|InterJournal Complex Systems, 345
|Manuscript Number: |
Submission Date: 417
|Self-organization of population substructure in biological systems|
Subject(s): CX.35, BG.24
Conventional wisdom in the field of population genetics suggests that discrete boundaries between distinctive, geographically adjacent biological populations must reflect the influence of external factors, such as differential selection or a barrier to dispersal. However, the ubiquitous factor of isolation by distance provides systemic viscosity and time lags of effects across a species range such that the system resembles those known to self-organize. Unfortunately, incorporation of isolation by distance into analytical models has proven elusive, and computing power has only recently achieved the level required to create large-scale simulations of populations with limited dispersal distances. I present results from such a computer simulation demonstrating that biological populations can self-organize into geographically identifiable subpopulations when viscosity is high relative to the scale of the system, without differences in selection regime or barriers to dispersal. When viscosity is not great enough relative to the scale of the system, no self-organization occurs. However, a threshold is reached when viscosity is increased where the system bifurcates into two subpopulations. This is biologically surprising, because dispersal across the boundary occurs with equal likelihood as dispersal within the bounds of a subpopulation. The locations of boundaries between adjacent subpopulations are arbitrary and the boundaries move across the landscape over time. Lineage sorting (i.e. the extinction and proliferation of alternative allelic lineages) is efficient within subpopulations, so little variation is found within them at any point in time. However, lineage sorting is inefficient among subpopulations so that the lineages occupying different subpopulations can be highly divergent. This observation provides another link to the behavior of other self-organizing systems, because the formation of population substructure greatly facilitates the dissipation of excess variation (generated by the constant input of mutation). This model suggests a new null hypothesis that can explain the occurrence of boundaries among subpopulations, and the observation of highly divergent alleles without intermediate forms, in natural populations.
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