Suppressed breeding in the field vole (Microtus agrestis): an adaptation to cyclically fluctuating predation risk

The densities of microtine rodents and their main predators,small mustelids, fluctuate synchronously in 3–5-year cyclesin central and northern Fennoscandia. Predation by small mustelidshas been suggested as one of the driving forces in microtinecyclicity, causing deep synchronous declines of several volespecies. We studied experimentally the effects of small mustelidson mating behavior, foraging, and breeding in nonwintered fieldvoles (Microtus agrestis) originating from a cyclic population.By using mustelid odors, we simulated a crash phase environmentwith high predation risk for breeding pairs of voles. In ourexperiments, 87% of the female field voles suppressed breedingwhen exposed to mustelid odors. Both female and male behaviorchanged, and no mating behaviors were observed under the simulatedpredation risk. Weights of both sexes decreased when exposedto mustelid odor, probably due to decreased foraging; weightsof the control females increased due to pregnancy; and no weightchanges occurred in control males. Decreased breeding and foragingpossibilities under high predation pressure may form the basisfor the ultimate explanation for breeding suppression. Thereare at least two different mechanisms for breeding suppression:either mating does not take place or malnutrition in femalesdoes not' allow breeding to occur. Delayed breeding under highrisk of predation, for whatever reason, could increase the probabilityof individuals, especially that of the females, to survive overthe crash to the next, safer breeding season when their youngwould have better possibilities to survive.     

Life-history variation among populations of Euphrasia rostkoviana Hayne (Scrophulariaceae) in relation to grassland management

Seeds from 39 natural populations of the annual hemiparasitic species Euphrasia rostkoviana were collected from nine different grassland habitats in the north-eastern part of the Swiss Alps. These populations were investigated in three comparative cultivation experiments. Statistical data for seed-weight, different life-history traits and habit characters were compared. Differences in the onset of flowering between the extreme populations are as much as 10 weeks while differences in the other examined life-history traits are not more than a few days. The onset of flowering is strongly correlated with the number of internodes but also with other habit characters. Assuming a genetic basis for differences in life-history traits and habit characters, the populations appear to be well-adapted to the management regimes of their grassland habitats in the onset of flowering as well as in their habit characteristics. There is evidence for some trade-offs. For example, few branches and few internodes are a trade-off for the early onset of flowering. The adaptations found in populations of E. rostkoviana from late-mown meadows and from mountain pastures are in the opposite direction to those of the populations of Rhinanthus alectorolophus from the same habitats. This seems to be due to the much smaller seed-size and the much longer individual flowering period of plants of Euphrasia species. Remarkable differentiation via heterochronic processes seems to be possible within few decades in relation to extremely strong selection pressures generated by grazing or cutting.     

Of crazy-ants and Curetinae: are Curetis butterflies tended by ants?

The larvae of the lycaenid subfamily Curetinae have never been reported to be associated with ants. Observations on Curetis regula Evans from Brunei are presented which show that this species may be tended by ants both as larvae and adults. The observations are discussed in relation to a recent review on lycaenid/ant associations, u is suggested that the Curetinae will be found to be associated with ants when more species have been reared, on evidence of the larval tentacle organs and apparent 'pore cupolas', both of which are ant adaptations. More studies are needed on Curetis biology and larval morphology to resolve the relationships of this enigmatic genus within the Lycaenidae.     

Effect of temperature on early development of white and lake sturgeon,Acipenser transmontanus and A. fulvescens

Synopsis The effect of constant incubation temperatures (between 10°C and 26°C) on the developmental rates was found to fit a similar exponential relationship in both the lake and white sturgeon embryos and larvae. Although the lake sturgeon had an overall slower rate of development than the white sturgeon, no statistically significant difference was detected in the slopes of the exponential equations describing the effect of temperature on developmental rate. The effect of these incubation temperatures on embryonic survival also did not differ between these two species. Both species exhibited optimal survival between 14–17° C and incipient mortalities occurred at 20°C. Temperatures above 20°C were lethal for white sturgeon embryos. No effect of low incubation temperature on survival was evident from this study. A comparison of these North American species with Eurasian acipenserids suggests that all the sturgeon that have been examined exhibit a similar influence of incubation temperature on developmental rate.     

Extreme water efficiency of Cape gannet Morus capensis chicks as an adaptation to water scarcity and heat stress in the breeding colony

Cape gannet Morus capensis chicks depend entirely on fish prey and metabolic water for water requirements during development. Water loss through evaporative cooling due to heat stress is substantial. We measured water flux and field metabolic rates (FMR) of Cape gannet chicks and adults to determine if gannets developed water saving strategies. The water economy index (WEI, g kJ^?1) decreased with chick age according to the model WEI = 0.676 – 0.272 × log₁₀(t), indicating that water efficiency increased with age. At fledging, the WEI of chicks was at the level expected of adult desert birds. Desert birds maintain a low WEI by also having a low FMR, whereas Cape gannet chicks have FMR comparable to other seabird species’ nestling requirements. We propose that maintaining low WEI is adaptive for Cape gannets because (1) chicks need to balance water loss through evaporative cooling, (2) fledglings need to overcome a period of up to a week when they cannot ingest any water and (3) adults spend extended periods in the breeding colony during which water can become a limiting factor. Understanding the physiological mechanism of maintaining low WEI will become increasingly important with future rising temperatures.     

Influence of radiata pine seedlings on chemical properties of some New Zealand montane grassland soils

Interaction between soil acidity and vegetation phenolic concentration was investigated to identify mechanisms by which forests sustain productivity on extremely acidic, infertile soils. Contrasting soils on well-preserved marine terraces of the “Ecological Staircase’ near Mendocino, CA comprise an extreme edaphic gradient. Pygmy forests of dwarf (< 5m) Mendocino cypress (Cupressus pygmaea), Bolander pine (Pinus contorta var. bolanderi), and Bishop pine (Pinus muricata) are found on the oldest, most acidic soils, and along a gradient that includes three distinct levels of soil acidity, with pH(CaCl₂) ranging from 5.0 to 3.0 in the upper mineral soil and from 4.0 to 2.0 in the litter layer where fine roots are concentrated. Mature foliage was collected from five sites on this edaphic gradient. Aqueous methanol extracts of the samples were analyzed for concentrations of total phenols and condensed tannin by the Prussian blue and acidified vanillin assays, respectively. There were significant differences (p<0.05) in foliar condensed tannin and phenolic concentrations within each species and concentrations were inversely related to soil pH, approximately doubling along the gradient. Natural selection for soil-regulated variation in polyphenol concentration is interpreted in the context of plant-litter-soil interactions as an adaptation that permits these conifers to survive in extremely acidic soils. H Lambers Section editor     

Patterns of growth of the mandibular corpus in spotted hyenas (Crocuta crocuta) and cougars (Puma concolor)

Differences in jaw morphology among adult carnivorans are well established, but the ontogenetic mechanisms by which these differences arise are largely unexplored. Mandibular ontogeny in Crocuta crocuta and Puma concolor is analysed biomechanically using principles of beam theory. In each species, the development of cross-sectional properties of the mandibular corpus associated with rigidity under loading follows a biphasic pattern of growth. In early postnatal growth, deposition of cortical bone appears to be constrained by the overall weaker tissue with which juvenile skeletons are constructed and by the need to volumelrically accommodate the developing teeth within their bony crypts. Thus, this stage of growth is characterized by a net periosteal deposition of bone and a swelling of the medullary cavity. In late postnatal growth, the constraints on endosteal deposition of bone are relieved as the permanent teeth erupt; thus, cortical thicknesses increase sharply by periosteal expansion as well as medullary contraction. Finally, it is noted that basic differences in jaw construction between Crocuta and Puma appear to develop prenatally as they are largely in place at birth. Hence, postnatal development enhances, but does not soley contribute to, the biomechanical differences in the jaws of these species.     

The Western Aleutians: Cultural Isolation and Environmental Change

Recent research in the western Aleutians addresses two primary issues: the nature and extent of cultural exchange along the Aleutian chain, and Holocene environmental change and its effects on the development of Aleut culture. Cultural isolation is a major paradigm of researchers working in the Aleutians. Review of the distribution of several cultural traits suggests the Aleuts adopted many cultural elements originating outside the chain, but the distribution of these to the western islands was uneven.     

Growth rates and morphological adaptations of aquatic and terrestrial forms of amphibious Littorella uniflora (L.) Aschers.

Morphological – anatomical features of the terrestrial and the aquatic life form of the rosette species Littorella uniflora, inhabiting nutrient poor soils of oligotrophic lakes, were investigated together with growth rates of both life forms and of transplants. Growth rates were the same for the two life forms. However, growth of transplanted plants was somewhat reduced by transition from one environment to another. This was especially true for aquatic plants, which may be stressed by desiccation when moved to the terrestrial environment. The morphological – anatomical differences between the life forms were small compared with many other amphibious species which produce highly specialized leaves and life forms in air and under water. It is suggested that the conservative leaf morphology of Littorella is a consequence of the high dependence on rhizospheric CO₂ of both the aquatic and the terrestrial form of Littorella, making production of leaves specialized for carbon uptake in one specific environment unnecessary.