Coalescence increases abiotic stress tolerance in sporelings of Mazzaella laminarioides (Gigartinales, Rhodophyta)

Abstract

Chimerism theoretically increases the genetic heterogeneity of coalescing organisms, which in turn may increase phenotypic variability in chimeras, allowing them greater tolerance to environmental changes when compared with non-coalescing individuals. In order to test this hypothesis, we compared abiotic stress tolerance between coalescing and non-coalescing organisms. The specific daily growth was compared using discs formed with 1, 5, and 20 Mazzaella laminarioides carpospores. These were cultivated under three different temperature (6, 12, and 25 degrees C) and salinity (10, 35, and 50 g L-1) conditions. Growth of the disc area was measured after 30 days of cultivation under controlled conditions. Sporeling survival similarly was calculated under each of these temperatures and salinities in order to record whether stress-resistant phenotypes were present. The results showed that, under stressful conditions, non-coalescing specimens experienced a significant reduction in the specific growth rate compared with those under non-stressful conditions. The reduction in growth falls off, however, as the number of coalescing spores increases. The cultivation of spore populations also indicates the presence of sporelings with the capacity to survive alone in stressful situations. The results suggest that the coalescing discs exhibit higher tolerance to environmental stressors than non-coalescing discs, allowing them to survive and grow under these conditions. This can be explained by an increase in phenotypic plasticity, resulting from greater genetic heterogeneity due to somatic fusion of a larger number of spores.