Insights into the costs of complex maternal care behavior in the burrower bug (Sehirus cinctus)

The evolution of life history characters, including parental care behaviors, depends on costs and benefits. When offspring can influence parental behaviors, parent-offspring conflict over parental care can occur, but only if these parental behaviors are costly. Mother burrower bugs (Sehirus cinctus) exhibit extended and complex care of offspring. Mothers guard eggs until hatching and then attend and provision offspring for approximately 2 weeks after hatching. Using four experimental treatments, we attempted to identify the costs associated with specific components of these behaviors. Under laboratory conditions, egg guarding increases inter-clutch interval, but provisioning does not appear to be very costly. We discuss additional ecological factors that may be important in mediating provisioning costs under natural conditions. Through analysis of individual maternal performance, we find no evidence for trade-offs between successive clutches. These data suggest that variation in overall condition may obscure variation in allocation strategies.Communicated by F. Trillmich     

Food abundance and parental care in yellow warblers (Dendroica petechia)

Emlen and Oring (1977) suggested that monogamy in birds is maintained because of the need for strict biparental care. A corollary of their suggestion is that paternal care should decrease under conditions of high food abundance. An alternative is that paternal care would increase if males take advantage of the higher food abundance by trying to reduce the length of the nestling feeding period. We tested these two ideas using yellow warblers (Dendroica petechia) by providing some pairs with supplemental food, thereby reducing the importance of biparental care. However, the extra food did not decrease paternal effort, nor did it increase it (Fig. 2). Early in the nestling period experimental females brooded more but visited their nestlings less than did control females, but later, when brooding times decreased, experimental females fed their nestlings more than did control females (Fig. 3). There were no significant differences in nestling survival (Fig. 5), but nestlings in the control treatment were larger and heavier up to 6 days old (Fig. 6). The main effect of supplemental food was on maternal, not paternal behaviour. Models of biparental care assume interdependence between the parental effort of both parents. In this species, however, males and females provide for their brood independently from each other.     

Reproductive effort in relation to maternal social rank in reindeer (<Emphasis Type="Italic">Rangifer tarandus</Emphasis>)

In polygynous mammals, high-quality females may increase their fitness by providing superior care to their offspring. Based on the agonistic interactions of female reindeer in an experimental herd during two consecutive years (1997 and 1998), we tested whether maternal social rank influenced: (1) winter body-mass change of females, (2) preparturition reproductive effort (measured as fecundity, the birth mass and the birth date of their calves), (3) preweaning maternal effort (measured as calves preweaning mortality, early preweaning and late preweaning growth rate and September body mass of calves), and (4) postweaning maternal effort (measured as calves body-mass change during their first winter). In the models, we included September females body mass as a covariate to separate the effects of maternal rank and body mass. We also tested whether the effect of social rank on maternal efforts was dependent on offspring sex. High-ranked females gained body mass whereas low-ranked females lost weight during the winter. Fecundity was higher and date of birth was earlier in high-ranked females than in subordinates, whereas no effect of females rank on birth mass of calves was found. Early preweaning growth rate and September body mass of calves increased with increasing females social rank, whereas late preweaning daily growth rate of calves was not influenced by females rank. Calves preweaning mortality was only influenced by year, which also explained most of the variance in the winter body-mass change of calves. The effects of females rank on the reproductive-efforts parameters studied were not specific to offspring sex. These findings suggest that females rank influences reproductive effort during the preparturition, as well as the preweaning, period, the effect being sex independent.Communicated by R. Gibson     

Common goldeneyes adjust maternal effort in relation to prior brood success and not current brood size

Parental investment theory predicts that parental effort should be related to the reproductive value of the current brood. This depends on both the number of young and the survival prospects of each of them. Thus parents may provide more care to larger broods either because of (1) the direct effect of brood size per se on reproductive value (the “brood size” hypothesis) or because (2) past mortality, reflected in current brood size, predicts future mortality of the brood and hence its reproductive value (the “brood success” hypothesis). Earlier studies have not attempted to distinguish between these alternatives. We tested the hypotheses in the precocial, nidifugous common goldeneye Bucephala clangula, a species with uniparental female care. Maternal effort was measured as the time spent by the female in rearing the brood. We found that brood size itself is not associated with maternal effort, but that females modify their maternal effort according to the mortality already experienced by the brood, supporting the prediction of the brood success hypothesis. We also found that brood mortality varied considerably between broods and that previous mortality predicts future mortality within broods, basic assumptions of the brood success hypothesis. Received: 30 January 1996 / Accepted after revision: 27 October 1996     

Effects of prenatal yolk androgens on armaments and ornaments of the ring-necked pheasant

Mothers may profoundly affect offspring phenotype and performance by adjusting egg components, including steroid hormones. We studied the effects of elevated prenatal testosterone (T) exposure in the ring-necked pheasant on the expression of a suite of male and female traits, including perinatal response to stress, immune response, growth, and secondary sexual traits. Prenatal T levels were increased by injecting the yolk of unincubated eggs with physiological doses of the hormone. Yolk T injection resulted in a reduced length of male tarsal spurs, a trait which positively predicts male success in intra- and intersexual selection and viability, whereas no direct effect on male wattle characteristics or plumage traits of either sex was observed. Female spur length was also negatively affected by T, but to a lesser extent than in males. In addition, the covariation between male secondary sexual traits, which are reliable quality indicators, differed between T and control males, suggesting that the manipulation may have altered the assessment of overall male quality by other males and females. In conclusion, the negative effects of elevated yolk T on spur length, a trait which positively predicts male fitness, coupled with the lack of effects on growth or other traits in both sexes, provided limited evidence for mothers being subjected to a trade-off between positive and negative consequences of yolk T deposition on offspring traits and suggest that directional selection for reduced yolk T levels may occur in the ring-necked pheasant.     

Demonstration of spontaneously dividing male fetal cells in maternal blood by negative magnetic cell sorting and fish

We investigated a case of massive feto-maternal bleeding by using negative magnetic cell sorting (MACS) and fluorescent in situ hybridization (FISH). A 37-year-old pregnant woman had an uncomplicated amniocentesis for advanced maternal age at 16 weeks' gestation. The fetal karyotype was 46, XY. At 19 weeks' gestation, she had a minor car accident and slight vaginal bleeding. A subsequent Kleihauer-Betke test showed a 140 ml feto-maternal haemorrhage. Serial sonographic examinations indicated a normal fetus and placenta. We performed FISH analysis on maternal peripheral blood at 25 weeks. Anti-CD45 and MACS were used to deplete maternal leucocytes, enriching the proportion of fetal nucleated erythrocytes present. The isolated cells were analysed by using dual-colour FISH with X and Y specific probes. Approximately 65 800 nucleated cells were obtained after MACS depletion. A total of 234 cells were analysed by FISH. The results revealed that 70 of the nucleated cells (30 per cent) were male with one X and one Y signal. Among these cells, six male metaphases were observed in spontaneously dividing cells.     

Amniotic fluid-AFP in Down syndrome and other chromosome abnormalities

80·2 Per cent of 111 Down syndrome pregnancies had amniotic fluid (AF) alpha fetoprotein (AFP) levels on or below the median and 10·8 per cent at or below 0·5 MoM compared with 41·9 and 1·4 per cent of controls. These differences were even more striking when the gestational age was < 18 weeks compared with ⩾ 18 weeks. No such association was seen for other chromosome abnormalities including trisomy 18,45,X and mosaics, 47,XXY, 47,XXX, and other structural abnormalities and triploidy, even when high levels due to defects such as omphalocele and cystic hygroma were excluded. All cases of trisomy 13 and 80 per cent with 47,XYY had AF-AFP levels above the median. Selection of cases for karyotyping by a low level of AF-AFP would clearly fail to detect aneuploidies other than Down syndrome and is not recommended. A possible weak association between low maternal serum (MS) and AF-AFPs in Down syndrome was most evident at < 18 weeks, suggesting that MS screening between 16 and 18 weeks may be the most informative time.     

Transabdominal chorionic villus sampling in the second trimester of pregnancy: Feto-maternal transfusions in relation to pregnancy outcome

Volumes of feto-maternal transfusions (FMTs) in transabdominal chorionic villus sampling (TACVS) in the second trimester of pregnancy were calculated from the difference between maternal alpha-fetoprotein (AFP) concentrations before and 1 h after TACVS. In 50 pregnancies, there existed no correlation between FMT volume and the amount of villi collected or the number of TACVS attempts. The expected risk of fetal exsanguination due to very voluminous FMT could not be substantiated. In one case, immunization could have been the cause of hydrops fetalis, although only a volume of 0.15 ml could be calculated.     

Fetal erythroblasts from maternal blood identified with 2,3-bisphosphoglycerate (BPG) and in situ hybridization (ISH) using Y-specific probes

Different types of fetal nucleated cells can be found in maternal blood, providing the possibility of non-invasive prenatal diagnosis. For this purpose, we have studied fetal erythroblasts. We discovered that haemoglobin-containing cells treated with 2,3-bisphosphoglycerate (BPG) can be visualized by a peroxidase reaction, which at the same time visualizes an in situ hybridization (ISH) signal, specific for the X, Y or 21 chromosome. In order to prove that the BPG-positive cells were erythroid, an anti-glycophorin A (GPA) antiserum combined with a staphylococcal rosette technique was used. To enrich for erythroblasts, leukocytes were depleted from maternal blood by treatment with anti-CD45 monoclonal antibody and passage over an anti-mouse IgG-coated glass bead column. To evaluate the potential of the method for clinical use, we studied maternal blood samples from 18 women referred to us for prenatal diagnosis between 6 and 19 weeks of gestation. Erythroblasts were found in 13 out of 14 normal pregnancies. Erythroblasts with a Y-signal were found as early as 9 weeks of gestation, but at 6 weeks the Y-signal was seen in BPG-negative cells only. These cells showed an epithelioid morphology indicating that they were cytotrophoblasts. The BPG-ISH method provides a simple technique for identifying erythroblasts and simultaneously visualizing a desired probe.     

Cardiac blood flow studies in fetuses with haemoglobin bart's disease

Blood flow across the atrioventricular valves and outflow tracts was measured in 55 normal fetuses and 32 fetuses with haemoglobin (Hb) Bart's disease between 18 and 26 weeks of gestation. The mean velocities remained unchanged in both normal and affected fetuses over the gestations studied. The volume flow across both atrioventricular valves and outflow tracts increased as the gestation advanced in both normal and affected fetuses, but was significantly higher in affected than in normal fetuses. The same magnitude of increased flow was found in both hydropic and non-hydropic fetuses with Hb Bart's disease. These findings suggest that fetuses with severe and long-standing anaemia have a remarkable cardiac compensatory mechanism for the maintenance of tissue oxygenation. In response to anaemia and circulatory loading, the cardiac chambers and outflow tracts enlarge proportionately up to twice the normal values. Because of this response and the operation of the Frank-Starling mechanism, the heart is able to maintain a normal mean velocity of propulsion and the net output is increased to two to three times that in normal fetuses. Hydropic changes in these anaemic fetuses appear unrelated to cardiac failure as cardiac failure is not observed at the time that hydropic changes develop.