How to build a puncture- A nd breakage-resistant eggshell? Mechanical and structural analyses of avian brood parasites and their hosts

A. V. LOPEZ; BOLMARO, RAÚL E.; AVALOS, MARTINA CECILIA; LIA GERSCHENSON; JUAN C. REBOREDA; VANINA FIORINI; VANINA TARTALINI; PABLO RISSO; MARK E. HAUBER

JOURNAL OF EXPERIMENTAL BIOLOGY

COMPANY OF BIOLOGISTS LTD

Lugar: Cambridge; Año: 2021 vol. 224 p. 1 - 20

0022-0949

Evolved eggshell strength is greater in several lineages of obligateavian brood parasites (birds that lay their eggs in other species? nests)than in their hosts. Greater strength is typically indirectly implied byeggshell thickness comparisons between parasites and hosts.Nevertheless, there is strong evidence that the eggshell structuralorganization differentially influences its mechanical properties.Using instrumental puncture tests and SEM/EBSD and XRDtechniques, we studied the most relevant eggshell mechanical,textural, ultrastructural and microstructural features between severalhost species and their parasitic cowbirds (Molothrus spp.). Theseparasitic species display different egg-destructive behaviors,reducing host reproductive fitness, including the more frequentlyhost-egg puncturing M. rufoaxillaris and M. bonariensis, and the hostegg-removing M. ater. The results, analyzed using a phylogeneticcomparative approach, showed interspecific patterns in themechanical and structural features. Overall, the eggshells of the twoegg-puncturing parasites (but not of M. ater) were stronger, stiffer andrequired greater stress to produce a fracture than the respective hosts?eggs. These features were affected by eggshell microstructure andultrastructure, related to the increase in the intercrystalline boundarynetwork acting in cooperation with the increase in palisade layerthickness. Both structural features generate more options and greaterlengths of intercrystalline paths, increasing the energy consumed incrack or fissure propagation. The reported patterns of all these diverseeggshell features support a new set of interpretations, confirmingseveral hypotheses regarding the impact of the two reproductivestrategies (parasitic versus parental) and parasitic egg destructionbehaviors (more versus less frequently puncturing)