Eggshell structure in Caiman latirostris eggs improves embryo survival during nest inundation

CÉSAR CEDILLO-LEAL; MELINA S. SIMONCINI; PAMELA M. L. LEIVA; ALEJANDRO LARRIERA; JEFFREY W. LANG; CARLOS I. PIÑA

PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON. SERIES B: BIOLOGICAL SCIENCES.

ROYAL SOC

Lugar: Londres; Año: 2017 vol. 284

0962-8452

Egginundation often results in poor hatch success in crocodilians. However, howtolerant eggs are to submergence, and/or how eggshell ultrastructure may affectembryo survival when inundated, are not well understood. In this study, ourobjective was to determine if embryo survival in Caiman latirostris is affected by eggshell surface roughness, wheneggs are submerged under water. Tolerance to inundation was tested early (day30) vs. late (day 60) in development, using 8 clutches (4 per time treatments),subdivided into 4 groups: rough eggshell-inundated, smooth eggshell-inundated,rough, eggshell-non inundated, smooth-non inundated (N = 9 per clutch pertreatment; 9 x 4 = 36 eggs per group). ?Rough? eggshell represented thenatural, unmodified eggshell surface structure. ?Smooth? eggshell surfacestructure was created by mechanically sanding the natural rough surface toremove surface columnar elements and secondary layer features, e.g., irregularitiesthat result in ?roughness.? When inundated by submerging eggs under water for10 hours atday 30, ?smooth? eggshell structure resulted in more than twice as many deadembryos (16 vs. 6, smooth vs. rough; N = 36), and more than half as manyhealthy embryos (6 vs. 13, smooth vs. rough respectively; N = 36). In contrast, at day 60, inundation resulted invery low hatching success, regardless of eggshell surface structure. Only twohatchlings survived the inundation, notably in the untreated group with intact,rough eggshells. Inundation produced a high rate of malformations (58% at day30), but did not affect hatchling size. Our results indicate that eggshell roughnessenhances embryo survival when eggs are inundated early in development, but notlate in development. Apparently, the natural surface ?roughness? entraps airbubbles at the eggshell surface during inundation, thereby facilitating gasexchange through the eggshell even when the egg is submerged under water.