Cytogenetic and Hybridization studies of geographic populations of Teleogryllus connodus (Walker) and T. oceanicus (Le Guillou) (Orthoptera : Gryllidae)

Abstract

Cytogenetic studies of geographic populations of the Australian field cricket T. commodus reveal that, although morphologically similar, the northern non-diapausing populations and the southern diapausing populations show marked chromosomal differences. The number of chromosomes is the same (2nB = 26+XO) but the centromere position and the size of some of the autosomes as well as of the sex chromosome differ. In further studies the chromosomes of T. oceanicus (2nB = 26+XO) were compared: the northern populations of T. commodus showed a closer relationship to T. oceanicus than to T. commodus from southern Australia. In hybridization experiments, the F1 hybrids of the northern and southern populations of T. commodus were sterile. This sterility was due to several kinds of meiotic disturbance during spermatogenesis and to the abnormal development of the ovaries in the hybrid progeny. Hybridization experiments between T. oceanicus and the two different "races" of T. commodus were also carried out. The present study, in conjunction with that of the stridulation patterns presented by Leroy, leads to the conclusion that the crickets from northern Australia, at present designated T. commodus, are in reality more closely related to T. oceanicus, of which they should be regarded as a geographic or chromosomal race, there being no evidence of reproductive isolation. The meiosis of these populations and their hybrids, in addition to the cytological data available from the congeneric Japanese species, provides evidence as to the course of evolution of the group.