Some studies on blood of the Florida manatee, Trichechus manatus latirostris

Ancestral chromosomal signatures of Paenungulata (Afroteria) reveal the karyotype of Amazonian manatee (Trichechus inunguis, Sirenia: Trichechidae) as the oldest among American manatees

BACKGROUND

Chromosomal painting in manatees has clarified questions about the rapid evolution of sirenians within the Paenungulata clade. Further cytogenetic studies in Afrotherian species may provide information about their evolutionary dynamics, revealing important insights into the ancestral karyotype in the clade representatives. The karyotype of Trichechus inunguis (TIN, Amazonian manatee) was investigated by chromosome painting, using probes from Trichechus manatus latirostris (TML, Florida manatee) to analyze the homeologies between these sirenians.

RESULTS

A high similarity was found between these species, with 31 homologous segments in TIN, nineteen of which are whole autosomes, besides the X and Y sex chromosomes. Four chromosomes from TML (4, 6, 8, and 9) resulted in two hybridization signals, totaling eight acrocentrics in the TIN karyotype. This study confirmed in TIN the chromosomal associations of Homo sapiens (HSA) shared in Afrotheria, such as the 5/21 synteny, and in the Paenungulata clade with the syntenies HSA 2/3, 8/22, and 18/19, in addition to the absence of HSA 4/8 common in eutherian ancestral karyotype (EAK).

CONCLUSIONS

TIN shares more conserved chromosomal signals with the Paenungulata Ancestral Karyotype (APK, 2n = 58) than Procavia capensis (Hyracoidea), Loxodonta africana (Proboscidea) and TML (Sirenia), where TML presents less conserved signals with APK, demonstrating that its karyotype is the most derived among the representatives of Paenungulata. The chromosomal changes that evolved from APK to the T. manatus and T. inunguis karyotypes (7 and 4 changes, respectively) are more substantial within the Trichechus genus compared to other paenungulates. Among these species, T. inunguis presents conserved traits of APK in the American manatee genus. Consequently, the karyotype of T. manatus is more derived than that of T. inunguis.

Blood Reference Intervals for Antillean Manatees (Trichechus manatus manatus) from Puerto Rico

Antillean manatees (Trichechus manatus manatus) are endangered throughout the southwestern Gulf of Mexico, the Caribbean coast of Central and South America, the Greater Antilles, and the northeastern coast of South America to Brazil. Establishing blood reference intervals is essential as a tool in classifying health status, diagnosing, establishing treatment regimens, and monitoring the progress of a disease in rescued manatees. We collected blood samples from 44 free-ranging and 26 rescued manatees from Puerto Rico between 1992 and 2020 for hematology and blood chemistry analysis. We obtained values for white blood cell count and red blood cell count, hemoglobin, hematocrit, platelet, mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration, and red cell distribution width. A manual leukocyte differential allowed for the evaluation of different cell types. In addition, we performed a comprehensive metabolic panel on serum samples. These analytes were grouped based on six physiologic processes: liver-associated enzymes and pigments; muscle-associated enzymes; kidney-associated compounds and products; sugars, lipids, and pancreatic-associated enzymes; proteins; and electrolytes. For every parameter, summary statistics of values were calculated on all the samples. Reference ranges were determined as ±1 standard deviation around the mean. An unpaired two-sample T-test was done comparing males versus females and adults versus calves for any significant differences (p ≤ 0.05). We establish the reference intervals of hematology and blood chemistry for the population of Antillean manatees in Puerto Rico and compare them with those established for manatees from Belize, Brazil, Florida, Guyana, and Mexico.

Karyotypical Confirmation of Natural Hybridization between Two Manatee Species, Trichechus manatus and Trichechus inunguis

Two species of manatees are found in Northern Brazil—the Antillean manatee (Trichechus manatus), which is found along the coast from Florida to Northeastern Brazil, and the Amazonian manatee (Trichechus inunguis), endemic to the Amazon drainage basin. These species show a sympatric distribution in the region of the Marajó Archipelago, an estuarine area surrounding the Amazon River mouth. There is evidence of the occurrence of interspecific hybrids in this area, based on mitochondrial DNA analyses, although the use of nuclear markers has not corroborated this proposal. Considering that these species show very distinct karyotypes, despite being closely related (2n = 48 in T. manatus and 2n = 56 in T. inunguis), hybrids would present distinct chromosome numbers. Based on this, we conducted cytogenetic analyses using classic and molecular techniques in three calves found stranded in the Marajó Island and Amapá coast. The results showed that one of them, morphologically classified as T. inunguis, presented the correspondent karyotype, with 2n = 56. However, the other two, which were phenotypically similar to T. manatus, showed 2n = 49. Despite the same diploid number, their G-banding patterns revealed some differences. The results of the distribution of some microsatellite sequences have also confirmed the heterozygosity of some chromosomal pairs in these two individuals. These results are the first indubitable confirmation of the occurrence of natural hybrids between T. manatus and T. inunguis, and also brings about some issues concerning the viability of hybrids, considering that these two individuals do not correspond to an F1 hybrid, but instead, both presented a possible F2 karyotype.

Emergence of a Chimeric Globin Pseudogene and Increased Hemoglobin Oxygen Affinity Underlie the Evolution of Aquatic Specializations in Sirenia

As limits on O₂ availability during submergence impose severe constraints on aerobic respiration, the oxygen binding globin proteins of marine mammals are expected to have evolved under strong evolutionary pressures during their land-to-sea transition. Here, we address this question for the order Sirenia by retrieving, annotating, and performing detailed selection analyses on the globin repertoire of the extinct Steller’s sea cow (Hydrodamalis gigas), dugong (Dugong dugon), and Florida manatee (Trichechus manatus latirostris) in relation to their closest living terrestrial relatives (elephants and hyraxes). These analyses indicate most loci experienced elevated nucleotide substitution rates during their transition to a fully aquatic lifestyle. While most of these genes evolved under neutrality or strong purifying selection, the rate of nonsynonymous/synonymous replacements increased in two genes (Hbz-T1 and Hba-T1) that encode the α-type chains of hemoglobin (Hb) during each stage of life. Notably, the relaxed evolution of Hba-T1 is temporally coupled with the emergence of a chimeric pseudogene (Hba-T2/Hbq-ps) that contributed to the tandemly linked Hba-T1 of stem sirenians via interparalog gene conversion. Functional tests on recombinant Hb proteins from extant and ancestral sirenians further revealed that the molecular remodeling of Hba-T1 coincided with increased Hb–O₂ affinity in early sirenians. Available evidence suggests that this trait evolved to maximize O₂ extraction from finite lung stores and suppress tissue O₂ offloading, thereby facilitating the low metabolic intensities of extant sirenians. In contrast, the derived reduction in Hb–O₂ affinity in (sub)Arctic Steller’s sea cows is consistent with fueling increased thermogenesis by these once colossal marine herbivores.

Hematology of healthy Florida manatees (Trichechus manatus)

BACKGROUND

Hematologic analysis is an important tool in evaluating the general health status of free-ranging manatees and in the diagnosis and monitoring of rehabilitating animals.

OBJECTIVES

The purpose of this study was to evaluate diagnostically important hematologic analytes in healthy manatees (Trichechus manatus) and to assess variations with respect to location (free ranging vs captive), age class (small calves, large calves, subadults, and adults), and gender.

METHODS

Blood was collected from 55 free-ranging and 63 captive healthy manatees. Most analytes were measured using a CELL-DYN 3500R; automated reticulocytes were measured with an ADVIA 120. Standard manual methods were used for differential leukocyte counts, reticulocyte and Heinz body counts, and plasma protein and fibrinogen concentrations.

RESULTS

Rouleaux, slight polychromasia, stomatocytosis, and low numbers of schistocytes and nucleated RBCs (NRBCs) were seen often in stained blood films. Manual reticulocyte counts were higher than automated reticulocyte counts. Heinz bodies were present in erythrocytes of most manatees. Compared with free-ranging manatees, captive animals had slightly lower MCV, MCH, and eosinophil counts and slightly higher heterophil and NRBC counts, and fibrinogen concentration. Total leukocyte, heterophil, and monocyte counts tended to be lower in adults than in younger animals. Small calves tended to have higher reticulocyte counts and NRBC counts than older animals.

CONCLUSIONS

Hematologic findings were generally similar between captive and free-ranging manatees. Higher manual reticulocyte counts suggest the ADVIA detects only reticulocytes containing large amounts of RNA. Higher reticulocyte and NRBC counts in young calves probably reflect an increased rate of erythropoiesis compared with older animals.

Chromosome painting in the manatee supports Afrotheria and Paenungulata

BACKGROUND

Sirenia (manatees, dugongs and Stellar's sea cow) have no evolutionary relationship with other marine mammals, despite similarities in adaptations and body shape. Recent phylogenomic results place Sirenia in Afrotheria and with elephants and rock hyraxes in Paenungulata. Sirenia and Hyracoidea are the two afrotherian orders as yet unstudied by comparative molecular cytogenetics. Here we report on the chromosome painting of the Florida manatee.

RESULTS

The human autosomal and X chromosome paints delimited a total of 44 homologous segments in the manatee genome. The synteny of nine of the 22 human autosomal chromosomes (4, 5, 6, 9, 11, 14, 17, 18 and 20) and the X chromosome were found intact in the manatee. The syntenies of other human chromosomes were disrupted in the manatee genome into two to five segments. The hybridization pattern revealed that 20 (15 unique) associations of human chromosome segments are found in the manatee genome: 1/15, 1/19, 2/3 (twice), 3/7 (twice), 3/13, 3/21, 5/21, 7/16, 8/22, 10/12 (twice), 11/20, 12/22 (three times), 14/15, 16/19 and 18/19.

CONCLUSION

There are five derived chromosome traits that strongly link elephants with manatees in Tethytheria and give implicit support to Paenungulata: the associations 2/3, 3/13, 8/22, 18/19 and the loss of the ancestral eutherian 4/8 association. It would be useful to test these conclusions with chromosome painting in hyraxes. The manatee chromosome painting data confirm that the associations 1/19 and 5/21 phylogenetically link afrotherian species and show that Afrotheria is a natural clade. The association 10/12/22 is also ubiquitous in Afrotheria (clade I), present in Laurasiatheria (clade IV), only partially present in Xenarthra (10/12, clade II) and absent in Euarchontoglires (clade III). If Afrotheria is basal to eutherians, this association could be part of the ancestral eutherian karyotype. If afrotherians are not at the root of the eutherian tree, then the 10/12/22 association could be one of a suite of derived associations linking afrotherian taxa.

A study of manatee leukocytes using peroxidase stain

Leukocytes of the manatee, dog, cat, horse, rabbit, bird, and human were stained with modified Wright-Giemsa stain and myeloperoxidase stain. The predominant segmented leukocyte of the manatee stained positive for myeloperoxidase in a manner similar to the human, dog, cat, and horse neutrophil. Rabbit and bird heterophils stained unlike the manatee predominant leukocyte with myeloperoxidase stain. Eosinophils of all species examined also stained differently from the predominant manatee leukocyte. We conclude that the predominant segmented cell type of the manatee is not biochemically similar to the heterophil of the bird and rabbit or to the eosinophil of the human, dog, cat, horse, bird, and rabbit.

Renal anatomy of the manatee, Trichechus manatus, Linnaeus

The manatee kidney is composed of several closely apposed lobes. These are formed by cortical folds (plicae corticales) that completely isolate the medullae, except where the medullae of adjacent lobes are partially fused. The cortex is continuous; its folds usually are separated, but only partially, by interlobar septa extending from the renal capsule. The cortex makes up approximately 57% of renal mass in adults and 68% in the calf. There are about 3 million glomeruli per kidney. The average is somewhat less than that expected of an adult eutherian of equal mass. The glomeruli, however, are large; they form 7.38% +/- 1.33 of cortical mass, which is above that for at least ten unrelated adult eutherians. The number of glomeruli per gram of cortex is considerably greater in the calf than in the adult. The medullae are about 43% of renal mass. The cortico-medullary thickness ratio is 0.08 to 0.24. All terminal collecting ducts open at a crater (cratera cribrosa) of varying depth. Hair-pin loops occur at all levels of medulla, and apparently all loops bend at their thick segment. Cortical loops occur in the medullary rays. Vascular bundles were evident at the cortico-medullary border and thin tubules extended into the medulla from the central ends of the medullary rays (cortical) in seven out of the nine kidneys. The renal pelvis is separated from the central ends of the cortical folds by delicate fascia through which pass the interlobar vessels. There are no fornices and no infundibula. The collagenous tissue of the pelvic wall extends across most of the pelvic surface of the outer medulla.

Heart rates and gas exchange in the Amazonian manatee (Trichechus inunguis) in relation to diving

Unrestrained Amazonian manatees (Trichechus inunguis) maintained a constant heart rate during diving and exhibited a slight tachycardia during breathing. 'Forcing' the manatees to dive caused a marked bradycardia. They exhibited a more pronounced tachycardia during breathing after 'forced' dives and hyperventilated during recovery dives. Manatees are capable of dives exceeding 10 min duration without having to resport to anaerobic metabolism, and even after 10 min dives recover within 3-4 short dives. The ability of manatees to make long dives, in spite of relatively poor O2 stores, is due to their low metabolic rate, while the rapid recovery is aided by their high CO2 stores which minimizes CO2 storage in the body. In manatees the changes in alveolar O2 and CO2 pressure (PAO2 and PACO2) in relation to dive time are slower and more variable than in other marine mammals. The lower rate of change is probably due to the manatees' reduced metabolic rate, while the greater variability is due to their breathing pattern, in which both ventilation and body gas stores influence alveolar gases.

Oxygen affinity of sea turtle blood

The oxygen binding properties of whole blood in adult sea turtles (green, Chelonia mydas; loggerhead, Caretta caretta) were measured as a function of pH, and carbon dioxide partial pressure using the 'Hemoscan Oxygen Dissociation Analyser' with modifications that improved the performance of the method. Under approximately physiological conditions (25.7 degrees C, PCO2 = 37 Torr; pH 7.45) there is a marked affinity difference between the two species (green, P50 = 29 Torr; loggerhead, 47 Torr). It is suggested that the large affinity difference between blood of green and loggerhead turtles may be related to differences in depths to which they typically dive. The Hill coefficient at 50% saturation is 2.4 in the green under these conditions, and 2.7 in loggerhead. Hill plots of both species curve upward and have significant regions with n approaching 1 at low saturation with the effect that the lower end of the binding curve is more hyperbolic than sigmoidal. The fixed acid and CO2 Bohr effects in both species are strongly saturation dependent, being very low at low saturation and increasing markedly at higher saturation. The fixed acid Bohr effects are similar in the two species but the green is more sensitive to CO2, at constant pH, and so has a larger CO2 Bohr effect. The hyperbolic shape of the lower end of the binding curves, and low pH sensitivity in this region, would tend to favor oxygen loading during a dive, when lung PO2 and blood pH are falling. These properties might therefore favor more complete utilization of the lung oxygen store. We suggest that diving vertebrates can usefully be divided into two groups, those that use the lung as the main oxygen stores and those that use tissue (blood and myoglobin) stores.

Hematology of the West Indian Manatee (Trichechus manatus)

Hemograms on blood obtained from 10 clinically normal West Indian Manatees (Trichechus manatus) were studied. The red cells were large and in lower number than in most terrestrial species. The manatee does not have a neutrophil as is present in most species, but it has a heterophil whose granules stain pink with the Wright-Giemsa stain. The eosinophil has uniform red-staining granules that make its differentiation from heterophils difficult. Both large and small lymphocytes, monocytes and basophils are present. The total number of white blood cells was comparable to that of common domestic species as were the platelet numbers. No reticulocytes were found.