Speciation in Chitaura grasshoppers (Acrididae: Oxyinae) on the island of Sulawesi: colour patterns, morphology and contact zones

Abstract

We investigate colour pattern and morphological variation in Chitaura grasshoppers on the Indonesian island of Sulawesi, and examine the relationship between divergence in these two sets of characters and population history, as reflected by variation in mitochondrial DNA. Analysis of colour pattern variation identifies a total of 21 distinct Operational Taxonomic Units in Sulawesi, the majority of which have parapatric distributions. Patterns of phenotypic variation at two contact zones in north Sulawesi suggest genetic independence between three of these colour forms, indicating that speciation has occurred. Despite this, colour pattern divergence is only coincident with morphological differentiation at one of these contact zones. In addition, neither type of phenotypic divergence is associated with geographical structuring in mitochondrial DNA, suggesting that historical isolation has had little influence on evolutionary diversification. Instead, divergence in colour pattern and morphology appears to have occurred rapidly or under conditions of continued gene flow, possibly in response to spatially variable natural selection. This result has implications for the identification of conservation units based solely on molecular markers.