Galaxias brevipinnis (Jarvis and Closs, 2015)

Augspurger, Jason M., Jarvis, Matt G., Wallis, Graham P., King, Tania M., Ingram, Travis, Hicks, Andy S. & Closs, Gerard P., 2023, Landscape biogeography and population structuring of a facultatively amphidromous galaxiid fish, Galaxias brevipinnis, Cybium 47 (4), pp. 417-430 : 422-425

Genetics of G. brevipinnis populations

All loci were highly polymorphic, ranging from 21 alleles at Gbr 12 to 32 at Gvu 05. Population mean H o ranged from 0.64 to 0.83 (mean 0.76) and H e from 0.57 to 0.82 (mean 0.75; Table I). Allelic richness across all loci tended to be lower in lake-developing populations, ranging from 2.8 in Lake Christabel to 4.9 in Lake Wānaka, while coastal populations ranged from 3.9 to 6.3. Departures from Hardy- Weinberg equilibrium were found in 49 out of 240 locus-

population combinations before stepwise Bonferroni cor- rection. As 11 of these occurred at Gbr 130, and 21 occurred at Gbr 140, these loci were excluded. Bonferroni corrections were then applied with only 1 of 192 remaining out of equilibrium after stepwise Bonferroni corrections (p <0.0003). No locus was affected by null alleles in any sample, so all loci were used in the study.

All landlocked kōaro populations showed a higher degree of genetic structuring on a lake-by-lake basis, when compared to diadromous populations ( Fig. 2A ), regardless of distance from coastal populations (Mantel p = 0.07). Landlocked systems had pairwise F ST values of approximately 0.03-0.06 when compared to immediate downstream sites less than 5 km away ( Fig. 2A, B ). Kōaro populations from lakes located in the same catchments (e.g. L. Rotoiti, L. Rotoroa), had lower F ST values, indicating increasing genetic difference with greater distance (Mantel p = 0.04). Comparisons among coastal streams had lower F ST values, but significantly increase with geographic distance (Mantel, p = 0.04). High structuring levels were present in these comparisons even when geographic distance was relatively small and sites were within the same catchment, such as an F ST value of 0.05 for Smoke-ho and Stony Creeks which are only 18 km apart. Structuring within the respective tributaries of L. Wānaka and L. Wakatipu was relatively low, comparable to that of among coastal stream comparisons (F ST = 0.01- 0.03), with no clear pattern evident in the STRUCTURE analysis.

bel are clearly split form the other

West Coast lakes ( Fig. 3 ). Within lake STRUCTURE results did not show distinct population clustering for tributaries of L. Wakatipu or

L. Wānaka. Mg, Cu, Ni were useful in stock dis- crimination, with linear discriminant (LD1) explaining> 67% of variation in all systems (Table II).

At the largest (system) spatial scale, evidence of population structuring was clear, with samples from coastal, L. Wānaka and L. Wakatipu all forming distinct clusters (Fig. 4A), with reclassification to system of capture 96% successful (Table II). At a finer scale (within-system regions), regional clusters of otolith trace element signatures were generally well-defined (Fig. 4B), and reclassification success rates were again high: 94% for coastal regions, 86% within L. Wānaka and 71% within L. Wakatipu (Table II). At the finest spatial scale, otoliths from individual sampling sites still showed distinct, though less well-defined, trace element clustering (Fig. 4B), and reclassification success rates for coastal, L. Wānaka, and L. Wakatipu sites were 62.5%, 78.6%, and 60%, respectively (Table II). Reclassification success was reflected in the LDA plots, with clear clustering present at high reclassification levels (e.g. L. Wānaka), and greater overlap occurring with lower reclassification levels (e.g. Wakatipu) ( Fig. 3B ).

Figures

Figure 2. – A: Heat map of FST pairwise comparisons where red represents relatively high FST values approaching 0.15, while white and mauve rep- resent numbers approaching closer to zero. Sites within the same catchment are denoted by a shared letter follow- ing site name. Sites located upstream of lakes are denoted by “Lake” prior to site name, whereas all other sites are located downstream of lakes. Coastal creeks and rivers that have no lake or larger catchment affiliation are denoted with “F”. B: Scatter plot with trend lines of FST pairwise comparison val- ues (n = 246 total comparisons) and riverine site distance (km), showing lake-lake (cross, dotted line), lake-coast (triangle, dashed line), and coast-coast (circle, solid line) comparisons.

Figure 3. – Average STRUCTURE results aggregated using CLUMPAK for populations 2–6 and 9. K = 6 was selected as the most like- ly population estimate using Evanno’s method. STRUCTURE initially separated the lakes draining to the east coast (L. Wānaka and L. Wakatipu) from all other sites at K = 2. The West Coast lakes were split away next (K = 3), with L. Moeraki and L. Paringa splitting at K = 4 and L. Cristabel at K = 5. East coast L. Wānaka and L. Wakatipu were split at K = 6. L. Paringa and L. Moeraki are split form each other at K = 9.