Description of the karyotypes of Stejneger's beaked whale (Mesoplodon stejnegeri) and Hubbs’ beaked whale (M. carlhubbsi)

Abstract

The genus Mesoplodon (Cetacea: Odontoceti: Ziphiidae) is one of the few cetacean genera with the karyotype 2n = 42. The 2n = 42 karyotype of M. europaeus and M. carlhubbsi is largely consistent with the general cetacean karyotype 2n = 44, although other 2n = 42 karyotypes do not exhibit clear homologies with the general cetacean karyotype. Therefore, the chromosomes of Mesoplodon species may be the key to understanding cetacean karyological evolution. In the present study, the male karyotypes of M. stejnegeri and M. carlhubbsi were examined. In both species, the diploid number of the male karyotype was 42. Both species had the following characteristics: 1) a huge subtelocentric X chromosome with a large C-block; 2) a small metacentric Y chromosome; 3) nucleolus organizer regions (NORs) in the terminal regions of a large autosome and one or two small metacentric autosomes; 4) small metacentric autosomes; 5) large submetacentric and subtelocentric autosomes; 6) less accumulated C-heterochromatin in the centromeric region; and 7) heteromorphism in C-heterochromatin accumulation between homologues. Characteristics 1 and 3 are peculiar to only the karyotypes of Mesoplodon species, whereas characteristics 4, 5, 6, and 7 are also found in the species with the general cetacean karyotype 2n = 44.

An Indo-Pacific Humpback Dolphin Genome Reveals Insights into Chromosome Evolution and the Demography of a Vulnerable Species

“…Based on these HSBs, we reconstructed the ancestral chromosomes for Cetruminantia (28), Bovidae (30), and Odontoceti (22) ( Tables S8–S10 ). This analysis confirmed that the number of ancestral chromosomes of Odontoceti is the same as that of most extant cetacean families (22 chromosome pairs) and different from that of superfamily Physeteroidea ( ÁRnason, 1974 ) and family Ziphiidae ( Kurihara et al., 2017 ) (21 chromosome pairs). Thus, we propose a model of chromosome evolution in cetaceans in which a chromosome fusion event likely occurred in the physeterids (i.e., sperm whales).…”

In Vitro Cytotoxicity and Risk Assessments of Environmental Pollutants Using Fibroblasts of a Stranded Finless Porpoise (Neophocaena asiaeorientalis)

“…Most studies on cell cultures of wild cetaceans have thus targeted fibroblasts. In previous studies, cetacean fibroblast cells have been isolated from skin, ,− lungs, testes, muscle, and cartilage . This study proposed a non-invasive and efficient cell culture method using the flipper tip of a stranded cetacean.…”

“…In previous studies, cetacean fibroblast cells have been isolated from skin, 26,33−41 lungs, 38 testes, 38 muscle, 42 and cartilage. 42 This study proposed a non-invasive and efficient cell culture method using the flipper tip of a stranded cetacean. Although elapsed time after death (including the time spent for sampling) is a critical issue for cell culture, the tissue samples can be easily collected from the edge of the flipper.…”

The Karyotype of Blainville’s Beaked Whale, <b><i>Mesoplodon densirostris</i></b>

“…M. carlhubbsi in the study of Arnason et al [1977] were female. In the paper by Kurihara et al [2017], the Y chromosomes of M. stejnegeri and M. carlhubbsi appear to be small and metacentric. In the current individual of M. densirostris, the Y is significantly larger.…”

“…There are currently 22 recognised species of beaked whales. Fifteen of these are contained within the genus Mesoplodon, and only 3 of these species have been karyotyped: Mesoplodon europaeus [Arnason et al, 1977], M. carlhubbsi [Arnason et al, 1977;Kurihara et al, 2017], and M. stejnegeri [Kurihara et al, 2017]. These 3 species have an X chromosome with a large distal heterochromatic block on the long arm and also have 42 chromo-somes, whereas most cetaceans have 44 [Arnason et al, 1977].…”