Avian obligate brood parasitic lineages evolved variable complex polycrystalline structures to build tougher eggshells

Analía V López; Seung Choi; Yong Park; Daniel Hanley; Jin-Won Lee; Marcel Honza; Raúl E Bolmaro

doi:10.1016/j.isci.2023.108552

Avian obligate brood parasitic lineages evolved variable complex polycrystalline structures to build tougher eggshells

iScience. 2023 Nov 22;26(12):108552. doi: 10.1016/j.isci.2023.108552. eCollection 2023 Dec 15.

Authors

Analía V López¹, Seung Choi², Yong Park³, Daniel Hanley⁴, Jin-Won Lee^{5

6}, Marcel Honza⁷, Raúl E Bolmaro⁸

Affiliations

¹ Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
² Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
³ School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, South Korea.
⁴ Department of Biology, George Mason University, Fairfax, VA 22030, USA.
⁵ Department of Biology, Kyung Hee University, Seoul 02447, South Korea.
⁶ Korea Institute of Ornithology, Kyung Hee University, Seoul 02447, South Korea.
⁷ Institute of Vertebrate Biology, Czech Academy of Sciences, 603 65 Brno, Czech Republic.
⁸ Instituto de Física Rosario, CONICET-UNR, Rosario, Prov. de Santa Fe S2000EKF, Argentina.

Abstract

Avian brood parasites and their hosts display varied egg-puncture behaviors, exerting asymmetric co-evolutionary selection pressures on eggshells' breaking strength. We investigated eggshell structural and textural characteristics that may improve its mechanical performance. Parasitic eggshell calcified layers showed complex ultra- and microstructural patterns. However, stronger parasitic eggshells are not due to lower textural severity (characterized by lower preferred crystallographic orientation, larger local grain misorientation and smaller Kearns factor), but rather to grain boundary (GB) microstructure characteristics within the eggshell outermost layer (palisade layer, PL). Accordingly, the thicker the PL and the more complex the GB pathways are, the tougher the parasitic eggshells will be. These characteristics, which we can identify as a "GB Engineering" driven co-evolutionary process, further improve eggshell breaking strength in those parasitic species that suffer relatively high frequencies of egg-puncturing by congeneric or hosts. Overall, plain textural patterns are not suitable predictors for comparing mechanical performance of bioceramic materials.

Keywords: Evolutionary biology; Ornithology; Zoology.