2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Stress during pregnancy in mammals can harm offspring, in particular, inhibiting its growth. However, in some cases, the growth of offspring even outstrips the growth of the control group - it all depends on at what point in pregnancy the mother experienced stress. This was discovered by German researchers, whose work is published in the journal Proceedings of the National Academy of Sciences.
In mammals, maternal prenatal stress affects the development of the offspring, and, in particular, its growth, but this effect is ambiguous even within the species: some researchers report a slowdown in growth, others - an accelerated growth. Scientists debate whether prenatal stress is an inevitable obstacle to the development of a young individual, or whether there is room for adaptive change. Scientists who view prenatal stress as an obstacle report low growth rates, short life cycles, and reduced reproductive success. Their small body size negatively affects the next generation. Proponents of the theory of adaptive changes, in contrast to the former, expect higher growth rates and other phenotypic changes, for example, reproduction at an earlier age, in response to prenatal stress, and support their opinion with the corresponding results. Andreas Berghänela from the University of New Mexico, along with his German colleagues, undertook to collect all this data and try to explain them. They suggested that offspring growth slows down due to a decrease in the "return" to the mother during pregnancy and lactation, and then adaptive growth variability takes effect, and the relative importance of these two processes changes as the individual matures.
To test this hypothesis, the researchers collected data from 719 studies from 388 scientific publications involving 21 mammals. They classified prenatal maternal stress into "early" and "late", where early was at the beginning of pregnancy, and late at its later stages. In all studies, there was a control group in which the pregnant female did not experience stress. Scientists also took into account the type of stimulus, in particular, they studied cases in which maternal stress was provoked not by external stimuli, such as lack of food or the presence of predators, but by an artificial change in the level of glucocorticoids, which help the body fight stress. They set controls for other potentially significant factors, such as the length of the stress period and the sex of the offspring. The dependent variable was the proportion of jobs with the corresponding result.
Growth rates of offspring (orange - enhanced growth, gray - comparable to the control group, blue - slower growth). The graphs on the left correspond to the data of the group in which the mother experienced stress in the early stages of pregnancy, the graphs in the middle correspond to the groups with stress in the late stages of pregnancy. On the x-axis, data are grouped by growth rate at different stages of offspring development (during pregnancy, during breastfeeding, and after breastfeeding). The graphs on the right summarize the results for the “early” and “late” groups. The y-axis indicates the percentage of jobs reporting related results. The total number of studies (N) is indicated by the numbers above each bar.
They studied how the growth rate of offspring changed depending on the stage of their development, and found differences: the more independent the individual became from the mother, the less restrained their growth was. After the end of the breastfeeding period, the growth rate of individuals accelerated, and the proportion of studies that reported negative effects of prenatal stress decreased. The relative growth rates of offspring were found to be higher in the group with early prenatal maternal stress compared with late maternal stress. Moreover, individuals who experienced prenatal stress in the early stages were characterized by high growth rates subsequently at all stages of maturation as compared to the control group.
In cases where stress was triggered by a lack of food resources, the growth suppression effect was exacerbated, but the detected pattern persisted even when stress was triggered by a change in glucocordicoid levels.
Growth rates after the end of the breastfeeding period were positively correlated with individual size at that time (P <0.001), and with size at birth (P <0.001).
Overall, the results support both theories and explain where offspring growth is accelerated. It turns out that the stress in the early stages leaves room for the subsequent acceleration of growth as the suppression effect weakens with increasing independence of the offspring from the mother. Prenatal stress changes the trajectory of offspring development, allowing you to smooth out, level, and even compensate for the effect of growth suppression. Nevertheless, this mechanism can hardly be called compensatory, since it is directly less pronounced among individuals with small body sizes. The main limitation of the new study, which is also mentioned by its authors, is that the proportion of studies acts as an independent variable, and not quantitative indicators of growth, therefore, many possible subtleties of the phenomenon were not taken into account in it.
We have previously written about how a lack of food in fathers affects the development of their offspring, and how a mother's diet affects their taste preferences and growth rates. Weight loss has a number of consequences and has recently been linked to early menopause in women.