The Experts below are selected from a list of 22926 Experts worldwide ranked by ideXlab platform
Michael R Mcgowen - One of the best experts on this subject based on the ideXlab platform.
-
phylogenomic resolution of the Cetacean tree of life using target sequence capture
Systematic Biology, 2020Co-Authors: Paul Jepson, Michael R Mcgowen, Georgia Tsagkogeorga, Sandra Alvarezcarretero, Mario Dos Reis, Monika Struebig, Robert Deaville, Simon N Jarman, Andrea M PolanowskiAbstract:The evolution of Cetaceans, from their early transition to an aquatic lifestyle to their subsequent diversification, has been the subject of numerous studies. However, although the higher-level relationships among Cetacean families have been largely settled, several aspects of the systematics within these groups remain unresolved. Problematic clades include the oceanic dolphins (37 spp.), which have experienced a recent rapid radiation, and the beaked whales (22 spp.), which have not been investigated in detail using nuclear loci. The combined application of high-throughput sequencing with techniques that target specific genomic sequences provide a powerful means of rapidly generating large volumes of orthologous sequence data for use in phylogenomic studies. To elucidate the phylogenetic relationships within the Cetacea, we combined sequence capture with Illumina sequencing to generate data for $\sim $3200 protein-coding genes for 68 Cetacean species and their close relatives including the pygmy hippopotamus. By combining data from $>$38,000 exons with existing sequences from 11 Cetaceans and seven outgroup taxa, we produced the first comprehensive comparative genomic data set for Cetaceans, spanning 6,527,596 aligned base pairs (bp) and 89 taxa. Phylogenetic trees reconstructed with maximum likelihood and Bayesian inference of concatenated loci, as well as with coalescence analyses of individual gene trees, produced mostly concordant and well-supported trees. Our results completely resolve the relationships among beaked whales as well as the contentious relationships among oceanic dolphins, especially the problematic subfamily Delphinidae. We carried out Bayesian estimation of species divergence times using MCMCTree and compared our complete data set to a subset of clocklike genes. Analyses using the complete data set consistently showed less variance in divergence times than the reduced data set. In addition, integration of new fossils (e.g., Mystacodon selenensis) indicates that the diversification of Crown Cetacea began before the Late Eocene and the divergence of Crown Delphinidae as early as the Middle Miocene. [Cetaceans; phylogenomics; Delphinidae; Ziphiidae; dolphins; whales.].
-
the evolutionary history of Cetacean brain and body size
Evolution, 2013Co-Authors: Stephen H Montgomery, Michael R Mcgowen, Lori Marino, Jonathan H Geisler, Charlotte Fox, John GatesyAbstract:Cetaceans rival primates in brain size relative to body size and include species with the largest brains and biggest bodies to have ever evolved. Cetaceans are remarkably diverse, varying in both phenotypes by several orders of magnitude, with notable differences between the two extant suborders, Mysticeti and Odontoceti. We analyzed the evolutionary history of brain and body mass, and relative brain size measured by the encephalization quotient (EQ), using a data set of extinct and extant taxa to capture temporal variation in the mode and direction of evolution. Our results suggest that Cetacean brain and body mass evolved under strong directional trends to increase through time, but decreases in EQ were widespread. Mysticetes have significantly lower EQs than odontocetes due to a shift in brain:body allometry following the divergence of the suborders, caused by rapid increases in body mass in Mysticeti and a period of body mass reduction in Odontoceti. The pattern in Cetacea contrasts with that in primates, which experienced strong trends to increase brain mass and relative brain size, but not body mass. We discuss what these analyses reveal about the convergent evolution of large brains, and highlight that until recently the most encephalized mammals were odontocetes, not primates.
Ming-ching Yang - One of the best experts on this subject based on the ideXlab platform.
-
Modeling the Impacts of Cetacean-Focused Tourism in Taiwan: Observations from Cetacean Watching Boats: 2002–2005
Environmental Management, 2011Co-Authors: Yung-ping Tseng, Yu-chin Huang, Gerard T. Kyle, Ming-ching YangAbstract:Cetacean-focused tourism in Taiwan has grown rapidly since 1997. This development, measured in terms of both number of tour boats and visitors, has resulted in many resource management challenges stemming from the absence of regulation and scientific data. To fill this void in empirical evidence, we used 464 sighting records from 2002 to 2005 to model the impact of Cetacean-focused tourism. Cox proportional hazard analysis indicated Cetacean avoidance responses to Cetacean watching boats were strongly associated with pod size, mother–calf pairs, and Cetacean-vessel distances. Mother–calf pairs abandoned their avoidance tactic by 55% compared to noncalf groups when tour boats approached. Second, the hazard ratio of abundance was 0.996, suggesting that the odds of encountering avoidance responses by the Cetaceans decreased by 42% for every 100-member increase in the Cetacean pod size. Last, distances maintained by boats from the Cetaceans was positively related to avoidance responses (i.e., less avoidance behavior with closer interaction). Based on our findings, we have the following recommendations: (a) limit vessels from approaching mothers with calves, (b) limit vessels from approaching small groups of Cetaceans, (c) reduced avoidance behavior to boat traffic may be a red flag for potential long-term disturbance, and (d) apply the “precautionary principle” based on the best scientific information available in Cetacean-based tourism in Taiwan. These recommendations will help contribute to the sustainable development of Cetacean-focused tourism in Taiwan.
J. G. M. Thewissen - One of the best experts on this subject based on the ideXlab platform.
-
From Land to Water: the Origin of Whales, Dolphins, and Porpoises
Evolution: Education and Outreach, 2009Co-Authors: J. G. M. Thewissen, Lisa Noelle Cooper, John C. George, Sunil BajpaiAbstract:Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Even though all modern Cetaceans are obligate aquatic mammals, early Cetaceans were amphibious, and their ancestors were terrestrial artiodactyls, similar to small deer. The transition from land to water is documented by a series of intermediate fossils, many of which are known from India and Pakistan. We review raoellid artiodactyls, as well as the earliest families of Cetaceans: pakicetids, ambulocetids, remingtonocetids, protocetids, and basilosaurids. We focus on the evolution of Cetacean organ systems, as these document the transition from land to water in detail.
-
Vestibular evidence for the evolution of aquatic behaviour in early Cetaceans
Nature, 2002Co-Authors: F. Spoor, S. T. Hussain, S. Bajpai, K. Kumar, J. G. M. ThewissenAbstract:Early Cetaceans evolved from terrestrial quadrupeds to obligate swimmers, a change that is traditionally studied by functional analysis of the postcranial skeleton 1 . Here we assess the evolution of Cetacean locomotor behaviour from an independent perspective by looking at the semicircular canal system, one of the main sense organs involved in neural control of locomotion^ 2 . Extant Cetaceans are found to be unique in that their canal arc size, corrected for body mass, is approximately three times smaller than in other mammals. This reduces the sensitivity of the canal system, most plausibly to match the fast body rotations that characterize Cetacean behaviour. Eocene fossils show that the new sensory regime, incompatible with terrestrial competence, developed quickly and early in Cetacean evolution, as soon as the taxa are associated with marine environments. Dedicated agile swimming of Cetaceans thus appeared to have originated as a rapid and fundamental shift in locomotion rather than as the gradual transition suggested by postcranial evidence. We hypothesize that the unparalleled modification of the semicircular canal system represented a key ‘point of no return’ event in early Cetacean evolution, leading to full independence from life on land.
-
Skeletons of terrestrial Cetaceans and the relationship of whales to artiodactyls
Nature, 2001Co-Authors: J. G. M. Thewissen, E. M. Williams, S. T. HussainAbstract:Modern members of the mammalian order Cetacea (whales, dolphins and porpoises) are obligate aquatic swimmers that are highly distinctive in morphology, lacking hair and hind limbs, and having flippers, flukes, and a streamlined body. Eocene fossils document much of Cetaceans' land-to-water transition, but, until now, the most primitive representative for which a skeleton was known was clearly amphibious and lived in coastal environments. Here we report on the skeletons of two early Eocene pakicetid Cetaceans, the fox-sized Ichthyolestes pinfoldi , and the wolf-sized Pakicetus attocki . Their skeletons also elucidate the relationships of Cetaceans to other mammals. Morphological cladistic analyses have shown Cetaceans to be most closely related to one or more mesonychians, a group of extinct, archaic ungulates, but molecular analyses have indicated that they are the sister group to hippopotamids. Our cladistic analysis indicates that Cetaceans are more closely related to artiodactyls than to any mesonychian. Cetaceans are not the sister group to (any) mesonychians, nor to hippopotamids. Our analysis stops short of identifying any particular artiodactyl family as the Cetacean sister group and supports monophyly of artiodactyls.
-
Phylogenetic aspects of Cetacean origins: A morphological perspective
Journal of Mammalian Evolution, 1994Co-Authors: J. G. M. ThewissenAbstract:The evolutionary steps leading up to the origin of Cetaceans involved pervasive changes in the masticatory apparatus, the ear, and limb morphology. These changes bear heavily on the phylogenetic relationships of Cetacea, and are investigated here on the basis of two of its earliest members: Pakicetus and Ambulocetus . A phylogenetic analysis of Cetaceans, five groups of mesonychians, and five other groups of ungulates indicates that Pakicetus is the sister group to all other Cetaceans, and that Cete (mesonychians and Cetacea) is a monophyletic group.
Philip D. Gingerich - One of the best experts on this subject based on the ideXlab platform.
-
Body Weight and Relative Brain Size (Encephalization) in Eocene Archaeoceti (Cetacea)
Journal of Mammalian Evolution, 2016Co-Authors: Philip D. GingerichAbstract:Calibration of the Brownian diffusion model of Felsenstein indicates that phylogeny may have an influence on body length and other phenotypic measures in Cetacea for as many as 10,000 generations or about 180,000 years, which is negligible in the 35 million year history of extant Cetacea. Observations of phenotypic traits in Cetacean species living today are independent of phylogeny and independent statistically. Four methods for estimating body weight in fossil Cetaceans are compared: (1) median serial regression involving a set of multiple regressions of log body weight on log centrum length, width, and height for core vertebrae; (2) regression of log whole body weight on log body length for individuals; (3) regression of log whole body weight on log body length for species means; and (4) regression of log lean body weight on log body length for individuals. These yield body weight estimates for the Eocene archaeocete Dorudon atrox of 1126, 1118, 1132, and 847 kg, respectively, with consistency and applicability to partial skeletons favoring the first approach. The whole-body weight expected, P_e (in kg), for a given body length, L_i (in cm), is given by log_10 P_e = 2.784 • log_10 L_i − 4.429. Negative allometry of body weight and body length (slope 2.784
-
Body Weight and Relative Brain Size (Encephalization) in Eocene Archaeoceti (Cetacea)
Journal of Mammalian Evolution, 2015Co-Authors: Philip D. GingerichAbstract:Calibration of the Brownian diffusion model of Felsenstein indicates that phylogeny may have an influence on body length and other phenotypic measures in Cetacea for as many as 10,000 generations or about 180,000 years, which is negligible in the 35 million year history of extant Cetacea. Observations of phenotypic traits in Cetacean species living today are independent of phylogeny and independent statistically. Four methods for estimating body weight in fossil Cetaceans are compared: (1) median serial regression involving a set of multiple regressions of log body weight on log centrum length, width, and height for core vertebrae; (2) regression of log whole body weight on log body length for individuals; (3) regression of log whole body weight on log body length for species means; and (4) regression of log lean body weight on log body length for individuals. These yield body weight estimates for the Eocene archaeocete Dorudon atrox of 1126, 1118, 1132, and 847 kg, respectively, with consistency and applicability to partial skeletons favoring the first approach. The whole-body weight expected, Pe (in kg), for a given body length, Li (in cm), is given by log10 Pe = 2.784 • log10 Li − 4.429. Negative allometry of body weight and body length (slope 2.784 < 3.000) means that small Cetaceans are shorter and more maneuverable than expected for their weight, while large Cetaceans are longer and more efficient energetically than expected for their weight. Encephalization is necessarily quantified relative to a reference sample, most mammals are terrestrial, and terrestrial mammals provide a logical baseline. The encephalization residual for living terrestrial mammals as a class (ERTC), is the difference between observed log2 brain weight (Ei in g) and expected log2 brain weight (Ee in g), where the latter is estimated from body weight (Pi in g), as log2 Ee = 0.740 • log2 Pi − 4.004. ERTC is positive for brains that are larger than expected for a given body size, and negative for brains that are smaller than expected. Base-2 logarithms make the ERTC scale intuitive, in uniform units of halving or doubling. Encephalization quotients (EQ) are unsuitable for comparison because they are proportions on a non-uniform scale. Middle Eocene archaeocetes have ERTC values close to −2 (two halvings compared to expectation), while late Eocene archaeocetes have ERTC values close to −1 (one halving compared to expectation). ERTC is not known for fossil mysticetes, but living mysticetes have ERTC values averaging about −2. Oligocene-Recent odontocetes appear to have ERTC values averaging about +1 (one doubling compared to expectation) through their temporal range. Definitive interpretation of the evolution of encephalization in Cetacea will require better documentation for Oligocene–Recent mysticetes and odontocetes.
Yung-ping Tseng - One of the best experts on this subject based on the ideXlab platform.
-
Modeling the Impacts of Cetacean-Focused Tourism in Taiwan: Observations from Cetacean Watching Boats: 2002–2005
Environmental Management, 2011Co-Authors: Yung-ping Tseng, Yu-chin Huang, Gerard T. Kyle, Ming-ching YangAbstract:Cetacean-focused tourism in Taiwan has grown rapidly since 1997. This development, measured in terms of both number of tour boats and visitors, has resulted in many resource management challenges stemming from the absence of regulation and scientific data. To fill this void in empirical evidence, we used 464 sighting records from 2002 to 2005 to model the impact of Cetacean-focused tourism. Cox proportional hazard analysis indicated Cetacean avoidance responses to Cetacean watching boats were strongly associated with pod size, mother–calf pairs, and Cetacean-vessel distances. Mother–calf pairs abandoned their avoidance tactic by 55% compared to noncalf groups when tour boats approached. Second, the hazard ratio of abundance was 0.996, suggesting that the odds of encountering avoidance responses by the Cetaceans decreased by 42% for every 100-member increase in the Cetacean pod size. Last, distances maintained by boats from the Cetaceans was positively related to avoidance responses (i.e., less avoidance behavior with closer interaction). Based on our findings, we have the following recommendations: (a) limit vessels from approaching mothers with calves, (b) limit vessels from approaching small groups of Cetaceans, (c) reduced avoidance behavior to boat traffic may be a red flag for potential long-term disturbance, and (d) apply the “precautionary principle” based on the best scientific information available in Cetacean-based tourism in Taiwan. These recommendations will help contribute to the sustainable development of Cetacean-focused tourism in Taiwan.