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Relationship between the total number of radii (TR) in anterior and posterior scales and the fork length of Owens, Lahontan, and hybrid Tui Chub individuals.
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The Owens Tui Chub Siphateles bicolor snyderi has become endangered by introgressive hybridization with the Lahontan Tui Chub S. bicolor obesa since the 1960s. Adequate conservation strategies require prior identification of pure populations, which is usually difficult because the diagnostic features presented in the formal subspecies description d...
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... radii.-The TR (dc#2) exhibited the same tendency and the ANOVA test showed significant differences in the main factors without interaction (Table 3). Post hoc tests found differences between the three groups (P < 0.001 in all the comparisons). Therefore, the mean TR was 12 (range, 6-20) for Lahontan Tui Chub and 21 (7-42) for Owens Tui Chub on anterior scales (12 [6][7][8][9][10][11][12][13][14][15][16][17][18][19] and 19 in posterior scales, respectively). The TR of hybrids fall between those of parental species with 16 ) in anterior and 15 ) in posterior scales. The overlap between the ranges of the three groups is mainly a consequence of the relationship among TR and FL. Differences in TR are more evident in larger fish for both types of scales ( Figure 3). Individuals of the three groups have a similar number of radii when young but diverge with growth; Lahontan Tui Chub remain low in the number of TR compared with Owens, while hybrids remain in a midway position. Basal shield.-The development of the basal shield (dc#3) was evaluated by means of the relative position of the focus (F/L) and the roundness of the scale shape (Wd/L). On one hand, the ANOVA test revealed significant differences in the relative position of the focus in both main factors but no inter- action (Table 3). The interaction plot displays an increased rel- ative position of the focus when moving from Lahontan to Owens Tui Chub individuals (Figure 4), with hybrids having an intermediate value (significant differences in all post hoc comparisons); the posterior scales show a smaller basal shield (larger F/L values) in the three groups. On the other hand, the ANOVA test detected significant differences in main factors but also interaction on the scale-shape ratio ( Table 3). The interaction plot reveals a progressive change to a more rounded shape (ratio values close to 1) in the anterior scales when moving from Lahontan to Owens individuals, the hybrids having an intermediate shape (Figure 4). However, scales from the posterior zone, which are more elongated than anterior ones, did not change in an equivalent manner. This differential response between scales of different zones and subspecies suggests the calculation of another parameter, the length ratio of scales of the anterior and posterior zone (L a /L p ). (Figure 4), meaning that anterior scales are rela- tively smaller than posterior ...
Citations
... Robust hybrid populations now occupy lakes and streams throughout the Owens River basin (Chen et al., 2007). The phenotypic consequences of this rapid introgression and its effects on population fitness are largely unknown (but see Galicia et al., 2015;Leunda et al., 2013). ...
... Deviations from expectations based on water flow alone are not uncommon in the literature (e.g., Hendry et al., 2006;McGuigan et al., 2003;Neat et al., 2003), and morphology interacts with a number of environmental and ecological demands that affect fish fitness. Despite low intrapopulation variation in body shape, introgressed Tui Chub varied considerably across populations, consistent with prior work on bone morphology in hybrid Tui Chub (Galicia et al., 2015). This interpopulation variation perhaps reflects the wide range of ecological and environmental conditions encapsulated within our "lake" and "stream" categories (Appendix S1). ...
Introgressive hybridization may erode phenotypic divergence along environmental gradients, collapsing locally adapted populations into a hybrid swarm. Alternatively, introgression may promote phenotypic divergence by providing variation on which natural selection can act. In freshwater fishes, water flow often selects for divergent morphological traits in lake versus stream habitats. We tested the effects of introgression on lake–stream morphological divergence in the minnow Owens Tui Chub (Siphateles bicolor snyderi), which has been rendered endangered by introgession from the introduced Lahontan Tui Chub (Siphateles bicolor obesa). Using geometric morphometric analysis of 457 individual Tui Chub from thirteen populations, we found that both native and introgressing parent taxa exhibited divergent body and caudal fin shapes in lake versus stream habitats, but their trajectories of divergence were distinct. In contrast, introgressed populations exhibited intermediate body and caudal fin shapes that were not differentiated by habitat type, indicating that introgression has eroded phenotypic divergence along the lentic–lotic gradient throughout the historic range of the Owens Tui Chub. Individuals within hybrid populations were less morphologically variable than those within parent populations, suggesting hybrid adaptation to selective agents other than water flow or loss of variance by drift. Introgressive hybridization can either erode or promote adaptive phenotypic divergence along environmental gradients. We tested the effects of widespread introgressive hybridization on morphological divergence between lake and stream habitats in the minnow Tui Chub. We found that hybridization has eroded morphological divergence, but comparisons of morphological variance between parent and hybrid populations suggest this outcome may not be maladaptive.
... The newly described T. kandai is the first sand-dune species known to be restricted to the southern Owens Valley. The region has been relatively well studied for changes in plant communities (Koehler & Anderson, 1995;Elmore, Mustard & Manning, 2003) and fish conservation (Galicia et al., 2015). However, the sand dunes, which are comprised of particles originating from the surrounding Sierra Nevada and Coso mountains (Lancaster et al., 2015), have not had any beetle species reported only from them (Andrews, Hardy & Giuliani, 1979). ...
The genus Trogloderus LeConte, 1879, which is restricted to dunes and sandy habitats in the western United States, is revised using morphological and molecular information. Six new species are described from desert regions: Trogloderus arcanus New Species (Lahontan Trough); Trogloderus kandai New Species (Owens Valley); Trogloderus major New Species (Mohave Desert); Trogloderus skillmani New Species (eastern Great Basin and Mohave Desert); Trogloderus verpus New Species (eastern Colorado Plateau); and Trogloderus warneri New Species (western Colorado Plateau). A molecular phylogeny is presented for the genus and used to infer its historical biogeography. The most recent common ancestor of Trogloderus is dated to 5.2 mya and is inferred to have inhabited the Colorado Plateau. Current species most likely arose during the mid-Pleistocene where the geographic features of the Lahontan Trough, Bouse Embayment and Kaibab Plateau were significant factors driving speciation.
