CONICET | Buscador de Institutos y Recursos Humanos

Survival and reproduction are the core elements of darwinian fitness. In the context of a fixed energy budget, organisms tend to allocate resources in order to maximize one at the expense of the other, in what has been called the lifespan-reproduction trade-off. Reproductive arrest and extended lifespan are common responses to low temperatures in many insects including fruit flies. In this study, we aim to understand the overwintering strategy of two closely-related Drosophila species. We compared survival, lifespan, ovarian maturation, and reproductive output (fecundity and fertility) of virgin and mated adult individuals of both Drosophila buzzatii and Drosophila koepferae after long-term cold exposure at dormancy-inducing conditions (10°C, 10:14 L:D). Compared to control, cold-acclimated flies increased lifespan by 200%, with some individuals reaching over 170 days of lifespan. Meanwhile, arrested ovarian maturation was observed in 97% of virgin flies, even after several weeks of cold exposure. Cold-induced reproductive arrest preserves, at least partially, reproductive capacity; virgin flies that were mated after 6 weeks at dormancy-inducing conditions reached similar fecundity scores as the control group (an average of 96 eggs/female), while those that mated before cold-exposure had on average six times lower fecundity than controls (14.3 eggs/female). Finally, we found that in both species males were much more susceptible to fertility loss than females. This fact would suggest that, in these species, male fertility thermal limits could account for the temporal window for reproduction in temperate regions. However, only females of D. buzzatii were capable of protecting stored sperm from cold damage and produced viable progeny. Such species-specific effects of low temperature over fitness likely contributed to the divergence of these closely-related species and to the spread of D. buzzatii into cooler environments.

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