Segregate or cooperate- a study of the interaction between two species of Dictyostelium

Abstract

<p>Abstract</p> <p>Background</p> <p>A major challenge for evolutionary biology is explaining altruism, particularly when it involves death of one party and occurs across species. Chimeric fruiting bodies of <it>Dictyostelium discoideum </it>and <it>Dictyostelium purpureum </it>develop from formerly independent amoebae, and some die to help others. Here we examine co-aggregation between <it>D. discoideum </it>and <it>D. purpureum</it>, determine its frequency and which party benefits, and the extent of fair play in contribution to the altruistic caste.</p> <p>Results</p> <p>We mixed cells from both species in equal proportions, and then we analyzed 198 individual fruiting bodies, which always had either a <it>D. discoideum </it>or <it>D. purpureum </it>phenotype (<it>D. discoideum</it>- 98, <it>D. purpureum</it>- 100). Fifty percent of the fruiting bodies that looked like <it>D. discoideum </it>and 22% of the fruiting bodies that looked like <it>D. purpureum </it>were chimeric, though the majority of spores in any given fruiting body belonged to one species (<it>D. discoideum </it>fruiting bodies- 0.85 ± 0.03, <it>D. purpureum </it>fruiting bodies- 0.94 ± 0.02). Clearly, there is species level recognition occurring that keeps the cells mostly separate. The number of fruiting bodies produced with the <it>D. discoideum </it>phenotype increased from 225 ± 32 fruiting bodies when <it>D. discoideum </it>was alone to 486 ± 61 in the mix treatments. However, the number of <it>D. discoideum </it>spores decreased, although not significantly, from 2.75e⁷± 1.29e⁷spores in the controls to 2.06e⁷± 8.33e⁶spores in the mix treatments. <it>D. purpureum </it>fruiting body and spore production decreased from 719 ± 111 fruiting bodies and 5.81e⁷± 1.26e⁷spores in the controls to 394 ± 111 fruiting bodies and 9.75e⁶± 2.25e⁶spores in the mix treatments.</p> <p>Conclusion</p> <p>Both species appear to favor clonality but can cooperate with each other to produce fruiting bodies. Cooperating amoebae are able to make larger fruiting bodies, which are advantageous for migration and dispersal, but both species here suffer a cost in producing fewer spores per fruiting body.</p