How does the "ancient" asexual Philodina roseola (Rotifera: Bdelloidea) handle potential UVB-induced mutations?

Abstract

Summary 15Like other obligate asexuals, bdelloid rotifers are expected to suffer from degradation of their 16 genomes through processes including the accumulation of deleterious mutations. However, 17 sequence-based analyses in this regard remain inconclusive. Instead of looking for historical 18 footprints of mutations in these ancient asexuals, we directly examined the susceptibility and 19 ability to repair point mutations by the bdelloid Philodina roseola Ehrenberg, 1832 by 20 inducing cyclobutane-pyrimidine dimers (CPDs) via exposure to UVB radiation (280-320 21 nm). For comparison, we performed analogous experiments with the facultative asexual 22 monogonont rotifer Brachionus rubens Ehrenberg, 1838. Different strategies were found for 23 the two species. P. roseola appeared to shield itself from CPD induction through 24 uncharacterized UV-absorbing compounds and, except for the genome reconstruction that 25 occurs after desiccation, was largely unable to repair UVB-induced damage. By contrast, B. 26 rubens was more susceptible to UVB-irradiation, but could repair all induced damage in about 27 two hours. In addition, whereas UV-irradiation had a significant negative impact on the 28 reproductive output of P. roseola, and especially so after desiccation, that of B. rubens was 29 unaffected. Although the strategy of P. roseola might suffice under natural conditions where 30 UVB-irradiation is less intense, the lack of any immediate CPD repair mechanisms in this 31 species remains perplexing. It remains to be investigated how typical these results are for 32 bdelloids as a group and therefore how reliant these animals are on desiccation-dependent 33 genome repair to correct potential DNA damage given their obligate asexual lifestyle. 34 35

Gateway to genetic exchange? DNA double‐strand breaks in the bdelloid rotifer Adineta vaga submitted to desiccation

“…This is consistent with data collected in the chironomid species Polypedilum verplanki where the genome integrity was retrieved only after 96 h of repair (Gusev et al, 2010). Fischer et al (2013) also found that the repair of cyclobutane-pyrimidine dimers (CPDs) induced by UV-B radiation on hydrated bdelloid P. roseola was almost complete at 96 h. Moreover, in this latter study, they demonstrated that UV-B damage was only repaired when P. roseola went through a desiccated state. Desiccation therefore appears a key factor to induce DNA repair in bdelloids (Fischer et al, 2013).…”

“…() also found that the repair of cyclobutane‐pyrimidine dimers (CPDs) induced by UV‐B radiation on hydrated bdelloid P. roseola was almost complete at 96 h. Moreover, in this latter study, they demonstrated that UV‐B damage was only repaired when P. roseola went through a desiccated state. Desiccation therefore appears a key factor to induce DNA repair in bdelloids (Fischer et al ., ).…”

“…It has been hypothesized that desiccationinduced DNA DSBs shape bdelloid genomes and promote gene conversion through mitotic recombination during DNA DSB repair (Flot et al, 2013). The desiccation process also appears to be a key mechanism to repair DNA damage, as it was observed in hydrated P. roseola individuals where DNA damage induced by UV-B was only efficiently repaired after a round of desiccation (Fischer et al, 2013). The interplay between the genome structure and DNA repair of DSBs following desiccation events remains to be deciphered.…”

The oxidative damage initiation hypothesis for meiosis

“…These aspects of diploid–haploid cycles, however, do not directly relate to the putative repair functions at the prophase of meiosis I, but rather support a concept that meiosis has various different DNA restoration functions (Hörandl 2009 ). Some ancient asexual animals (bdelloid rotifers) seem to have colinear chromosomes with special DNA repair mechanisms, which may also reflect a special adaptation to regular desiccation (Fischer et al 2013 ; Schon and Martens 2003 ).…”

Effects of UVB radiation on grazing of two cladocerans from high-altitude Andean lakes

“…UVB effects on zooplankton have been amply studied in rotifers [18, 19], copepods [20–22] and cladocerans [23–26]. For all of them, UVB radiation acts as a considerable stressor leading to reduced survival [23, 27] and, limited reproduction capacity [19].…”