Abstract
Male alliances are an intriguing phenomenon in the context of reproduction since, in most taxa, males compete over an indivisible resource, female fertilization. Adult male bottlenose ...dolphins (Tursiops aduncus) in Shark Bay, Western Australia, form long-term, multilevel alliances to sequester estrus females. These alliances are therefore critical to male reproductive success. Yet, the long-term processes leading to the formation of such complex social bonds are still poorly understood. To identify the criteria by which male dolphins form social bonds with other males, we adopted a long-term approach by investigating the ontogeny of alliance formation. We followed the individual careers of 59 males for 14 years while they transitioned from adolescence (8–14 years of age) to adulthood (15–21 years old). Analyzing their genetic relationships and social associations in both age groups, we found that the vast majority of social bonds present in adolescence persisted through time. Male associations in early life predict alliance partners as adults. Kinship patterns explained associations during adolescence but not during adulthood. Instead, adult males associated with males of similar age. Our findings suggest that social bonds among peers, rather than kinship, play a central role in the development of adult male polyadic cooperation in dolphins.
Multilevel cooperation in adult male bottlenose dolphins is based on friendships that are formed among similarly aged males during their adolescence. Although cooperative behaviors in many animals are found among relatives, this is not the case in dolphins. Our findings reveal the existence of enduring friendships in a complex marine mammal society, similar to those that have been described in many primate species including humans.
Bottlenose dolphins (Tursiops truncatus) are one of the most popular dolphin species housed in aquaria in Japan. Previous studies have demonstrated that respiratory infections, mainly caused by ...bacteria and occasionally fungi, are one of the most common diseases in this species. Both Candida spp. and Aspergillus spp. are the most important species as the cause of respiratory fungal infections for this species in Japan. Since these fungi are ubiquitous in the environment surrounding dolphins and aquaria, and the spores may scatter easily in their habitats (poolside), it is very difficult to remove these fungi from their habitats. Therefore, in aquaria in Japan, preventing respiratory fungal infections and treating these infections appropriately in this species including in pregnant and lactating animals and their calves are necessary to maintain the health and number of the current population; this approach must also be applied for respiratory bacterial infections. In this review, to gain a better understanding regarding respiratory fungal infections in this species, the current status of these infections and results of clinical studies in the Port of Nagoya Public Aquarium (PNPA) are described. Moreover, future issues that have been revealed as a result of treating these infections in this species including in pregnant and lactating animals and their calves in the PNPA and that need to be solved are described.
The quantity and quality of individual social relationships is a fundamental feature of social structure for group-living species. In many species, individuals preferentially associate with close ...relatives, which can amplify social benefits through inclusive fitness. Reproductive variation, dispersal and other factors may nevertheless impact relative kin availability, especially for species with slow life histories. As such, variation in family size can affect the social integration of the individual. Here, we investigated the effects of family size on female sociality in a population of Indo-Pacific bottlenose dolphins, Tursiops aduncus, in Shark Bay, Australia. This population exhibits high fission–fusion dynamics, with females varying widely in gregariousness and both sexes remaining philopatric, providing females with both matrilineal and nonmatrilineal kin as potential associates. We used genetic relatedness data obtained from a large single nucleotide polymorphism (SNP) panel and a spatially explicit null model to measure females' propensities to form affiliations with both related and unrelated individuals. We found that females had strong social preferences for matrilineal close (first, second and third degree) kin, but also significant preferences for nonmatrilineal close and more distant kin compared to unrelated individuals. Despite these preferences, we found only small effects of kin availability on individual social position. Stronger and more consistent effects were attributable to individual foraging ecology, although much of the variation remains unexplained. Overall, our models suggest that while female dolphins have strong kin preferences, their social connectivity is not determined by family size; rather, individual foraging strategies and high fission–fusion dynamics enable a diverse repertoire of social strategies to coexist within a population.
•We investigated effects of family size on female sociability in Tursiops aduncus.•Females had strong social preferences for matrilineal and nonmatrilineal kin.•Matrilineal close kin had small effects on number of affiliations and centrality.•Number of kin had no effect on affiliations with unrelated individuals.•Family size explained only a small amount of variation in female sociability.
Epigenetic age estimation has the potential to influence conservation approaches for wildlife. DNA extracted from a small skin sample can be analyzed for methylation changes, which can be related to ...chronological age through an epigenetic clock to obtain a DNA-based age estimate (DNAm age). For a wide range of cetacean species, skin samples can be obtained remotely using dart biopsy. We tested multiple modeling approaches (elastic net regression, random forest regression, and a hybrid of elastic net and random forest classification) using DNA methylation data from 426 skin samples from observed-age wild bottlenose dolphins (Tursiops spp.), and 50 managed care dolphins, to develop an epigenetic clock. The hybrid model gave highly accurate age predictions for calf (<2 yrs., n = 28), subadult (2–15 yrs., n = 273) and adult (15–25 yrs., n = 110) age classes with median absolute errors (MAE) of 0.149, 1.46 and 3.25 yrs., respectively. In the oldest individuals (>25 yrs., n = 65), age predictions were less accurate, with MAE of 5.90 yrs. The overall MAE across all ages (n = 476) was 1.91 yrs. DNAm age has been linked to health in humans, with higher age residuals (i.e., higher DNAm age as compared to actual age) being associated with increased risk of morbidity and mortality. We compared dolphin age residuals with previously reported health scores that are predictive of one year mortality risk. Our findings suggest that analysis of DNA methylation patterns is a viable approach, not only for estimating age of dolphins, but potentially also to assess individual and population health.
Small-scale fisheries represent an economically marginalized sector, that struggles to balance operational costs and profit from catches. Economic revenues from catches have declined due to ...overfishing, and additional costs may jeopardise the sustainability of the sector. In Greece, reported net damage from interaction with marine megafauna, especially the bottlenose dolphin (Tursiops truncatus) is a common occurrence for many coastal areas, where small-scale fisheries operate. A seasonal experimental trial took place during 2016–2017 in the northern Aegean Sea, in an area where large actively swimming marine organisms other than dolphins were lacking. Three gangs of different panels of net (mixed gill nets and trammel nets) were deployed in three different depth zones. For each gang, we recorded the number, size, and position of holes on each net, and assessed overall damage. Multifactor analysis was used to identify possible links between fishing practices and damage intensity. Results showed a correlation between reduced net damage by dolphins with larger mesh sizes and increasing depth. In the case of small mesh sizes, one should seek a combination of solutions, as changes in deployment depths alone, do not seem to be adequate for the depth ranges studied. The adoption of larger than 22 mm mesh size is proposed for all set nets, to increase net selectivity and decrease accumulated damage. Fishers should focus on adjusting, substituting or even ceasing specific fishing tactics to have the lowest possible economic loss, whereas fisheries scientists, managers and policy makers must monitor and offer guidance for this transition.
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•A set net selectivity experimental design for dolphin interaction studies.•A proper combination of mesh size and depth could limit dolphin interaction.•Small mesh sizes deployed within the 60 m depth contour remain vulnerable.•Mesh sizes smaller than 22 mm (bar length) should be avoided.
•Discovery of the first pegivirus sequenced from a cetacean species.•Dolphin pegivirus is a new species within the genus Pegivirus, family Flaviviridae.•Potential role of dolphin pegivirus in hepatic ...disease in bottlenose dolphins.
We report the discovery of the first cetacean pegivirus (family Flaviviridae) using a next-generation sequencing approach. One of two infected bottlenose dolphins had elevated activities of liver enzymes, which may suggest hepatocellular injury. Further research is needed to determine the epidemiology and pathogenicity of dolphin pegivirus.
The coexistence of sympatric species with similar ecological requirements involves niche partitioning via interspecific differences in resource use and behaviour. Behavioural patterns of coexisting ...species can also be indicative of the functions of interspecific interactions, including those between species that form mixed-species groups. Here, we used Markov chain analysis applied to behavioural focal follow data of Australian humpback, Sousa sahulensis (hereafter ‘humpback dolphins’) and Indo-Pacific bottlenose dolphins, Tursiops aduncus (hereafter ‘bottlenose dolphins’) observed around the North West Cape, Western Australia, to investigate potential behavioural coexistence mechanisms and the functions of their mixed-species groups. During six austral winter (April to October) field seasons (2013–2015, 2018–2019 and 2021), we recorded 560 dolphin sightings from which we obtained 562 sequences of behavioural transitions: 222 humpback dolphin single-species sequences, 262 bottlenose dolphin single-species sequences and 78 mixed-species sequences. Humpback dolphins spent more time travelling in addition to having higher transition probabilities towards travelling and longer bout lengths of travelling, while bottlenose dolphins spent more time foraging and had longer foraging bouts. These behavioural patterns indicate that humpback and bottlenose dolphins differ in their use of the study area. In particular, they suggest interspecific temporal differences in foraging behaviour, which may facilitate coexistence. When in mixed-species groups, humpback and bottlenose dolphins altered their behavioural patterns by exhibiting higher transition probabilities towards socializing and increasing time spent socializing, suggesting that their mixed-species groups may have a social function. Overall, our results indicate that behavioural differences may play an important role in facilitating the coexistence of sympatric delphinids and that social benefits may be a key driver of the formation of mixed-species groups.
•Behaviour indicates coexistence mechanisms and functions of mixed-species groups.•We used Markov chain analysis of humpback and bottlenose dolphin focal follow data.•We compared behavioural transitions, bout lengths, budgets and cumulative budgets.•Temporal differences in foraging reduce competition and facilitate coexistence.•Increased socializing in mixed-species groups supports social advantage hypothesis.
Although the presence of Brucella spp. in the western Pacific has been suggested by epidemiological studies on cetaceans, it has not been confirmed by bacterial isolation. Here, for the first time, ...we report that a marine Brucella strain was isolated in the western Pacific from a bottlenose dolphin with osteomyelitis. The isolate from the lesion was confirmed to be B. ceti of sequence type 27 by multilocus sequence typing and Bruce-ladder PCR. Infrequent-restriction-site PCR and omp2 gene sequencing revealed that molecular characteristics of this isolate were similar to those of Brucella DNA previously detected from minke whales in the western North Pacific. These results suggest that genetically related Brucella strains circulate in cetacean species in this region.
Polychlorinated biphenyls (PCBs), chlorinated pesticides (i.e., dichlorodiphenyltrichloroethane (DDT) and its metabolites, chlordanes (CHLs), dieldrin, hexachlorobenzene (HCB), and mirex), ...polybrominated diphenyl ethers (PBDEs), perfluorinated chemicals (PFCs), and polyaromatic hydrocarbons (PAHs) were measured in blubber biopsy samples collected from 139 wild bottlenose dolphins (
Tursiops truncatus) during 2003–2005 in Charleston (CHS), SC and the Indian River Lagoon (IRL), FL. Dolphins accumulated a similar suite of contaminants with ∑
PCB dominating (CHS 64%, IRL 72%), followed by ∑
DDT (CHS 20%, IRL 17%), ∑
CHLs (CHS 7%; IRL 7%), ∑
PBDE (CHS 4%, IRL 2%), PAH at 2%, and dieldrin, PFCs and mirex each 1% or less. Together ∑
PCB and ∑
DDT concentrations contributed ∼
87% of the total POCs measured in blubber of adult males. ∑
PCBs in adult male dolphins exceed the established PCB threshold of 17
mg/kg by a 5-fold order of magnitude with a 15-fold increase for many animals; 88% of the dolphins exceed this threshold. For male dolphins, CHS (93,980
ng/g lipid) had a higher ∑
PCBs geomean compared to the IRL (79,752
ng/g lipid) although not statistically different. In adult males, the PBDE geometric mean concentration was significantly higher in CHS (5920
ng/g lipid) than the IRL (1487
ng/g). Blubber ∑
PFCs concentrations were significantly higher in CHS dolphins. In addition to differences in concentration of PCB congeners, ∑
PBDE, TEQ, ∑
CHLs, mirex, dieldrin, and the ratios ∑
DDE/∑DDT and trans-nonachlor/cis-nonachlor were the most informative for discriminating contaminant loads in these two dolphin populations. Collectively, the current ∑
PCB, ∑
DDT, and ∑
PBDEs blubber concentrations found in CHS dolphins are among the highest reported values in marine mammals. Both dolphin populations, particularly those in CHS, carry a suite of organic chemicals at or above the level where adverse effects have been reported in wildlife, humans, and laboratory animals warranting further examination of the potential adverse effects of these exposures.
Electric boats are thought to be noiseless, but in-situ measurements are generally rare. The Underwater Radiated Noise (URN) of 8-m Trimaran Pontoon Boat with two outboard electric engines was ...measured in the Miramare Marine Protected Area (Trieste, Italy), together with the URN of a fibreglass 5-m boat, with a outboard gasoline engine, for comparisons. International standards and guidelines for shallow waters were considered. URN were provided in one-third octave band and in narrow band spectra. The electric boat produced a low input of underwater noise at low frequencies. Given a low-frequency hearing sensitivity, the listening space reduction (LSR) was lower when generated by the electric than by combustion engine boat for the brown meagre, a local Teleost fish. No difference was found for the bottlenose dolphin LSR although continuous, tonal, high frequency components generated by the electric boat are expected to be highly detrimental for the bottlenose dolphin.
•Underwater Radiated Noises of an electric vsnon-electric boats were provided.•Electric boat had a reduced anthropogenic footprint at low frequencies.•Electric boat caused a small listening space reduction in the brown meagre.•Electric boat noise showed intense high-frequency tonal components.•Electric boat tonal components can be detrimental for the bottlenose dolphin.
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