Phylogenetic implications of phasmid absence in males of three genera in heteroderinae

Area of Science:

• Nematology
• Developmental Biology
• Evolutionary Biology

Background:

• Phasmids are sensory organs in nematodes with poorly understood functions.
• Previous research has focused on female phasmids, particularly in relation to reproduction.

Purpose of the Study:

• To investigate the presence and development of phasmids in males of Heterodera schachtii, Verutus volvingentis, and Cactodera eremica.
• To explore the evolutionary relationships of phasmids within the Heteroderinae subfamily.
• To determine the potential function of phasmids, ruling out female pheromone reception.

Main Methods:

• Transmission electron microscopy was used to examine phasmid structures in different developmental stages (J2, M3, M4, M5) of the studied nematode species.
• Histochemical staining with Coomassie blue and cobalt sulfide was employed to detect phasmid components.
• Comparative analysis of phasmid structures and variations in ampulla shape was conducted for phylogenetic insights.

Main Results:

• The male phasmid was consistently absent in all developmental stages of H. schachtii, V. volvingentis, and C. eremica.
• Postpenetration second-stage juveniles (J2) of H. schachtii lacked all phasmid structures except the canal and ampulla.
• Prepenetration J2 of V. volvingentis possessed only a canal remnant, differing from H. schachtii.
• Evidence suggests parallel evolution of phasmids in these species, despite similarities in ampulla shape.

Conclusions:

• The absence of male phasmids throughout development may be linked to an amphimictic reproductive mode.
• Female pheromone reception is unlikely to be a primary function of phasmids.
• Variations in ampulla shape serve as valuable phylogenetic characters for understanding Heteroderinae evolution.