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Adaptive evolution and inherent tolerance to extreme thermal environments.

ABSTRACT: BACKGROUND:When introduced to novel environments, the ability for a species to survive and rapidly proliferate corresponds with its adaptive potential. Of the many factors that can yield an environment inhospitable to foreign species, phenotypic response to variation in the thermal climate has been observed within a wide variety of species. Experimental evolution studies using bacteriophage model systems have been able to elucidate mutations, which may correspond with the ability of phage to survive modest increases/decreases in the temperature of their environment. RESULTS:Phage PhiX174 was subjected to both elevated (50 degrees C) and extreme (70 degrees C+) temperatures for anywhere from a few hours to days. While no decline in the phage's fitness was detected when it was exposed to 50 degrees C for a few hours, more extreme temperatures significantly impaired the phage; isolates that survived these heat treatments included the acquisition of several mutations within structural genes. As was expected, long-term treatment of elevated and extreme temperatures, ranging from 50-75 degrees C, reduced the survival rate even more. Isolates which survived the initial treatment at 70 degrees C for 24 or 48 hours exhibited a significantly greater tolerance to subsequent heat treatments. CONCLUSIONS:Using the model organism PhiX174, we have been able to study adaptive evolution on the molecular level under extreme thermal changes in the environment, which to-date had yet to be thoroughly examined. Under both acute and extended thermal selection, we were able to observe mutations that occurred in response to excessive external pressures independent of concurrently evolving hosts. Even though its host cannot tolerate extreme temperatures such as the ones tested here, this study confirms that PhiX174 is capable of survival.

SUBMITTER: Cox J

PROVIDER: S-EPMC2850354 | biostudies-literature | 2010 Mar

REPOSITORIES: biostudies-literature

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Adaptive evolution and inherent tolerance to extreme thermal environments.

Cox Jennifer J Schubert Alyxandria M AM Travisano Michael M Putonti Catherine C

BMC evolutionary biology 20100312

<h4>Background</h4>When introduced to novel environments, the ability for a species to survive and rapidly proliferate corresponds with its adaptive potential. Of the many factors that can yield an environment inhospitable to foreign species, phenotypic response to variation in the thermal climate has been observed within a wide variety of species. Experimental evolution studies using bacteriophage model systems have been able to elucidate mutations, which may correspond with the ability of phag ...[more]

PMID: 20226044

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Project description:Climate change is increasingly exposing populations to rare and novel environmental conditions. Theory suggests that extreme conditions will expose cryptic phenotypes, with a concomitant increase in trait variation. Although some empirical support for this exists, it is also well established that physiological mechanisms (e.g. heat shock protein expression) change when organisms are exposed to constant versus fluctuating temperatures. To determine the effect of common, rare and novel temperatures on the release of hidden variation, we exposed fathead minnows, Pimephales promelas, to five fluctuating and four constant temperature regimes (constant treatments: 23.5, 25, 28.5 and 31°C; all fluctuating treatments shared a minimum temperature of 22°C at 00.00 and a maximum of 25, 28, 31, 34 or 37°C at 12.00). We measured each individual's length weekly over 60 days, critical thermal maximum (CTmax), five morphometric traits (eye anterior-posterior distance, pelvic fin length, pectoral fin length, pelvic fin ray count and pectoral fin ray count) and fluctuating asymmetry (FA, absolute difference between left and right morphometric measurements; FA is typically associated with stress). Length-at-age in both constant and fluctuating conditions decreased with temperature, and this trait's variance decreased with temperature under fluctuating conditions but increased and then decreased in constant temperatures. CTmax in both treatments increased with increasing water temperature, while its variance decreased in warmer waters. No consistent pattern in mean or variance was found across morphometric traits or FA. Our results suggest that, for fathead minnows, variance can decrease in important traits (e.g. length-at-age and CTmax) as the environment becomes more stressful, so it may be difficult to establish comprehensive rules for the effects of rarer or stressful environments on trait variation. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Project description:In the face of global warming, both the absolute thermal tolerance of an ectotherm, and its ability to shift its tolerance level via acclimation, are thought to be fundamentally important. Understanding the links between tolerance and its plasticity is therefore critical to accurately predict vulnerability to warming. Previous studies in a number of ectotherm taxa suggest trade-offs in the evolution of thermal tolerance and its plasticity, something which does not, however, apply to Deronectes diving beetles, where these traits are instead positively correlated. Here we revisit the relationship between thermal tolerance and plasticity in these beetles, paying attention to a recently discovered morphological adaptation supporting under water respiration - setal tracheal gills. Hollow setae on the elytra interconnect with the beetle's tracheal system, providing a gas exchange surface that allows oxygen to be extracted directly from the water. This enables individuals to stay submerged for longer than their subelytral air stores would allow. We show that hypoxia reduced heat tolerance, especially when individuals were denied access to air, forcing them to rely solely on aquatic gas exchange. Species with higher densities of these gas-exchanging setae exhibited improved cold tolerance, but reduced heat tolerance and lower plasticity of heat tolerance. Differences in setal tracheal gill density across species were also related to habitat use: species with low gill density were found mainly in intermittent, warmer rivers, where underwater gas exchange is more problematic and risks of surfacing may be smaller. Moreover, when controlling for differences in gill density we no longer found a significant relationship between heat tolerance and its plasticity, suggesting that the previously reported positive relationship between these variables may be driven by differences in gill density. Differences in environmental conditions between the preferred habitats could simultaneously select for characteristic differences in both thermal tolerance and gill density. Such simultaneous selection may have resulted in a non-causal association between cold tolerance and gill density. For heat tolerance, the correlations with gill density could reflect a causal relationship. Species relying strongly on diffusive oxygen uptake via setal tracheal gills may have a reduced oxygen supply capacity and may be left with fewer options for matching oxygen uptake to oxygen demand during acclimation, which could explain their reduced heat tolerance and limited plasticity. Our study helps shed light on the mechanisms that underpin thermal tolerance and plasticity in diving air-breathing ectotherms, and explores how differences in thermal tolerance across species are linked to their selected habitat, morphological adaptations and evolutionary history.

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Adaptive evolution and inherent tolerance to extreme thermal environments.

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Adaptive evolution and inherent tolerance to extreme thermal environments.

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