Aquatic Carnivores Research Articles

Osteological profiling of femoral diaphysis and neck in aquatic, semiaquatic, and terrestrial carnivores and rodents: effects of body size and locomotor habits

The increased limb bone density documented previously for aquatic tetrapods has been proposed to be an adaptation to overcome buoyancy during swimming and diving. It can be achieved by increasing the amount of bone deposition or by reducing the amount of bone resorption, leading to cortical thickening, loss of medullary cavity, and compaction of trabecular bone. The present study examined the effects of locomotor habit, body size, and phylogeny on the densitometric, cross-sectional, and biomechanical traits of femoral diaphysis and neck in terrestrial, semiaquatic, and aquatic carnivores, and in terrestrial and semiaquatic rodents (12 species) by using peripheral quantitative computed tomography, three-point bending, and femoral neck loading tests. Groupwise differences were analyzed with the univariate generalized linear model and the multivariate linear discriminant analysis supplemented with hierarchical clustering. While none of the individual features could separate the lifestyles or species adequately, the combinations of multiple features produced very good or excellent classifications and clusterings. In the phocid seals, the aquatic niche allowed for lower femoral bone mineral densities than expected based on the body mass alone. The semiaquatic mammals mostly had high bone mineral densities compared to the terrestrial species, which could be considered an adaptation to overcome buoyancy during swimming and shallow diving. Generally, it seems that different osteological properties at the levels of mineral density and biomechanics could be compatible with the adaptation to aquatic, semiaquatic, or terrestrial niches.

Quantifying bird diversity at three sites of differing herbivore presence

Large herbivores directly and indirectly influence ecosystem function, positively and negatively affecting diversity of plants and animals, including birds. Such cascading effects are clearly important, particularly given ongoing global declines in large herbivores and many avian communities. We examined relationships between bird diversity (species richness and Shannon-Weiner Index, at a species and functional group level) at three similarly vegetated and flooded sites in northern Botswana. We explored the role that herbivore presence plays in ecosystem functioning considering bird species richness was significantly higher at the site of intermediate presence, followed by the high presence site. At a functional group level, the site of highest presence consistently had the greatest functional group richness. Also, at a functional group level we identified higher species richness and diversity in the two sites where herbivores were present at high levels. This was particularly pronounced for the avian aquatic carnivore, terrestrial herbivore, and aerial invertivore functional groupings. Large herbivores probably increased habitat complexity through their browsing and grazing, altering habitat structure, alongside other benefits such as faeces deposition and mutualistic relationships, creating more niches for avian communities. Fencing out large herbivores to reduce their grazing and browsing may therefore reduce bird diversity, and correspondingly, allowing large herbivores to increase in abundance through protected areas may indirectly increase bird diversity, acknowledging over abundance may be detrimental.

Interaction of freshwater microplastics with biota and heavy metals: a review

The worldwide contamination of waters by microplastics is an emerging health and environmental issue. Despite being relatively inert, microplastics may adsorb and carry other aquatic pollutants such as heavy metals. Adsorption of heavy metals onto microplastics is a spontaneous process controlled by the microplastic surface. Marine microplastics have been well discussed, yet there are actually a few reviews on microplastics in freshwater. Here, we review microplastic contamination in freshwater systems with focus on adsorption of heavy metals. We present microplastic abundance, distribution, impact of microplastic size, affinity for heavy metals and combined toxic effects of the co-occurrence of microplastic and heavy metals. Remarkably, the concentration of metals on polystyrene and polyvinyl chloride was 800 times higher than in the surrounding environment. Combined toxic effects include endocrine disrupting and reduced predatory behavior of aquatic carnivores.

Viral Pathogenesis, Recombinant Vaccines, and Oncolytic Virotherapy: Applications of the Canine Distemper Virus Reverse Genetics System.

Canine distemper virus (CDV) is a highly contagious pathogen transmissible to a broad range of terrestrial and aquatic carnivores. Despite the availability of attenuated vaccines against CDV, the virus remains responsible for outbreaks of canine distemper (CD) with significant morbidity and mortality in domesticated and wild carnivores worldwide. CDV uses the signaling lymphocytic activation molecule (SLAM, or CD150) and nectin-4 (PVRL4) as entry receptors, well-known tumor-associated markers for several lymphadenomas and adenocarcinomas, which are also responsible for the lysis of tumor cells and apparent tumor regression. Thus, CDV vaccine strains have emerged as a promising platform of oncolytic viruses for use in animal cancer therapy. Recent advances have revealed that use of the CDV reverse genetic system (RGS) has helped increase the understanding of viral pathogenesis and explore the development of recombinant CDV vaccines. In addition, genetic engineering of CDV based on RGS approaches also has the potential of enhancing oncolytic activity and selectively targeting tumors. Here, we reviewed the host tropism and pathogenesis of CDV, and current development of recombinant CDV-based vaccines as well as their use as oncolytic viruses against cancers.

A meta-analysis of home range studies in the context of trophic levels: Implications for policy-based conservation.

Home ranges have been widely-used as ecological tools, though using home range estimates in decision-support for conservation biology is a relatively new idea. However, trophic levels are rarely taken into consideration when estimating home range. This lapse could present issues when interpreting past studies, especially in policy-based conservation. The objectives of this study were to survey the current literature, to critically analyse published articles with home range analyses, and to compare home range size by species’ trophic level. We predicted that animals residing in higher trophic levels would have significantly larger home ranges than animals occupying lower trophic levels. We found that terrestrial carnivores had larger home ranges than terrestrial herbivores, though terrestrial mesocarnivores had the largest home ranges. We also found that aquatic herbivores had larger home ranges than both aquatic carnivores and aquatic mesocarnivores. Our results are important to consider for planning and management sectors, to avoid the implementation of ineffective conservation policies.

The gastrointestinal tract of the Australian water rat (Hydromys chrysogaster) – its morphological adaptations to a carnivorous diet

The Australian water rat (Hydromys chrysogaster), unlike most murine rodents, has a carnivorous diet. In the present study the morphology of its gastrointestinal tract is described and compared with that of other muroid rodents with more typical diets. It was found that the stomach of the water rat is relatively small and has a greater proportion of glandular epithelium than that of other species so far investigated. Comparisons of relative intestinal lengths showed that in the Australian water rat there is a comparatively long small intestine that constitutes ~90% of the total intestinal length, a short large intestine, and a small caecum. This divergent morphology of the gastrointestinal tract of the Australian water rat probably relates to the animal’s protein-rich diet, with the differences from those of other hydromyine rodents indicating considerable plasticity in the evolution of the gastrointestinal tract in this group of mammals. It suggests that, whilst the morphological adaptations of the water rat’s gastrointestinal tract probably evolved before the colonisation of Australia, its highly derived morphology has enabled this species to exploit the Australian environment as an aquatic carnivore.

Beyond phylogeny: pelecaniform and ciconiiform birds, and long-term niche stability

Phylogenetic trees are a starting point for the study of further evolutionary and ecological questions. We show that for avian evolutionary relationships, improved taxon sampling, longer sequences and additional data sets are giving stability to the prediction of the grouping of pelecaniforms and ciconiiforms, thus allowing inferences to be made about long-term niche occupancy. Here we report the phylogeny of the pelecaniform birds and their water-carnivore allies using complete mitochondrial genomes, and show that the basic groupings agree with nuclear sequence phylogenies, even though many short branches are not yet fully resolved. In detail, we show that the Pelecaniformes (minus the tropicbird) and the Ciconiiformes (storks, herons and ibises) form a natural group within a seabird water-carnivore clade. We find pelicans are the closest relatives of the shoebill (in a clade with the hammerkop), and we confirm that tropicbirds are not pelecaniforms. In general, the group appears to be an adaptive radiation into an ‘aquatic carnivore’ niche that it has occupied for 60–70 million years. From an ecological and life history perspective, the combined pelecaniform–ciconiform group is more informative than focusing on differences in morphology. These findings allow a start to integrating molecular evolution and macroecology.

Interactions between the Neotropical otter (Lontra longicaudis) and gillnet fishery in the southern Brazilian coast

The Neotropical otter (Lontra longicaudis) is an aquatic carnivore that interacts with fisheries activities and competes with fisherman for resources. Information about the biology and conservation issues of a species can be obtained from traditional ecological knowledge collected from the communities that share the same resources. In this sense, the objective of this study was to describe conflicts between the otters and two fishing communities (Imbé and Tramandaí) in the Tramandaí Lagoon (29°57′S; 50°11′W), in southern Brazil. We conducted 36 interviews that represented 72% of the local fishermen that use gillnets in the lagoon. All fishermen reported that otters interfered with fishing activities, by feeding on fish in the gillnets, and 75% of those interviewed reported gear damage. Fifty percent of the fishermen reported that observed the otters used the lagoon daily. Many fishermen (41.6%) also reported that the amount of damage attributed to the otters was considered “small”, but the depredation was reported as occurring daily (55.5%). Fishermen from Imbé have a more negative perception of the interaction with otters, probably because they usually fish near to the area most frequently used by otters. This amplifies the magnitude of the conflict and damage. In order to minimize the depredation of fish by otters directly on the gillnets, we suggested some measures to fishery management, as well as additional studies about the potential prey overlap between the Neotropical otter and the fishery.

Inhibition of viral RNA synthesis in canine distemper virus infection by proanthocyanidin A2

Canine distemper virus (CDV) is a contagious and multisystemic viral disease that affects domestic and wild canines as well as other terrestrial and aquatic carnivores. The disease in dogs is often fatal and no specific antiviral therapy is currently available.In this study, we evaluated the in vitro antiviral activity against CDV of proanthocyanidin A2 (PA2), a phenolic dimer belonging to the class of condensed tannins present in plants. Our results showed that PA2 exerted in vitro antiviral activity against CDV with a higher selectivity index compared to ribavirin, included in our study for the previously tested anti-CDV activity. The time of addition assay led us to observe that PA2 was able to decrease the viral RNA synthesis and to reduce progeny virus liberation, at different times post infection suggesting multiple mechanisms of action including inhibition of viral replicative complex and modulation of the redox milieu. These data suggest that PA2, isolated from the bark of Aesculus hippocastanum, has potential usefulness as an anti-CDV compound inhibiting viral replication.

Body size of insular carnivores: evidence from the fossil record

AbstractAim Our goals here are to: (1) assess the generality of one aspect of the island rule – the progressive trend towards decrease in size in larger species – for fossil carnivores on islands; (2) offer causal explanations for this pattern and deviations from it – as far as fossil carnivores are concerned; and (3) estimate the speed of this trend.Location Oceanic and oceanic‐like islands world‐wide.Methods Body size estimates of fossil insular carnivores and of their phylogenetically closest mainland relative were obtained from our own data and the published literature. Our dataset consisted of 18 species from nine islands world‐wide. These data were used to test whether the body size of fossil insular carnivores varies as a function of body size of the mainland species in combination with characteristics of the island ecosystem.Results Dwarfism was observed in two canid species. Moderate decrease in body mass was observed in one hyena species. Gigantism was observed in one otter species. Moderate body mass increase was observed in two otter species, one galictine mustelid and perhaps one canid. Negligible or no change in body mass at all was observed in five otter species, three galictine mustelids and one genet. Size changes in teeth do not lag behind in comparison to skeletal elements in the dwarfed canids. The evolutionary speed of dwarfism in a canid lineage is low.Main conclusions Size change in fossil terrestrial insular carnivores was constrained by certain ecological conditions, especially the availability of prey of appropriate body size. When such alternative prey was not available, the carnivores retained their mainland size. The impact of competitive carnivores seems negligible. The case of (semi‐)aquatic carnivores is much less clear. The species that maintained their ancestral body mass may have changed their diet, as is evidenced by their dentition. Among the otters, one case of significant size increase was observed, perhaps best explained as being due to it entering the niche of an obligate aquatic otter. Dwarfism was not observed in otters. The island rule seems to apply to fossil carnivores, but with exceptions. The dependency of the island rule on resource availability is emphasized by the present study.

Learning, climate and the evolution of cultural capacity

Patterns of environmental variation influence the utility, and thus evolution, of different learning strategies. I use stochastic, individual-based evolutionary models to assess the relative advantages of 15 different learning strategies (genetic determination, individual learning, vertical social learning, horizontal/oblique social learning, and contingent combinations of these) when competing in variable environments described by 1/ f noise. When environmental variation has little effect on fitness, then genetic determinism persists. When environmental variation is large and equal over all time-scales (“white noise”) then individual learning is adaptive. Social learning is advantageous in “red noise” environments when variation over long time-scales is large. Climatic variability increases with time-scale, so that short-lived organisms should be able to rely largely on genetic determination. Thermal climates usually are insufficiently red for social learning to be advantageous for species whose fitness is very determined by temperature. In contrast, population trajectories of many species, especially large mammals and aquatic carnivores, are sufficiently red to promote social learning in their predators. The ocean environment is generally redder than that on land. Thus, while individual learning should be adaptive for many longer-lived organisms, social learning will often be found in those dependent on the populations of other species, especially if they are marine. This provides a potential explanation for the evolution of a prevalence of social learning, and culture, in humans and cetaceans.

Diet mixing in an aquatic carnivore, the harbour seal

To determine the effects of diet mixing on digestive performance, harbour seals (Phoca vitulina L., 1758) were offered either pure diets of Pacific herring (Clupea pallasii Valenciennes, 1847) or walleye pollock (Theragra chalcogramma (Pallas, 1814)) or a 1:1 mix of herring and pollock. Regardless of diet, retention time decreased approximately 40% as intake quadrupled. The mean apparent digestible dry matter (ADDM) was greatest on mixed diets during low feeding frequency trials; ADDM during high feeding frequency trials was significantly reduced as intake increased for animals on the single-species (pollock or herring) diets. As intake increased, up to 45% more digestible energy was assimilated from the mixed diet than from either single-species diet. The findings of this study suggest that a mixed diet consisting of prey differing in lipid and protein amounts increased digestible energy intake in harbour seals. Our measures of intake and ADDM in harbour seals revealed digestive flexibility and indicated that digestion in harbour seals was more efficient on a mixed diet.

THE EVOLUTION OF LACTATION STRATEGIES IN PINNIPEDS: A PHYLOGENETIC ANALYSIS

Pinnipeds are a diverse group of aquatic carnivores that exhibit wide variation in body size, milk composition, lactation strategies, and the length of maternal care. We used 12 pinniped life‐history and ecological traits to test hypotheses concerning the influence of phylogeny, maternal body size, breeding substrate, and other factors on the evolution of lactation strategies. We used independent contrasts to account for phylogenetic effects on correlations between traits. Our findings indicate that the negative relationships between maternal mass and lactation length and between maternal mass and the percentage of time spent at sea by females during lactation are not recent adaptations, but likely a result of phylogenetic history and an evolutionary grade shift in lactation length, which occurred when the phocids diverged from the otariids. Differences in body size between the ancestral phocid and otariid impacted their foraging strategies and metabolic rates, which subsequently influenced lactation strategies. The fat‐storage abilities of large phocids may have allowed them to exploit remote and patchy prey resources and thereby reduce time spent feeding during lactation. We also suggest that an early divergence in the mammary gland structure of phocids and otariids is a fundamental influence on pinniped lactation strategies. Although estimates are lacking for several key species, body size appears to have little adaptive influence on the lactation length of extant species. Instead, an abbreviated lactation period seems to be adaptive in minimizing the relative milk energy expended over lactation, although it may have initially evolved to reduce maternal overhead, especially in ancestral fasting phocids. Subsequently, a brief lactation in phocids was also selected through the effects of terrestrial predation, the instability of breeding on pack‐ice, and the energy benefits of increasing milk energy output.

Digestive constraints on an aquatic carnivore: effects of feeding frequency and prey composition on harbor seals.

We hypothesized that increased feeding frequency in captive harbor seals would increase nutrient loads and thus reduce retention time and the digestive efficiency of natural prey. We measured daily feed intake and excretion during 6 feeding trials and fed herring (49% lipid), pollock (22% lipid) or an equal mix of each diet over 24 months. Animals were accustomed to feeding at either high or low frequency. Body mass and intake did not vary with season. Although mean retention times were similar between diets and feeding frequencies, solute and particulate digesta markers separated at high feeding frequency. Consistent dry matter digestibility resulted in greater gut fill from pollock than from herring. Digestible energy intakes from pollock were approximately 25% greater than from either herring or the mixed diet. Lipid digestibility of herring declined from 90% to 50% when lipid intake exceeded 60 g kg(-0.75) day(-1). Our hypothesis of a trade-off between intake and digestion was not supported for protein but was supported for lipid. Results of this study imply that a flexible digestive system for harbor seals can compensate for ingesting prey of lower energy density by increasing gut fill and enhancing protein and lipid assimilation, to sustain digestible energy intake.

Flippers versus feet: comparative trends in aquatic and non‐aquatic carnivores

SummaryIt is commonly accepted that many adaptations characterize carnivores that live in water. However, no comparative tests have ever shown systematic differences between aquatic and terrestrial carnivore species as a whole. We examine numerous hypotheses that purport to distinguish aquatic and terrestrial carnivores using 20 morphological, life history, physiological and ecological traits. Using the method of independent contrasts with a complete species‐level phylogeny of extant carnivores, we found few differences between aquatic and terrestrial species. Compared to terrestrial sister taxa, aquatic carnivores are streamlined (increased head and body length for a given body weight), have larger brains, smaller litter sizes, shorter interbirth intervals, and shorter lifespans. Some of these differences are important functionally. Larger brain size may be related to increased cognitive and sensory needs required for an amphibious lifestyle; smaller litters are likely associated with increased neonatal survival amidst competition for suitable breeding sites and advantages accruing to increased precociality. We conclude that broad differentiation of carnivores into aquatic and terrestrial ecotypes is not useful given that adaptive differences between these groups are limited and seemingly no more numerous than those that occur within each ecological group.

A comparative study of the anatomy of the iris and ciliary body in aquatic mammals

The ciliary muscle exhibits considerable variation in its development among the vertebrates. The muscle is considered to be well developed in humans, primates, ungulates, and aquatic carnivores, and the extent of development is thought to correspond to the amplitude of accommodation. The recent finding of a well-developed ciliary muscle in the hooded seal (Cystophora cristata) has initiated interest in an accommodative mechanism for vision in air and in water. This study is a comparative investigation of the ciliary muscle in a number of aquatic mammals. The methods include gross inspection of the ciliary region and histological examination of the ciliary body and iris by means of light microscopy. The results indicate that in completely aquatic mammals the ciliary muscle is rudimentary, and in fact, appears to be lacking in one species (beluga whale). The ciliary muscle appears to be better developed in the amphibious pinnipeds (California sea lion, elephant seal, and walrus). The presence of circular muscle bundles suggests that the muscle is more developed in the elephant seal and California sea lion than in the walrus. The degree of ciliary muscle development and the need for accommodation can be related to the natural history of each species.

FACTORS GOVERNING PATTERNS OF FORAGING ACTIVITY IN LITTORAL MARINE HERBIVOROUS MOLLUSCS

Relationships of feeding activity to tidal and day/night cycles in a variety of littoral herbivorous molluscs are reviewed. Most species are active while submerged by the tide, both by day and night. There are also many that are active only while emersed, with variation in relation to day/night cycles dependent upon micro-habitat. The third pattern is for activity to occur while awash by the tide, often with continued feeding while the rocks remain damp. Most species in these three groups have endogenous rhythms. The fourth type is one with no relation to tidal activity, and is confined to supra-littoral and sub-littoral species. Major proposed causes of the evolution of these patterns are: desiccation, together with osmotic and thermal stress which may have selected for nocturnal activity; dislodgement by waves; and predation by aquatic carnivores, which is often avoided by feeding at low tide. Of these desiccation and predation are widely regarded as most important. A study of Patella vulgata suggests that while predation and desiccation are major factors controlling activity patterns, they do not fully explain observed activity. A discussion of the importance of food supply is given, and it is proposed that where competition for food is low, night-time feeding should predominate; where competition is high, day-time feeding should predominate. This pattern fits observations on limpets at Lough Hyne, but needs testing in other field situations.

Function of the digastric muscle in carnivores.

The general form and adaptation of the digastric muscle in carnivores are reviewed and discussed. The digastric muscle differs from the general plan in certain aquatic carnivores and felids. In the pertinent aquatic species the muscle is enlarged. The observations suggest that the enlargement is an adaptation for rapidly opening the jaws against the resistance of water. In felids, the insertion of the muscle is much farther forward than in most other carnivores. The observations suggest that the development of short jaws in felids necessitated a compensatory anterior relocation of the digastric insertion in order to preserve the ability to achieve a large gape.

Energy extraction efficiency in some chosen insects.

The termsenergy extraction efficiency andabsorption/assimilation efficiency are defined. The grasshopperPoecilocerus pictus extracts 15 or 27% energy contained in the food plantCalotropis gigantea, when the test animals were fed from hatching to death at 26 or 36°C. The energy extraction efficiency of some insects (Bombyx andHyalophora: terrestrial herbovores;Pyrrhosoma: aquatic carnivore) is about 7%, though their assimilation efficiency ranges from 42 to 97%. High ash content of food organisms deviates the energy extraction efficiency inPyrrhosoma and the aquatic dipteran herbivoreHedriodiscus.

The pyramidal tract of an aquatic carnivore (seal).

Journal of Comparative NeurologyVolume 106, Issue 2 p. 425-431 Article The pyramidal tract of an aquatic carnivore (seal)† A. M. Lassek, A. M. Lassek Department of Anatomy, Boston University School of Medicine, 80 East Concord St., Boston 18, MassachusettsSearch for more papers by this authorPaul Karlsberg, Paul Karlsberg Department of Anatomy, Boston University School of Medicine, 80 East Concord St., Boston 18, MassachusettsSearch for more papers by this author A. M. Lassek, A. M. Lassek Department of Anatomy, Boston University School of Medicine, 80 East Concord St., Boston 18, MassachusettsSearch for more papers by this authorPaul Karlsberg, Paul Karlsberg Department of Anatomy, Boston University School of Medicine, 80 East Concord St., Boston 18, MassachusettsSearch for more papers by this author First published: December 1956 https://doi.org/10.1002/cne.901060210Citations: 6 † This investigation was supported by a research grant from the division of Neurological Diseases and Blindness, National Institute of Health, U. S. Public Health Service. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume106, Issue2December 1956Pages 425-431 RelatedInformation