Effects of heat treatment on the symbiotic system of Blattoidea: Morphofunctional alterations of bacteriocytes

Abstract

The purpose of the research was to study the morphological alterations that were produced in the symbiotic equilibrium of individuals of Leucophaea maderae, Periplaneta americana and Nauphoeta cinerea heat-treated at + 39° C. The bacteria localized in the bacteriophorous vacuoles in the bacteriocytes of the samples treated underwent a series of structural modifications that led to protoplast formation. This phenomenon is similar to that which occurs in free-living bacteria. The protoplasts were then further digested into the bacteriophorous vacuoles which had become cytolysosomes, to the point that they became residual bodies. When the process of endocellular lysis involved the whole symbiotic complement, the nucleus and the cytoplasmatic organelles of the bacteriocyte began to degenerate. These alterations were irreversible and could lead to the death of the cell. As a result, the number of bacteriocytes diminished. Heat treatment, which had lethal effects on the bacteria, altered the equilibrium which was established during the process of coevolution between the symbiotic prokaryote and the host cell. The bacteriocyte, deprived of its symbiotic complement, did not survive the loss of its morphofunctional equilibrium.

Dissecting genome reduction and trait loss in insect endosymbionts

“…In return for their contribution, the host provides a stable environment for the bacteria with a permanent supply of resources, thereby making the association a mutualistic one (a term reserved for the symbiotic relationships where each partner benefits from the activity of the other). Supporting this hypothesis, experimental studies dealing with the generation of aposymbiotic insects in the pea aphid Acyrthosiphon pisum , the tsetse fly Glossina morsitans , and different cockroaches have shown that aposymbiotic females generally display reduced reproduction rates and a decrease in fertility or even complete sterility. Hence, these symbionts are required for the correct development of their hosts and thus have been termed primary obligate endosymbionts .…”

Heritable symbionts in a world of varying temperature

“…Many examples of this come from insects, where the obligate symbionts reside in specialised cells known as bacteriocytes (Sacchi et al, 1993;Montllor et al, 2002). Thermal stress commonly causes the death of bacteriocytes that, once killed, do not regenerate.…”

“…In field cages, aphid clones carrying the reduced heat tolerance strain of Buchnera outcompete clones carrying the tolerant strain at low temperatures, but these clones are outcompeted where heat shocks occur (Harmon et al, 2009). Heat treatments in weevils (Heddi et al, 1999) and cockroaches (Sacchi et al, 1993) kill their bacteriocytes in a similar manner. Mealybug symbionts are also killed at elevated temperature, though this only has an impact on survival/fertility if it occurs during preadult development (Parkinson et al, 2014).…”

Mutualism meltdown in insects: bacteria constrain thermal adaptation

“…In cockroaches, various heat treatments were found to destroy some bacteria, but the authors did not identify conditions that completely eliminated bacteria without also killing the roach host (presumably due to heat stress) [36]. More recently, Sacchi et al [37] found that cockroach endosymbionts deteriorate under heat stress of 39°C for several (>18) days. While additional experiments in diverse host-symbiont associations are needed to test the generality of this trend, current data indicate that many primary symbionts are thermosensitive.…”