Evidence for association of chromosomal form and development time from complex clines and geographic races in the grasshopperCaledia captiva(Orthoptera: Acridadae)

Abstract

Evidence for an association between chromosomal form and development time in the grasshopper Caledia captiva (F.) was obtained through comparison of two geographic taxa and analysis of a complex latitudinal cline within one of the taxa. Northern populations of the Moreton taxon possess a metacentric genome and are slow-developing. In contrast, the Torresian taxon, distributed throughout northern, coastal Australia, a region of pronounced seasonality in rainfall, and southern populations of the Moreton taxon, which inhabit a region of pronounced seasonality in temperature, both have an acrocentric genome and are fast-developing. The convergence of chromosomal form and development time between Torresian and southern Moreton populations appears to be driven by convergence in life history. Seasonality limits grasshoppers to one generation per year and favours fast development. The transition between relatively acrocentric southern Moreton populations and relatively metacentric northern Moreton populations is gradual but not monotonic. Instead, a shift to a bivoltine life history in the middle of the transect occurs and is associated with shifts in both development time and chromosomal form. These results imply an adaptive role for chromosomal form, although the causative link between chromosomal variation and variation in development time remains to be established.

A Comparison of Five Hybrid Zones of the Weta Hemideina Thoracica (Orthoptera: Anostostomatidae): Degree of Cytogenetic Differentiation Fails to Predict Zone Width

“…In contrast, chromosome hybrid zones in other orthopteran species are not thought to have their widths determined by reduction in fitness of hybrids resulting from chromosome rearrangements (Shaw 1981;Harrison and Rand 1989;Butlin 1998). For example, the width of the hybrid zone between the Moreton and Torresian races of Caledia captiva on the eastern coast of Australia does not appear to be determined by the chromosome rearrangements even though evidence for karyotype selection has been found (Groeters and Shaw 1996). Although hybrid zone width may not be determined by the chromosome rearrangements in a number of studies, the chromosome clines themselves do seem to be influenced by chromosome heterozygote disadvantage.…”

Latitudinal clines in the grasshopperDichroplus elongatus: Coevolution of the A genome and B chromosomes?

“…In some species of insects a ‘saw‐tooth’ pattern has been described. The ‘saw‐tooth’ pattern occur where a species shift the life cycle from bivoltine (two generations per year) to univoltine (one generation per year) (Masaki, ; Mousseau & Roff, ; Brennan & Fairbairn, ; Groeters & Shaw, ; Mousseau, ; Johansson, ; Nygren et al ., ). According to this pattern, body size of insect tends to increase at lower latitudes in univoltine and bivoltine areas.…”

A Comparison of Five Hybrid Zones of the Weta Hemideina Thoracica (Orthoptera: Anostostomatidae): Degree of Cytogenetic Differentiation Fails to Predict Zone Width

“…At Taupo (Zone 5), an earlier study of unlinked nuclear markers revealed that this hybrid zone was reducing the introgression of the chromosomal markers more than genic markers (allozyme and microsatellite) and therefore cline width might be controlled by the reduction in fitness of hybrids resulting from the actual chromosome rearrangement have their widths determined by reduction in fitness of hybrids resulting from chromosome rearrangements (Shaw 1981;Harrison and Rand 1989;Butlin 1998). For example, the width of the hybrid zone between the Moreton and Torresian races of Caledia captiva on the eastern coast of Australia does not appear to be determined by the chromosome rearrangements even though evidence for karyotype selection has been found (Groeters and Shaw 1996). Although hybrid zone width may not be determined by the chromosome rearrangements in a number of studies, the chromosome clines themselves do seem to be influenced by chromosome heterozygote disadvantage.…”