Range instability leads to cytonuclear discordance in a morphologically cryptic ground squirrel species complex

Area of Science:

• Evolutionary Biology
• Genetics
• Ecology

Background:

• Cytonuclear discordance, where genetic markers from the nucleus and mitochondria disagree, often has unclear causes.
• The Otospermophilus beecheyi species complex exhibits three distinct mitochondrial DNA lineages (Northern, Central, Southern) with only the Northern lineage showing concordance with nuclear genes.

Purpose of the Study:

• To investigate how differing histories of range stability and fluctuation influence cytonuclear concordance and discordance in ground squirrel lineages.
• To test hypotheses derived from species distribution models using demographic methods and exon capture data.

Main Methods:

• Employed exon capture data and demographic modeling.
• Analyzed genetic divergence and gene flow among Northern, Central, and Southern lineages of Otospermophilus beecheyi.
• Assessed historical range dynamics and climatic influences since the last interglacial period.

Main Results:

• Mitochondrial DNA lineages likely formed in allopatry during the Pleistocene and responded differently to climatic shifts.
• The Northern lineage maintained a stable range, showing genetic distinctiveness and low migration.
• The Southern lineage expanded, potentially overwhelming the Central lineage, with male-biased dispersal preserving some historical introgression signals in certain genetic markers.

Conclusions:

• Range stability is crucial for maintaining distinct phylogeographic lineages.
• Unstable range dynamics, characterized by expansion and contraction, can lead to lineage merging upon secondary contact.
• Contrasting historical range dynamics explain observed cytonuclear concordance and discordance in ground squirrels.