Timing Of First Reproduction Research Articles

Ontogeny of the middle ear and auditory sensitivity in the Natterjack toad (Epidalea calamita).

In most anuran amphibians, acoustic communication is of prime importance for mate localization and selection. The tympanic middle ear increases auditory sensitivity and directionality and is therefore expected to be favoured by natural selection. However, especially within the family of true toads (Bufonidae) there is a tendency for species to lose parts of the middle ear apparatus and consequently have a reduced sensitivity to high-frequency sounds (above 1 kHz). Part of the explanation for this may be that development of the middle ear is especially slow in bufonids, and thus the middle ear would be more likely to be lost or non-functional in paedomorphic species. However, a timeline of development of the middle ear has not been established previously. The goal of the present study was to investigate middle ear development in a toad species that has a well-known natural history and acoustic communication behaviour. We made a detailed study of anatomy and biophysics of the middle ear with measurements of auditory sensitivity across age in post-metamorphic natterjack toads (Epidalea calamita). The tadpoles and toadlets were raised in the laboratory, so their exact age was known, their auditory sensitivity was measured using auditory brainstem responses, and middle ear development and function were assessed by anatomical studies and laser vibrometry. We found that the developmental stage of the middle ear depends on the size of the toad rather than its age. The middle ear was functional at the earliest at a snout-vent length of 40 mm, which for these toads was around 500 days post-metamorphosis, close to the time of first reproduction. The functional, adult-like middle ear was shown to have 30 dB increased sensitivity to the dominant frequency of the mating call compared with sensitivities measured in newly metamorphosed individuals.

Long-term demographics of a coral-reef fish: growth, survival and abundance at several spatial scales

In marine organisms, pelagic larval dispersal often results in genetic panmixis among widely separated populations; however, local conditions may produce populations of marine organisms that differ in key life history traits. Here, we assess spatial differences in growth, body condition, survivorship and movement over a decade for lemon damselfish Pomacentrus moluccensis. Newly recruited fish were tagged on the southern (One Tree Island, 23°S), and northern Great Barrier Reef (Lizard Island, 15°S), 1200 km apart, and monitored for over a decade to provide direct data on growth and survivorship. New recruit physiological condition (lipid content) had a weak positive influence on early survival, but not on long-term persistence or growth, and the larval supply signal was lost after 2 years, suggesting post-settlement processes were key in long-term population persistence. Fish exhibited extreme site fidelity, with older/larger fish moving most (all less than 7 m). At Lizard Island, under 5% of individuals remained after 3 years, none after 4 years, while at One Tree Island 5% of individuals survived over 5 years, with 1% remaining after a decade, suggesting Lizard Island populations may require more frequent replenishment to persist. Among-site (within location) variation in mortality was high, and not related to density, suggesting local conditions such as wave exposure and predators were important. Surprisingly, mean growth at the two locations, which differ by around 2 °C on average in sea temperature, was practically identical, levelling off after 3 years, but with high variation among nearby sites within each location, which would affect size-based fecundity and time of first reproduction at these smaller spatial scales. Neither early post-settlement growth nor mortality were density-dependent, and early growth was not related to overall longevity. These small reef fishes are highly sedentary and some demographic parameters, but not others, differ at a range of scales, with post-settlement populations likely driven largely by mortality patterns at the larger spatial scale. Latitudinal and smaller-spatial scale differences in performance (growth, survival) of this species, leading to offsets in expected time to maturity an fecundity, are contrasted by evidence of stability of adult populations over two decades at One Tree Island, which suggests that resilience to environmental change/climate change and other externalities differ considerably across this species’ distribution.

Evaluation of toxicity and environmental safety in use of spinosad to rationalize control strategies against Aedes aegypti

Spinosad is a naturally-occurring insecticide used for the management of Ae. aegypti larvae. The assessment of ecotoxicological parameters of spinosad is required for verifying the environmentally-friendly behavior of the compound and for evaluating toxicity values on non-target species. Thus, the aim of the study was to conduct toxicity tests using Daphnia magna as model organism after exposure to different concentrations of spinosad. Immobility effects were observed in both acute and chronic toxicity tests at the concentration of 2.5 μg/L, and D. magna exhibited an EC50-48 h of 4.1 μg/L and EC50-7d of 9.3 μg/L. Also, the reproductive test showed a significant increase in the time of first reproduction and decrease in the number of neonates per female. However, due to the rapid decay of spinosad, other reproductive parameters were not markedly affected. Thereby, considering the satisfactory control performance against Aedes aegypti, a 100-fold lower concentration of spinosad can be used against the larvae, and owing to the residual efficacy observed, the application of the pesticide in the field may be rationalized while offering environmental safety.

Ecotoxicological effects of larvicide used in the control of Aedes aegypti on nontarget organisms: Redefining the use of pyriproxyfen

ABSTRACTThe continued widespread use of larvicides in Aedes aegypti control programs is still a necessary strategy, since there are no apparent efficient vaccines against arboviruses. However, chemical approaches may affect nontarget organisms and produce detrimental effects to environmental health. Therefore, the aim of this study was to conduct toxicity testing for pyriproxyfen at different concentrations using Daphnia magna and Artemia salina as model organisms to evaluate the ecotoxicological parameters. This study describes the toxicological effects of pyriproxyfen on both microcrustaceans, which are widely used in bioassays because of their sensitivity to changes in hydrosphere. Data demonstrated that the calculated EC50-48h value of pyriproxyfen was 2.5 μg/for D. magna and A. salina; the no-observed-effect concentration (NOEC) and the lowest-observed-effect concentration (LOEC) of pyriproxyfen were found to be 0.63 and 1.25 μg/L for Artemia salina and Daphnia magna, respectively. In chronic toxicity and reproduction tests on D. magna, a calculated CL50-7day (lethality on 50% of daphnids after 7 days of chronic test) and an EC50-21day (50% reduction in the reproductive output of parental daphnids after 21 days of exposure) higher than 1.25 μg/L pyriproxyfen were observed. The time of first reproduction was significantly increased in D. magna after exposure to environmentally relevant concentrations of pyriproxyfen, but other reproduction parameters were not markedly altered. Environmental risk assessment revealed that pyriproxyfen is highly toxic for both branchiopods. Data demonstrated that pyriproxyfen may produce adverse effects on the aquatic ecosystem at concentrations required to control Ae. aegypti.

Adolescent fertility and risky environments: a population-level perspective across the lifespan

Timing of first reproduction is a key life-history variable with important implications for global economic development and health. Life-history theory predicts that human reproductive strategies are shaped by mortality regimes. This study provides the first test of the relationship between population-level adolescent fertility (AF) and extrinsic risk at two time points. Data are from United Nations database and were analysed using mediation and moderation techniques. The goals were to determine whether (i) early risk has a stronger impact on fertility than current risk; (ii) current risk mediates the relationship between early risk and fertility outcomes; and (iii) different levels of early risk influence the relationship between current risk and fertility. Results indicated that current risk partially mediated the relationship between early risk and fertility, with early risk having the strongest impact on reproduction. Measures for early and current mortality did not show significant interaction effects. However, a series of separate regression analyses using a quantile split of early risk indicated that high levels of early risk strengthened the relationship between current risk and AF. Overall, these findings demonstrate that reproductive strategies are significantly influenced by fluctuations of early mortality as well as current environmental cues of harshness.

Life-history theory, chronic childhood illness and the timing of first reproduction in a British birth cohort

Life-history theoretical models show that a typical evolutionarily optimal response of a juvenile organism to high mortality risk is to reach reproductive maturity earlier. Experimental studies in a range of species suggest the existence of adaptive flexibility in reproductive scheduling to maximize fitness just as life-history theory predicts. In humans, supportive evidence has come from studies comparing neighbourhoods with different mortality rates, historical and cross-cultural data. Here, the prediction is tested in a novel way in a large (n = 9099), longitudinal sample using data comparing age at first reproduction in individuals with and without life-expectancy-reducing chronic disease diagnosed during childhood. Diseases selected for inclusion as chronic illnesses were those unlikely to be significantly affected by shifting allocation of effort away from reproduction towards survival; those which have comparatively large effects on mortality and life expectancy; and those which are not profoundly disabling. The results confirmed the prediction that chronic disease would associate with early age at first reproduction: individuals growing up with a serious chronic disease were 1.6 times more likely to have had a first child by age 30. Analysis of control variables also confirmed past research findings on links between being raised father-absent and early pubertal development and reproduction.

Reproductive constraints, not environmental conditions, shape the ontogeny of sex‐specific mass–size allometry in roe deer

In polygynous mammals, sex‐specific patterns of body growth are linked to divergent selection pressures on male and female body size, resulting in sexual dimorphism (SD). For males, reproductive success is generally linked to body size, hence, males should prioritise early growth. For females, reproductive success is linked to resource availability, so they may adopt a more conservative growth tactic. Using longitudinal monitoring of known‐age animals in two contrasting populations and an allometric approach to disentangle the relative contribution of structural size and physiological condition to SD, we addressed these issues in the weakly polygynous roe deer. Despite very different environmental conditions, we found remarkably similar patterns in the two populations in the mass–size allometric relationship at each life history stage, suggesting that relative allocation to structural size and physiological condition is highly constrained. SD in structural size (indexed by hind foot length) involved sex‐specific growth trajectories governed by a single mass–size allometric relationship during the juvenile stage, such that males were both bigger and heavier than females. In contrast, SD in physiological condition (indexed by the allometric relationship between body mass and hind foot length, expressed as body mass for a given body size) developed markedly during the sub‐adult stage in relation to sex differences in the timing of first reproduction. Among adults, males were heavier for a given size than females, suggesting that, relative to females, males express a capital breeder tactic, accumulating fat reserves to offset reproductive costs. By the senescent stage, SD in physiological condition had disappeared, with both sexes governed by a single allometric relationship, suggesting more rapid senescence in males than females. Individuals born into poor cohorts were generally lighter for a given size, indicating growth priority for skeletal size over physiological condition in both sexes. However, sex differences in cohort effects among sub‐adults resulted in lower size‐specific SD in poor cohorts, indicating that body condition of sub‐adult females is buffered against environmental harshness. We conclude that sex‐differences in reproductive tactics impose constraints on the ontogeny of SD in roe deer, leading to sex‐specific trajectories in structural size and physiological condition.

Toxicity evaluation of verapamil and tramadol based on toxicity assay and expression patterns of Dhb, Vtg, Arnt, CYP4, and CYP314 in Daphnia magna

In this study, the toxicities of two pharmaceuticals, verapamil and tramadol were evaluated in Daphnia magna using the conventional toxicity tests (acute and chronic test) and the expression patterns of five stress responsive genes. In the chronic toxicity test, several parameters, such as the survival percentage, the body length of D. magna, the time of first reproduction, and the number of offspring per female, were adversely affected during the exposure to 4.2 mg L(-1) verapamil and 34 mg L(-1) tramadol. During the 24-h short-term exposure, verapamil particularly caused a downregulated expression of the CYP4 and CYP314 genes, whereas tramadol upregulated the expression of the CYP314 gene. Neither pharmaceutical affected the expression of Dhb, Arnt, and Vtg. However, during the 21-day long-term exposure, both verapamil and tramadol significantly reduced the expression level of the Vtg gene, a biomarker of the reproduction ability in an oviparous animal, whereas neither affected the other genes.

Alcohol dependence and reproductive onset: findings in two Australian twin cohorts.

Although early alcohol use is a strong predictor of future alcohol problems and adolescent drinking is associated with risky sexual behavior predictive of early childbearing, reproductive dysfunctions associated with delayed childbearing have been reported in adult drinkers. We examine the relationship between lifetime history of alcohol dependence (AD) and timing of first childbirth across reproductive development. Data were drawn from two cohorts of Australian twins born between 1893 and 1964 (3634 female and 1880 male twins) and between 1964 and 1971 (3381 female and 2748 male twins). Survival analyses were conducted using Cox proportional hazards regression models predicting age at first childbirth from AD, with sociodemographic characteristics, regular smoking, history of psychopathology, and family and childhood risks included as control variables in adjusted models. Results suggest alcoholic women in both cohorts show overall delayed reproduction, with little effect of AD on timing of first reproduction in men. Effects of AD are particularly strong for women in the older cohort, where AD is associated with 73% decreased likelihood of first childbirth after age 29 [hazard ratio (HR) = 0.27, 95% CI: 0.10-0.75]. In adjusted models, effects reduce only slightly (HR = 0.29, 95% CI: 0.11-0.80). For women in the young cohort, AD is associated with delayed reproduction after age 24, with 40% decreased likelihood of first childbirth (HR = 0.60, 95% CI: 0.48-0.75). AD remains predictive in adjusted models, but without age interaction (HR = 0.72, 95% CI: 0.62-0.85). Findings of delayed reproductive onset in alcoholic women are consistent with alcohol-related reproductive dysfunctions, although underlying mechanisms remain largely unknown. To better understand AD differences in reproductive onset, continued research on both biological and psychosocial risks is needed.

Start of reproduction and allozyme heterozygosity in Pinus sibirica under different techniques of artificial forest stand establishment

Siberian stone pine (Pinus sibirica Du Tour) is one of the main forest-forming tree species in boreal forests of Eurasia. Large edible seeds of this species have an important resource value because of their high nutritious properties. Development of approaches to establishment of early cone producing Siberian stone pine stands including utilization of corresponding genetic background is one of the priorities of forest resource management. The goal of our study was to evaluate the effect of stand density on the differentiation of trees by the age of first reproduction and the relationship of allozyme heterozygosity and morphological traits variability in Siberian stone pine. Morphological and allozyme variability in artificial Pinus sibirica stands with high and low density was investigated. In the high-density stand the distance between trees was 0.7 and 3 meters (4080 trees per ha) while in the lowdensity stand it was 8 and 8 meters (144 trees per ha). Age of formation of first male and female cones was evaluated by retrospective method based on analysis of tracks of cones on a shoot bark. Tree height, diameter and number of male, female and vegetative shoots in a crown of model trees were measured. Genotypes of the trees were determined by 29 isozyme loci coding for 16 enzymes (ADH, FDH, FEST, GDH, GOT, IDH, LAP, MDH, MNR, PEPCA, 6-PGD, PGI, PGM, SDH, SKDH, SOD). In the low-density stand, the portion of generative trees was higher and differentiation of trees by age of reproduction starting was lower in spite of the smaller age of trees as compared to the high-density stand. In both samples, the age of formation of first generative organs was related negatively with stem height, stem diameter and number of female shoots. In the high-density stand, positive relation of age of first reproduction with total number of shoots and number of male shoots was found. In both samples nonreproductive trees were less heterozygous at isozyme loci as compared to trees starting cone production. Allozyme heterozygosity correlated positively with the age of first cone production in the high-density stand only. We conclude that the degree of competition between trees due to different stand density determined age and timing of first reproduction and development of tree crowns. The relationship of allozyme heterozygosity and the age of first reproduction was expressed more in the high-density stand of Siberian stone pine.

Sociality, age at first reproduction and senescence: comparative analyses of birds

Evolutionary theories of senescence suggest that aging evolves as a consequence of early reproduction imposing later viability costs, or as a consequence of weak selection against mutations that act late in life. In addition, highly social species that live in sites that are protected from extrinsic mortality due to predation should senesce at a slower rate than solitary species. Therefore, species that start reproducing late in life should senesce at a slower rate than species that start reproducing early. In addition, social species should senesce more slowly than solitary species. Here I investigate the rate of senescence using an extensive data set on longevity records under natural field conditions to test predictions about the evolution of senescence among 271 species of birds. Longevity records increased with sampling effort and body mass, but once these confounding variables were controlled statistically, there was a strongly positive relationship between relative longevity and relative adult survival rate. Relative longevity after controlling statistically for sampling effort, body mass and adult survival rate, increased with age at first reproduction, but not with degree of breeding sociality. These findings suggest that the evolution of senescence is related to timing of first reproduction, but that the evolution of breeding sociality has played a negligible role in the evolution of senescence.

Cladoceran Densities, Day-to-Day Variability in Food Selection by Smelt, and the Birth-Rate-Compensation Hypothesis

Late-evening gut inspection of a dominant planktivore (smelt) and evaluation of densities, fecundities, and body-size distributions in dominant zooplankton prey (cladocerans) were made in day-to-day sequences in June–July (24 days in 1999 and 24 days in 2000). This was conducted as a field test of the hypothesis that species-specific population densities in cladocerans result from size-selective predation by a dominant fish assumed to be a general predator, switching from one prey to another as relative abundance changes. Little of the expected coincidence has been revealed between population density declines and increased numbers of a given prey in smelt diet. However, the data were consistent with the notion that fish would switch from one prey to another depending on the prey relative abundance (the number of prey a fish would see in its reaction field volume). Each cladoceran population fluctuated around its species-specific density level, lower or higher, depending on individual susceptibility to smelt predation, from 0.2 ind. l−1 in large-bodied Daphnia hyalina and Leptodora kindtii, to 30.0 ind. l−1 in small-bodied Daphnia cucullata andBosmina thersites. In spite of high fish-to-fish and day-to-day variability in both smelt diet and smelt selectivity for different prey, all cladocerans (also copepods and midge larvae) were equally persistent in smelt diet, and smelt selectivity was similar for small- and large-bodied prey categories, but lower for elongated-(Daphnia, Diaphanosoma) than for compact-body (Bosmina, Chydorus) species, when integrated for the entire sampling time. Closer examination of D. cucullata and B. thersites revealed strong smelt selection for later instars and females with greater clutches, showing that size distribution in a cladoceran population might be structured by fish predation in a similar way to that a cladoceran community (species relative abundance) is structured in a lake habitat. The “birth-rate-compensation hypothesis” is offered to explain why the value of food selectivity index in a planktivorous fish would remain the same for alternate prey categories with similar life-history traits, unless they differ in susceptibility to predation before the time of first reproduction.

Size-dependent reproductive pattern and short-term reproductive cost in Rumex obtusifolius L

This paper analyses the size-dependent reproductive pattern of Rumex obtusifolius L. growing in lucerne crops (Medicago sativa L.), and its importance in determining the existence of a short-term reproductive cost. Size effects on reproductive pattern were evaluated by determining the role of plant size at the time of first reproduction, and the size-dependency of flowering probability (estimated as the proportion of flowering plants), plant fecundity, and reproductive effort (estimated as the ratio between reproductive and vegetative biomass). These parameters were recorded over the reproductive episodes determined by crop harvesting during the reproductive period. The results showed that size was much more important than age in determining time of first reproduction. Seed output decreased progressively over the reproductive period, probably in relation to an increasing short-term reproductive cost caused by a gradual depletion of plant resources. Probability of flowering over the successive reproductive episodes increased with plant size. The allometric relationship of vegetative versus reproductive biomass indicated that reproductive biomass increased less sharply than vegetative biomass and, consequently, reproductive effort decreased as plant size increased. Assuming a direct relationship between reproductive effort and reproductive cost, the size-dependent flowering probability could reflect, in turn, the existence of a size-dependent reproductive cost that would decrease as plant size increased. Ecological implications of these results are discussed.

Age, Growth, and Long-Term Site Fidelity in the Terrestrial Plethodontid SalamanderPlethodon kentucki

Based on mark-recapture data collected over seven years on the salamander Plethodon kentucki, I examined (1) longevity and long-term site fidelity, (2) growth curves for each sex derived from both cross-sectional and longitudinal data on body size, (3) whether growth curves generated from the two kinds of data were comparable, and (4) how the relationship between adult body size and age in this species compares to that in other plethodontid salamanders. Recapture rates indicate that about 86% of males and 82% of females survived and remained in the study area from one year to the next. Most individuals recaptured at the end of the study period were within, or less than 2 m from, the home range they occupied at the beginning. Maximum age estimates were 13 yr for males and 16 yr for females. Growth curves derived from cross-sectional and longitudinal data were very similar. For both sexes, there is rapid growth up to the time of first reproduction (about 4 and 5 yr for males and females, respectively) and continued growth for 2 to 4 yr afterward but relatively little growth after 9 yr of age. Males may have a greater rate of growth prior to sexual maturity, but females grow for a longer period and attain a greater body size. There is much variance in adult body size within a given age class for both sexes. The correlation between body size and age was slightly greater in males than in females, and the correlation was significant for the combined data. Similarly, the size-age correlation in other plethodontid species is stronger for males than for females, which may be because of a greater variability in growth after sexual maturity in females than in males.

Optimal timing of first reproduction in parasitic nematodes

Abstract The time between infection and the onset of reproduction (maturation time) is a key determinant of body size, fecundity and generation time in parasitic nematodes. An optimality model for maturation time is developed centred on prematurational growth, the duration of which has opposing consequences for fecundity and for survival to reproductive age. The maturation time favoured by natural selection is found to be inversely proportional to prematurational mortality rate. The product of maturation time and mortality rate is predicted to be an invariant number equal to the allometric slope linking daily fecundity to maturation time. Predictions are tested using comparative data on mammalian gastrointestinal nematode taxa. Half the cross-species variation in prepatent period (the time from infection until propagules are shed from the host) is accounted for by this adaptive trade-off hypothesis, even though many biological details are not explicitly modelled. These results are discussed in the light of previous studies and in the context of general models of life history evolution.

Environmentally Contingent Reproductive Strategies in Mayan and Ache Males

This research explores male reproductive parameters, particularly the timing of first reproduction, in two traditional populations. Predictions are drawn from theoretical arguments that have their roots in evolutionary psychology and behavioral ecology, and that interpret variation in reproductive outcomes as environmentally contingent adaptations. In both Ache and Mayan samples, father absence, predicted to act as a stressor that causes precocious sexuality and reproduction as well as unstable pair bonds, did not affect the timing of first reproduction in male offspring in the expected way. Father absence in Mayan men, however, was found to be associated with responses to questionnaire items indicating lack of willingness to pay time and energy costs to maintain existing sexual unions. The results suggest that father absence affects male mating strategy, but that strategic differences did not translate into reproductive outcomes in the sample. In the Mayan population, education was associated with early reproduction, more lifetime sex partners, and higher fertility, which was also contrary to the predicted pattern based on a life-history tradeoff approach. Parental resources were associated with earlier reproduction in the Mayan sample, confirming the prediction that restricted resources should delay reproduction.

Effects of diazinon on some population parameters ofMoina Macrocopa (Cladocera)

The effects of the organophosphate insecticide diazinon on selected population parameters of the freshwater cladoceran Moina macrocopa were studied. Survivorship and average longevity were affected by exposure to 1.00 μg L-1 or higher concentrations. Exposure to diazinon had no effect on the time of first reproduction, but animals did not reproduce in 10.00 μg L-1 and the number of offspring produced by a female during her entire life span was reduced in 1.00 μg L-1. The intrinsic rate of population growth and the generation time were not significantly affected by exposure to diazinon.

Genotypic and Plastic Variation in Plant Size: Effects on Fecundity and Allocation Patterns in Lychnis Flos-Cuculi Along a Gradient of Natural Soil Fertility

1 Genotypic and plastic variation in plant size, and trade-offs among components of reproduction were studied using cloned individuals from 24 parental plants of the perennial hay-meadow species Lychnis-flos-cuculi, planted in four sites along a gradient of natural soil fertility. 2 Plant biomass, survival and fecundity differed significantly among clones and sites. Differences in survival and early components of fecundity among clones were strongly average rosette biomass attained during the first year. 3 There were significant clone-site interactions. However, a small number of clones which ranked high for plant biomass and fruit production at all sites, made a large contribution to local fruit production within a year across the entire gradient. 4 Patterns of biomass allocation and timing of first reproduction differed significantly among clones. A large part of this variation could be explained by clonal differences in average plant biomass attained during the first year. We conclude therefore that clonal variation in allocation patterns reflected differences in resource acquisition, rather than differences in partitioning strategies underlying life-history evolution. 5 Consequences of delaying first reproduction varied among sites. Precocity was favoured in the least productive site, whereas at intermediate soil fertility individuals that postponed reproduction gained a three-fold increase in fecundity at first reproduction, with no significant reduction in survival to this stage. Optimal timing of reproduction may thus vary at a small scale. 6 Genetically based trade-offs between only observed in the less productive sites. Costs of reproduction were also only apparent at such sites, supporting the idea that the expression of trade-offs and costs is most likely under low resource conditions. 7 In the more productive sites, within- and among-clone correlations between etative and generative reproduction, and among five components of fecundity were generally insignificant or positive. This available, differences in both microsite quality and resource a governed patterns of covariance. 8 Fruit predation by caterpillars of the noctuid Hadena bicruris was dependant on plant size. In the site with lowest individual fecundity, conferring a relative advantage to smaller sized individuals. [KEYWORDS: Allocation trade-offs; fecundity components; hadena bicruris; phenotypic plasticity; size hierarchies Reproductive characteristics; seedling performance; impatiens-capensis; viola-sororia; lanceolata l; selection; population;environment; yield; variability]

Specificity of predator-induced neck spine and alteration in life history traits in Daphnia pulex

It has been proposed that the predator-induced defensive neck spine in Daphnia pulex has a demographic cost. Our results show that this cost is not merely an allocation cost related to the formation and maintenance of the neck spine. In a life table experiment, we tested whether spine induction and life history traits in D. pulex are affected by different invertebrate predators: first and third instar Chaoborus, fourth instar Mochlonyx and two size classes of Notonecta and Dytiscus larvae. D. pulex showed sensitivity to the different predators. Predator-exposure affected one or more of the following life history traits of D. pulex: the timing of first reproduction, clutch size, and growth. In some cases, exposure to predators altered life history traits when neck spine induction did not occur. These shifts in life history traits occurring in the absence of spine induction may be caused by behavioral or physiological changes triggered by the predators.

Morphotypic Differentiation in the South-Western Australian Restiad Lyginia barbata R.Br (Restionaceae)

Study of Lyginia barbata across its distribution range in south-western Australia identified five distinctive morphotypes, viz. a tall-culmed, densely tufted fire-sensitive obligate seeder (S morphotype), a tall densely tufted fire-resistant resprouter (R1), a short flexuose-culmed, tufted resprouter (R2), a weakly clonal, semi-tufted resprouter (R3) and a short-culmed, widely spreading clonal form (R4). There was little variation within a morphotype between habitat locations and no evidence of intergrading of cohabiting morphotypes. Morphotype-specific differences were observed in culm height, rhizome morphology, culm density and spikelet morphology. Differences in reproductive biology related to the time of first reproduction in juvenile recruits, spikelet number per male and female culm, ovule number per female culm and seed : ovule ratio. Differences of a physiological nature were observed in seedling growth rates and proportional biomass (dry matter) allocations to culms, rhizomes, spikelets and seeds. Comparative quantitative scorings of the above features according to concepts of r- and K-selection rated the S form strongly r-selected, the R4 form equally strongly K-selected and the other forms (R1, R2 and R3) intermediate and with the R1 form possibly more r-selected than the others. It is suggested that the data provide a basis on which future taxonomic decisions regarding the taxon might be made.