Rapid vertebrate speciation via isolation, bottlenecks, and drift

Area of Science:

• Evolutionary Biology
• Genetics
• Conservation Science

Background:

• Speciation is typically attributed to selective pressures like local adaptation or mate choice.
• Neutral processes, such as genetic drift, are less commonly considered primary drivers of speciation, especially over short evolutionary timescales.

Purpose of the Study:

• To investigate the primary drivers of a rapid speciation event in the White Sands pupfish (Cyprinodon tularosa).
• To determine if genetic drift or divergent selection is responsible for the genetic differentiation between two Evolutionarily Significant Units (ESUs) of this endangered species.

Main Methods:

• Whole-genome resequencing of two ESUs of White Sands pupfish.
• Analysis of genome-wide differentiation (FST) and identification of divergence islands.
• Demographic modeling using joint allele frequency spectrum.

Main Results:

• High and uniform genome-wide differentiation (global FST ≈ 0.40) between the two ESUs.
• Absence of discrete islands of divergence, even in candidate genes, suggesting lack of strong divergent selection.
• Demographic modeling indicated a split ~4-5 kya and significant population bottlenecks within the last 2.5 millennia.

Conclusions:

• Rapid speciation in White Sands pupfish was primarily driven by neutral genetic drift, exacerbated by isolation and repeated population bottlenecks.
• These findings challenge the traditional view of selection as the sole driver of rapid speciation.
• Understanding drift-driven speciation is crucial for the conservation management of endangered species like the White Sands pupfish.