Effects of Simulated Cold Fronts on the Survival and Behaviour of Yellow Perch Perca Flavescens Yolk-sac Fry

Acute reductions in water temperature (i.e. cold fronts) may influence larval fish survival directly via limits on physiological tolerance or indirectly by acting as a sublethal stressor. The primary objective was to quantify survivorship of yellow perch yolk-sac fry exposed to two different temperature declines (4 and 8°C) and compare survivorship to that of perch fry under ambient temperatures representative of natural conditions. Behaviour of yolk-sac fry following temperature declines was also qualitatively assessed. Mean survival in the control, −4, and −8 treatment tanks was 90, 91 and 97%, respectively, and no significant differences in percent survival were observed between the control and the −4 treatment (ts = −0.10; df = 7; P = 0.93), the control and −8 treatment (ts = −1.85; df = 7; P = 0.11) or the −4 and −8 treatments (ts = −1.33; df = 7; P = 0.22). Observations of yellow perch eggs and fry behaviour following temperature declines differed among treatments. Any remaining eggs in the control treatment and −4 treatments continued to hatch during the experiment, and fry were documented swimming throughout the water column in all tanks. However, in the −8 treatment, any eggs that had not hatched remained inactive and all fry within all −8 treatment tanks ceased swimming activity and settled to the bottom of the tanks once the temperature reached 3.9°C. Fry remained at the bottom of the tanks for the entire 48 h simulated cold-front. Fry resumed swimming activity once water temperatures began to increase (by approximately 6°C). Results indicated that drops in temperature (i.e. cold fronts) similar to or greater than those found in small impoundments did not cause direct mortality of yellow perch during the yolk-sac fry (post-hatch larvae) stage. Although an acute drop in temperature may not induce sudden high mortality, it may be a sub-lethal stressor, leading to increased starvation or predation risk

First trimester growth delay: An early marker of triploidy

Triploidy is one the most common chromosomal abnormality in humans, complicating about 1% of all human pregnancies. Most affected conceptions undergo spontaneous abortion in the first trimester, making the prevalence of second trimester triploidy low. Viable triploidy is associated with high rates of maternal morbidity, including hypertensive disorders, hemorrhage, and persistent trophoblasic disease, as well as fetal and neonatal severe adverse outcomes. Given these complications, early identification of triploidy in ongoing pregnancies may inform patient counseling and management

Evidence for foliar endophytic nitrogen fixation in a widely distributed subalpine conifer.

Coniferous forest nitrogen (N) budgets indicate unknown sources of N. A consistent association between limber pine (Pinus flexilis) and potential N2 -fixing acetic acid bacteria (AAB) indicates that native foliar endophytes may supply subalpine forests with N. To assess whether the P. flexilis-AAB association is consistent across years, we re-sampled P. flexilis twigs at Niwot Ridge, CO and characterized needle endophyte communities via 16S rRNA Illumina sequencing. To investigate whether endophytes have access to foliar N2 , we incubated twigs with (13) N2 -enriched air and imaged radioisotope distribution in needles, the first experiment of its kind using (13) N. We used the acetylene reduction assay to test for nitrogenase activity within P. flexilis twigs four times from June to September. We found evidence for N2 fixation in P. flexilis foliage. N2 diffused readily into needles and nitrogenase activity was positive across sampling dates. We estimate that this association could provide 6.8-13.6 μg N m(-2)  d(-1) to P. flexilis stands. AAB dominated the P. flexilis needle endophyte community. We propose that foliar endophytes represent a low-cost, evolutionarily stable N2 -fixing strategy for long-lived conifers. This novel source of biological N2 fixation has fundamental implications for understanding forest N budgets