Genetic Relatedness Influences Plant Biomass Accumulation in Eelgrass (Zostera marina)

Abstract

In multispecies assemblages, phylogenetic relatedness often predicts total community biomass. In assemblages dominated by a single species, increasing the number of genotypes increases total production, but the role of genetic relatedness is unknown. We used data from three published experiments and a field survey of eelgrass (Zostera marina), a habitat-forming marine angiosperm, to examine the strength and direction of the relationship between genetic relatedness and plant biomass. The genetic relatedness of an assemblage strongly predicted its biomass, more so than the number of genotypes. However, contrary to the pattern observed in multispecies assemblages, maximum biomass occurred in assemblages of more closely related individuals. The mechanisms underlying this pattern remain unclear; however, our data support a role for both trait differentiation and cooperation among kin. Many habitat-forming species interact intensely with conspecifics of varying relatedness; thus, genetic relatedness could influence the functioning of ecosystems dominated by such species.

Genetic distance predicts trait differentiation at the subpopulation but not the individual level in eelgrass,Zostera marina

“…Trait differences within and among species can influence ecological processes at multiple levels, from populations to ecosystems (e.g., Bolnick et al., 2011; Hector et al., 1999; Macarthur & Levins, 1967; Stachowicz, Kamel, Hughes & Grosberg, 2013; Wojdak & Mittelbach, 2007). However, identifying the traits that matter to ecological processes a priori is often challenging and context‐dependent (Naeem & Wright, 2003).…”

“…Furthermore, measuring continuous trait variation among individuals within a species requires extensive effort and may not be practical for assemblages with a large number of taxa. Both of these challenges raise the question of whether measures of genetic distance can be used as proxies for functional divergence, based on the assumption that phylogenies, genealogies, or estimates of relatedness can reflect integrated phenotypic differences among taxa or individuals (Cadotte, Cardinale & Oakley, 2008; Felsenstein, 1985; Harvey & Pagel, 1991; Stachowicz et al., 2013). …”

“…Similar approaches indicate that both trait diversity and genetic relatedness within species can influence the outcome of ecological interactions (Abbott & Stachowicz, 2016; Dudley & File, 2007; Stachowicz et al., 2013). For example, trait differences could lead to niche partitioning reducing competition among individuals and promoting coexistence (Chesson, 2000); alternatively, trait differences could lead to competitive exclusion if certain traits allow individuals to be competitively dominant in that habitat (e.g., Abbott & Stachowicz, 2016).…”

“…For example, trait differences could lead to niche partitioning reducing competition among individuals and promoting coexistence (Chesson, 2000); alternatively, trait differences could lead to competitive exclusion if certain traits allow individuals to be competitively dominant in that habitat (e.g., Abbott & Stachowicz, 2016). Relatedness could influence intraspecifc interactions indirectly if it is correlated with trait differentiation (Jousset, Schmid, Scheu & Eisenhauer, 2011; Stachowicz et al., 2013) or directly through kin recognition (Aguirre, Miller, Morgan & Marshall, 2013; Dudley & File, 2007). However, the degree to which genetic relatedness serves as a reliable proxy for trait differentiation remains a key question.…”

“…Multiple genotypes potentially interact at an even finer scale, because as many as four unique genotypes can grow highly intertwined in a 10 cm by 10 cm area (J. Abbott and J. Stachowicz, unpublished data). Previous work shows that eelgrass genotypes differ in traits such as individual growth rate, nutrient uptake, susceptibility to herbivores, and detrital production (Hughes, Stachowicz & Williams, 2009; Tomas et al., 2011), and that these trait differences can predict assemblage performance (Stachowicz et al., 2013). Although much of the differentiation in traits observed in eelgrass across tidal heights is due to phenotypic plasticity (Dennison & Alberte, 1986; Li, Kim, Kim, Kim & Lee, 2013), there can be genetic differentiation in eelgrass growing at different depths (Kim et al., 2017; Ort et al., 2012), suggesting that there may be genetically based trait variation across depths.…”