Description of Calling, Courtship and Mating Behaviour of Six Species of the Genus Zyginidia (Auchenorrhyncha: Cicadellidae)

Simple Summary This paper explores the pre-mating reproductive barriers in a group of leafhopper species living vicariously in the Palaearctic region by producing hybrid zones and compares them with a closely related species of the same genus living in sympatry with some of the species of the investigated group. The results confirm the usefulness of a cheap, though neglected, methodology for recording substrate-borne vibrations and concern the basic clues that separate these species during their mating; i.e., which of the parameters of the substrate-borne vibrations they produce for calling the opposite sex and courting once the two sexes meet are necessary as pre-mating reproductive barriers. The basic behavioural isolation mechanisms are the pulse period of the female call and the main part of the courtship ritual performed by the male. An excursus into the existing literature on leafhopper bioacoustics and reproductive behaviour is undertaken to point out common aspects, propose explanations of biological phenomena-including the formation of hybrid zones, which led, in the past, to the description of several fictitious new species throughout the Palaearctic-and place the grounds for further research on pre-mating and post-mating reproductive barriers. The vibrational communication and mating behaviour of the graminicolous leafhoppers Zyginidia pullula, Z. ribauti, Z. scutellaris, Z. serpentina, Z. sohrab, and Z. biroi were investigated to explain why the first five species hybridize. Z. biroi was used as a control species. All species behaved in the same way and no significant statistical differences were detected with regard to male calls, while female calls and the male courtship song differed in Z. biroi, thus showing that a specific pre-mating isolation mechanism was used by the latter species and the first five ones lacked such a mechanism. In addition, Z. sohrab is missing in Italy, while the other species live allopatrically in Italy, with the only exceptions being Z. serpentina and Z. biroi, which live in Sicily and are often found in sympatry, and Z. scutellaris and Z. biroi, which live in Sardinia. All these species can be distinguished by means of male genital appendages; however, Z. biroi is longer and has a different body colour. The existence of natural hybrids of Z. pullula, Z. ribauti, and Z. scutellaris in the Italian peninsula and their hybridization in the laboratory with Z. serpentina and Z. sohrab require the investigation of possible post-mating reproductive barriers before re-considering their systematic validity.