Tracing species replacement in Iberian marbled newts

Area of Science:

• Evolutionary Biology
• Population Genetics
• Speciation Studies

Background:

• Secondary contact between closely related species can create hybrid zones, facilitating interspecific gene flow.
• Hybrid zone movement, driven by competitive advantages, can lead to species replacement and leave asymmetric gene flow footprints.
• Previous studies suggested hybrid zone movement in Iberian marbled newts, evidenced by asymmetric gene flow and a relict population of *Triturus marmoratus*.

Purpose of the Study:

• To investigate the presence of a *Triturus marmoratus* genomic footprint in the Lisbon peninsula, south of a known relict population.
• To test for asymmetric gene flow and introgressive hybridization between *T. marmoratus* and *T. pygmaeus*.

Main Methods:

• Development and application of a panel of nuclear and mitochondrial single nucleotide polymorphism (SNP) markers.
• Genetic analysis using STRUCTURE software to assess population structure and admixture.
• Principal Component Analysis (PCA) to visualize genetic variation within *T. pygmaeus* populations.

Main Results:

• No additional populations of *T. marmoratus* were identified south of the enclave.
• STRUCTURE analysis revealed no detectable genetic traces of *T. marmoratus* in the *T. pygmaeus* populations studied.
• PCA indicated some genetic variation within local *T. pygmaeus*, but introgressive hybridization from *T. marmoratus* could not be confirmed.

Conclusions:

• The findings suggest species replacement between *T. marmoratus* and *T. pygmaeus* may have occurred without significant introgressive hybridization.
• Alternatively, hybridization might have occurred, but the genomic footprint has been largely eroded by purifying selection.
• Further investigation north of the relict population is predicted to clarify the role of hybridization in this species replacement event.