A macroscopic classification of the embryonic development of the one-sided livebearer Jenynsia multidentata (Teleostei: Anablepidae)

Abstract

This study proposes eight stages according to the main discernible changes recorded throughout the embryonic development of Jenynsia multidentata. The development of morphological embryo structures, pigmentation, and changes in tissues connecting mother and embryo were included in the stage characterization. From the fertilized egg (Stage 1), an embryo reaches the intermediary stages when presenting yolk syncytial layer (Stage 2), initial pigmentation of the outer layers of the retina and dorsal region of the head (Stage 3), and the sprouting of the caudal (Stage 4), dorsal and anal fins (Stage 5). During the later stages, the ovarian folds enter the gills, and the body pigmentation becomes more intense (Stage 6), the body becomes elongated (Stage 7), and there is a greater intensity in body pigmentation and increased muscle mass (Stage 8).The dry weight of the batches varied between 0.6 ± 0.3 mg (Stage 3) to 54.6 ± 19.7 mg (Stage 8), but the dry weight of the maternal-embryonic connecting tissues remained almost constant. After controlling the effect of those reproductive tissues, the gain in dry weight of the batches throughout development increased exponentially from Stage 6, reflecting the increase in size and weight of the embryos due to matrotrophy.Keywords: Developmental stages, Dry weight, Matrotrophy, Morphology, Viviparity.Este estudio propone una clasificación constituida por ocho etapas, establecidas con base en los principales cambios macroscópicos registrados a lo largo del desarrollo embrionario de Jenynsia multidentata. El desarrollo de estructuras embrionarias, los patrones de pigmentación y los cambios en los tejidos de conexión entre la madre y el embrión fueron incluidos en la caracterización de cada etapa. Inicia con el huevo fertilizado (Etapa 1), siguiendo con etapas intermedias del embrión en las cuales es visible la capa sincitial del vitelo (Etapa 2), la pigmentación inicial de las capas externas de la retina y el dorso de la cabeza (Etapa 3), y la aparición de las aletas caudal (Etapa 4), dorsal y anal (Etapa 5). En las etapas posteriores, los pliegues del tejido ovárico se introducen por las branquias y se intensifica la pigmentación corporal (Etapa 6), el cuerpo se extiende (Etapa 7) y hay un marcado aumento en la pigmentación corporal y masa muscular (Etapa 8). El peso seco de los lotes varió entre 0,6 ± 0,3 mg (Etapa 3) y 54,6 ± 19,7 mg (Etapa 8); sin embargo, el peso seco del tejido que conecta a la madre con el embrión se mantuvo prácticamente constante. Después de controlar el efecto del peso seco de estos tejidos, la ganancia de peso seco de los lotes de embriones a lo largo del desarrollo aumentó de forma exponencial a partir de la Etapa 6, evidenciándose en el aumento en tamaño y peso de los embriones debido a la matrotrofia.Palabras clave: Etapas del desarrollo, Matrotrofia, Morfología, Peso seco, Viviparidad.

Ovarian changes and development of the branchial placenta occurring in Jenynsia lineata (Cyprinodontiformes, Anablepidae)

“…While prior studies have mentioned the presence of a branchial placenta of J. lineata and describe some morphological aspects (Schindler & de Vries, 1988;Turner, 1940;Wourms et al, 1988), this is the first work where its morphology is analyzed in conjunction with histochemical changes and cell proliferation. The current study revealed the presence of the branchial placenta in ovaries corresponding to gestational stages 6-8 (López-Rodríguez et al, 2017). In each of them, ovarian branches were observed to penetrate the embryonic opercular clefts in apposition with the developing gill, forming a branchial placenta.…”

“…In the 15 ovaries observed in pregnant females, the entire ovarian lumen was found dilated and occupied by 10–21 embryos, arranged parallel to the longitudinal axis of the organ. All embryos were assigned to gestational stages 6–8 according to López‐Rodríguez et al (2017). Therefore, the ovarian follicles were observed only in the cephalic portion and were characterized by being scarce, small in size, and found in the first stages of follicular development.…”

“…The latter species was used in this work because it is a major animal model for toxicology experiments and is widely distributed in temperate and shallow waters of our region (Ringuelet et al, 1967). The genus Jenynsia is characterized by eggs with little yolk, which in the case of J. lineata is resorbed when embryos are 6 mm long (Schindler & Hamlett, 1993;Turner, 1947;Wourms, 1981), which corresponds to gestational stage 4 according to López-Rodríguez et al (2017). Therefore, maternally derived nutrients would continue embryonic nutrition for the remainder of gestation, implying exclusive matrotrophic nutrition.…”

“…The genus Jenynsia is characterized by eggs with little yolk, which in the case of J . lineata is resorbed when embryos are 6 mm long (Schindler & Hamlett, 1993; Turner, 1947; Wourms, 1981), which corresponds to gestational stage 4 according to López‐Rodríguez et al (2017). Therefore, maternally derived nutrients would continue embryonic nutrition for the remainder of gestation, implying exclusive matrotrophic nutrition.…”

“…Scale bar: 100 µm, H&E. Blood vessels (BV); lumen (L); luminal epithelium (Le); lamina propria-submucosa (Lp-Sm); melanomacrophage centers (MMCs); ovarian follicles (Oc); ovarian folds (OF); previtellogenic follicles (POc); tunica mucosa (TM); tunica muscularis (TMu); tunica serosa (TS); vitellogenic follicles (VOc); cephalic portion (green arrow); caudal portion (black arrow).parallel to the longitudinal axis of the organ. All embryos were assigned to gestational stages 6-8 according toLópez-Rodríguez et al (2017). Therefore, the ovarian follicles were observed only in the cephalic portion and were characterized by being scarce, small in size, and found in the first stages of follicular development.…”