Although resilient youth provide an important model of successful adaptation to adversity, we know relatively little about the origins of their positive outcomes, particularly the role of biological mechanisms. The current study employed a series of methylome-wide association studies to identify methylomic biomarkers of resilience in a unique sample of 276 twins within 141 families residing in disadvantaged neighborhoods. Results revealed methylome-wide significant differentially methylated probes (DMPs) for social and academic resilience and suggestive DMPs for psychological resilience and resilience across domains. Pathway analyses informed our understanding of the biological underpinnings of significant differentially methylated probes. Monozygotic twin difference analyses were then employed to narrow in on DMPs that were specifically environmental in origin. Our findings suggest that alterations in the DNA methylome may be implicated in youth resilience to neighborhood adversity and that some of the suggestive DMPs may be environmentally engendered. Importantly, our ability to replicate our findings in a well-powered sample was hindered by the scarcity of twin samples with youth exposed to moderate to substantial levels of adversity. Thus, although preliminary, the present study is the first to identify DNA methylation biomarkers of academic and social resilience.

Deficits in executive functioning both run in families and serve as a transdiagnostic risk factor for psychopathology. The present study employed twin modeling to examine parenting as an environmental pathway underlying the intergenerational transmission of executive functioning in an at-risk community sample of children and adolescents (N = 354 pairs, 167 monozygotic). Using structural equation modeling of multi-informant reports of parenting and a multi-method measure of child executive functioning, we found that better parent executive functioning related to less harsh, warmer parenting, which in turn related to better child executive functioning. Second, we assessed the etiology of executive functioning via the nuclear twin family model, finding large non-shared environmental effects (E = .69) and low-to-moderate heritability (A = .22). We did not find evidence of shared environmental effects or passive genotype–environment correlation. Third, a bivariate twin model revealed significant shared environmental overlap between both warm and harsh parenting and child executive functioning (which may indicate either passive genotype–environment correlation or environmental mediation), and non-shared environmental overlap between only harsh parenting and child executive functioning (indicating an effect of harsh parenting separable from genetic confounds). In summary, genetics contribute to the intergenerational transmission of executive functioning, with environmental mechanisms, including harsh parenting, also making unique contributions.

The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural–geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.

Available twin-family data on sex differences in antisocial behavior (ASB) simultaneously suggest that ASB is far more prevalent in males than in females, and that its etiology (i.e. the effects of genes, environments, hormones, culture) does not differ across sex. This duality presents a conundrum: How do we make sense of mean sex differences in ASB if not via differences in genes, environments, hormones, and/or cultures? The current selective review and critique explores possible contributions to these seemingly incompatible sets of findings. We asked whether the presence of sex differences in behavior could be smaller than is typically assumed, or confined to a specific set of behaviors. We also asked whether there might be undetected differences in etiology across sex in twin-family studies. We found little evidence that bias or measurement invariance across sex account for phenotypic sex differences in ASB, but we did identify some key limitations to current twin-family approaches. These included the questionable ability of qualitative sex difference analyses to detect gender norms and prenatal exposure to testosterone, and concerns regarding specific analytic components of quantitative sex difference analyses. We conclude that the male preponderance in ASB is likely to reflect a true sex difference in observed behavior. It was less clear, however, that the genetic and environmental contributions to ASB are indeed identical across sex, as argued by prior twin-family studies. It is our hope that this review will inspire the development of new, genetically-informed methods for studying sex differences in etiology.

Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990–1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.

Corn (Zea mays L.) was grown in EPTC-(S-ethyl dipropylthiocarbamate) and butylate-(S-ethyl diisobutylthiocarbamate) treated soil at 33 and 15% moisture in growth chambers at 30 and 20 C. EPTC (6 and 18 ppm) and butylate (19 and 50 ppm) reduced corn growth more at 30 than at 20 C. The days before emergence of the corn coleoptile were the most critical time for thiocarbamate injury. When plants were grown at 30 C before emergence more injury occurred at 33% soil moisture than at 15% except with butylate at 19 ppm. At 20 C, however, plants grew as tall or taller at 33% soil moisture than at 15% except for butylate at 19 ppm. Addition of R-25788 (N,N-diallyl-2,2-dichloroacetamide) to EPTC and butylate increased by about 10 times the amount of herbicide required to injure corn. With R-25788 the toxicity of these two herbicides was not influenced greatly by either temperature or soil moisture.

The differential response of three selections of johnsongrass (Sorghum halepense (L.) Pers.) to different temperatures and dark periods was studied in two experiments conducted in growth chambers. The three selections of johnsongrass were obtained from locations representing different climates. At 20 C all three selections grew equally with respect to most parameters of growth studied; however, at 35 C the selection from the southern climate produced more total fresh weight than the other two selections. Rhizome production and the number of stems also were greater in the southern selection at 35 C. An 8-hr dark period prevented flowering in all three selections and significantly reduced rhizome production in two selections compared to the 12-hr dark period. Flowering occurred most rapidly in the selection from a northern climate and most slowly in the selection from a southern climate. The results are discussed in relation to the possible plant adaptive changes and the possibility of weed control through dark period interruption.

Leaching of EPTC (S-ethyl dipropylthiocarbamate) plus R-25788 (N,N-diallyl-2,2-dichloroacetamide) through columns of four soils resulted in the separation of R-25788. Separation of R-25788 from EPTC was greater in coarser than in finer textured soils. When soil columns were placed under drying conditions for 6 days after leaching, R-25788 moved upward in the columns faster than EPTC.

Glyphosate [(N-phosphonomethyl) glycine] was evaluated for three years as a foliar herbicide for the control of johnsongrass [Sorghum halepense (L.) Pers.]. In the greenhouse, maximum rhizome kill resulted from foliar applications of glyphosate at 1.12 to 2.24 kg/ha. In several field studies, plowing from 4 to 21 days following glyphosate application had little effect on johnsongrass control; plowing within 0.5 hr following glyphosate application resulted in less control than when plowing was delayed for 12 days. In stage of growth studies, control was better when glyphosate was applied to johnsongrass in the boot to full head stage than earlier when johnsongrass was 45 to 60 cm in height. In ‘York’ soybeans [Glycine max (L.) Merr.], glyphosate at 1.12 to 2.24 kg/ha applied 12 to 14 days prior to plowing and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated prior to planting provided good johnsongrass control. In ‘3369A’ corn (Zea mays L.) directed postemergence applications of glyphosate provided good johnsongrass control but caused extensive crop injury.

Susceptible and resistant ecotypes of Canada thistle (Cirsium arvense L.) were grafted in various combinations of stock and scion to determine if the activity of 3-amino-l,2,4-triazole (amitole) was altered by passage through the plant tissue. It appeared that the differential susceptibilities of ecotypes of Canada thistle were not caused by a change in the activity of amitrole.

Canada thistle (Cirsium arvense L.) plants containing one elongated and one recently emerged shoot from the same root segment were treated with 14C-ring labeled atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Fourteen days after atrazine application to the elongated shoot 98% of the recovered activity remained in this shoot. The distribution pattern of 14C suggested movement with the transpiration stream. Of the 14C in the treated shoot, 82% was in the form of unaltered atrazine at 14 days after application. Greenhouse studies with nonlabeled atrazine indicated that this herbicide had only an indirect effect on portions of the plant located basipetally to the area of application.

The susceptibility of corn (Zea mays L. ‘Pioneer 3334A’) at different stages of growth to EPTC (S-ethyl dipropylthiocarbamate) plus a herbicide-protectant, R-25788 (N,N-diallyl-2,2-dichloroacetamide), was studied in the greenhouse. Corn was treated with either 25 ppm or 12.5 ppm EPTC containing R-25788 at planting and at 2, 4, 6, and 8 weeks thereafter. The herbicide was soil-applied and immediately incorporated by watering. Phytotoxicity and plant height were observed periodically for 56 days after herbicide treatment. Within 21 days after treatment with 25 ppm EPTC containing R-25788, injury and plant height reduction occurred in corn treated at planting, or at 2 and 4 weeks but not at 6 or 8 weeks after planting. At 56 days, however, corn treated at planting or 2 weeks after planting had outgrown all injury symptoms and was as tall as the controls (>84%). Corn treated at 4 weeks after planting, however, still remained injured and was 45% as tall as its respective control. Corn treated at 6 to 8 weeks showed no injury during the entire period of observations. The data indicates that corn is most susceptible to EPTC plus R-25788 at 4 weeks after planting. The results of this greenhouse study are discussed in relation to corn injury as observed in the field.

The influence of several factors on the injury to corn (Zea mays L.) seedlings from high rates of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) was determined in growth chambers. This herbicide combination severely injured 6% of the corn seedlings at rates as low as 14 ppm if the herbicide was poorly incorporated into the soil. If thoroughly incorporated, severe injury did not occur unless the rate of application exceeded 56 ppm. Decreased injury resulted when seed were placed so as to insure rapid shoot emergence. Seed planted at 2 cm with its coleoptile pointed upward or horizontally (with posterior facing upward) was injured less than in other positions, Corn cultivars differ in their susceptibility to EPTC + R-25788 at 30 but not at 20 C. Of the several corn cultivars tested at 30 C, SX-98 was the least injured by EPTC + R-25788. Corn injury was progressively reduced as leaching volumes were increased and as the time from herbicide application to corn planting was increased.

Three selections of johnsongrass (Sorghum halepense (L.) Pers.) were collected from three locations and designated as the N, NS, and S selections, respectively. The selections were studied for growth differences and for a differential response to dalapon (2,2-dichloropropionic acid). The N selection control plants flowered 2 weeks earlier than the other selections. The S selection yielded significantly greater root, rhizome, and total fresh weight than the NS and N selections. The N selection exhibited the most susceptibility to dalapon by producing the shortest plants, the least stem and leaf numbers, and the lowest shoot, root, rhizome, and total fresh weight of the three selections.

Twelve different johnsongrass (Sorghum halepense L.) clones were selected from four different regions of the United States and were grown in the greenhouse. The johnsongrass clones grew differently depending upon the environment from which they were originally obtained, suggesting that geographical ecotypes of johnsongrass exist. The parameter of growth most closely correlated to the latitude from which the plants were obtained was the time required for floral initiation. Plants from a more northern latitude consistently flowered earlier than plants obtained from a more southern latitude. Differences in height, stem number, and the weight of rhizomes, shoots, and roots also supported the hypotheses that geographical ecotypes of johnsongrass exist. Susceptibility to dalapon (2,2-dichloropropionic acid) appeared not to be correlated to the latitude from which the plants were obtained.

The toxicity of several toluidine and thiocarbamate herbicides to johnsongrass [Sorghum halepense (L.) Pers.] rhizome tissue was determined by a triphenyl tetrazolium chloride (TTC) assay. Rhizome sections were incubated in herbicide solutions for 24 hr and then in TTC solution for 24 hr. The amount of reduced TTC was a quantitative measure of herbicide toxicity. Concentrations of the different herbicides required to cause 100% tissue injury indicated that the order of decreasing herbicide toxicity was: USB-3584 (N3,N3-diethyl-2,4-dinitro-6-trifluoromethyl-1,3-phenylendiamine); trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine); benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2-6-dinitro-p-toluidine); nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline]; San-9789 [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazione]; and A-820 (Nsec-butyl-4-tert-butyl-2,6-dinitroaniline). In another study CGA-11607 (N-ethyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline); AN-5647 [N,N-bis(2-chloroethyl)-2,6-dinitro-p-toluidine]; and CGA-10832 (Nn-propyl-N-cyclopropylmethyl-4-trifluoromethyl-2,6-dinitroaniline) were less toxic than trifluralin to johnsongrass rhizomes. Complete tissue injury caused by the thiocarbamates occurred in the same concentration range (10−3 to 10−2M) as the toluidine herbicides. At a concentration required for complete kill the toxicity in decreasing order was: EPTC (S-ethyl dipropylthiocarbamate); vernolate (S-propyl dipropylthiocarbamate); butylate (S-ethyl diisobutylthiocarbamate); and pebulate (S-propyl butylethylthiocarbamate). R-25788 (N,N-diallyl-2,2-dichloroacetamide) at 6.7 × 10−5 M had no effect on vernolate, EPTC, or pebulate activity; but it increased the toxicity of butylate to johnsongrass rhizome tissue.

Vapors of 11 dinitroaniline herbicides from soil were trapped in a Florisil column under controlled laboratory conditions for a 3-hr period. No vapor losses of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were detected at the highest temperature, 50 C, from moist Lakeland sand with an air flow of 50 ml/min; whereas, under the same conditions vapor losses approached 25% for benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Vapor losses for the remaining herbicides studied were moderate with values ranging between 2 and 13%. Volatility of all herbicides increased with increasing temperatures of 30, 40, and 50 C. Vapor losses for each herbicide from Hagerstown clay loam, Littleton silt loam and Lakeland sand were statistically different for five of the 11 herbicides.