Population Dynamics of Transposable Elements: Copy Number Regulation and Species Invasion Requirements

Claudio J. Struchiner
FIOCRUZ
Rio de Janeiro

José M.C. Ribeiro
Laboratory of Parasitic Diseases
National Institutes of Health
Bethesda, MD 20892

Margaret G. Kidwell
Department of Ecology and Evolutionary Biology
The University of Arizona
Tucson, AZ 85721

A population dynamics model of the spread of transposable elements in sexually reproducing populations is presented. The population is modeled by a 3 parameter equation describing host reproductive capacity, population size and the strength of the density dependence, while transposable element dynamics were modeled based on the maximum ability of the element to copy itself in the absence of regulation (), the regulatory effect of copy number decreasing transposition (), and the deleterious effect of each new transposition on host fitness (). The model is general because no assumptions about the mechanism of transposition control are made, except that this is some function of copy number. Results indicate that non-regulated elements cannot fix in host populations, and that prediction of stable copy number following successful invasion is mainly a function of the combination of and values. Fitness reduction does not affect the final copy number after successful invasion of the element. Fitness reduction, however, will affect the surface of the Å~ parameter space leading to successful invasion of the transposable element. Invasion of host populations by eight or more individuals containing elements with appropriate parameters will lead to successful element fixation at any size of the host population. A small area of the Å~ parameter space indicates the possibility of host population extinction due to the invasion of transposable elements. The results are insensitive to host population dynamics parameters, and the shape of the functions defining regulation of transposition.