Killer whale predation on an Antarctic minke whale in the northern Antarctic Peninsula.

We describe the seldom observed event of a group of type A killer whale (Orcinus orca) predating on an Antarctic minke whale (Balaenoptera bonaerensis) in austral summer 2019. A pod of 11-13 individuals was observed - and documented by photographs and video - as they killed and fed on the minke whale in the Bransfield Strait, northern Antarctic Peninsula. The pod was being observed for about one hour, when some killer whale's individuals were noticed to be performing hunting behaviour. This lasted about 10 minutes, at the end of which the minke whale was killed. Three different species of seabirds were observed feeding on the minke carcass. A video of the encounter is provided.

Acoustic recording of false killer whale (Pseudorca crassidens) from Mexico (L).

This study collected acoustic information on false killer whales (Pseudorca crassidens) in Mexican waters, close to Roca Partida Island, Revillagigedo Archipelago. In total, 321 whistles were collected after we found a group with at least ten individuals. The high prevalence of ascending contour types [upsweep (type I): 42.99%] contradicted the idea that false killer whales mostly produce constant whistles. Lack of well-established reproducibility criteria for whistle type categorization among studies may have generated results different from those expected for signal modulation. Future acoustic and ecological studies should be conducted to help clarify these findings and expand the limited knowledge about this species.

Cetacean Morbillivirus Infection in a Killer Whale (Orcinus orca) from Brazil.

We provide pathological, immunohistochemical and molecular evidence of cetacean morbillivirus (CeMV) infection in a live-stranded adult female killer whale (Orcinus orca), which stranded alive in Espírito Santo State, Brazil, in 2014. Although attempts were made to release the animal, it stranded again and died. The main pathological findings were severe pulmonary oedema, pleural petechiation, multifocal, lymphoplasmacytic meningoencephalitis and leptomeningomyelitis with perivascular cuffing and gliosis, chronic lymphocytic bronchointerstitial pneumonia and multicentric lymph node and splenic lymphoid depletion. Other pathological findings were associated with the 'live-stranding stress response'. Immunohistochemical analysis revealed multifocal morbilliviral antigen in neurons and astrocytes, and in pneumocytes, histiocytes and leukocytes in the lung. CeMV was detected by a novel reverse transcriptase polymerase chain reaction method in the brain and kidney. Phylogenetic analysis of part of the morbillivirus phosphoprotein gene indicates that the virus is similar to the Guiana dolphin (Sotalia guianensis) morbillivirus strain, known to affect cetaceans along the coast of Brazil. To the authors' knowledge, this is the first report of morbillivirus disease in killer whales.

Osteochondromatosis (multiple cartilaginous exostoses) in an immature killer whale Orcinus orca.

An immature killer whale Orcinus orca found dead on the southeastern Brazilian coast had multiple bone proliferations: on the skull, vertebrae, hemal arches, and ribs. The bony formations were characterized as multiple osteochondromas, as defined by osteochondromatosis. The diagnosis was based on macroscopic and radiographic observations. These benign osseocartilaginous tumors affect young individuals and grow until skeletal maturity is achieved. Case reports of this condition, besides humans, include other mammals, with most reports for pets and domestic mammals such as cattle, and a report in a fossil canid (Hesperocyon) from the Oligocene. The etiology, diagnosis, developmental characteristics, and occurrence of osteochondromas are distinct among different species. This report describes the first case of multiple osteochondromas in a wild cetacean.

Imitation of novel conspecific and human speech sounds in the killer whale (Orcinus orca).

Vocal imitation is a hallmark of human spoken language, which, along with other advanced cognitive skills, has fuelled the evolution of human culture. Comparative evidence has revealed that although the ability to copy sounds from conspecifics is mostly uniquely human among primates, a few distantly related taxa of birds and mammals have also independently evolved this capacity. Remarkably, field observations of killer whales have documented the existence of group-differentiated vocal dialects that are often referred to as traditions or cultures and are hypothesized to be acquired non-genetically. Here we use a do-as-I-do paradigm to study the abilities of a killer whale to imitate novel sounds uttered by conspecific (vocal imitative learning) and human models (vocal mimicry). We found that the subject made recognizable copies of all familiar and novel conspecific and human sounds tested and did so relatively quickly (most during the first 10 trials and three in the first attempt). Our results lend support to the hypothesis that the vocal variants observed in natural populations of this species can be socially learned by imitation. The capacity for vocal imitation shown in this study may scaffold the natural vocal traditions of killer whales in the wild.

Revisão bibliográfica: comparação entre a coluna vertebral da orca (Orcinus orca) e do cavalo (Equus caballus) / Literature review: comparison between the vertebral column of the orca (Orcinus orca) and the horse (Equus caballus)

A coluna vertebral é constituída por conjuntos de vértebras conectadas por disco-intervertebrais, que se articulam pela articulação sinovial presente nos processos articulares. Devido a orca (Orcinus orca) e o cavalo (Equus caballus) habitarem ambientes diferentes, a formula vertebral difere numérica e morfologicamente. O objetivo desse trabalho consistiu em identificar diferenças morfológicas e características adaptativas nas colunas vertebrais de Orcinus orca e Equus caballus. A pesquisa foi realizada através de levantamento bibliográfico, descrevendo características como a quantidade, formato e características morfofuncionais adaptativas das vértebras de cada espécie. Foram consideradas referências bibliográficas que descreviam a evolução de cada espécie e artigos científicos relacionados à coluna vertebral de mamíferos aquáticos. Levantou-se que ambas espécies devem ter evoluído a partir de um único modelo de coluna vertebral ancestral, através de pressões ambientais seletivas diferenciais. A quantidade numérica de cada segmento que forma a coluna também mostrou diferenças entre O. orca e E. caballus, sendo que a fusão das cervicais de Atlas a C3 e o fusionamento de C4 a C7 foram as mais notáveis. A fórmula vertebral da Orcinus orca [C7, T11­13, L10­12, Ca20­24 = 50­54] e Equus caballus [C7, T18, L6, S5, Ca15-21 = 51-57] claramente corroboram a hipótese de origem a partir do modelo único.

The spine is composed of a set of vertebrae, connected by intervertebral discs. It is articulated through synovial joints present in the articular processes. Because the orca (Orcinus orca) and the horse (Equus caballus) evolved in different habitats, their vertebral formula differs numerically and morphologically. This study aimed to identify and compare morphological differences and adaptive features of the vertebral column of Orcinus orca and Equus caballus. Data was collected through a literature review on number of vertebrae, vertebral shape and morphofunctional adaptive characters for each subject species and related aquatic mammals. According to the literature, both species must have evolved from a single vertebral column morphological model under differential selective environmental pressures. The number of vertebrae per column segment also differs between O. orca and E. caballus, notably because of cervical vertebrae fusion from Atlas to C3 and C4 to C7. Comparing the vertebral formula of Orcinus orca C7, T11-13, L10-12, Ca20-24 = 50-54, and Equus caballus C7, T18, L6, S5, Ca15-21 = 51-57, clearly corroborates the single model hypothesis.

Killer whale (Orcinus orca) whistles from the western South Atlantic Ocean include high frequency signals.

Acoustic parameters of killer whale (Orcinus orca) whistles were described for the western South Atlantic Ocean and highlight the occurrence of high frequency whistles. Killer whale signals were recorded on December of 2012, when a pod of four individuals was observed harassing a group of sperm whales. The high frequency whistles were highly stereotyped and were modulated mostly at ultrasonic frequencies. Compared to other contour types, the high frequency whistles are characterized by higher bandwidths, shorter durations, fewer harmonics, and higher sweep rates. The results add to the knowledge of vocal behavior of this species.

Random Leslie matrices in population dynamics.

We generalize the concept of the population growth rate when a Leslie matrix has random elements (correlated or not), i.e., characterizing the disorder in the vital parameters. In general, we present a perturbative formalism to deal with linear non-negative random matrix difference equations, then the non-trivial effective eigenvalue of which defines the long-time asymptotic dynamics of the mean-value population vector state is presented as the effective growth rate. This effective eigenvalue is calculated from the smallest positive root of a secular polynomial. Analytical (exact and perturbative calculations) results are presented for several models of disorder. In particular, a 3 × 3 numerical example is applied to study the effective growth rate characterizing the long-time dynamics of a biological population model. The present analysis is a perturbative method for finding the effective growth rate in cases when the vital parameters may have negative covariances across populations.

The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru.

The modern giant sperm whale Physeter macrocephalus, one of the largest known predators, preys upon cephalopods at great depths. Lacking a functional upper dentition, it relies on suction for catching its prey; in contrast, several smaller Miocene sperm whales (Physeteroidea) have been interpreted as raptorial (versus suction) feeders, analogous to the modern killer whale Orcinus orca. Whereas very large physeteroid teeth have been discovered in various Miocene localities, associated diagnostic cranial remains have not been found so far. Here we report the discovery of a new giant sperm whale from the Middle Miocene of Peru (approximately 12-13 million years ago), Leviathan melvillei, described on the basis of a skull with teeth and mandible. With a 3-m-long head, very large upper and lower teeth (maximum diameter and length of 12 cm and greater than 36 cm, respectively), robust jaws and a temporal fossa considerably larger than in Physeter, this stem physeteroid represents one of the largest raptorial predators and, to our knowledge, the biggest tetrapod bite ever found. The appearance of gigantic raptorial sperm whales in the fossil record coincides with a phase of diversification and size-range increase of the baleen-bearing mysticetes in the Miocene. We propose that Leviathan fed mostly on high-energy content medium-size baleen whales. As a top predator, together with the contemporaneous giant shark Carcharocles megalodon, it probably had a profound impact on the structuring of Miocene marine communities. The development of a vast supracranial basin in Leviathan, extending on the rostrum as in Physeter, might indicate the presence of an enlarged spermaceti organ in the former that is not associated with deep diving or obligatory suction feeding.

Vulnerability of a killer whale social network to disease outbreaks.

Emerging infectious diseases are among the main threats to conservation of biological diversity. A crucial task facing epidemiologists is to predict the vulnerability of populations of endangered animals to disease outbreaks. In this context, the network structure of social interactions within animal populations may affect disease spreading. However, endangered animal populations are often small and to investigate the dynamics of small networks is a difficult task. Using network theory, we show that the social structure of an endangered population of mammal-eating killer whales is vulnerable to disease outbreaks. This feature was found to be a consequence of the combined effects of the topology and strength of social links among individuals. Our results uncover a serious challenge for conservation of the species and its ecosystem. In addition, this study shows that the network approach can be useful to study dynamical processes in very small networks.