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ABSTRACT 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 F₁neonates 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 F₁and F₅generations. 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. 

Abstract Aquatic species found in habitats with limited shade and little dissolved organic carbon (DOC) have increased vulnerability to ultraviolet radiation (UVR) damage. Pigmentation is a common mechanism used by animals for protection from UVR. A pigmented bdelloid rotifer,Philodina, occurs in high densities in shallow rock pools in El Paso Co., TX, and is subject to repeated desiccation and high UVR. To understand the roles of DOC, pigmentation, and dormancy in reducing the effects of UVR exposure in these rotifers: (1) DOC levels in rock pools were measured before and after the summer monsoon season and (2) hydrated or dormant bdelloids (desiccated for 0, 1, 7, or 32 d) that differed in degree of pigmentation (highly, moderately, lightly, and none) were exposed to three intensities of UVB radiation (low, mid, or high) and monitored for survival after 48 h. Pigmented bdelloids were found in rock pools with lower DOC concentrations. Logistic regression analysis indicated that pigmentation level, desiccation time, and UVB intensity all affected survival. Bdelloids in the dormant form for 1 d were more resistant to UVB exposure at all pigmentation levels. However, as desiccation time increased, the odds of surviving decreased. Hydrated highly pigmented bdelloids were three times more likely to survive desiccation, UVB radiation, and their combined effects. Prolonged periods of drought due to the changing climate will alter DOC concentrations, causing photoprotection to become an increasingly important survival strategy for aquatic invertebrates, especially those inhabiting shallow waters. 

Based on observations of preserved samples, Jaramillo-Londoño & Pinto-Coelho (2010) describe a putative ecological relationship between the rotifer Hexarthra intermedia and the cladoceran Bosmina longirostris as a fusion of parasitism and interference competition. They argue that H. intermedia enter the filtering chamber of B. longirostris allowing the rotifer to exploit food collected by Bosmina, while simultaneously receiving protection from predators. In addition, they surmise that the result of this interaction can lead to death of Bosmina. We posit two simpler explanations for their observations. (1) Presence of H. intermedia in the cladoceran’s filtering chamber is an artifact of the collection methods. (2) Statistical correlations between the population levels of these two species simply means that the environment was suitable for their growth. Thus until additional evidence corroborates their findings, the simpler explanations should prevail.