Genetic and morphological data demonstrate hybridization and backcrossing in a pair of salamanders at the far end of the speciation continuum

Arntzen, JW; Jehle, R; Wielstra, B

Abstract

Deeply diverged yet hybridizing species provide a system to investigate the final stages of the speciation
process. We study a hybridizing pair of salamander species — the morphologically and genetically
drastically different newts Triturus cristatus and T. marmoratus — with a panel of 32 nuclear and
mitochondrial genetic markers. Morphologically identified hybrids are mostly of the F1 generation and
mothered by T. cristatus. The sex ratio of the F1 hybrid class is reciprocally skewed, with a preponderance
of females in T. cristatus-mothered hybrids and males in T. marmoratus-mothered hybrids. This amounts
to the Haldane effect operating in one direction of the cross. Deeper generation hybrids are occasionally
produced, possibly including F1 hybrid * backcross hybrid offspring. Interspecific gene flow is low, yet
skewed towards T. cristatus. This asymmetry may be caused by hybrid zone movement, with the
superseding species being predisposed to introgression. The persisting gene flow between deeply
differentiated species supports the notion that full genetic isolation may be selected against. Conversely,
published morphological data suggest that introgressive hybridization is detrimental, with digital
malformations occurring more frequently in the area of sympatry. Finally, to assist field
identification, both within the area of natural range overlap and concerning anthropogenic introductions
elsewhere, we document the phenotypical variation of two generations of hybrids compared to both
parental species. We suggest that fluctuating range boundaries, ecological segregation, cytonuclear
incompatibilities and hybrid breakdown through Bateson–Dobzhansky–Muller incompatibilities all contribute to species integrity, despite incomplete isolation during secondary contact.

Citation

Arntzen, J., Jehle, R., & Wielstra, B. (2021). Genetic and morphological data demonstrate hybridization and backcrossing in a pair of salamanders at the far end of the speciation continuum. Evolutionary Applications, 14(12), 2784-2793. https://doi.org/10.1111/eva.13312

• Journal Article Type: Article
• Acceptance Date: Oct 1, 2021
• Online Publication Date: Oct 24, 2021
• Publication Date: Dec 16, 2021
• Deposit Date: Oct 11, 2021
• Publicly Available Date: Nov 1, 2021
• Journal: Evolutionary Applications
• Print ISSN: 1752-4563
• Electronic ISSN: 1752-4571
• Publisher: Wiley
• Volume: 14
• Issue: 12
• Pages: 2784-2793
• DOI: https://doi.org/10.1111/eva.13312
• Publisher URL: https://doi.org/10.1111/eva.13312
• Related Public URLs: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1752-4571/