Chondria tumulosa

Williams, Taylor M., Krueger-Hadfield, Stacy A., Hill-Spanik, Kristina M., Kosaki, Randall K., Stoeckel, Solenn & Spalding, Heather L., 2024, The reproductive system of the cryptogenic alga Chondria tumulosa (Florideophyceae) at Manawai, Papahānaumokuākea Marine National Monument, Phycologia 63 (1), pp. 36-44 : 40-41

Chondria tumulosa genets

We initially extracted 10 mg of dried material from each thallus clump (N = 124). The thallus material we preserved in silica gel was not the same material as we observed for reproductive structures under the microscope. We had preserved thalli in the field in silica gel, whereas we haphazardly selected thalli for observation under the microscope in the laboratory in Charleston. However, clumps were composed of tightly woven thalli and we likely preserved multiple genotypes in silica. We observed multiple alleles for many of our 124 putative ‘individuals’. Thus, we reextracted DNA from a single thallus piece to ensure a single genet was extracted. This reduced our genetic data set from 124 thalli to 41 thalli but reflected a more conservative approach to ensure we genotyped a single thallus as a putative genet.

Microsatellite loci

All five loci were polymorphic with either two or three alleles ( Table S1 ). All loci had an average rounding error below the recommended error threshold as assessed by TANDEM ( Matschiner & Salzburger 2009) except for locus Chondria _39 ( Table S1 ). Poorly binned alleles for Chondria _39 were checked manually (see also Krueger-Hadfield et al. 2013). Null allele frequencies were very small ranging from 0%–4% ( Table S2 ).

Proportion of reproductive thalli

Approximately 80% of thalli were vegetative (lacking visually identifiable reproductive structures) at the time of collection (302 out of 372 thalli; c. 81%). Approximately 20% of thalli were reproductive tetrasporophytes (70 out of 372 thalli; c. 19%). No reproductive gametophytes (zero out of 372) were observed during surface scans ( Fig. 6 ).

Ploidy assignment and ratio

All 41 genotyped thalli were heterozygous at one or more loci and were considered tetrasporophytes. All sites sampled at Manawai, therefore, deviated from the predicted ploidy ratio of √2:1 and PHD was 0.

Genotypic and genetic diversity

Twenty seven distinct MLGs were observed across the 41 genotyped thalli (R = 0.475, E.5 = 0.342; Table 3 ). Six genotypes were re-encountered at least once, and one genotype was re-encountered eight times within a single site ( Table S3 ). Several thalli were found to share the same MLG within each site. Although MLGs were also shared between sites, these were always considered distinct genets based on Psex p -values ( Table S3 ).

Average expected heterozygosity (HE) at Manawai was 0.52 and observed heterozygosity (HO) was 0.77 ( Table 2 ). Heterozygote excess was observed with single locus FIS values ranging from –0.37 to 0.08 with a variance of 0.490 ( Table 2 ). The Pareto β index was small but>0.7 (Pareto β = 0.729). There was little evidence of linkage disequilibrium (� rD = 0.062; Table 3 ) and low probability of identity between sibs (pid = 0.003; Table 3 ).

Figures

Fig. 6. Proportion of Chondria tumulosa tetrasporophytic to vegetative thalli by site across Manawai (NTOTAL = 372 samples, 74–75 thalli per site).