Signature information and individual recognition in the isolation calls of Amazonian manatees,Trichechus inunguis (Mammalia: Sirenia)

Acoustic signals are assumed to form the basis of manatee communication. Empirical evidence of individual vocal recognition has been reported. If manatees can recognize one another by acoustical means, it should be possible to identify individual vocal patterns. We recorded vocalizations of 14 individually housed Amazonian manatees and then digitized selected vocalizations, allowing seven variables to be measured and subjected to multivariate statistical treatment. Discriminant function analysis indicated that individuals can be separated on the basis of variables related to the fundamental frequency and signal duration. We observed significant differences in the vocal patterns between sexes and age classes. Females tended to have greater fundamental frequency and shorter note duration than males. Calves had shorter note durations and greater values for the fundamental frequency range than subadults and adults. An inverse relationship between total body length and fundamental frequency range suggests that the fundamental frequency becomes more defined as the animal ages. The similar individual patterns in the vocalizations of a mother and calf pair are discussed. Individual recognition by Amazonian manatees according to their vocal patterns is suggested through a preliminary playback experiment.     

TLR4 and TLR8 variability in Amazonian and West Indian manatee species from Brazil

Amazonian (Trichechus inunguis) and West Indian (Trichechus manatus) manatees are aquatic mammals vulnerable to extinction found in the Amazon basin and the coastal western Atlantic. Toll-like receptors (TLR) play a key role in recognizing pathogen-associated molecular patterns using leucine-rich repeats (LRRs). We described the diversity of TLR4 and TLR8 genes in these two species of manatee. Amazonian manatee showed seven SNPs in TLR4 and the eight in TLR8, while West Indian manatee shared four and six of those SNPs, respectively. In our analysis, TLR4 showed one non-conservative amino acid replacement substitution in LRR7 and LRR8, on the other hand, TLR8 was less variable and showed only conserved amino acid substitutions. Selection analysis showed that only one TLR4 site was subjected to positive selection and none in TLR8. TLR4 in manatees did not show any evidence of convergent evolution compared to species of the cetacean lineage. Differences in TLR4 and TLR8 polymorphism may be related to distinct selection by pathogens, population reduction of West Indian manatees, or an expected consequence of population expansion in Amazonian manatees. Future studies combining pathogen association and TLR polymorphism may clarify possible roles of these genes and be used for conservation purposes of manatee species.     

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.     

MORBILLIVIRUS INFECTION IN MANATEES

The first evidence of exposure of free-ranging Florida manatees ( Trichechus manatees latirostris ) to a morbillivirus is reported. Blood samples were collected from 148 Florida manatees between 1977 and 1994. The sample included manatees that were under rehabilitation (n = 97), free-ranging (n = 40) and fresh necropsy specimens (n = 11). Serum from six animals (4%) neutralized porpoise and dolphin morbilliviruses to a higher titer than any other member of the Morbillivirus genus. Antibodies were not detected in sera from 12 free-ranging Antillean manatees ( T. manatus manatus ) from Guyana sampled in 1992 or from 12 hand-reared Amazonian manatees ( T. inunguis ) sampled in 1984. Immunoprecipitation studies using radio-labelled canine distemper virus protein and serum from Florida manatees showed precipitation of the nucleo-capsid (N) protein. The combination of low antibody titers and absence of clinical disease suggest that the Florida manatee is a dead-end host. Sporadic infection may occur following contact with another species in which infection is enzootic. Morbillivirus could, either by fatal infection or more insidious effects on the immune system or reproduction, pose a problem to this already threatened species.     

INFLUENCE OF POWER PLANTS AND OTHER WARM-WATER REFUGES ON FLORIDA MANATEES

Because of limited tolerance to cold, most Florida manatees survive cold winter periods by aggregating at warm‐water discharges from power plants and natural springs in central and northern Florida. Many power plants used by manatees may soon be retired. When this occurs, some people assume manatees will move to warmer areas in southern Florida; others fear they will stay near retired plants and sustain high levels of cold‐related deaths causing a decline in abundance. To assess these possibilities, we examine warm‐water habitats, population structure and movement, cold‐related deaths, and information on possible historical manatee distribution. Winter water temperatures even in southernmost Florida periodically fall below manatee tolerance levels. To survive such periods, manatees use two types of warm‐water refuges: warm‐water discharges, and passive thermal basins that cool slowly, thereby temporarily retaining warm temperatures. During the coldest periods, perhaps 60% of all manatees use 10 power plants and 15% use four natural springs; most others use thermal basins in southern Florida. Site fidelity to these refuges appears to be the principal factor segregating manatees into at least four subpopulations. Since 1986, rates of cold‐related deaths in southernmost Florida (10.0%) have exceeded those in areas with natural springs in central and northern Florida (8.8%). Our findings suggest that warm‐water springs in northern Florida offer better winter habitat than thermal basins in southern Florida and are better able to support large numbers of manatees. Although evidence is scant, we suggest that manatees historically overwintered principally at northern springs, but that Pre‐Columbian and European hunting restricted their winter range to southernmost Florida by the early 1900s. We also suggest that southernmost Florida may not be able to sustain a large influx of displaced of manatees in the absence of power plants, and that warm‐water springs in northern Florida should be considered the most important source of natural warm‐water habitat.     

Digesta passage rates in the Florida manatee (Trichechus manatus latirostris)

The Florida manatee, Trichechus manatus latirostris (Sirenia: Trichechidae), is an herbivorous marine mammal found within coastal areas throughout the state of Florida, which feeds on both fresh and salt water sea grasses. Manatees, like other Sirenians, are a tropical species with little tolerance for water temperatures below 20°C, rely on a relatively poor nutritional food source, and have a low metabolic rate. Although manatees are hindgut fermenting herbivores, they are very efficient at extracting nutrients from the plants on which they feed. Slow passage rates of digesta have been suggested to be a factor in this increased efficiency. Two studies monitored the digesta passage times and mixing of particulate digesta within the manatee digestive tract using MicroGrits colored corncob grit as a fecal marker. Fecal samples were collected subsequently from four manatees in Study 1 and 3 manatees in Study 2, grit pieces removed, counted, and measured. The digesta passage times ranged from 6 and 10 days in Study 1, and 4.3 and 8.3 days in Study 2, supporting data presented in previous studies. When two different colored markers were administered on sequential days, minimal to no mixing was seen in recovered feces, suggesting that the digesta from a given day traveled through the tract as a bolus. Less than 1% of the marker fed was recovered and we hypothesize that perpendicular folds of the large intestine may be the major contributing factor, with pieces being retained and eventually digested. Zoo Biol 26:503–515, 2007. © 2007 Wiley‐Liss, Inc.     

Activity patterns and spatial use of facility by a group of captive female manatees (Trichechus manatus latirostris)

As a means to compare and contrast to free‐ranging Florida manatees, we examined the behavior and movement patterns of nine adult‐female captive manatees at Homosassa Springs Wildlife State Park (HSWSP). HSWSP has a unique manatee exhibit that consists of a natural river and a man‐made pool. Because the manatees are exposed to a natural environment including natural food resources, the study of various aspects of behavioral and physiological parameters of the captive manatees is especially valuable with this group. We determined activity pattern and spatial use of the facility by manatees over three allotted periods of a day (noon, mid‐afternoon, and late‐afternoon) and three seasons (winter, spring, and summer). Behavioral strategies of the manatees were: 1) to remain “inactive,” probably to conserve energy, during the day while the park provisioned food; 2) to alter locations during the course of the afternoon, apparently with the direction of the sun, possibly to assist with thermoregulation; and 3) to change location seasonally where and when food resources became abundant, showing a strong interest in natural vegetation as it became available. Spatial use and activity pattern of the HSWSP captive manatees apparently were influenced by energy constraints and nutrient intake by provisioned food availability over the day and natural vegetation over the study period. The behavior of the female group of manatees may have been affected by the single‐sex living arrangement. In addition, these manatees are subject to a largely invariable temperature (ca. 23°C) that may have created thermal stress and immunological suppression over time. This study demonstrated that for these captive manatees the activity patterns and spatial use were comparable to that of free‐ranging manatees in relation to the availability of food resources. Zoo Biol 0:1–17, 2006. © 2006 Wiley‐Liss, Inc.     

Social interactions in captive female Florida manatees

The Florida manatee (Trichechus manatus latirostris) is considered a semi‐social species with strong bonds developed primarily between mother and offspring. Some field studies suggest sociality may be more developed and such social relationships may facilitate survival. Seven facilities in Florida house manatees, many of which were brought into captivity because of injury or illness sustained in the wild. Decisions to release such manatees consider individual history and health. We examined social interactions in adult female captive manatees to assess level of association and implications for manatee care and release. We investigated the degree of contact among 20 manatees in captivity at four facilities housing two to nine adult female manatees. We used all contact behavior occurrences sampling and continuous recording for 180 continuous minutes per day over 3 consecutive days at each facility. Virtually all contacts were non‐aggressive. The number of contacts between manatees increased as the number of manatees per unit volume of water increased. Contacts did not fit a Poisson distribution, however, and were not random. When more than two manatees were present, manatees only associated with a subset of individuals in the aquarium. Relationships maintained in captivity indicate the potentially social nature of manatees, and suggest that further research is needed to examine the benefit of these relationships to the health and rehabilitation of manatees in captivity and conservation in the wild. Zoo Biol 24:135–144, 2005. © 2005 Wiley‐Liss, Inc.     

Detection of hydrodynamic stimuli by the Florida manatee (Trichechus manatus latirostris)

Florida manatees inhabit the coastal and inland waters of the peninsular state. They have little difficulty navigating the turbid waterways, which often contain obstacles that they must circumnavigate. Anatomical and behavioral research suggests that the vibrissae and associated follicle–sinus complexes that manatees possess over their entire body form a sensory array system for detecting hydrodynamic stimuli analogous to the lateral line system of fish. This is consistent with data highlighting that manatees are tactile specialists, evidenced by their specialized facial morphology and use of their vibrissae during feeding and active investigation/manipulation of objects. Two Florida manatees were tested in a go/no-go procedure using a staircase method to assess their ability to detect low-frequency water movement. Hydrodynamic vibrations were created by a sinusoidally oscillating sphere that generated a dipole field at frequencies from 5 to 150 Hz, which are below the apparent functional hearing limit of the manatee. The manatees detected particle displacement of less than 1?μm for frequencies of 15–150 Hz and of less than a nanometer at 150 Hz. Restricting the facial vibrissae with various size mesh openings indicated that the specialized sensory hairs played an important role in the manatee’s exquisite tactile sensitivity.     

Polymorphic microsatellite DNA markers for the Florida manatee (Trichechus manatus latirostris)

Florida manatees (Trichechus manatus latirostris) are marine mammals that inhabit the coastal waters and rivers of the southeastern USA, primarily Florida. Previous studies have shown that Florida manatees have low mitochondrial DNA variability, suggesting that nuclear DNA loci are necessary for discriminatory analyses. Here we report 10 polymorphic microsatellite loci with an average of 4.2 alleles per locus, and average heterozygosity of 50.1%. These loci have been developed for use in population studies, parentage assignment, and individual identification.     

Alterations in blood and urine parameters in two florida manatees (Trichechus manatus latirostris) from simulated conditions of release following rehabilitation

In an effort to manage the existing population of the endangered Florida manatee (Trichechus manatus latirostris), as many individuals as possible are rehabilitated from illness or injury and released back into the waters of the state of Florida. It is not uncommon, however, for manatees recaptured for health assessment following release from rehabilitation to have elevated concentrations of serum creatinine. Although such elevated levels would be indicative of kidney failure in most other mammals, problems associated with renal function have not been evident in these recaptured manatees. To determine the possible cause(s) of the serum creatinine increase, two captive Florida manatees were manipulated to simulate many of the environmental and physical changes that occur during and shortly after release. Routine chemical analyses of serum and urine, complete blood counts, serum cortisol concentrations, and lymphocyte proliferation responses were measured. Serum creatinine concentrations increased significantly in response to decreased food intake and changes in food type. The increases differed depending on the salinity of the water in which the animals were maintained. It was found that significant changes in urinary creatinine and serum creatine kinase occurred as well, but serum cortisol concentrations were elevated only during simulated transport. Lymphocyte proliferation assays indicated that immune function was potentially impaired by extreme levels of dietary restriction and by changes in salinity. These results suggest that serum creatinine elevations and subsequent effects on the immune system might be minimized by adapting manatees undergoing rehabilitation to the diet and salinity they would encounter following release. Zoo Biol 22:103–120, 2003. © 2003 Wiley‐Liss, Inc.     

Behavioral response of manatees to variations in environmental sound levels

Florida manatees (Trichechus manatus latirostris) inhabit coastal regions because they feed on the aquatic vegetation that grows in shallow waters, which are the same areas where human activities are greatest. Noise produced from anthropogenic and natural sources has the potential to affect these animals by eliciting responses ranging from mild behavioral changes to extreme aversion. Sound levels were calculated from recordings made throughout behavioral observation periods. An information theoretic approach was used to investigate the relationship between behavior patterns and sound level. Results indicated that elevated sound levels affect manatee activity and are a function of behavioral state. The proportion of time manatees spent feeding and milling changed in response to sound level. When ambient sound levels were highest, more time was spent in the directed, goal‐oriented behavior of feeding, whereas less time was spent engaged in undirected behavior such as milling. This work illustrates how shifts in activity of individual manatees may be useful parameters for identifying impacts of noise on manatees and might inform population level effects.     

Movement patterns of Antillean manatees in Chetumal Bay (Mexico) and coastal Belize: A challenge for regional conservation

Information from 15 satellite‐tracked Antillean manatees (Trichechus manatus manatus) was analyzed in order to assess individual movements, home ranges, and high‐use areas for conservation decisions. Manatees were captured in Chetumal Bay, Mexico, and tagged with Argos‐monitored satellite transmitters. Location of the manatees and physical characteristics were assessed to describe habitat properties. Most manatees traveled to freshwater sources. The Maximum Area Size (MAS) for each manatee was determined using the observation‐area method. Additional kernel densities of 95% home range and 50% Center of Activity (COA) were also calculated, with manatees having 1–3 COAs. Manatees exhibited two different movement patterns: remaining in Chetumal Bay, and long‐distance (up to 240 km in 89 d). The residence time in Chetumal Bay was higher for females (89.6% of time) than for males (72.0%), but the daily travel rate (0.4–0.5 km/d) was similar for both sexes. Most of the COAs fell within Natural Protected Areas (NPA). However, manatees also travel for long distances into unprotected areas, where they face uncontrolled boat traffic, fishing activities, and habitat loss. Conservation of movement corridors may promote long‐distance movements and facilitate genetic exchange.     

Genetic diversity and spatial structure of the Rufous‐throated Antbird (Gymnopithys rufigula), an Amazonian obligate army‐ant follower

Amazonian understory antbirds are thought to be relatively sedentary and to have limited dispersal ability; they avoid crossing forest gaps, and even narrow roads through a forest may limit their territories. However, most evidence for sedentariness in antbirds comes from field observations and plot‐based recapture of adult individuals, which do not provide evidence for lack of genetic dispersal, as this often occurs through juveniles. In this study, we used microsatellite markers and mitochondrial control‐region sequences to investigate contemporary and infer historical patterns of genetic diversity and structure of the Rufous‐throated Antbird (Gymnopithys rufigula) within and between two large reserves in central Amazonia. Analyses based on microsatellites suggested two genetically distinct populations and asymmetrical gene flow between them. Within a population, we found a lack of genetic spatial autocorrelation, suggesting that genotypes are randomly distributed and that G. rufigula may disperse longer distances than expected for antbirds. Analyses based on mitochondrial sequences did not recover two clear genetic clusters corresponding to the two reserves and indicated the whole population of the Rufous‐throated Antbird in the region has been expanding over the last 50,000 years. Historical migration rates were low and symmetrical between the two reserves, but we found evidence for a recent unilateral increase in gene flow. Recent differentiation between individuals of the two reserves and a unilateral increase in gene flow suggest that recent urban expansion and habitat loss may be driving changes and threatening populations of Rufous‐throated Antbird in central Amazonia. As ecological traits and behavioral characteristics affect patterns of gene flow, comparative studies of other species with different behavior and ecological requirements will be necessary to better understand patterns of genetic dispersal and effects of urban expansion on Amazonian understory antbirds.     

Amazon fish bacterial communities show structural convergence along widespread hydrochemical gradients

The world's richest freshwater fish community thrives in gradients of contrasting environments in Amazonia, ranging from ion‐poor acidic black waters, to ion‐rich circumneutral white waters. These hydrochemical gradients structure Amazonian fish assemblages via ecological speciation events. Fish bacterial communities contain an important genetic heritage essential for their hosts' survival and are also involved in adaptive divergence via niche adaptation processes, but the extent to which they evolve in response to hydrochemical gradients in Amazonia is unknown. Here we investigated bacterial communities (gut and skin mucus) of two ecologically and phylogenetically divergent host species (Mesonauta festivus and Serrasalmus rhombeus) distributed throughout these hydrochemical gradients. The goal was to characterize intra‐ and interspecific Amazonian fish microbiome variations across multiple scales. Using a 16S metabarcoding approach, we investigated the microbiota of 43 wild M. festivus, 32 S. rhombeus and seven water samples, collected at seven sampling sites encompassing both water colours. Taxonomical structures of bacterial communities from both host species were significantly correlated to the environmental continua of magnesium, sodium, dissolved organic carbon, calcium, dissolved O₂, pH, potassium, hardness and chloride. Analysis of discriminating features in community structures across multiple scales demonstrated intra‐ and interspecific structural parallelisms in the response to the hydrochemical gradients. Together, these parallelisms suggest the action of selection on bacterial community structures along Amazonian hydrochemical gradients. Functional approaches along with reciprocal transplant experiments will provide further insights on the potential contribution of Amazonian fish microbiomes in host adaptation and ecological speciation events.     

The existence value of the Antillean manatee in the unprotected Hondo River (Mexico) as a fundamental component for its conservation

The Hondo River is the natural border between Mexico and Belize, and it is part of the distribution area of the Endangered Antillean manatee Trichechus manatus manatus. Currently, the Hondo River does not have any special protection. Employing qualitative research methods, we documented the social perception and local knowledge from riverside communities to assess conservation status and trends of manatees in the area. Fifty semi-structured interviews were carried out to river users in 16 Mexican communities, distributed in six segments along the riverbed. The claims of the inhabitants agree with boat-based surveys: most of the current and historical manatee sightings were reported in segments of the main watercourses, but also in small tributaries, which are usually shallow and rich in aquatic vegetation. Additionally, the local perception about manatee conservation status can be helpful to understand population trends and threats: 48 % of the interviewees claimed that nowadays the number of sighted manatees is less than that observed 10 years ago. The responders identified water pollution due to cane cultivation practices, motorized vessels traffic, and presence of fishing nets as potential threats to manatees. This study provides evidence of relevant local knowledge about the manatee ecology and its habitat, critical in the construction of binational conservation strategies for the species. Therefore, local resources users may play an increasingly significant role in manatee management and monitoring. Although manatees are poached for their meat in several areas of their distribution, the most common value attributed to manatees in Hondo River was non-use existence values. Local people recognize the challenges to observe this cryptic species in this river, but also identified manatees as potential flag species, suggesting that it may represent a valuable resource for ecotourism. We suggest that the non-extractive use of manatees has the potential for promoting species conservation and local economic growth.     

Phylogeography and Sex-Biased Dispersal across Riverine Manatee Populations (Trichechus inunguis and Trichechus manatus) in South America

Phylogeographic patterns and sex-biased dispersal were studied in riverine populations of West Indian (Trichechus manatus) and Amazonian manatees (T. inunguis) in South America, using 410bp D-loop (Control Region, Mitochondrial DNA) sequences and 15 nuclear microsatellite loci. This multi-locus approach was key to disentangle complex patterns of gene flow among populations. D-loop analyses revealed population structuring among all Colombian rivers for T. manatus, while microsatellite data suggested no structure. Two main populations of T. inunguis separating the Colombian and Peruvian Amazon were supported by analysis of the D-loop and microsatellite data. Overall, we provide molecular evidence for differences in dispersal patterns between sexes, demonstrating male-biased gene flow dispersal in riverine manatees. These results are in contrast with previously reported levels of population structure shown by microsatellite data in marine manatee populations, revealing low habitat restrictions to gene flow in riverine habitats, and more significant dispersal limitations for males in marine environments.     

Pelagic to demersal transition in a coral‐reef fish,the orbicular batfish Platax orbicularis

Behavioural and ecological observations were made on young, reared Platax orbicularis in Opunohu Bay, Moorea, French Polynesia, during their transition from the pelagic, dispersive stage to the reef‐orientated demersal stage. Seventy‐two young P. orbicularis (17–75 mm standard length, L_S) were released in the pelagic zone and 20 (40–70 mm L_S) adjacent to the reefs. Swimming speed was slow (mean 5·2 cm s^?1) and independent of size. An ontogenetic descent was observed: the smallest P. orbicularis swam at the surface, medium‐sized P. orbicularis swam in midwater (mean 5–13 m) and the largest P. orbicularis swam to the bottom, where many lay on their sides. Platax orbicularis swam southerly on average, away from the ocean and into the bay. Smaller P. orbicularis were more likely to swim directionally than larger individuals. Young P. orbicularis released near reef edges swam at similar, but more variable speeds (mean 6·6 cm s^?1). About half of those released near reefs swam away, but fewer swam away from an inshore fringing reef than from a patch reef near the bay mouth. Many P. orbicularis swam up the slope onto the reef top, but the little settlement observed was near the reef base. Average, near‐reef swimming direction was also southerly. Some reef residents, in particular the triggerfish Balistapus undulatus, harassed young P. orbicularis.     

Thrust reversal by tubular mastigonemes: immunological evidence for a role of mastigonemes in forward motion of zoospores ofPhytophthora cinnamomi

Summary The role of tubular mastigonemes in the reversal of thrust of the anterior flagellum ofPhytophthora cinnamomi was analysed using mastigoneme-specific monoclonal antibodies and immunoflu-orescence and video microscopy. Exposure of live zoospores ofP. cinnamomi to the mastigoneme-specific Zg antibodies caused alterations in the arrangement of mastigonemes on the flagellar surface and at Zg concentrations above 0.3 /ml, mastigonemes became detached from the flagellum. As a consequence of antibody binding to the mastigonemes there were concentration-dependent perturbations in zoospore swimming behaviour and anterior flagellum beat pattern. With increasing antibody concentration zoospores swam more slowly and other parameters of their swimming pattern, such as the wavelength of the swimming helix and the frequency of rotation, were also reduced. The effects of Zg antibodies were specific at two levels: control immunoglobulins or antibodies that bound to other flagellar surface components did not have an effect on motility, and Zg antibodies did not interfere with the motility of zoospores of oomycete species to which they did not bind. The effects of antibody-induced disruption of mastigoneme arrangement strongly support previous hypotheses that tubular mastigonemes are responsible for thrust reversal by the anterior flagellum, enabling it to pull the cell through the surrounding medium.