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We have investigated the effects of cytochalasin D on first cleavage of fertilized eggs from the sea urchin Strongylocentrotus purpuratus. Cytochalasin D inhibits the cortical actin filament reorganization that occurs immediately after fertilization in sea urchin eggs, and arrests cell division by preventing normal contractile ring formation which inhibits cytokinesis. In this study, eggs were incubated in 2 or 4 μg/mL cytochalasin D within the first 5 minutes post-fertilization, for 10, 20, or 30 minutes, followed by washout with artificial sea water. At 2 μg/mL, two groups of results were obtained; a 20–25 minute delay in cytokinesis irrespective of exposure time, and a time-dependent response where longer incubation times produced lengthier delays in cytokinesis. The time-dependent delays in cell division also occurred at 4 μg/mL cytochalasin D, along with cytotoxic effects that correlated to the length of drug exposure. The results show that disruption of the normal actin cytoskeleton reorganization which occurs within the first 30 minutes after fertilization can affect the timing of first cleavage, suggesting that the state of the actin cytoskeleton is somehow monitored as cells enter cytokinesis.
In this study, stimulus objects (frozen blood balls, fresh zebra dung, scented squash, and cardboard boxes) were utilized in an enrichment program aimed to increase the diversity of behaviors exhibited by one female and three male tigers (Panthera tigris sumatrae) and two male lions (Panthera leo leo). Three enrichment sessions consisting of pre-enrichment control, enrichment, and post-enrichment trials of 30-min each were conducted over a two-day period. Stimulus objects were present only in the enrichment trials. The enrichment sessions were replicated three times for each stimulus object. Behavioral states, discrete behaviors, and object-directed behaviors were recorded. Behavioral diversity indices (BDIs) for each trial were calculated using the Shannon Diversity Index. The stimulus objects increased behavioral diversity during the enrichment trials compared to the control trials, but this effect did not persist to the post-enrichment trials the following day. The lions benefited the most from the enrichment, exhibiting increased activity, decreased sleeping, and the greatest increase in discrete behaviors BDIs during the enrichment trials. The type of stimulus object did not affect behavioral states or discrete behaviors BDIs, but the frozen blood balls elicited lower object-directed BDIs than other stimulus objects. Responses to enrichment did not change over time, suggesting that the subjects did not habituate to the stimulus objects during the 10 weeks of the study. Enrichment utilizing stimulus objects was successful in increasing behavioral diversity of lion and tiger subjects. Differences in the study among subjects in their response to enrichment suggest that the effects of enrichment on animals of different age, sex, and species should be further explored and taken into consideration in the design of enrichment programs.