Manatee
Research in Dr. Iske Larkin’s Laboratory
A descriptive analysis of Florida manatee (Trichechus manatus latirostris) embryology
The overall goal is to help us better understand embryological and fetal development of the endangered Florida manatee. By understanding normal development, we can better understand when problems in development lead to death in a calf during pregnancy or shortly after birth (i.e. neonatal and perinatal mortality).
The Florida Manatee, Trichechus manatus latirostris, is an aquatic mammal of the order Sirenia. Studies of manatee reproduction have thus far focused on natural history data such as gestation length, birthing interval, age at sexual maturity, and associated mating behavior. Little work has been done to focus on embryological and fetal development of the manatee. Understanding normal manatee embryological
development may provide critical information for understanding trends in early mortality, allowing us to differentiate between healthy and unhealthy states.
The long life and low reproductive rate of the Florida manatee makes it susceptible to population crashes when negative trends in reproduction occur. As pollutant levels rise in manatee habitats, the affect of toxins on growing embryos may become a factor in development. Decreases in the quality of manatee sea grass beds may impact manatee nutrition, thus affecting potential congenital defects of developing embryos and fetuses. A standard description of normal manatee development is needed to provide comparative data for healthy and unhealthy states. This data also provides a comparison among species in similar environments or which are evolutionarily related.
Behavioral and histological evaluation of the chemical senses of the Florida manatee, Trichechus manatus latirostris
This work is being conducted by Meghan Bills, a PhD student in Dr. Larkin and Dr. Samuelson’s laboratory
The Florida manatee has many interesting and unexpected traits including the apparent use of taste and smell. Although one would not expect an aquatic animal to be able to smell airborne scents, the manatee possesses the ability to do this. The question is whether or not this animal uses its ability to smell and taste to find a mate. It appears that a male manatee can find a female from far away, even though he cannot see or hear her. Manatees also are frequently seen “kissing” and “smelling” each other underwater and even at the surface. This leads us to believe that the female manatee is expressing a signal, most likely in urine, feces, or vaginal secretions, to the male manatee when she is ready to mate. To determine if this is true, we will use microscopic examination of the lips, hard palate, tongue, and nasal passages to find any receptors for these signals. The samples for these analyses will come from dead animals which were brought from all over the state of Florida to the Marine Mammal Pathobiology laboratory, in St. Petersburg, FL. No animals will be harmed for the purposes of this project. We will also determine the chemical composition of the female’s urine when they are reproductively active to find out what signals are being broadcast. Through these experiments the ability of the manatee to smell and taste will be further defined. We will also be able to find out more about their reproductive behavior through future studies using those chemicals isolated from the urine. Additionally, this will be the first in depth project examining the sense of taste and smell in an aquatic mammal and therefore will help in future studies involving other marine mammals.
Comparing fecal cortisol levels among captive West Indian manatees: Are they stressed?
This work is being conducted by Kyle Donnelly, an undergraduate student in Dr. Larkin’s laboratory
The effects of stress can be damaging to health, and this is of particular interest to West Indian manatees (Trichechus manatus) since the overall health of an endangered species is of the utmost concern to ensure their future. The primary stress hormone or glucocorticoid released by adrenocortical activity in all marine mammals is cortisol. We propose to non-invasively measure fecal cortisol concentrations to estimate the level of overall stress in captive manatees. In our pilot studies comparing captive and wild animals in Florida, we found captive animal fecal cortisol concentrations from a single facility were significantly higher. This trend also has been seen in studies comparing other species of captive and wild populations. We propose to determine how other manatee facilities compare with the known stressed facility, since our preliminary data cannot be generalized to other groups of captive manatees. Adrenocortical activity can be severely damaging to the health, reproduction, and welfare of animals if it is chronically elevated and not stopped or suppressed. Thus, the captive population of manatees will potentially benefit if this research reveals stressful environments that can be remedied. All captive manatees are part of a rehabilitation program and may be at differing stages of recovery, from medical treatment of injuries or disease to recuperation until the animal is either the appropriate age, weight or it is the correct time of year for release. Comparisons will be made between facilities, season, wild vs. captive manatees, and clinically healthy vs. unhealthy captive manatees. It is hoped that the results of this study will identify areas that need improvement and assist managerial decisions to enhance the condition of these captive environments to prevent or reduce any stress and suffering of future manatees housed in captive facilities.
Tracking Study – Studies of the Florida manatee reproductive cycle: Behavior and correlated hormones in free ranging animals
The Florida manatee is a unique herbivorous marine mammal, which can be observed in fresh and salt coastal waters throughout the state of Florida. This endangered species has captured the fascination of many people who come to Florida to watch these animals in their natural habitat. Threats to this species include collisions with boats, reduction or loss of habitat, pollution, entanglement in fishing gear and ingestion of debris leading to injury and often death. As wild populations are reduced, genetic variability may be lost and reproductive success may be compromised. In monitoring species, understanding reproductive rates is critical for modeling population numbers, and thus influences management decisions. Various factors can impact reproduction, including those with social and hormonal characteristics. Drs. Larkin and Schulte have been collaborating on studies of behavior and hormones for several years. Through our research, we have validated non-invasive fecal hormone assays, found that manatees are reproductively active throughout the warm months of the year, but are limited in the winter, and females have an estrous cycle that averages 24 ±5.4 days long. Manatees are found within our study area, Crystal River, Florida, throughout the year, and are composed primarily of mother-calf pairs and juvenile males during the warmer months. This provides an exceptional study site to focus on reproduction. In utilizing behavioral and physiological techniques in this study, a more complete and biologically relevant picture of manatee reproduction can be drawn, thus providing more accurate assessments of reproductive rates and means of saving this endangered species.
The goals of this study are to monitor the manatee reproductive cycle of three wild female manatees with second year calves. We will focus on calf weaning, the estrous cycle (mating), and early pregnancy. Behavioral and hormonal data will be collected to characterize normal baseline data of reproduction in this species. This will expand our knowledge of the real reproductive potential of female manatees and will in turn affect modeling of the population dynamics of the species. In addition, a clear understanding of the basic reproductive physiology of the manatee in a normal state will allow us to identify abnormal or unhealthy states. These critical aspects are needed to manage and help save this endangered species from extinction. We also plan to provide an educational experience for middle and high school students and teachers during field work to teach about manatee natural history, conservation and the scientific process. Students and teachers will be invited on our boat to observe manatee tracking and be asked questions about their knowledge at the beginning and again at the end of our trip, to identify the efficacy of our learning experience.
For more information please visit Dr. Larkin’s profile which contains contact information and the Publications page.
Histology Research in Dr. Samuelson’s Laboratory on the Florida manatee and other selected Paenungulate species
Individuals who have participated in our laboratories in ongoing research studies involving the Florida manatee and relatives over the past 12 months:
Don Samuelson, Jennifer McGee, Kimberly Goldbach, Kelly Cuthbert, Danielle Lore, Liesl Flandenmeyer, Michael Wong, Greg Reppas, Pat Lewis, Carolyn Valle, Ramiro Isaza, Esther Greenbarg, Mallorie McCormack, Nicole Helmers, Peter McGuire, Gil Ben-Shlomo, Kathleen Barrie.
The Nasolacrimal System
During the course of vertebrate evolution, the nasolacrimal system is believed to be developed among the first animals to become terrestrial. In doing so, the anterior portion of the eyes of these ‘land invaders’ were kept moistened so as to maintain corneal clarity as well as provide protection against potential microbial pathogens.
The nasolacrimal system of the Florida manatee and other members representing the three paenungulate (“near-ungulate”) orders, Hyracoidea, Proboscidea, and Sirenia, have been little understood. We have discovered that the Asian elephant (Elephas maximus), the rock hyrax (Procavia capensis), and the West Indian manatee (Trichecus manatus) do not form the
traditional nasolacrimal system as they lack lacrimal glands, lacrimal punctae, nasolacrimal ducts and the tarsal glands (Meibomian glands). Instead, these animals possess unusual nasolacrimal systems not previously encountered among mammalian species or other vertebrates for that matter.
The present study primarily involves anatomical examination of the nasolacrimal systems associated with the paenunugulate eye. The three orders that the present species represent have been ancestrally linked through both morphological and molecular evidence. To date, the evidence for the close phylogenetic relationship of the Sirenia, Proboscidea and Hyracoidea, which collectively form the clade Paenungulata, consists of a combination of similiarities across a wide breadth of characteristics, such as hemoglobin sequences, lens protein construction, mitochondrial rRNA sequences, as well as dental, taxepodial and other skeletal features. In spite of the variety of supporting findings, some of the morphological features have been questioned or refuted as being primitive or convergent. In the present study, the lack of traditional nasolacrimal systems in the Florida manatee, Asian elephant and rock hyrax strongly supports their common evolutionary origin. The absence of the lacrimal gland among terrestrial vertebrate spp is rare (snakes), especially among mammals. Its agenesis among humans is an extremely rare mutative event that involves a concomitant loss of salivary glands, but not a loss of the drainage puncta or other orbital glands. The loss of both lacrimal and tarsal glands as well as those components for tear drainage strongly suggests that the Paenungulata shared an aquatic past.
Fairly recently, embryological development of the renal, respiratory and male reproductive systems indicated that the elephant evolved originally from an aquatic or semi-aquatic ancestor. Comparable ontogenetic findings have yet to be made in the hyrax. Among nonmammals, the presence of sebaceous glands within the nictitating membrane is common. However, among mammals the Harderian gland becomes much more lacrimal in function, losing its sebaceous nature largely due to the formation of Meibomian glands. The different ways that sebum-forming glands were reformed so that an oily layer is able to cover the seromucous portion of tears of the Asian elephant and the rock hyrax most likely are the result of the different ecological pressures encountered during their subsequent evolution. A series of articles are presently being submitted to a variety of journals that detail the unique features of the re-evolved nasolacrimal systems of the three distantly related species and their shared past.
Associated publications:
Samuelson, D.A., Reppas, G., Lewis, P.A., Valle, C., and Isaza, R. The loss of the classic nasolacrimal system in the Florida manatee and other selected paenungulate species. Intern. Assoc. Aquat. Anim. Med. 38th Ann. Conf. 71-72, 2007.
Samuelson, D.A., Reppas, G., Wong, M., Lewis, P.A., Barrie, K.P. and Graham, A.R. Re-invented nasolacrimal system among selected subungulate species. Invest. Ophthalmol. Vis Sci. (ARVO Suppl.) 47:S1214, 2007.
Elephant 3rd eyelid gland H&E x20
The Conjunctival-Associated Lymphoid Tissue (CALT)
We have begun investigating in the Florida manatee the association of tears with their health. In addition to examining those structures involved in the production of tears, we have started to investigate the composition of tears, especially antimicrobial components and the cells that produce them. These components consist primarily of enzymes and antibodies that are formed by conjunctival-associated lymphatic tissue (CALT). Jennifer McGee, a PhD student who joined the Graduate Studies program at the College of Veterinary Medicine at the beginning of the Fall semester of 2007, has presented some of her findings on the CALT of the Florida manatee at the FMMH conference at St. Augustine, Florida. She presented a poster at that conference entitled “Morphological description of conjunctiva-associated lymphoid tissue (CALT) in the Florida manatee, Trichechus manatus latirostris.” She also attended the International Association for Aquatic Animal Medicine (IAAAM) conference, which was held from May 10-14th. To that end, two undergraduate students, Esther Greenbarg, and Danielle Lore, have begun to analyze histologically CALT and other portions of the accessory lymphatic system throughout the body known collectively as the mucous-associated lymphatic tissue (MALT) as well as lymph nodes and spleen, respectively.
Manatee eyelid accessory gland H&E x20
Manatee eyelid accesory gland duct surrounded by adenoid tissue H&E x100
Associated publications:
McGee, J.L., Samuelson, D.A., Lewis, P.A., Farina, L., and deWit, M. Morphological description of conjunctiva-associated lymphoid tissue (CALT) in the Florida manatee,Trichechus manatus latirostris. Fl. Mar. Mam. Health Conf. 3rd Conf. 34, 2008.
McGee, J.L., Samuelson, D.A., Lewis, P.A., Lore, D., Schwarz, E., Greenbarg, E. and Goldbach, K. Morphological and histochemical description of conjunctiva-associated lymphoid tissue (CALT) in the Florida manatee, Trichechus manatus latirostris. Intern. Assoc. Aquat. Anim. Med. 39th Ann. Conf. 19-20, 2008.
The Immune System
Over the last 12 months, we have had another graduate student join our study, Kimberly Goldbach, who is pursuing her M.S. degree. Kimberly is working with the undergraduate students, Esther Greenbarg, and Danielle Lore, who have been analyzing histologically, and immunohistochemically the lymph nodes and spleen, respectively. Kimberly is also presently working with another graduate student, Mallorie McCormack, on the thymus of the Florida manatee and associated changes during development and aging, especially with regard to involution. Selected specimens from normal appearing samples and those from individuals who had died from asepticemia, cold stress and red tide exposure continue to be viewed by light microscopy. Serial sections of the spleen and lymph nodes are being made in order to appreciate the architectural design of these structures. Special stains, including immunohistochemistry, will be employed in order to identify specific cell types.
Red Tide
In the past year, we have been investigating the presence of red tide in the Florida manatee. Red tides occur almost annually along the west coast of Florida, usually in the late summer and autumn. One of the main causes of the decline in the population is the exposure of the manatees to Florida “red tide” brevetoxins. Red tide is caused by periodic blooms of Karenia brevis, which is a single-celled dinoflagellate organism normally restricted to the Gulf of Mexico and the Caribbean, and is often referred to as an algae or phytoplankton. Each cell of these small organisms produces up to nine toxins, including a neurotoxin called brevetoxin, which can be fatal to fish, birds, and mammals. The most severe events occurred in 1971, 1973 to 1974, 1996, and 2005. Until recently, blooms had only been reported on the west coast of Florida, but harmful blooms were reported on the east coast in September of 2007 (FWRI 2007). Even though these red tide explosions have been observed since the sixteenth century, it is suspected that in recent years an increase in frequency and duration of blooms has been promoted by nutrients from coastal pollution.
Our initial goal was to demonstrate exposure of red tide in the Florida manatee by revealing the presence of the dinoflagellate within portions of the different organ systems of the Florida manatee by IHC. From this study we will examine specimens of all manatees that have been determined histopathologically to have died from red tide exposure. Specimens from other manatees collected from the same regions but determined to have died from other causes will be similarly analyzed. We hope to reveal possible associations that red tide exposure may have had with regard to increased mortality of the Florida manatee. To date, we have found localization of the organism in both the respiratory and gastrointestinal systems of the same animal. We have also been able to demonstrate the presence of K. brevis by IHC localization in all five individuals that died from red tide exposure. The localization was found, in part, to be similar to that previously observed for brevetoxin. It is hoped that an intensity distribution of the organism within these immune components can be established in order to shed light further on the impact of red tide on the Florida manatee.
IHC localization of K. brevis in the mandibular lymph node.
IHC localization of K. brevis in a Peyer’s patch of the small intestine.
Associated publications:
Samuelson, D., Flandenmeyer, L., Lewis, P., Helmers, N., McGee, J., and McGuire, P. Presence of red tide in the Florida manatee by immunohistochemical localization ofKarenia brevis. Intern. Assoc. Aquat. Anim. Med. 39th Ann. Conf. 69-71, 2008.
For more information please visit Dr. Samuelson’s profile which contains publication and contact information.
Manatee Sensory Sytems Research in Dr. Roger Reep’s Laboratory is located under Comparitive Neurological and Sensory Physiology.