Localized Expression of Olfactory Receptor Genes in the Olfactory Organ of Common Minke Whales.

Baleen whales (Mysticeti) possess the necessary anatomical structures and genetic elements for olfaction. Nevertheless, the olfactory receptor gene (OR) repertoire has undergone substantial degeneration in the cetacean lineage following the divergence of the Artiodactyla and Cetacea. The functionality of highly degenerated mysticete ORs within their olfactory epithelium remains unknown. In this study, we extracted total RNA from the nasal mucosae of common minke whales (Balaenoptera acutorostrata) to investigate ORs' localized expression. All three sections of the mucosae examined in the nasal chamber displayed comparable histological structure. However, the posterior portion of the frontoturbinal region exhibited notably high OR expression. Neither the olfactory bulb nor the external skin exhibited the expression of these genes. Although this species possesses four intact non-class-2 ORs, all the ORs expressed in the nasal mucosae belong to class-2, implying the loss of aversion to specific odorants. These anatomical and genomic analyses suggest that ORs are still responsible for olfaction within the nasal region of baleen whales, enabling them to detect desirable scents such as prey and potential mating partners.

Distribution and Local Movement of Humpback Whales in Okinawan Waters Depend on Sex and Reproductive Status.

The distribution and local movement patterns of humpback whales in waters off the west coast of Okinawa Island, southwest Japan, were investigated using line transect and photo-identification methodologies. Line transect surveys were conducted from 2011 to 2014 and photo-identification survey from 2006 to 2012. During the surveys, humpback whales aggregated in the areas around Ie and Kerama Islands, and tended to travel along the inshore coast of Okinawa Island when they move locally between those two sites. A total of 496 humpback whales of the known sex were photo-identified (322 males, 75 females and 99 females with a calf). Of these, 24.8% were confirmed moving locally between the sites of Ie and Kerama Islands within the same season. Frequency rates of the local movement for males, females and females with a calf were 41.9, 25.0, and 15.1%, respectively; the frequency of local movement for males was significantly higher than that for females and females with a calf. These results indicate that male humpback whales tend to move more actively between the local breeding sites as compared to females and females with a calf. We speculate that the males search for more opportunities to mate, whereas females with a calf tend to remain in the same areas to nurse their calves. These findings extend our knowledge of the habitat use and reproductive ecology of humpback whales in Okinawan waters, which remain poorly understood.

Spatial and temporal variation of PCBs and organochlorine pesticides in the Antarctic minke whales, Balaenoptera bonaerensis, in the period 1987-2005.

Concentrations of polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), hexachlorobenzene (HCB) and chlordane compounds (CHLs) were determined in the blubber of males (20-25 years old) of Antarctic minke whales, Balaenoptera bonaerensis, from the International Whaling Commission (IWC) management Areas IV (70°-130°E) and V (130°E-170°W), south 60°S. The ranges of concentrations (ng g(-1) lipid wt.) for each compound were, PCBs: 7.7-89; DDTs: 29-340; HCHs: 0.20-4.3; HCB: 75-430; CHLs: 10-120, which were much lower than those in common minke whales, Balaenoptera acutorostrata, from the northern hemisphere. The levels of PCBs, HCHs, HCB and CHLs in Area IV were significantly higher than those in Area V, while the levels of DDTs in both areas were similar. For comparing the fate among four pesticides in the Antarctic Ocean avoiding the effect of variance due to food intake, the ratios of the pesticides to PCBs, which has an extremely high chemical stability and environmental persistence, were examined. The HCHs/PCBs ratio decreased by a factor of about 20 in a span of 16 years in both Areas IV and V, while temporal trends of DDTs/PCBs, HCB/PCBs and CHLs/PCBs ratios were not observed. These results indicate that PCBs, DDTs, HCB and CHLs levels did not vary or slightly decreased in Areas IV and V during the study period. However HCHs levels clearly decreased. Spatial differences seems to be related to differences in food intake among whales, and temporal differences seems to be related to the length stay of OCs in the Antarctic Ocean.

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.

Attempt at intracytoplasmic sperm injection of in vitro matured oocytes in common minke whales (Balaenoptera acutorostrata) captured during the Kushiro Coast Survey.

The present study was conducted during the Kushiro Coast Survey in an attempt to produce common minke whale embryos. In Experiment 1, we attempted to determine the appropriate culture duration (30 or 40 h) for in vitro maturation (IVM) of immature oocytes using the Well of the Well method. In Experiment 2, and intracytoplasmic sperm injection (ICSI) was applied to matured oocytes from prepubertal and adult common minke whales after IVM culture (40 or 48 h), and then their embryonic development was assessed. In Experiment 1, the maturation rate of oocytes cultured for 40 h (30.4%) was significantly higher than that of oocytes cultured for 30 h (6.8%; P<0.01). In Experiment 2, a total of 35 and 46 immature oocytes derived from adult (n=2) and prepubertal (n=6) minke whales, respectively, were cultured for 40 or 48 h. The maturation rate in the oocytes from the adult whales (34.2%) tended to be higher than that of the oocytes from the prepubertal whales (19.6%), but there was no significant difference. Following ICSI, 3 out of the 10 inseminated and cultured oocytes from the adult whales cleaved (2-, 8-, and 16-cell stages); all of these oocytes had been matured for 40 in culture. However, these oocytes did not develop to further stages. Only one of the 6 oocytes derived from the prepubertal whales, IVM cultured for 40 h and inseminated, developed to the 4-cell stage. The present results indicate that a 40 h IVM culture produces significantly higher rates of in vitro maturation than a 30 h IVM culture for common minke whale oocytes. Following ICSI, some oocytes cleaved to the 16-cell stage, but no further development was observed.

Mitochondrial phylogenetics and evolution of mysticete whales.

The phylogenetic relationships among baleen whales (Order: Cetacea) remain uncertain despite extensive research in cetacean molecular phylogenetics and a potential morphological sample size of over 2 million animals harvested. Questions remain regarding the number of species and the monophyly of genera, as well as higher order relationships. Here, we approach mysticete phylogeny with complete mitochondrial genome sequence analysis. We determined complete mtDNA sequences of 10 extant Mysticeti species, inferred their phylogenetic relationships, and estimated node divergence times. The mtDNA sequence analysis concurs with previous molecular studies in the ordering of the principal branches, with Balaenidae (right whales) as sister to all other mysticetes base, followed by Neobalaenidae (pygmy right whale), Eschrichtiidae (gray whale), and finally Balaenopteridae (rorquals + humpback whale). The mtDNA analysis further suggests that four lineages exist within the clade of Eschrichtiidae + Balaenopteridae, including a sister relationship between the humpback and fin whales, and a monophyletic group formed by the blue, sei, and Bryde's whales, each of which represents a newly recognized phylogenetic relationship in Mysticeti. We also estimated the divergence times of all extant mysticete species, accounting for evolutionary rate heterogeneity among lineages. When the mtDNA divergence estimates are compared with the mysticete fossil record, several lineages have molecular divergence estimates strikingly older than indicated by paleontological data. We suggest this discrepancy reflects both a large amount of ancestral polymorphism and long generation times of ancestral baleen whale populations.