Unveiling introgression in bumblebee (Bombus terrestris) populations through mitogenome-based markers

Area of Science:

• Ecology
• Genetics
• Conservation Biology

Background:

• The commercial bumblebee subspecies Bombus terrestris terrestris has expanded its range globally.
• This expansion poses a threat to native pollinators, including the Iberian subspecies Bombus terrestris lusitanicus.
• Mitochondrial genomes are valuable for studying hybridization due to low recombination and maternal inheritance.

Purpose of the Study:

• To sequence the mitogenomes of B. t. terrestris and B. t. lusitanicus.
• To develop molecular markers for detecting introgression between these subspecies.
• To assess the dispersion and impact of the non-endemic subspecies in the Iberian Peninsula.

Main Methods:

• Metagenomics was employed to obtain approximately 17 kbp of mitochondrial genome sequences for both subspecies.
• Comparative analysis identified 358 bp differences between the mitogenomes (excluding the AT-rich region).
• Restriction Fragment Length Polymorphism (RFLP) in the nad2 gene was utilized as a diagnostic marker.

Main Results:

• Sequences for both subspecies' mitogenomes were obtained, providing a molecular framework for marker selection.
• Four mitogenomic fragments were identified as potential subspecific diagnostic markers.
• RFLP analysis in the nad2 gene proved effective for assessing the spread of B. t. terrestris.
• Subspecific haplotypes were found in both subspecies, indicating introgression in natural and human-mediated contact zones.

Conclusions:

• The nad2 gene RFLP is a cost-effective tool for monitoring the invasive subspecies.
• Evidence of introgression suggests a threat to the native Iberian subspecies.
• Understanding genetic exchange is crucial for the conservation of native pollinator populations.