When the going gets rough: effect of maternal size manipulation on larval quality

Variation in larval size has been shown to be an important factor for the post-metamorphic performance of marine invertebrates but, despite its importance, few sources of this variation have been identified. For a range of taxa, offspring size is positively correlated with maternal size but the reasons for this correlation remain unclear. We halved the size of colonies in the bryozoan Bugula neritina 1 wk prior to reproduction (but during embryogenesis) to determine if larval size is a fixed or plastic trait. We manipulated colonies in such a way that the ratio of feeding zooids to reproductive zooids was constant between treatment and control colonies. We found that manipulating colony size strongly affects larval size; halved colonies produced larvae that were similar to13% smaller than those produced by intact colonies. We entered these data into a simple model based on previous work to estimate the likely post-metamorphic consequences of this reduction in larval size. The model predicted that larvae that came from manipulated colonies would suffer similar to300% higher post-metamorphic mortality and similar to50% lower fecundity as adults. Colonies that are faced with a stress appear to be trading off current offspring fitness to maximize their own long-term fitness and this may explain previous observations of compensatory growth in colonial organisms. This study demonstrates that larval size is a surprisingly dynamic trait and strong links exist between the maternal phenotype and the fitness of the offspring. The performance of settling larvae may be determined not only by their larval experience but also by the experience of their mothers.

Induction and transmission of Bacillus thuringiensis tolerance in the flour moth Ephestia kuehniella

The use of Bacillus thuringiensis (Bt) endotoxins to control insect vectors of human diseases and agricultural pests is threatened by the possible evolution of resistance in major pest species. In addition to high levels of resistance produced by receptor insensitivity (5, 16, 17), several cases of tolerance to low to medium levels of toxin have been reported in laboratory colonies of lepidopteran species (3, 18). Because the molecular basis of some of these cases of tolerance to the toxin are not known, we explored alternative mechanisms. Here, we present evidence that tolerance to a Bt formulation in a laboratory colony of the flour moth Ephestia kuehniella can be induced by preexposure to a low concentration of the Bt formulation and that the tolerance correlates with an elevated immune response. The data also indicate that both immune induction and Bt tolerance can be transmitted to offspring by a maternal effect and that their magnitudes are determined by more than one gene.

Offspring size affects the post-metamorphic performance of a colonial marine invertebrate

The positive relationship between offspring size and offspring fitness is a fundamental assumption of life-history theory, but it has received relatively little attention in the marine environment. This is surprising given that substantial intraspecific variation in offspring size is common in marine organisms and there are clear links between larval experience and adult performance. The metamorphosis of most marine invertebrates does not represent a newbeginning, and larval experiences can have effects that carry over to juvenile survival and growth. We show that larval size can have equally important carryover effects in a colonial marine invertebrate. In the bryozoan Bugula neritina, the size of the non-feeding larvae has a prolonged effect on colony performance after metamorphosis. Colonies that came from larger larvae survived better, grew faster, and reproduced sooner or produced more embryos than colonies that came from smaller larvae. These effects crossed generations, with colonies from larger larvae themselves producing larger larvae. These effects were found in two populations (in Australia and in the United States) in contrasting habitats.

Offspring size effects in the marine environment: A field test for a colonial invertebrate

A central tenet of life-history theory is the presence of a trade-off between the size and number of offspring that a female can produce for a given clutch. A crucial assumption of this trade-off is that larger offspring perform better than smaller offspring. Despite the importance of this assumption empirical, field-based tests are rare, especially for marine organisms. We tested this assumption for the marine invertebrate, Diplosoma listerianum, a colonial ascidian that commonly occurs in temperate marine communities. Colonies that came from larger larvae had larger feeding structures than colonies that came from smaller larvae. Colonies that came from larger larvae also had higher survival and growth after 2 weeks in the field than colonies that came from smaller larvae. However, after 3 weeks in the field the colonies began to fragment and we could not detect an effect of larval size. We suggest that offspring size can have strong effects on the initial recruitment of D. listerianum but because of the tendency of this species to fragment, offspring size effects are less persistent in this species than in others.

The Galilean turn in population ecology

The standard mathematical models in population ecology assume that a population's growth rate is a function of its environment. In this paper we investigate an alternative proposal according to which the rate of change of the growth rate is a function of the environment and of environmental change. We focus on the philosophical issues involved in such a fundamental shift in theoretical assumptions, as well as on the explanations the two theories offer for some of the key data such as cyclic populations. We also discuss the relationship between this move in population ecology and a similar move from first-order to second-order differential equations championed by Galileo and Newton in celestial mechanics.

Mechanisms of inducible resistance against Bacillus thuringiensis endotoxins in invertebrates

Abstract Resistance in insect pests against the endotoxin of Bacillus thuringiensis (Berliner) (Bt) is a major threat to the usefulness of this biopesticide, both used as traditional formulations and in transgenic crops. A crucial requirement for the development of successful resistance management strategies is a molecular understanding of the nature and inheritance of resistance mechanisms. This information can be used to design management strategies that will delay or counteract Bt resistance. The best known Bt resistance mechanism is inactivation of brush border membrane receptors. This type of resistance has a largely recessive mode of inheritance, which has enabled the design of resistance management approaches involving high dose and refuge strategies. Recent observations suggest that other resistance mechanisms are possible, including a mechanism that sequesters the toxin in the gut lumen through inducible immune reactions. The elevated immune status associated with tolerance to the toxin can be transmitted to subsequent generations by a maternal effect, which has implications for resistance management in the field. The high dose/refuge strategy may not be appropriate for the management of these alternative resistance mechanisms and other strategies have to be developed if inducible dominant resistance or tolerance mechanisms occur frequently in the field.

Effect of maternal epidural analgesia on fetal intrapartum oxygen saturation

The use of maternal epidural analgesia in labor may be associated with nonreassuring fetal heart rate (FHR) patterns. Fetal oxygen saturation (FSpO(2)) monitoring may improve assessment of fetal well-being during this time. Mean FSpO(2) values were compared over seven 5-minute epochs: 5 minutes prior to an epidural event (combined insertion of epidural/top-up epidural analgesia and infusion pump bolus), to 30 minutes following the event, including possible effects of maternal position and FHR pattern on FSpO(2) values. Mean FSpO(2) values were significantly different between the 5 minutes prior (49.5%) versus 16-20 minutes (44.3%, p

Treatment of maternal syphilis in rural South Africa: effect of multiple doses of benzathine penicillin on pregnancy loss

OBJECTIVES Despite few data, the treatment of syphilis in pregnant women using a single dose of benzathine penicillin is the standard of care in many resource-poor settings. We examined the effect of various doses of benzathine penicillin on pregnancy loss among women with a positive Rapid Plasma Reagin (RPR) test result in a rural South African district. METHODS All pregnant women making their first antenatal care visit during pregnancy were screened for syphilis using the RPR test. Those testing positive were counselled to receive three weekly doses of benzathine penicillin, and received a partner notification card. Pregnancy outcomes were determined from facility records or home visits where necessary. RESULTS Of 8917 women screened, 1043 (12%) had reactive syphilis serology; of those with titre data available, 30% had titres of 1:8 or greater. While 41% (n = 430) of women received all three doses as counselled, 30% (n = 312) received only one dose, and 20% (n = 207) did not return to the clinic to receive treatment. Among the 947 women with pregnancy outcome data available, there were 17 miscarriages and 48 perinatal deaths observed. There was a strong trend towards reduced risk of pregnancy loss among women receiving multiple doses of penicillin (adjusted OR for perinatal mortality for each additional dose received, 0.63; 95% CI, 0.48-0.84). CONCLUSIONS While this association requires further investigation, these results suggest that there may be substantial benefit to providing multiple doses of benzathine penicillin to treat maternal syphilis in this setting.

Effect after introducing Bacillus thuringiensis gene on nitrogen metabolism in cotton

Bacillus thuringiensis (Bt) transgenic cotton has shown changes of vegetative and reproductive growth characteristics. The objective of this study was to investigate the physiological change of nitrogen metabolism that related closely to the growth in Bt cotton cultivars. The study Was undertaken on two 131 transgenic cotton cultivars and their parents, one conventional (Xingyang822) and recurrent parent (Sumian No. 9), the other a hybrid (Kumian No. 1) and female parent (Yumian No. 1), during the 2001 and 2002 growing seasons at the Yangzhou University Farm, Yangzhou, China. In the 2001 study, The results indicated that the Bt cotton cultivars were higher than their parents in leaf total nitrogen, free amino acid and soluble protein content, greater in NR and GPT activity, and lower in protease activity, during peak square and boll developing period. The biggest increase of total nitrogen was at peak boll period, which increased by 36.01 and 18.96% for Kumian No. I and Xingyang822, respectively. There were similar results for free amino acid and soluble protein content. The results showed further in 2002 study that NR activity increased dramatically at peak square and early boll open period, the biggest increase at early boll open period, with Kumian No. I and Xingyan,822 being 87.5 and 61.4% higher than their parent, respectively, the biggest increase of GPT activity was at peak boll period, with Kumian No. I and Xingyang822 being 39.1 and 29.1% higher than their parent, respectively. However, protease activity of Bt cultivars reduced significantly before flowering and early boll open period, the biggest decrease was before flowering period, with Kumian No. I being more than 30%, Xingyang822 being 26.5% at peak square period. Moreover, the boll total nitrogen content reduced sharply. The results suggest that the Bt cotton cultivars have higher intensity of leaf nitrogen metabolism than their parent, especially during square and boll development period. It is disadvantage for square development and earlier boll maturity under high nitrogen condition. The cultural practice should aim at reducing leaf nitrogen metabolic strength and keep the balance of vegetative and reproductive growth. (C) 2003 Elsevier B.V. All rights reserved.

Using molecular markers to assess the effect of introgression on quantitative attributes of common bean in the Andean gene pool

Progress in bean breeding programs requires the exploitation of genetic variation that is present among races or through introgression across gene pools of Phaseolus vulgaris L. Of the two major common bean gene pools, the Andean gene pool seems to have a narrow genetic base, with about 10% of the accessions in the CIAT core collection presenting evidence of introgression. The objective of this study was to quantify the degree of spontaneous introgression in a sample of common bean landraces from the Andean gene pool. The effects of introgression on morphological, economic and nutritional attributes were also investigated. Homogeneity analysis was performed on molecular marker data from 426 Andean-type accessions from the primary centres of origin of the CIAT common bean core collection and two check varieties. Quantitative attribute diversity for 15 traits was studied based on the groups found from the cluster analysis of marker prevalence indices computed for each accession. The two-group summary consisted of one group of 58 accessions (14%) with low prevalence indices and another group of 370 accessions (86%) with high prevalence indices. The smaller group occupied the outlying area of points displayed from homogeneity analysis, yet their geographic origin was widely distributed over the Andean region. This group was regarded as introgressed, since its accessions displayed traits that are associated with the Middle American gene pool: high resistance to Andean disease isolates but low resistance to Middle American disease isolates, low seed weight and high scores for all nutrient elements. Genotypes generated by spontaneous introgression can be helpful for breeders to overcome the difficulties in transferring traits between gene pools.

Correlating gene expression with larval competence and the effect of age and parentage on metamorphosis in the tropical abalone Haliotis asinina

The non-geniculate crustose coralline alga (CCA) Mastophora pacifica can induce the metamorphosis of competent Haliotis asinina (Vetigastropoda) larvae. The ability to respond to this natural cue varies considerably with larval age, with a higher proportion of older larvae (e.g. 90 h) able to metamorphose in response to M. pacifica than younger larvae (e.g. 66 h). Here we document the variation in time to acquisition of competence within a larval age class. For example, after 18 h of exposure to M. pacifica, approximately 15 and 36% of 84 and 90-h-old H. asinina larvae had initiated metamorphosis, respectively. This age-dependent response to M. pacifica is also observed when different aged larvae are exposed to CCA for varying periods. A higher proportion of older larvae require shorter periods of exposure to CCA than younger larvae in order to initiate metamorphosis. In this experiment, as in the previous, a small proportion of young larvae were able to respond to brief periods of CCA exposure, suggesting that they had developed the same state of competency as the majority of their older counterparts. Comparisons of the proportions of larvae undergoing metamorphosis between families reveals that parentage also has a significant (P < 0.05) affect on whether an individual will initiate metamorphosis at a given age. These familial differences are more pronounced when younger, largely pre-competent larvae (i.e. 66 h old) are exposed to M. pacifica, with proportions of larvae undergoing metamorphosis differing by as much as 10 fold between families. As these data suggest that variation in the rate of development of the competent state has a genetic basis, and as a first step towards identifying the molecular basis to this variation, we have identified numerous genes that are differentially expressed later in larval development using a differential display approach. Spatial expression analysis of these genes suggests that they may be directly involved in the acquisition of competence, or may play a functional role in the postlarva following metamorphosis.

The effect of larval age on morphology and gene expression during ascidian metamorphosis

Metamorphosis is both an ecological and a developmental genetic transition that an organism undergoes as a normal part of ontogeny. Many organisms have the ability to delay metamorphosis when conditions are unsuitable. This strategy carries obvious benefits, but may also result in severe consequences for older larvae that run low on energy. In the marine environment, some lecithotrophic larvae that have prolonged periods in the plankton may begin forming postlarval and juvenile structures that normally do not appear until after settlement and the initiation of metamorphosis. This precocious activation of the postlarval developmental program may reflect an adaptation to increase the survival of older, energy-depleted larvae by allowing them to metamorphose more quickly. In the present study, we investigate morphological and genetic consequences of delay of metamorphosis in larvae of Herdmania momus (a solitary stolidobranch ascidian). We observe significant morphological and genetic changes during prolonged larval life, with older larvae displaying significant changes in RNA levels, precocious migration of mesenchyme cells, and changes in larval shape including shortening of the tail. While these observations suggest that the older H. momus larvae are functionally different from younger larvae and possibly becoming more predisposed to undergo metamorphosis, we did not find any significant differences in gene expression levels between postlarvae arising from larvae that metamorphosed as soon as they were competent and postlarvae developing from larvae that postponed metamorphosis. This recalibration, or convergence, of transcript levels in the early postlarva suggests that changes that occur during prolonged larval life of H. momus are not necessarily associated with early activation of adult organ differentiation. Instead, it suggests that an autonomous developmental program is activated in H. momus upon the induction of metamorphosis regardless of the history of the larva.