Ocean Acidification Disrupts Chemical Signaling In Marine Organisms

The relationship between the apparently inexorable increase in atmospheric carbon dioxide (CO2) as a direct result of human activity and the increasing acidity in the world’s oceans has been well documented. The current projected estimate is that at the current rate of atmospheric CO2 buildup, the pH in the oceans will drop from the current and historic range of 8.15 – 8.25 to ~ 7.8 or below by the end of the 21st century.

In addition to the disastrous impact of acidification upon the calcification that impedes coral and shell formation in the affected organisms, there is an additional side effect of this acidification that is worthy of attention. Many of the waterborne biologically-significant chemical signals, such as pheromones, that play essential roles in marine biology are disrupted by changes in the pH of the local marine environment. These signaling processes play a crucial role in important biological activities associated with mating, foraging, recruitment and alarm mechanisms.

The impact of this chemical disruption resides on two distinct levels. Increased acidity can affect the signaling compounds directly, and, secondly, impact their required interaction with specific receptor proteins designed to bind with the signaling molecule. This specific interaction between a signaling compound and its unique receptor represents the essential first step in producing the desired effect. This kind of interaction is found throughout metazoan biology.

The mechanism of this disruption caused by increased acidity within the marine environment can be attributed to changes in hydrogen bonding, electrostatic potential and hydrophilic and hydrophobic interactions that affect both ligands and their specific receptors. The types of organic compounds that are so affected include pheromones, nucleosides, thiols (sulfur-based compounds) organic acids and others.

The critical behavioral patterns that suffer from continued acidification of the oceans include sexual reproduction, recognition of the presence of predators, fertilization, larval settlement and many others. Unfortunately, the rate of acidification exceeds the ability of evolutionary mechanisms to respond to the kinds of changes described. This kind of impact of the increase of greenhouse gases within the natural environment needs further study, for the implications can prove to be devastating.

Epigenetics

Epigenetics is the study of the changes in phenotype brought about by modification of genetic expression rather than through changes in the actual structural information found within the DNA i.e. genetic mutations.

Although the individual organisms within a species share the same essential blueprint imbedded within the DNA, they express individual phenotypes.  In addition, complex traits and diseases cannot be fully explained via differences in genotype.  This suggests that developmental and environmental factors that are unique to the individual play an important role in determining the terminal phenotype.

The kinds of chemical modifications that are associated with epigenetics are DNA methylation and histone modification.  Histones are the family proteins that are intimately associated with DNA and play an important role in genetic expression.  Other factors that have been implicated in epigenetics are nonocoding RNAs and nucleosome location.

Since much current genetic research is focused on the role of epigenetics in determining phenotypic characteristics, there has been considerable confusion as to what constitutes epigenetics.  An epigenetic system needs to meet the following criteria:

• Heritable
• Self-perpetuating
• Reversible.

Prions – infectious proteins – meet these criteria since they perpetuate themselves through altered protein folding states and may, in fact, serve as indicators of environmental stressors.  Prions certainly alter phenotype as exemplified by the diseases they produce – Creutzfeldt-Jakob disease (CJD) being an example.

Some metazoans – metazoans encompass all animals advanced enough to have differentiated tissue - undergo genome-wide reprogramming of DNA methylation and histone modifications during gametogenesis and embryogenesis as a way of clearing those epigenetic changes that were introduced by environmental factors during the life of the individual.  Furthermore, there is evidence that small noncoding RNAs may serve as tags for marking deleterious sequences within the DNA. This Reprogramming may play a critical role in cell differentiation, and has been linked to pluripotency in both gametes and zygotes.

The field of epigenetics is undergoing rapid expansion; the implication of the critical role epigenetic processes play in the development of the individual is just beginning to be understood.