General and specific microscopic characteristics of the dorsal tail scales and the spines of the crest in the tuatara Sphenodon pucntatus (Reptilia; Rhynchocephalia; Sphenodontidae).

Dorsal crest scales and those of the tail spines of the tuatara (Sphenodon punctatus) represent different specializations involved in display and protection. Erection of the dorsal crest occurs in males during combat and courtship, but tail spines are not noticeably involved in these activities. In both scale derivatives corneous beta proteins (CBPs, formerly called beta-keratins) and intermediate filaments keratins (IFKs) were determined by immunolabelling. The dermis is dense with few sparse fibrocytes surrounded by collagen bundles, the latter rather randomly oriented in the crest scales. In the tail ridge scales banded collagen I fibrils form more regular, orthogonally aligned bundles of alternating layers with connections to the basal epidermal membrane. A conglomerate of dermal melanonophores and iridophores is present under the epidermis. The iridophores are the likely origin of the whitish colour of the crest. The epidermis shows a thicker beta-layer with serrated/indented corneocytes in the tail scales while the beta layer is reduced in the crest but contains CBPs. A relatively thick mesos layer is present in both scale derivatives, especially in the crest where its role, aside from limiting transpiration, is not known. The alpha-layer is formed by corneocytes with irregular perimeter and sparse desmosomal remnants. The high labelling intensity for CBPs in the beta-layer disappears in the mesos layer but occurs, albeit strongly reduced, in the alpha-layer as in the other body scales. The take-home message is that the dense dermis and its apical beta-layer strengthen mechanically the ridge spines while the crest is mainly supported by the firm but pliable and less dense or regular dermis.

Two nematodes (Nematoda: Diplogastridae, Rhabditidae) from the invasive millipede Chamberlinius hualienensis Wang, 1956 (Diplopoda, Paradoxosomatidae) on Hachijojima Island in Japan.

Millipedes may cause unexpected damage when they are introduced to new locations, becoming invaders that leave behind their old parasites and predators. Therefore, it was interesting to find numerous rhabditid nematodes within the gut of the invasive phytophagous millipede Chamberlinius hualienensis Wang, 1956 (Diplopoda, Paradoxosomatidae) from Hachijojima (Japan) in November, 2014. This millipede originated in Taiwan but was discovered in Japan in 1986. The nematodes were identified as juvenile Oscheius rugaoensis (Zhang et al., 2012) Darsouei et al., 2014 (Rhabditidae), and juvenile and adult Mononchoides sp. (Diplogastridae) based on images, morphometrics, and sequences of 18S and 28S rDNA. A novel short 28S sequence of a separate population of Oscheius necromenus SB218 from Australian millipedes was also included in a phylogenetic comparison of what can now be characterized as a species complex of millipede-associated Oscheius. The only other nematode associates of millipedes belong to Rhigonematomorpha and Oxyuridomorpha, two strictly parasitic superorders of nematodes. These nematode identifications represent new geographic and host associations.Millipedes may cause unexpected damage when they are introduced to new locations, becoming invaders that leave behind their old parasites and predators. Therefore, it was interesting to find numerous rhabditid nematodes within the gut of the invasive phytophagous millipede Chamberlinius hualienensis Wang, 1956 (Diplopoda, Paradoxosomatidae) from Hachijojima (Japan) in November, 2014. This millipede originated in Taiwan but was discovered in Japan in 1986. The nematodes were identified as juvenile Oscheius rugaoensis (Zhang et al., 2012) Darsouei et al., 2014 (Rhabditidae), and juvenile and adult Mononchoides sp. (Diplogastridae) based on images, morphometrics, and sequences of 18S and 28S rDNA. A novel short 28S sequence of a separate population of Oscheius necromenus SB218 from Australian millipedes was also included in a phylogenetic comparison of what can now be characterized as a species complex of millipede-associated Oscheius. The only other nematode associates of millipedes belong to Rhigonematomorpha and Oxyuridomorpha, two strictly parasitic superorders of nematodes. These nematode identifications represent new geographic and host associations.

The association between anxiety and C-reactive protein (CRP) levels: results from the Northern Finland 1966 birth cohort study.

BACKGROUND: Anxiety frequently accompanies low-grade inflammation-associated conditions like depression, insulin resistance, coronary heart disease and metabolic syndrome. The association between anxiety and low-grade inflammation is, unlike between depression and low-grade inflammation, a very sparsely studied area in general populations. The aim of the present study was to investigate whether anxiety symptoms as well as comorbid anxiety and depressive symptoms are associated with low-grade inflammation at population level. METHODS: The general population-based Northern Finland 1966 Birth Cohort was followed until age 31 (n=2688 males and 2837 females), when the highly sensitive CRP concentrations were measured. Anxiety and depressive symptoms were defined by Hopkins Symptom Checklist-25 (HSCL-25). RESULTS: After adjusting for confounders, logistic regression analyses showed that anxiety symptoms alone increased the probability for elevated hs-CRP levels (>3.0mg/L) in males over two-fold (2.19 CI 95% 1.08-4.46), while comorbid anxiety and depressive symptoms caused a 1.7-fold (1.76 CI 95% 1.13-2.74) increase in the probability for elevated hs-CRP levels (1.0-3.0mg/L). CONCLUSIONS: Our results support the hypothesis that anxiety as well as comorbid anxiety and depression can be associated with an increased risk for low-grade inflammation in males at population level.

Clockwork blue: on the evolution of non-image-forming retinal photoreceptors in marine and terrestrial vertebrates.

This paper presents a hypothesis that could explain why blue light appears to dominate non-image-forming (NIF) ocular photoreception in marine as well as terrestrial vertebrates. Indeed, there is more and more evidence suggesting that 'novel' retinal photoreceptors, which are sensitive to blue light and were only discovered in the 1990s, could be a feature shared by all vertebrates. In our view, blue light photoreception evolved and persisted as NIF photoreception because it has been useful in the colonisation of extensive photo-dependent oceanic habitats and facilitated the move of vertebrates from an aquatic to a terrestrial environment. Because the available scattered evidence is compatible with the validity of our hypothesis, we hope that our rationale will be followed up. Indeed, it (1) involves testable predictions, (2) provides plausible explanations for previous observations, (3) unites phenomena not previously considered related to one another and (4) suggests tests that have not been carried out before. Overall, our approach not only embraces cross-disciplinary links; it, moreover, serves as a reminder of an all-embracing evolutionary history, especially with regard to a ubiquitous photoreceptive 'clockwork-blue' in marine and terrestrial vertebrates.

Glowworms: a review of Arachnocampa spp. and kin.

The term 'glowworm' is used in connection with the flightless females of lampyrid fireflies and to describe the luminescent larvae of certain fungus gnats that belong to the subfamilies Arachnocampinae, Keroplatinae and Macrocerinae of the dipteran family Keroplatidae. This review focuses on the luminescent larval fungus gnats. The weakly luminescent species of the Holarctic feed mainly on fungal spores, but some, such as Orfelia fultoni, have turned to a carnivorous diet. Larval Australian and New Zealand Arachnocampa spp. produce brighter in vivo (but not necessarily in vitro) lights, live in cool, damp and dark places and are exclusively predatory. They lure their prey (usually small flying insects) with the help of their blue-green light emissions towards snares consisting of vertical silk threads coated with sticky mucus droplets. Fungus gnats with similar 'fishing lines' are found in the Neotropics, but they are not luminescent. The larval stage is longest in the life cycle of Arachnocampa, lasting up to a year, depending on climatic conditions such as temperature and humidity as well as food supply. In A. luminosa, but not the Australian A. flava, female pupae and even female imagines are luminescent. However, it remains to be demonstrated whether it is the light of the female, a pheromone or both that attract the males. Light organs and the chemical reactions to produce light differ between the holarctic and the Australian/New Zealand species. Prey is attracted only by the glowworm's light; odours of the fishing lines or the glowworms themselves are not involved. Recognition of the prey by the glowworm involves mechano- and chemoreception. The eyes of both larval and adult glowworms are large and functional over a spectral range covering UV to green wavelengths. Adults are poor fliers, live only for a few days, have degenerate mouth parts and do not feed. Maintenance of glowworms in captivity is possible and the impact of tourism on glowworms in natural settings can be minimized through appropriate precautions.

Depressive symptoms and insulin resistance in young adult males: results from the Northern Finland 1966 birth cohort.

The association between insulin resistance (IR) and depression is a subject of growing research interest, especially as previous population-based studies have presented conflicting findings. The present study extends our understanding about the putative impact of the severity of depressive symptoms on this association and it provides further epidemiological evidence in support of earlier findings, suggesting that the association between IR and depression is present already in young adult males. To determine the impact of the severity of depressive symptoms on the putative association between IR and depression in young adult males, we were given access to the Northern Finland 1966 Birth Cohort database. During the 31-year follow-up survey of this genetically homogeneous birth cohort, IR was assessed by 'Qualitative Insulin Sensitivity Check Index' (QUICKI), and severity of depressive symptoms by 'Hopkins' Symptom Checklist-25' (HSCL-25). This study involved 2,609 male cohort members with complete variable information. In men, the means of the QUICKI-values decreased (i.e., IR increased) in line with the increased severity of depressive symptoms as assessed by HSCL-25 subgroups (analysis of covariance P-value for trend, P=0.003). In multivariate generalized logistic regression analyses, after adjusting for confounders, IR was positively associated with current severe depressive symptoms, the odds ratio (OR) being over threefold (adjusted OR 3.15, 95% confidence interval 1.48-6.68) and the value of OR increased in parallel with a tighter definition of IR (P-value for trend=0.007). The results indicate that in young males, a positive association exists specifically with severe depressive symptoms.

Photoreceptor cell types in the retina of the tuatara (Sphenodon punctatus) have cone characteristics.

The tuatara Sphenodon punctatus, restricted to a few New Zealand offshore islands and now strictly protected, belongs to the Rhynchocephalia, the smallest order of extant reptiles. Earlier light microscopical studies on the retina of this species described photoreceptors with both rod- and cone-like features and the presence of a fovea. A limited amount of retinal material from S. punctatus has now allowed us to prepare the first-ever electron microscopic observations on the eye of this reptile. We were able to distinguish three types of photoreceptor, all with fine structural features characteristic of cone cells. Large single cones as well as double cones had open discs in their outer segments and straight axons with pedicle-type terminals. An additional cone type, characterized by somewhat more slender inner and outer segments, vitreally-displaced cell bodies and oblique axons, resembled short-wavelength cones known from other sauropsids. No cells with rod characteristics could be confirmed in the samples, although they might occur in retinal regions not available for this study. We conclude that the tuatara has cone-like photoreceptors, which-as in other crepuscular or nocturnal reptiles-have acquired rod-like features. The phenotypic adaptations notwithstanding, the set of photoreceptor types is quite typical of the reptilian eye and in some respects reminiscent of those seen in lizards and turtles.

Atopy and depression: results from the Northern Finland 1966 Birth Cohort Study.

Several studies have suggested an association between IgE-mediated atopic allergies and depression. The present study extends our understanding about putative gender differences of this association and provides further epidemiological evidence for our previous finding that the association between atopy and depression may be characteristic for females only. In order to clearly determine the presence of atopic disorders and depression, we used more valid tools than had been employed earlier and we had access to a database (the Northern Finland 1966 Birth Cohort), in which individuals were followed up prospectively until the age of 31 years. The information on allergic symptoms, verified by skin-prick tests and comprising data of 5518 individuals, was used to ascertain the presence of atopy. Depression was assessed with the help of Hopkins' Symptom Checklist-25 and self-reported doctor-diagnosed depression. After adjusting for a father's social class, mother's parity, and place of residence, logistic regression analyses showed that the risk of developing depression increased in parallel with the increasing severity of depression and, when compared with nonatopic subjects, was 3.0 to 4.7-fold up in atopic females and statistically significant. In atopic males, the association between atopy and depression was statistically significant only in the highest depression scores, the odds ratio being 6.3-fold. The results indicate that females suffering from atopic diseases might possess an elevated risk of developing depression already during early adulthood. In males, the association between these two disorders is evident only among the most severe manifestations of depression. Possible background theories, that is, genetic abnormalities in serotonin metabolism, HPA-axis dysfunction, and histamine theory are discussed.

First immunocytochemical study of echinoderm smooth muscle: the Antarctic cushionstar Odontaster validus Koehler (Echinodermata, Asteroidea).

Our immunocytochemical observations reveal that the muscle present in the tips of the arms of the Antarctic cushionstar Odontaster validus contains caldesmon and calponin but not troponin. Thus, the muscle clearly belongs to the smooth muscle category. Distributions of contractile proteins such as actin, myosin (the latter a typical vertebrate muscle filament protein), paramyosin, and miniparamyosin (the latter two being characteristic of thick invertebrate muscle filaments) were also determined immunocytochemically. The results suggest that the thin filaments of the starfish smooth muscle are similar to those of the vertebrate muscle, but that the thick filaments differ from those of vertebrates and possess traits that are also seen in the muscle organization of invertebrates. The absence from the O. validus muscle of titin and nebulin, proteins so far known almost exclusively from the striated vertebrate muscle, comes as no surprise, but immunoreactivity to mini-titin (a protein of the same family as titin and its replacement in invertebrates) was strong and unambiguously recognizable between filaments. Odontaster validus' histochemical characteristics may be a reflection of the phylogenetic position of the echinoderms as deuterostome invertebrates or they may express an adaptation of the muscle to the harsh environmental conditions under which it has to function in the Antarctic water.

Suicides in persons suffering from rheumatoid arthritis.

OBJECTIVE: To assess the demographic and psychosocial profiles of patients with rheumatoid arthritis (RA) who committed suicide. Two control groups were used: osteoarthritis (OA) and suicide victims with neither RA nor OA. METHOD: A study based on a prospective, 13-yr follow-up database with linkage to national hospital discharge registers of all suicides (1296 males, 289 females) committed during the years 1988-2000 in the province of Oulu situated in northern Finland. RESULTS: Females were significantly over-represented among RA patients who committed suicide (52.6% RA women vs 17.3% women with neither RA nor OA). Comorbid depressive disorders preceded suicides in 90% of the female RA patients. Before their suicide, 50% of the female RA patients (vs 11% of the male RA patients) had experienced at least one suicide attempt. The method of suicide was violent in 90% of the RA females. RA males were less often depressive, but committed suicide after experiencing shorter periods of RA and fewer admissions than females. CONCLUSION: Attempted suicides and especially depression in female RA patients should be taken more seriously into account than previously in clinical work so that the most appropriate psychiatric treatment can be provided for such patients.

Microanatomical characteristics of marginal ommatidia in three different size-classes of the semi-terrestrial isopod Ligia exotica (Crustacea / Isopoda)

The aims of this paper have been (a) to characterize marginal ommatidia from different eye regions through a detailed description of their distinct ultrastructural features in three different size-classes of L. exotica, and (b) to compare microanatomical characteristics of the marginal ommatidia with those of ommatidia of the same eye, but located further centrally. On the basis of transverse as well as longitudinal sections we conclude that new ommatidia are added from a crescentic dorso-anterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone-, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different (much less regular) from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first microvilli have appeared. The diameters of rhabdom microvilli (approx. 55 nm) do not differ in ommatidia from the five investigated eye regions in small specimens (< 1.5 cm body length), but show a tendency to be slightly wider in the anterior (= frontal or rostral) regions of the eye (approx. 65 nm) in larger specimens (> 2.0 cm body length).

Microanatomical characteristics of marginal ommatidia in three different size-classes of the semi-terrestrial isopod Ligia exotica (Crustacea / Isopoda)

The aims of this paper have been (a) to characterize marginal ommatidia from different eye regions through a detailed description of their distinct ultrastructural features in three different size-classes of L. exotica, and (b) to compare microanatomical characteristics of the marginal ommatidia with those of ommatidia of the same eye, but located further centrally. On the basis of transverse as well as longitudinal sections we conclude that new ommatidia are added from a crescentic dorso-anterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone-, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different (much less regular) from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first microvilli have appeared. The diameters of rhabdom microvilli (approx. 55 nm) do not differ in ommatidia from the five investigated eye regions in small specimens (< 1.5 cm body length), but show a tendency to be slightly wider in the anterior (= frontal or rostral) regions of the eye (approx. 65 nm) in larger specimens (> 2.0 cm body length). (AU)

Ultrastructural investigations of testes and spermiogenesis in two species of halacarid mites (Halacaridae, Actinedida, Actinotrichida): Thalassarachna basteri from the Baltic Sea and Halacarellus thomasi from McMurdo Sound (Antarctica).

Testes and sperm cells of two species of halacarid mites, Thalassarachna basteri from the Baltic Sea and Halacarellus thomasi from McMurdo Sound (Antarctica), were investigated. Testes are paired structures, composed of a glandular and a germinal part. The testicular lumen is filled with a very complex secretion that contributes to sperm cell aggregates. Early spermatids of T. basteri display unusual chromatin condensation within the nucleus, but the formation of an acrosomal complex with a small acrosomal vesicle and a long acrosomal filament can be regarded as typical for the group. Tubular invaginations of the plasmalemma occur at the cell periphery. A deep, ring-like infold divides the cell into one part containing the chromatin body and another containing mainly the invaginations and the acrosomal complex. The mature sperm cell is ovoid, aflagellate and surrounded by a distinct secretion sheath. In H. thomasi only a limited number of spermiogenesis stages were observable. Chromatin condensation was rather similar and peripheral invaginations also occurred. However, no acrosomal complex was observed in the early stages. The division of the mature sperm cells into two halves was even more pronounced in H. thomasi, since one half of the cell contained masses of convoluted structures. The same half also contained a structure that remotely resembled an acrosomal complex. The observed differences between T. basteri and H. thomasi sperms support the placing of the two halacarids in separate genera.

Selective photoreceptor damage in four species of insects induced by experimental exposures to UV-irradiation.

Damage to photoreceptive cells of insect compound eyes exposed to abnormally high doses of UV-radiation of 350nm peak wavelength manifests itself in at least two different ways. In the butterflies Papilio xuthus and Pieris napi from Japan and northern Finland, respectively, only the cell bodies of retinula cells 1 and 2, (identified as short wavelength receptors), but not their corresponding rhabdomeres, exhibit damage with apoptotic features. In the eye of UV-irradiated adult crickets, however, cell bodies and cytoplasm remain normal, while the rhabdomeres of cells 7 and 8 exhibit signs of severe membrane disruptions. No signs of damage whatsoever occurred in the eyes of northern Finnish bumblebees exposed to UV. It is suggested that metabolic shortfalls in the UV-sensitive cells of the butterfly eyes result in cellular shut-down, but that in the cricket receptors UV-induced changes of the membrane lipids dominate, leading to membrane instability without concomittant cell death. The strong resistance of the bumblebee eye to UV-induced damage requires further investigation, but since preconditioning to light can reduce photic damage in the rat eye, the 24h daylight experienced by northern Finnish bumblebees during the summer season could be involved.

Smooth muscle proteins as intracellular components of the chromatophores of the Antarctic fishes Pagothenia borchgrevinki and Trematomus bernacchii (Nototheniidae).

Melanophores, xanthophores, and iridophores from the skins of the two Antarctic fish species Pagothenia borchgrevinki and Trematomus bernacchii were tested immunocytochemically for the presence of a variety of muscle proteins. Actin, myosin, and calmodulin, not surprisingly, were confirmed for all three chromatophore types of the two fishes, but the presence of caldesmon and calponin, both characteristic proteins of smooth muscle fibers, represents a new discovery. It is not known at this stage whether these proteins occur also in the chromatophores of other fishes and are not restricted to Antarctic species. Since, however, motility control of particles in fish chromatophores and the regulation of smooth muscle tension both involve the sympathetic nervous system, the presence of similar target proteins should not come as a surprise. The fact that none of the chromatophores tested positive for troponin shows that there is no close relationship between pigment cells and striated muscle. The lack of alpha-actinin in iridophores, but its presence in melanophores and xanthrophores, is thought to be a reflection of the considerably greater pigment translocations within the latter two types of chromatophore cells.

Effects of light and darkness on cell deaths in damaged retinal ganglion cells of the carp retina.

Effects of light and darkness on the apoptosis of retinal ganglion cells (RGCs) in young carp were measured by TUNEL method after transection of the optic nerve. Following the operation, the fish were kept under one of four regimens; constant darkness (DD), constant light (LL), 12 hr light and 12 hr dark (LD) and 3 hr of flickering light followed by 21 hr in the dark (FL). On day 3, the highest ratio of apoptotic RGCs was seen under conditions of DD, followed by LL, LD, and FL. On day 6, the percentages of apoptotic RGCs were lower under every experimental condition than what they had been earlier on day 3, but the same ranking order was maintained. Immunohistochemically it could be shown that phosphorylated ERKs were more intensively localized in FL rather than DD retinas. The results suggest that illumination regimens, and in particular cyclic diurnal light/dark changes, have an influence on the degree of apoptosis of damaged RGCs, and that inhibition of apoptosis is correlated with the higher expression of phosphorylated ERKs.

Light of my life--messages in the dark.

Luminescent lures, counter-shading in the dark blue sea, flashes of light intensive enough to temporarily blind a predator, love fireworks in the night to impress a mate, and toadstools that glow to attract parasitic wasps--these are just some of the many examples of bioluminescence at work in Nature. But how is the biological light produced? What are its evolutionary roots? Why are there so many different uses for the light?

Diurnal changes in retinula cell sensitivities and receptive fields (two-dimensional angular sensitivity functions) in the apposition eyes of Ligia exotica (Crustacea, Isopoda).

The structural organization of the retinula cells in the eye of Ligia exotica changes diurnally. At night, the microvilli elongate, losing the regular and parallel alignment characteristic of the day condition. Crystalline cones and distal rhabdom tips are not pushed into each other during the day, but at night the rhabdoms protrude into the crystalline cones by up to 5 microm. Screening pigment granules in the retinula cells disperse during the night, but migrate radially towards the vicinity of the rhabdom during the day. No such displacements of the pigment granules of either distal or proximal screening pigment cells were observed. The sensitivity of the eye, monitored by electroretinogram (ERG) recordings, changes diurnally: values at midnight are, on average, 10 times those occurring during the day. However, intracellular recordings from single retinula cells (50 during the day and 50 at night) indicate that the difference between night and day sensitivities is only 2.5-fold. Two-dimensional angular sensitivity curves, indicative of a single unit's spatial sensitivity, had considerably less regular outlines at night than during the day. If based on the 50 % sensitivity level, day and night eyes possessed receptive fields of almost identical width (approximately 2 degrees), but if sensitivities below the 50 % limit were included, then receptive fields at night were significantly more extensive. We suggest that the morphological adaptations and diurnal changes in chromophore content seen in the apposition eye of L. exotica allow this animal to improve its photon capture at night while preserving at least some of the spatial resolving power characteristic of the light-adapted state. This would explain why this animal is capable of performing complex escape behaviours in the presence of predators both in bright and in very dim light.

The crustacean eye: dark/light adaptation, polarization sensitivity, flicker fusion frequency, and photoreceptor damage.

Compound eyes, nauplius eyes, frontal organs, intracerebral ocelli, and caudal photoreceptors are the main light and darkness detectors in crustaceans, but they need not be present all at once in an individual and in some crustaceans no photoreceptors whatsoever are known. Compound eye designs reflect on their functions and have evolved to allow the eye to operate optimally under a variety of environmental conditions. Dark-light-adaptational changes manifest themselves in pigment granule translocations, cell movements, and optical adjustments which fine-tune an eye's performance to rapid and unpredictable fluctuations in ambient light intensities as well as to the slower and predictable light level changes associated with day and night oscillations. Recycling of photoreceptive membrane and light-induced membrane collapse are superficially similar events that involve the transduction cascade, intracellular calcium, and membrane fatty acid composition, but which differ in aetiology and longterm consequence. Responses to intermittant illumination and linearly polarized light evoke in the eye of many crustaceans characteristic responses that appear to be attuned to each species' special needs. How the visual responses are processed more centrally and to what extent a crustacean makes behavioural use of e-vector discrimination and flickering lights are questions, however, that still have not been satisfactorily answered for the vast majority of all crustacean species. The degree of light-induced photoreceptor damage depends on a large number of variables, but once manifest, it tends to be progressive and irreversible. Concomittant temperature stress aggravates the situation and there is evidence that free radicals and lipid hydroperoxides are involved.