Spiroplasma Display an Intricate Continuum of Infection Heterogeneity and Persistence in Myrmica Ants

Area of Science:

• Microbiology
• Insect Symbiosis
• Genomics

Background:

• Facultative bacterial symbionts spread in insect populations via horizontal and maternal transmission.
• Co-infections can influence the dynamics of symbiont spread, but are often undetected due to limited genotyping.
• Spiroplasma bacteria have diverse symbiotic associations with insects, with unclear transmission and co-infection patterns.

Purpose of the Study:

• To investigate the transmission patterns and co-infection dynamics of Spiroplasma symbionts in Myrmica ants.
• To identify cryptic co-infections and characterize their prevalence and stability.
• To explore the evolutionary stability of Spiroplasma symbiosis in ants.

Main Methods:

• Exhaustive genotyping of Spiroplasma in 75 Myrmica ant colonies across seven species.
• Phylogenomic and functional genomic analyses.
• Assessment of infection frequency variation by ant caste and species.

Main Results:

• Multiple cryptic Spiroplasma co-infections were discovered, involving two distinct clades with differing infection frequencies.
• Infection heterogeneity varied by ant caste, being lower in Myrmica ruginodis workers.
• The sMyr Spiroplasma variant showed widespread infection across four Myrmica species and was prevalent in both queens and workers.
• Phylogenomic data suggest an exceptionally stable symbiosis for sMyr, with an estimated seven-million-year persistence in the Myrmica scabrinodis species group.

Conclusions:

• Spiroplasma symbiosis in ants exhibits complex infection heterogeneity, including cryptic co-infections.
• An evolutionary stable, maternally acquired infection strategy can evolve in Spiroplasma symbionts.
• The sMyr variant represents a long-term, stable insect-microbe association within the Myrmica genus.