Abstract
Heterozygosity has been positively associated with fitness and population survival. However, the relationship between heterozygosity and adaptive phenotypic plasticity (i.e., plasticity which results in fitness homeostasis or improvement in changing environments) is unclear and has been poorly explored in seaweeds. In this study, we explored this relationship in the clonal red seaweed, Gracilaria chilensis by conducting three growth rate plasticity experiments under contrasting salinity conditions and by measuring heterozygosity with five microsatellite DNA markers. Firstly, we compared growth rate plasticity between the haploid and diploid phases. Secondly, we compared growth rate plasticity between diploids with different numbers of heterozygous loci. Finally, we compared growth rate plasticity between diploid plants from two populations that are expected to exhibit significant differences in heterozygosity. We found that, (i) diploids displayed a higher growth rate and lower growth rate plasticity than haploids, (ii) diploids with a higher number of heterozygous loci displayed lower growth rate plasticity than those exhibiting less heterozygosity, and (iii) diploid sporophytes from the population with higher heterozygosity displayed lower growth rate plasticity than those with lower heterozygosity. Accordingly, this study suggests that heterozygosity is inversely related to growth rate plasticity in G. chilensis. However, better genetic tools in seaweeds are required for a more definitive conclusion on the relationship between heterozygosity and phenotypic plasticity.
Highlights
Genetic diversity is usually considered necessary for population survival and adaptability in changing environments (Booy, Hendriks, Smulders, Van Groenendael, & Vosman, 2000)
Diploid organisms could potentially show some degree of heterozygosity, which is expected to increase with greater levels of ploidy (Leary, Allendorf, Knudsen, & Thorgaard, 1985)
The genetic characterization confirmed the samples ploidy, with hemizygous gametophytes of G. chilensis and with diploid sporophytes displaying a similar level of heterozygosity than what had previously been reported in the sampled population (Maullín; Guillemin et al, 2008)
Summary
Genetic diversity is usually considered necessary for population survival and adaptability in changing environments (Booy, Hendriks, Smulders, Van Groenendael, & Vosman, 2000). Diploid organisms could potentially show some degree of heterozygosity (and usually do), which is expected to increase with greater levels of ploidy (Leary, Allendorf, Knudsen, & Thorgaard, 1985) In this context, several authors have suggested that the positive correlation sometimes found between ploidy and growth rate (e.g., Guillemin, Sepúlveda, Correa, & Destombe, 2013; Mendoza & Haynes, 1974; Petit et al 1996), and between ploidy and stress resistance (Van Laere et al, 2011) is related to heterosis. Considering the perceived importance of heterozygosity to organism performance, we explored the relationship between heterozygosity—using five microsatellite DNA markers—and growth rate plasticity in the clonal red seaweed, G. chilensis, cultured under different salinity conditions. To this end, the ideal would be to construct strictly heterozygous and homozygous strains in the laboratory and compare their response. The results are discussed in terms of the controversial relationship between heterozygosity and phenotypic plasticity and their conjunct potential role in population survival under changing environments
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