Gap sampling of phenotypic Spotted Bass and Guadalupe Bass from the Little River Watershed

Lutz-Carrillo, Dijar
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This is an unpublished report regarding genetic analysis of tissues and specimens held at the University of Texas Biodiversity Collections. Samples of phenotypic Micropterus treculii (GB: Guadalupe Bass; n = 93), M. punctulatus (SP: Spotted Bass; n = 19), and M. salmoides (LM: Largemouth Bass; n = 98) were collected from the Little River watershed as part of the Texas Natural History Collection’s (TNHC) gap sampling effort. Tissue from these samples were lent to the Analytical Services Laboratory for analysis. For all GB and SP, isolated DNA was genotyped at 16 species informative SNPs (assays BBID1 and BBID2). For a subset of LM (n = 16) the same assays were applied. Multilocus genotypes were then used to assign taxonomic status based on manual inspection, for diagnostic alleles, and using the Bayesian inference algorithm implemented within STRUCTURE (Pritchard et al. 2000; burn-in 20000, mcmc 250000, admix model, allele freq corr, update allele freq w pop flag = 1, K = 4, 20 unknowns per run). Results based on manual inspection and Bayesian inference were congruent among all samples sans four individuals where the estimated hybrid type differed. All phenotypic LM were genetically consistent with LM and were not evaluated further here. Most phenotypic SP (17 of 19) were genetically consistent with SP x GB hybrids, except for two individuals identified as non-introgressed SP (Appendix 1). A majority of these hybrids (15 of 17) were inferred to have greater genetic influence from the SP lineage than from GB (mean SP influence in hybrids: 63%; Figure 1). Both non-introgressed SP were recovered from the same site (Figure 2). Most phenotypic GB (62 of 93) were genetically consistent with SP x GB hybrids. A majority of these hybrids (55 of 62) were inferred to have greater genetic influence from the GB lineage than from SP (mean GB influence in hybrids: 64%; Figure 1). Other hybrid types were also resolved including GB x SM (M. dolomieu – Smallmouth Bass) (5 of 93; mean GB influence 86%) and tribrids (SP x GB x SM; 5 of 93; mean GB influence 46%, mean SP influence 36%, mean SM influence 17%). Non-introgressed taxa were also recovered including GB (18 of 93) and LM (3 of 93). A majority of non-introgressed GB (12 of 18) were recovered from a single site (Brushy Creek) (Figure 2). Outside of phenotypic LM most fish collected were hybrids. Samples identified to species by phenotype were typically hybrids of the described taxon with a majority of their genome derived from the lineage of the described taxon. Results support previous work indicating that non-introgressed GB could be consistently recovered from Brushy Creek but that GB were not consistently located in surrounding drainages (TPWD, unpublished data). Results are also consistent with previous work (Lutz-Carrillo et al. 2018, Transactions of the American Fisheries Society) suggesting that the Brazos River drainage was part of a natural hybrid zone between Spotted Bass and Guadalupe Bass.