A predictive adaptive response (PAR) is a developmental trajectory taken by an

organism In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multicellular o ...

during a period of developmental

plasticity Plasticity may refer to: Science * Plasticity (physics), in engineering and physics, the propensity of a solid material to undergo permanent deformation under load * Neuroplasticity, in neuroscience, how entire brain structures, and the brain it ...

in response to perceived

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

al cues. This PAR does not confer an immediate advantage to the developing organism; however, if the PAR correctly anticipates the

postnatal The postpartum (or postnatal) period begins after childbirth and is typically considered to end within 6 weeks as the mother's body, including hormone levels and uterus size, returns to a non-pregnant state. The terms puerperium, puerperal perio ...

environment it will be advantageous in later life, if the environment the organism is born into differs from that anticipated by the PAR it will result in a mismatch. PAR mechanisms were first recognized in research done on human fetuses that investigated whether poor nutrition results in the inevitable diagnosis of Type 2 diabetes in later life. PARs are thought to occur through

epigenetic mechanisms In biology, epigenetics is the study of stable phenotypic changes (known as ''marks'') that do not involve alterations in the DNA sequence. The Greek prefix '' epi-'' ( "over, outside of, around") in ''epigenetics'' implies features that are "o ...

that alter gene expression, such as

DNA methylation DNA methylation is a biological process by which methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene promoter, DNA methylation typically acts ...

and

histone modification In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei. They act as spools around which DNA winds to create structural units called nucleosomes. Nucleosomes in turn are w ...

, and do not involve changes to the DNA sequence of the developing organism. Examples of PARs include greater helmet development in Daphnia cucullata in response to maternal exposure to predator pheromones, rats exposed to

glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every verte ...

during late gestation led to an intolerance to

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usi ...

as adults, and coat thickness determination in vole pups by the

photoperiod Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...

length experienced by the mother. Two hypotheses to explain PAR are the "

thrifty phenotype Thrifty phenotype refers to the correlation between low birth weight of neonates and the increased risk of developing metabolic syndromes later in life, including type 2 diabetes and cardiovascular diseases. Although early life undernutrition is th ...

" hypothesis and the

developmental plasticity Developmental plasticity is a general term referring to changes in neural connections during development as a result of environmental interactions as well as neural changes induced by learning. Much like neuroplasticity or brain plasticity, develo ...

hypothesis.

The thrifty phenotype hypothesis

The

hypothesis is the idea that if an organism suffers from inadequate nutrition in fetal development it will subsequently be predisposed to certain genetic outcomes as an adult. A study done examining glucose tolerance of individuals born during a famine in the Netherlands in 1944-1945 favors the “thrifty phenotype” hypothesis. The results of the experiment showed that exposure to famine, particularly in late gestation, led to a decrease in the glucose tolerance of the adults. Other studies on humans have shown cardiovascular and diabetes mortality has been shown to correspond to the nutrition uptake of the parents and grandparents of an offspring during their years before puberty, hypertension in both sexes is the highest in individuals that had been small babies with large placentas, and larger female babies have decreased ovarian suppression compared to smaller babies after intermediate levels of activity in adulthood. All these studies support the thrifty phenotype hypothesis because the prenatal environment determined the phenotype that would be expressed later in life.

The developmental plasticity hypothesis

Another proposed hypothesis for the presence of PARs is the

hypothesis. A longitudinal study performed in Helsinki, Finland investigated whether catch-up growth of smaller children increased the risk of coronary heart disease later in life. The results of this study coincide with the developmental plasticity hypothesis because as the nutrition of the small participants improved after birth, these undernourished small individuals grew at a quicker rate and had an increased chance of coronary heart disease. Another study further confirms the longitudinal study performed in Finland by showing that low weight children develop visceral fat during the catch-up growth period which can potentially result in diabetes later in life. Infants that have a low birth weight have been shown to have a reduction in functioning cells, which would instantly have a negative effect on their adult life. Additionally, a study testing drastic changes in childhood body-mass index showed that after two years of age, thin infants who have a comparatively large body-mass index from their birth weight are associated with disorders such as diabetes. The developmental plasticity hypothesis is apparent in each of these findings because the post birth development determines the health of the individual during adulthood.

Potential future impacts

Continued research into predictive adaptive responses has the potential to gain crucial insight into the reasons diseases such as diabetes are so widespread.

References

{{Reflist Evolutionary biology terminology