It has recently come to general attention that transposable elements (TE) may have a significant influence on speciation and evolution of species. Thus understanding of transposon behavior and evolution seems crucial to deepening our knowledge on evolution of species.

The problem of transposon proliferation has been extensively studied from a theoretical point of view, and many models of this process have already been proposed. Most of such preexisting models are based on the concept of transposition-selection equilibrium (TSE) that is, the transposon counts within modeled populations are controlled by the struggle between transposons' selsh drive to duplicate regardless of the effect on their host, and the evolutionary drive to eliminate hosts with high transposon counts (which create a genetic burden resulting in lower viability of host organisms).

In TSE models, the transposons are in a state of equilibrium, while in nature they usually proliferate in short, intense bursts interspersed with long periods of relative calm. The burst periods are often related to a period of intense environmental stress, such as might be experienced when the species is colonizing a new ecological niche, or undergoing domestication by humans.

In most existing models of TE dynamics, the environment was considered constant. However, results of several experimental studies suggested that it should be viewed as one of the major factors when modeling the behavior of TEs in host genomes. In our approach, we analyze through stochastic simulations a model of TE dynamics that accounts for environmental pressure on host populations, i.e. the mutagenic activity  of TEs, under the assumption of constant environmental conditions, is detrimental to host organisms.
However, in a changing environment it may become beneficial because it allows the host population to adapt to the environment more efficiently. At the same time, stress lessens  the usual negative effect of  high mutability induced by heightened TE activity.

Our preliminary, computational, stochastic model dealt away with the concept of TSE, and instead it tracked the organisms' phenotypes (which were modified by transposition-induced mutations). The model was implemented for organisms undergoing asexual propagation. Here, we attempt to apply the same basic concept to investigate TE dynamics in sexually reproducing organisms.

Namely, we assume that each organism contains two, independent lists of transposons (two pairs of homologous chromosomes). In the course of reproduction it produces gametes containing a set of randomly chosen transposons from its genome, represented by the mentioned lists. Moreover, each transposon carries a unique value describing its contribution to the modification of the host phenotype. Finally, throughout the simulation we apply environmental stress, e.g. meteor impact or global warming scenarios as we did in the basic model. Under these new conditions we try to answer the question: What is the impact of sexual reproduction on proliferation of transposable elements as evolutionary helpers?

population biology, mobile genetic elements, transposon activity, environmental stress, sexual model, simulations