Landscape-scale assessment of tree crown dieback following extreme drought and heat in a Mediterranean eucalypt forest ecosystem

Mediterranean regions are under increasing pressure from global climate changes. Many have experienced more frequent extreme weather events such as droughts and heatwaves, which have severe implications for the persistence of forest ecosystems. This study reports on a landscape-scale assessment investigating potential associated factors of crown dieback in dominant tree species following an extreme dry and hot year/summer of 2010/11 in the Northern Jarrah Forest of Western Australia. Analyses focussed on the influence of (i) geology, (ii) topography, (iii) climate, and (iv) fire history. The results showed that trees on specific soils were more likely to show canopy dieback. Generally, trees on rocky soils with low water holding capacity were found to be affected more frequently. Other explanatory factors identified that dieback occurred (i) on sites that were close to rock outcrops, (ii) in areas that received a slightly higher amount of annual rainfall compared to the surrounding landscape, (iii) on sites at high elevations and (vi) on steep slopes, and (v) in areas that were generally slightly warmer than their surroundings. These results expand our understanding of how landscape-scale factors contribute to the effects of an extreme drought and heating event in Mediterranean forest ecosystems, and give indications of where changes are likely to occur within the landscape in the future. The analogues with other Mediterranean climate regions make the results of this study transferable and a starting point for further investigations.     

Identification of unique DNA sequences present in highly virulent 2009 Alabama isolates of Aeromonas hydrophila

In 2009, a disease outbreak caused by Aeromonas hydrophila occurred in 48 catfish farms in West Alabama, causing an estimated loss of more than 3 million pounds of food size channel catfish. Virulence studies have revealed that the 2009 isolates of A. hydrophila are at least 200-fold more virulent than a 1998 Alabama isolate AL98-C1B. However, up to now, no molecular markers have been identified to differentiate the highly virulent 2009 isolates from other isolates of A. hydrophila. To understand the genetic differences between the highly virulent 2009 isolates and the less virulent AL98-C1B at molecular level, PCR-select bacterial genome subtractive hybridization was used in this study. A total of 96 clones were selected from the subtractive genomic DNA library. Sequencing results revealed that the 96 clones represented 64 unique A. hydrophila sequences. Of the 64 sequences, three (hypothetical protein XAUC_13870, structural toxin protein RtxA, and putative methyltransferase) were confirmed to be present in the three virulent 2009 Alabama isolates but absent in the less virulent AL98-C1B. Using genomic DNAs from nine field isolates of A. hydrophila with different virulence as templates, two sequences (hypothetical protein XAUC_13870 and putative methyltransferase) were found to be only present in highly virulent A. hydrophila isolates, but absent in avirulent isolates.     

Estimation of additive and non-additive genetic effects for fertility and reproduction traits in North American Holstein cattle using genomic information

Non-additive genetic effects are usually ignored in animal breeding programs due to data structure (e.g., incomplete pedigree), computational limitations and over-parameterization of the models. However, non-additive genetic effects may play an important role in the expression of complex traits in livestock species, such as fertility and reproduction traits. In this study, components of genetic variance for additive and non-additive genetic effects were estimated for a variety of fertility and reproduction traits in Holstein cattle using pedigree and genomic relationship matrices. Four linear models were used: (a) an additive genetic model; (b) a model including both additive and epistatic (additive by additive) genetic effects; (c) a model including both additive and dominance effects; and (d) a full model including additive, epistatic and dominance genetic effects. Nine fertility and reproduction traits were analysed, and models were run separately for heifers (N = 5,825) and cows (N = 6,090). For some traits, a larger proportion of phenotypic variance was explained by non-additive genetic effects compared with additive effects, indicating that epistasis, dominance or a combination thereof is of great importance. Epistatic genetic effects contributed more to the total phenotypic variance than dominance genetic effects. Although these models varied considerably in the partitioning of the components of genetic variance, the models including a non-additive genetic effect did not show a clear advantage over the additive model based on the Akaike information criterion. The partitioning of variance components resulted in a re-ranking of cows based solely on the cows’ additive genetic effects between models, indicating that adjusting for non-additive genetic effects could affect selection decisions made in dairy cattle breeding programs. These results suggest that non-additive genetic effects play an important role in some fertility and reproduction traits in Holstein cattle.     

Fenbendazole in equids: further controlled tests with emphasis on activity of multiple doses against naturally occurring infections of migratory large strongyles

Two controlled tests (experiments D and E) were done to evaluate a fenbendazole (FBZ) paste dosage regimen (10 mg/kg once a day for 5 days) for activity against naturally occurring infections of migrating Strongylus vulgaris and S edentatus in the mesenteric arteries and ventral abdominal wall, respectively. Data were also obtained on other internal parasites of the gastrointestinal tract and eyes in experiment E. Eight pony yearlings were used in experiment D (4 treated and 4 nontreated) and 6 horse weanlings were used in experiment E (3 treated and 3 nontreated). Intervals, expressed as days between treatment and necropsy of animals, were 42 (n = 1) or 52 (n = 7) for experiment D and 52 or 53 for experiment E. Animals were on pasture during all or a portion of post-treatment intervals of both experiments. Efficacious killing of retroperitoneal forms of S edentatus in the ventral abdominal wall was observed in both experiments. The average numbers of live 4th-stage forms in equids were 0.0 (treated) and 2.25 (nontreated) for experiment D and 2.0 (treated) and 1.7 (nontreated) for experiment E. The average numbers of 5th-stage S edentatus were 0.5 (treated) and 4.0 (nontreated) for experiment D and 1.3 (treated) and 23.3 (nontreated) for experiment E. Fragments of dead specimens of S edentatus were also found in nodules in treated animals in both experiments, but not in nontreated animals. Consistency of the retroperitoneal lesions provided additional evidence of the killing action of the FBZ treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ascaridoid nematodes and associated lesions in stomachs of subadult male northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska: (1987-1999).

Stomachs from subadult male northern fur seals (SAMs) (Callorhinus ursinus) (n = 5,950) from St. Paul Island, Alaska, were examined from 1987 to 1999 for lesions and parasites. On gross examination of these stomachs, parasite nodules were evident in 92% of the stomachs and active and healing ulcers were found in 14% and 10%, respectively. Prevalence of nematodes from 1987 to 1997 was 88% for 5,700 SAMs for which numbers of parasites were estimated but not identified to the genus level. All nematodes recovered from 250 SAMs examined in 1998 (n = 124; 99% infected) and in 1999 (n = 126; 91% infected) were identified and counted. Prevalences in 1998 and 1999 were 5% and 0% for Anisakis spp., 52% and 18% for Contracaecum spp., and 96% and 89% for Pseudoterranova spp., respectively.     

Controlled tests of activity of ivermectin against natural infections of migratory large strongyles and other internal parasites of equids

Four controlled tests (experiments A, B, C, and D) were conducted in naturally infected yearling equids to evaluate activity of ivermectin (0.2 mg/kg IM) against migrating Strongylus vulgaris and S edentatus in mesenteric arteries and ventral abdominal wall, respectively. Data were also obtained on activity against other internal parasites of the gastrointestinal tract and eyeworms. The type and number of equids in the experiments were as follows: experiment A-3 ponies, 2 treated and 1 non-treated; experiment B-4 mixed-bred horses, 2 treated and 2 nontreated; experiment C-5 mixed-bred horses, 3 treated and 2 nontreated; experiment D-4 mixed-bred horses, 2 treated and 2 nontreated. Intervals between treatment and necropsy were 35 days in experiment A, 52 to 53 days in experiment B, 38 to 41 days in experiment C, and 45 days in experiment D. Efficacious killing of retroperitoneal forms of S edentatus in the ventral abdominal wall was obtained in the 4 experiments. Only dead worms or fragments were recovered from treated animals, while living 4th-stage and/or 5th-stage S edentatus was present in nontreated equids in each test. A similar killing effect on S vulgaris in cranial mesenteric arteries was recorded in 2 experiments (B and D); only 1 dead 5th-stage worm was found in 1 of the treated yearlings in experiment B, whereas living 4th- and 5th-stages of S vulgaris were found in the nontreated controls in both experiments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of land use legacies and habitat fragmentation on salamander abundance

Context

Landscape modification is an important driver of biodiversity declines, yet we lack insight into how ongoing landscape change and legacies of historical land use together shape biodiversity.

Objectives

We examined how a history of agricultural land use and current forest fragmentation influence the abundance of red-backed salamanders (Plethodon cinereus). We hypothesized that historical agriculture and fragmentation cause changes in habitat quality and landscape structure that limit abundance.

Methods

We measured salamander abundance at 95 forested sites in New York, USA, and we determined whether sites were agricultural fields within the last five decades. We used a structural equation model to estimate relationships between historical agriculture and salamander abundance mediated by changes in forest vegetation, microclimate, and landscape structure.

Results

Historical agriculture affected salamander abundance by altering forest vegetation at a local scale and forest cover at a landscape scale. Abundance was lowest at post-agricultural sites with low woody vegetation, leaf litter depth, and canopy cover. Post-agricultural sites had limited forest cover in the surrounding landscape historically, and salamander abundance was positively related to historical forest cover, suggesting that connectivity to source populations affects colonization of regenerating forests. Abundance was also negatively related to current forest fragmentation.

Conclusions

Historical land use can have legacy effects on animal abundance on par with effects of ongoing landscape change. We showed that associations between animal abundance and historical land use can be driven by altered site conditions and surrounding habitat area, indicating that restoration efforts should consider local site conditions and landscape context.