Mammals as prey: Estimating ingestible size

Most mammals have deformable bodies, making it difficult to measure the size of living or freshly killed ones accurately. Because small rodents are common prey of many snakes, and because nearly all snakes swallow their prey whole, we explored four methods for determining the ingestible size (the smallest cross‐sectional area that the largest part of the rodent can be made into without breaking bones or dislocating joints) of 100 intact rodents, including 50 Musmusculus and 50 Rattus norvegicus. Cross‐sectional areas derived from maximal height and width of specimens at rest or the same specimens wrapped snout to pelvic girdle are roughly 1.5× higher than areas calculated either by the height and width of the same specimens rolled into cylinders or by volumetric displacement. Rolling rodents into cylinders reduces cross‐sectional area by straightening the vertebral column, lengthening the abdominal cavity, elevating the sternum, compressing the thoracic cavity, and protracting the shoulder joint, that is, changes similar to those seen in rodents eaten by snakes. Reduced major axis regression of the smallest attainable cross‐sectional area, y, on mass, x, shows that y (in log mm²) approximates 1.53x (in log grams)^0.69 for rats and 1.63x^0.64 for mice. Our results suggest that visual cues provided by live rodents might lead most predators, like snakes, to overestimate ingestible size and hence rarely attack prey too large to ingest. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Endemic dengue associated with the co-circulation of multiple viral lineages and localized density-dependent transmission

Dengue is one of the most important infectious diseases of humans and has spread throughout much of the tropical and subtropical world. Despite this widespread dispersal, the determinants of dengue transmission in endemic populations are not well understood, although essential for virus control. To address this issue we performed a phylogeographic analysis of 751 complete genome sequences of dengue 1 virus (DENV-1) sampled from both rural (Dong Thap) and urban (Ho Chi Minh City) populations in southern Viet Nam during the period 2003-2008. We show that DENV-1 in Viet Nam exhibits strong spatial clustering, with likely importation from Cambodia on multiple occasions. Notably, multiple lineages of DENV-1 co-circulated in Ho Chi Minh City. That these lineages emerged at approximately the same time and dispersed over similar spatial regions suggests that they are of broadly equivalent fitness. We also observed an important relationship between the density of the human host population and the dispersion rate of dengue, such that DENV-1 tends to move from urban to rural populations, and that densely populated regions within Ho Chi Minh City act as major transmission foci. Despite these fluid dynamics, the dispersion rates of DENV-1 are relatively low, particularly in Ho Chi Minh City where the virus moves less than an average of 20 km/year. These low rates suggest a major role for mosquito-mediated dispersal, such that DENV-1 does not need to move great distances to infect a new host when there are abundant susceptibles, and imply that control measures should be directed toward the most densely populated urban environments.     

Lionfish in the eastern Pacific: a cellular automaton approach to assessing invasion risk

The lionfish invasion in the Atlantic and Caribbean has proceeded with vigor since their introduction in the 1980s or early 1990s. Lionfish affect recruitment of juvenile fish to reefs due to predation and are found in densities far surpassing that of their native Indo-Pacific. There is concern that the lionfish may become introduced and proliferate (through aquarium releases, transport on floating debris, or passage through the Panama Canal in ship ballast water) in the eastern tropical and north Pacific. This study presents the first known prediction of the potential for establishment of lionfish in the eastern Pacific Ocean. Through computational modeling, we compare and contrast the dynamics of random hypothetical introductions of lionfish into the eastern Pacific and Atlantic Oceans in order to highlight the different potentials for invasion in both basins. Connectivity between discrete regions (precincts) in both the Atlantic and eastern Pacific are examined and settlement densities are calculated to indicate possible locations of establishment of breeding lionfish populations. Our results suggest that lionfish, which are successful invaders in the Atlantic, may not be as successful in the eastern Pacific due to weak mesoscale connectivity which reduces the rapid spread of lionfish larvae.     

Assessment of DNA damage and repair in adults consuming allyl isothiocyanate or Brassica vegetables

Allyl isothiocyanate (AITC) is a dietary component with possible anticancer effects, though much information about AITC and cancer has been obtained from cell studies. To investigate the effect of AITC on DNA integrity in vivo, a crossover study was conducted. Adults (n= 46) consumed AITC, AITC-rich vegetables [mustard and cabbage (M/C)] or a control treatment with a controlled diet for 10 days each. On day 11, volunteers provided blood and urine before and after consuming treatments. Volunteers were characterized for genotype for GSTM1 and GSTT1 (glutathione S-transferases) and XPD (DNA repair). DNA integrity in peripheral blood mononuclear cells was assessed by single-cell gel electrophoresis. Urine was analyzed for 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG) and creatinine. Ten-day intake of neither AITC nor M/C resulted in statistically significant differences in DNA strand breaks [least squares mean (LSmean) % DNA in tail±S.E.M.: 4.8±0.6 for control, 5.7±0.7 for AITC, 5.3±0.6 for M/C] or urinary 8-oxodG (LSmean μg 8-oxodG/g creatinine±S.E.M.: 2.95±0.09 for control, 2.88±0.09 for AITC, 3.06±0.09 for M/C). Both AITC and M/C increased DNA strand breaks 3 h postconsumption (LSmean % DNA in tail±S.E.M.: 3.2±0.7 for control, 8.3±1.7 for AITC, 8.0±1.7 for M/C), and this difference disappeared at 6 h (4.2±0.9 for control, 5.7±1.2 for AITC, 5.5±1.2 for M/C). Genotypes for GSTM1, GSTT1 and XPD were not associated with treatment effects. In summary, DNA damage appeared to be induced in the short term by AITC and AITC-rich products, but that damage disappeared quickly, and neither AITC nor AITC-rich products affected DNA base excision repair.     

Do Earthworms Have a Greater Influence on Nitrogen Dynamics Than Atmospheric Nitrogen Deposition?

Elevated levels of inorganic nitrogen (N) deposition and earthworm invasion have the potential to alter N dynamics in eastern North American temperate forests. A regional comparison was conducted across 21 sugar maple (Acer saccharum Marsh) stands in southern Ontario, where forest floor C:N ratios ranged from 17 to 38 showed that, similar to many other studies, rates of potential net mineralization and nitrification increased below a forest floor C:N ratio threshold of approximately 25 and that nitrification rates are positively correlated with foliar N concentration. However, detailed measurements at four representative stands, receiving between 9.8 and 19 kg N ha^?1 y^?1 in throughfall, showed that foliar N levels were highest at the site with the lowest N deposition. The primary difference amongst these sites was the presence of invasive earthworms. Specifically, sites without earthworms had significantly higher forest floor N with a lower C:N ratio than the sites with earthworms. There was no significant difference in the rate of sugar maple litter decomposition or chemistry amongst the sites assessed after 540 days using fine (2-mm mesh) litter bags, suggesting that differences in forest floor N levels were most likely due to consumption of litter by large earthworm species and that the lower C:N ratio of the forest floor in sites without earthworms is brought about primarily by a much longer residence time. This work supports the conclusions that forest floor N concentration (or C:N ratio) has a very strong control on N dynamics in forests, but shows that the presence of earthworms can have an impact on forest floor C:N ratio and hence N dynamics that is greater than current levels of atmospheric inorganic N deposition in temperate forests of Ontario.