Cirkadijalni ritam, disanje i ponašanje hipogejskih i epigejskih repaša

Comparisons of circadian rhythmicity, behavior, and metabolism between surface and cavedwelling salamanders enable elucidation of evolutionary trends in these processes. The obligate cave-dwelling proteid Proteus anguinus did not show any apparent daily rhythm of activity or resting metabolic rate. In contrast, the surface-dwelling salamandrid Euproctus asper had a circadian SMR and activity cycle. These circadian rhythms possessed an endogenous component. The lives of both salamanders studied were characterized by long periods of inactivity punctuated by bouts of foraging or exploratory/predatory behavior. Proteus anguinus had reduced resting metabolic and spontaneous activity rates (considerably lower than most surface-dwelling amphibians), and therefore appears to be a good example of a vertebrate as a low-energy system. The low metabolic and activity rates of P. anguinus are interpreted as adaptations to a subterranean existence where poor and discontinuous food supplies and/or intermittent hypoxia may be present for long periods.Usporedbe cirkadijalnog ritma, ponašanja i metabolizma kod površinskih i špiljskih proteida omogućuju rasvjetljavanje evolucijskih trendova u tim procesima. Obligatorni stanovnik špilja, proteid Proteus anguinus, nije pokazivao nikakav vidljiv dnevni ritam aktivnosti ili posebni metabolizam prilikom odmora. Naprotiv, salamandrid Euproctus asper koji boravi na površini, imao je cirkadijalni SMR i ciklus aktivnosti. Ti cirkadijalni ritmovi imali su endogenu komponentu. Životi obaju proučavanih životinja bili su karakterizirani dugim periodima neaktivnosti, prekidanih hranjenjem ili izviđačkim/predatorskim ponašanjem. Proteus anguinus imala je smanjen metabolizam tijekom odmaranja i tijekom spontane aktivnosti (znatno niži od većine površinskih vodozemaca), pa se čini dobrim primjerom kralježnjaka kao niskoenergetskog sustava. Niske vrijednosti metabolizma i aktivnosti P. anguinus interpretiraju se kao prilagodbe na život u podzemlju, gdje je u duljim periodima prisutna slaba i nekontinuirana opskrba hranom i/ili hipoksija

Invasiveness of an introduced species: the role of hybridization and ecological constraints

International audienceIntroduced species are confronted with new environments to which they need to adapt. However, the ecological success of an introduced species is generally difficult to predict, especially when hybridizations may be involved in the invasion success. In western Europe, the lake frog Pelophylax ridibundus appears to be particularly successful. A reason for this species' success might be the presence of the invader's genetic material prior to the introduction in the form of a hybrid between P. ridibundus and a second indigenous water frog species. These hybrids reproduce by hybridogenesis, only transmitting the ridibundus genome to gametes and backcrossing with the indigenous species (i.e. P. lessonae). This reproductive system allows the hybrid to be independent from P. ridibundus, and allows the ridibundus genome to be more widely spread than the species itself. Matings among hybrids produce newly formed P. ridibundus offspring (N), if the genomes are compatible. Therefore, we hypothesize that hybridogenesis increases the invasiveness of P. ridibundus (1) by enhancing propagule pressure through N individuals, and/or (2) by increasing adaptation of invaders to the native water frogs' habitat through hybrid-derived ridibundus genomes that are locally adapted. We find support for the first hypothesis because a notable fraction of N tadpoles is viable. However, in our semi-natural experiments they did not outperform ridibundus tadpoles in the native water frogs' habitat, nor did they differ physiologically. This does not support the second hypothesis and highlights ecological constraints on the invasion. However, we cannot rule out that these constraints may fall with ongoing selection, making a replacement of indigenous species highly probable in the future

Impact of different acclimation temperatures and duration on the chill coma temperature and oxygen consumption in the tenebrionid beetle Alphitobius diaperinus

International audienceWhen the ambient temperature is lowered to an insect's lower thermal limit, the insect enters into chill coma. Chill coma temperature and chill coma recovery can vary within species as a result of thermal acclimation, although the physiological basis of the onset of chill coma remains poorly understood. The present study investigates how the temperature of acclimation (0, 5, 10, 15 and 20 ◦C for 2 or 7 days) affects chill coma temperature and oxygen consumption in adult Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae). It is hypothesized that the threshold decline in metabolic rate corresponds to the entry into chill coma. Oxygen consumption (as a proxy of metabolism) is measured across the chill coma temperature threshold, and a strong decline in oxygen consumption is expected at entry into chill coma. The acclimation decreases the chill coma temperature significantly from 6.6 ± 1.1 ◦C in control insects to 3.1 ± 0.7 ◦C in those acclimated to 10 ◦C. The change in metabolic rate (Q10) after acclimation to temperatures ranging from 10 to 20 ◦C is 3.7. Despite acclimation, the metabolic rate of A. diaperinus conforms to Arrhenius kinetics, suggesting that the response of this beetle does not show metabolic compensation. The data suggest the existence of a threshold decline in metabolic rate during cooling that coincides with the temperature at which an insect goes into chill coma

Physiological and metabolic responses to rising temperature in Gammarus pulex (Crustacea) populations living under continental or Mediterranean climates

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Differential regulation of hsp70 genes in the freshwater key species Gammarus pulex (Crustacea, Amphipoda) exposed to thermal stress: effects of latitude and ontogeny

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Effect of climate-related change in vegetation on leaf litter consumption and energy storage by Gammarus pulex from Continental or Mediterranean populations.

As a consequence of global warming, it is important to characterise the potential changes occurring for some functional processes through the intra-specific study of key species. Changes in species distribution, particularly when key or engineer species are affected, should contribute to global changes in ecosystem functioning. In this study, we examined the potential consequences induced by global warming on ecosystem functioning in term of organic matter recycling. We compared consumption of leaf litter by some shredder populations (Gammarus pulex) between five tree species inhabiting continental (i.e., the northern region of the Rhône River Valley) and/or Mediterranean (i.e., the southern region of the Rhône River Valley) conditions. To consider any potential adaptation of the gammarid population to vegetation in the same climate conditions, three populations of the key shredder Gammarus pulex from the northern region and three from the southern region of the Rhône River Valley were used. We experimentally compared the effects of the geographical origin of both the gammarid populations and the leaf litter species on the shredding activity and the physiological state of animals (through body triglyceride content). This study demonstrated that leaf toughness is more important than geographical origin for determining shredder leaf litter consumption. The overall consumption rate of the gammarid populations from the southern region of Rhône Valley was much higher than that of the populations from the northern region, but no clear differences between the origins of the leaf litter (i.e., continental vs. Mediterranean) were observed. The northwards shift of G. pulex populations adapted to warmer conditions might significantly modify organic matter recycling in continental streams. As gammarid populations can demonstrate local adaptations to certain leaf species as a trophic resource, changes in riparian vegetation associated with climate change might locally affect the leaf litter degradation process by this shredder

Effects of rising temperature on a functional process: consumption and digestion of leaf litter by a freshwater shredder

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Effects of temperature on biological and biochemical indicators of the life-history strategy of bullhead Cottus gobio

International audienceThe biological and biochemical effects of temperature on life-history strategy of female bullhead Cottus gobio were investigated. Fish from two populations (Bez Basin, south-east France) experiencing contrasted thermal environments (i.e. more or less stable) were reared during 4 months at three distinct temperatures (7, 9 or 12° C). Both somatic (soma fresh mass and muscle triglyceride content) and reproductive (gonad fresh mass, fecundity, mean diameter of eggs and gonad triglyceride content) indicators were examined. Mixed models indicated that an increasing temperature had significant negative effects on all life-history indicators except for soma fresh mass. Differences in life-history strategy with regard to muscle and gonad triglyceride contents, however, suggest that populations experiencing more variable thermal environments may be better adapted than others to cope with an increasing temperature. These findings may have important implications for C. gobio populations, within the context of climate warming

Behavioural and physiological effects of the trophically transmitted cestode parasite, Cyathocephalus truncatus, on its intermediate host, Gammarus pulex.

9 pagesInternational audienceSome parasites with complex life-cycles are able to manipulate the behaviour of their intermediate hosts in a way that increases their transmission to the next host. Gammarids infected by the tapeworm Cyathocephalus truncatus (Cestoda: Spathebothriidea) are known to be more predated by fish than uninfected ones, but potential behavioural manipulation by the parasite has never been investigated. In this study, we tested the hypothesis that C. truncatus is able to manipulate the behaviour of one of its intermediate hosts, Gammarus pulex (Crustacea: Amphipoda). To assess if any behavioural change was linked to other phenotypic alterations, we also measured the immunity of infected and uninfected individuals and investigated the pathogenic effects of the parasite. Infected gammarids were significantly less photophobic than uninfected ones, but no effect of infection on the level of immune defence was found. The results on survival, swimming activity and oxygen consumption suggest that the parasite also has various pathogenic effects. However, the alteration in host phototaxis was not correlated to some of these pathogenic effects. Therefore, we propose that the modification in host reaction to light is a behavioural manipulation, explaining the previously observed increase of gammarid predation rate