Ecological speciation in anemone-associated snapping shrimps (Alpheus armatus species complex).

Divergent natural selection driven by competition for limited resources can promote speciation, even in the presence of gene flow. Reproductive isolation is more likely to result from divergent selection when the partitioned resource is closely linked to mating. Obligate symbiosis and host fidelity (mating on or near the host) can provide this link, creating ideal conditions for speciation in the absence of physical barriers to dispersal. Symbiotic organisms often experience competition for hosts, and host fidelity ensures that divergent selection for a specific host or host habitat can lead to speciation and strengthen pre-existing reproductive barriers. Here, we present evidence that diversification of a sympatric species complex occurred despite the potential for gene flow and that partitioning of host resources (both by species and by host habitat) has contributed to this diversification. Four species of snapping shrimps (Alpheus armatus, A. immaculatus, A. polystictus and A. roquensis) are distributed mainly sympatrically in the Caribbean, while the fifth species (A. rudolphi) is restricted to Brazil. All five species are obligate commensals of sea anemones with a high degree of fidelity and ecological specificity for host species and habitat. We analysed sequence data from 10 nuclear genes and the mitochondrial COI gene in 11-16 individuals from each of the Caribbean taxa and from the only available specimen of the Brazilian taxon. Phylogenetic analyses support morphology-based species assignments and a well-supported Caribbean clade. The Brazilian A. rudolphi is recovered as an outgroup to the Caribbean taxa. Isolation-migration coalescent analysis provides evidence for historical gene flow among sympatric sister species. Our data suggest that both selection for a novel host and selection for host microhabitat may have promoted diversification of this complex despite gene flow.

Maternal obesity and body composition of the neonate.

Obese women generally deliver heavier infants, but the body composition of these infants is unknown. The principal objective of this study was to determine if neonates of obese women have more adipose tissue. At 35-36 weeks of gestation, a fasting blood sample was collected from 37 pregnant women. Shortly after birth, the body fat of the neonates was measured with an infant total-body electrical conductivity (TOBEC) instrument using a prediction equation derived from 10 miniature pigs. At 6 weeks post partum, the infant body fat was measured a second time, and the body fat of each mother was measured using an adult TOBEC instrument. We found no differences between the obese (n = 16) and lean subjects (n = 21) in the concentrations of glycerol, beta-hydroxybutyrate, triglyceride, total cholesterol, high-density lipoprotein cholesterol, or glucose in the blood. However, the insulin concentration was elevated in the obese women (199 +/- 57 pmol/l) as compared with the lean women (128 +/- 68 pmol/l, p < 0.01). At birth, maternal adiposity (% body fat) was significantly associated with infant adiposity (r = 0.37, p < 0.05). However, by 6 weeks post partum the association no longer existed. Multiple regression analysis showed that maternal adiposity, fasting glucose level, and gestational age are independently associated at birth with infant adiposity.

Hypertriglyceridemia during late pregnancy is associated with the formation of small dense low-density lipoproteins and the presence of large buoyant high-density lipoproteins.

Late pregnancy is a unique metabolic state where there are transient increases in the concentrations of plasma triglyceride (TG), cholesterol, and apolipoprotein (apo) B. Despite the hypertriglyceridemic environment, we recently reported that there is an unusual shift in high-density lipoprotein (HDL) subclass distribution from smaller HDL subclasses to the largest, most buoyant HDL2b subclass. In the present investigation, we determined whether the subclasses of low-density lipoprotein (LDL) also change during this transient hyperlipidemic state and whether such changes were associated with plasma TG and apolipoprotein concentrations. Thirty-six Hispanic subjects at 35 to 36 weeks' gestation and at 6 weeks' postpartum were studied. At 35 to 36 weeks of gestation, plasma concentrations of TG, cholesterol, and apo B were increased (218 +/- 62, 234 +/- 48, and 130 +/- 35 mg/dL, respectively) over levels at 6 weeks' postpartum (112 +/- 69, 197 +/- 36, and 97 +/- 25 mg/dL respectively). However, lipoprotein(a) [Lp(a)] concentrations were not changed during pregnancy compared with postpartum. LDL subclass patterns (A, B, or I) were determined by nondenaturing polyacrylamide gradient gel electrophoresis in our group of 36 pregnant women. During late pregnancy, 97% of subjects were categorized as LDL subclass patterns B or I, indicating that small, dense LDL particles predominated. This predominance of small, dense LDL was associated with plasma TG concentration, where there was a significant inverse relationship (r = -.45, P < .01) between the LDL peak particle diameter and plasma TG concentration. In an apparent anomaly, there were significant increases in the concentrations of HDL cholesterol (HDL-C) and HDL2 mass, even though small, dense LDL particles predominated.(ABSTRACT TRUNCATED AT 250 WORDS)

Unusual high-density lipoprotein subclass distribution during late pregnancy.

Plasma lipoprotein distribution during late pregnancy is unusual since high-density lipoprotein (HDL) levels are increased in the presence of hypertriglyceridemia; the latter is usually associated with decreases in HDL levels. To determine whether there is a relationship between late-pregnancy lipid levels and specific HDL subclasses, HDL size distribution was determined by nondenaturing gradient gel electrophoresis (GGE) in a group of 36 women at 35 to 36 weeks of gestation and again at 6 weeks' postpartum, and in a group of 10 nonpregnant women. At 35 to 36 weeks of gestation, plasma triglyceride (TG) and cholesterol concentrations were significantly increased over postpartum levels (218 +/- 62 v 112 +/- 69 mg/dL and 234 +/- 48 v 197 +/- 36 mg/dL, respectively). During late pregnancy, apolipoprotein A-I (apo A-I) and HDL cholesterol concentrations were also increased relative to postpartum levels (211 +/- 42 v 168 +/- 20 mg/dL and 63 +/- 13 v 53 +/- 11 mg/dL, respectively). GGE analysis indicated that at 35 to 36 weeks of gestation, 86% of the subjects had a substantial increase of the most buoyant and largest of the HDL species, HDL2b; postpartum and nonpregnant HDL subclass distribution was characterized by the predominance of HDL3a, which are smaller, more dense HDL. The shift in the HDL subclass distribution during late pregnancy was associated with significant positive correlations between HDL2b and apo A-I (r = .50, P < .05) and HDL cholesterol (r = .60, P < .001). There were significant elevations in the concentrations of cholesteryl ester transfer protein (CETP) and estrogen during late pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)