Abstract
Chimerism occurs when two genetically distinct conspecific individuals fuse together generating a single entity. Coalescence and chimerism in red seaweeds has been positively related to an increase in body size, and the consequent reduction in susceptibility to mortality factors, thus increasing survival, reproductive potential and tolerance to stress in contrast to genetically homogeneous organisms. In addition, they showed that a particular pattern of post-fusion growth maintains higher genetic diversity and chimerism in the holdfast but homogenous axes. In Chilean kelps (brown seaweeds), intraorganismal genetic heterogeneity (IGH) and holdfast coalescence has been described in previous research, but the extent of chimerism in wild populations and the patterns of distribution of the genetically heterogeneous thallus zone have scarcely been studied. Since kelps are under continuous harvesting, with enormous social, ecological and economic importance, natural chimerism can be considered a priceless in-situ reservoir of natural genetic resources and variability. In this study, we therefore examined the frequency of IGH and chimerism in three harvested populations of Lessonia spicata. We then evaluated whether chimeric wild-type holdfasts show higher genetic diversity than erect axes (stipe and lamina) and explored the impact of this on the traditional estimation of genetic diversity at the population level. We found a high frequency of IGH (60–100%) and chimerism (33.3–86.7%), varying according to the studied population. We evidenced that chimerism occurs mostly in holdfasts, exhibiting heterogeneous tissues, whereas stipes and lamina were more homogeneous, generating a vertical gradient of allele and genotype abundance as well as divergence, constituting the first time “within- plant” genetic patterns have been reported in kelps. This is very different from the chimeric patterns described in land plants and animals. Finally, we evidenced that IGH affected genetic differentiation among populations, showed lower levels of FST index when we compared holdfast than lamina samples. In the light of this, future studies should evaluate the significance of chimeric holdfasts in their ability to increase kelps resilience, improve restoration and ecosystem service.
Highlights
Genetic diversity is important for population viability and survival [1, 2, 3, 4]
Intraorganismal genetic heterogeneity involves the existence of different genomes within a single body [10], changing the traditional notion of individuals characterized by physiological unity, genetic homogeneity, and uniqueness [11]
We focus on chimerism and its frequency in wild populations of the kelp Lessonia spicata
Summary
Genetic diversity is important for population viability and survival [1, 2, 3, 4]. Greater diversity increases population’s ability to adapt and evolve in changing conditions [5, 6, 7]. Studies on genetic diversity include the individual, population and regional levels [8], but often the effect of intraorganismal genetic heterogeneity on individual fitness and the capacity to evolve [9] is not considered. Chimerism occurs when two genetically distinct conspecific individuals fuse together or coalesce, generating a single entity [12] It occurs in a specific group of organisms including fungi, slime molds [13], grafting plants [14], colonial invertebrates (sponges, hydroids, corals, bryozoans and ascidians [15, 16, 17, 18, 19]), humans, other mammals [15] and macroalgae [12]
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