Experimental study of temperature effects on the sex ratio of broods in Terrestrial Crustacea Armadillidium vulgare Latr. Possible implications in natural populations

Abstract

The woodlouse Armadillidium vulgare is characterized by female heterogamety (ZW) and male homogamety (ZZ). However, in several populations, sex determination is influenced by cytoplasmic sex factors (endosymbiotic bacteria = F). At 20 °C these maternally transmitted bacteria reverse genetic males into functional neo‐females (ZZ + F) producing highly female broods. When these neo‐females were reared at 30° C, the sex ratio of their broods became male‐biased. The major process involved in this heat‐induced sex ratio inversion was the disappearance of bacteria in embryos in the course of their development, which allowed the young to express a phenotype that conforms with their genotype (i.e. male ZZ). No heat‐sensitive stage of development was observed, but at least 35 days at 30° C seem to be necessary to induce F‐degradation. The presence of F at 30° C (before its degradation) also induced mortality during vitellogenesis. Daily thermoperiods including a thermophase at 30° C had effects on F similar to that of a constant temperature of 30° C. A. vulgare can live in climates having such thermoperiods (at least during one period of the year), temperature appears to be capable of limiting the presence of F‐bacteria in natural populations, and then modifying the evolution of sex‐determining mechanisms in such populations. Copyright © 1991, Wiley Blackwell. All rights reserved