Evolutionary genetics of ruminant lysozymes

Comparative studies of mammalian lysozymes and their genes have contributed to knowledge of how new functions arise during evolution. The recruitment of lysozymes for functioning in the stomach fluid of ruminants has occurred in response to selection pressures that are partly known and on a time-scale that is known. A semiquantitative analysis of adaptive evolution is thus made possible by the ruminant lysozyme system. Large-scale production of lysozyme by the stomach lining entailed gene duplication as well as a change in gene expression. Remoulding of the lysozyme for working and lasting in the stomach fluid involved accelerated amino acid replacements, which may have been facilitated by intergenic recombination. The possibility that multigene families can accelerate adaptive evolution, by virtue of their capacity for bringing together functionally coupled substitutions, receives emphasis in this review.     

The Growth, Anatomy and Morphogenetic Potential of Callus and Cell Suspension Cultures of Hevea brasiliensis

Callus cultures have been initiated from stem explants of youngplants of Hevea brasiliensis and maintained over long periodsat 30 ?C by serial subculture in Murashige and Skoog mediumcontaining 2 mg 1^–1 2,4-D and 0.5 mg 1^–1 kinetin.Newly-initiated cultures spontaneously initiated roots but,on serial subculture, this property was lost and the culturesbecame heterogeneous (consisting of proliferating light segmentsand darker compact non-growing segments). Serially propagatedcultures continued to differentiate a few scattered latex vesselscontaining particulate material similar to that in the rootlaticifers. This callus (O callus) did not yield a growing cellsuspension when transferred to agitated liquid medium. However,the large cell aggregates which could be recovered after twopassages in liquid medium, when again grown on solid mediumyielded a highly friable light-coloured fast-growing homogeneouscallus (R callus) which retained its distinctive character onsubculture. This callus when transferred back to agitated liquidmedium yielded a fine rapidly growing cell suspension culturewhich could be serially propagated at 30 ?C in the same mediumas that used for callus culture. Both the O and R cultures were2,4-D dependent, but differed in their responses to 2,4-D. Bothretained their diploid character when serially propagated. Serially-propagatedsuspensions came to contain a proportion of polyploid cells.When the suspensions were maintained for several months withoutsubculture the larger cell aggregates which developed gave riseto embryo-like structures. Attempts to promote the further developmentof these embryo-like structures into plantlets were unsuccessful.     

Macro-zooplankter responses to simulated climate warming in experimental freshwater microcosms

1. We report data collected from 48 replicated microcosm communities created to mimic plant‐dominated shallow lake and pond environments. Over a 2‐year period, the microcosms were subjected to warming treatments (continuous 3 °C above ambient and 3 °C above ambient during summer only), a nutrient addition treatment and the presence or absence of fish. We tracked macro‐zooplankter dynamics, censusing cladoceran populations at the species level, copepods at the order level and ostracods as a class. 2. Responses to warming were subtle. Cladoceran diversity and overall abundance were not significantly affected by warming, although measures of community evenness increased. Warming effects on patterns of population trajectories tended to be strongly seasonal and most apparent during periods of pronounced increase. Populations of the prevalent cladocerans, Chydorus sphaericus and Simocephalus vetulus, displayed idiosyncratic patterns, with evidence in the case of S. vetulus for a negative relationship between warming and body‐size at maturity. Copepod populations were reduced in size by warming, but those of ostracods increased. 3. The effects of the nutrient addition and fish treatments were strong and consistent, interacting little with warming effects in statistical models. Zooplankter abundance tended to be the highest in the fish‐free microcosms receiving additional nutrient inputs and lowest when fish were present and no nutrients were added. Both treatments reduced cladoceran diversity and community evenness. 4. We suggest that warming, independently, is unlikely to supplant the effects of changing nutrient loading and fish predation as the major driver of zooplankter dynamics in shallow lakes and ponds. Moreover, in the situations where warming was of significant influence in our experiment, the distinction between summer‐only warming and year‐around warming was blurred. This suggests that warming effects were most pervasive during the summer, at the upper end of the temperature spectrum.