Researchers studied how group-living social spiders avoid getting sick. One researcher involved says that the research may also be relevant in understanding how other group-living animals, such as livestock, cope with exposure to parasites and pathogens.
Researchers wondered what social spiders do to avoid getting sick since they live in large groups and are often closely related, so that bacteria and viruses can infect an entire colony at the same time more easily.
To determine what social spiders do to avoid disease-related mass extinction, researchers investigated whether the spiders might be able to make epigenetic changes in their DNA in response to infections.
The research shows that something changes the spiders’ DNA when a group is infected but that this is not necessarily related to genes known to affect the immune system.
According to a researcher behind the study, the research could affect many species other than spiders.
“Many animals live in large social groups with many members from the same family, making them vulnerable to bacterial and viral infections. This applies not only to spiders but also to other types of animals. Our research on spiders has made us more aware of how these animals try to protect themselves against outbreaks of disease,” explains David Fisher, School of Biological Sciences, University of Aberdeen, United Kingdom.
The research has been published in Heredity.
Problematic when animals live in large groups
The problem associated with living in large social groups and being closely related is that once a bacterial or viral pathogen discovers how to infect one member of the group, it can usually infect the whole group because the immune response differs little between family members.
Bacterial and viral pathogens can therefore easily spread between individual animals living in large social groups.
The big question is what these animals do to avoid being wiped out by bacterial and viral pathogens.
“We would expect social animals to have an extra layer of immune response to meet this threat, but so far we do not know what this extra layer is,” says David Fisher.
Studied social spiders in southern Africa
To improve understanding of the immune responses of social animals, David Fisher and colleagues studied Stegodyphus dumicola social spiders in South Africa, Namibia and Botswana.
This species typically lives in social groups of up to several hundred, and South America has spiders that live in groups of more than 10,000.
The researchers studied several groups of spiders in periods shortly before nest extinction by bacterial pathogens and have monitored the spiders for many years, during which time they selected individuals for further examination.
This meant that, for the study mentioned, they could examine spiders from at least six months before nest extinction to just before extinction and determine how their epigenetics changed.
Epigenetics describes modifications to DNA so that some genes become easier for the cell to read and others become more difficult, thereby enabling an organism to increase the gene expression of relevant pathways that influence the immune response.
The researchers specifically investigated the type of epigenetics called methylation, in which a methyl group attached to the DNA either activates or deactivates genes.
Methylation is probably not part of the immune response
The results show that methylation is probably not part of the spiders’ strategy for combatting the threat from pathogens, and the researchers found that the methylation of DNA generally increased little.
The researchers also studied the individual chromosomes and found that chromosome 13 was often methylated, indicating that part of the spiders’ immune response is located on this chromosome. However, this methylation did not occur in genes known to affect the immune system.
“All this indicates that methylation probably does not have a role when social spiders try to combat the threat of bacterial and viral pathogens infecting them more easily than animals that live alone or animals that are not closely related. But we have not yet discovered why methylation occurs on chromosome 13,” explains David Fisher.
He elaborates that methylation is not the only type of epigenetic change that can occur in response to pressure from bacterial and viral pathogens.
“One possibility is that the spiders do not react at all to the threat from the pathogens, but this is unlikely,” adds David Fisher.
Focus should perhaps switch direction
Although the study could not prove that methylation has a role in the immune response of social spiders, the researchers advanced knowledge of study methods in this field.
Methylation varies and can occur in different contexts depending on the sequence of the DNA building blocks to which the methyl group is attached. These contexts are named CpG, CHG and CHH, and the results indicate that the changes that the researchers identified occurred in the CHG contexts.
This might indicate that further research should focus in this direction. This also applies to understanding the immune response in social spiders and in other animals.
“Researchers have generally investigated the significance of methylation in CpG more than the other contexts, but we suggest that paying more attention to CHG contexts might make sense. This applies to social spiders but also to livestock typically living in large groups of closely related animals. They experience the same challenges as the spiders, and identifying how spiders have solved this problem may show how livestock solve this problem too,” concludes David Fisher.
