Estimating the adaptive potential of critical thermal limits: Methodological problems and evolutionary implications

1.Current studies indicate that estimates of thermal tolerance limits in ectotherms depend on the experimental protocol used, with slower and presumably more ecologically relevant rates of warming negatively affecting the upper thermal limits (CTmax). Recent empirical evidence also gives credence to earlier speculations suggesting that estimates of heritability could drop with slower heating rates. 2.Using published data from the fruit fly Drosophila melanogaster, we show that empirical patterns can be explained if flies' physical condition decreases with experimental time in thermal tolerance assays. This problem could even overshadow potential benefits of thermal acclimation, also suggesting that a drop in CTmax with slower heating rates does not necessarily rule out beneficial acclimatory responses. 3.Numerical results from a simple illustrative model show that no clear conclusions can be obtained on how the phenotypic variance in CTmax will be affected with different rates of thermal change. Conversely, the genetic variance and estimated heritabilities are expected to drop with slower heating rates, hence ramping rates in experiments aiming to study the evolutionary potential of thermal tolerance to respond to global warming should be as fast as possible (within the range in which measurement accuracy and physical condition are not affected). 4.Measurements under ecologically realistic warming rates should also consider the impact of other physiological and behavioural strategies that might partly compensate the negative effects of slow heating rates. However, there are situations in which slow heating rates closely mimic natural conditions, as those encountered by some aquatic ectotherms. These heating rates may be an issue of major concern in these species, given its negative impact on CTmax and its adaptive potential. © 2010 The Authors. Functional Ecology © 2010 British Ecological Society.Peer Reviewe

Age-dependent genetic variance in a life-history trait in the mute swan

Genetic variance in characters under natural selection in natural populations determines the way those populations respond to that selection. Whether populations show temporal and/or spatial constancy in patterns of genetic variance and covariance is regularly considered, as this will determine whether selection responses are constant over space and time. Much less often considered is whether characters show differing amounts of genetic variance over the life-history of individuals. Such age-specific variation, if present, has important potential consequences for the force of natural selection and for understanding the causes of variation in quantitative characters. Using data from a long-term study of the mute swan Cygnus olor, we report the partitioning of phenotypic variance in timing of breeding (subject to strong natural selection) into component parts over 12 different age classes. We show that the additive genetic variance and heritability of this trait are strongly age-dependent, with higher additive genetic variance present in young and, particularly, old birds, but little evidence of any genetic variance for birds of intermediate ages. These results demonstrate that age can have a very important influence on the components of variation of characters in natural populations, and consequently that separate age classes cannot be assumed to be equivalent, either with respect to their evolutionary potential or response

Trying to predict 'dangerous' bladders in children: The area under the curve concept

Objective: Children with neurological and non-neurological lower urinary tract dysfunction normally undergo video urodynamics. One reason is to try to diagnose 'dangerous' bladders. Currently, bladder compliance is used to predict 'dangerous' bladders; however, in children there are no standardized methods of measurement and thus no 'cut-off' values. Compliance may also be normal even though high-pressure detrusor overactivity waves may exist during the filling phase of urodynamics. We tried to determine whether measuring the area under the detrusor pressure curve (AUC) during the filling phase of urodynamics would be a useful parameter in predicting 'dangerous' bladders. Patients and methods: Children referred to the urodynamics unit at Southmead Hospital, a tertiary referral centre, from 2000 to 2004 were investigated. Although 130 patients were identified, only 15 patients had raw data which were analysable using the available computer software. Results: There was no correlation between the AUC and predicting 'dangerous' bladders possibly due to limitations in the computer software. Conclusion: Although the study did not reveal any correlation between the AUC and 'dangerous' bladders, it revealed the limitations of the available computer software in determining AUC, and highlighted the need for new standardized software and multinational, multi-centre trials to look into the concept of AUC. There is also a need for the International Continence Society to standardize methods and terminology in predicting 'dangerous' bladders. © 2005 Journal of Pediatric Urology Company. Published by Elsevier Ltd. All rights reserved