Patterns of acoustic and morphometric variation in species of genus Tettigettalna (Hemiptera: Cicadidae): Sympatric populations show unexpected differences

Abstract

Tettigettalna (Hemiptera: Cicadidae) is a genus of small sized cicadas occurring in south-western Europe, which consists of a complex of sibling species that are morphologically difficult to distinguish from each other but their calling songs can be used as the main character for their identification. These sibling species may sometimes occur in sympatry, therefore, this genus is a suitable model for addressing questions on isolation mechanisms and recognition processes. For this study, we selected T. argentata (the species with the broadest distribution) and the three other species of Tettigettalna (T. mariae, T. estrellae and T. josei) that are known to occur in sympatry with T. argentata at some locations in their distribution ranges. Thus, the present study investigates calling song and variation in external morphology in selected sympatric and allopatric populations of four species of Tettigettalna in order to determine whether there are patterns in population divergence that provide evidence of species recognition and reproductive isolation. The interspecific analysis of the calling songs showed that most time domain variables are species-specific although an overlap was found between the maximum and minimum values in T. argentata and T. mariae populations for four time domain variables. When only sympatric popu- lations of T. argentata and T. mariae are compared, time domain variables show less variation leading to a reduced overlap between this pair of sibling species. The morphometric variables showed low interspecific variability and did not allow a complete separation of the four species, both in allopatric and sympatric populations. Sympatric populations of both T. argentata and T. mariae showed lower frequencies and bigger general body sizes than the allopatric ones. The pattern of variation found does not correspond to the pattern expected in species undergoing character displacement.