Ontogenia dos ossos do esqueleto da tartaruga-da-amazônia Podocnemis expansa Schweigger, 1812 (Testudines, Podocnemididae)

Abstract

CHAPTER 2: The freshwater turtle Podocnemis expansa is found all over the Amazon basin and appears in almost all of its tributaries. The vertebrate skeleton is composed of cartilage and bone and represents the cell product of three different embryonic lineages. The cranium is formed by cells of the neural crest. Knowledge of the biological criterion for the sequence of bone formation is of highest importance for the understanding of ontogeny. Thus, the purpose of the present study was to establish normal stages of the formation and ossification sequence of the bony elements of the cranium in P. expansa, in the different stages of pre and post natal development. Embryos and nestlings were collected as from the 18th day of natural incubation. Morphometics occurred and the embryos were submitted to the diaphanous (clearing) technique and coloring of the bones. Neurocranium: in stage 19 the basisphenoid and basioccipital present the ossification center; in stage 20 the supraoccipital and opisthotic, in stage 21 the exoccipital and only in stage 24 the prootic. Dermatocranium: the squamosal, pterygoid and maxilla are the first elements to begin the ossification process, which occurs in stage 16. But most of these bone elements present ossification centers in stage 17, they are: frontal, jugal, postorbital, parietal, premaxilla, prefrontal, followed by the palatine and quadratojugal in stage 19 and last of all the vomer in stage 25. The esplancnocranium quadrate, in stage 23. Ossification of the mandible and hyoid apparatus: as much the dentary, coronoid and the surangular present ossification centers in stage 16 and the branchial body I in stage 17. The sequence and synchronization of the ossification in P. expansa show similarities, as well as differences, when compared with other chelonian species. It is evident that more quantitative studies are necessary to document the natural variability of formation of the bones. CHAPTER 3: The scleral ossicles are small bony plates located in the eyeball of many vertebrates and differ in their morphology, development and position within different groups of vertebrates. With the objective of investigating the development, number form and disposition of the scleral ossicles, in Podocnemis expansa 15 embryos were collected, as from the 18th day of natural incubation and 16 adult specimens, belonging to the LAPAS, from which the eyeballs were removed.The embryos and the eyeballs were submitted to the diafanization (Clearing) technique and coloration of the bones. On found out that the scleral ossicles, in Testudines species, have a square form, vary from 10 to 13 with 11,25 ± 0,93 and 11,43 ± 0,81, in the right eye and in the left eye, respectively, and they occupy a set position close to the front border of the sclera. The ossicles develop in an intramembranous form and begin to present ossification centers in stage 21, with ten ossification centers in the right eye and eight in the left eye. In stage 23, all ossicles of the sclerotic ring increase in length and approach the adjacent ossicles, forming a ring. In stage 26 the scleral ossicles have already presented themselves in the definitive disposition. CHAPTER 4: With the objective of investigating the formation sequence of the bony elements which form the spine, in the different stages of pre and post natal development in Podocnemis expansa, embryos and nestlings were collected, as from the 18th day of natural incubation. Morphometrics occurred and the embryos and nestlings were submitted to the diafanization and coloration technique of the bones and cartilages. The P. expansa spine comprises eight cervical vertebras, ten back vertebras, two sacral vertebras and twenty tale vertebras. In stage 15 the vertebras are still constituted by cartilage. In stage 17 the cartilage begins to be substituted by bone, and this takes place in the cranium-tail direction. In stage 19 all the back vertebras present ossification centers, as well as the two sacral vertebras. As from stage 20 the tail vertebras begin to present ossification centers. CHAPTER 5: Brazil has the richest fauna in all of Central and South America, but most of the information about reptiles is still incomplete. Podocnemis expansa, known popularly as the giant Amazon river turtle, is widely distributed through the basin of the Amazon and its tributaries. To investigate the sequence of the formation of the bone elements comprising the carapace in the various stages of pre- and postnatal development in P. expansa, embryos and newborns were collected, starting from the 18th day of natural incubation. Biometric measurements were taken and the embryos were subjected to the clearing technique and to bone and cartilage staining. The carapace is composed of 8 pairs of costal bones, 11pairs ribs, 7 neural bones, 11 pairs of peripheral bones, 1 nuchal bone that is part of the cranial portion of the carapace, 1 suprapigal bone, and 1 pigal bone that forms the caudal part of the carapace. In stage 16, ossification centers are present in the first seven pairs of ribs. In stage 17, the last pair of ribs begins to ossify. The bone expansions in the more cranial ribs begin in stage 19. The neural bones begin to ossify in stage 20, followed by the nuchal bone in stage 21. The first pair of peripheral bones presents ossification centers in stage 23, while the ossification process in the suprapigal and pigal scutes begins in stage 26. The bones that form the rigid armor of the carapace only begin to come together 46 days after hatching. CHAPTER 6: The Podocnemis expansa is known popularly as the giant Amazon river turtle and is considered one of the wild species more exploited most in zoo technology. With the objective of investigating the formation sequence of the bony elements which form the plastron/breastplate, in the different pre and post natal development stages, embryos and nestlings were collected, as from the 18th day of natural incubation. Morphometrics occurred and the embryos and nestlings were submitted to the diafanization and coloration technique of bones and cartilages. The epiplastron, endoplastron, hioplastron, hipoplastron, xifiplastron and the mesoplastron bones form the breastplate of these turtles. In stage 16 ossification centers are observed in the great majority of the breastplate bones. With regard to the retention of the alizarin the sequence is: first the hioplastron and the hipoplastron, then the endoplastron, followed by the xifiplastron and lastly the mesoplastron. The epiplastron bone showns itself with ossification center in stage 20 only. All these elements have independent ossification centers and they join together later. The closing of the breastplate only takes place seven months after hatching. CHAPTER 7: With the objective of investigating the sequence of bone formation of the breast bone and thoracic member, in the different stages of development be they pre or post natal Podocnemis expansa, embryos and newly born nestlings were collected, as from the 18th day of natural incubation. Morphometrics occurred and the embryos and nestlings were submitted to the diafanization and coloration technique of bones and cartilages. The arm skeleton (stylopodium) is composed by the humerus bone and the forearm skeleton (zeugopodium) consists of two bones, the ulna and the radius. The hand skeleton (autopodium) is formed by the following bones: carpus ulnare (UC), carpus central 2 (C2), carpus central 3 (C3), distal carpus bones (DCI, DCII, DCIII, DCIV and DCV), carpus pisiform (PC), intermediate carpus bone (IC), 5 metacarpus bones (MCI, MCII, MCIII, MCIV and MCV) and 14 phalanges, two in the first finger and three in each one of the other fingers, whose phalanx formula is 2:3:3:3:3. In stage 19, the scapula, the acromion and coracoid process already show ossification centers. In stage 16, ossification centers were observed in the humerus bone, followed by the ulna bone and, finally, the radius bone. In stage 23, the IC presents an ossification center, in stage 24, the whole distal row presented ossification centers, except for DC V. Still in that stage ossification centers were also verified in UC, CII and CIII. Only DCV showed ossification centers at the beginning of stage 25. PC is only seen 40 days after hatching. Retention of the stain in the metacarpi occurs in the following order: M III > M II = M IV > M I > M V. In stage 20, it is evident that, in all the metacarpi, the ossification centers progress in the direction of the epiphyses. The sequence of stain retention in the distal phalanges (DP) occurs in the order: DP III > DP II > DP IV > DP I > DP V. In the medial phalanges (MP), the stain retention sequence is: MP III > MP IV > MP II > MP V. Lastly, the proximal phalanges (PP) retain staining in the following sequence: PP I > PP III > PP IV > PP II > PP V. The differences and similarities in the synchronization of ossification of Podocnemis expansa and comparable species are evident. Thus, there is no osteogenetic pattern common to all chelonians, due to variations in the initial site of bone formation and the sequence of ossification. CHAPTER 8: With objective of investigating the sequence of bone formation of the pelvic girdle and pelvic members, in the different stages of pre and post-natal development in Podocnemis expansa, embryos and nestlings, as from the 18th day of natural incubation, were collected. Morphometrics took place and the embryos were submitted to the diafanization technique with coloration of bones and cartilages. The stylopodium area is composed by the femur bone, the zeugopodim consists of two bones, tibia and fibula and the autopodium is formed by the following bones: intermedium of tarso (IT), fibulare of tarso (FT), centrale of tarso (CT), distal bones of tarso (DTI, DTII, DT III and DTIV), 5 metatarsos (MtI, MtII, MtIII, MtIV and MtV) and 14 phalanges, two in the fifth finger and three in each one of the other fingers, whose phalange formula is 3:3:3:3:2. In stage 16 the femur, tibia and fibula present ossification centers in the diaphysis progressing from the epiphysis. In stage 19, the bones of the pelvic waist line show ossification centers. In the tarsal bones the DT I is the first to present ossification centers, at the beginning of stage 24, proceeding with IT, later CT and DT II at the end of stage 24, DT III and DT IV in stage 25. FT shows ossification center in the last embryonic stage, which is stage 26. Retention of the stain in the metatarsal occurs in the following order: M III > M II = M IV > M V > M I. In stage 20, it is evident that, in all the metatarsal, the ossification centers progress in the direction of the epiphyses. The sequence of stain retention in the distal phalanges (DP) occurs in the order: DP V > DP IV > DP III > DP II >DP I. In the medial phalanges (MP), the stain retention sequence is: MP III > MP IV > MP II > MP I. Lastly, the proximal phalanges (PP) retain staining in the following sequence: PP V > PP I > PP II > PP III > PP IV. The differences and similarities in the synchronization of ossification of Podocnemis expansa and comparable species are evident. Thus, there is no osteogenetic pattern common to all chelonians, due to variations in the initial site of bone formation and the sequence of ossification.