Natural parasites in conjunction with behavioral and color traits explain male agonistic behaviors in a lizard

Male competition conforms to a cost-benefit model, because while aggression may increase reproductive prospects, it can also increase the risk of injury. We hypothesize that an additional cost in aggressive males would be an increase in parasite load associated with a high energy investment into sexual competition. Some of these infections, in turn, may downmodulate the level of host aggression via energetic trade-offs. We staged dyadic male contests in the lab to investigate the relationships of multiple parasites with the agonistic behavior of lizard hosts, Sceloporus occidentalis. We also included both color and behavioral traits from opponents in the analyses because (1) color patches of lizards may serve as intraspecific signals used by conspecifics to assess the quality of opponents, and (2) contests between male lizards fit classical models of escalated aggression, where lizards increase aggression displays in response to an opponent's behavior. The results conform to our hypothesis because male lizards displayed more pushups when they had more ticks. Moreover, some parasites may modulate the levels of aggression because lizards infected by hematic coccidians performed fewer pushups. Interestingly, lizards also displayed fewer pushups when both the chroma and size of the opponent's blue patch were greater. The results thus also supported the role of the blue patch of S. occidentalis as a sexual armament, because it contributed to the deterrence of aggression from opponent lizards. We revealed that natural parasitic infections in lizard hosts can contribute to their agonistic behavior. We encourage future studies to account for parasites in behavioral tests with lizards.

Environmental conditions and male quality traits simultaneously explain variation of multiple colour signals in male lizards

Male lizards often display multiple pigment‐based and structural colour signals which may reflect various quality traits (e.g. performance, parasitism), with testosterone (T) often mediating these relationships. Furthermore, environmental conditions can explain colour signal variation by affecting processes such as signal efficacy, thermoregulation and camouflage. The relationships between colour signals, male quality traits and environmental factors have often been analysed in isolation, but simultaneous analyses are rare. Thus, the response of multiple colour signals to variation in all these factors in an integrative analysis remains to be investigated.

Here, we investigated how multiple colour signals relate to their information content, examined the role of T as a potential mediator of these relationships and how environmental factors explain colour signal variation.

We performed an integrative study to examine the covariation between three colour signals (melanin‐based black, carotenoid‐based yellow–orange and structural UV), physiological performance, parasitism, T levels and environmental factors (microclimate, forest cover) in male common lizards Zootoca vivipara from 13 populations.

We found that the three colour signals conveyed information on different aspects of male condition, supporting a multiple message hypothesis. T influenced only parasitism, suggesting that T does not directly mediate the relationships between colour signals and their information content. Moreover, colour signals became more saturated in forested habitats, suggesting an adaptation to degraded light conditions, and became generally brighter in mesic conditions, in contradiction with the thermal melanism hypothesis.

We show that distinct individual quality traits and environmental factors simultaneously explain variations of multiple colour signals with different production modes. Our study therefore highlights the complexity of colour signal evolution, involving various sets of selective pressures acting at the same time, but in different ways depending on colour production mechanism.

Intense nocturnal warming alters growth strategies, colouration and parasite load in a diurnal lizard

In the past decades, nocturnal temperatures have been playing a disproportionate role in the global warming of the planet. Yet, they remain a neglected factor in studies assessing the impact of global warming on natural populations. Here, we question whether an intense augmentation of nocturnal temperatures is beneficial or deleterious to ectotherms. Physiological performance is influenced by thermal conditions in ectotherms and an increase in temperature by only 2°C is sufficient to induce a disproportionate increase in metabolic expenditure. Warmer nights may expand ectotherms' species thermal niche and open new opportunities for prolonged activities and improve foraging efficiency. However, increased activity may also have deleterious effects on energy balance if exposure to warmer nights reduces resting periods and elevates resting metabolic rate. We assessed whether warmer nights affected an individual's growth, dorsal skin colouration, thermoregulation behaviour, oxidative stress status and parasite load by exposing yearling common lizards (Zootoca vivipara) from four populations to either ambient or high nocturnal temperatures for approximately 5 weeks. Warmer nocturnal temperatures increased the prevalence of ectoparasitic infestation and altered allocation of resources towards structural growth rather than storage. We found no change in markers for oxidative stress. The thermal treatment did not influence thermal preferences, but influenced dorsal skin brightness and luminance, in line with a predicted acclimation response in colder environments to enhance heat gain from solar radiation. Altogether, our results highlight the importance of considering nocturnal warming as an independent factor affecting ectotherms' life history in the context of global climate change. ​.

Climate dependent heating efficiency in the common lizard

Regulation of body temperature is crucial for optimizing physiological performance in ectotherms but imposes constraints in time and energy. Time and energy spent thermoregulating can be reduced through behavioral (e.g., basking adjustments) or biophysical (e.g., heating rate physiology) means. In a heterogeneous environment, we expect thermoregulation costs to vary according to local, climatic conditions and therefore to drive the evolution of both behavioral and biophysical thermoregulation. To date, there are limited data showing that thermal physiological adjustments have a direct relationship to climatic conditions. In this study, we explored the effect of environmental conditions on heating rates in the common lizard (Zootoca vivipara). We sampled lizards from 10 populations in the Massif Central Mountain range of France and measured whether differences in heating rates of individuals correlated with phenotypic traits (i.e., body condition and dorsal darkness) or abiotic factors (temperature and rainfall). Our results show that heat gain is faster for lizards with a higher body condition, but also for individuals from habitats with higher amount of precipitation. Altogether, they demonstrate that environmentally induced constraints can shape biophysical aspects of thermoregulation.

Reduction in baseline corticosterone secretion correlates with climate warming and drying across wild lizard populations

Climate change should lead to massive loss of biodiversity in most taxa, but the detailed physiological mechanisms underlying population extinction remain largely elusive so far. In vertebrates, baseline levels of hormones such as glucocorticoids (GCs) may be indicators of population state as their secretion to chronic stress can impair survival and reproduction. However, the relationship between GC secretion, climate change and population extinction risk remains unclear. In this study, we investigated whether levels of baseline corticosterone (the main GCs in reptiles) correlate with environmental conditions and associated extinction risk across wild populations of the common lizard Zootoca vivipara. First, we performed a cross-sectional comparison of baseline corticosterone levels along an altitudinal gradient among 14 populations. Then, we used a longitudinal study in eight populations to examine the changes in corticosterone levels following the exposure to a heatwave period. Unexpectedly, baseline corticosterone decreased with increasing thermal conditions at rest in females and was not correlated with extinction risk. In addition, baseline corticosterone levels decreased after exposure to an extreme heatwave period. This seasonal corticosterone decrease was more pronounced in populations without access to standing water. We suggest that low basal secretion of corticosterone may entail downregulating activity levels and limit exposure to adverse climatic conditions, especially to reduce water loss. These new insights suggest that rapid population decline might be preceded by a downregulation of the corticosterone secretion.

Multiple color patches and parasites in Sceloporus occidentalis: differential relationships by sex and infection

Parasites generally have a negative influence on the color expression of their hosts. Sexual selection theory predicts resistant high-quality individuals should show intense coloration, whereas susceptible low-quality individuals would show poor coloration. However, intensely colored males of different species of Old and New World lizards were more often infected by hemoparasites. These results suggest that high-quality males, with intense coloration, would suffer higher susceptibility to hemoparasites. This hypothesis remains poorly understood and contradicts general theories on sexual selection. We surveyed a population of Sceloporus occidentalis for parasites and found infections by the parasite genera Lankesterella and Acroeimeria. In this population, both males and females express ventral blue and yellow color patches. Lankesterella was almost exclusively infecting males. The body size of the males significantly predicted the coloration of both blue and yellow patches. Larger males showed darker (lower lightness) blue ventral patches and more saturated yellow patches that were also orange-skewed. Moreover, these males were more often infected by Lankesterella than smaller males. The intestinal parasite Acroeimeria infected both males and females. The infection by intestinal parasites of the genus Acroeimeria was the best predictor for the chroma in the blue patch of the males and for hue in the yellow patch of the females. Those males infected by Acroeimeria expressed blue patches with significantly lower chroma than the uninfected males. However, the hue of the yellow patch was not significantly different between infected and uninfected females. These results suggest a different effect of Lankesterella and Acroeimeria on the lizards. On the one hand, the intense coloration of male lizards infected by Lankesterella suggested high-quality male lizards may tolerate it. On the other hand, the low chroma of the blue coloration of the infected males suggested that this coloration could honestly express the infection by Acroeimeria.

The first ecological study on the oldest allochthonous population of European cave salamanders (Hydromantes sp.)

The introduction of allochthonous species often represents a serious problem for ecosystems and native species. Usually, these cases involve common widespread species that show high adaptability and strong competitiveness against local species. Within amphibians, the introduction of allochthonous species mainly deals with anurans, while cases involving caudata are few and poorly studied. We report the first assessment of an introduced population of European plethodontid salamanders. This population is located in the French Pyrenees and represents the oldest allochthonous Hydromantes population. We reconstructed the history of its introduction and collected data on the ecology and feeding habits of this population. Our results show that this population is stable and reproductive, showing strong similarities to Italian mainland species of Hydromantes. This study provided the base for further studies focused on this allochthonous population of European cave salamanders.

[Displacement of the instantaneous center of rotation of the humeral head during abduction: implication for scapulohumeral muscular function]

PURPOSE OF THE STUDY

To date, studies of glenohumeral stress forces have been based on the notion of a unique center of rotation situated at the geometric center of the humeral head. Early work, e.g. Fisher et al in 1977, suggested that the instantaneous center of rotation can migrate during abduction producing muscle vectors with variable moments and consequently variable stress forces. We conducted a kinematic analysis of the shoulder forces during continuous movement.

MATERIAL AND METHODS

An imaging device commonly used for angiography enabled acquisition of one image per second during a continuous movement of abduction. Images were obtained for twenty healthy shoulders in ten subjects.

RESULTS

The instantaneous center of rotation was not situated at the geometric center of the humeral head. Although interindividual variability was significant, the preferential positions of the instantaneous center of rotation implied a constant reproducible succession of gliding, rolling, and translation in variable proportions during the abduction movement. When the same movement was performed with a 3500g load held in the hand, the ICR migrated towards the upper part of the humeral head implying a predominance of the rolling motion over the gliding and translation motions. Between 40 degrees and 60 degrees glenohumeral abduction, the instantaneous center of rotation exhibited a metaphyseal displacement producing a longer lever arm for the supaspinatus and an abduction function for the infraspinatus and the subscapularis, unrecognized to date. After 60 degrees, medialization of the instantaneous center of rotation lengthened the lever arm of the deltoid.

DISCUSSION

A valid analysis of the glenohumeral stress forces must take into consideration the localization of the instantaneous center of rotation. In the clinical setting, our findings demonstrate that the infraspinatus and the subscapularis play an important role which must be considered both in surgery and in rehabilitation.

Contribution to the vascular origin of the unicameral bone cyst

Vascular occlusion between bone cyst and intramedullary venous system seems to be the primum movens in the genesis of a unicameral bone cyst. High speed injection of saline and alternative aspiration injection of the cyst fluid and reaming of the medullary cavity clearly open vascular channels connecting the bone cyst to the intramedullary venous system. This was monitored by pre- and postmanipulative radiographs. This technique was employed in 12 patients with a unicameral bone cyst. All but one went on to healing with increasing diameter of the cortical bone and filling of the cystic cavity.

[Internal tibial pain in runners]

Certain pains located along the internal boundary of the tibia in its middle third appear sometimes in young athletes who have come to racing comparatively late. The pains improve with rest, but nevertheless end up by being subintrant. The worst pain is located at the tibial insertion point of the common flexor of the toes, and of the soleus muscle. An accentuation of tarsal pronation often accompanies the pain syndrome, this in turn sometimes being accompanied by excessive valgisation of the back of the foot. Torsion disorders of the lower limb are another component of the picture. Intensive training and certain propulsion exercises on tiptoe seem to trigger off these disorders. Radiography can show moniliform cortical adaptations. Bone scintigraphies using marked technetate mainly show the areas of longitudinal hypercaptation on the internal boundary of the tibia. Pain is triggered off by the excessive use of the common flexor of the toes and by partial rupture of the aponeurosis at the point of tibial insertion of the soleus. The pressure measurements of the deep posterior space do not suggest a lodge syndrome; however, certain histopathological pictures do suggest the existence of an ischemical phenomenon. The orthopaedic treatment is based on an understanding of the deficient mechanisms functioning during foot pressure on the ground in racing. Corrective footwear and slow, gradual training techniques can help with these problems. Sometimes the pains become resistant to all conservative treatment and will respond favourably to an aponeurotomy associated with partial disinsertion of the soleus and common flexor of the toes.

[Medial tibial pain in runners]

Pain at the site of the tibial insertion of the flexor digitorum longus and the soleus near the middle third of the medial border of the tibia may be encountered in young athletes, who have usually started to run in late adolescence. Heel valgus, abnormal mid-foot pronation and excessive tibial torsion may be seen in association. The symptoms are brought on after excessive training. Radiographs may show cortical thickening at the site of the pain, and a bone scan may demonstrate a mild increase in the uptake of the isotope at this site. The pain appears to be related to a strain of the attachment of the flexor digitorum longus and the aponeurotic insertion of the soleus into the tibia. The pressure in the deep posterior compartment of the tibia is normal. Histological examination of specimens from the flexor digitorum longus may demonstrate ischaemic changes in the muscle. Treatment is based on an understanding of the biomechanics of the foot in running, modification of training methods and the use of suitable orthotics. If these measures fail, partial division of the aponeurotic attachment of soleus and freeing of the insertion of the flexor digitorum longus is usually successful.

[A case of melorheostosis]

A patient with melorheostosis of the right lower limb is described with the clinical findings and radiographic appearances which include angiographs and microradiographs. Tissue was taken from the knee joint at the time of arthrodesis and examined by histological, histochemical and biomechanical techniques. It is concluded that the bone in melorheostosis is not different from normal bone.