| Popis: |
Obligate brood parasitic birds typically lay eggs with shells that are thicker and stronger than their hosts’ eggshells. Eggs with greater external strength may also likely be structurally stronger internally, with the possible cost that parasitic embryos would require greater effort to hatch. However, eggshell mechanical and structural features are dynamic during embryonic development. We characterized and compared eggshell shifts prior and at the end of incubation between two brood parasites’ and three of their frequent hosts’ species. Through direct mechanical and ultrastructural eggshell measurements during controlled puncture tests and microscopic imaging, we demonstrate that interspecific patterns in the eggshell features were affected both by parasitism (parasitic vs. host) status and by incubation progress during embryonic development. Specifically, even though the parasites had stronger, stiffer and tougher than hosts’ eggshells at the time of laying, theses difference diminished and/or were no longer statistically present by the time of hatching, even when the parasitic eggshells were still thicker than the eggshells of the hosts’ species after incubation stage. All these patterns converge to indicate that parasitic eggshells are stronger and stiffer at laying, while the parasitic embryos do not need to engage in greater effort during hatching, relative to the hosts. |
