| Summary: | The study of insect reproductive ecology is essential to determine species distributions and fate under changing environments. Species adapted to harsh environments are good examples to investigate the reproductive mechanisms that allow them to cope with the challenging conditions. We here focus on studying for the first time the reproductive ecology of a cold-adapted D. obscura strain collected in Finland (subarctic climate region). We tested several reproductive traits such as fertility and fecundity to observe the onset of reproduction and gauge when sexual maturity is reached in both males and females. We combined these measures with an analysis of changes of their reproductive organs shortly after eclosion. We found that males matured several days before females and that this process was underpinned by female egg maturation and male accessory gland growth, while sperm was already present in two-day old males. This delayed maturation is not observed to the same extent in other closely related species and might be a signature of exposure to harsh environments. Whether this delay is an adaptation to cope with variation in resource availability or prolonged unfavorable temperatures is though not clear. Finally, our study adds to the set of reproductive mechanisms used by cold adapted species and the information presented here contributes to understanding the breadth of Drosophila reproductive ecology. The data sets concerning egg number and offspring counts contain missing values represented as NA when one of the individuals escaped or died during the experiment. Data sets regarding the analysis of the male reproductive system contain missing values (also represented as NA), when the picture was not good enough to measure the organ area or the wing length (e.g., broken tissue).
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