Temperature increases can often speed up embryonic development and shorten gestation times in viviparous and ectothermic vertebrates. Viviparity is rare among invertebrates, however, and it is unclear what effects modest rises in temperature have on viviparous animals with exoskeletons. The intertidal marine isopod Cirolana harfordi in Australia is a species whose female members incubate their young inside their thorax and give birth to live young. This mode of reproduction contrasts the typical oviparous reproductive mode of most isopods. We investigated the impacts of increased temperature on the length of pregnancy and the number of offspring produced by C. harfordi individuals. Populations of C. harfordi were maintained at control (18 degrees C, to represent average environment temperature at the start of the breeding season) and two increased temperature treatments (20 degrees C and 22 degrees C). Increased temperature reduced development time to the juvenile stage and increased the number of young produced. It appears that the reproductive physiology of this viviparous invertebrate is affected by modest changes in temperature.
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