Climate-induced reaction norms for life-history traits in pythons

Climate change modelers predict increasingly frequent “extreme events,” so it is critical to quantify whether organismal responses (such as reproductive output) measured over the range of usual climatic conditions can predict responses under more extreme conditions. In a 20-year field study on water pythons (Liasis fuscus), we quantified the effects of climatically driven annual variation in food supply on demographic traits of female pythons (feeding rate, body size, body mass, and reproductive output). Reaction norms linking food supply to feeding rates and residual body mass were broadly linear, whereas norms linking food supply to female body size became curvilinear when a dramatic (flooding-induced) famine reduced the mean body size at sexual maturity. Thus, the reaction norms recorded over 16 years of “normal” (albeit highly variable) climatic conditions gave little insight into the population's response to a more extreme nutritional crisis.

Individual (co)variation in thermal reaction norms of standard and maximal metabolic rates in wild-caught slimy salamanders

Standard metabolic rate (SMR) and maximal metabolic rate (MMR) are fundamental measures in ecology and evolution because they set the scope within which animals can perform activities that directly affect fitness. In ectotherms, both SMR and MMR are repeatable over time when measured at a single ambient temperature (Ta). Many ectotherms encounter variable Ta from day to day and over their lifetime, yet it is currently unknown whether individual differences hold across an ecologically relevant range of Ta (i.e. thermal repeatability; RT). Moreover, it is possible that thermal sensitivity of SMR and MMR are important individual attributes, and correlated with one another, but virtually nothing is known about this at present. We measured SMR and MMR across an ecologically relevant Ta gradient (i.e. from 10 to 25 °C) in wild-caught salamanders (Plethodon albagula) and found that RT was significant in both traits. SMR and MMR were also positively correlated, resulting in a lower RT in absolute and factorial aerobic scopes (AAS and FAS). We found significant individual differences in thermal sensitivity for both SMR and MMR, but not for AAS and FAS. The intercept (at Ta = 0 °C) and the slope of the thermal reaction norms were negatively correlated; individuals with low MR at low Ta had a higher thermal sensitivity. Finally, individuals with a high thermal sensitivity for SMR also had high thermal sensitivity for MMR. Our results suggest that natural selection occurring over variable Ta may efficiently target the overall level of - and thermal sensitivity in - SMR and MMR. However, this may not be the case for metabolic scopes, as the positive correlation between SMR and MMR, in addition to their combined changes in response to Ta, yielded little individual variation in AAS and FAS. Our results support the idea that organisms with low metabolism at low Ta have a high metabolic thermal sensitivity as a compensatory mechanism to benefit in periods of warmer environmental conditions. Hence, our study reveals the importance of considering within-individual variation in metabolism, as it may represent additional sources of adaptive (co)variation.

Changes in catch rates and length and age at maturity, but not growth, of an estuarine plotosid (cnidoglanis macrocephalus) after heavy fishing

The hypothesis that heavy fishing pressure has led to changes in the biological characteristics of the estuary cobbler (Cnidoglanis macrocephalus) was tested in a large seasonally open estuary in southwestern Australia, where this species completes its life cycle and is the most valuable commercial fish species. Comparisons were made between seasonal data collected for this plotosid (eeltail catfish) in Wilson Inlet during 2005-08 and those recorded with the same fishery-independent sampling regime during 1987-89. These comparisons show that the proportions of larger and older individuals and the catch rates in the more recent period were far lower, i.e., they constituted reductions of 40% for fish ≥430 mm total length, 62% for fish ≥4 years of age, and 80% for catch rate. In addition, total mortality and fishing-induced mortality estimates increased by factors of ~2 and 2.5, respectively. The indications that the abundance and proportion of older C. macrocephalus declined between the two periods are consistent with the perception of long-term commercial fishermen and their shift toward using a smaller maximum gill net mesh to target this species. The sustained heavy fishing pressure on C. macrocephalus between 1987-89 and 2005-08 was accompanied by a marked reduction in length and age at maturity of this species. The shift in probabilistic maturation reaction norms toward smaller fish in 2005-08 and the lack of a conspicuous change in growth between the two periods indicate that the maturity changes were related to fishery-induced evolution rather than to compensatory responses to reduced fish densities.

Phenological response of sea turtles to environmental variation across a species' northern range

Variations in environmental parameters (e. g. temperature) that form part of global climate change have been associated with shifts in the timing of seasonal events for a broad range of organisms. Most studies evaluating such phenological shifts of individual taxa have focused on a limited number of locations, making it difficult to assess how such shifts vary regionally across a species range. Here, by using 1445 records of the date of first nesting for loggerhead sea turtles (Caretta caretta) at different breeding sites, on different continents and in different years across a broad latitudinal range (25-39 degrees ' N), we demonstrate that the gradient of the relationship between temperature and the date of first breeding is steeper at higher latitudes, i.e. the phenological responses to temperature appear strongest at the poleward range limit. These findings support the hypothesis that biological changes in response to climate change will be most acute at the poleward range limits and are in accordance with the predictions of MacArthur's hypothesis that poleward range limit for species range is environmentally limited. Our findings imply that the poleward populations of loggerheads are more sensitive to climate variations and thus they might display the impacts of climate change sooner and more prominently.

Personality and plasticity: consistent responses within-, but not across-temperature situations in crabs

Recent research suggests that repeated assays of behaviour, conducted both within and across situations, could reveal important insights into two traditionally distinct areas of study: animal personality and individual differences in behavioural plasticity. However, at present relatively few studies present such data, and few consider how changing abiotic conditions affect behavioural plasticity. Individual differences in metabolic rate have been suggested as a proximate mechanism promoting personality, leading one to speculate that individual differences in metabolic sensitivity to temperature may affect behavioural responses in ectotherms. At present, only one study (out of two) has tested for and shown individual differences in behavioural responses to temperature. Here, we repeatedly assayed the behaviour of a marine crab across a narrow range of temperatures to test for individual differences in responses to temperature. We observed large inter-individual differences in behaviour that were consistent over time at a given temperature (evidence for personality), and individual differences in responses to temperature (evidence for plasticity). This study adds to the very scant literature on ectotherm behavioural sensitivity to temperature, and suggests the phenomenon might be widespread. We speculate about the role of metabolism as a proximate mechanism that might explain these individual differences in plasticity and make suggestions for future research to test this hypothesis. © Koninklijke Brill NV, Leiden, The Netherlands.

Individual variation in thermal performance curves: swimming burst speed and jumping endurance in wild-caught tropical clawed frogs

The importance of studying individual variation in locomotor performance has long been recognized as it may determine the ability of an organism to escape from predators, catch prey or disperse. In ectotherms, locomotor performance is highly influenced by ambient temperature (Ta), yet several studies have showed that individual differences are usually retained across a Ta gradient. Less is known, however, about individual differences in thermal sensitivity of performance, despite the fact that it could represent adaptive sources of phenotypic variation and/or additional substrate for selection to act upon. We quantified swimming and jumping performance in 18 wild-caught tropical clawed frogs (Xenopus tropicalis) across a Ta gradient. Maximum swimming velocity and acceleration were not repeatable and individuals did not differ in how their swimming performance varied across Ta. By contrast, time and distance jumped until exhaustion were repeatable across the Ta gradient, indicating that individuals that perform best at a given Ta also perform best at another Ta. Moreover, thermal sensitivity of jumping endurance significantly differed among individuals, with individuals of high performance at low Ta displaying the highest sensitivity to Ta. Individual differences in terrestrial performance increased with decreasing Ta, which is opposite to results obtained in lizards at the inter-specific and among-individual levels. To verify the generality of these patterns, we need more studies on individual variation in thermal reaction norms for locomotor performance in lizards and frogs.

Using repeatability to study physiological and behavioural traits: ignore time-related change at your peril

© 2015 The Association for the Study of Animal Behaviour. Broad sense repeatability, which refers to the extent to which individual differences in trait scores are maintained over time, is of increasing interest to researchers studying behavioural or physiological traits. Broad sense repeatability is most often inferred from the statistic R (the intraclass correlation, or narrow sense repeatability). However, R ignores change over time, despite the inherent longitudinal nature of the data (repeated measures over time). Here, we begin by showing that most studies ignore time-related change when estimating broad sense repeatability, and estimate R with low statistical power. Given this problem, we (1) outline how and why ignoring time-related change in scores (that occurs for whatever reason) can seriously affect estimates of the broad sense repeatability of behavioural or physiological traits, (2) discuss conditions in which various indices of R can or cannot provide reliable estimates of broad sense repeatability, and (3) provide suggestions for experimental designs for future studies. Finally, given that we already have abundant evidence that many labile traits are 'repeatable' in that broad sense (i.e. R>. 0), we suggest a shift in focus towards obtaining robust estimates of the repeatability of behavioural and physiological traits. Given how labile these traits are, this will require greater experimental (and/or statistical) control and larger sample sizes in order to detect and quantify change over time (if present).