Shedding light on fertilization dynamics in Decapodiformes (Cephalopoda): from tracing sperm pathway to unraveling egg encapsulation

• Grant number: 24/18533-0
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• Start date: February 12, 2025
• End date: August 11, 2025
• Field of knowledge: Biological Sciences - Zoology - Morphology of Recent Groups
• Principal Investigator: José Eduardo Amoroso Rodriguez Marian
• Grantee: Aline Akemi Taba
• Supervisor: Yoko Iwata
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: University of Tokyo, Japan
• Associated to the scholarship: 23/09622-6 - Evolution of egg-laying strategies in Decapodiformes (Cephalopoda): how a nektonic clade became completely independent from the ocean floor, BP.MS

Abstract

Decapodiform cephalopods (e.g., squid, cuttlefish, pygmy squid, bobtail squid) represent an interesting group for the study of the evolution of fertilization mechanisms in aquatic animals, due to their unique type of fertilization ("confined external fertilization"). In this clade, fertilization probably takes place during egg encapsulation, as the forming egg capsule travels through sperm storage locations along the female body. Therefore, understanding both (1) the pathway of sperm from the storage site to the egg and (2) the egg capsule formation may potentially elucidate fertilization mechanisms in cephalopods. However, there is considerable variation in sperm storage mechanisms and egg capsule structure in decapodiforms, which poses a challenge for exploring such intriguing questions. With that in mind, the present project aims to elucidate fertilization processes in Decapodiformes by investigating both (1) the sperm-to-egg ratio and the spatial distribution of sperm along fresh egg capsules, and (2) the egg capsule structure in species with distinct egg capsule organizations (single vs. multiple eggs) and sperm storage locations (buccal membrane, mantle cavity, bursa copulatrix and nuchal pockets). For that, Idiosepius paradoxus, Heterololigo bleekeri, Sepiola birostrata and Watasenia scintillans egg masses will be collected and compared. Hoechst staining will be applied on fresh egg capsules to reveal possible sperm distribution patterns under UV light, and histological techniques will be applied to compare the fine structure of the egg capsule between species. We expect that the results will shed light on the peculiar fertilization mechanisms of this clade, and, ultimately, provide important insights into the evolution of fertilization in aquatic animals.