Migration and thermotaxis of Dictyostelium discoideum slugs, a model study

Dictyostelium discoideum slugs show a pronounced thermotaxis. We have model led the motion of the D. discoideum slug in the absence and in the presence of a thermal gradient. Our model is an extension of the hybrid cellular au tomata/partial differential equation model, as formulated by Savill and Hog eweg [J. theor. Biol., (1997) 184, 229-235]. The modelled slugs maintain th eir shape and crawl, with a velocity depending on slug size, as found in ex periments. Moreover, they show thermotactic behaviour: independent of the i nitial orientation, after some transient process, the slugs start moving al ong the temperature gradient. The slug behaviour in our model is due to the collective behaviour of the amoebae. Individual amoebae can neither respon d to a shallow temperature gradient, nor show differentiation in motion vel ocity. The behaviour is achieved by a modification of the cyclic AMP waves: differences in temperature alter the excitability of the cell, and thereby the shape of the cyclic AMP wave. Chemotaxis towards cyclic AMP causes the slug to turn. We show that the mechanism still functions at very low signa l-to-noise ratios. (C) 1999 Academic Press.