Abstract
Declines in genetic diversity within a species can affect the stability and functioning of populations. The conservation of genetic diversity is thus a priority, especially for threatened or endangered species. The importance of genetic variation, however, is dependent on the degree to which it translates into phenotypic variation for traits that affect individual performance and ecological processes. This is especially important for predominantly clonal species, as no single clone is likely to maximise all aspects of performance. Here we show that intraspecific genotypic diversity as measured using microsatellites is a strong predictor of phenotypic variation in morphological traits and shoot productivity of the threatened, predominantly clonal seagrass Posidonia australis, on the east coast of Australia. Biomass and surface area variation was most strongly predicted by genotypic richness, while variation in leaf chemistry (phenolics and nitrogen) was unrelated to genotypic richness. Genotypic richness did not predict tissue loss to herbivores or epiphyte load, however we did find that increased herbivore damage was positively correlated with allelic richness. Although there was no clear relationship between higher primary productivity and genotypic richness, variation in shoot productivity within a meadow was significantly greater in more genotypically diverse meadows. The proportion of phenotypic variation explained by environmental conditions varied among different genotypes, and there was generally no variation in phenotypic traits among genotypes present in the same meadows. Our results show that genotypic richness as measured through the use of presumably neutral DNA markers does covary with phenotypic variation in functionally relevant traits such as leaf morphology and shoot productivity. The remarkably long lifespan of individual Posidonia plants suggests that plasticity within genotypes has played an important role in the longevity of the species. However, the strong link between genotypic and phenotypic variation suggests that a range of genotypes is still the best case scenario for adaptation to and recovery from predicted environmental change.
Highlights
The link between biodiversity and ecosystem function is well-established at the species level, with communities that support a wide range of species often better able to stabilise multiple ecosystem processes in response to disturbance or change than species poor communities (Loreau et al, 2001; Hooper et al, 2005; Stachowicz, Bruno & Duffy, 2007; Tilman, Reich & Isbell, 2012; Cardinale et al, 2013; Lefcheck et al, 2015)
Positive linear relationships were found between the number of genotypes per meadow and the mean of the coefficient of variation for four traits
We detected no significant increase in the highest levels of shoot productivity with greater genotypic richness, but did detect a negative relationship between genotypic richness and the likelihood of having low productivity shoots
Summary
The link between biodiversity and ecosystem function is well-established at the species level, with communities that support a wide range of species often better able to stabilise multiple ecosystem processes in response to disturbance or change than species poor communities (Loreau et al, 2001; Hooper et al, 2005; Stachowicz, Bruno & Duffy, 2007; Tilman, Reich & Isbell, 2012; Cardinale et al, 2013; Lefcheck et al, 2015). Genetic diversity within species, as measured by the number of genotypes, can enhance productivity (Aguirre & Marshall, 2012), increase resilience (Massa et al, 2013) and have cascading benefits to the surrounding ecosystem (Hughes et al, 2008; Ellers, 2009). It is necessary to quantify the degree of phenotypic variation among genotypes within species to better predict how loss of genotypes can affect the performance of populations (Lande & Shannon, 1996; Ellers, 2009; Forsman & Wennersten, 2015), during periods of changing climatic conditions and increased anthropogenic stressors (Best, Stone & Stachowicz, 2015). It is expected that multiple genotypes will contribute to multiple different processes and/or thrive under different conditions
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