Significant Fixed Effect Research Articles

Consumer Demand for Low-Acrylamide-Forming Potato Products: Evidence from Lab Auctions

A probable human carcinogen—acrylamide—was discovered about a decade ago to form naturally in potato products cooked at high temperatures. Using incentive compatible lab auctions and adult consumers from three distant U.S. locations, we test food labeling and information effects on willingness-to-pay (WTP) for conventional and genetically engineered potatoes, fries, and chips to reduce acrylamide levels. These new potato products are the first biotech products to have enhanced food safety for a popular food in the American and European diets. Relative to an environmental group’s perspective, scientific and industry information significantly increase WTP for biotech relative to conventional potato products. In addition, we find significant location-specific fixed effects of information treatments. Scientific and industry information can be used to nudge consumers towards improved decision making and healthy diets.

Analysis of transaction records of live freshwater finfish in China: A case study of customers’ claims of fish mortality using cross-classified modeling

Customers of finfish in China place a high priority on healthy fish at the point of sale but factors that increase the risk of morbidity and mortality during transportation have had limited study. We designed a case study to investigate variation of mortalities claimed by customers receiving fish at markets with above-normal mortalities. We used daily transaction records of the 3 species transported from a company located in Guangdong province to its destination markets in Beijing between April and July 2013: largemouth bass (Micropterus salmoides), Chinese perch (Siniperca chuatsi), and longsnout catfish (Leiocassis longirostris). We quantified magnitudes and patterns of weekly mortalities of transported fish, and used cross-classified random-effect modeling to explore variation and clustering of fish mortality claims at wholesale destinations. Random effects for customer and market-week were interpreted by variance partition coefficients (VPC) and intraclass correlation coefficients (ICC). A significant fixed effect of market was found in the model of mortality claims for longsnout catfish (p<0.05), and changing patterns of VPC and ICC suggested that customers ordering longsnout catfish had more variation in claims than those ordering the other 2 species. Our findings indicate a need for better customer communication for live fish transportation and a need for detailed measurements during the process including physiological factors and transportation conditions, to better understand their role in reported mortalities.

International Tourists Spending in Northern Thailand: Multilevel Linear Regression Based Hierarchical Data

This paper applies the multilevel linear regression (MLM) model to investigate factors that affect international tourists' spending per day when travelling in the northern region of Thailand. Four hundred questionnaires were collected by a convenience sampling method in 9 provinces of northern Thailand (Chiang Mai, Chiang Rai, Lamphun, Lampang, Uttaradit, Pitsanulok, Sukhothai, Kampaeng Phet and Nakonsawan) from October, 2015 to December, 2015. The results represent the mixed affected model which contains significant fixed effect explanatory variables (age, intention of revisit, and the attitude to reuse domestic land transportation) and random variance components, including individual income. In addition, the MLM can explain that the overall international tourists' spending per day in the region level (level 1) statistically depends on the individual income in the province level (level 2).

Effect of multiple stress factors (thermal, nutritional and pregnancy type) on adaptive capability of native ewes under semi-arid environment

This study was conducted to evaluate the effect of multiple stress factors (thermal, nutritional and pregnancy type) on two different native track breeds of ewes as reflected by their adaptive capability under semi-arid environment. The multiple stressor experiment was conducted in twenty-four ewes (12 Santa Inês and 12 Morada Nova ewes). Both heat stress and pregnancy stress was common to all four groups. However, the animals were divided into further two groups within each breed on the basis of nutrition regimen. According the groupings were: Group 1 (Six Santa Ines ewes; heat stress; nutrition at 0.5% of BW; single pregnancy); Group 2 (Six Santa Ines ewes; heat stress; nutrition at 1.5% BW; twin pregnancy); groups Group 3 (Six Morada Nova ewes; heat stress; nutrition at 0.5% of BW; single pregnancy); Group 4 (Six Morada Nova ewes; heat stress; nutrition at 1.5% BW; twin pregnancy). All the animals in the experiment were pregnant. Heat stress was induced by exposing all animals to summer heat stress in outside environment while the nutritional regimen followed was at 0.5% and 1.5% level of body weight (BW) respectively in each breed. The experiment was conducted in a completely randomized design with two breeds, two nutritional treatments and two pregnancy types, 10 repetitions for physiological parameters and six for blood parameters, with repeated measures over time. Physiological parameters (respiratory rate, pulse rate and rectal temperature) were measured with the animals at rest in the morning and afternoon, 0600-0700 and 1300–1400h, respectively, every seven days. Blood samples were collected every 14d for determination of serum glucose, triglycerides, cholesterol, urea and creatinine. We found interaction effect between breed and pregnancy type on respiratory rate and rectal temperature with greater values in Santa Inês ewes than Morada Nova ewes. However, there was no significant fixed effect of pregnancy type and supplementation level on physiological responses of breeds. Environmental factor (period of the day) had influenced the physiological responses of ewes during all gestational period. Santa Inês ewes had greater serum glucose concentration at 105d and 120d of gestation compared to the Morada Nova ewes. Morada Nova ewes had greater concentrations of triglycerides, urea at 120d, 150d and also greater cholesterol at 105d, 135d and 150d of gestation compared with Santa Inês ewes. The present result indicates that thermal condition was most important factor that modified the physiological responses of ewes in a semi-arid tropical environment.

The Effect of a Community-Based Exercise Program on Inflammation, Metabolic Risk, and Fitness Levels Among Persons Living with HIV/AIDS.

The human immunodeficiency virus (HIV) pandemic remains a top national health priority. Chronic inflammation may be a critical component in the disease course of HIV as C-reactive protein (CRP) is elevated and associated with increased mortality. This study examined the effect of 3 months of combined aerobic and resistance exercise training among a diverse cohort of HIV-infected men and women. The fixed effect of time for CRP was found to be non-significant (F[1,57.3]=1.7, p=0.19). There was a significant fixed effect for time for upper body (F[1,51.6]=18.1, p<0.05) and lower body strength (F[1,48.0]=15.7, p<0.05) and significant declines in diastolic blood pressure (p=0.002) and waist circumference (p=0.027). Though levels of CRP were not impacted after 3 months training, participants demonstrated a significant increase in muscular strength as well as beneficial changes in metabolic risk factors. Future studies should focus on determining the optimal exercise intervention length and mode to reduce inflammation among individuals living with HIV.

Effects of extraordinary snowfall on traffic safety

Snowfall affects traffic safety by causing changes in roadway surface and visibility that result in crashes, spinouts, and breakdowns. Using data collected at a site that regularly receives nearly 1000cm of snow during the snow season, this study examines the impact of snowfall quantity, gap between snow events, and weather conditions on crash and incident frequencies. Estimation results from regression analysis show that snowfall severity significantly impacts crashes and incidents but the impact diminishes marginally with each additional centimeter of snow. Gap has a significant fixed effect on crashes but its impact on incidents varies significantly across observations. The effect of the mixed precipitation condition is smaller in comparison to an all-snow condition. These results will help inform policy for snow removal and traffic enforcement in areas of high snowfall.

Effect Of A Community-Based Exercise Program On Inflammation And Fitness Among Persons Living With HIV/AIDS

The Human Immunodeficiency Virus (HIV) pandemic remains a top national health priority. Chronic inflammation may be a critical component in the disease course of HIV as C-reactive protein (CRP) is elevated and associated with increased mortality. PURPOSE: To examine the effect of three months of combined aerobic and resistance exercise training on inflammation and metabolic risk among a diverse cohort of HIV-infected men and women. METHODS: Ninety male and female participants were enrolled in the Healthy Living for Better Days community-based exercise program for persons living with HIV/AIDS. All participants were encouraged to attend supervised exercise sessions held four times a week, but also given open access to the fitness center at the University of Miami. High sensitivity CRP, physical fitness, and metabolic risk factors were assessed for each participant at baseline and three months. Linear Mixed Modeling was used to assess the fixed effect of time on changes in the outcome variables from baseline to three months follow up. Paired t-tests were used to assess changes in metabolic risk factors. RESULTS: Fifty-five percent of total participants were non-compliant with the prescribed exercise, though nearly one-quarter of participants were meeting physical activity recommendations after three months. Mean levels of CRP were elevated at baseline (5.75 ± 0.82 mg/L). The fixed effect of time for CRP was found to be non-significant (F[1,57.3]=1.7, p=0.19). There was a significant fixed effect for time for upper body (F[1,51.6]=18.1, p<0.05) and lower body strength (F[1,48.0]=15.7, p<0.05) and significant declines in diastolic blood pressure (p=0.002) and waist circumference (p=0.027). CONCLUSION: Though levels of CRP were not impacted after three months training, participants demonstrated a significant increase in muscular strength as well as beneficial changes in metabolic risk factors. Low compliance to the prescribed exercise limited our ability to make definitive conclusions about the impact of exercise on systemic inflammation. Future studies should focus on effective ways of engaging and retaining HIV-infected minorities in structured exercise interventions and discerning the optimal dose and duration of exercise to reduce inflammation.

IMPACT OF HEMODIALYSIS ON THE LEVEL OF HIGH-SENSITIVITY CARDIAC TROPONINS T IN PATIENTS WITH END-STAGE RENAL DISEASE

AIM The majority of patients with end-stage renal disease have chronically elevated concentrations of troponins, thus obscuring the diagnosis of myocardial infarction. We conducted a prospective study to examine the impact of hemodialysis on the level of high-sensitivity cardiac troponins T in asymptomatic patients with end-stage renal disease. METHODS High-sensitivity cardiac troponins T were measured in 43 patients, before and after three dialysis sessions, over a one week period. RESULTS Following dialysis, an average decrease of 7.6 pg/mL in high-sensitivity cardiac troponin T levels was observed which represents a 10.3% drop from baseline. Mutlivariable mixed linear regression models taking into account dialysis session (session 1, 2 or 3), sampling moment (before and after dialysis) and repeated measures on individuals revealed that the presence of coronary artery disease and elevated body mass index were associated with higher high-sensitivity cardiac troponin T levels when the other variables were held constant (CAD: β [fixed effect estimate]=31.13 pg/mL, P=0.022, 95%CI 4.46-57.80; body mass index: β=2.57 kg/m2, P=0.008, 95%CI 0.68-4.46). The significant fixed effect estimate for the interaction between gender and sampling moment indicated that the drop in high-sensitivity cardiac troponin T levels following dialysis was greater for women than for men (β=5.75, P=0.049, 95% CI 0.02-11.47). When controlling for the variables mentioned above, this analysis confirmed that hemodialysis accounted for an 11.31 pg/mL decrease in high-sensitivity cardiac troponin T levels (P<0.001, 95%CI -15.99 - -6.62) and that the values were higher in the first dialysis session than in the third (P=0.007; 95%CI 1.62-9.79). Ten patients (23%) were found to have no decrease or an increase in troponin levels after hemodialysis. CONCLUSION In stable asymptomatic patients with end-stage renal disease, we have shown that hemodialysis reduces the blood concentration of high-sensitivity cardiac troponins T by at least 10%. Further studies are needed to confirm these results and determine their prognostic significance.

Distance of the Repellency of Dead Reticulitermes flavipes (Isoptera: Rhinotermitidae) Nestmates

Small arenas were constructed to test the distance at which the repellency of dead subterranean termite nestmates, Reticulitermes flavipes (Kollar), could affect termite feeding on wooden blocks. The study used groups of 20 dead nestmates placed 1 cm distant from the wood blocks (5, placed in a series) in the treatment, and no dead nestmates in the controls. Data for each of 3 colonies were combined for analysis. The interaction of treatment x distance was a significant fixed effect. On average, in control arenas termite feeding decreased with distance, whereas in treatment arenas termite feeding increased with distance. These results indicate that whereas there is some feeding repellency associated with dead nestmates, this repellency has a short distance of influence.

Estimation of health-related utility (EQ-5D index) in subjects with seasonal allergic rhinoconjunctivitis to evaluate health gain associated with sublingual grass allergen immunotherapy

BackgroundGrass allergen immunotherapy (AIT) reduces symptom severity in seasonal allergic rhinoconjunctivitis (ARC) but its impact on general health-related utility has not been characterised for the purposes of economic evaluation. The aim of this study was to model the preferred measure of utility, EQ-5D index, from symptom severity and estimate incremental quality adjusted life years (QALYs) associated with SQ-standardised grass immunotherapy tablet (GRAZAX®, 75,000 SQ-T/2,800 BAU, ALK, Denmark).MethodsData were analysed from five consecutive pollen seasons in a randomised placebo controlled trial of GRAZAX®. Binomial and Gaussian mixed effects modelling related weekly EQ-5D index score to daily symptom and medication scores (DSS & DMS respectively). In turn, daily EQ-5D index was estimated from ARC symptoms and medication use.ResultsDSS and DMS were the principal predictors of ‘perfect’ health (EQ-5D = 1.000; binomial) and ‘imperfect’ health (EQ-5D < 1.000; Gaussian). Each unit increase in DSS and DMS reduced the odds of ‘perfect’ health (EQ-5D = 1.000) by 27% and 16% respectively, and reduced ‘imperfect’ health by 0.17 and 0.13, respectively. Gender remained the only other significant main fixed effect (Male odds ratio [OR] = 1.82). Incremental estimated EQ-5D index utility for GRAZAX® was observed from day -30 to day +70 of the pooled pollen season; mean daily utility for GRAZAX® = 0.938 units (95%CI 0.932-0.943) vs. 0.914 (0.907-0.921) for placebo, an incremental difference of 0.0238 (p < 0.001). This translates into an incremental 0.0324 Quality Adjusted Life Years over the five year study period.ConclusionsARC symptoms and medication use are the main predictors of EQ-5D index. The incremental QALYs observed for GRAZAX® may not fully describe the health benefits of this treatment, suggesting that economic modelling may be conservative.

Factors That Affect Proliferation of Salmonella in Tomatoes Post-Harvest: The Roles of Seasonal Effects, Irrigation Regime, Crop and Pathogen Genotype

Main ObjectivesFresh fruits and vegetables become increasingly recognized as vehicles of human salmonellosis. Physiological, ecological, and environmental factors are all thought to contribute to the ability of Salmonella to colonize fruits and vegetables pre- and post-harvest. The goal of this study was to test how irrigation levels, fruit water congestion, crop and pathogen genotypes affect the ability of Salmonella to multiply in tomatoes post-harvest.Experimental DesignFruits from three tomato varieties, grown over three production seasons in two Florida locations, were infected with seven strains of Salmonella and their ability to multiply post-harvest in field-grown tomatoes was tested. The field experiments were set up as a two-factor factorial split plot experiment, with the whole-plot treatments arranged in a randomized complete-block design. The irrigation treatment (at three levels) was the whole-plot factor, and the split-plot factor was tomato variety, with three levels. The significance of the main, two-way, and three-way interaction effects was tested using the (type III) F-tests for fixed effects. Mean separation for each significant fixed effect in the model was performed using Tukey’s multiple comparison testing procedure.Most Important Discoveries and SignificanceThe irrigation regime per se did not affect susceptibility of the crop to post-harvest proliferation of Salmonella. However, Salmonella grew significantly better in water-congested tissues of green tomatoes. Tomato maturity and genotype, Salmonella genotype, and inter-seasonal differences were the strongest factors affecting proliferation. Red ripe tomatoes were significantly and consistently more conducive to proliferation of Salmonella. Tomatoes harvested in the driest, sunniest season were the most conducive to post-harvest proliferation of the pathogen. Statistically significant interactions between production conditions affected post-harvest susceptibility of the crop to the pathogen. UV irradiation of tomatoes post-harvest promoted Salmonella growth.

The effects of windrow composting on the viability of Parascaris equorum eggs

Parascaris equorum generally infects horses less than 18 months old and its pathological effects can be severe. Infection occurs when larvated eggs, present in pastures, paddocks, stalls, and on feeding and watering equipment are ingested. The purpose of this study was to examine the effects of windrow composting on the viability of P. equorum eggs at a cooperating central Kentucky horse farm. Three grams of feces containing 2216 P. equorum eggs per gram were sealed in filter bag sentinel chambers. Chambers were exposed to 1 of 3 treatments: constant exposure or intermittent exposure to the interior of the windrow; controls were stored at 4°C. At day 0, all chambers in the experimental treatments were placed in the center of 10 locations of the windrow. On subsequent days when the windrow was turned, chambers in the constant exposure treatment were returned to the interior of the windrow and chambers in the intermittent exposure treatment were alternated between resting on top of, or inside, the windrow. Chambers from each treatment and control chambers were removed at days 2, 4, 6, 8, 10, 12, 14, and 18; and incubated for 21 days at room temperature (24°C). After incubation, eggs were recovered from the chambers using double centrifugation flotation. Eggs were evaluated microscopically, staged according to development and classified as viable or nonviable based on whether embryonation to the larval stage had occurred. Results were reported as the mean percent viable eggs for each treatment and time point. A mixed linear model with repeated measures was used to evaluate the influence of experimental day and treatment on the percent viability of P. equorum eggs. Chambers treated with constant exposure contained 10.73% (SD=0.29) viable eggs on day 2 and declined to an average of 0.00% by day 8. Chambers exposed to the intermittent treatment contained 16.08% (SD=0.26) viable eggs on day 2 and decreased to 0.00% by day 6. Control chambers for days 2, 4, 6, 8, 10, 12, 14, and 18 all had viabilities above 79.00%. A significant fixed effect of experimental day (p<0.0001) and compost treatment (p<0.0001) was observed. There was no significant interaction between experimental day and compost treatment (p>0.7459). The results of this study demonstrate that windrow composting was effective at rendering P. equorum eggs nonviable when it was tested under the conditions at a working horse farm.

Estimates of heritability for reproductive traits in captive rhesus macaque females.

Records from a colony of captive Indian rhesus macaques (Macaca mulatta) were used to estimate heritability for a number of reproductive traits. Records were based on a total of 7,816 births by 1,901 females from 1979 to 2007. Heritability was estimated with a linear animal model using a multiple trait derivative free REML set of programs. Because no male parents were identified, the numerator relationship matrix contained female kinships established over six generations. Reproductive traits included female age at the birth of the first, second and last infant, age at death, inter-birth intervals, number of infants born per female and infant survival. Heritability for each trait was estimated as the ratio of the additive genetic variance to phenotypic variance adjusted for significant fixed effects. Estimates of heritability for early reproduction ranged from 0.000+/-0.072 for birth interval after the first reproduction to 0.171+/-0.062 for age of female at the first infant. Higher estimates of heritability were found for female longevity [0.325+/-0.143] and for productivity of deceased females born before 1991 [0.221+/-0.138]. Heritability for infant survival ranged from 0.061+/-0.018 for survival from 30 days to 1 year to 0.290+/-0.050 for survival from birth to 30 days when adjusted to an underlying normal distribution. Eight of the 13 estimates of heritability for reproductive traits in this study were different from zero [P<0.05]. Generally, heritability estimates reported in this study for reproductive traits of captive rhesus macaque females are similar to those reported in the literature for free-ranging rhesus macaque females and for similar reproductive traits of other species. These estimates of heritability for reproductive traits appear to be among the first for a relatively large colony of captive rhesus macaque females.

Quantification and statistical modeling--part I: breathing-zone concentrations of monomeric and polymeric 1,6-hexamethylene diisocyanate.

We conducted a repeated exposure-assessment survey for task-based breathing-zone concentrations (BZCs) of monomeric and polymeric 1,6-hexamethylene diisocyanate (HDI) during spray painting on 47 automotive spray painters from North Carolina and Washington State. We report here the use of linear mixed modeling to identify the primary determinants of the measured BZCs. Both one-stage (N = 98 paint tasks) and two-stage (N = 198 paint tasks) filter sampling was used to measure concentrations of HDI, uretidone, biuret, and isocyanurate. The geometric mean (GM) level of isocyanurate (1410 microg m(-3)) was higher than all other analytes (i.e. GM < 7.85 microg m(-3)). The mixed models were unique to each analyte and included factors such as analyte-specific paint concentration, airflow in the paint booth, and sampler type. The effect of sampler type was corroborated by side-by-side one- and two-stage personal air sampling (N = 16 paint tasks). According to paired t-tests, significantly higher concentrations of HDI (P = 0.0363) and isocyanurate (P = 0.0035) were measured using one-stage samplers. Marginal R(2) statistics were calculated for each model; significant fixed effects were able to describe 25, 52, 54, and 20% of the variability in BZCs of HDI, uretidone, biuret, and isocyanurate, respectively. Mixed models developed in this study characterize the processes governing individual polyisocyanate BZCs. In addition, the mixed models identify ways to reduce polyisocyanate BZCs and, hence, protect painters from potential adverse health effects.

Inheritance of pulmonary arterial pressure in Angus cattle and its correlation with growth1

Pulmonary arterial pressure (PAP) is an indicator of resistance to blood flow through the lungs and when measured at high altitude is a reliable predictor of susceptibility of an animal to brisket disease, a noninfectious cardiac pulmonary condition. (Co)-variance components for PAP, birth weight, and adjusted 205-d weaning weight were estimated from 2,305 spring-born, registered Angus cattle from a Colorado ranch at an elevation of 1,981 m. A single measure of PAP was collected after weaning on animals born from 1984 to 2003. The same licensed veterinarian measured every animal. Multitrait animal models with and without PAP maternal effects were fitted for a pedigree including 132 sires and 793 dams. The interaction of year x sex was a significant fixed effect (P <0.05) for PAP, but age of dam was not. Age at PAP testing was a significant (P <0.1) linear covariate for PAP, and scores increased 0.012 +/- 0.007 mmHg X d(-1) of age. Heritability of PAP direct was 0.34 +/- 0.05. Maternal heritability converged to a boundary at 0.0, and the model with maternal genetic effects for PAP was not significantly better than a model with only direct effects. Phenotypically, PAP was uncorrelated with birth or weaning weights. Genetically, PAP appeared to have positive, unfavorable relationships with direct effects for birth (0.49 +/- 0.12) and weaning weight (0.50 +/- 0.18). Positive correlations imply sires whose offspring exhibited resistance to brisket disease had lower weights and gains. A model that evaluated PAP in females and males as different traits had heritability estimates for each sex of 0.38 +/- 0.07 and 0.46 +/- 0.09, respectively, with a genetic correlation of 0.64 +/- 0.12 between the sexes and was not significantly better than the model assuming homogeneity by sex and a unit genetic correlation between sexes. The results suggest that PAP is moderately heritable in spring-born Angus cattle acclimatized and tested at high altitude, and selection for low PAP scores would be effective. Selection for growth at low altitude will produce cattle less suited to high altitude.

Prevalence and inheritance of canine elbow dysplasia in German Rottweiler

SummaryA total of 2114 scores of elbow arthrosis from the official screening programme of the German Rottweiler Breeding Association (ADRK) were analysed in respect of prevalence and genetic disposition. 45.8% showed no signs of arthritis, 40.6% were scored in Grade 1 with minor osteophytes and 13.6% were affected by arthritis of clinical relevance (Grade 2 and 3). REML estimates showed a heritability of 28% and a litter variance of 6.4%. The only significant environmental fixed effect was gender. 39.1% of the male and 51.5% of the female were free from ED which corresponds with 19.2% of the male and only 8.8% of the female in the critical ED classes of Grade 2 and 3. Differences between the years of examination could be explained by genetic gain. Month of birth as well as age at examination, in the range covered by this study, was not significant. It was stated that the effect of bodyweight should be tested before starting a breeding programme.

Genetic analysis of rebreeding intervals, litter traits, and production traits in sows of the National Czech nucleus

Weaning to service (WTS), weaning to conception (WTC) and weaning to farrowing (WTF) intervals of 2896 Large White and Landrace sows of the National Czech nucleus herds were used to evaluate genetic relationships with litter and production traits. Univariate and bivariate analyses were used to estimate genetic and environmental parameters using a restricted maximum likelihood method. Data were adjusted for significant fixed effects and covariates. Univariate analyses were done with and without maternal effects in models. Maternal effects were found to be important for litter weight and backfat and were included in bivariate analyses with these traits. In a second analysis, phenotypic interval distributions were regarded as a mixture of normal and exponential distributions and evaluated with an extended maximum likelihood algorithm. Contrasts of average breeding values (EBV) for the other traits between sows with normal and prolonged intervals were estimated. Direct heritabilities for WTS, WTC, and WTF were, respectively, 0.12, 0.08, and 0.08. Maternal heritabilities were near zero for all traits except litter weight ( h m 2 = 0.05) and backfat ( h m 2 = 0.06). Genetic correlations of intervals with other traits were between −0.20 and 0.20, and the correlation between WTS and WTC was 0.93. Common environmental effects on repeated sow rebreeding intervals and reproductive traits were small, but common environmental effects of litter of origin were important for backfat and average daily gain ( c 2 = 31 and 58%, respectively). Variance components for WTC and WTF were similar. Combined EBV contrasts for backfat (BF), litter weight-maternal, total number born, and number born alive for WTS were significant and had the same sign as the genetic correlations. Selection for litter weight and BF may cause prolonged intervals, but genetic relationships are not strong.