[Structure of the double clicks of echolocation of the globicephalus (odontocete Cetacea)].
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[Comparative studies on ferritin isolated from various animal species. 3. I. Fractionation of ferritin from the spleen of dolphin (Dolphinus cetacea). II. Comparative studies of ferritin from the spleens of terrestial mammals (horses, rabbits) and marine mammals (tunafish, dolphins)].
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Animals↗
Ontogenetic habitat selection by Hadwenius pontoporiae (Digenea: Campulidae) in the intestine of franciscanas (Cetacea).
The linear habitat selection of 4 sequential maturity stages (1, 2, 3, and 4) of the trematode Hadwenius pontoporiae in the intestines of 26 South American dolphins Pontoporia blanvillei was investigated. The franciscana is a suitable host for H. pontoporiae because all 26 hosts were infected, the infrapopulations being composed mostly of gravid (stage 4) worms. Most trematodes were found in the first third of the intestine. The niches of the maturity stages decreased from stage 1 to 4. Gravid worms favored the most anterior part of the duodenum, whereas stages 1, 2, and 3 occurred more posteriorly in every host. The distributions of the maturity stages showed a narrow site fidelity and were ordered following the developmental sequence. The positions of stages 2, 3, and 4 covaried positively when the effect of intensity was controlled. All this evidence suggests that H. pontoporiae undergoes an anteriad ontogenetic migration from the posterior to the most anterior duodenum. At high intensities, the distribution of stages 2, 3, and 4 expanded and shifted posteriorly. According to the maturity structure of H. pontoporiae at the infrapopulation level, it is proposed that there might be more developing worms at high intensities, and, therefore, the expansion and shift might result, at least partly, from the presence of more migrating worms along the fundamental niche of H. pontoporiae. Other Hadwenius species show a similar general pattern of distribution to H. pontoporiae. This raises the possibility that the habitat selection behavior of H. pontoporiae may be due to the inheritance of prior phylogenetic constraints.
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[Parasitic metazoans of Stenella coeruleoalba (Cetacea: Delphinidae) stranded along the coast of Latium, 1985-1991].
The striped dolphin represents the most common species of cetacean stranded along the Italian coasts. A parasitological survey on 17 specimens of Stenella coerulecaiba stranded along coasts of Latium from 1985 to 1991, has been carried out. The morphological study enabled the identification of the following parasites. The sites are reported in brackets. DIGENEA: Campula rochebruni (liver), Campula palliata (liver), Pholeter gastrophilus (pyloric stomach). CESTODA: Tetrabothrium forsteri (intestine), Strobilocephalus triangularis (intestine), Monorygma grimaldii, larvae (abdominal cavity, mesentery, testes), Phyliobothrium delphini, larvae (subcutaneous fat). NEMATODA: Skrjabinalius sp. (lungs). COPEPODA: Pennella sp. (skin). ISOPODA: Ceratothoa parallela (mouth, stomach). AMPHIPODA: Syncyamus aequus (blowhole).
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Localization of regulatory peptides in the gastrointestinal tract of the striped dolphin, Stenella coeruleoalba (Mammalia: Cetacea). An immunohistochemical study.
Samples of oesophagus, first, second and third stomach, duodenal ampulla, proximal intestine and distal intestine including rectum were obtained from striped dolphins (Stenella coeruleoalba) stranded along Italian coasts, fixed in formalin and used for immunohistochemistry. The possible presence of neuropeptides and the biogenic amine serotonin was investigated by a labelled streptavidin-biotin method. Neuropeptide Y (NPY)-, substance P-, calcitonin gene-related peptide (CGRP)-, metenkephalin-, gastrin releasing peptide (GRP)/bombesin-, and somatostatin-like immunoreactivities were present in the submucosal as well as the myenteric plexuses, even with differences of distribution in the various organs. Vasoactive intestinal poly-peptide (VIP)-like immunoreactivity was detected in the submucosal plexus, whereas beta-endorphin- and leu-enkephalin-like immunoreactivities were shown in the myenteric plexus only. NPY-, substance P-, CGRP- and VIP-like-immunoreactivities were also observed in perivascular nerve fibres. In addition, VIP-, GRP- and somatostatin-like immunoreactivities were detected in myelinated nervous bundles. These were localized in the submucosal and muscular layers all along the gastrointestinal tract, and possibly sustain an exceptionally rapid response of the target structures. It is note-worthy that peptidergic axons in the wall of the gut of the majority of mammals are unmyelinated. A somatostatin-like peptide was identified in epithelial cells only in the second stomach, whereas in terrestrial mammals this endocrine cell type occurs widely. Immunoreactivity to serotonin was never detected, and this is a further difference in comparison with the majority of other mammals.
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[Development of the vestibular apparatus of the lesser rorqual in comparison to development of auditory structures (Cetacea: Mysticeti- Balaenoptera acutorostrata)].
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Development of the cetacean nasal skull.
The adaptation of cetaceans to aquatic life habits is reflected, in their nasal region, in three marked changes from the original relations found in land mammals. These changes include (1) the loss of the sense of smell, (2) translocation of the nostrils from the tip of the rostrum to the vertex of the head, and (3) elongation of the anterior head to form a rostrum protruding far towards anterior. The morphogenetic processes taking place during embryogenesis of the nasal skull play a decisive part in the development of all these changes. The lateral parts of the embryonic nasal capsule, encompassing the nasal passages, change their position from horizontal to vertical. At the same time, the structures of the original nasal floor (the solum nasi) are shifted in front of the nasal passages towards the rostrum. The structures of the original nasal roof (the tectum nasi) and of the nasal side wall (the paries nasi) are translocated behind the nasal passages towards the neurocranium. The medial nasal septum (the septum nasi) mostly loses its connection to the nasal passages and is produced into a point protruding far towards anterior. The transformed embryonic nasal skull of the Cetacea can be divided into three sections: 1. The median structures. These include the cartilaginous structures, viz., the rostrum nasi, the septum interorbitale and the spina mesethmoidalis, which are accompanied by the dermal bones, the vomer and the praemaxillare. In adult cetaceans the rostrum nasi is mostly preserved as a robust cartilage of the skull, which may possibly serve as a sound transmitting structure of the sonar system, or it may be responsible for the sensing of water streams and vibrations. 2. The posterior side wall structures. These include the following cartilaginous structures that are mostly heavily reduced or mutually fused: the cupula nasi anterior, the tectum nasi, the lamina cribrosa, the paries nasi, the commissura orbitonasalis, the cupula nasi posterior, the processus paraseptalis posterior, the crista semicircularis, the frontoturbinale, the ethmoturbinale I and the maxilloturbinale. The cartilaginous structures are largely accompanied by the dermal bone, the maxillare. Of these embryonic elements, very little is preserved in adult cetaceans. The cartilages of the cupula nasi anterior form the variable skeleton around the nostrils. In Physeter the tectum nasi forms a very long cartilaginous bar that passes through the whole giant anterior head of the sperm whale as a structure accompanying the left nasal passage. 3. The anterior side wall structures. These include the cartilaginous structures, viz., the cartilago ductus nasopalatini, the cartilago paraseptalis, the processus lateralis ventralis and the lamina transversalis anterior, accompanied by the dermal bones, the praemaxillare and the vomer. These structures participate in the formation of the robust rostrum of the cetacean skull, and they are partly preserved even in adults in the form of the isolated ossa pararostralia (the Meckelian ossicles). The comparison of morphogeny of the nasal skull has also made it possible to draw certain conclusions on the phylogeny and systematics of Cetacea. Already the earliest embryonic stages permit us to discern weighty transformations of the original nasal skull of land mammals. These transformations are common to all embryos examined. This fact indicates a common origin of all Cetacea, which thus form a single monophyletic order. However, later embryonic stages show some different modifications of the nasal capsule according to which at least three major groups can be distinguished within the order Cetacea, probably ranking as superfamilies: Balaenopteroidea, Physeteroidea and Delphinoidea. Our observations, being in full accordance with other morphological, and embryological, as well as molecular biological results, suggest that the division of the order Cetacea into two suborders, Mysticeti and Odontoceti, is no longer tenable.
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Phylogenetic relationships of artiodactyls and cetaceans as deduced from the comparison of cytochrome b and 12S rRNA mitochondrial sequences.
A data set of complete mitochondrial cytochrome b and 12S rDNA sequences is presented here for 17 representatives of Artiodactyla and Cetacea, together with potential outgroups (two Perissodactyla, two Carnivora, two Tethytheria, four Rodentia, and two Marsupialia). We include seven sequences not previously published from Hippopotamidae (Ancodonta) and Camelidae (Tylopoda), yielding a total of nearly 2.1 kb for both genes combined. Distance and parsimony analyses of each gene indicate that 11 clades are well supported, including the artiodactyl taxa Pecora, Ruminantia (with low 12S rRNA support), Tylopoda, Suina, and Ancodonta, as well as Cetacea, Perissodactyla, Carnivora, Tethytheria, Muridae, and Caviomorpha. Neither the cytochrome b nor the 12S rDNA genes resolve the relationships between these major clades. The combined analysis of the two genes suggests a monophyletic Cetacea +Artiodactyla clade (defined as "Cetartiodactyla"), whereas Perissodactyla, Carnivora, and Tethytheria fall outside this clade. Perissodactyla could represent the sister taxon of Cetartiodactyla, as deduced from resampling studies among outgroup lineages. Cetartiodactyla includes five major lineages: Ruminantia, Tylopoda, Suina, Ancodonta, and Cetacea, among which the phylogenetic relationships are not resolved. Thus, Suiformes do not appear to be monophyletic, justifying their split into the Suina and Ancodonta infraorders. An association between Cetacea and Hippopotamidae is supported by the cytochrome b gene but not by the 12S rRNA gene. Calculation of divergence dates suggests that the Cetartiodactyla could have diverged from other Ferungulata about 60 MYA.
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Mitogenomic analyses provide new insights into cetacean origin and evolution.
The evolution of the order Cetacea (whales, dolphins, porpoises) has, for a long time, attracted the attention of evolutionary biologists. Here we examine cetacean phylogenetic relationships on the basis of analyses of complete mitochondrial genomes that represent all extant cetacean families. The results suggest that the ancestors of recent cetaceans had an explosive evolutionary radiation 30-35 million years before present. During this period, extant cetaceans divided into the two primary groups, Mysticeti (baleen whales) and Odontoceti (toothed whales). Soon after this basal split, the Odontoceti diverged into the four extant lineages, sperm whales, beaked whales, Indian river dolphins and delphinoids (iniid river dolphins, narwhals/belugas, porpoises and true dolphins). The current data set has allowed test of two recent morphological hypotheses on cetacean origin. One of these hypotheses posits that Artiodactyla and Cetacea originated from the extinct group Mesonychia, and the other that Mesonychia/Cetacea constitutes a sister group to Artiodactyla. The current results are inconsistent with both these hypotheses. The findings suggest that the claimed morphological similarities between Mesonychia and Cetacea are the result of evolutionary convergence rather than common ancestry.
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Ankle morphology of the earliest Cetaceans and its implications for the phylogenetic relations among ungulates.
Recent molecular studies are inconsistent with ungulate phylogenetic trees that are based on morphological traits. These inconsistencies especially relate to the position of cetaceans and perissodactyls. Evaluation of the close phylogenetic ties between artiodactyls and cetaceans has been hampered by the absence of tarsal bones of primitive cetaceans, as artiodactyls are often diagnosed on the basis of their tarsus. We here describe newly discovered tarsal bones that are the oldest cetacean tarsals known. We present a character analysis for primitive ungulate tarsals and evaluate their impact on the ungulate phylogenetic tree. Tarsal data are consistent with some molecular studies in suggesting that the extant sister group of Cetacea is Artiodactyla or that Cetacea should be included within the latter order. Tarsal data do not support Cete (Mesonychia plus Cetacea) and are consistent with the exclusion of perissodactyls from paenungulates as suggested by some molecular studies.
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Phylogenetic relationships among eutherian orders estimated from inferred sequences of mitochondrial proteins: instability of a tree based on a single gene.
The phylogenetic relationships among Primates (human), Artiodactyla (cow), Cetacea (whale), Carnivora (seal), and Rodentia (mouse and rat) were estimated from the inferred amino acid sequences of the mitochondrial genomes using Marsupialia (opossum), Aves (chicken), and Amphibia (Xenopus) as an outgroup. The overall evidence of the maximum likelihood analysis suggests that Rodentia is an outgroup to the other four eutherian orders and that Cetacea and Artiodactyla form a clade with Carnivora as a sister taxon irrespective of the assumed model for amino acid substitutions. Although there remains an uncertainty concerning the relation among Artiodactyla, Cetacea, and Carnivora, the existence of a clade formed by these three orders and the outgroup status of Rodentia to the other eutherian orders seems to be firmly established. However, analyses of individual genes do not necessarily conform to this conclusion, and some of the genes reject the putatively correct tree with nearly 5% significance. Although this discrepancy can be due to convergent or parallel evolution in the specific genes, it was pointed out that, even without a particular reason, such a discrepancy can occur in 5% of the cases if the branching among the orders in question occurred within a short period. Due to uncertainty about the assumed model underlying the phylogenetic inference, this can occur even more frequently. This demonstrates the importance of analyzing enough sequences to avoid the danger of concluding an erroneous tree.
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Molecular evolution of the mitochondrial 12S rRNA in Ungulata (mammalia).
The complete 12S rRNA gene has been sequenced in 4 Ungulata (hoofed eutherians) and 1 marsupial and compared to 38 available mammalian sequences in order to investigate the molecular evolution of the mitochondrial small-subunit ribosomal RNA molecule. Ungulata were represented by one artiodactyl (the collared peccary, Tayassu tajacu, suborder Suiformes), two perissodactyls (the Grevy's zebra, Equus grevyi, suborder Hippomorpha; the white rhinoceros, Ceratotherium simum, suborder Ceratomorpha), and one hyracoid (the tree hyrax, Dendrohyrax dorsalis). The fifth species was a marsupial, the eastern gray kangaroo (Macropus giganteus). Several transition/transversion biases characterized the pattern of changes between mammalian 12S rRNA molecules. A bias toward transitions was found among 12S rRNA sequences of Ungulata, illustrating the general bias exhibited by ribosomal and protein-encoding genes of the mitochondrial genome. The derivation of a mammalian 12S rRNA secondary structure model from the comparison of 43 eutherian and marsupial sequences evidenced a pronounced bias against transversions in stems. Moreover, transversional compensatory changes were rare events within double-stranded regions of the ribosomal RNA. Evolutionary characteristics of the 12S rRNA were compared with those of the nuclear 18S and 28S rRNAs. From a phylogenetic point of view, transitions, transversions and indels in stems as well as transversional and indels events in loops gave congruent results for comparisons within orders. Some compensatory changes in double-stranded regions and some indels in single-stranded regions also constituted diagnostic events. The 12S rRNA molecule confirmed the monophyly of infraorder Pecora and order Cetacea and demonstrated the monophyly of the suborder Ruminantia was not supported and the branching pattern between Cetacea and the artiodacytyl suborders Ruminantia and Suiformes was not established. The monophyly of the order Perissodactyla was evidenced, but the relationships between Artiodactyla, Cetacea, and Perissodactyla remained unresolved. Nevertheless, we found no support for a Perissodactyla + Hyracoidea clade, neither with distance approach, nor with parsimony reconstruction. The 12S rRNA was useful to solve intraordinal relationships among Ungulata, but it seemed to harbor too few informative positions to decipher the bushlike radiation of some Ungulata orders, an event which has most probably occurred in a short span of time between 55 and 70 MYA.
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Episodic molecular evolution of pituitary growth hormone in Cetartiodactyla.
The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased substantially. As a result the sequences of higher primate and ruminant GHs differ markedly from sequences of other mammalian GHs. In order to increase knowledge of GH evolution in Cetartiodactyla (Artiodactyla plus Cetacea) we have cloned and characterized GH genes from camel (Camelus dromedarius), hippopotamus (Hippopotamus amphibius), and giraffe (Giraffa camelopardalis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, these GH genes comprise five exons and four introns. Two very similar GH gene sequences (encoding identical proteins) were found in each of hippopotamus and giraffe. The deduced sequence for the mature hippopotamus GH is identical to that of dolphin, in accord with current ideas of a close relationship between Cetacea and Hippopotamidae. The sequence of camel GH is identical to that reported previously for alpaca GH. The sequence of giraffe GH is very similar to that of other ruminants but differs from that of nonruminant cetartiodactyls at about 18 residues. The results demonstrate that the apparent burst of rapid evolution of GH occurred largely after the separation of the line leading to ruminants from other cetartiodactyls.
Amino Acid Sequence↗
Cone visual pigments of aquatic mammals.
It has long been hypothesized that the visual systems of animals are evolutionarily adapted to their visual environment. The entrance many millions of years ago of mammals into the sea gave these new aquatic mammals completely novel visual surroundings with respect to light availability and predominant wavelengths. This study examines the cone opsins of marine mammals, hypothesizing, based on previous studies [Fasick et al. (1998) and Levenson & Dizon (2003)], that the deep-dwelling marine mammals would not have color vision because the pressure to maintain color vision in the dark monochromatic ocean environment has been relaxed. Short-wavelength-sensitive (SWS) and long-wavelength-sensitive (LWS) cone opsin genes from two orders (Cetacea and Sirenia) and an additional suborder (Pinnipedia) of aquatic mammals were amplified from genomic DNA (for SWS) and cDNA (for LWS) by PCR, cloned, and sequenced. All animals studied from the order Cetacea have SWS pseudogenes, whereas a representative from the order Sirenia has an intact SWS gene, for which the corresponding mRNA was found in the retina. One of the pinnipeds studied (harp seal) has an SWS pseudogene, while another species (harbor seal) appeared to have an intact SWS gene. However, no SWS cone opsin mRNA was found in the harbor seal retina, suggesting a promoter or splice site mutation preventing transcription of the gene. The LWS opsins from the different species were expressed in mammalian cells and reconstituted with the 11-cis-retinal chromophore in order to determine maximal absorption wavelengths (lambda(max)) for each. The deeper dwelling Cetacean species had blue shifted lambda(max) values compared to shallower-dwelling aquatic species. Taken together, these findings support the hypothesis that in the monochromatic oceanic habitat, the pressure to maintain color vision has been relaxed and mutations are retained in the SWS genes, resulting in pseudogenes. Additionally, LWS opsins are retained in the retina and, in deeper-dwelling animals, are blue shifted in lambda(max).
Amino Acid Sequence↗
Phylogenetic assessment of molecular and morphological data for eutherian mammals.
The interordinal relationships of eutherian (placental) mammals were evaluated by a phylogenetic analysis of four published data sets (three sequences and one morphological). The nature and degree of support and conflict for particular groups were assessed by separate bootstrap and homogeneity tests, which were followed by combined analyses of the sequence and morphological data. Between orders, strong support (i.e., > or = 95% bootstrap scores) was found for a paraphyletic Artiodactyla (relative to Cetacea) and a monophyletic Cetartiodactyla (Artiodactyla and Cetacea) and Paenungulata (Hyracoidea, Proboscidea, and Sirenia). In turn, some reasonable to strong evidence (> or = 85%) was obtained for Hyracoidea with Sirenia, Dermoptera with Scandentia, Glires (Lagomorpha with Rodentia), and Afrotheria (Amblysomus, Macroscelidea, Paenungulata, and Tubulidentata). Otherwise, no other interordinal clades were supported at these reasonable to strong levels. This overall lack of resolution for eutherian interordinal clusters agrees with other studies that suggest further progress will continue to be slow and difficult. Further resolution will require the integration of more recently published data, the continued sampling of taxa and characters, and the use of more powerful methods of data analysis.
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Evidence from milk casein genes that cetaceans are close relatives of hippopotamid artiodactyls.
The inferred transition from terrestrial hoofed mammal to fully aquatic cetacean has been intensively studied with fossil evidence. However, large sections of this remarkable evolutionary sequence are missing. Phylogenetic analysis of extant taxa may help to fill in some of these gaps. In this report, kappa-casein (exon 4) and beta-casein (exon 7) milk protein genes from cetaceans and other placental mammals were PCR-amplified, sequenced, and aligned to previously published sequences. Phylogenetic analyses of the casein data suggest that hippopotamid artiodactyls are more closely related to cetaceans than to other artiodactyls (even-toed hoofed mammals). An analysis of the nuclear casein sequences combined with published mitochondrial cytochrome b DNA sequences also supports the Cetacea/Hippopotamidae sister group. This affinity implies that some of the aquatic traits of cetaceans were derived in the common ancestor of Cetacea and Hippopotamidae. An extant "missing link" to Cetacea may have been overlooked by science since the description of the semiaquatic Hippopotamus in 1758. Paleontological information is grossly inconsistent with this hypothesis. If the casein phylogeny is accurate, large gaps in the fossil record as well as extensive morphological reversals and convergences must be acknowledged.
Amino Acid Sequence↗
More DNA support for a Cetacea/Hippopotamidae clade: the blood-clotting protein gene gamma-fibrinogen.
Recent phylogenetic analyses of DNA sequences suggest that cetaceans (whales) and hippopotamid artiodactyls (hippos) are extant sister taxa. Consequently, the shared aquatic specializations of these taxa may be synapomorphies. This molecular view is contradicted by paleontological data that overwhelmingly support a monophyletic Artiodactyla (even-toed ungulates) and a close relationship between Cetacea and extinct mesonychian ungulates. According to the fossil evidence, molecular, behavioral, and anatomical resemblances between hippos and whales are interpreted as convergences or primitive retentions. In this report, competing interpretations of whale origins are tested through phylogenetic analyses of the blood-clotting protein gene gamma-fibrinogen from cetaceans, artiodactyls, perissodactyls (odd-toed ungulates), and carnivores (cats, dogs, and kin). In combination with published DNA sequences, the gamma-fibrinogen data unambiguously support a hippo/whale clade and are inconsistent with the paleontological perspective. If the phylogeny favored by fossil evidence is accepted, the convergence at the DNA level between Cetacea and Hippopotamidae is remarkable in its distribution across three genetic loci: gamma-fibrinogen, the linked milk casein genes, and mitochondrial cytochrome b.
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[Evolution of the allantoid placenta in placental mammals].
The article surveys the literature concerning comparative morphology of allantoic placenta and presents some evolutionary-morphological conclusions. The initial form of allantoic placenta is non-deciduate that occurs in 7 orders of placental mammals. The non-deciduate placenta is especially characteristic for lower primates and Cetacea. The non-deciduate placenta in lower primates and the fact that in some modern species of insectivores the non-deciduate placenta is also preserved speaks in favour of the opinion that insectivores of the Cretaceous period had non-deciduate placenta. The non-deciduate placenta in Cetacea that take their origin from ancient carnivores (from procreodonts) demonstrates, in its turn, that the non-deciduate placenta was the initial form. The deciduate placenta was the means for changing many of vital activities of the organism--it is connected with shortening or lengthening of individual life duration and duration of pregnancy. In the course of evolution the allantoic placenta improved towards intensified metabolism between the embryo (fetus) and the maternal organism. Relations between the evolution of mature specimens and evolutional changes in placenta are at their initial stage of investigation.
Adaptation, Biological↗