Genetic and morphological diversity in sympatric kelps with contrasting reproductive strategies

Abstract

The evolution of asexual reproduction is considered a response to environmental conditions where it incurs less cost than sexual reproduction, maintains adapted genotypes and allows rapid proliferation into new areas. In rare circumstances, some species have evolved distinct asexual morphs or lineages in response to ubiquitous environmental conditions. Understanding the implications of, and the mechanisms underpinning, such reproductive strategies will be important for assessing the vulnerability of populations to environmental change. We examined morphological and genetic variation between 2 morphs of the kelp Ecklonia radiata, with sympatric haplodiplontic and vegetatively reproducing individuals growing side by side in Western Australia. Using 6 microsatellite markers, we show that vegetative morphs had a great propensity for asexual reproduction, with all attached haptera (8−20 per plant) being genetically identical to their parent plant. Moreover, for 8 multilocus genotypes (MLGs), Psex (probability that each MLG had clonal origins) scores were significant, suggesting clonal origins, and members of these MLGs were overwhelmingly dominated by individuals of the vegetative morph. Vegetative morphs were morphologically distinct, less morphologically variable, had lower genetic diversity and an excess of heterozygotes relative to haplodiplontic morphs. Nevertheless, vegetative morphs still produced and released zoospores at the same densities as haplodiplontic individuals, suggesting that they still complete an alternation of generations life history strategy. This likely accounted for weak genetic differentiation between morphs and suggests ongoing gene flow. Given that genetic diversity often confers adaptive capacity through change, low diversity may have implications for the vulnerability of this unique vegetative morph to local climatic and environmental stressors.

Genetic tropicalisation following a marine heatwave

“…It is a perennial species with an alternation of generations life cycle with macroscopic sporophytes (sampled here) alternating with microscopic gametophytes 30 . E. radiata does not reproduce asexually, except for the distinctive E. brevipes morphotype in Hamelin Bay 34 which was not sampled here. Samples of E. radiata sporophytes for genetics were collected across 800 km of coastline that experienced the highest thermal anomalies during the heatwave (up to 5.5 °C at Jurien Bay, Fig.…”

Genomic signatures of clonality in the deep water kelp Laminaria rodriguezii

“…Theoretical models predict that when clonality predominates, it will increase heterozygosity (Marshall & Weir, 1979;Balloux et al, 2003;De Meeûs et al, 2006), which may ultimately lead to higher levels of observed heterozygosity (Ho) than those expected (He) under panmixia. This deviation has been observed empirically through negative values of fixation index FIS, reported in various partially clonal populations (in animals Adjeroud et al, 2014; angiosperms Alberto et al, 2002;Alberto et al, 2005;, and red and brown macroalgae Guillemin et al, 2008;Ardehed et al, 2015;Coleman & Wernberg, 2018, Pardo et al, 2019. Without sex, alleles do not segregate independently, which implies that heterozygosity can be preserved rather than reduced over generations (Judson & Normark, 1996).…”

Restore or Redefine: Future Trajectories for Restoration

“…The risk associated with restoring populations in the absence of empirical genetic knowledge is that restored populations will inadvertently lack diversity or appropriate adaptive capacity to cope with extant or future conditions (e.g., Williams, 2001), which may be particularly pertinent for species that exhibit small scale dispersal and are therefore susceptible to reduced gene flow, increased inbreeding or asexual propagation (e.g., Guillemin et al, 2008;Coleman et al, 2011aColeman and Wernberg, 2018;Miller et al, 2019). This risk is exacerbated given increasing habitat fragmentation and deterioration often characterizes the seascapes from which donor adults or propagules must be sourced for restoration (Coleman and Kelaher, 2009).…”