Resurrection of genus Phocanema Myers, 1959, as a genus independent from Pseudoterranova Mozgovoi, 1953, for nematode species (Anisakidae) parasitic in pinnipeds and cetaceans, respectively.

Species of the genus Pseudoterranova, infect kogiid cetaceans and pinnipeds. However, there is mounting molecular evidence that those from cetaceans and pinnipeds are not congeneric. Here, we provide further evidence of the non-monophyly of members of Pseudoterranova from phylogenetic analyses of the conserved nuclear LSU rDNA gene, entire ITS rDNA region and mtDNA cox2 gene, and identify morphological characters that may be used to distinguish the members of the two clades. We propose the resurrection of the genus Phocanema, with Ph. decipiens (sensu stricto) as the type species, to encompass Ph. decipiens, Ph. azarasi, Ph. bulbosa, Ph. cattani and Ph. krabbei, all parasites of pinnipeds. We propose to restrict the conception of genus Pseudoterranova, which now harbours two species infecting kogiid whales; Ps. kogiae (type species) and Ps. ceticola. Members of the genera Phocanema and Pseudoterranova differ by the shape and orientation of the lips, relative tail lengths, adult size, type of final host (pinniped vs. cetacean) and phylogenetic placement based on nuclear rDNA and mtDNA cox2 sequences.

Genetic diversity and demographic history of the leopard seal: A Southern Ocean top predator.

Leopard seals (Hydrurga leptonyx) are top predators that can exert substantial top-down control of their Antarctic prey species. However, population trends and genetic diversity of leopard seals remain understudied, limiting our understanding of their ecological role. We investigated the genetic diversity, effective population size and demographic history of leopard seals to provide fundamental data that contextualizes their predatory influence on Antarctic ecosystems. Ninety leopard seals were sampled from the northern Antarctic Peninsula during the austral summers of 2008-2019 and a 405bp segment of the mitochondrial control region was sequenced for each individual. We uncovered moderate levels of nucleotide (π = 0.013) and haplotype (Hd = 0.96) diversity, and the effective population size was estimated at around 24,000 individuals (NE = 24,376; 95% CI: 16,876-33,126). Consistent with findings from other ice-breeding pinnipeds, Bayesian skyline analysis also revealed evidence for population expansion during the last glacial maximum, suggesting that historical population growth may have been boosted by an increase in the abundance of sea ice. Although leopard seals can be found in warmer, sub-Antarctic locations, the species' core habitat is centered on the Antarctic, making it inherently vulnerable to the loss of sea ice habitat due to climate change. Therefore, detailed assessments of past and present leopard seal population trends are needed to inform policies for Antarctic ecosystems.

Multi-tissue DNA methylation aging clocks for sea lions, walruses and seals.

Age determination of wild animals, including pinnipeds, is critical for accurate population assessment and management. For most pinnipeds, current age estimation methodologies utilize tooth or bone sectioning which makes antemortem estimations problematic. We leveraged recent advances in the development of epigenetic age estimators (epigenetic clocks) to develop highly accurate pinniped epigenetic clocks. For clock development, we applied the mammalian methylation array to profile 37,492 cytosine-guanine sites (CpGs) across highly conserved stretches of DNA in blood and skin samples (n = 171) from primarily three pinniped species representing the three phylogenetic families: Otariidae, Phocidae and Odobenidae. We built an elastic net model with Leave-One-Out-Cross Validation (LOOCV) and one with a Leave-One-Species-Out-Cross-Validation (LOSOCV). After identifying the top 30 CpGs, the LOOCV produced a highly correlated (r = 0.95) and accurate (median absolute error = 1.7 years) age estimation clock. The LOSOCV elastic net results indicated that blood and skin clock (r = 0.84) and blood (r = 0.88) pinniped clocks could predict age of animals from pinniped species not used for clock development to within 3.6 and 4.4 years, respectively. These epigenetic clocks provide an improved and relatively non-invasive tool to determine age in skin or blood samples from all pinniped species.

Fragmented habitat compensates for the adverse effects of genetic bottleneck.

In the face of the human-caused biodiversity crisis, understanding the theoretical basis of conservation efforts of endangered species and populations has become increasingly important. According to population genetics theory, population subdivision helps organisms retain genetic diversity, crucial for adaptation in a changing environment. Habitat topography is thought to be important for generating and maintaining population subdivision, but empirical cases are needed to test this assumption. We studied Saimaa ringed seals, landlocked in a labyrinthine lake and recovering from a drastic bottleneck, with additional samples from three other ringed seal subspecies. Using whole-genome sequences of 145 seals, we analyzed the distribution of variation and genetic relatedness among the individuals in relation to the habitat shape. Despite a severe history of genetic bottlenecks with prevalent homozygosity in Saimaa ringed seals, we found evidence for the population structure mirroring the subregions of the lake. Our genome-wide analyses showed that the subpopulations had retained unique variation and largely complementary patterns of homozygosity, highlighting the significance of habitat connectivity in conservation biology and the power of genomic tools in understanding its impact. The central role of the population substructure in preserving genetic diversity at the metapopulation level was confirmed by simulations. Integration of genetic analyses in conservation decisions gives hope to Saimaa ringed seals and other endangered species in fragmented habitats.

Nasopulmonary mites (Acari: Halarachnidae) as potential vectors of bacterial pathogens, including Streptococcus phocae, in marine mammals.

Nasopulmonary mites (NPMs) of the family Halarachnidae are obligate endoparasites that colonize the respiratory tracts of mammals. NPMs damage surface epithelium resulting in mucosal irritation, respiratory illness, and secondary infection, yet the role of NPMs in facilitating pathogen invasion or dissemination between hosts remains unclear. Using 16S rRNA massively parallel amplicon sequencing of six hypervariable regions (or "16S profiling"), we characterized the bacterial community of NPMs from 4 southern sea otters (Enhydra lutris nereis). This data was paired with detection of a priority pathogen, Streptococcus phocae, from NPMs infesting 16 southern sea otters and 9 California sea lions (Zalophus californianus) using nested conventional polymerase chain reaction (nPCR). The bacteriome of assessed NPMs was dominated by Mycoplasmataceae and Vibrionaceae, but at least 16 organisms with pathogenic potential were detected as well. Importantly, S. phocae was detected in 37% of NPM by nPCR and was also detected by 16S profiling. Detection of multiple organisms with pathogenic potential in or on NPMs suggests they may act as mechanical vectors of bacterial infection for marine mammals.

Geographically dispersed zoonotic tuberculosis in pre-contact South American human populations.

Previous ancient DNA research has shown that Mycobacterium pinnipedii, which today causes tuberculosis (TB) primarily in pinnipeds, infected human populations living in the coastal areas of Peru prior to European colonization. Skeletal evidence indicates the presence of TB in several pre-colonial South and North American populations with minimal access to marine resources- a scenario incompatible with TB transmission directly from infected pinnipeds or their tissues. In this study, we investigate the causative agent of TB in ten pre-colonial, non-coastal individuals from South America. We reconstruct M. pinnipedii genomes (10- to 15-fold mean coverage) from three contemporaneous individuals from inland Peru and Colombia, demonstrating the widespread dissemination of M. pinnipedii beyond the coast, either through human-to-human and/or animal-mediated routes. Overall, our study suggests that TB transmission in the pre-colonial era Americas involved a more complex transmission pathway than simple pinniped-to-human transfer.

Spectral tuning and deactivation kinetics of marine mammal melanopsins.

In mammals, the photopigment melanopsin (Opn4) is found in a subset of retinal ganglion cells that serve light detection for circadian photoentrainment and pupil constriction (i.e., mydriasis). For a given species, the efficiency of photoentrainment and length of time that mydriasis occurs is determined by the spectral sensitivity and deactivation kinetics of melanopsin, respectively, and to date, neither of these properties have been described in marine mammals. Previous work has indicated that the absorbance maxima (λmax) of marine mammal rhodopsins (Rh1) have diversified to match the available light spectra at foraging depths. However, similar to the melanopsin λmax of terrestrial mammals (~480 nm), the melanopsins of marine mammals may be conserved, with λmax values tuned to the spectrum of solar irradiance at the water's surface. Here, we investigated the Opn4 pigments of 17 marine mammal species inhabiting diverse photic environments including the Infraorder Cetacea, as well as the Orders Sirenia and Carnivora. Both genomic and cDNA sequences were used to deduce amino acid sequences to identify substitutions most likely involved in spectral tuning and deactivation kinetics of the Opn4 pigments. Our results show that there appears to be no amino acid substitutions in marine mammal Opn4 opsins that would result in any significant change in λmax values relative to their terrestrial counterparts. We also found some marine mammal species to lack several phosphorylation sites in the carboxyl terminal domain of their Opn4 pigments that result in significantly slower deactivation kinetics, and thus longer mydriasis, compared to terrestrial controls. This finding was restricted to cetacean species previously found to lack cone photoreceptor opsins, a condition known as rod monochromacy. These results suggest that the rod monochromat whales rely on extended pupillary constriction to prevent photobleaching of the highly photosensitive all-rod retina when moving between photopic and scotopic conditions.

Predicting sample success for large-scale ancient DNA studies on marine mammals.

In recent years, nonhuman ancient DNA studies have begun to focus on larger sample sizes and whole genomes, offering the potential to reveal exciting and hitherto unknown answers to ongoing biological and archaeological questions. However, one major limitation to such studies is the substantial financial and time investments still required during sample screening, due to uncertainty regarding successful sample selection. This study investigates the effect of a wide range of sample properties including latitude, sample age, skeletal element, collagen preservation, and context on endogenous content and DNA damage profiles for 317 ancient and historic pinniped samples collected from across the North Atlantic and surrounding regions. Using generalised linear and mixed-effect models, we found that a range of factors affected DNA preservation within each of the species under consideration. The most important findings were that endogenous content varied significantly within species according to context, the type of skeletal element, the collagen content and collection year. There also appears to be an effect of the sample's geographic origin, with samples from the Arctic generally showing higher endogenous content and lower damage rates. Both latitude and sample age were found to have significant relationships with damage levels, but only for walrus samples. Sex, ontogenetic age and extraction material preparation were not found to have any significant relationship with DNA preservation. Overall, skeletal element and sample context were found to be the most influential factors and should therefore be considered when selecting samples for large-scale ancient genome studies.

Karyotype Evolution in 10 Pinniped Species: Variability of Heterochromatin versus High Conservatism of Euchromatin as Revealed by Comparative Molecular Cytogenetics.

Pinnipedia karyotype evolution was studied here using human, domestic dog, and stone marten whole-chromosome painting probes to obtain comparative chromosome maps among species of Odobenidae (Odobenus rosmarus), Phocidae (Phoca vitulina, Phoca largha, Phoca hispida, Pusa sibirica, Erignathus barbatus), and Otariidae (Eumetopias jubatus, Callorhinus ursinus, Phocarctos hookeri, and Arctocephalus forsteri). Structural and functional chromosomal features were assessed with telomere repeat and ribosomal-DNA probes and by CBG (C-bands revealed by barium hydroxide treatment followed by Giemsa staining) and CDAG (Chromomycin A3-DAPI after G-banding) methods. We demonstrated diversity of heterochromatin among pinniped karyotypes in terms of localization, size, and nucleotide composition. For the first time, an intrachromosomal rearrangement common for Otariidae and Odobenidae was revealed. We postulate that the order of evolutionarily conserved segments in the analyzed pinnipeds is the same as the order proposed for the ancestral Carnivora karyotype (2n = 38). The evolution of conserved genomes of pinnipeds has been accompanied by few fusion events (less than one rearrangement per 10 million years) and by novel intrachromosomal changes including the emergence of new centromeres and pericentric inversion/centromere repositioning. The observed interspecific diversity of pinniped karyotypes driven by constitutive heterochromatin variation likely has played an important role in karyotype evolution of pinnipeds, thereby contributing to the differences of pinnipeds' chromosome sets.

Adaptations to a semiaquatic lifestyle in the external ear of southern pinnipeds (Otariidae and Phocidae, Carnivora): Morphological evidences.

Pinnipeds are semiaquatic carnivorans that spend most of their lives in water and use coastal terrestrial, or ice pack, environments to breed, molt and rest. Certain characteristics of the ear have been linked to ecological aspects. In our contribution we focus on the study of the macroscopic and microscopic morphology of the external ear (with the exception of the osseous outer ear canal) of six species of Southern pinnipeds. In order to recognize the different components of tissues, sections were stained following several routine protocols. In addition, double-staining and enzymatic clearing (Alcian blue-alizarin red) was performed to assess the arrangement of skeletal elements in the OEC. The basic structure of the pinna in the southern otariids studied match those previously analyzed for Northern Hemisphere species. The cartilage macro anatomy of the OEC of Mirounga leonina and Arctocephallus gazella is different from that of the Northern Hemisphere species, with only one plate of cartilage, but markedly different between them. The histology of the otariids OEC is homogeneous along the entire extension, but phocids has three different regions (distal, middle, and proximal). The cartilage histology of most phocids is also different from that of analyzed otariids, with an elastic cartilage that resembles a myxoid-like tissue, but is not present in M. leonina, were the tissue around the OEC is very rich in adipocytes. The southern elephant seal M. leonina OEC has a combination of features similar to both the rest of the phocids and to the otariids. An auditory organ that is functional both over and under water could be essential for social behavior in these species.

Low guanylyl cyclase activity in Weddell seals: implications for peripheral vasoconstriction and perfusion of the brain during diving.

Nitric oxide (NO) is a potent vasodilator, which improves perfusion and oxygen delivery during tissue hypoxia in terrestrial animals. The vertebrate dive response involves vasoconstriction in select tissues, which persists despite profound hypoxia. Using tissues collected from Weddell seals at necropsy, we investigated whether vasoconstriction is aided by downregulation of local hypoxia signaling mechanisms. We focused on NO-soluble guanylyl cyclase (GC)-cGMP signaling, a well-known vasodilatory transduction pathway. Seals have a lower GC protein abundance, activity, and capacity to respond to NO stimulation than do terrestrial mammals. In seal lung homogenates, GC produced less cGMP (20.1 ± 3.7 pmol·mg protein-1·min-1) than the lungs of dogs (-80 ± 144 pmol·mg protein-1·min-1 less than seals), sheep (-472 ± 96), rats (-664 ± 104) or mice (-1,160 ± 104, P < 0.0001). Amino acid sequences of the GC enzyme α-subunits differed between seals and terrestrial mammals, potentially affecting their structure and function. Vasoconstriction in diving Weddell seals is not consistent across tissues; perfusion is maintained in the brain and heart but decreased in other organs such as the kidney. A NO donor increased median GC activity 49.5-fold in the seal brain but only 27.4-fold in the kidney, consistent with the priority of cerebral perfusion during diving. Nos3 expression was high in the seal brain, which could improve NO production and vasodilatory potential. Conversely, Pde5a expression was high in the seal renal artery, which may increase cGMP breakdown and vasoconstriction in the kidney. Taken together, the results of this study suggest that alterations in the NO-cGMP pathway facilitate the diving response.

Demographic histories and genetic diversity across pinnipeds are shaped by human exploitation, ecology and life-history.

A central paradigm in conservation biology is that population bottlenecks reduce genetic diversity and population viability. In an era of biodiversity loss and climate change, understanding the determinants and consequences of bottlenecks is therefore an important challenge. However, as most studies focus on single species, the multitude of potential drivers and the consequences of bottlenecks remain elusive. Here, we combined genetic data from over 11,000 individuals of 30 pinniped species with demographic, ecological and life history data to evaluate the consequences of commercial exploitation by 18th and 19th century sealers. We show that around one third of these species exhibit strong signatures of recent population declines. Bottleneck strength is associated with breeding habitat and mating system variation, and together with global abundance explains much of the variation in genetic diversity across species. Overall, bottleneck intensity is unrelated to IUCN status, although the three most heavily bottlenecked species are endangered. Our study reveals an unforeseen interplay between human exploitation, animal biology, demographic declines and genetic diversity.

Pinniped Diphyly and Bat Triphyly: More Homology Errors Drive Conflicts in the Mammalian Tree.

Homology is perhaps the most central concept of phylogenetic biology. At difficult to resolve polytomies that are deep in the Tree of Life, a few homology errors in phylogenomic data can drive spurious phylogenetic results. Feijoo and Parada (2017) assembled three phylogenomic data sets for mammals and reported methodological discrepancies and unexpected results that contradict the monophyly of well-established clades in Pinnipedia and Yangochiroptera. Examination of Feijoo and Parada's (2017) data sets reveals extensive homology errors (paralogous sequences, alignments of different exons to each other) and cross-contamination of sequences from different species. These problems predictably result in distorted estimates of gene trees, species trees, bootstrap support, and branch lengths. Correction of these errors resulted in robust support for conventional relationships in Pinnipedia and Yangochiroptera. Phylogenomic data sets are not immune to the problems of homology errors in sequence alignments. Rather, sequence alignments underlie all inferences in molecular phylogenetics and evolution and should be spot-checked for obvious errors via manual inspection of alignments and gene trees.

Hundreds of Genes Experienced Convergent Shifts in Selective Pressure in Marine Mammals.

Mammal species have made the transition to the marine environment several times, and their lineages represent one of the classical examples of convergent evolution in morphological and physiological traits. Nevertheless, the genetic mechanisms of their phenotypic transition are poorly understood, and investigations into convergence at the molecular level have been inconclusive. While past studies have searched for convergent changes at specific amino acid sites, we propose an alternative strategy to identify those genes that experienced convergent changes in their selective pressures, visible as changes in evolutionary rate specifically in the marine lineages. We present evidence of widespread convergence at the gene level by identifying parallel shifts in evolutionary rate during three independent episodes of mammalian adaptation to the marine environment. Hundreds of genes accelerated their evolutionary rates in all three marine mammal lineages during their transition to aquatic life. These marine-accelerated genes are highly enriched for pathways that control recognized functional adaptations in marine mammals, including muscle physiology, lipid-metabolism, sensory systems, and skin and connective tissue. The accelerations resulted from both adaptive evolution as seen in skin and lung genes, and loss of function as in gustatory and olfactory genes. In regard to sensory systems, this finding provides further evidence that reduced senses of taste and smell are ubiquitous in marine mammals. Our analysis demonstrates the feasibility of identifying genes underlying convergent organism-level characteristics on a genome-wide scale and without prior knowledge of adaptations, and provides a powerful approach for investigating the physiological functions of mammalian genes.

Contrasting responses to a climate regime change by sympatric, ice-dependent predators.

BACKGROUND: Models that predict changes in the abundance and distribution of fauna under future climate change scenarios often assume that ecological niche and habitat availability are the major determinants of species' responses to climate change. However, individual species may have very different capacities to adapt to environmental change, as determined by intrinsic factors such as their dispersal ability, genetic diversity, generation time and rate of evolution. These intrinsic factors are usually excluded from forecasts of species' abundance and distribution changes. We aimed to determine the importance of these factors by comparing the impact of the most recent climate regime change, the late Pleistocene glacial-interglacial transition, on two sympatric, ice-dependent meso-predators, the emperor penguin (Aptenodytes forsteri) and Weddell seal (Leptonychotes weddellii). METHODS: We reconstructed the population trend of emperor penguins and Weddell seals in East Antarctica over the past 75,000 years using mitochondrial DNA sequences and an extended Bayesian skyline plot method. We also assessed patterns of contemporary population structure and genetic diversity. RESULTS: Despite their overlapping distributions and shared dependence on sea ice, our genetic data revealed very different responses to climate warming between these species. The emperor penguin population grew rapidly following the glacial-interglacial transition, but the size of the Weddell seal population did not change. The expansion of emperor penguin numbers during the warm Holocene may have been facilitated by their higher dispersal ability and gene flow among colonies, and fine-scale differences in preferred foraging locations. CONCLUSIONS: The vastly different climate change responses of two sympatric ice-dependent predators suggests that differing adaptive capacities and/or fine-scale niche differences can play a major role in species' climate change responses, and that adaptive capacity should be considered alongside niche and distribution in future species forecasts.

The complete mitochondrial genome sequence of Alopex lagopus (Caniformia: Canidae).

The phylogenetic and taxonomic positions of the blue fox (Alopex lagopus) have long been unclear. In this study, we determined and described the complete mitogenome sequence of A. lagopus for the first time, which is 16,629 bp in length and contains 37 genes, including 13 protein-coding genes, 2 rRNAs, 22 tRNAs, 1 origin of replication on the light-strand and a putative control region. The overall base composition is A: 31.3%, T: 27.8%, C: 26.1% and G: 14.8%, with a slight AT bias (59.1%). Most of them have TAA as the stop codon, except ND2 uses TAG, ND4 uses AGG, Cytb uses AGA and COX3 and ND3 use an incomplete stop codon TA. This information could not only contribute to provide useful molecular data for the species identification, but also to further taxonomic and phylogenetic studies of Alopex and Canidae.

Uridine Diphosphate-Glucuronosyltransferase (UGT) Xenobiotic Metabolizing Activity and Genetic Evolution in Pinniped Species.

There are various interspecies differences in xenobiotic-metabolizing enzymes. It is known that cats show slow glucuronidation of drugs such as acetaminophen and strong side effects due to the UGT1A6 pseudogene. Recently, the UGT1A6 pseudogene was found in the Northern elephant seal and Otariidae was suggested to be UGT1A6-deficient. From the results of measurements of uridine diphosphate-glucuronosyltransferase (UGT) activity using liver microsomes, the Steller sea lion, Northern fur seal, and Caspian seal showed UGT activity toward 1-hydroxypyrene and acetaminophen as low as in cats, which was significantly lower than in rat and dog. Furthermore, UGT1A6 pseudogenes were found in Steller sea lion and Northern fur seal, and all Otariidae species were suggested to have the UGT1A6 pseudogene. The UGT1 family genes appear to have undergone birth-and-death evolution based on a phylogenetic and synteny analysis of the UGT1 family in mammals including Carnivora. UGT1A2-1A5 and UGT1A7-1A10 are paralogous genes to UGT1A1 and UGTA6, respectively, and their numbers were lower in cat, ferret and Pacific walrus than in human, rat, and dog. Felidae and Pinnipedia, which are less exposed to natural xenobiotics such as plant-derived toxins due to their carnivorous diet, have experienced fewer gene duplications of xenobiotic-metabolizing UGT genes, and even possess UGT1A6 pseudogenes. Artificial environmental pollutants and drugs conjugated by UGT are increasing dramatically, and their elimination to the environment can be of great consequence to cat and Pinnipedia species, whose low xenobiotic glucuronidation capacity makes them highly sensitive to these compounds.

Impact of the terrestrial-aquatic transition on disparity and rates of evolution in the carnivoran skull.

BACKGROUND: Which factors influence the distribution patterns of morphological diversity among clades? The adaptive radiation model predicts that a clade entering new ecological niche will experience high rates of evolution early in its history, followed by a gradual slowing. Here we measure disparity and rates of evolution in Carnivora, specifically focusing on the terrestrial-aquatic transition in Pinnipedia. We analyze fissiped (mostly terrestrial, arboreal, and semi-arboreal, but also including the semi-aquatic otter) and pinniped (secondarily aquatic) carnivorans as a case study of an extreme ecological transition. We used 3D geometric morphometrics to quantify cranial shape in 151 carnivoran specimens (64 fissiped, 87 pinniped) and five exceptionally-preserved fossil pinnipeds, including the stem-pinniped Enaliarctos emlongi. Range-based and variance-based disparity measures were compared between pinnipeds and fissipeds. To distinguish between evolutionary modes, a Brownian motion model was compared to selective regime shifts associated with the terrestrial-aquatic transition and at the base of Pinnipedia. Further, evolutionary patterns were estimated on individual branches using both Ornstein-Uhlenbeck and Independent Evolution models, to examine the origin of pinniped diversity. RESULTS: Pinnipeds exhibit greater cranial disparity than fissipeds, even though they are less taxonomically diverse and, as a clade nested within fissipeds, phylogenetically younger. Despite this, there is no increase in the rate of morphological evolution at the base of Pinnipedia, as would be predicted by an adaptive radiation model, and a Brownian motion model of evolution is supported. Instead basal pinnipeds populated new areas of morphospace via low to moderate rates of evolution in new directions, followed by later bursts within the crown-group, potentially associated with ecological diversification within the marine realm. CONCLUSION: The transition to an aquatic habitat in carnivorans resulted in a shift in cranial morphology without an increase in rate in the stem lineage, contra to the adaptive radiation model. Instead these data suggest a release from evolutionary constraint model, followed by aquatic diversifications within crown families.

Cope's rule and the evolution of body size in Pinnipedimorpha (Mammalia: Carnivora).

Cope's rule describes the evolutionary trend for animal lineages to increase in body size over time. In this study, we tested the validity of Cope's rule for a marine mammal clade, the Pinnipedimorpha, which includes the extinct Desmatophocidae, and extant Phocidae (earless seals), Otariidae (fur seals and sea lions), and Odobenidae (walruses). We tested for the presence of Cope's rule by compiling a large dataset of body size data for extant and fossil pinnipeds and then examined how body size evolved through time. We found that there was a positive relationship between geologic age and body size. However, this trend is the result of differences between early assemblages of small-bodied pinnipeds (Oligocene to early Miocene) and later assemblages (middle Miocene to Pliocene) for which species exhibited greater size diversity. No significant differences were found between the number of increases or decreases in body size within Pinnipedimorpha or within specific pinniped clades. This suggests that the pinniped body size increase was driven by passive diversification into vacant niche space, with the common ancestor of Pinnipedimorpha occurring near the minimum adult body size possible for a marine mammal. Based upon the above results, the evolutionary history of pinnipeds does not follow Cope's rule.

Ferrets exclusively synthesize Neu5Ac and express naturally humanized influenza A virus receptors.

Mammals express the sialic acids N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) on cell surfaces, where they act as receptors for pathogens, including influenza A virus (IAV). Neu5Gc is synthesized from Neu5Ac by the enzyme cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH). In humans, this enzyme is inactive and only Neu5Ac is produced. Ferrets are susceptible to human-adapted IAV strains and have been the dominant animal model for IAV studies. Here we show that ferrets, like humans, do not synthesize Neu5Gc. Genomic analysis reveals an ancient, nine-exon deletion in the ferret CMAH gene that is shared by the Pinnipedia and Musteloidia members of the Carnivora. Interactions between two human strains of IAV with the sialyllactose receptor (sialic acid--α2,6Gal) confirm that the type of terminal sialic acid contributes significantly to IAV receptor specificity. Our results indicate that exclusive expression of Neu5Ac contributes to the susceptibility of ferrets to human-adapted IAV strains.