Direct visualization of blood flow through the interaortic foramen of the eastern diamondback rattlesnake, Crotalus adamanteus, using echocardiography and color Doppler imaging

The bases of the left and right aortae in snakes are joined by the interaortic foramen. Previous anatomical and physiological studies have raised the possibility of blood flow through this foramen playing an important role in the redistribution of blood throughout the body, particularly during periods of hemostatic stress. Echocardiography was employed to view the heart of unanesthetized specimens of the eastern diamondback rattlesnake, Crotalus adamanteus. The echocardiographic images, and particularly the color Doppler imaging, revealed that the patency of the interaortic foramen changes during the cardiac cycle, and that blood regularly flowed through the interaortic foramen between the two aortae. J. Exp. Zool. 284:742-745, 1999. Copyright 1999 Wiley-Liss, Inc.     

Variations in atrioventricular valve innervation in four species of mammals

In this series of studies, the innervation patterns of whole-mount preparations of bicuspid and tricuspid valves were studied by light microscopy in the mouse, rat, guinea pig, and opossum. The acetylcholinesterase-positive networks of nerve fibers showed many similarities in the basic patterns of valve innervation in all of the species studied, but several interspecies variations were observed. The basal zone of the valve adjacent to the fibromuscular atrioventricular ring displayed the most dense plexus of nerves, with acetylcholinesterase-positive fibers being seen across the width of the valve. In the intermediate zone of the valve, less dense plexuses of nerve fibers were found; and these were more numerous in the cuspal areas and less numerous in the intervening commissural areas. In the distal portions of the valve, nerve networks arborized extensively, with some of their nerve fibers extending toward the chordae tendineae and the free edges of the valve cusps. Only in the guinea pig and opossum did these fibers reach the free margin of the valve cusp, where they either ended directly as free nerve endings or lay parallel to the free edge of the cusp, often running between adjacent chordae tendineae. Although the patterns of innervation were similar in both bicuspid and tricuspid valves, the innervation density of the bicuspid valve was greater than that of the tricuspid valve for each species examined. A distinguishing feature of guinea pig and opossum tricuspid valves was that their chordae tendineae were relatively more prominent and more densely innervated than the bicuspid chordae tendineae. Free nerve endings with no light microscopic evidence of specialization were present throughout the bicuspid and tricuspid valves of all species studied. Some nerve endings in the opossum showed evidence of specialization, with brush-like arborizations leading to presumed free terminals seen chiefly in the distal zone of the valve cusps. Although some general tendencies were apparent, we have demonstrated that interspecies heterogeneity exists in the terminal networks of the atrioventricular valves of mouse, rat, guinea pig, and opossum.     

Vascular-nervous relationships in the valves of the heart]

Method of silver nitrate impregnation was used in order to study 50 preparations of not-changed atrioventricular valves of the heart of domestic bulls and 30 preparations of the same valves of adult humans. It has been shown that in heart valves there are certain relationships between striated muscle fibres, blood vessels and nerve elements. The nerve structures of the valves are represented by nerve bundles of different thickness. In their composition there are comparatively thin non-myelinated and thicker myelinated fibres. Towards the free edge of cusps the nerve bundles become thinner and the nerve trunks give off separate thin nerve fibres disposed along the vessels of a capillary type and in some places getting around them. In certain portions of cusps the nerve bundles, some of which have zigzag sinuosity, cross blood vessels in different directions. In man the major mass of blood vessels and nerve elements are disposed near the base of the valve cusps, accompanying the muscle fibre bundles penetrating from the base side. In the bull heart valves an amount of blood vessels and nerve elements is found in considerable portions of the cusps not connected with muscle fibres.     

The relationships of phytosterols and oxyphytosterols in plasma and aortic valve cusps in patients with severe aortic stenosis

Phytosterols such as campesterol and sitosterol are susceptible to oxidation by reactive oxygen species. We hypothesize that the plant sterols (PS) campesterol and sitosterol and their 7-oxygenated metabolites (POPs) correlate within and between human plasma and aortic valve cusps tissues. Plasma and tissue concentrations of PS and POPs were analyzed by gas chromatography–mass spectrometry-selected ion monitoring. Prior to analysis valve cusps tissue was mechanically separated from the calcified parts. PS and POP levels per dry cusps tissue weight were significantly higher compared with the concentrations in the calcified part. Against our hypothesis we found that despite the fact that there is a high correlation between plant sterols in and between plasma and valves cusps tissue, as well as a high correlation between plant sterols and oxyphytosterols and oxyphytosterols themselves within the valve cusps tissue, there was hardly any correlation in the amount of oxyphytosterols in plasma and between plasma and valves. Because plasma samples are easily accessible for large scale population based studies, we have to understand in more detail what the analysis of POPs implies in terms of CVD risk for the future.     

Biochemical characterization of individual normal, floppy and rheumatic human mitral valves.

Human mitral valves (32 floppy and 17 rheumatic) obtained at surgery were analysed and compared with 35 normal (autopsy) valves. Total amounts of collagen, proteoglycan and elastin were increased approx. 3-fold in floppy and rheumatic valves. The water content of rheumatic cusps was lower than normal. The most significant changes in floppy valves were the 59% increase in mean value of the proteoglycan content, a large increase in the ease of extractability of proteoglycans from 26.7 to 57.2% of the total and a 62% increase in mean value of the elastin content in the anterior cusps. Normal human mitral valve cusps contained a mean proportion of 29.3 (and chordae 26.6) type III collagen (as % of total types III + I collagen), the values increasing significantly to 33.2 and 36.3% respectively in chronic rheumatic disease. The ratio observed in floppy valves depended on the extent of secondary surface fibrosis, which could be demonstrated histologically; in valve cusps with considerable secondary fibrosis, the percentage of type III increased significantly (to 34.4%), whereas it decreased significantly (to 25.2%) when fibrosis was negligible. It is concluded that the ratio of collagen types in floppy valves reflects the extent of secondary fibrosis rather than the pathogenesis of the disrupted collagen in the central core of the valve.     

Valve orientation and functional morphology of the foramen of some siphonotretacean and acrotretacean brachiopods

It has recently been suggested that the foramen of siphonotretacean and acrotretacean brachiopods functioned as an exhalant siphon and that it was a feature of the dorsal valve. In representatives of these superfamilies the pedicle was considered to have emerged from between the valves. Re-examination of the evidence on which these arguments were based suggests that some of it is capable of more than one interpretation. The remainder, together with consideration of the mantle canal patterns, cemented mode of attachment, and comparative morphology of some discinaceans and siphonotretaceans, strongly supports the traditional view that the foramen of these forms was located in the ventral valve and that it served as a pedicle opening.     

Endothelial deletion of ADAM17 in mice results in defective remodeling of the semilunar valves and cardiac dysfunction in adults

Global inactivation of the metalloproteinase ADAM17 during mouse development results in perinatal lethality and abnormalities of the heart, including late embryonic cardiomegaly and thickened semilunar and atrioventricular valves. These defects have been attributed in part to a lack of ADAM17-mediated processing of HB-EGF, as absence of soluble HB-EGF results in similar phenotypes. Because valvular mesenchymal cells are largely derived from cardiac endothelial cells, we generated mice with a floxed Adam17 allele and crossed these animals with Tie2-Cre transgenics to focus on the role of endothelial ADAM17 in valvulogenesis. We find that although hearts from late-stage embryos with ablation of endothelial ADAM17 appear normal, an increase in valve size and cell number is evident, but only in the semilunar cusps. Unlike Hbegf^?/? valves, ADAM17-null semilunar valves do not differ from controls in acute cell proliferation at embryonic day 14.5 (E14.5), suggesting compensatory processing of HB-EGF. However, levels of the proteoglycan versican are significantly reduced in mutant hearts early in valve remodeling (E12.5). After birth, aortic valve cusps from mutants are not only hyperplastic but also show expansion of the glycosaminoglycan-rich component, with the majority of adults exhibiting aberrant compartmentalization of versican and increased deposition of collagen. The inability of mutant outflow valve precursors to transition into fully mature cusps is associated with decreased postnatal viability, progressive cardiomegaly, and systolic dysfunction. Together, our data indicate that ADAM17 is required in valvular endothelial cells for regulating cell content as well as extracellular matrix composition and organization in semilunar valve remodeling and homeostasis.     

The effect of elastin damage on the mechanics of the aortic valve

Porcine bioprosthetic heart valves degenerate and fail mechanically through a mechanism that is currently not well understood. It has been suggested that damage to the elastin component of prosthetic valve cusps could be responsible for changes in the mechanical function of the valve that would predispose it to increased damage and ultimate failure. To determine whether damage to elastin can produce the structural and mechanical changes that could initiate the process of bioprosthetic valve degeneration, we developed an elastase treatment protocol that fragments elastin and negates its mechanical contribution to the valve tissue. Valve cusps were mechanically tested before and after digestion to measure the mechanical changes resulting from elastin damage. Elastin damage produced a decrease in radial and circumferential extensibility (from 43 to 18% strain radially and 12 to 7% strain circumferentially), with a slight increase in stiffness (1.3-2.6kN/m for radial and 10.6-11.9kN/m for circumferential directions). Digestions with trypsin, which does not cleave elastin, confirmed that the changes in mechanics of the circumferential samples were likely due to the nonspecific removal of proteoglycans by elastase, while the changes in the radial samples were indeed due to elastin damage. Removing the mechanical contribution of elastin alters the mechanical behavior of the aortic valve cusp, primarily in the radial direction. This finding implies that damage to elastin will distend the cusps, reduce their extensibility, and increase their stiffness. Damage to elastin may therefore contribute to the degeneration and failure of prosthetic valves.     

Morphology and evolution of the snake cornea

To investigate whether the thickness of the cornea in snakes correlates with overall anatomy, habitat or daily activity pattern, we measured corneal thickness using optical coherence tomography scanning in 44 species from 14 families (214 specimens) in the collection at the Natural History Museum (Denmark). Specifically, we analyzed whether the thickness of the cornea varies among species in absolute terms and relative to morphometrics, such as body length, spectacle diameter, and spectacle thickness. Furthermore, we examined whether corneal thickness reflects adaptation to different habitats and/or daily activity patterns. The snakes were defined as arboreal (n = 8), terrestrial (n = 22), fossorial (n = 7), and aquatic (n = 7); 14 species were classified as diurnal and 30 as nocturnal. We reveal that the interspecific variation in corneal thickness is largely explained by differences in body size, but find a tendency towards thicker corneas in diurnal (313 ± 227 μm) compared to nocturnal species (205 ± 169 μm). Furthermore, arboreal snakes had the thickest corneas and fossorial snakes the thinnest. Our study shows that body length, habitat, and daily activity pattern could explain the interspecific variation in corneal morphology among snakes. This study provides a quantitative analysis of the evolution of the corneal morphology in snakes, and it presents baseline values of corneal thickness of multiple snake species. We speculate that the cornea likely plays a role in snake vision, despite the fact that results from previous studies suggest that the cornea in snakes is not relevant for vision (Sivak, Vision Research, 1977, 17, 293–298).     

Gravitational gradients and blood flow patterns in specialized arboreal (Ahaetulla nasuta) and terrestrial (Crotalus adamanteus) snakes

Blood pressure and blood flow patterns were recorded from the carotid artery and aortae of a thick-bodied terrestrial snake (Crotalus adamanteus) and a thin-bodied arboreal species (Ahaetulla nasuta) anesthetized with ketamine hydrochloride. Hemodynamic stress induced by rotation resulted in pronounced changes in the blood flow patterns and pressure in C. adamanteus: rotation of A. nasuta produced changes of a similar type, but of a much lower magnitude. The markedly different responses of these two species, the baroreceptor reflexes of which were disrupted, suggest that morphological factors – such as differential gross cardiac displacement, or variation in the interaortic foramen – in addition to physiological factors, are important in determining a snake's ability to withstand hemodynamic stress. Accepted: 8 April 1997     

Functional morphology and palaeontological significance of the conchiolin layers in corbulid pelecypods

The Corbulidae, which today are slow, cumbersome, very shallow burrowers, developed special morphological features by which they obtained an outstanding capability to withstand the physical and biological stresses characteristic of their preferred habitat. These features are: an inequivalve, globose shape, thick shells, and conchiolin layers (at least one) embedded within their valves in a unique way. These features enable the corbulids to close their valves tightly during the unfavourable environmental conditions (e.g. low salinity, low oxygen content) which may prevail in the marginal marine regions inhabited by several corbulid species. The conchiolin layers act as a barrier preventing all chemically boring organisms from penetrating into the bivalve shell, or shell dissolution by sea water undersaturated with respect to calcium carbonate. The layered conchiolin weakens the shell mechanically, however, especially during fossilization, when the conchiolin is decomposed. The valve splits apart into two shells so completely different in appearance that they may be attributed to different taxa. The conchiolin layers are therefore of great ecological and palaeontological significance. The nature of these conchiolin layers in Corbula (Varicorbula) gibba (Olivi) is described and illustrated and their functional significance discussed in relation to other living and fossil corbulid species.     

Gravity and the evolution of cardiopulmonary morphology in snakes

Physiological investigations of snakes have established the importance of heart position and pulmonary structure in contexts of gravity effects on blood circulation. Here we investigate morphological correlates of cardiopulmonary physiology in contexts related to ecology, behavior and evolution. We analyze data for heart position and length of vascular lung in 154 species of snakes that exhibit a broad range of characteristic behaviors and habitat associations. We construct a composite phylogeny for these species, and we codify gravitational stress according to species habitat and behavior. We use conventional regression and phylogenetically independent contrasts to evaluate whether trait diversity is correlated with gravitational habitat related to evolutionary transitions within the composite tree topology. We demonstrate that snake species living in arboreal habitats, or which express strongly climbing behaviors, possess relatively short blood columns between the heart and the head, as well as relatively short vascular lungs, compared to terrestrial species. Aquatic species, which experience little or no gravity stress in water, show the reverse — significantly longer heart-head distance and longer vascular lungs. These phylogenetic differences complement the results of physiological studies and are reflected in multiple habitat transitions during the evolutionary histories of these snake lineages, providing strong evidence that heart-to-head distance and length of vascular lung are co-adaptive cardiopulmonary features of snakes.     

Eastern Hog-Nosed Snake Habitat Selection at Multiple Spatial Scales in Ontario,Canada

Habitat loss is the greatest contributor to the decline of species globally. To prioritize protection of imperiled species, it is important to examine habitat use at multiple spatial scales because the availability of different resources and habitat features is scale dependent. We conducted a radio-telemetry study in the Long Point region of Ontario, Canada, in 2009 and 2010 to examine habitat selection at multiple spatial scales by eastern hog-nosed snakes (Heterodon platirhinos), a species at risk in Canada. We documented the habitat composition of home ranges compared to the surrounding landscape, the selection of locations within home ranges based on classified satellite imagery, and the use of microhabitat features based on site characterization in the field. At the scale of the home ranges, hog-nosed snakes avoided areas of agriculture and selected sand barrens. Within home ranges, hog-nosed snakes selectively used areas altered by humans (e.g., residential sites, openings in tree plantations). Microhabitats used by hog-nosed snakes had more woody debris, logs, and lower vegetative coverage than adjoining random sites. Because hog-nosed snakes prefer open areas and require sandy soils for nesting, management efforts should focus on the conservation and maintenance of sand barrens and patches of early successional forest. © 2021 The Wildlife Society.     

Molecular and functional characteristics of heart-valve interstitial cells

The cells that reside within valve cusps play an integral role in the durability and function of heart valves. There are principally two types of cells found in cusp tissue: the endothelial cells that cover the surface of the cusps and the interstitial cells (ICs) that form a network within the extracellular matrix (ECM) within the body of the cusp. Both cell types exhibit unique functions that are unlike those of other endothelial and ICs found throughout the body. The valve ICs express a complex pattern of cell-surface, cytoskeletal and muscle proteins. They are able to bind to, and communicate with, each other and the ECM. The endothelial cells on the outflow and inflow surfaces of the valve differ from one another. Their individual characteristics and functions reflect the fact that they are exposed to separate patterns of flow and pressure. In addition to providing a structural role in the valve, it is now known that the biological function of valve cells is important in maintaining the integrity of the cusps and the optimum function of the valve. In response to inappropriate stimuli, valve interstitial and endothelial cells may also participate in processes that lead to valve degeneration and calcification. Understanding the complex biology of valve interstitial and endothelial cells is an important requirement in elucidating the mechanisms that regulate valve function in health and disease, as well as setting a benchmark for the function of cells that may be used to tissue engineer a heart valve.     

Snake behavior and seasonal variation in nest survival of northern cardinals Cardinalis cardinalis

Seasonal variation in nest success is well documented for many bird species. Predator behavior has been suggested as a mechanism behind these seasonal patterns, but this hypothesis has received little attention. Here we test the hypothesis that predator behavior produces seasonal patterns of nest success by relating nest success of northern cardinals Cardinalis cardinalis to the activity of Texas rat snakes Elaphe obsoleta. Cardinal nest survival varied over the season and was lower when rat snakes were more active. The probability that a nest survived was associated both with when cardinals nested and with nest height, indicating that both temporal and habitat factors affected predation risk. The increased success of higher nests could be associated with some aspect of rat snakes’ climbing ability. In combination with results for two other species studied previously at the same location, our results for cardinals suggest that the specific seasonal pattern of nest success expected for a given bird species will depend on how its nesting season coincides with predator activity. Determining the generality of seasonal variation in predator behavior as a mechanism for producing seasonal patterns of avian nest success will require additional studies that investigate birds and their nest predators simultaneously.     

Discordant patterns of population structure for two co‐distributed snake species across a fragmented Ontario landscape

Aim The goal of our study was to investigate the effects of a fragmented landscape on the genetic population structure of two sympatric snake species that differ in habitat preference. The eastern garter snake (Thamnophis sirtalis sirtalis) is a common, habitat generalist, whereas the endangered eastern foxsnake (Mintonius [Elaphe] gloydi) is rarer, geographically restricted, and a marsh‐specialist. We were most interested in comparing the genetic population structure of both species and identifying any natural and human‐created features of the landscape that overlap with genetic disjunctions. Location Southwestern Ontario, Canada, surveying over half of the remaining range of the eastern foxsnake. Methods We utilized DNA microsatellite markers to examine genetic population structure of both species. The number of genetically distinct clusters for each species was determined using both Bayesian spatial assignment and spatial principal component analyses (sPCA). Genetic clusters were overlaid onto a habitat map to deduce possible physiognomic barriers to gene flow. Results Spatial assignment revealed three genetic clusters for garter snakes and five for foxsnakes. Each individual garter snake had a near equal probability of membership to two or more clusters with no cluster mapping onto a discrete geographic region, indicating that garter snakes comprise a single genetic population. The identified foxsnake clusters correspond to geographically circumscribed locations on the landscape, roughly coincident with isolated patches of suitable habitat. sPCAs revealed significant global allelic structure for foxsnakes, but not for garter snakes. No significant local structure was found for either species. Main Conclusions Our results imply that foxsnakes and garter snakes are differentially impacted by the same landscape or have dramatically different effective population sizes. Unsuitable intervening habitat such as agricultural tracts and roads between existing populations of foxsnakes appears to act as barriers to gene flow, while garter snake movement appears unrestricted by these features. Our findings have important implications for the management of eastern foxsnakes.     

Temperate Snake Community in South America: Is Diet Determined by Phylogeny or Ecology?

Communities are complex and dynamic systems that change with time. The first attempts to explain how they were structured involve contemporary phenomena like ecological interactions between species (e.g., competition and predation) and led to the competition-predation hypothesis. Recently, the deep history hypothesis has emerged, which suggests that profound differences in the evolutionary history of organisms resulted in a number of ecological features that remain largely on species that are part of existing communities. Nevertheless, both phylogenetic structure and ecological interactions can act together to determine the structure of a community. Because diet is one of the main niche axes, in this study we evaluated, for the first time, the impact of ecological and phylogenetic factors on the diet of Neotropical snakes from the subtropical-temperate region of South America. Additionally, we studied their relationship with morphological and environmental aspects to understand the natural history and ecology of this community. A canonical phylogenetical ordination analysis showed that phylogeny explained most of the variation in diet, whereas ecological characters explained very little of this variation. Furthermore, some snakes that shared the habitat showed some degree of diet convergence, in accordance with the competition-predation hypothesis, although phylogeny remained the major determinant in structuring this community. The clade with the greatest variability was the subfamily Dipsadinae, whose members had a very different type of diet, based on soft-bodied invertebrates. Our results are consistent with the deep history hypothesis, and we suggest that the community under study has a deep phylogenetic effect that explains most of the variation in the diet.     

An Examination of Scale-Dependent Resource Use by Eastern Hognose Snakes in Southcentral New Hampshire

ABSTRACT The decline of many snake populations is attributable to habitat loss, and knowledge of habitat use is critical to their conservation. Resource characteristics (e.g., relative availability of different habitat types, soils, and slopes) within a landscape are scale-dependent and may not be equal across multiple spatial scales. Thus, it is important to identify the relevant spatial scales at which resource selection occurs. We conducted a radiotelemetry study of eastern hognose snake (Heterodon platirhinos) home range size and resource use at different hierarchical spatial scales. We present the results for 8 snakes radiotracked during a 2-year study at New Boston Air Force Station (NBAFS) in southern New Hampshire, USA, where the species is listed by the state as endangered. Mean home range size (minimum convex polygon) at NBAFS (51.7 ± 14.7 ha) was similar to that reported in other parts of the species’ range. Radiotracked snakes exhibited different patterns of resource use at different spatial scales. At the landscape scale (selection of locations within the landscape), snakes overutilized old-field and forest edge habitats and underutilized forested habitats and wetlands relative to availability. At this scale, snakes also overutilized areas containing sandy loam soils and areas with lower slope (mean slope = 5.2% at snake locations vs. 6.7% at random locations). We failed to detect some of these patterns of resource use at the home range scale (i.e., within the home range). Our ability to detect resource selection by the snakes only at the landscape scale is likely the result of greater heterogeneity in macrohabitat features at the broader landscape scale. From a management perspective, future studies of habitat selection for rare species should include measurement of available habitat at spatial scales larger than the home range. We suggest that the maintenance of open early successional habitats as a component of forested landscapes will be critical for the persistence of eastern hognose snake populations in the northeastern United States.     

THE VALUE OF ECHOCARDIOGRAPHY IN THE MANAGEMENT OF ACUTE AORTIC INSUFFICIENCY

Three cases of acute rupture of the aortic cusp complicating bacterial endocarditis are described. Special emphasis is placed on the value of serial echocardiography as a means of identifying progressive changes in aortic valve anatomy during the destructive process of the disease. Prior to the results of blood cultures, an echocardiogram confirmed a diagnosis of vegetations on the valve cusps. It also demonstrated flailing of the aortic cusp, which was confirmed at operation. Echocardiographic findings of flailing aortic valves in these patients coincided with the onset of acute aortic insufficiency and contributed to the timing of surgical intervention for replacement of the affected valves.