V. M. Zakharov’s research while affiliated with Koltzov Institute of Developmental Biology and other places

The stability of biological systems ensures their viability under the influence of environmental factors. The homeostatic mechanisms of the body ensure the stability of the process of individual development (developmental homeostasis, or homeoresis). The stability of biosystems of a higher rank is determined by the diversity and stability of the constituent elements. New opportunities for the implementation of homeostatic mechanisms appear at the level of society.

We examine temporal variation in a measure of developmental stability, the degree of fluctuating asymmetry of the characters of skull morphology, of the common shrew (Sorex araneus L., 1758) in Central Siberia. Four-year cycles in this population in the last century were accompanied by significant changes in the level of developmental stability. Population fluctuations under the climate change conditions in this century commonly occur without essential changes in developmental stability. Deterioration of developmental stability takes place occasionally in case of adverse overpopulation impact in the year of peak population abundance that is beyond the certain threshold level increased due to the climate change.

Variation of the meristic characteristics of pholidosis in the sand lizard, Lacerta agilis, was studied both in laboratory experiments and in natural populations. The total phenotypic variability was assessed by the variation of the sum of the number of scales on the left and on the right sides of the body (l + r), while the measure of developmental stability, providing insight into the degree of fluctuating asymmetry, or developmental variability, was assessed by the variation of the difference in the character values on the left and on the right (l − r). Experimental incubation of eggs at different temperatures demonstrates that the minimal level of both kinds of variability corresponds to a certain temperature, which can be characterized as an optimal one, increasing both with an increase and with a decrease in the temperature from this regime. The data demonstrate the crucial role of the temperature impact for the phenotypic variation under study. An increase in the level of developmental variability to the north and to the south from the center part of the species range, in the absence of an obvious trend in geographic variation of the level of total phenotypic variability, assumes an increase in the role of developmental variability in the observed phenotypic diversity at the periphery of the species range. The results obtained indicate the importance of a population phenogenetic approach, based on the developmental stability study in natural populations, to provide certain information supposing the possible nature of phenotypic diversity in a species range.

Developmental noise is a variety that is not related to the usually distinguished sources of phenotypic diversity, i.e., differences in the genotype and in the environment. This variation arises in the process of the realization of genetic information and reflects the imperfection of ontogenetic processes. The most common measure of it is the value of fluctuating asymmetry as slight deviations from the symmetry. Developmental noise proves to be one of the main sources of intrapopulation phenotypic diversity. The magnitude of this variability is an ontogenetic response to environmental or genetic stress, and its assessment, in fact, provides a unique opportunity to estimate the developing system condition. The level of developmental noise, characterizing an organism’s condition, acts as another population parameter that allows to approach the evaluation of the community condition. Initial deviations in the system condition can be detected even against the background of optimal estimates of abundance, biodiversity, and ecosystem functioning.

Fluctuating asymmetry as a special kind of asymmetry can be defined as deviations from a known predetermined ratio of the parts of morphological structure under study. As a special type of phenotypic variability fluctuating asymmetry is a manifestation of ontogenetic noise or developmental variability. This type of variability is ubiquitous and plays a significant role in the observed phenotypic diversity. The level of fluctuating asymmetry turns out to be an indicator of optimal developmental conditions and genetic coadaptation. It is also considered as a parameter of fitness. Thus, fluctuating asymmetry acts as a measure of developmental stability in developmental biology and as a measure of population condition in population biology.

We examine possible temporal variation in a measure of developmental stability, providing insight into the degree of fluctuating asymmetry of several characters of skull morphology, of the common shrew, Sorex araneus L., 1758, in Central Siberia. The level of fluctuating asymmetry during the study period in the beginning of this century (2002–2013) is not correlated with population abundance, while at the end of the last century it was correlated with population abundance, suggesting that high density was the important negative factor affecting breeding females. The absence of an adverse effect of high abundance on developmental stability in the current situation can be related to both an impact of oscillations in environmental conditions and an increase in habitat carrying capacity due to the climate change. Positive correlation of population abundance with the number of adults born last summer and young specimens born this summer indicates the influence of winter and summer conditions on population size. If in the last century developmental stability was correlated with breeding success, indicating that both parameters were affected by the physiological condition of breeding females, in this century these two parameters vary independently, suggesting that breeding success may be affected by other population and habitat factors. Thus, the situation in the population under study is more similar to the noncyclic dynamics than to the four-year cycles, which were revealed for the population in the last century. The results indicate an importance of monitoring possible changes in developmental stability measure, as another population parameter, under climate change.

Developmental noise—which level may vary within a certain backlash allowed by natural selection—is a reflection of the state of a developing system or developmental stability. Phenotypic variations inside the genetically determined norm observed in case of fluctuating asymmetry provide a unique opportunity for evaluating this form of ontogenetic variability. Low levels of developmental noise for the biologic system under study is observed under certain conditions, while its increase acts as a measure of stress. The concordance of changes in developmental stability with changes in other parameters of developmental homeostasis indicates the significance of fluctuating asymmetry estimates. All this determines the future prospects of the study of fluctuating asymmetry not only for developmental biology, but also for population biology. The study of developmental stability may act as the basis of an approach of population developmental biology to assess the nature of the phenotypic diversity and the state of natural populations under various impacts and during evolutionary transformations.