STAGE-DEPENDENT SUSCEPTIBILITY TO UV-B RADIATION IN Bufo arenarum EMBRYOS

LUIS A. CASTAÑAGA, CRISTINA S. PÉREZ-COLL AND JORGE HERKOVITS

Baltimore, Maryland

Congreso; XXVI Annual meeting SETAC N. A.; 2005

Setac N. A.

  The depletion of the stratospheric ozone layer causes great concern due to the higher intensities of UV-B radiation on living organisms and seems to be one of the factors related to the decline of amphibian populations worldwide.  The main purpose of this study was to evaluate the susceptibility of Bufo arenarum embryos at different developmental stages to  UV-B radiation. Groups of ten embryos by duplicate at the developmental stages of  Blastula (B), Gastrula (G),  Neurula (N), Tail bud (TB), Gill circulation (GC), Opercular fold (OF) and Complete operculum (CO)  were treated  with a range of UV-B radiant exposure  from 547.2 to 27360 J/m2 (administered within 100 min.) and mortality was evaluated from 24 hours up to 168 hr post exposure. The LD10, LD50 and LD90 values were obtained and plotted as isolethality curves.  Malformations exerted by UV-B were also evaluated. The LD10, 50 and 90 values in J/m2 at 168 hr post exposure were: B: 8552; 18931 and 41902;  G: 5022, 10157, and 20539; N:17960; 22176 and 27381;   TB: 3539, 5235 and 7744;  GC: 1793,  2307 and 2994;  OF: 2542, 3180 and 3979; CO: 2003, 2829 and 4036. As an average most of the embryos died within the acute post treatment period.  Malformations were obtained in all developmental stages but UV-B resulted  teratogenic (Teratogenic Index higher than 1.5) in N, GC and CO. GC stage resulted the most susceptible to UV-B as  irradiation ranging from 547.2 to 1641.6 J/m2 exerted severe malformations in 100% of the treated embryos.  The most common alterations were:  persistent yolk plug, bifid spine, reduced body size, delayed development, asymmetry, microcephaly and anencephaly, flexure in tail and  body toward the irradiation side, agenesis or partial gill development, abnormal pigment distribution, hypermotility. The results allow  to conclude  that after a very high UV-B resistance at early developmental stages (e.g.  blastula-gastrula and neurula), the susceptibility of Bufo arenarum embryos to this agent increases very significantly for both lethality and malformations.