Itaropsis

Jaiswara, Ranjana, Balakrishnan, Rohini, Robillard, Tony, Rao, Karthik, Cruaud, Corinne & Desutter-Grandcolas, Laure, 2012, Testing concordance in species boundaries using acoustic, morphological, and molecular data in the field cricket genus Itaropsis (Orthoptera: Grylloidea, Gryllidae: Gryllinae), Zoological Journal of the Linnean Society 164 (2), pp. 285-303 : 299-300

ITAROPSIS CRICKETS

At the species level, there have been a number of studies demonstrating the concordance between differences in acoustic features and reproductive isolation (reviewed in Gerhardt & Huber, 2002). The infraspecific level has received less attention, and this is the level at which our study could help by analysing the role of advertisement signals in cricket diversification.

Our results show a broad congruence between studied lines of evidence: acoustic clusters and the clades resulting from morphological, molecular (both mitochondrial and nuclear), and combined analyses are broadly similar, and all the data sets seem to have evolved jointly. Incongruence in character evolution is often related to faster divergence in some characters than in others ( Orr & Smith, 1998), especially characters involved in prezygotic reproductive isolation such as calling songs ( Padial et al., 2009; Gonzalez, Ornelas & Gutiérrez-Rodriguez, 2011). The lack of incongruence in our results does not support the hypothesis that acoustic signals could have directed lineage diversification in Itaropsis , especially at such a low level of diversification. An alternative hypothesis would consider that allopatric populations of Itaropsis diverge for all their characters in the same time, by genetic drift for example.

The striking variation in temporal features in this genus, extending from short chirps to extremely long trills, and from the relatively short syllables typical of field crickets to exceptionally long syllables, is not matched by the changes in carrier frequency. The carrier frequency of the ancestral form is estimated at about 7 kHz: the Valparai clade has, on average, somewhat lower frequencies (6–7 kHz), and the Kadari clade, somewhat higher frequencies (7–8 kHz), while the Bombay –Bangalore clade shows no distinct pattern and is characterized by high variation. The song divergence in this genus is thus largely explained through changes in temporal rather than spectral features, as usually observed in crickets ( Alexander, 1962; Otte, 1992; Robillard & Desutter- Grandcolas, 2011) even though diversification in frequency values and spectra has been documented in some clades (Robillard, Grandcolas & Desutter- Grandcolas, 2007).

Itaropsis is also characterized by considerable within-clade variation in songs: the Bombay – Bangalore clade in particular shows high interindividual variation in both carrier frequency and syllable period, two song features that are usually critical for species recognition in crickets ( Gerhardt & Huber, 2002). It would be interesting to examine whether female responses in this clade are relatively broadly tuned. Similarly, the Kadari clade shows striking variation in call duration: this raises the possibility of polymorphisms within this clade, although the identical syllable repetition rates and carrier frequencies throughout this clade suggest that females may be evaluating these two features and ignoring the others. The call duration could also be a dynamic feature (sensu Gerhardt, 1991) that is under sexual selection. This population also needs to be studied in greater detail to examine the causes and consequences of high song variation within clades.