Parallel introgression, not recurrent emergence, explains apparent elevational ecotypes of polyploid Himalayan snowtrout. Issue 10 (27th October 2021)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Royal Society open science. Volume 8:Issue 10(2021)
• Publication Date: 2021-10-27
• Subjects: adaptation -- ecotype -- convergent evolution -- parallel evolution -- polyploidy -- introgression; Science -- Periodicals; 500
• DOI: 10.1098/rsos.210727
• Languages: English
• ISSNs: 2054-5703

Abstract

Abstract : 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: Schizothorax ). However, parallel patterns of differential introgression during secondary contact are a viable alternative hypothesis. Here, we used ddRADseq ( N = 35 319 de novo and N = 10 884 transcriptome-aligned SNPs), as derived from Nepali/Bhutanese samples ( N = 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.