Accelerated rate of development can cause fatal consequences

Accelerating the pace of development is generally seen as an advantage. However, a new study conducted at the University of Haifa and the University of California on salamanders found that speeding up the rate increases mortality. Research leader Assaf Sade: The results are also relevant to humans

Accelerating the rate of development in animals, which is usually seen as an advantage, entails physiological costs that may even be fatal, according to a new study conducted at the University of Haifa in collaboration with the University of California, Santa Cruz and published in an article in the scientific journal, PLoS ONE. "The findings of our study, which was conducted on salamanders, and are consistent with the findings of similar studies on other animals, turn the spotlight on research on the acceleration of development rates in humans as well," said Assaf Sade, the leader of the study.

The current study, which is part of Sade's doctoral thesis in the ecology laboratory of Prof. Leon Blaustein from the University of Haifa, was conducted as mentioned on the common salamander. Partners in the study were Noa Troskanov from the University of Haifa and Mark Mengel from the University of California. The common salamander breeds in seasonal ponds that fill during the winter rains and usually dry up during the spring, so the salamander tadpoles must complete their development for terrestrial life before the pond dries up, where failure to meet the schedule means certain death.

In the first part of the study, the researchers wanted to check whether the salamander tadpoles have an early warning mechanism that instructs them to speed up their rate of development to avoid dehydration if necessary. Their hypothesis focused on the remains of tadpoles that had died following previous desiccation. To test the hypothesis, an experimental group of salamander tadpoles was placed in a pond sprinkled with a minimal dose of powder produced from the remains of tadpoles that died in natural ponds due to dehydration, compared to a control group that was not exposed to this powder. It turns out that the tadpoles are able to sense, immediately after they spawn in the pond, the dried remains. These tadpoles significantly accelerated their rate of development compared to the control group. The researchers hypothesize that the tissues of the desiccated tadpoles change their chemical composition as they dry in the sun, a process that creates a unique "death smell" that is released into the water when the pond is flooded again. This "smell of death" provides information to the tadpoles that are subsequently spawned about the pond's inability to hold water for a long time and thus they know that in this pond they should set a rapid developmental rate in order to avoid a similar fate.

In the second part of the study, the researchers changed the water levels for the two groups of tadpoles so as to simulate actual conditions of dehydration or non-dehydration. It was found that after a while the tadpoles know how to correct the initial development rates according to the actual changes in the water level in the pond.

However, it turns out that rapid development has a price: the main findings show that tadpoles that responded with rapid development suffered increased mortality, most likely as a result of a physiological cost associated with the rapid rate of development. A particularly high mortality occurred among tadpoles that did not receive advance warning from the "smell of death" and had to speed up their development radically in response to changes in the water level. According to the researchers, the physiological mechanisms underlying these prices are not yet known, but they hypothesize that they include factors at the cellular level such as oxidative damage as a result of an increased metabolic rate, as well as factors at the tissue level such as the overuse of stem cells or the violation of the balance between the differentiation and growth processes of different tissues in the body.

They also added that these results are in line with the results of other studies recently carried out on the cost of accelerating growth after a period of starvation in insects, fish, amphibians and mammals. Following the similar findings among different types of animals, the researchers say that it is very important to study accelerated development in humans, such as motor, immune, sexual and cognitive development. "The research may be significant for our perceptions regarding the optimal development of the child. Although stimulating a certain aspect of the child's development allows him to deal better with the environment, it is necessary to check whether it might come at the expense of another developmental aspect, and cause the child difficulties in dealing with other environmental challenges," said the researchers, who emphasized that research in this field is still in its infancy , and further work is required before practical conclusions can be drawn about human development.