Biology subjects

Killen, S. S.

Publications and source records attributed to Killen, S. S..

7 recordsLinked to original sources

bioRxiv2025

Evidence of physiological assortment and movement dynamics among social groups of a coral reef fish

The trade-offs of group living are modulated by the phenotypes of individual members of a social group, particularly in dynamic and diverse habitats like coral reefs. Little is known about the patterns of physiological traits among fishes within social groups and the mechanisms that promote these patterns, which could elucidate the drivers of group composition and their downstream ecological and evolutionary impacts. Here, in the gregarious damselfish species Chromic viridis, we examined inter-group differences in whole-animal physiological traits and the tendency for fish to move either within sites (i.e., sections of continuous reef) or among habitats (i.e., reefs separated by sandy substratum) to a new social group. Using oxygen uptake as a proxy for aerobic metabolic rate, we found significant differences in maximum metabolic rate (MMR) and aerobic scope (AS) among schools from different habitats, with these traits higher in habitats with faster water flow rates. However, we found no differences in any metabolic traits (standard metabolic rate, SMR, MMR, AS) between groups from the same site. These trends could stem from a range of mechanisms, as mark-recapture studies of this species indicated a willingness to migrate to a new social group in over 30% of recollected fish. However, there were no effects of either body size or perceived habitat risk on the distance moved or movement type (i.e., over coral or sand). Our results indicate that, in social species, a combination of mechanisms may influence phenotypic differences among groups over different spatial scales.

physiology↗

bioRxiv2021

Evidence that standard metabolic rate and risk-taking to breathe air are linked to boldness, activity level and exploratory behaviour in a catfish.

We used an air-breathing catfish, Clarias gariepinus, to investigate the hypothesis that individual variation in metabolic rate, and the propensity to take risks to obtain a resource (oxygen from air), would be correlated with behavioural tendencies such as boldness, activity level and exploratory behaviour. The standard metabolic rate (SMR) of 58 juvenile catfish was positively correlated with their rates of aerial respiration in daylight when surfacing was inherently risky. SMR was positively correlated with boldness measured in two contexts, namely the time-lag to resume air-breathing in a potentially dangerous environment (T-res, measured in a respirometer), and the timelag to enter the centre of a novel environment (T-centre, measured in an open field test (OFT)). These two measures of boldness were very highly correlated. Thus, these data support the hypothesis that high SMR and an associated tendency to take risks to acquire resources are linked to increased boldness in animals. Individual SMR was positively correlated with the proportion of time the fish spent moving in the OFT, but was negatively correlated with movement speed. The data confirmed previous observations that these catfish may exhibit a bimodal distribution of T-res phenotypes, whereby individuals either resumed air-breathing relatively rapidly (< 85 min, bold n = 26) or more slowly (> 115 min, shy n = 31) after a startle stimulus. Bold T-res phenotypes had significantly higher SMR than shy; breathed more air during the day, and showed greater boldness but less activity and exploration in the OFT. No parallel bold/shy dichotomy was observed, however, in any measure of boldness in the OFT. Therefore, the data support propositions regarding how SMR and risk-taking should relate to boldness, but provide mixed results about how SMR relates to activity and exploration, and whether bold/shy is a dichotomy or spectrum.

animal behavior and cognition↗

bioRxiv2020

Intraspecific variation in thermal tolerance differs between tropical and temperate fishes

How ectothermic animals will cope with global warming, especially more frequent and intense heatwaves, is a critical determinant of the ecological impacts of climate change. There has been extensive study of upper thermal tolerance limits among fish species but how intraspecific variation in tolerance may be affected by habitat characteristics and evolutionary history has not been considered. Intraspecific variation is a primary determinant of species vulnerability to climate change, with implications for global patterns of impacts of ongoing warming. Using published critical thermal maximum (CTmax) data on 203 marine and freshwater fish species, we found that intraspecific vsariation in upper thermal tolerance varies according to a species latitude and evolutionary history. Notably, freshwater tropical species have lower variation in tolerance than temperate species in the northern hemisphere, which implies increased vulnerability to impacts of thermal stress. The extent of variation in CTmax among fish species has a strong phylogenetic signal, which may indicate a constraint on evolvability to rising temperatures in tropical fishes. That is, in addition to living closer to their upper thermal limits, tropical species may have higher sensitivity and lower adaptability to global warming compared to temperate counterparts. This is evidence that tropical fish communities, worldwide, are especially vulnerable to ongoing climate change.

physiology↗

bioRxiv2020

A comprehensive framework for handling location error in animal tracking data

Animal tracking data are being collected more frequently, in greater detail, and on smaller taxa than ever before. These data hold the promise to increase the relevance of animal movement for understanding ecological processes, but this potential will only be fully realized if their accompanying location error is properly addressed. Historically, coarsely-sampled movement data have proved invaluable for understanding large scale processes (e.g., home range, habitat selection, etc.), but modern fine-scale data promise to unlock far more ecological information. While GPS location error can often be ignored in coarsely sampled data, fine-scale data require more care, and tools to do this have not kept pace. Current approaches to dealing with location error largely fall into two categories--either discarding the least accurate location estimates prior to analysis or simultaneously fitting movement and error parameters in a hidden-state model. In some cases these approaches can provide a level of correction, but they have known limitations, and in some cases they can be worse than doing nothing. Here, we provide a general framework to account for location error in the analysis of triangulated and trilatcralizcd animal tracking data, which includes GPS, Argos Doppler-shift, triangulated VHF, trilatcralized acoustic and cellular location data. We apply our error-modelselection framework to 190 GPS, cellular, and acoustic devices representing 27 models from 14 manufacturers. Collectively, these devices were used to track a wide range of taxa comprising birds, fish, reptiles, and mammals of different sizes and with different behaviors, in urban, suburban, and wild settings. In almost half of the tested device models, error-model selection was necessary to obtain the best performing error model, and in almost a quarter of tested device models, the reported DOP values were actually misinformative. Then, using empirical tracking data from multiple species, we provide an overview of modern, error-informed movement analyses, including continuous-time path reconstruction, home-range distribution, home-range overlap, speed, and distance estimation. Adding to these techniques, we introduce new error-informed estimators for outlier detection and autocorrelation visualization. Because error-induced biases depend on many factors--sampling schedule, movement characteristics, tracking device, habitat, etc.--differential bias can easily confound biological inference and lead researchers to draw false conclusions. We demonstrate how error-informed analyses on calibrated tracking data can provide more accurate estimates are that are insensitive to location error, and allow researchers to use all of their data.

ecology↗

bioRxiv2019

Reduction in standard metabolic rate after multigenerational exposure to elevated temperatures in the wild

O_LIIn light of global climate change, there is a pressing need to understand and predict the capacity of populations to respond to rising temperatures. Metabolic rate is a key trait that is likely to influence the ability to cope with climate change. Yet, empirical and theoretical work on metabolic rate responses to temperature changes has so far produced mixed results and conflicting predictions. C_LIO_LIOur study addresses this issue using a novel approach of comparing fish populations in geothermally warmed lakes and adjacent ambient-temperature lakes in Iceland. This unique natural experiment provides repeated and independent examples of populations experiencing contrasting thermal environments for many generations over a small geographic scale, thereby avoiding the confounding factors associated with latitudinal or elevational comparisons. Using Icelandic sticklebacks from three warm and three cold habitats, we measured individual metabolic rates across a range of acclimation temperatures to obtain reaction norms for each population. C_LIO_LIWe found a general pattern for a lower standard metabolic rate in sticklebacks from warm habitats when measured at a common temperature, as predicted by Kroghs rule. Metabolic rate differences between warm- and cold-habitat sticklebacks were more pronounced at more extreme acclimation temperatures, suggesting the release of cryptic genetic variation upon exposure to novel conditions, which can reveal hidden evolutionary potential. We also found a stronger divergence in metabolic rate between thermal habitats in allopatry than sympatry, indicating that gene flow may constrain physiological adaptation when dispersal between warm and cold habitats is possible. C_LIO_LIIn sum, our study suggests that fish may diverge toward a lower standard metabolic rate in a warming world, but this might depend on connectivity and gene flow between different thermal habitats. C_LI

physiology↗

bioRxiv2019

Temperature preference does not evolve in sticklebacks despite multigenerational exposure to elevated temperatures

Given the threat of climate change to biodiversity, a growing number of studies are investigating the potential for organisms to adapt to rising temperatures. Earlier work has predicted that physiological adaptation to climate change will be accompanied by a shift in temperature preferences, but empirical evidence for this is lacking. Here, we test whether exposure to different thermal environments has led to changes in preferred temperatures in the wild. Our study takes advantage of a natural experiment in Iceland, where freshwater populations of threespine sticklebacks (Gasterosteus aculeatus) are found in waters warmed by geothermal activity year-round (warm habitats), adjacent to populations in ambient-temperature lakes (cold habitats). We used a shuttle-box approach to measure temperature preferences of wild-caught sticklebacks from three warm-cold population pairs. Our prediction was that fish from warm habitats would prefer higher water temperatures than those from cold habitats. We found no support for this, as fish from both warm and cold habitats had an average preferred temperature of 13{degrees}C. Thus, our results challenge the assumption that there will be a shift in ectotherm temperature preferences in response to climate change. In addition, since warm-habitat fish can persist at relatively high temperatures despite a lower temperature preference, this suggests that preferred temperature alone may be a poor indicator of a populations adaptive potential to a novel thermal environment.

evolutionary biology↗

bioRxiv2019

Testing the predictability of morphological evolution in naturally warmed stickleback populations

In light of climate change, the ability to predict evolutionary responses to temperature changes is of central importance for conservation efforts. Prior work has focused on exposing model organisms to different temperatures for just one or a few generations under laboratory conditions. Using a natural experiment, we show that studying parallel evolution in wild populations from contrasting thermal environments presents a more powerful approach for understanding and predicting responses to climate change. More specifically, we used a unique study system in Iceland, where freshwater populations of threespine sticklebacks (Gasterosteus aculeatus) are found in waters warmed by geothermal activity, adjacent to populations in ambient-temperature water. We used three sympatric and three allopatric warm-cold population pairs to test for repeated patterns of morphological divergence in relation to thermal habitat. We found that thermal habitat explained over 50% of body shape variation: fish from warm habitats had a deeper mid-body, a shorter jaw, and smaller eyes. Our common garden experiment showed that most of these morphological differences between thermal habitats were heritable. Lastly, absence of gene flow seems to facilitate parallel divergence across thermal habitats: all three allopatric population pairs were on a common evolutionary trajectory, whereas sympatric pairs followed different trajectories. Our findings therefore suggest that morphological responses to rising temperatures can be predictable when there is limited gene flow. On the other hand, migration of individuals between different thermal habitats or microhabitats can exaggerate nonparallel evolution and reduce our ability to predict evolutionary responses.

evolutionary biology↗