Serum immunoglobulin G levels are positively related to reproductive performance in a long-lived seabird, the common tern (Sterna hirundo)

The evolution of longevity requires a low risk of mortality from extrinsic factors, relative to intrinsic factors, so that individuals that differentially invest in physiological self-maintenance and minimize their annual reproductive costs will maximize lifetime fitness through a prolonged reproductive lifespan. The trade-off between reproductive effort and self-maintenance, as measured by immune function, has been well documented in short-lived birds, but is difficult to demonstrate in long-lived birds. To assess self-maintenance in a long-lived seabird, we measured serum protein levels, including immunoglobulin G (IgG = IgY), in 30 breeding pairs of common terns (Sterna hirundo) and their first-hatched (A) chicks. Most parents were of known age from banding as hatchlings; our sample was selected to contrast young breeders (6–9 years) with very old birds (17–23 years). Body-mass of the parents declined by 5% during the chick-rearing period, while serum protein levels were stable. Serum IgG levels were higher in parents of offspring with faster growth rates, while IgG levels were lower in parents whose broods were reduced by starvation. A-chicks in broods of two had higher IgG levels than singleton chicks. Albumin levels were not related to reproductive performance. Thus, despite adequate statistical power, we could find no evidence for a trade-off between reproduction and self-maintenance in common terns, even in old age. The results are consistent with life-history predictions for long-lived vertebrates, in which selection favors sustained self-maintenance across the reproductive lifespan. The positive relationships between IgG levels and reproductive performance indicate that IgG can be used as an index of parental “quality.”     

Incidence of diapause varies among populations of <Emphasis Type="Italic">Daphnia pulicaria</Emphasis>

Dormancy is a common way in which organisms survive environmental conditions that would be lethal to the active individual. However, while dormant, individuals forgo reproduction. Hence theory suggests an optimal time in which to enter dormancy, depending on risks associated with both remaining active and entering dormancy. When these relative risks differ among habitats, dormancy strategies are predicted to vary as well. For freshwater zooplankton, it has been suggested that sensitivity to the cues that initiate dormancy should be selected against when females have the opportunity to remain in the water column year round. We tested this prediction with 12 populations of lake-dwelling Daphnia pulicaria (Crustacea: Cladocera). Differences among lakes in basin morphometry, predators and resources create a gradient of risk for Daphnia in the water column. Some populations persist in high numbers year round while others are abundant only in spring. We used this difference in persistence ability as an estimate of risk in the water-column. For 3 years of field sampling we found consistent differences among the lake populations in the incidence of dormancy. In some populations, only a small fraction of females switched to producing dormant eggs each year whereas in others the majority of eggs produced in the late spring were dormant. In general, populations that experienced predictably low abundances in the active form exhibited higher incidence of dormancy than did populations that persisted in high abundance year round, but there were exceptions. Our results confirm that the incidence of dormancy varies considerably among populations in a fashion consistent with general theory, but suggest that persistence in the water column is not the sole predictor of the diapause strategy found in any particular lake.     

Reproductive and developmental responses in the self-fertilizing fish,Rivulus marmoratus,induced by the plasticizer,di-n-butylphthalate

Synopsis Specialized life-history attributes of the cyprinodontiform fish, Rivulus marmoratus, allow continuous life cycle testing to reveal effects of chemicals or environmental stresses upon fertilization, fecundity, egg viability, embryonic development, sex ratios, frequency of growth or skeletal anomalies, as well as other biological markers. This study reports responses in fecundity, viability of embryos, and skeletal anomalies during and after exposure of parental fish to the plasticizer, di-n-butylphthalate (DBP). Skeletal anomalies among offspring were classified as mild, moderate, or severe compared with non-deformed normal offspring. The frequency of skeletal anomalies increased from 4% (all categories combined) in controls, to 10% and 19% of the offspring from adults exposed to 1 and 2 mg I^-1 DBP, respectively. DBP treatment was conducted over a 21 week interval, followed by a 9 week post-treatment observation interval. During post-treatment, frequency of skeletal anomalies decreased to less than 5% in all groups. Contributions No. 610, Environmental Research Laboratory, Gulf Breeze, Florida 32561 U.S.A. The information in this document has been funded wholly by the U.S. Environmental Protection Agency, and has been subjected to the Agency's peer and administrative review. Mention of commercial products or trade names does not constitute the Agency's endorsement or recommendation for use.     

Within-population variability in morphology and life history of Plantago major L. ssp. pleiosperma Pilger in relation to environmental heterogeneity

Summary An attempt was made to relate variation in life-history characteristics within a population of Plantago major ssp. pleiosperma to small-scale environmental variability. At a beach plain, embanked in 1966, a mosaic environment was distinguished with spatial variability in vegetation structure as well as in nutrient availability and water content of the soil. Differences between three subsites in comtemporary selection were demonstrated, e.g. in shoot morphology and allocation to reproductive tissue. The effects of nutrient supply and waterlogging on morphology and life history were studied on lines from the three subsites in a greenhouse. For most of the traits high levels of phenotypic plasticity were observed, covering almost entirely the observed phenotypic variability at the beach plain. In all treatments lines from the shrubs had, however, a higher leaf-area ratio as well as delayed flowering when compared to lines from more open subsites. In addition, in a reciprocal transplant experiment it was demonstrated that lines from the shrubs had larger shoots with e.g. broader leaves in the shady environment of the shrubs than other lines.From the experiments no indications were obtained that lines from any subsite were especially adapted to specific levels of nutrient supply or water content of the soil. With respect to these environmental factors P. major ssp. pleisoperma might occur and reproduce at all subsites by means of phenotypic plasticity, e.g. in plant form. However, it is suggested that spatial variability in vegetation structure caused a population subdivision in allocation patterns, leaf form and life history at the beach plain, over distances of about 15–25 m. This differentation occurred during primary succession over a period of twenty years.     

The reproductive biology and early development of the African pike,Hepsetus odoe,in the Okavango Delta,Botswana

Synopsis The reproductive biology of the African pike,Hepsetus odoe, was studied over a four-year period in the Okavango Delta, Botswana. Spawning takes place between August and May in different parts of the Delta. Fish in the seasonal swamp and drainage rivers have a truncated spawning season between August and January, while those in the perennial swamp have an extended spawning season from September to May. The variation in spawning season appears to be associated with the degree of environmental perturbation brought about by the annual flood cycle. Male and female pike mature at 140 and 160 mm standard length (SL) respectively. Females predominate in the population and produce an average of 6440 eggs per season and are multiple spawners. The number of eggs per spawning averages about 2630. The eggs are deposited in a foam nest which is guarded by the parents. Newly hatched embryos suspend themselves below the nest via a cement gland and remain in the vicinity of the spawning site until they have reached a relatively advanced stage in their development. The larval period is relatively short which implies that this species undergoes nearly a direct development. Foam nests appear to be a predator avoidance mechanism as well as an adaptation to fluctuating oxygen and water levels. The initiation of the spawning season is more closely associated with water temperature than with the annual flood cycle which appears to be more important in regulating the size of the spawning stock.     

Adaptive walks on changing landscapes: Levins' approach extended

The assumption that trade-offs exist is fundamental in evolutionary theory. Levins (Am. Nat. 96 (1962) 361-372) introduced a widely adopted graphical method for analyzing evolution towards an optimal combination of two quantitative traits, which are traded off. His approach explicitly excluded the possibility of density- and frequency-dependent selection. Here we extend Levins method towards models, which include these selection regimes and where therefore fitness landscapes change with population state. We employ the same kind of curves Levins used: trade-off curves and fitness contours. However, fitness contours are not fixed but a function of the resident traits and we only consider those that divide the trait space into potentially successful mutants and mutants which are not able to invade ('invasion boundaries'). The developed approach allows to make a priori predictions about evolutionary endpoints and about their bifurcations. This is illustrated by applying the approach to several examples from the recent literature.     

Life-history variation in Crepis tectorum (Asteraceae)

Summary Populations of the monocarpic plant Crepis tectorum were grown in a series of uniform environments to test the hypothesis that weedy populations are more r-selected than populations from a more natural habitat. Weedy populations exhibited a combination of r- and K-selected traits. The relatively rapid growth, the potential for a summer annual habit, and the relatively high fecundity that characterized at least one of the two weed populations studied were considered as r-selected traits favored in habitats of unpredictable duration. However, high levels of competition from other weedy species or from the crop in arable fields may explain at least some presumably K-selected traits observed in the weedy populations, e.g. relatively large seeds and late flowering in the summer. Results indicated that stress due to abiotic factors (strong winds, desiccation and nutrient deficiency) has been a more important selective factor than r- or K-selection, in non-weedy populations from calcareous grasslands (alvars) on the Baltic islands.     

棕色田鼠消化道形态变化与能量需求的关系

为研究能量代谢与消化道形态结构变化及其某些生活史特征之间的关系，采用食物平衡法、耗氧量测定、形态测量和组织学方法，分别测定了雄性、非繁殖雌性及哺乳雌性棕色田鼠(Mirotus mandarinus)的摄食量、每日消化能、静止代谢率和胃肠器官长度、重量以及肠道各段管径和黏膜厚度。结果表明：哺乳雌鼠摄食量、每日消化能、静止代谢率高于非繁殖雌鼠和雄鼠，且消化道各器官有最大的重量、管径和黏膜厚度。由此可见，哺乳雌鼠能量需求增加，促使消化道形态结构进行一些有益的调节。棕色田鼠在哺乳期代谢率增加时，仅有消化道器官重量、黏膜厚度及小肠管径的明显变化，这可能与其哺乳期较长，胎仔数较少，生后生长缓慢等生活史特征有关。同时也说明在未受到十分严峻的能量胁迫的情况下，动物并不需付出昂贵的代价去增加消化器官的长度。     

Wing dimorphism in Gryllus rubens: genetic basis of morph determination and fertility differences between morphs

Summary The genetic basis of wing morph determination and fertility differences between wing morphs were studied in the wing-dimorphic cricket, Gryllus rubens. Using pair corsses, a significant effect of genotype on morph determination was documented in F₃ progeny of field-collected crickets. The effect of genotype was significantly stronger in females than in males. Results are consistent with an earlier study (Zera and Tiebel 1988) showing that wing development is more strongly buffered from environmental variation in females. Segregation patterns were consistent with a polygenic mode of inheritance and provided no evidence for the existence of genes of major effect, maternal effects, or sex linkage. Only a weak morph x sex association was observed. These results contrast those of Walker (1987) where sex-linked loci of major effect on morph determination were identified in crosses between long-wing and short-wing-selected strains of G. rubens. Short-winged female G. rubens began ovipositing earlier and oviposited significantly more eggs than long-winged females during the first 24 days after adult eclosion. The greater reproductive output of the short-winged morph was due entirely to greater oviposition during the first two weeks after adult eclosion. Preliminary results indicate that flight may further accentuate the reduced reproductive output of long-winged versus short-winged females. These data provide the foundation for investigating the endocrine basis of morph-associated fertility variation in G. rubens and its mechanistic relationship with morph determination.