Biological Rhythmicity in Subterranean Animals: A Function Risking Extinction?

In this chapter, we discuss evidence of regression of circadian locomotor activity in exclusively subterranean species (troglobites), having fishes as models, by comparing such findings with observations on related epigean (surface) species, that may also form self-sustained subterranean (troglophilic) populations. These results favor the hypothesis of regression of a function which may have lost its adaptive value for species permanently isolated in hypogean habitats for many generations—regression similar to the reduction of eyes and dark pigmentation, typical of troglobites in general. Recent data on feeding behavior of blind catfish compared to epigean congeners suggest a process of partial regression, affecting locomotion but not feeding, due perhaps to the persistence of regular food availability in the otherwise continuously dark cave environment. Among non-troglobitic subterranean animals, trogloxenes present regular, cyclical movements between hypogean and epigean habitats, whereas troglophiles may move between these habitats, promoting genetic connectivity between surface and subterranean populations, but without following well-defined rhythmic patterns

The enigma of sclera-specific autoimmunity in scleritis

Scleritis is a severe and painful ophthalmic disorder, in which a pathogenic role for collagen-directed autoimmunity was repeatedly suggested. We evaluated the presence of sclera-specific antibodies in a large cohort of patients with non-infectious scleritis. Therefore, we prospectively collected serum samples from 121 patients with non-infectious scleritis in a multicenter cohort study in the Netherlands. In addition, healthy (n = 39) and uveitis controls (n = 48) were included. Serum samples were tested for anti-native human type II collagen antibodies using a validated enzyme-linked immunosorbent assay (ELISA). Further, sclera-specific antibodies were determined using indirect immunofluorescence (IIF) on primate retinal/scleral cryosections. Lastly, human leukocyte antigen (HLA) typing was performed in 111 patients with scleritis. Anti-type II collagen antibodies were found in 13% of scleritis patients, in 10% of healthy controls and in 11% of uveitis controls (p = 0.91). A specific reaction to scleral nerve tissue on IIF was observed in 33% of patients with scleritis, which was higher than in healthy controls (11%; p = 0.01), but similar to uveitis controls (25%; p = 0.36). Reactivity to the scleral nerve tissue was significantly associated with earlier onset of scleritis (48 versus 56 years; p &lt; 0.001), bilateral involvement (65% versus 42%; p = 0.01), and less frequent development of scleral necrosis (5% versus 22%; p = 0.02). HLA-B27 was found to be twice as prevalent in patients with scleritis (15.3%) compared to a healthy population (7.2%). In conclusion, scleral nerve autoantibody reactivity was more common in scleritis and uveitis patients in contrast to healthy controls. Further research is needed to characterize these scleral-nerve directed antibodies and assess their clinical value.</p

Circadian rhythms in Mexican blind cavefish Astyanax mexicanus in the lab and in the field

Biological clocks have evolved as an adaptation to life on a rhythmic planet, synchronising physiological processes to the environmental light–dark cycle. Here we examine circadian clock function in Mexican blind cavefish Astyanax mexicanus and its surface counterpart. In the lab, adult surface fish show robust circadian rhythms in per1, which are retained in cave populations, but with substantial alterations. These changes may be due to increased levels of light-inducible genes in cavefish, including clock repressor per2. From a molecular standpoint, cavefish appear as if they experience ‘constant light’ rather than perpetual darkness. Micos River samples show similar per1 oscillations to those in the lab. However, data from Chica Cave shows complete repression of clock function, while expression of several light-responsive genes is raised, including DNA repair genes. We propose that altered expression of light-inducible genes provides a selective advantage to cavefish at the expense of a damped circadian oscillator