Seasonal and diel transitions in physiology and behavior in the migratory dark-eyed junco

Body mass, fat stores, activities of lipogenic and lipolytic enzymes, and plasma corticosterone were measured throughout seasonal and diel transitions from fall through spring encompassing the non-migratory stages of early and mid winter, the prealternate molt, and the spring migratory stage in captive dark-eyed juncos to determine the physiological mechanisms underlying adaptations for migration. On a seasonal basis, lipid enzymes and corticosterone varied little throughout the stages even though the birds underwent dramatic alterations in mass, fat deposition, behavior, and activation of the reproductive axis. By contrast, diel changes were found in lipogenesis, lipolysis, muscle lipoprotein lipase, and plasma corticosterone when comparing birds in the two phases of spring migration--active flight and resting, as during times of stopover. In these two phases of migration, coordination of the lipogenic and lipolytic systems appear to maximize storage of fatty acids during rest and delivery/utilization during flight. Diel patterns of corticosterone revealed fairly consistent peaks during the night time (23:00) throughout the nonmigratory period. The profile of this pattern altered during the migratory period with variation between the flight and resting phases. In sum, the results from these captive studies offer a new approach for studying the regulation of migratory physiology in free-living birds.     

Phenotypic plasticity and interpopulation differences in life history traits of<Emphasis Type="Italic"> Armadillidium vulgare</Emphasis> (Isopoda:Oniscidae)

The hypothesis that the balance of trade-offs between survivorship, growth and reproductive allocation in the terrestrial isopod Armadillidium vulgare will change when resource input is increased has been investigated experimentally. When the quality of food available was increased, by adding a mixture of litter from herbaceous dicotyledonous plants to a background low-quality food of dead grasses, survivorship was found to be the most phenotypically plastic trait, increasing by 168%. Growth rates increased by 99% but reproductive allocation by only 21%. In the field, members of a population from a site with more high-quality food grew more than twice as fast as those from a site where less high-quality food was available. The population from the site with higher food availability, contrary to predictions from the laboratory study, did not survive as well as that from the site with less available high-quality food. This may be because the site that is more favourable for growth has a more stressful physical environment due to much bigger temperature fluctuations, which are known to be an important cause of mortality in this species. When individuals from both populations were reared under controlled laboratory conditions, both the parental and F1 generations from the poor growth environment survived better than those from the good growth habitat. However, even when given an excess of high-quality food those from the poor growth environment continued to grow more slowly and had a lower reproductive allocation than those from the site with higher food availability. We conclude that microevolutionary changes may have occurred in the balance of resource allocation between survivorship, growth and reproductive allocation, to favour higher survivorship during the longer prereproductive period at the site where growth to the threshold size for reproduction takes longer.     

Individual variation in testosterone and parental care in a female songbird; The dark-eyed junco (Junco hyemalis)

When competition for sex-specific resources overlaps in time with offspring production and care, trade-offs can occur. Steroid hormones, particularly testosterone (T), play a crucial role in mediating such trade-offs in males, often increasing competitive behaviors while decreasing paternal behavior. Recent research has shown that females also face such trade-offs; however, we know little about the role of T in mediating female phenotypes in general, and the role of T in mediating trade-offs in females in particular. Here we examine the relationship between individual variation in maternal effort and endogenous T in the dark-eyed junco, a common songbird. Specifically, we measure circulating T before and after a physiological challenge (injection of gonadotropin releasing hormone, GnRH), and determine whether either measure is related to provisioning, brooding, or the amount of T sequestered in egg yolk. We found that females producing more T in response to a challenge spent less time brooding nestlings, but provisioned nestlings more frequently, and deposited more T in their eggs. These findings suggest that, while T is likely important in mediating maternal phenotypes and female life history tradeoffs, the direction of the relationships between T and phenotype may differ from what is generally observed in males, and that high levels of endogenous T are not necessarily as costly as previous work might suggest.     

直播羊草在不同pH土壤环境下的生物学特性和生理反应

采用人工配制的不同pH梯度的碱化土进行盆栽试验,研究了直播羊草在不同pH土壤环境下的生物学特性和生理反应.结果表明:pH 8.50以下的弱碱性土壤环境有利于直播羊草的生长,但随着土壤pH的升高其分蘖和地上部生物量均呈下降趋势;当土壤pH达到9.78时,直播后第2年羊草总株数比对照(pH 7.15)降低了42.0%,地上部干质量比对照降低了74.1%.此外,在盐碱胁迫下,羊草地上部含水量、可溶性糖、叶绿素和K 含量亦呈下降趋势,Na 含量和叶片外渗液电导率显著升高,地上部K /Na 比值从对照的28.5下降到1.6(pH 9.78),说明较高的K 水平以及较高的K /Na 比值可能是羊草耐盐碱的重要生理机制.     

Developmental and age-specific effects of selection on divergent virgin life span on fat content and starvation resistance in Drosophila melanogaster

Investigations into the genetic basis of longevity variation have shown life span to be positively correlated with starvation resistance and negatively with female fecundity, both of which rely on lipid content. To assess the firmness of this relation, we assayed correlated responses in age-specific relative fat content (RFC) and starvation resistance in lines successfully selected for divergent virgin life span. We have previously demonstrated that genetic differentiation in female fecundity between our selection lines had disappeared during relaxation of selection. Therefore, we also expected genetic differences in lipid content and starvation resistance to have disappeared. However, RFC and starvation resistance were still significantly lower in short-lived flies than in control flies. Surprisingly, also in long-lived flies RFC and starvation resistance were mostly, but not invariably, found to be significantly lower than in control flies. These results indicate that the genetic correlation of RFC and starvation resistance with reproduction has broken down. Furthermore, the relationship between life span and starvation resistance appears to be more complex than previously anticipated. Also, we could demonstrate that differences in RFC were not brought about by differences in lipid accumulation during adult life, but were already present at eclosion. These findings suggest that pre-adult developmental pathways already impact on the rate of ageing of the adult fly.     

Host plant utilization in the comma butterfly: sources of variation and evolutionary implications

A major challenge in the study of insect-host plant interactions is to understand how the different aspects of offspring performance interact to produce a preference hierarchy in the ovipositing females. In this paper we investigate host plant preference of the polyphagous butterfly Polygonia c-album (Lepidoptera: Nymphalidae) and compare it with several aspects of the life history of its offspring (growth rate, development time, adult size, survival and female fecundity). Females and offspring were tested on four naturally used host plants (Urtica dioica, Ulmus glabra, Salix caprea, and Betula pubescens). There was substantial individual variation in host plant preference, including reversals in rank order, but the differences were largely confined to differences in the ranking of Urtica dioica and S. caprea. Different aspects of performance on these two plants gave conflicting and complementary results, implying a trade-off between short development time on U. dioica, and larger size and higher fecundity on S. caprea. As all performance components showed low individual variation the large variation in host plant preference was interpreted as due to alternative oviposition strategies on the basis of similar performance hierarchies. This indicates that the larval performance component of host-plant utilization may be more conservative to evolutionary change than the preference of ovipositing females. Possible macro-evolutionary implications of this are discussed.     

Mobility and lifetime fecundity in new versus old populations of the Glanville fritillary butterfly

Life history theory often assumes a trade-off between dispersal and reproduction, and such a trade-off is commonly observed in wing-dimorphic insects. The results are less consistent for wing-monomorphic species, for which it is more difficult to assess dispersal capacity and rate. Three replicate experiments were carried out in consecutive years on the Glanville fritillary butterfly in a large outdoor population cage to study the relationship between lifetime egg production and mobility. The experimental material included females originating from newly-established and old populations, as previous studies have shown dispersal capacity to depend on population age. There was a consistent and significant interaction between mobility and population age, such that in newly-established populations mobile females had higher fecundity than less mobile females, while in old populations there was no such relationship. As selection favours individuals with the highest fecundity, selection pressure on mobility is likely to be different between the two population types, which may contribute to maintenance of variation in dispersal rate in the metapopulation as a whole. Several other female traits also affected lifetime fecundity, including lifespan, number of matings and date of eclosion, although these effects were not consistent across the years. These results highlight the importance of conducting experiments in more than one year before generalizing about patterns in life history variation.     

Genetic and morphological evolution following a founder event in the dark-eyed junco, Junco hyemalis thurberi

An isolated population of dark-eyed juncos, Junco hyemalis, became established on the campus of the University of California at San Diego (UCSD), probably in the early 1980s. It now numbers about 70 breeding pairs. Populations across the entire natural range of the subspecies J. h. thurberi are weakly differentiated from each other at five microsatellite loci (FST = 0.01). The UCSD population is significantly different from these populations, the closest of which is 70 km away. It has 88% of the genetic heterozygosity and 63% of the allelic richness of populations in the montane range of the subspecies, consistent with a harmonic mean effective population size of 32 (but with 95% confidence limits from four to > 70) over the eight generations since founding. Results suggest a moderate bottleneck in the early establishment phase but with more than seven effective founders. Individuals in the UCSD population have shorter wings and tails than those in the nearby mountains and a common garden experiment indicates that the morphological differences are genetically based. The moderate effective population size is not sufficient for the observed morphological differences to have evolved as a consequence of genetic drift, indicating a major role for selection subsequent to the founding of the UCSD population.     

Morph-dependent fatty acid oxidation in a wing-polymorphic cricket: implications for the trade-off between dispersal and reproduction

Although a considerable amount of information is available on the ecology and physiology of wing polymorphism, much less is known about the biochemical-genetic basis of morph specialization for dispersal versus reproduction. Previous studies have shown that the dispersing morph of the wing-polymorphic cricket, Gryllus firmus, prioritizes the accumulation of triglyceride flight fuel over ovarian growth, while the opposite occurs in the flightless morph during the first week of adulthood. In this study, we compared the in vivo rate of lipid oxidation between genetic stocks of flight-capable versus flightless morphs to determine the role of lipid catabolism in morph specialization for flight versus reproduction. During the first five days of adulthood, in the absence of flight, fatty acid oxidation was substantially lower in the dispersing morph relative to the flightless morph, when either radiolabeled acetate or palmitate was used as a substrate. Differences between the morphs in fatty acid oxidation were genetically based, occurred co-incident with morph-specific differences in triglyceride accumulation and ovarian growth, and were observed on a variety of diets. A genetically based trade-off in the relative conversion of palmitate into CO(2) versus triglyceride was observed in morphs of G. firmus. Decreased oxidation of fatty acid and increased biosynthesis of triglyceride, both appear to play an important role in flight fuel accumulation, and hence morph specialization for flight. Conversely, increased oxidation of fatty acid likely fuels the enhanced ovarian growth in the flightless morph. The results of the present study on fatty acid catabolism, and previous studies on triglyceride and phospholipid biosynthesis, provide the first direct evidence that genetically based differences in in vivo flux through pathways of intermediary metabolism underlie a trade-off between flight capability and reproduction--a trade-off of central importance in insects.     

Egg weight variation in the butterfly Lycaena hippothoe: more small or fewer large eggs?

Fecundity, egg weight, hatching success of eggs, and adult (offspring) weight were compared between three geographically separated populations (i.e., subspecies) of the butterfly Lycaena hippothoe. All these traits differed substantially between populations. Our data suggest that, on an interpopulational level, egg size is traded off against egg number, egg size varies independent of adult size, and there is (given equal egg size) a positive relationship between adult weight (body size) and fecundity. The significantly heavier eggs of the alpine population Lycaena hippothoe eurydame showed strikingly increased hatchability, especially at high temperatures, as compared to the other populations. However, the ultimate reasons favoring large egg size in the alpine population, whether as a result of direct selection on egg size, as a correlated response based on other selective pressures, or reflecting relaxed selection for maximized fecundity, remain to be discovered. Received: November 10, 2000 / Accepted: February 5, 2001     

Seasonal life history trade-offs in two leafwing butterflies: Delaying reproductive development increases life expectancy

Surviving inhospitable periods or seasons may greatly affect fitness. Evidence of this exists in the prevalence of dormant stages in the life cycles of most insects. Here I focused on butterflies with distinct seasonal morphological types (not a genetic polymorphism) in which one morphological type, or form, delays reproduction until favorable conditions return, while the other form develops in an environment that favors direct reproduction. For two butterflies, Anaea aidea and A. andria, I tested the hypothesis that the development of each seasonal form involves a differential allocation of resources to survival at eclosion. I assayed differences in adult longevity among summer and winter forms in either a warm, active environment or a cool, calm environment. Winter form adults lived 40 times longer than summer form but only in calm, cool conditions. The magnitude of this difference provided compelling evidence that the winter form body plan and metabolic strategy (i.e. resource conservatism) favor long term survival. This research suggests that winter form adults maintain lowered metabolic rate, a common feature of diapause, to conserve resources and delay senescence while overwintering.     

Habitat preference in the dark-eyed junco (Junco hyemalis): The role of photoperiod and dominance

Wild-caught dark-eyed juncos (Junco hyemalis), simultaneously presented with projected slides of their winter and summer habitats, demonstrated distinct preferences (in terms of time spent in front of particular slides) consistent with their season of capture and prior laboratory experience. Juncos caught in and kept on winter or summer photoperiods preferred winter and summer habitat slides respectively. A gradual increase in photoperiod up to natural summer conditions induced a switch from winter to summer habitat preference: a decrease in photoperiod induced a range of slide preferences correlated with the junco's size, a measure of the bird's dominance rank.     

Evolution of feeding structure plasticity in marine invertebrate larvae: a possible trade-off between arm length and stomach size

The ability of an organism to alter its morphology in response to environmental conditions (phenotypic plasticity) occurs in several species of marine invertebrates. Examples are sea urchin and sand dollar larvae (plutei). When food is scarce, plutei produce longer food-gathering structures (larval arms and a ciliary band) and smaller stomachs than when food is abundant. However, it is unclear whether stomach size is actually induced through changes in morphogenesis or simply by food distending the stomach. Distinguishing between these two hypotheses is possible because plutei morphologically respond to food concentrations and change the length of their food-gathering structures before they are capable of feeding. More importantly, these two hypotheses provide insights to whether a trade-off exists between the response in food-gathering structures and the response in stomach size—a possible explanation for the evolution of feeding-structure plasticity in marine invertebrate larvae. In this study, I investigated whether sea urchin larvae (Strongylocentrotus purpuratus and S. franciscanus) reared in different amounts of food produced stomachs of different sizes before they were capable of feeding. Prior to having the ability to ingest food, larvae produced larger stomachs and shorter arms when food was abundant than when food was scarce, consistent with the hypothesis that food induced changes in morphogenesis. In addition, there was a strong negative correlation between the magnitude of plasticity in larval arm length and the magnitude of plasticity in stomach size. These results are consistent with the idea that a trade-off exists between the response in arm length and the response in stomach size, and at least in part, explains the evolution of feeding structure plasticity in plutei. This may also explain why feeding-structure plasticity has evolved in larvae of other taxa (e.g. other echinoderms and gastropods).     

Angiopoietin-2 stimulates migration of endothelial progenitors and their interaction with endothelium

The factors controlling recruitment of endogenous and transplanted endothelial progenitor cells (EPC) to areas of neovascularization are largely unknown. In this study, we have examined the possibility that EPC migration and adhesion could be regulated by angiopoietin-2 (Ang2), a soluble ligand expressed by endothelial cells at sites of vessel remodelling and angiogenesis. We show for the first time that Ang2 causes a marked stimulation of EPC migration. This was specific for EPC as the ligand failed to affect endothelial cell migration. Ang2-stimulated EPC migration was inhibited by soluble Tie2 ectodomain. Furthermore, the ligand stimulated adhesion between EPC and endothelial monolayers.     

Dietary effects on life history traits in a terrestrial isopod: the importance of evaluating maternal effects and trade-offs

Studies of life history aim to explain patterns in the evolution of reproductive investment, growth, and survival. Trade-offs between traits are a fundamental component of life history theory. In herbivorous arthropods life history traits are often responsive to variation in numerous environmental factors, especially diet quality. Using three artificial diets under controlled laboratory conditions, we examined changes in life history traits (i.e. growth rate, offspring number, offspring size, incubation period), trade-offs between traits, and maternal effect on the growth rate of offspring, in the common woodlouse (terrestrial isopod), Porcellio laevis. The high protein diet had significant impacts on offspring production, triggering a smaller-sized offspring, and demonstrating a trade-off between these last two traits. The high carbohydrate diet seldom exerted a significant effect on incubation period. The quality of dietary items evidently has important consequences on the life history of the mother and, thus, on offspring growth; the directions of these effects, however, were opposite. Mothers fed diets with high protein concentrations presented significant maternal effects, measured as offspring growth rate during later ontogeny. Our results support the notion that protein, rather than carbohydrate, concentrations in the diet limit herbivorous arthropods, and have significant consequences on life history traits, as was seen for P. laevis. Clearly, the change in phenotypic correlations between incubation period and offspring number from negative to positive is an empirical demonstration of the context dependence of life history trait trade-offs.     

A morph-specific daily cycle in the rate of JH biosynthesis underlies a morph-specific daily cycle in the hemolymph JH titer in a wing-polymorphic cricket

A previous study documented a high amplitude, morph-specific daily cycle in the hemolymph JH titer in the wing-polymorphic cricket, Gryllus firmus. The JH titer rose and fell 10-20 fold in the flight-capable [LW(f), long-winged] morph during the late-photophase-early scotophase, while it was relatively constant during that time in the flightless (SW, short-winged) morph. In the present study we documented a dramatic morph-specific daily cycle in the in vitro rate of juvenile hormone (JH) biosynthesis that was tightly correlated with the hemolymph JH titer on days 5-7 of adulthood. Biosynthetic rates rose and fell 1-2 fold between the late photophase-early scotophase on each of days 5-6 and 6-7 of adulthood in the LW(f) morph, while biosynthetic rates were relatively constant during this period in the flightless, short-winged morph (SW), except for a slight dip in the rate of biosynthesis late in the photophase on these days. Similar morph-specific patterns of JH biosynthesis were observed whether rates were measured on corpora allata attached to corpora cardiaca in males or females, or on corpora allata alone. Hemolymph juvenile hormone esterase activity was significantly higher in the LW(f) vs. the SW morph during the beginning of scotophase, when the JH titer is decreasing rapidly in the LW(f) morph. Results indicate that the morph-specific daily cycle in the JH titer in G. firmus is primarily regulated by a morph-specific daily cycle in the rate of JH biosynthesis and to a lesser degree by hemolymph JH esterase activity. This is the first documentation of a diurnal cycle in the rate of JH biosynthesis in any insect, or a daily cycle in the rate of JH biosynthesis that is correlated with a specific morph in a polymorphic species. Results have important implications for the endocrine regulation of dispersal polymorphism, circadian rhythms of insect hormone titers and their regulators, and general studies of the JH titer and its regulation in insects.     

Biochemical basis of specialization for dispersal vs. reproduction in a wing-polymorphic cricket: morph-specific metabolism of amino acids

The biochemical basis of specializations for dispersal vs. reproduction is an understudied aspect of dispersal polymorphism in insects. Using a radiolabelled amino acid, we quantified differences in in vivo amino acid metabolism between morphs of the wing-polymorphic cricket, Gryllus firmus, that trade-off early age reproduction and dispersal capability. Studies were conducted in crickets fed a variety of diets expected to influence amino acid and lipid metabolism. On the day of molt to adulthood, prior to the morph-specific trade-off between ovarian growth and biochemical preparation for flight (e.g. biosynthesis of triglyceride flight fuel), morphs did not differ in any aspect of amino acid metabolism. However, on day 5 of adulthood, when the morph-specific trade-off between ovarian growth and flight fuel production was manifest, the morphs differed substantially in each of the three aspects of amino acid metabolism studied: conversion to protein, oxidation, and conversion to lipid. Morphs also differed in degree of allocation of products of amino acid metabolism to ovaries vs. the soma. Most importantly, morphs differed in the relative metabolism of radiolabelled glycine through these pathways (i.e. biochemical trade-offs), and in the relative allocation of end products of amino acid metabolism to the soma vs. ovaries (allocation trade-offs). A functionally important interaction between amino acid and lipid metabolism was noted: greater oxidation of amino acids in the flight-capable morph spared fatty acids for enhanced conversion into triglyceride flight fuel. By contrast, greater oxidation of fatty acids by the flightless morph spared amino acids for enhanced conversion into ovarian protein. Diet significantly affected amino acid metabolism. However, MORPHxDIET interactions were rare and morphs differed in amino acid metabolism to a similar degree under the range of diets tested.     

On the development and reproduction of Botryllus schlossen (Tunicata) colonies from the eastern Mediterranean Sea: plasticity of life history traits

Summary

Analysis of developmental patterns of Botryllus schlosseri colonies from the eastern Mediterranean coast has been performed on 143 genets under different temperature regimens (15,20,27 °C) for up to 22 weeks. While the average maximal size as the length of the blastogenic cycle (BC) varied in respect to water temperature, ontogeny at all temperatures was characterized by 4 developmental stages: 1. the lag phase (the first 1–3 BCs, 1 bud/BC), 2. the exponential growth phase (5.5–7.8 BCs, up to 3 buds/BC), 3. the plateau phase, (7.4–8.2 BCs, 1 bud/BC), 4. the degenerative or the variable phase. Many (40.6%) colonies were not sexually reproductive, the others were male only (30.1%) or hermaphrodites. Colonies at the peak of reproduction develop 1.2 oocytes/zooid, and up to 57.7% produced >4 clutches. Analysing onset of reproduction with maximal colony size revealed 4 patterns, two for “male only” colonies and two for hermaphrodites that varied at different sea water temperatures. In two patterns, the onset of reproduction precedes colony maximal size, and in the others it starts at the peak size or thereafter. Zooids at the colony's periphery developed almost twice as many buds as did zooids at the center, but produced significantly lower numbers of eggs. Fragmentation was recorded in large colonies and was temperature dependent. Results are compared with the data available on populations from other localities indicating for dramatically different developmental modes characteristic to this cosmopolitan species.     

Phenotypic plasticity and the possible role of genetic assimilation: Hypoxia-induced trade-offs in the morphological traits of an African cichlid

In this study we investigate the possible role of phenotypic plasticity and genetic assimilation in the process of adaptation and evolutionary change in the cichlid Pseudocrenilabrus multicolor victoriae . In the field we compared a population of a stable hypoxic habitat with one of a stable well-oxygenated habitat. In the laboratory, we compared individuals from the same mother raised under hypoxic or well-oxygenated conditions to examine phenotypic plasticity. Morphological parameters of three categories were measured: (a) the gill apparatus, (b) the surrounding structural elements, and (c) the outer shape of the fish. Swamp-dwelling fish had a 29% greater total gill surface area than fish from the well-oxygenated habitat due to their larger gill filament length and greater lamellar area. In the plasticity experiment, total gill surface area was 18% greater in the hypoxia group due to a larger number of longer filaments. Surrounding elements and outer shape also differed between the field populations and between fish grown under hypoxic and well-oxygenated conditions, but there was disparity between the field results and the plasticity experiment. The disparity between field and experimental fish may be due to: (a) differences in selection pressures between populations, (b) different constraints for genetic and plasticity changes, or (c) selection against plastic responses to hypoxia. Our results suggest that both (a) and (c) are involved.