Complex patterns of chromosomal variation along a latitudinal cline in the grasshopper Caledia captiva

Abstract

An analysis of chromosomal variation along a 1500-km latitudinal cline in the Moreton subspecies of Caledia captiva has revealed the existence of complex and systemic changes to genome structure. These changes involved variation in the position of the centromere on every chromosome, from medial locations in northern populations to more distal or terminal locations in the southern populations. At the ends of this genomic cline, two contrasting chromosomal patterns were evident. In the north, the genome was fixed for metacentric chromosomes whereas at the southern limit, the genome was homozygous for acrocentric and telocentric chromosomes. Intermediate populations showed highly complex patterns of chromosomal polymorphisms. All populations along the cline were homogeneous for mitochondrial DNA restriction fragment length polymorphisms, highly repeated DNA sequences, and allozyme variation, with no evidence of genetic differentiation or inhibition of gene flow. It is argued that these complex patterns of genomic change reveal evidence of an adaptive role for both fixed and polymorphic chromosomal rearrangements within the same taxon.Key words: chromosome variation, natural selection, Caledia, grasshopper.