Minke whales maximise energy storage on their feeding grounds.

Seasonal trends in energy storage of the minke whale (Balaenoptera acutorostrata), a capital breeder, were investigated in Iceland, a North Atlantic feeding ground. The aim was to better understand the energy acquisition strategies of minke whales and the energetic costs that different reproductive classes face during the breeding season. We modelled total blubber volume, using blubber thickness and morphometric measurements of individual whales. Blubber volume was influenced by body length, and was higher for pregnant females than mature whales. Blubber volume increased linearly through the feeding season at the same rate for mature (mean ± s.e.m.=0.0028 ± 0.00103 m(3) day(-1); N=61 male, 5 female) and pregnant whales (0.0024 ± 0.00100 m(3) day(-1); N=49), suggesting that minke whales aim to maximise energy storage while on the feeding grounds. The total amount of blubber accumulated over the feeding season (0.51 ± 0.119 m(3) for mature and 0.43 ± 0.112 m(3) for pregnant whales), together with energy stored as muscle and intra-abdominal fats, constitutes the total amount of energy available for reproduction (fetus development and lactation) on the breeding grounds, as well as migration, daily field metabolic rates, growth and body maintenance. No seasonal variation was observed for immature whales (N=4 male, 12 female), suggesting that they are investing most of their excess energy into growth rather than reproduction, in order to reach the length of sexual maturity faster and start reproducing earlier. Our novel modelling approach provides insight into large whale bioenergetics and life history strategies, as well as the relationship between single-site measurement of blubber thickness and total blubber volume.

Structure and steroidogenesis of the placenta in the Antarctic minke whale (Balaenoptera bonaerensis).

There are few reports describing the structure and function of the whale placenta with the advance of pregnancy. In this study, therefore, the placenta and nonpregnant uterus of the Antarctic minke whale were observed morphologically and immunohistochemically. Placentas and nonpregnant uteri were collected from the 15th, 16th and 18th Japanese Whale Research Programme with Special Permit in the Antarctic (JARPA) and 1st JARPA II organized by the Institute of Cetacean Research in Tokyo, Japan. In the macro- and microscopic observations, the placenta of the Antarctic minke whale was a diffuse and epitheliochorial placenta. The chorion was interdigitated to the endometrium by primary, secondary and tertiary villi, which contained no specialized trophoblast cells such as binucleate cells, and the interdigitation became complicated with the progress of gestation. Furthermore, fetal and maternal blood vessels indented deeply into the trophoblast cells and endometrial epithelium respectively with fetal growth. The minke whale placenta showed a fold-like shape as opposed to a finger-like shape. In both nonpregnant and pregnant uteri, many uterine glands were distributed. The uterine glands in the superficial layer of the pregnant endometrium had a wide lumen and large epithelial cells as compared with those in the deep layer. On the other hand, in the nonpregnant endometrium, the uterine glands had a narrower lumen and smaller epithelial cells than in the pregnant endometrium. In immunohistochemical detection, immunoreactivity for P450scc was detected in most trophoblast cells, but not in nonpregnant uteri, suggesting that trophoblast epithelial cells synthesized and secreted the sex steroid hormones and/or their precursors to maintain the pregnancy in the Antarctic minke whale.

A prediction of the minke whale (Balaenoptera acutorostrata) middle-ear transfer function.

The lack of baleen whale (Cetacea Mysticeti) audiograms impedes the assessment of the impacts of anthropogenic noise on these animals. Estimates of audiograms, which are difficult to obtain behaviorally or electrophysiologically for baleen whales, can be made by simulating the audiogram as a series of components representing the outer, middle, and inner ear (Rosowski, 1991; Ruggero and Temchin, 2002). The middle-ear portion of the system can be represented by the middle-ear transfer function (METF), a measure of the transmission of acoustic energy from the external ear to the cochlea. An anatomically accurate finite element model of the minke whale (Balaenoptera acutorostrata) middle ear was developed to predict the METF for a mysticete species. The elastic moduli of the auditory ossicles were measured by using nanoindentation. Other mechanical properties were estimated from experimental stiffness measurements or from published values. The METF predicted a best frequency range between approximately 30 Hz and 7.5 kHz or between 100 Hz and 25 kHz depending on stimulation location. Parametric analysis found that the most sensitive parameters are the elastic moduli of the glove finger and joints and the Rayleigh damping stiffness coefficient ß. The predicted hearing range matches well with the vocalization range.

Multiaxial movements at the minke whale temporomandibular joint.

Mandibular mobility accompanying gape change in Northern and Antarctic minke whales was investigated by manipulating jaws of carcasses, recording jaw movements via digital instruments (inclinometers, accelerometers, and goniometers), and examining osteological and soft tissue movements via computed tomography (CT)-scans. We investigated longitudinal (α) rotation of the mandible and mediolateral displacement at the symphysis (Ω1 ) and temporomandibular joint (Ω2 ) as the mouth opened (Δ). Results indicated three phases of jaw opening. In the first phase, as gape increased from zero to 8°, there was slight (<1°) α and Ω rotation. As gape increased between 20 and 30°, the mandibles rotated slightly laterally (Mean 3°), the posterior condyles were slightly medially displaced (Mean 4°), and the anterior ends at the symphysis were laterally displaced (Mean 3°). In the third phase of jaw opening, from 30° to full (≥90°) gape, these motions reversed: mandibles rotated medially (Mean 29°), condyles were laterally displaced (Mean 14°), and symphyseal ends were medially displaced (Mean 1°). Movements were observed during jaw manipulation and analyzed with CT-images that confirmed quantitative inclinometer/accelerometer data, including the unstable intermediate (Phase 2) position. Together these shifting movements maintain a constant distance for adductor muscles stretched between the skull's temporal fossa and mandible's coronoid process. Mandibular rotation enlarges the buccal cavity's volume as much as 36%, likely to improve prey capture in rorqual lunge feeding; it may strengthen and stabilize jaw opening or closure, perhaps via a simple locking or unlocking mechanism. Rotated lips may brace baleen racks during filtration. Mandibular movements may serve a proprioceptive mechanosensory function, perhaps via the symphyseal organ, to guide prey engulfment and water expulsion for filtration.

Morphological varieties of the Purkinje fiber network in mammalian hearts, as revealed by light and electron microscopy.

Purkinje fibers in mammalian hearts are known to comprise the following three groups depending on their structure: group I found commonly in ungulates, group II in humans, monkeys and dogs, and group III in rodents. The aim of the present study was to document precisely the cytoarchitecture of a network of Purkinje fibers in different species by light and electron microscopy. Light microscopy of silver impregnated tissues revealed the reticular fibers ensheathing individual Purkinje strands consisting of 2-8 cells in both the ungulates (i.e., sheep and goats) and cetaceans (whales and dolphins) while they encircled each Purkinje cell in the primates (humans and monkeys), carnivores (dogs and seals), and rodents (rats). Scanning electron microscopy of NaOH digested tissues showed the ungrates (group I) to have a Purkinje fiber network composed of Purkinje strands; the cells in the strands were oval and made side-to-side and/or end-to-end connections. The Purkinje fiber network in the primates and carnivores (group II) was delicate and complicated; the Purkinje cells were usually cylindrical and connected end-to-end, the exception being their polygonal or stellate shapes at the bifurcations. Purkinje cells in the rodents (group III) resembled ventricular cardiac myocytes in cytoarchitecture. Morphologically, whales and seals respectively belonged to Purkinje cells of group I and group II. These findings indicate that the structural variety of the Purkinje fiber network may reflect the conducting function and be related to the phylogeny of the mammalian species.

Organization of the sleep-related neural systems in the brain of the minke whale (Balaenoptera acutorostrata).

The current study analyzed the nuclear organization of the neural systems related to the control and regulation of sleep and wake in the basal forebrain, diencephalon, midbrain, and pons of the minke whale, a mysticete cetacean. While odontocete cetaceans sleep in an unusual manner, with unihemispheric slow wave sleep (USWS) and suppressed REM sleep, it is unclear whether the mysticete whales show a similar sleep pattern. Previously, we detailed a range of features in the odontocete brain that appear to be related to odontocete-type sleep, and here present our analysis of these features in the minke whale brain. All neural elements involved in sleep regulation and control found in bihemispheric sleeping mammals and the harbor porpoise were present in the minke whale, with no specific nuclei being absent, and no novel nuclei being present. This qualitative similarity relates to the cholinergic, noradrenergic, serotonergic and orexinergic systems, and the GABAergic elements of these nuclei. Quantitative analysis revealed that the numbers of pontine cholinergic (274,242) and noradrenergic (203,686) neurons, and hypothalamic orexinergic neurons (277,604), are markedly higher than other large-brained bihemispheric sleeping mammals. Small telencephalic commissures (anterior, corpus callosum, and hippocampal), an enlarged posterior commissure, supernumerary pontine cholinergic and noradrenergic cells, and an enlarged peripheral division of the dorsal raphe nuclear complex of the minke whale, all indicate that the suite of neural characteristics thought to be involved in the control of USWS and the suppression of REM in the odontocete cetaceans are present in the minke whale. J. Comp. Neurol. 524:2018-2035, 2016. © 2015 Wiley Periodicals, Inc.

The neocortex of cetartiodactyls: I. A comparative Golgi analysis of neuronal morphology in the bottlenose dolphin (Tursiops truncatus), the minke whale (Balaenoptera acutorostrata), and the humpback whale (Megaptera novaeangliae).

The present study documents the morphology of neurons in several regions of the neocortex from the bottlenose dolphin (Tursiops truncatus), the North Atlantic minke whale (Balaenoptera acutorostrata), and the humpback whale (Megaptera novaeangliae). Golgi-stained neurons (n = 210) were analyzed in the frontal and temporal neocortex as well as in the primary visual and primary motor areas. Qualitatively, all three species exhibited a diversity of neuronal morphologies, with spiny neurons including typical pyramidal types, similar to those observed in primates and rodents, as well as other spiny neuron types that had more variable morphology and/or orientation. Five neuron types, with a vertical apical dendrite, approximated the general pyramidal neuron morphology (i.e., typical pyramidal, extraverted, magnopyramidal, multiapical, and bitufted neurons), with a predominance of typical and extraverted pyramidal neurons. In what may represent a cetacean morphological apomorphy, both typical pyramidal and magnopyramidal neurons frequently exhibited a tri-tufted variant. In the humpback whale, there were also large, star-like neurons with no discernable apical dendrite. Aspiny bipolar and multipolar interneurons were morphologically consistent with those reported previously in other mammals. Quantitative analyses showed that neuronal size and dendritic extent increased in association with body size and brain mass (bottlenose dolphin < minke whale < humpback whale). The present data thus suggest that certain spiny neuron morphologies may be apomorphies in the neocortex of cetaceans as compared to other mammals and that neuronal dendritic extent covaries with brain and body size.

Developmental changes in the skull morphology of common minke whales Balaenoptera acutorostrata.

We investigated growth-related and sex-related morphological changes in the skulls of 144 North Pacific common minke whales Balaenoptera acutorostrata. Measurement was conducted at 39 points on the skull and mandible to extract individual allometric equations relating the length and zygomatic width of the skull. The results revealed no significant differences in skull morphology by sex except for width of occipital bone. The size relative to the skull of the anatomical parts involved in feeding, such as the rostrum and mandible, increased after birth. In contrast, the sensory organs and the anatomical regions involved in neurological function, such as the orbit, tympanic bullae, and foramen magnum, were fully developed at birth, and their relative size reduced over the course of development. This is the first study to investigate developmental changes in the skull morphology using more than 100 baleen whale specimens, and we believe the results of this study will contribute greatly to multiple areas of baleen whale research, including taxonomy and paleontology.

On the olfactory anatomy in an archaic whale (Protocetidae, Cetacea) and the minke whale Balaenoptera acutorostrata (Balaenopteridae, Cetacea).

The structure of the olfactory apparatus is not well known in both archaic and extant whales; the result of poor preservation in most fossils and locational isolation deep within the skulls in both fossil and Recent taxa. Several specimens now shed additional light on the subject. A partial skull of an archaic cetacean is reported from the Pamunkey River, Virginia, USA. The specimen probably derives from the upper middle Eocene (Piney Point Formation) and is tentatively assigned to the Protocetidae. Uncrushed cranial cavities associated with the olfactory apparatus were devoid of sediment. CT scans clearly reveal the dorsal nasal meatus, ethmoturbinates within the olfactory recess, the cribriform plate, the area occupied by the olfactory bulbs, and the olfactory nerve tract. Several sectioned skulls of the minke whale (Balaenoptera acutorostrata) were also examined, and olfactory structures are remarkably similar to those observed in the fossil skull from the Pamunkey River. One important difference between the two is that the fossil specimen has an elongate olfactory nerve tract. The more forward position of the external nares in extant balaenopterids when compared with those of extant odontocetes is interpreted to be the result of the need to retain a functional olfactory apparatus and the forward position of the supraoccipital/cranial vertex. An increase in the distance between the occipital condyles and the vertex in balaenopterids enhances the mechanical advantage of the epaxial musculature that inserts on the occiput, a specialization that likely stabilizes the head of these enormous mammals during lunge feeding.

Rins de Baleia Minke (Baleanoptera acutorostrata): arquitetura e estrutura / Kidney of Minke Whale (Baleanoptera acutorostrata): architecture and structure

Entre os mamíferos marinhos, a baleia é um dos animais que mais desperta atenção, especialmente no atinente ao seu sistema urinário. Este sistema segue o padrão entre os mamíferos quanto a sua constituição, entretanto, difere na morfologia renal, em número de lobos, que por sua vez, forma renículos completos, aglutinados às centenas. Esta estrutura é sustentada por tecido conjuntivo fibroso, mas altamente capaz de manter o equilíbrio hidroeletrolítico. Foram dissecados 6 pares de rins de baleia Minke (Balaenoptera acutorostrata), colhidos em 1982, Cabedelo, Estado da Paraíba, Brasil, na última pesca autorizada. Estes rins estavam conservados em formol 10% e apresentaram uma camada histológica de colágeno muito grande circundando a parede medular. O duto coletor urinário forma cálices papilares, desembocando num único centro coletor que desemboca no ureter. Verificou-se que o rim da baleia Minke apresenta característica lobulada possuindo em média 700 renículos, cada renículo possui características anatômicas e funcionais de um rim unipiramidal, com uma camada interna (medula), e uma camada externa (córtex), e irrigação independente, com formação das artérias arqueadas individualmente, como observadas em mamíferos terrestres unipiramidais. Entretanto, o conjunto destes renículos constitui ao final um rim multilobular e polipiramidal, contrariando a morfologia da maioria dos mamíferos terrestres. Não foi possível distinguir ao nível de microscopia de luz as estruturas do córtex renicular da baleia Minke. Na microscopia eletrônica de varredura foi possível visualizar uma camada cortical que fica localizada entre duas cápsulas fibrosas. Esta junção por sua vez é feita por tecido conjuntivo o qual juntamente com uma camada de colágeno e fibras elásticas, separa o córtex da medula , foram visualizados os glomérulos renais, completamente tomados pelos vasos glomerulares e dispostos em várias camadas. Percebe-se que a cavidade glomerular é praticamente um espaço virtual para onde o filtrado glomerular é drenado, não apresentando o formato globular. A vascularização intensifica-se ao chegar à região medular. A diferença entre rins de mamíferos terrestres e marinhos está na disposição dos componentes morfológicos, favorecendo a fisiologia do órgão.

Among marine mammals, whale is one of the most attention-arousing animals, especially concerning its urinary tract. This system follows the pattern of mammals with regard to its constitution, however, it differs in renal morphology and number of lobes, which, in turn, form complete reniculi, agglutinated in hundreds. This structure is supported by fibrous connective tissue, but highly capable of maintaining electrolyte balance. Six pairs of kidneys of Minke whale (Balaenoptera acutorostrata), collected in 1982, in Cabedelo, Paraiba, Brazil, in the last fishing allowed, were dissected. These kidneys were preserved in 10% formaldehyde and they presented a very large histologic layer of collagen surrounding the medullary wall. The urinary collecting duct form papillary glasses, that reach a single collecting center which discharges in the ureter. It was found that the kidney of Minke whale has a lobe characteristic, with, on average, 700 reniculi; each reniculus has anatomical and functional characteristics of a unipyramidal kidney, with an inner layer (medulla), and an outer layer (cortex), and independent irrigation, with formation of individually arcuate arteries, as observed in unipyramidal terrestrial mammals. However, the set gathering all these reniculi constitutes, in the end, a multilobular and polipyramidal kidney, contrary to the morphology of most terrestrial mammals. It was not possible to distinguish the renicular cortex structures of the Minke whale in the level of light microscopy. Through scanning electron microscopy, it was possible to visualize a cortical layer located between two fibrous capsules. This joint, in turn, consists of connective tissue, which, along with a layer of collagen and elastic fibers, separates the cortex from the medulla; the kidney glomeruli were visualized, completely taken by the glomerular vessels and arranged into several layers. One notices that the glomerular cavity is almost a virtual space into which the glomerular filtrate is drained, and it does not present a globular shape. Vascularization is increased in the medullary region. The difference between the kidneys of terrestrial and marine mammals consists in the arrangement of morphological components, favoring the organ's physiology.

Total neocortical cell number in the mysticete brain.

The cetacean brain has long been of scientific interest, not only because of its large size - the largest in the animal kingdom - but also because of its high gyrification. It shows several adaptations to the aquatic environment, especially in the cortical arrangements of functional areas. To study structural aspects of the mysticete brain we estimated neocortical features in the common minke whale using stereological methods. The neocortex was surprisingly thick, equal to that in humans. The total neocortical neuron number was 12.8 x 10(9), and the total neocortical glia number 98.2 x 10(9). Total cell numbers in the auditory and visual cortex were also estimated, and showed that the auditory cortex contained more cells than the visual cortex. In this small sample, no sexual dimorphism was seen within the neocortex of the common minke whale. Our aim was to estimate the total cell number, cortical volume and cell density in the entire mysticete neocortex and compare the total cell number in the auditory cortex with that of the visual cortex using stereological methods. Here, we used the common minke whale as a model of all mysticetes. We wanted to compare these neocortical features to those of other mammals to forward understanding of the evolution of the mammalian brain.