At present, only some of the factors that regulate the differentiation, expansion and contraction of populations of activated B and T cells are known, and the picture of the dynamics of their proliferation and death is incomplete [1], [2], [4] [10].
The concordant patterns of spatial and demographic expansions detected within phylogroups, together with the high incidence of ancestral haplotypes in southern regions of several phylogroups, suggests a pattern of contraction of populations into southern refugia during adverse climatic conditions from which subsequent northern expansions occurred.
These past climatic changes in the region have generally caused shifts in elevation, expansions, and contractions of populations in numerous species [ 28– 328.
The contraction of rural populations has led to an increase in the number of practicing physicians per population, despite the decrease of the latter in STMs with a small number of inhabitants (less than 200,000).
Then, subsequent aridification of the Sahara led to a contraction of Saharan populations into a few refugia, particularly in mountain areas (e.g. helenae), that behave as relic populations (Fig. 1a).
In addition, the results suggest that virulence (or attenuation) mechanisms may not be shared among all populations of parasites at the gene level, but instead may reflect expansion or contraction of the population structure in response to shifting milieus.
The contraction of the population pyramid will become more apparent not only in relative but also in absolute terms: the inertia of the fast increase in the past will become manifest, first in the total number of people in productive age 15-599 years old) and later in the number of people in old age (60 years and over).
They contribute to a better understanding of the processes involved in the development of contemporary patterns of variation, including the regional contraction and expansion of populations and refugia (Nevill et al. [2014]).
Our data suggest that marine transgression-regression cycles (eustatic changes) may have induced the repeated range expansion, contraction and fragmentation of populations of M. longipes, which appears currently split into several isolated and genetically divergent lineages adapted to a broad spectrum of salinity conditions.
For example, the association strength of a SNP might differ in different populations due to genetic drift, growth, or contraction of the two populations.
