of central importance to most animals, influencing population structure, speciation, and ultimately the survival of a species. Mating behavior of male brachionid rotifers is triggered by the product of a chemosensory gene, a glycoprotein on the body surface of females called the mate recognition pheromone. The mate recognition pheromone has been biochemically characterized, but little was known about the gene(s). We describe the isolation and characterization of the mate recognition pheromone gene through protein purification, N-terminal amino acid sequence determination, identification of the mate recognition pheromone gene from a cDNA library, sequencing, and RNAi knockdown to confirm the functional role of the mate recognition pheromone gene in rotifer mating. Results: A 29 kD protein capable of eliciting rotifer male circling was isolated by high-performance liquid chromatography. Two transcript types containing the N-terminal sequence were identified in a cDNA library; further characterization by screening a genomic library and by polymerase chain reaction revealed two genes belonging to each type. Each gene begins with a signal peptide region followed by nearly perfect repeats of an 87 to 92 codon motif with no codons between repeats and the final motif prematurely terminated by the stop codon. The two Type A genes contain four and seven repeats and the two Type B genes contain three and five repeats, respectively. Only the Type B gene with three repeats encodes a peptide with a molecular weight of 29 kD. Each repeat of the Type B gene products contains three asparagines as potential sites for N-glycosylation; there are no asparagines in the Type A genes. RNAi with Type A double-stranded RNA did not result in less circling than in the phosphate-buffered saline control, but transfection with Type B double-stranded RNA significantly reduced male circling by 17%. The very low divergence between repeat units, even at synonymous positions, suggests that the repeats are kept nearly identical through a process of concerted evolution. Information-rich molecules like surface glycoproteins are well adapted for chemical communication and aquatic animals may have evolved signaling systems based on these compounds, whereas insects use cuticular hydrocarbons. Conclusion: Owing to its critical role in mating, the mate recognition pheromone gene will be a useful molecular marker for exploring the mechanisms and rates of selection and the evolution of reproductive isolation and speciation using rotifers as a model system. The phylogenetic variation in the mate recognition pheromone gene can now be studied in conjunction with the large amount of ecological and population genetic data being gathered for the Brachionus plicatilis species complex to understand better the evolutionary drivers of cryptic speciation