Desenvolvimento embrionário de Podocnemis expansa (Testudines: Podocnemididae): descrição do pronefro e mesonefro e diferenciação gonadal em ambiente natural, Balbina, Amazonas
This study aimed to describe embryo, pronephros and mesonephros development, gonadal differentiation and to evaluate the thermosensitive period (TSP) in Podocnemis expansa in the natural environment. To do so, ten nests of P. expansa were randomly selected on an artificial beach in Balbina, Amazo...
| Autor principal: | Magalhães, Marcela dos Santos |
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| Grau: | Tese |
| Idioma: | por |
| Publicado em: |
Instituto Nacional de Pesquisas da Amazônia - INPA
2020
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| Assuntos: | |
| Acesso em linha: |
https://repositorio.inpa.gov.br/handle/1/11491 http://lattes.cnpq.br/4377486940988870 |
| Resumo: |
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This study aimed to describe embryo, pronephros and mesonephros development,
gonadal differentiation and to evaluate the thermosensitive period (TSP) in Podocnemis
expansa in the natural environment. To do so, ten nests of P. expansa were randomly
selected on an artificial beach in Balbina, Amazonas, and embryos were collected daily
throughout the incubation period. Macroscopic analyzes were carried out with the aid of
a stereoscope, light microscopy with paraffin and paraplast inclusion, and staining with
Hematoxylin and Eosin, in addition to analyses by transmission and scanning electron
microscopy, and immunohistochemistry for cytochrome P450 aromatase. The
thermosensitive period (TSP) of embryonic development for gender determination was
calculated based on the reaction norm for embryonic growth. The incubation period was
58 to 64 days, with a mean nest incubation temperature of 30.3°C. The main
characteristics used to describe and compare embryonic development were: eye
development, mandibular process, limbs, carapace and plastron. Based on the
descriptions, 26 stages were proposed for P. expansa. Throughout embryonic
development of P. expansa, the pronephros was first visualized on the 5th day of
development, composed of external glomeruli that are devoid of a capsule and protrude
into the coelomic cavity and internally composed of a network of capillaries. The
pronephros was already degenerated at 23 days of development. The first indication of
mesonephros appearance occurred around the 7th day of incubation by the onset of the
renal corpuscle formation. The mesonephros is composed by the renal corpuscles, neck
segment, proximal tubule, distal tubule, intermediate segment, collecting tubule and
collecting duct. From the 20th day, a significant increase in the width and number of
glomeruli of the mesonephros can be observed and a continuous decrease of these
parameters is observed from the 40th day onwards, indicating degeneration. The TSP
ranged between the 24th and the 42nd day of incubation in nest 4, and between the 32nd
and the 51 st day of incubation in nest 1 . Regarding gonadal development, primordial
germ cells (PGCs) were only visualized from the 5th day of incubation when they were
observed in the yolk sac, and it was possible to observe the migration of PGCs from the
vitelline sac toward the ventromedial region of the presumptive mesonephros wall
(genital crest region) between days 5 and 10 of incubation. On the 14th day, the PGCs
were established in the ventromedial region of the mesonephros, initiating formation of
the undifferentiated gonad with two distinct regions being identified; the external
cortical region characterized by the presence of PGCs, and the inner medullary region
where the primitive sexual cords were present. From day 35 of incubation, it was
possible to more clearly identify the organization of the gonad into testis through light
microscopy, while ovary differentiation was observed at 36 days of incubation. Low
aromatase immunoreactivity was observed in the gonads and mesonephros at 33 days.
The marking intensified after the beginning of the TSP and gonadal differentiation. At
45 days, the ovaries presented heavily marked epithelium lining and interstitial tissue,
whereas this positive marking in the testicles was restricted to the interstitial cells
between the seminiferous tubules. The time of appearance and disappearance of the
structures in P. expansa was generally more advanced than in other species of
chelonians during embryonic development in the natural environment. Pronephros
lasted approximately 13 days with functional characteristics, even if for a short period,
while the mesonephros was the embryonic kidney and remained functional even after
hatching. TSP started after the onset of the middle third and ended only in the last third
of development, while the onset of testicular differentiation did not vary significantly in
relation to the ovaries. |