薄殼生物材料保護與破壞機制之探討—以鳥蛋為例

Abstract

在長期的演化下，生物為了適應生存環境，而各自發展出獨特的生物材料及生活方式。其中，蛋殼與鳥巢為鳥類得以長時間生存下來，並於世界各地成功繁衍的關鍵。儘管目前對於鳥類蛋殼的研究很多元，但是大多僅針對單一物種進行討論，尤其以雞蛋居多，少有跨物種的討論，而對於蛋殼與鳥巢之間的關係仍存在著許多疑問。 因此，本研究利用線上資源整理了1,385個物種的鳥蛋與鳥巢資料，透過有限元素分析取得鳥蛋的機械性質，並定義一無因次化的勁度參數，對不同大小及形狀的蛋殼進行單一量化的比較。與鳥巢特徵—築巢地點、鳥巢型態、附著方式分別進行統計分析，發現對於使用較不穩定築巢地點與附著方式的鳥類，其蛋殼因具有較高碰撞風險而演化出較高的無因次參數，而鳥巢結構則對鳥蛋機械性質影響不大。另外，透過貝氏推論回推鳥類祖先之蛋殼無因次參數，發現其中位數於演化過程中為一不變量，但隨著新興鳥巢的出現，其標準差有越來越大的趨勢。鳥類蛋殼無因次參數隨著演化時間越趨多元，顯示鳥類為適應多樣的生存環境而進行無因次參數與築巢環境間的取捨。 本研究亦與台北市立動物園合作，建立一套實驗流程，一共分析了56個物種，超過800顆樣本。針對壓縮試驗過程中所觀察到的破壞現象，將蛋殼歸納出四種破壞機制：徑向破壞、環狀破壞、裂縫偏轉以及裂縫捕獲。並探討影響裂紋生長的因素，與不同破壞機制對鳥類繁殖方式的影響。 本研究以工程的觀點討論生物薄殼材料的保護與破壞機制，利用本研究所建立的分析方法，能對蛋殼有更深入及全面的了解。期許能為鳥類演化及生物材料領域，提出創新的想法及貢獻。

For several hundred million years of evolution, organisms have developed their own unique biological structures and lifestyles in order to adapt to various living environments. Among them, eggshells and nests are one of the reasons for avian to have survived for such a long period of time, and to be able to reproduce successfully all over the world. Despite the diversity of research on avian eggshells, they mainly focus on one specific species, mostly hen. There lacks investigation of bird interspecies, and the interactions between eggshells and nests remain inconclusive. Therefore, by using online resources, we obtained egg and nest data of 1,385 bird species. Mechanical properties of eggshells were calculated through finite element analysis, and a dimensionless stiffness parameter C was defined to eliminate the factors of size and shape of eggs from different bird species. They were then statistically analyzed with nest characters—site, structure, and attachment. We found that birds that build nests with unsteady sites and attachments tend to produce eggs with high resistance to collision damage, while nest structure has little effect on eggshells. In addition, while median C number remained an invariant across avian evolution, interspecific variations increased due to the emergence of new nest sites and attachments. Implying the trade-offs between steady nests or stronger eggshells. Moreover, in collaboration with Taipei Zoo, this study established a procedure for compression tests on eggshells. Analyzing over 50 species, we found that there are four fracture mechanisms: radial crack, ring crack, crack deflection, and crack arrest. Our findings illuminated the factors on affecting crack growth, and discussed how different reproductive strategies and living environments led to different fracture mechanisms. In this study, we focused on the engineering perspective on biological materials which is often overlooked. With this study, we are able to have a deeper and more comprehensive understanding for eggshells. We look forward to provide innovative insights and contributions for the avian evolution and the field of biological materials.