Survival of sheep x goat hybrid inner cell masses after injection into ovine embryos

Modified blastocyst injection techniques were used to inject immunosurgically isolated sheep x goat hybrid inner cell masses (ICM) into ovine blastocysts, with subsequent transfer of composite embryos to ovine recipients. Hybrid embryos were collected from does artificially inseminated with Barbados ram semen. A total of 13 live and 2 aborted offspring resulted from the 34 composite embryos transferred to recipient ewes (38% embryo survival). Of the 15 offspring, 4 exhibited phenotypic hybridism and 2 (13%) of these were determined to be hybrid mean value of -sheep chimeras by karyotype, serum protein and isoenzyme analyses, and fiber identification. Each of the 4 was produced by an injection procedure that involved damage of the ovine host ICM. One additional offspring was unusual in appearance, but the presence of hybrid cells was not proven. Similarly, caprine ICM were immunosurgically isolated and injected into ovine blastocysts that were then transferred to ovine recipients. Of the 13 composite embryos transferred, 12 offspring were produced (92% embryo survival). Eleven were overt goat mean value of -sheep chimeras and, of these, 7 were also blood chimeras. The hybrid ICM was shown to be capable of contributing to normal embryonic and fetal development after injection into an ovine blastocyst but may be less likely to be incorporated with the ovine host ICM than is the caprine ICM.     

Calcium and A23187-induced cytolysis of mouse thymocytes

The cytotoxic effects of ionophore A₂₃₁₈₇ were studied in parallel with its action on calcium uptake in isolated mouse thymocytes. Under conditions where the cells were preincubated in a calcium-containing medium prior to ionophore treatment a close relationship could be observed between the extent of cell lysis and the stimulation of calcium uptake in the presence of A₂₃₁₈₇. In addition, increasing concentrations of calcium ions in the incubation medium lead to a pronounced decrease of cell viability and to a stimulation of calcium uptake suggesting that calcium is critical for cell survival.     

Nonlinearity in interspecific interactions in response to climate change: Cod and haddock as an example

Climate change has profound ecological effects, yet our understanding of how trophic interactions among species are affected by climate change is still patchy. The sympatric Atlantic haddock and cod are co‐occurring across the North Atlantic. They compete for food at younger stages and thereafter the former is preyed by the latter. Climate change might affect the interaction and coexistence of these two species. Particularly, the increase in sea temperature (ST) has been shown to affect distribution, population growth and trophic interactions in marine systems. We used 33‐year long time series of haddock and cod abundances estimates from two data sources (acoustic and trawl survey) to analyse the dynamic effect of climate on the coexistence of these two sympatric species in the Arcto‐Boreal Barents Sea. Using a Bayesian state‐space threshold model, we demonstrated that long‐term climate variation, as expressed by changes of ST, affected species demography through different influences on density‐independent processes. The interaction between cod and haddock has shifted in the last two decades due to an increase in ST, altering the equilibrium abundances and the dynamics of the system. During warm years (ST over ca. 4°C), the increase in the cod abundance negatively affected haddock abundance while it did not during cold years. This change in interactions therefore changed the equilibrium population size with a higher population size during warm years. Our analyses show that long‐term climate change in the Arcto‐Boreal system can generate differences in the equilibrium conditions of species assemblages.