Ecology explains anhydrobiotic performance across tardigrades, but the shared evolutionary history matters more.

Desiccation stress is lethal to most animals. However, some microinvertebrate groups have evolved coping strategies, such as the ability to undergo anhydrobiosis (i.e. survival despite the loss of almost all body water). Tardigrades are one such group, where the molecular mechanisms of anhydrobiosis have been more thoroughly studied. Despite the ecological, evolutionary and biotechnological importance of anhydrobiosis, little is known about its inter- and intra-specific variability nor its relationship with natural habitat conditions or phylogenetic history. We developed a new index-anhydrobiotic recovery index (ARI)-to evaluate the anhydrobiotic performance of tardigrade populations from the family Macrobiotidae. Moreover, we compared the explanatory role of habitat humidity and phylogenetic history on this trait using a variance partitioning approach. We found that ARI is correlated with both microhabitat humidity and yearly rainfall, but it is mostly driven by phylogenetic niche conservatism (i.e. a high portion of ARI variation is explained by phylogeny alone). Finally, we showed that anhydrobiotic performance is highly variable, even between closely related species, and that their response to local ecological conditions is tightly linked to their phylogenetic history. This study not only presents key insights into an emerging model system, but also provides a new methodological approach for wider scale studies of the ecological and evolutionary implications of anhydrobiosis.

Differential diagnosis of chronic fatigue in children: behavioral and emotional dimensions.

A battery of self-report questionnaires and structured diagnostic interviews was administered to 20 children and adolescents who presented to a pediatric specialty clinic with chronic fatigue. Matched groups of healthy and depressed control subjects (aged 8 to 19 years) were also studied. Criteria were established to identify those items in the assessment battery that reliably differentiated among the three groups. Analysis of item content suggested several clusters of characteristics that discriminated among the subject groups, including life changes, cognitive difficulties, negative self-attributions, social relationship disruption, and somatic symptom presentation. The results suggest that certain psychological factors can discriminate chronic fatigue from depressive symptomatology, as well as normal functioning. Items discriminating among groups are presented in an organized questionnaire format to assist with the understanding and assessment of pediatric chronic fatigue cases.

Case control study of chronic fatigue in pediatric patients.

OBJECTIVE: To determine the demographic characteristics, medical features, psychological profile, and natural history of children with chronic fatigue. DESIGN: Case control study. SETTING: Pediatric Infectious Diseases Clinic of Kosair Children's Hospital, 1990 to 1992. PARTICIPANTS: Forty-four patients referred for persistent fatigue were evaluated. Twenty patients participated in a psychological study; 20 healthy controls of similar age and gender were recruited from community pediatric practices and 20 matched depressed controls were recruited from university psychiatry services (subjects were treated as groups in the analyses). MEASURES: Demographic data were obtained for all referred patients. Those with fatigue for at least 2 months and no alternative diagnosis received a detailed history, physical, and battery of laboratory tests (complete blood count, sedimentation rate, chemistry panel, chest X-ray thyroid stimulating hormone, thyroxine, anti-nuclear antibodies, urinalysis, immunoglobulins, and Epstein-Barr virus (EBV), toxoplasma, and cytomegalovirus serologies). Psychological study participants completed the following: background structured interview; Kaufman Brief Intelligence Test; Children's Depression Inventory; Child Behavior Checklist; Youth Self Report; Diagnostic Interview for Children and Adolescents-Revised; mail-in follow-up survey. RESULTS: The median age of fatigue patients was 14.3 years; 60% were female, 96% white, and 87% from the mid/upper socioeconomic status (SES). Fatigue patients were demographically similar to 21 patients referred for infectious mononucleosis (IM) but were older than other clinic patients (P < .0001). White race (P = .0568) and mid/upper SES (P = .0403) were over-represented among fatigue patients compared to patients referred for other diagnoses. Of 36 patients meeting criteria for further study, 5 had an IM-like illness including evidence of recent EBV infection. For the remaining 31 patients, clinical and laboratory evaluations were unrevealing. Psychological study subjects reported marked declines in quality-of-life and scored high on measures of internalizing, withdrawal, and social isolation. Nine met diagnostic criteria for depression, although depressive symptoms were not as prominent as those reported by depressed controls. Fatigue subjects scored higher on somatization than both control groups. The follow-up survey indicated symptomatic improvement in most patients. CONCLUSIONS: Chronic fatigue was a common reason for referral, with over-representation of white children from mid/upper SES. After exclusion of EBV-associated IM, screening laboratory tests were not helpful in establishing specific organic diagnoses. Whereas the natural history was favorable, chronic fatigue resulted in major quality-of-life changes and was associated with significant levels of psychosocial distress. IMPLICATIONS: Psychological evaluation is warranted in these patients, as some may have treatable psychological conditions. Given the absence of proved medical therapies, psychosocial interventions to improve quality-of-life should be studied.