Egg mimicry and allopaternal care: two mate-attracting tactics by which nesting striped darter (Etheostoma virgatum) males enhance reproductive success

In a variety of fish species with paternal care of offspring, females prefer to spawn in nests that already contain eggs. This female preference has been hypothesized to explain egg thievery in male sticklebacks, allopaternal care of eggs in minnows, and the evolution of egg-mimicking body features in male cichlids and darters. Here we employ microsatellite-based parentage analyses to evaluate the reproductive success of striped darter (Etheostoma virgatum) males that appear to utilize two of these functionally related tactics to entice females to spawn in their nests. In an isolated population (Clear Creek, Ky.), we observed that breeding males develop conspicuous white spots on their pectoral fins. If these spots are egg mimics, as we suspect, then this represents the fourth independent evolutionary origin of egg mimicry documented to date in darters, the first based on pigmentation (as opposed to physical structures), and the first in which the egg mimics vary greatly in number among males. From direct counts of microsatellite genotypes in clutches of embryos, at least 3.8 females contributed to the progeny within a typical nest, and females tended to spawn preferentially with males that were larger and displayed more egg-mimic spots. In another population (Hurricane Creek, Tenn.) without egg mimics, the multi-locus genetic data document that allopaternal care is common, especially among the smallest males who sometimes tend nests containing their own as well as an earlier sire's offspring. Thus, these foster males had adopted egg-containing nests and then successfully spawned with subsequent females. Overall, the genetic data on paternity and maternity, in conjunction with field observations, suggest that egg mimicry and allopaternal care are two mate-attracting reproductive tactics employed by striped darter males to exploit female preferences for spawning in nests with 'eggs'. Electronic Publication     

Down syndrome maternal serum marker screening after 18 weeks' gestation

Women having access to prenatal care late in pregnancy may still wish to benefit from maternal serum screening for Down syndrome. Therefore, we established reference values for α-feto protein (AFP) and free β-human chorionic gonadotrophin (β-hCG), and assessed the diagnostic value of maternal serum marker screening at 18–35 weeks' gestation based upon a series of 4072 sera from unaffected pregnancies and 118 sera from pregnant women with fetuses affected by Down syndrome. Using a 1/250 risk cut-off, a detection rate of 72.9% (95% CI = 71.5–74.3%) was achieved with a false-positive rate of 7.51% (95% CI = 6.71–8.3%). This was not significantly different from the percentages observed in our 14–17 weeks routine screening (50 596 patients): 71.9% (95% CI = 71.5–72.3%) and 6.48% (95% CI = 6.28–6.68%), respectively. Detection and screen-positive rates were, respectively, 51.3% (95% CI = 35.6–67.0%) and 5.95% (95% CI = 5.12–6.68%) in women aunder 35 years of age, and 84.8% (95% CI = 76.9–92.7%) and 24% (95% CI = 20.7–27.3%) in women aged 35 years and over. In conclusion, maternal serum marker screening is feasible at 18 weeks' gestation and later, which may be of interest in selected cases. Copyright © 2002 John Wiley & Sons, Ltd.     

Second trimester ultrasound screening for chromosomal abnormalities

The use of prenatal ultrasound has proven efficacious for the prenatal diagnosis of chromosomal abnormalities. The first sonographic sign of Down syndrome, the thickened nuchal fold, was first described in 1985. Since that time, multiple sonographically-identified markers have been described as associated with Down syndrome. The genetic sonogram, involving a detailed search for sonographic signs of aneuploidy, can be used to both identify fetuses at high risk for aneuploidy and, when normal, can be used to decrease the risk for aneuploidy for a pregnancy when no sonographic markers are identified. Combining the genetic sonogram with maternal serum screening may be the best method of assessing aneuploidy risk for women who desire such an assessment in the second trimester. Trisomy 18, Trisomy 13, and triploidy are typically associated with sonographically identified abnormalities and have a high prenatal detection rate. The use of the described sonographic signs in low-risk women requires further investigation, however, patients at increased risk for aneuploidy due to advanced maternal age or abnormal serum screening can benefit from a genetic sonogram screening for sonographic signs of aneuploidy to adjust their baseline risk of an affected fetus. Copyright © 2002 John Wiley & Sons, Ltd.     

CA-125 as a maternal serum marker for Down's syndrome in the first and second trimesters

CA-125, alpha-fetoprotein (AFP), and human chorionic gonadotropin (HCG) were determined in maternal serum in the first trimester from 14 women with a Down's syndrome fetus and 61 women with a healthy fetus. In the second trimester, 15 and 60 serum samples were determined from women with a Down's syndrome and a healthy fetus respectively. In both trimesters, maternal serum CA-125 was found to be elevated in Down's syndrome pregnancies compared with controls. Using discrimination functions, our preliminary results indicate that CA-125 is a better marker than AFP and HCG respectively for a Down's syndrome fetus in the first trimester and improves the detection rate in the second trimester.