Chafin Tyler K, Regmi Binod, Douglas Marlis R, Edds David R, Wangchuk Karma, Dorji Sonam, Norbu Pema, Norbu Sangay, Changlu Changlu, Khanal Gopal Prasad, Tshering Singye, Douglas Michael E
Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA.
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder 80309, USA.
R Soc Open Sci. 2021 Oct 27;8(10):210727. doi: 10.1098/rsos.210727. eCollection 2021 Oct.
The recurrence of similar evolutionary patterns within different habitats often reflects parallel selective pressures acting upon either standing or independently occurring genetic variation to produce a convergence of phenotypes. This interpretation (i.e. parallel divergences within adjacent streams) has been hypothesized for drainage-specific morphological 'ecotypes' observed in polyploid snowtrout (Cyprinidae: ). However, parallel patterns of differential introgression during secondary contact are a viable alternative hypothesis. Here, we used ddRADseq ( = 35 319 and = 10 884 transcriptome-aligned SNPs), as derived from Nepali/Bhutanese samples ( = 48 each), to test these competing hypotheses. We first employed genome-wide allelic depths to derive appropriate ploidy models, then a Bayesian approach to yield genotypes statistically consistent under the inferred expectations. Elevational 'ecotypes' were consistent in geometric morphometric space, but with phylogenetic relationships at the drainage level, sustaining a hypothesis of independent emergence. However, partitioned analyses of phylogeny and admixture identified subsets of loci under selection that retained genealogical concordance with morphology, suggesting instead that apparent patterns of morphological/phylogenetic discordance are driven by widespread genomic homogenization. Here, admixture occurring in secondary contact effectively 'masks' previous isolation. Our results underscore two salient factors: (i) morphological adaptations are retained despite hybridization and (ii) the degree of admixture varies across tributaries, presumably concomitant with underlying environmental or anthropogenic factors.
不同栖息地内相似进化模式的重现，往往反映了作用于现有或独立出现的遗传变异的平行选择压力，从而导致表型趋同。这种解释（即相邻溪流内的平行分化）已被假定用于多倍体雪鲮（鲤科：）中观察到的特定流域形态“生态型”。然而，二次接触期间差异渐渗的平行模式是一个可行的替代假说。在这里，我们使用了从尼泊尔/不丹样本（各48个）中获得的ddRADseq（35319个单核苷酸多态性位点，其中10884个与转录组比对）来检验这些相互竞争的假说。我们首先利用全基因组等位基因深度推导出合适的倍性模型，然后采用贝叶斯方法得出在推断期望下统计上一致的基因型。海拔“生态型”在几何形态测量空间中是一致的，但在流域水平上具有系统发育关系，支持独立出现的假说。然而，系统发育和混合分析的分区确定了受选择的基因座子集，这些子集与形态学保持谱系一致性，这反而表明形态学/系统发育不一致的明显模式是由广泛的基因组同质化驱动的。在这里，二次接触中发生的混合有效地“掩盖”了先前的隔离。我们的结果强调了两个显著因素：（i）尽管存在杂交，但形态适应仍得以保留；（ii）混合程度在各支流间有所不同，可能与潜在的环境或人为因素有关。
