Evolution of milk secretion inferred from elasmobranch embryonic feces

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K04064
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: Okinawa Churashima Foundation
• Principal Investigator: Tomita Taketeru 一般財団法人沖縄美ら島財団(総合研究センター), 総合研究センター 動物研究室, 主任研究員 (90774399)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 授乳 / 子宮ミルク / 板鰓類 / 炭酸カルシウム / 胎仔便 / 進化

Outline of Final Research Achievements

Uterine milk in elasmobranchs may be the oldest lactation in vertebrates, but its evolutionary process is not fully understood. In this study, we examined Myliobatid stingrays and Lamniform sharks, both of which are suspected to secrete uterine milk. We found that they have large-sized intestine and accumulate large amounts of embryonic feces in their intestines. These feces contains calcium carbonate crystals, suggesting that the intestines of the fetuses may be kept alkaline. This can be associated with the observation that the stomach is not yet functioning and the intestinal flora of the fetus differs from that of the parents. Intestinal crystals is known to be stably preserved for a long time the may provide direct evidence to clarify the evolutionary process of lactation in vertebrates.

Free Research Field

魚類学

Academic Significance and Societal Importance of the Research Achievements

本研究は、一般的に化石証拠として残りにくいと考えられる脊椎動物の授乳システムについて、初めて化石証拠として残りうる可能性を示した点で重要である。さらに、本研究を通して、未だ不明なことが多い板鰓類の子宮ミルクについて、ミルク分泌を行う子宮とミルク摂取を行う胎仔の両面から研究を行い、そのメカニズムの一部が解明されたことに意義があると考えられる。