Int. J. Dev. Biol. 65: 323 - 332 (2021)

https://doi.org/10.1387/ijdb.200157fo

Vol 65, Issue 4-5-6

Special Issue: Developmental Biology in Ibero-America - Part 2

The “Mexican dancer” in Ecuador: molecular confirmation, embryology and planktotrophy in the sea slug Elysia diomedea

Published: 26 August 2020

Lola Moreano-Arrobo¹, Oscar D. Pérez^1,2,3, Federico D. Brown^2,3, Fernanda X. Oyarzún*^,4,5,6 and Cristian B. Canales-Aguirre^6,7

¹Laboratorio de Biología del Desarrollo 113, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Ecuador, ²Departamento de Zoología. Instituto de Biociências, Universidade de Sao Paulo, Brazil, ³Centro de Biologia Marinha (CEBIMAR), Universidade de São Paulo, Brazil, ⁴Centro de Investigación en Biodiversidad y Ambientes Sustentables (CIBAS), Universidad Católica de la Santísima Concepción, Concepción, Chile, ⁵Departamento de Ecología, Universidad Católica de la Santísima de Concepción, Concepción, Chile, ⁶Centro i~mar, Universidad de Los Lagos, Puerto Montt, Chile and ⁷Núcleo Milenio de Salmónidos Invasores (INVASAL), Concepción, Chile

Abstract

Elysia diomedea, otherwise known as the “Mexican dancer”, aries in adult size and color across its geographical distribution in Ecuador. Because of morphological variation and the absence of genetic information for this species in Ecuador, we analyzed mtDNA sequences in three populations (Ballenita, La Cabuya, and Mompiche) and confirmed that individuals from the three locations belonged to E. diomedea and that there was no population structure that could explain their morphological differences. Next, we analyzed general aspects about the reproductive biology and embryology of this species. Live slugs from the Ballenita population were maintained and reproduced ex situ. Egg ribbons and embryos were fixed and observed by brightfield and confocal microscopy. We observed a single embryo per capsule, 98 embryos per mm² of egg ribbon, and compared the cleavage pattern of this species to that of other heterobranchs and spiralians. E. diomedea early development was characterized by a slight unequal first cleavage, occurrence of a 3-cell stage in the second cleavage, and the formation of an enlarged second quartet of micromeres. We observed clear yolk bodies in the egg capsules of some eggs ribbons at early stages of development. Both reproductive and embryological characteristics, such as presence of stomodeum in the larva, and ingestion of particles after hatching confirmed the planktotrophic veliger larvae of this species, consistent with the majority of sacoglossans from the Eastern and Northeast Pacific Oceans.

Keywords

extra-zygotic yolk (EZY), spiral cleavage, reproductive mode, Sacoglossa