Evaluating the reproductive cost of migration for females in a partially migrating pond-breeding amphibian

Populations of animals with resident and migratory individuals provide an ideal system for addressing questions concerning the evolution of migration. Partially migratory populations may persist because residents and migrants have equal fitness or because migration is based on conditional asymmetries. Studies measuring the costs and benefits of migration provide empirical data to test hypotheses concerning the maintenance of partial migration within a population. In this study, we measured the reproductive differences between resident and migrant females in a pond-breeding amphibian, the red-spotted newt Notophthalmus viridescens . We used large field enclosures to repeatedly sample egg laying over the prolonged breeding season of this species. Resident females did not lay a greater number of eggs or begin laying eggs earlier, despite beginning the breeding season earlier and having a higher mass than migrant newts. The only difference in reproduction we detected was that the eggs of resident females hatched into larger larvae compared with the larvae of migrant females. We discuss this result in the context of other potential trade-offs between residency and migration. This study illustrates the phenology of egg laying of N. viridescens and our results contribute to understanding the population dynamics of partially migratory species.     

Search for Oncogenic Properties in Various Viruses Found in Man: Positive Results with Adenovirus Types 12 and 18

Since the inoculation of newborn hamsters with polyoma virus results both in necrotizing lesions and virus-free tumours the possibility was raised that necrotizing viruses found in man acted similarly. Accordingly a group of viruses found in man were tested for oncogenic activity by injecting them into newborn hamsters. Most were observed for more than a year. As yet only Adenovirus Types 12 and 18 have induced tumours; the oncogenic properties of these were reported by Trentin et al., and Huebner et al., respectively, while this study was in progress. The significance of the findings with regard to man cannot as yet be evaluated but the point is made that Adenovirus Types 12 and 18, like polyoma and SV40 virus, only cause neoplasia under special circumstances. Further work will be required to discover if these circumstances or their equivalent occur under conditions of the natural spread of infection.     

Microradioisotopic assay for indoleamine N-methyltransferase and analysis of products by liquid chromatography

A rapid method for the separation of tryptamine, 5-hydroxytryptamine, and their N-methylated derivatives is described. The method involves liquid chromatography using a cation exchange column with the eluant monitored either by ultraviolet or fluorescence spectroscopy. The latter technique permits the detection of picogram quantities of indoleamines. Using normal-phase liquid chromatography a complete separation of tryptamine, its N-methylated derivatives, and their β-carboline analogs was also achieved. A radioisotopic assay with the potential to detect indoleamine N-methyltransferase activity in milligram quantities of rabbit lung tissue was developed. The radioisotopically labeled products formed from a number of substrates in such assays were characterized by liquid chromatography.     

Low levels of anterior tibial loading enhance knee extensor reflex response characteristics.

We examined whether neuromuscular reflexes were altered with anterior loads applied to the tibio-femoral joint. A ligament testing device was modified by attaching a reflex hammer to a steel mounted frame to illicit a patellar tendon tap, while anterior directed loads displaced the tibia on the femur. Five trials were acquired while anterior-directed loads (20, 50, 100 N; counterbalanced) were applied to the posterior tibia between 20 N pre (20 N(Pre)) and post (20 N(Post)) baseline conditions on two different days. Surface electromyography (sEMG) recorded mean quadriceps (Q) and hamstring (H) reflex time (R(Time)=ms) and reflex amplitude (R(Amp)=%MVIC). A load cell on the anterior tibia measured the timing (KE(Time)=ms) and amplitude (KE(Amp)=N) of the knee extension force, and was used to calculate electromechanical delay (EMD=ms) and peak knee extension moment (KE(Mom)=Nm/kg). Data from 19 recreationally active subjects revealed good to excellent response consistency between test days and between baseline conditions for R(Time), R(Amp), KE(Time) and KE(Amp). With anterior tibial loading, R(Time) was faster at 50 N vs. 20 N(Post), and R(Amp) was greater at 20 N(Pre) vs. 20 N(Post) (Q and H) and at 50 N vs. 100 N (Q only). KE(Mom) was greater at 20 N(Pre) and 50 N vs. 20 N(Post), and EMD was shorter at 50 N vs. 20 N, 20 N(Pre) and 20 N(Post). These results suggest that knee extensor reflex responses are enhanced with low (50 N) but not moderate (100 N) anterior loading of the knee.