Cytological and evolutionary implications of aberrant chromosome behavior in the harlequin lobe of some Pentatomidae (Heteroptera)

Summary

• 1. In the harlequin lobe of 21 species of Pentatomidae, the spermatogenesis always undergoes bizarre deviations from a normal meiosis.

• 2. The deviations affect the meiotic pairing in most cases and also involve irregularities in the meiotic divisions which result in a highly variable number of chromosomes in the spermatids.

• 3. There is good evidence that the chemical conditions within the harlequin lobe differ from those in normal lobes and that they are responsible for alterations in isopycnotic chromosomes that are most strikingly manifest in their mitotic behavior.

• 4. Evidently the changed chemical environment has comparatively little effect on chromatin which is in the heteropycnotic state. Hence the mitotic behavior of the sex chromosomes in the harlequin lobe is normal, and autosomes that are predominantly heteropycnotic show less deviation from the normal than do isopycnotic chromosomes.

• 5. The radically different behavior of chromosomes in adjoining regions of the same testis is a demonstration of the fact that chromosomal behavior is, to a considerable extent, determined by their immediate environment.

• 6. The question of how so wasteful an organ as the harlequin lobe could have been evolved, is briefly considered.