Consequences of interspecies antennal imaginal disc transplantation on organization of olfactory glomeruli and pheromone blend discrimination.

Abstract

The antennal imaginal disc was transplanted between male larvae of two different heliothine moth species, Heliothis virescens (HV) and Helicoverpa zea (HZ). Males of these species respond to distinct pheromone blends, have different peripheral and central olfactory neuron specificities, as well as distinct arrangements of antennal lobe olfactory glomeruli, in the specialized male macroglomerular complex (MGC). After pupal development and adult eclosion, unilateral (with one antennal disc left intact) and bilateral antennal transplant males were assayed in a wind tunnel to both species' pheromone blends to determine their ability to discriminate between the two signals. The postmetamorphic developmental effects of interspecific transplantation upon the primary olfactory centers in the moth brain were then examined in these same individuals. Behavioral tests showed that both types of unilateral transplant continued to exhibit upwind anemotactic flight to the normal recipient blend with occasional flights to the donor blend. In contrast, bilateral transplants preferred the HV pheromone blend regardless of the direction of transplant, with some males of each type also responding to the HZ blend. Neuroanatomic evaluation of the MGC revealed that the donor arrangement of MGC glomeruli was induced in 73% HZ donor to HV recipient transplants and 56% of the reciprocal transplant. Surprisingly, several V-Z bilateral transplant males responded to both HV and HZ pheromone blends and had two HV MGC structures. This behavioral outcome was unexpected, because responses to the HV blend are mediated by inputs that are normally antagonistic to HZ males and the normal HV antenna lacks olfactory receptor neurons capable of responding to the essential minor pheromone component of the HZ blend. These data indicate a plasticity in developmental pathways regulating the expression of peripheral olfactory receptor neurons and in the glomerular processing of species-specific olfactory information.