Age-related patterns of fertility in captive populations of birds and mammals.

We have analyzed birth records from the International Species Inventory System database of zoo animals to describe patterns of fertility as a function of age in birds and mammals. Unlike age at death, fertility in captive populations is partly controlled by animal keepers depending on availability of space and potential mates and on the aims of captive propagation programs. Thus, fertility records must be considered carefully to avoid potential age-specific biases. The zoo data suggest that fertility declines from a peak at young adult ages in most species. The rate of decline in reproductive function is correlated with the rate of somatic aging, indicated by the increase in mortality rate with age, and with the age at peak fertility. Over the sample as a whole, these patterns do not differ systematically between the sexes, nor do they differ between birds and mammals. While it is clear that the demographic consequences of aging of the reproductive system follow a different course than the aging of somatic tissue, the rates of each are correlated either through functional connections or through parallel evolutionary responses to common selective factors.

Predators as stressors? Physiological and reproductive consequences of predation risk in tropical stonechats (Saxicola torquata axillaris).

Tropical birds usually lay smaller clutches and are less likely to initiate a second brood than their temperate-zone relatives. This reduction in annual fecundity is generally explained as an adaptation either to higher rates of nest predation or to a more limited food supply concurrent with higher adult survival in the tropics. However, the physiological parameters associated with lower annual fecundity in tropical birds have not been well investigated. We compared the annual fecundity, behaviour and a number of physiological parameters of stonechat parents feeding fledged juveniles in territories with and without fiscal shrikes, a predator on adult and fledged birds. Stonechat pairs in territories with shrikes were less likely to initiate a second brood and delayed successive broods compared to pairs in territories without shrikes. After fledging of their young, males showed a greater propensity than females to initiate distraction calls after a human intrusion into their territory and, therefore, invested more in the defence of their young. In territories with shrikes stonechat males had higher initial plasma corticosterone levels and lower body conditions than males in territories without shrikes, suggesting that they were chronically stressed. In contrast, the females from both types of territory had low initial plasma corticosterone levels. We conclude that shrike presence might account for the delay in initiation of a second brood and the reduction in the tendency to initiate a second brood. Whether these effects are mediated by the elevated levels of corticosterone remains to be demonstrated.

Comparison of aging-related mortality among birds and mammals.

We use the Weibull model to characterize initial (extrinsic) mortality rates (m(0)) and rate of increase in mortality with age (omega) for natural and captive populations of birds and mammals. Weibull parameters can be estimated for small samples of ages at death by constructing survival curves and fitting the Weibull model by nonlinear least-squares regression. Both m(0) and omega decrease in captivity, on average, and omega bears a strong relationship to m(0), as it does in nature, irrespective of body mass or differences between birds and mammals. Rate of aging is most closely related to brain size in birds and to rate of postnatal growth in mammals. It is not related to duration of embryonic development, body size independently of brain size, or genome size. We suggest that causes of extrinsic mortality in nature may be replaced in captivity by intrinsically controlled causes of mortality related to processes that regulate the rate of aging.

Chemical defense of giant springtailTetrodontophora bielanensis (Waga) (Insecta: Collembola).

The giant springtail,Tetrodontophora bielanensis (Waga), is characterized by integumental openings (pseudocells) from which small droplets of a sticky defensive fluid are secreted after molestation. The secretion originates initially from secretory cells below the pseudocellae; subsequent irritations result in release of hemolymph, which was identified by both chemical and microscopical methods as well as by scanning electron microscopy. Bioassays with topically treated ground beetlesNebria brevicollis showed that the pseudocellular fluid evokes a total disorientation and cleansing behavior of the beetle. The main constituents were identified as the following pyridopyrazines: 2,3-dimethoxpyrido[2,3-b]pyrazine (1), 3-isopropyl-2-methoxypyrido[2,3-b]pyrazine (2), and 2-methoxy-4H-pyrido[2,3-b]pyrazine-3-one (3). These alkaloids are mainly present in the pseudocellar fluids of female and male springtails but are absent in their food or feces. Minor amounts are found in the hemolymph of adults, while larvae contain traces of2 only. All compounds were synthesized and tested for activity. In natural concentrations, the synthetic alkaloids elicited the same effects from the ground beetles as the pseudocellar fluid.