Adaptive shifts and diversification of Ferricixius planthoppers in Brazilian caves (Hemiptera: Cixiidae)

The genus Ferricixius Hoch and Ferreira, 2012 was originally described based on a single troglobitic species found in iron-rich caves in southeastern Brazil. Subsequent collections revealed additional species with varying degrees of troglomorphism, including the first epigean/subtroglophilic species of the genus. More recently, four new species have been discovered in Brazilian caves, exhibiting marked variation in troglomorphic features. These findings make Ferricixius a valuable model for investigating processes of subterranean colonization and speciation in tropical cave environments.

The new species are known only from their type localities, located in caves of the Quadrilátero Ferrífero, Minas Gerais, Brazil. Specimens were collected using moistened brushes, transferred to vials containing 96% ethanol for preservation, and later stored in 70% ethanol. Morphological analyses focused on troglomorphic characters (reduction in eyes, wings, and body size) and male genital structures. Descriptions follow the criteria established by Hoch and Ferreira (2012), with adaptations according to Santos et al. (2023).

Four new species of Ferricixius are described, representing the first troglobitic species in the genus that still retain functional eyes—indicating that eye reduction does not follow a uniform pattern. Independent variation in the degree of troglomorphism was observed among species, suggesting environmental influence on selective pressures. Although male genitalia are generally similar among species, they exhibit diagnostic differences that support their separation, suggesting rapid speciation events.

The data suggest multiple subterranean colonization events by a common ancestor, possibly in response to climatic events, followed by rapid adaptive diversification. This discovery highlights the importance of conserving Brazilian caves in the face of increasing threats from mining activities.