Shear stress paradigm for perinatal fractal arterial network remodeling in lambs with pulmonary hypertension and increased pulmonary blood flow

Congenital heart disease with increased blood flow commonly leads to the development of increased pulmonary vascular reactivity and pulmonary arterial hypertension by mechanisms that remain unclear. We hypothesized a shear stress paradigm of hemodynamic reactivity and network remodeling via the persistence and/or exacerbation of a fetal diameter bifurcation phenotype [parent diameter d(0) and daughters d(1) >or= d(2) with alpha < 2 in (d(1)/d(0))(alpha) + (d(2)/d(0))(alpha) and area ratio beta < 1 in beta = (d(1)(2)+ d(2)(2))/ d(0)(2)] that mechanically acts as a high resistance magnifier/shear stress amplifier to blood flow. Evidence of a hemodynamic influence on network remodeling was assessed with a lamb model of high-flow-induced secondary pulmonary hypertension in which an aortopulmonary graft was surgically placed in one twin in utero (Shunt twin) but not in the other (Control twin). Eight weeks after birth arterial casts were made of the left pulmonary arterial circulation. Bifurcation diameter measurements down to 0.010 mm in the Shunt and Control twins were then compared with those of an unoperated fetal cast. Network organization, cumulative resistance, and pressure/shear stress distributions were evaluated via a fractal model whose dimension D(0) approximately alpha delineates hemodynamic reactivity. Fetus and Control twin D(0) differed: fetus D(0)=1.72, a high-resistance/shear stress amplifying condition; control twin D(0) = 2.02, an area-preserving transport configuration. The Shunt twin (D(0)=1.72) maintained a fetal design but paradoxically remodeled diameter geometry to decrease cumulative resistance relative to the Control twin. Our results indicate that fetal/neonatal pulmonary hemodynamic reactivity remodels in response to shear stress, but the response to elevated blood flow and pulmonary hypertension involves the persistence and exacerbation of a fetal diameter bifurcation phenotype that facilitates endothelial dysfunction/injury.     

Can the invasive European rabbit (Oryctolagus cuniculus) assume the soil engineering role of locally-extinct natives?

Habitat modifying species can play crucial roles in ecosystem function. Invasive engineers may assume these roles where native engineers have been lost from the system. We compared the dynamics of the foraging pits of an invasive engineer, the European rabbit (Oryctolagus cuniculus) with two native mammals, the greater bilby (Macrotis lagotis) and the burrowing bettong (Bettongia lesueur). Foraging pits are small surface depressions created by animals when they forage for seeds, bulbs, roots, invertebrates and fungi. We measured foraging pit density and turnover, and density and richness of plant seedlings in pits and adjacent surfaces across three landforms representing a gradient in resource availability inside (bilbies and bettongs), and outside (rabbits only) a reserve in an arid Australian shrubland over 2 years. Pits of the native engineers contained 80% more seedlings (11.2 plants m⁻²) than rabbit pits (6.22 plants m⁻²). Further, rabbit pits supported 3.6-times fewer seedlings than equivalent non-pit surfaces outside the exclosure. Only one plant species was restricted entirely to pits. The reserve had more foraging pits and greater turnover than outside, but contrary to prediction, pit effects on seedling density were no greater in the more resource-limited dunes. There were some strong temporal and landscape effects on pit density and species composition, but generally trends were similar inside and outside the reserve. Overall, despite their functional similarities, invasive rabbits created fewer pits that were less favourable patches for seedlings than those of native engineers. Our work suggests that a suite of ecosystem processes associated with fertile patch creation has potentially been lost with the extirpation of bilbies and bettongs.     

Microhabitat amelioration and reduced competition among understorey plants as drivers of facilitation across environmental gradients: Towards a unifying framework

Studies of facilitative interactions as drivers of plant richness along environmental gradients often assume the existence of an overarching stress gradient that equally affects the performance of all the species in a given community. However, co-existing species differ in their ecophysiological adaptations, and do not experience the same stress level under particular environmental conditions. Moreover, these studies assume a unimodal relationship between richness and biomass, which is not as general as previously thought. We ignored these assumptions to assess changes in plant–plant interactions and their effect on local species richness across environmental gradients in semi-arid areas of Spain and Australia. We aimed to understand the relative importance of direct (microhabitat amelioration) and indirect (changes in the competitive relationships among the understorey species: niche segregation, competitive exclusion or intransitivity) mechanisms that might underlie the effects of nurse plants on local species richness. By jointly studying these direct and indirect mechanisms using a unifying framework, we found that nurse plants (trees, shrubs and tussock grasses) increased local richness not only by expanding the niche of neighbouring species but also by increasing niche segregation among them, though the latter was not important in all cases. The outcome of the competition-facilitation continuum varied depending on the study area, likely because the different types of stress gradient considered. When driven by both rainfall and temperature, or rainfall alone, the community-wide importance of nurse plants remained constant (Spanish sites), or showed a unimodal relationship along the gradient (Australian sites). This study expands our understanding of the relative roles of plant–plant interactions and environmental conditions as drivers of local species richness in semi-arid environments. The results can also be used to refine predictions about the response of plant communities to environmental change, and to clarify the relative importance of biotic interactions as drivers of such responses.     

High sero-prevalence of caseous lymphadenitis identified in slaughterhouse samples as a consequence of deficiencies in sheep farm management in the state of Minas Gerais, Brazil

Background

Multiple congenital ocular anomalies (MCOA) syndrome is a hereditary congenital eye defect that was first described in Silver colored Rocky Mountain horses. The mutation causing this disease is located within a defined chromosomal interval, which also contains the gene and mutation that is associated with the Silver coat color (PMEL17, exon 11). Horses that are homozygous for the disease-causing allele have multiple defects (MCOA-phenotype), whilst the heterozygous horses predominantly have cysts of the iris, ciliary body or retina (Cyst-phenotype). It has been argued that these ocular defects are caused by a recent mutation that is restricted to horses that are related to the Rocky Mountain Horse breed. For that reason we have examined another horse breed, the Icelandic horse, which is historically quite divergent from Rocky Mountain horses.

Results

We examined 24 Icelandic horses and established that the MCOA syndrome is present in this breed. Four of these horses were categorised as having the MCOA-phenotype and were genotyped as being homozygous for the PMEL17 mutation. The most common clinical signs included megaloglobus, iris stromal hypoplasia, abnormal pectinate ligaments, iridociliary cysts occasionally extending into the peripheral retina and cataracts. The cysts and pectinate ligament abnormalities were observed in the temporal quadrant of the eyes. Fourteen horses were heterozygous for the PMEL17 mutation and were characterized as having the Cyst-phenotype with cysts and occasionally curvilinear streaks in the peripheral retina. Three additional horses were genotyped as PMEL17 heterozygotes, but in these horses we were unable to detect cysts or other forms of anomalies. One eye of a severely vision-impaired 18 month-old stallion, homozygous for the PMEL17 mutation was examined by light microscopy. Redundant duplication of non-pigmented ciliary body epithelium, sometimes forming cysts bulging into the posterior chamber and localized areas of atrophy in the peripheral retina were seen.

Conclusions

The MCOA syndrome is segregating with the PMEL17 mutation in the Icelandic Horse population. This needs to be taken into consideration in breeding decisions and highlights the fact that MCOA syndrome is present in a breed that are more ancient and not closely related to the Rocky Mountain Horse breed.     

Significant patterns of population genetic structure and limited gene flow in a threatened macropodid marsupial despite continuous habitat in southeast Queensland, Australia

Many endangered species worldwide are found in remnant populations, often within fragmented landscapes. However, when possible, an understanding of the natural extent of population structure and dispersal behaviour of threatened species would assist in their conservation and management. The brush-tailed rock-wallaby (Petrogale penicillata), a once abundant and widespread rock-wallaby species across southeastern Australia, has become nearly extinct across much of the southern part of its range. However, the northern part of the species’ range still sustains many small colonies closely distributed across suitable habitat, providing a rare opportunity to investigate the natural population dynamics of a listed threatened species. We used 12 microsatellite markers to investigate genetic diversity, population structure and gene flow among brush-tailed rock-wallaby colonies within and among two valley regions with continuous habitat in southeast Queensland. We documented high and significant levels of population genetic structure between rock-wallaby colonies embedded in continuous escarpment habitat and forest. We found a strong and significant pattern of isolation-by-distance among colonies indicating restricted gene flow over a small geographic scale ( <10 km) and conclude that gene flow is more likely limited by intrinsic factors rather than environmental factors. In addition, we provide evidence that genetic diversity was significantly lower in colonies located in a more isolated valley region compared to colonies located in a valley region surrounded by continuous habitat. These findings shed light on the processes that have resulted in the endangered status of rock-wallaby species in Australia and they have strong implications for the conservation and management of both the remaining ‘connected’8 brush-tailed rock-wallaby colonies in the northern parts of the species’8 range and the remnant endangered populations in the south.     

Cytogenetic and molecular evaluation of centromere-associated DNA sequences from a marsupial (Macropodidae: Macropus rufogriseus) X chromosome

The constitution of the centromeric portions of the sex chromosomes of the red-necked wallaby, Macropus rufogriseus (family Macropodidae, subfamily Macropodinae), was investigated to develop an overview of the sequence composition of centromeres in a marsupial genome that harbors large amounts of centric and pericentric heterochromatin. The large, C-band-positive centromeric region of the X chromosome was microdissected and the isolated DNA was microcloned. Further sequence and cytogenetic analyses of three representative clones show that all chromosomes in this species carry a 178-bp satellite sequence containing a CENP-B DNA binding domain (CENP-B box) shown herein to selectively bind marsupial CENP-B protein. Two other repeats isolated in this study localize specifically to the sex chromosomes yet differ in copy number and intrachromosomal distribution. Immunocytohistochemistry assays with anti-CENP-E, anti-CREST, anti-CENP-B, and anti-trimethyl-H3K9 antibodies defined a restricted point localization of the outer kinetochore at the functional centromere within an enlarged pericentric and heterochromatic region. The distribution of these repeated sequences within the karyotype of this species, coupled with the apparent high copy number of these sequences, indicates a capacity for retention of large amounts of centromere-associated DNA in the genome of M. rufogriseus.     

Nematode community structure in the brush-tailed rock-wallaby, Petrogale penicillata: Implications of captive breeding and the translocation of wildlife

Despite an increasing appreciation of the disease risks associated with wild-life translocations, the effects which captive breeding programs exert on parasite communities remain understudied. This may be attributed, in part, to the current lack of rapid and cost-effective techniques for comparing parasite assemblages between host populations. Terminal restriction fragment length polymorphism (T-RFLP) analysis of the rDNA region encompassing the internal transcribed spacers (ITS-1 and ITS-2) and 5.8S rRNA gene was used to characterise bursate nematode communities (suborder Strongylida) across two captive and two non-captive colonies of the threatened brush-tailed rock-wallaby, Petrogale penicillata. A clone library was constructed and a restriction enzyme selected to differentiate the predominant operational taxonomic units (OTUs) by the unique peak profiles they generated. The prevalence, intensity of infection and comparative structure of strongylid assemblages was evaluated for each of the host colonies. Compared to wild conspecifics, captive wallabies exhibited a reduced prevalence of infection and significantly lower faecal egg counts. T-RFLP revealed that a high proportion of the OTUs co-occurred across three of the four study locations. Despite this, the composition of strongylid assemblages was significantly different between the colonies, even when host translocation events had occurred. These results suggest that captive breeding programs may exert a profound impact on parasitic helminth assemblages. Developing efficient techniques for characterising community dynamics in potentially pathogenic organisms is critical to the long term success of species recovery efforts worldwide.     

Novel insights into the phylogenetic relationships of the endangered marsupial genus Potorous

The three extant potoroo species of the marsupial genus Potorous -Potorous tridactylus, P. longipes and P. gilbertii - are all of conservation concern due to introduced predators and habitat loss associated with the European settlement of Australia. Robust phylogenies can be useful to inform conservation management, but past phylogenetic studies on potoroos have been unable to fully resolve relationships within the genus. Here, a multi-locus approach was employed, using three mitochondrial DNA (mtDNA): NADH dehydrogenase subunit 2, cytochrome c oxidase subunit 1 and 12S rRNA and four nuclear DNA (nuDNA) gene regions: breast and ovarian cancer susceptibility gene, recombination activating gene-1, apolipoprotein B and omega globin. This was coupled with widespread geographic sampling of the broadly distributed P. tridactylus, to investigate the phylogenetic relationships within this genus. Analyses of the mtDNA identified five distinct and highly divergent lineages including, P. longipes, P. gilbertii and three distinct lineages within P. tridactylus (northern mainland, southern mainland and Tasmanian). P. tridactylus was paraphyletic with the P. gilbertii lineage, suggesting that cryptic taxa may exist within P. tridactylus. NuDNA sequences lacked the resolution of mtDNA. Although they resolved the three currently recognised species, they were unable to differentiate lineages within P. tridactylus. Current management of P. tridactylus as two sub-species (mainland and Tasmania) does not recognise the full scope of genetic diversity within this species, especially that of the mainland populations. Until data from more informative nuDNA markers are available, we recommend this species be managed as the following three subspecies: Potorous tridactylus tridactylus (southern Queensland and northern New South Wales); Potorous tridactylus trisulcatus (southern New South Wales and Victoria) Potorous tridactylus apicalis (Tasmania). Molecular dating estimated that divergences within Potorous occurred in the late Miocene through to the early Pliocene.