Friends and strangers: a test of the Charnov-Finerty Hypothesis

Summary We tested the hypothesis that populations composed of unrelated animals should perform worse than those composed of related animals by setting up two moderatedly dense field populations in adjacent enclosures: one was composed of related females and one of unrelated females; both had unrelated males. The survival and reproductive success of a number of litters located by spooling were determined. Final population size, pregnancy success, number of young recruited per pregnancy, and survival were similar in both populations. Thus, differences in relatedness produced no differences in demography. We conclude that the Charnov-Finerty Hypothesis in unlikely to be an explanation for microtine population fluctuations.     

The occurrence of thermotolerance in non-proliferating rat hepatocytes in primary culture

The occurrence of thermotolerance, induced by an initial heat treatment at 42 degrees C for 30 min, was studied in adult non-proliferating rat hepatocytes in primary culture. Heat treatment at 42 degrees C for 30 min did not affect cell morphology, cell attachment, Na+, K+ pump activity, K+ content and lactate dehydrogenase accumulation into the medium. In contrast, after exposure to 44 degrees C for 30 min a dramatic change in all these parameters was observed. However, of the cells, which remained attached to the substratum 24 h after treatment, Na+, K+ pump activity and K+ content appeared to be normal compared with untreated cells. Cells, pre-treated at 42 degrees C for 30 min, followed by incubation at 37 degrees C for 16 h, were found to be completely thermal resistant against heat treatment at 44 degrees C, as judged by cell morphology, detachment from the substratum, lactate dehydrogenase accumulation, Na+, K+ pump activity and K+ content. These results show that induction and development of thermotolerance can be studied in non-proliferating cells in primary culture.     

Of mammals and milk: how maternal stress affects nursing offspring

1. A large body of research shows that maternal stress during an offspring’s early life can impact its phenotype in both the short and long term. In the Vertebrata, most research has been focused on maternal stress during the prenatal period. However, the postnatal period is particularly important in mammals because maternal milk provides a conduit by which maternal hormones secreted in response to stressors (glucocorticoids, GCs) can reach offspring. Moreover, lactation outlasts gestation in many species.
2. Though GCs were first detected in milk over 40 years ago, few studies have explored how they affect nursing offspring, and no reviews have been written on how maternal stress affects nursing offspring in the natural world.
3. We discuss the evolution of milk and highlight its importance in each of the three mammalian lineages: monotremes (subclass Monotremata), marsupials (infraclass Marsupialia), and eutherians (infraclass Placentalia). Most research on the effects of milk GCs on offspring has been focused on eutherians, but monotremes and marsupials rely on their mothers’ milk for a proportionally longer period of time, and so research on these taxa may yield more insight.
4. We show that GCs are important for milk production, both during an individual nursing bout and over the entire lactation period, and review evidence of GCs moving from maternal blood to milk, and eventually to nursing offspring. We examine evidence from rodents and primates of associations between GC levels in lactating females (either blood or milk) and offspring behaviour and growth rates. We discuss ways that maternal stress may impact these offspring phenotypes outside of milk GCs, such as changes to: (1) milk output, (2) other milk constituents (e.g. macronutrients, growth factors, cytokines), and (3) maternal care behaviour.
5. Critical to understanding the fitness impacts of elevated maternal GC levels during lactation is to place this within the context of the natural environment. Species-specific traits and natural histories will help us to understand why such maternal stress produces different offspring phenotypes that equip them to cope with and succeed in the environment they are about to enter.

     

Aggressive behavior of adult meadow voles (Microtus pennsylvanicus) towards young

Summary Field evidence indicates that adult microtines, especially females, may be a major cause of poor juvenile survival and this may be instrumental in their population regulation. This suggests that males and females behave differently towards young animals. To examine how adult males, nonlactating females, and lactating females behave towards strange young, I introduced young animals into the home cage of the adults. Lactating females were most aggressive towards young; most males investigated them; most nonlactating females ignored them. However, discriminant function analysis indicated a great deal of overlap in the behavior of the classes. None of the classes behaved differently towards young of either sex. Females did not vary their behavior during lactation. Behavior varied among lactating females, with 55% showing little aggression and 20% showing a great deal. Most lactating females showed similar behavior in each of their bouts: docile females remained docile, aggressive females remained aggressive. I conclude that lactating females are most aggressive towards strange young. These results are consistent with the field evidence, which suggests that adult females depress juvenile survival and recruitment and that the main culprits are breeding females.     

The effects of NPK fertilization for nine years on boreal forest vegetation in northwestern Canada

Abstract. Plant productivity is limited by mineral nutrient availability in many boreal forest ecosystems. This study is an analysis of the growth responses of components of a boreal plant community (cryptogams, herbaceous and woody perennials, the dominant shrubs Salix glauca (grey willow) and Betula glandulosa (bog birch) and the dominant tree Picea glauca (white spruce), to the addition of an NPK fertilizer over a nine-year period. The study was carried out in a low-nutrient boreal forest ecosystem in the Yukon territory in northwestern Canada. The following predictions were tested: (1) that there would be an overall increase in abundance (measured either as cover, density, or dry mass) of all components of the vegetation, (2) that vegetation composition would change as more competitive species increased in abundance and (3) that initial community changes in response to fertilization would be transient. In general, all predictions were found to be true. Species composition changed rapidly in response to fertilizer. Graminoids (e.g. Festuca altaica) and some dicots (e.g. Mertensia paniculata and Achillea millefolium) increased in cover, while other dicots (e.g. Anemone parviflora), dwarf shrubs (e.g. Arctostaphylos uvaursi), bryophytes and lichens declined. There was a significant increase in the growth rate of the two dominant shrubs and of Picea, but not in the cone crop or seed production by Picea. Surveys after 1 or 2 years showed responses by the vegetation but more stable patterns of response did not emerge until after 5 or 6 years. There were consistent and directional changes in the percent cover of some of the herbaceous species on control plots. Growth rates of Salix and Betula varied considerably from year to year, independently of treatment. Long-term studies are essential if we are to understand the role of nutrient limitation in this ecosystem.     

Regulation of Na+,K+ pump activity by nerve growth factor in chick embryo dorsal root ganglion cells

Nerve growth factor (NGF) is required for the growth and development of sensory and sympathetic neurons. Incubation of chick dorsal root ganglionic cells without NGF resulted in a decrease of active (Na+,K+-pump-mediated) K+ influx over a period of several hours. Addition of NGF to NGF-deprived cells caused 1) a return of the active K+ influx to the values occurring in cells continuously exposed to NGF, preceded by 2) a very rapid, but transient overstimulation of the Na+,K+-pump-mediated K+ influx. Restoration of normal Na+,K+-pump activity occurred at NGF concentrations of 1 biological unit/ml or greater, whereas the NGF concentration in the 1-100 biological unit/ml range affected the rapidity with which the pump restoration took place. The transient pump behavior was only observed in NGF-deprived cells and could not be elicited in NGF-supported steady-state cells or in cells having already received delayed NGF once. This transient Na+,K+-pump behavior was exclusively displayed in conjunction with a high intracellular Na+ concentration. Decreasing the external Na+ concentration below 70 mM reduced the hyperstimulation response to NGF, until at 10 mM Na+ the delayed presentation of NGF caused no overshoot at all. The effect of NGF on the Na+,K+-pump was specific for the NGF molecule and could not be mimicked by other proteins.