Exposing dwarf spiders to temperatures of 27–28 degrees Celsius did not change the sex of the individuals exposed to the heat, but their offspring and grandchildren appeared male again. The researchers found that the heat disrupted the balance of bacteria in the spider's body and impaired the ability of the Wolbachia bacterium to cause female development
A short period of high temperatures can affect the reproduction of Spiders Even two generations after the heat has passed. This is according to a study conducted by researchers fromThe Hebrew University and from the Universities of Kentucky and Illinois in the United States and was published in the journal Molecular Ecology.
The researchers examined a dwarf spider of the species Mermessus fradeorum, which carries up to five types of Bacteria which are passed from the mother to her offspring. One of them is a strain of Wolbachia, a bacterium capable of altering the sexual development of its host: genetically males develop as females.
For Wolbachia, this is an evolutionary advantage. Since the bacterium is transmitted mainly through eggs, increasing the number of females helps it spread through the population. However, in nature, Wolbachia does not completely take over spider populations, and the researchers wanted to find out what limits it.
The team, led by Prof. Yuval Gottlieb-Dror and doctoral student Virginia Mackievicius-Dubitzkaya from the Kurt School of Veterinary Medicine at the Hebrew University, exposed young spiders for one generation to temperatures of 27–28 degrees Celsius – conditions that simulate daytime ground surface temperatures in a hot summer.
The spiders that were directly exposed to heat developed into females as expected. The surprise came after they were returned to cooler conditions, at a temperature of 20 degrees: In their children and grandchildren, who were not exposed to heat themselves, the feminization process was impaired and males began to appear again.
Bacterial tests showed that exposure to heat changed the microscopic ecosystem inside the spiders. Initially, the number of Wolbachia increased, but its ability to successfully pass on to the next generation was impaired. At the same time, another bacterium, called Tisiphia, disappeared from the lineage.
In the next generation, there was an increase in the relative abundance of the bacterium Rickettsiella. The higher its proportion, the weaker the feminization. The researchers estimate that Rickettsiella competes with Wolbachia or suppresses its activity, so the mere presence of Wolbachia is not enough: to change the development of the spider, it must be dominant in the bacterial community.
“A short period of high temperatures disrupts the delicate competitive balance between symbionts,” the researchers explained. According to them, the environmental history of the animal can determine the stability of its bacterial community and the traits it generates.
The study also found that spiders carrying several strains of Wolbachia were more resistant to change. They maintained a more stable bacterial balance and the mating ratio returned to being more female-biased more quickly. It is possible, therefore, that the multiplicity of strains provides the bacterial system with stability in the face of heat stress.
The results do not prove that every heat wave will change the ratio of males to females in nature. However, they do show that a short heat event may leave an intergenerational imprint by changing the relationships between microorganisms living inside the animal. Given the increasing frequency of extreme heat events, such a mechanism may be important for understanding the effects of climate change on populations. Arthropods.
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