Local Adaptation? Enhanced Fitness Under Regional UVB Intensities in a Rock Pool Bdelloid Rotifer

Exposure to ultraviolet radiation (UVR) can decrease lifespan and reduce fecundity in aquatic invertebrates. Organisms inhabiting shallow waters are often unable to avoid UVR damage. Bdelloid rotifers are known for their resistance to extreme environments and ionizing radiation. However, conflicting results have been reported regarding their response to UVR. We hypothesized that exposure to UVB radiation would negatively affect survival and other life history characteristics (i.e., lifespan, net reproductive rate, intrinsic rate of increase) with increasing intensities and across multiple generations in bdelloids that inhabit shallow rock pools. To test these hypotheses, field-collected females (F₀) were exposed to two environmentally relevant and one extreme level of UVB for 2 h and individuals that survived were retained for further analysis. Their F₁ neonates were then cultured, and their offspring (F₂, F₄) were exposed to the same UVR treatment as the parental generation, and survival was again recorded. Lifetable analyzes were conducted using offspring of exposed mothers in the F₁ and F₅ generations. As predicted, exposure to UVB radiation negatively affected survival and resulted in cumulative damage after each subsequent exposure to UVB at all intensities. However, maternal exposure to low UVB levels resulted in increased lifespan (97%) and net reproductive rate (215%) in their progeny. At mid UVB intensities, net reproductive rate increased but to a lesser extent. This may reflect an adaptive response to environmental stress, enabling faster reproduction. However, increasing UVR intensity has adverse effects on longevity and fecundity which may compromise population fitness.