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At least 19 recordsLinked to original sources
PubMed1998

Absence of short-wavelength sensitive cones in the retinae of seals (Carnivora) and African giant rats (Rodentia).

Most non-primate mammals have two types of cone: short-wavelength sensitive (S) and middle-to-long-wavelength sensitive (M/L) cones. In two species of African giant rats, Cricetomys gambianus and C. emini, and in two species of earless seals, Phoca hispida and P. vitulina, the retinal cone types and cone distributions were assessed with antibodies specific for the M/L-cone opsin and the S-cone opsin, respectively. All four species were found to completely lack S-cones, while M/L-cones were present in low densities. M/L-cone densities, rod densities and cone/rod ratios were determined across the retina. Cone proportions are about 0.3-0. 5% in C. gambianus, 0.5-0.8% in C. emini, and 1.5-1.8% in P. hispida. An absence of S-cones has previously been reported in a few nocturnal mammals. As earless seals are visually active during night and day, we conclude that an absence of S-cones is not exclusively associated with nocturnality. The functional and comparative aspects are discussed.

Anatomy, Comparative↗
PubMed1993

The nucleotide sequence of the mitochondrial DNA molecule of the grey seal, Halichoerus grypus, and a comparison with mitochondrial sequences of other true seals.

The sequence of the mtDNA of the grey seal, Halichoerus grypus, was determined. The length of the molecule was 16,797 base pairs. The organization of the molecule conformed with that of other eutherian mammals but the control region was unusually long due to the presence of two types of repeated motifs. The grey seal and the previously reported harbor seal, Phoca vitulina, belong to different but closely related genera of family Phocidae, true (or earless) seals. In order to determine the degree of differences that may occur between mtDNAs of closely related mammalian genera, the 2 rRNA genes, the 13 peptide coding genes, and the 22 tRNA genes of the 2 species were compared. Total nucleotide difference in the peptide coding genes was 2.0-6.1%. The range of conservative difference was 0.0-1.5%. In the inferred peptide sequences the amino acid difference was 0.0-4.5%, and the difference with respect to chemical properties of amino acids was 0.0-3.0%. A gene that showed a limited degree of difference in one mode of comparison did not necessarily show a corresponding limited difference in another mode. The ratio for differences in codon positions 1, 2, and 3 was approximately 2.7:1:16. The corresponding ratio for conservative differences was approximately 1.8:1.1:1. The evolutionary separation of the two species was calculated to have taken place 2-2.5 million years ago. This dating gives the figure approximately 8 x 10(-9) as the mean rate of substitution per site and year in the entire mtDNA molecule. Comparison with the cytochrome b gene of the Hawaiian monk seal and the Weddell seal suggested that the lineage of these two species and that of the grey and harbor seals separated approximately 8 million years ago.

Animals↗
PubMed2001

For whales and seals the ocean is not blue: a visual pigment loss in marine mammals.

Most terrestrial mammals have colour vision based on two spectrally different visual pigments located in two types of retinal cone photoreceptors, i.e. they are cone dichromats with long-to-middle-wave-sensitive (commonly green) L-cones and short-wave-sensitive (commonly blue) S-cones. With visual pigment-specific antibodies, we here demonstrate an absence of S-cones in the retinae of all whales and seals studied. The sample includes seven species of toothed whales (Odontoceti) and five species of marine carnivores (eared and earless seals). These marine mammals have only L-cones (cone monochromacy) and hence are essentially colour-blind. For comparison, the study also includes the wolf, ferret and European river otter (Carnivora) as well as the mouflon and pygmy hippopotamus (Artiodactyla), close terrestrial relatives of the seals and whales, respectively. These have a normal complement of S-cones and L-cones. The S-cone loss in marine species from two distant mammalian orders strongly argues for convergent evolution and an adaptive advantage of that trait in the marine visual environment. To us this suggests that the S-cones may have been lost in all whales and seals. However, as the spectral composition of light in clear ocean waters is increasingly blue-shifted with depth, an S-cone loss would seem particularly disadvantageous. We discuss some hypotheses to explain this paradox.

Animals↗
PubMed1981

New Zealand's cetaceans and pinnipeds.

The 8 species of baleen whale in New Zealand waters range in length from 6 to 30+ metres, and the 25 species of toothed whale range up to 18 metres. A single porpoise species is known in New Zealand sub-Antarctic waters. The baleen whales and many of the toothed whales are migratory, and New Zealand straddles their well-defined routes: a combination which allowed whaling to flourish. The toothed whales are the more gregarious and may indulge in mass strandings. Current research aims to investigate the biology of all of the whale species. The otariid, or eared seals found in the New Zealand region are the New Zealand sealion and the New Zealand fur seal. The commonest of the phocid, or earless seals on the New Zealand coast are the elephant and leopard seals. All of these breed in the southern parts of the region but range further north. The fur seal population is rising slowly, but the small population size of the New Zealand sealion gives cause for concern. Marine mammals form an important part of the fauna of the New Zealand region, and veterinary knowledge and general research should be increased.

Animals↗
PubMed1993

Empirical and theoretical constraints on the evolution of lactation.

For 829 mammalian species, data on age at weaning or age at first solid food were analyzed with respect to body mass, phylogeny, habitat, diet, length of gestation, basal metabolism, and neonatal development. The primary influence on lactation length is female mass, but phylogenetic constraints are important. Thus, lactation can be characterized as short (earless seals and baleen whales), long (marsupials, bats, and primates), or average (remaining eutherians). Among average mammals, lagomorphs have short lactations. Lactation may have different functions, evolutionary constraints, and physiological control depending on whether young first eat solid food near weaning or well before it. First solid food eaten near weaning occurs in polytocous species with altricial young; in this case, lactation has a clear energetic role. In contrast, first solid food well before weaning is common for mammals with single, precocial offspring. For these species, the energetic and nutritional constraints on lactation may be less important than the benefits of maintaining contact between mother and young, such as reduced juvenile mortality and increased opportunities for learning social or foraging patterns. Thus, the age at first solid food relative to the age at weaning may indicate the function of lactation within the reproductive biology of a given mammal. Delayed development and implantation alter the timing of energetic investment during gestation, so too, the age at first solid food may alter or reflect the rate of energetic investment during lactation. Thus, the age at first solid food relative to the age at weaning may indicate the function of lactation within the reproductive biology of a given mammal. Testing these hypotheses will require data from diverse species on the nutritional and energetic value of milk before and after first solid food as well as on the mechanics and consequences of nursing or suckling during the course of lactation.

Age Factors↗