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Data from: Experimental evidence that density mediates negative frequency-dependent selection on aggression
Kilgour, R. Julia; McAdam, Andrew G.; Betini, Gustavo S.; Norris, D. Ryan — 2019-02-05 1. Aggression can be beneficial in competitive environments if aggressive individuals are more likely to access resources than non-aggressive individuals. However, variation in aggressive behaviour persists within populations, suggesting that high levels of aggression might not always be favoured. 2. The goal of this study was to experimentally assess the effects of population density and phenotypic frequency on selection on aggression in a competitive environment. 3. We compared survival of two strains of Drosophila melanogaster that differ in aggression across three density treatments and five frequency treatments (single strain groups, equal numbers of each strain, and strains mixed at 3:1 and 1:3 ratios) during a period of limited resources. 4. While there was no difference in survival across single-strain treatments, survival was strongly density-dependent, with declining survival as density increased. Furthermore, at medium and high densities, there was evidence of negative frequency-dependent selection, where rare strains experienced greater survival than common strains. However, there was no evidence of negative frequency-dependent selection at low density. 5. Our results indicate that the benefits of aggression during periods of limited resources can depend on the interaction between the phenotypic composition of populations and population density, both of which are mechanisms that could maintain variation in aggressive behaviours within natural populations.
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Data from: Behavioral classification of low frequency acceleration and temperature data from a free ranging small mammal
Studd, Emily K.; Landry-Cuerrier, Manuelle; Menzies, Allyson K.; Boutin, Stan; McAdam, Andrew G.; Lane, Jeffrey E.; Humphries, Murray M. — 2018-12-28 1. The miniaturization and affordability of new technology is driving a biologging revolution in wildlife ecology with use of animal-borne data logging devices. Among many new biologging technologies, accelerometers are emerging as key tools for continuously recording animal behavior. Yet a critical, but under-acknowledged consideration in biologging is the trade-off between sampling rate and sampling duration, created by battery- (or memory-) related sampling constraints. This is especially acute among small animals, causing most researchers to sample at high rates for very limited durations.Here, we show that high accuracy in behavioral classification is achievable when pairing low frequency acceleration recordings with temperature. 2. We conducted 84 hours of direct behavioral observations on 67 free-ranging red squirrels (200-300 g) that were fitted with accelerometers (2 g) recording tri-axial acceleration and temperature at 1 Hz. We then used a random forest algorithm and a manually-created decision tree, with variable sampling window lengths, to associate observed behavior with logger recorded acceleration and temperature. Finally, we assessed the accuracy of these different classifications using an additional 60 hours of behavioral observations, not used in the initial classification. 3. The accuracy of the manually-created decision tree classification using observational data varied from 70.6% to 91.6% depending on the complexity of the tree, with increasing accuracy as complexity decreased. Short duration behavior like running had lower accuracy than long duration behavior like feeding. The random forest algorithm offered similarly high overall accuracy, but the manual decision tree afforded the flexibility to create a hierarchical tree, and to adjust sampling window length for behavioral states with varying durations. 4. Low frequency biologging of acceleration and temperature allows accurate behavioral classification of small animals over multi-month sampling durations. Nevertheless, low sampling rates impose several important limitations, especially related to assessing the classification accuracy of short duration behavior.
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Data from: Signatures of selection in mammalian clock genes with coding trinucleotide repeats: implications for studying the genomics of high-pace adaptation
Prentice, Melanie B.; Bowman, Jeff; Lalor, Jillian L.; McKay, Michelle M.; Thomson, Lindsay A.; Watt, Cristen M.; McAdam, Andrew G.; Murray, Dennis L.; Wilson, Paul J. — 2017-08-23 Climate change is predicted to affect the reproductive ecology of wildlife; however, we have yet to understand if and how species can adapt to the rapid pace of change. Clock genes are functional genes likely critical for adaptation to shifting seasonal conditions through shifts in timing cues. Many of these genes contain coding trinucleotide repeats, which offer the potential for higher rates of change than single nucleotide polymorphisms (SNPs) at coding sites, and, thus, may translate to faster rates of adaptation in changing environments. We characterized repeats in 22 clock genes across all annotated mammal species and evaluated the potential for selection on repeat motifs in three clock genes (NR1D1, CLOCK, and PER1) in three congeneric species pairs with different latitudinal range limits: Canada lynx and bobcat (Lynx canadensis and L. rufus), northern and southern flying squirrels (Glaucomys sabrinus and G. volans), and white-footed and deer mouse (Peromyscus leucopus and P. maniculatus). Signatures of positive selection were found in both the interspecific comparison of Canada lynx and bobcat, and intraspecific analyses in Canada lynx. Northern and southern flying squirrels showed differing frequencies at common CLOCK alleles and a signature of balancing selection. Regional excess homozygosity was found in the deer mouse at PER1 suggesting disruptive selection, and further analyses suggested balancing selection in the white-footed mouse. These preliminary signatures of selection and the presence of trinucleotide repeats within many clock genes warrant further consideration of the importance of candidate gene motifs for adaptation to climate change.
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Data from: Predators, energetics and fitness drive neonatal reproductive failure in red squirrels
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Studd, Emily K.; Boutin, Stan; McAdam, Andrew G.; Krebs, Charles J.; Humphries, Murray M. — 2015-08-04 Neonatal reproductive failure should occur when energetic costs of parental investment outweigh fitness benefits. However, little is known about the drivers of neonatal reproductive failure in free ranging species experiencing continuous natural variation in predator abundance and in the energetic and fitness costs and benefits associated with parental investment. Long-term comprehensive studies are required to better understand how biotic, abiotic, and life history conditions interact to drive occurrences of reproductive failure in the wild. Using 24 years (1987-2011) of reproductive data from a northern boreal population of North American red squirrels in southwestern Yukon, we examined the effects of predator abundance, energetics (resource availability, ambient temperature and litter size), and fitness benefits (probability of overwinter juvenile survival and maternal age) on occurrences of neonatal reproductive failure (494/2670 reproductive attempts; 18.5%). Neonatal reproductive failure was driven by a combination of predator abundance, and the energetic and fitness costs and benefits of parental investment. The abundance of mustelids and maternal age were positively related to the occurrence of neonatal reproductive failure. High energy costs associated with a combination of low resource availability and cold ambient temperatures or large litters, corresponded to increased occurrences of neonatal reproductive failure. However, the strength of these relationships was influenced by variation in juvenile overwinter survival (i.e. fitness benefits). We provide evidence that predation pressure is an important driver of neonatal reproductive failure. In addition, we found a trade-off occurs between resource-dependent energetic and fitness costs and benefits of raising the current litter to independence
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Data from: Multilevel and sex-specific selection on competitive traits in North American red squirrels.
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Fisher, David N.; Boutin, Stan; Dantzer, Ben; Humphries, Murray M.; Lane, Jeffrey E.; McAdam, Andrew G. — 2022-04-26 Individuals often interact more closely with some members of the population (e.g. offspring, siblings or group members) than they do with other individuals. This structuring of interactions can lead to multilevel natural selection, where traits expressed at the group-level influence fitness alongside individual-level traits. Such multilevel selection can alter evolutionary trajectories, yet is rarely quantified in the wild, especially for species that do not interact in clearly demarcated groups. We quantified multilevel natural selection on two traits, postnatal growth rate and birth date, in a population of North American red squirrels (Tamiasciurus hudsonicus). The strongest level of selection was typically within-acoustic social neighbourhoods (within 130m of the nest), where growing faster and being born earlier than nearby litters was key, while selection on growth rate was also apparent both within-litters and within-study areas. Higher population densities increased the strength of selection for earlier breeding, but did not influence selection on growth rates. Females experienced especially strong selection on growth rate at the within-litter level, possibly linked to the biased bequeathal of the maternal territory to daughters. Our results demonstrate the importance of considering multilevel and sex-specific selection in wild species, including those that are territorial and sexually monomorphic.
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Data from: Daily energy expenditure during lactation is strongly selected in a free-living mammal
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Fletcher, Quinn E.; Speakman, John R.; Boutin, Stan; Lane, Jeffrey E.; McAdam, Andrew G.; Gorrell, Jamieson C.; Coltman, David W.; Humphries, Murray M. — 2015-06-13 1. Energy expenditure is a trait of central importance in ecological and evolutionary theory. We examined the correlates of, the strength of selection on, and the heritability of, daily energy expenditure (DEE; kJ/day) during lactation in free-ranging North American red squirrels (Tamiasciurus hudsonicus). 2. Over seven years, lactating squirrels with greater DEE had higher annual reproductive success (ARS; standardized selection gradient: β’ = 0.47; top 12% of published estimates). Surprisingly, positive fecundity selection on lactation DEE for increased ARS did not result because lactation DEE was correlated with typical measures of reproductive performance and/or investment. 3. We found no evidence of costs of elevated lactation DEE acting through female survival, subsequent year lactation DEE, or subsequent year reproduction. 4. Lactation DEE was not significantly repeatable and heritability was not significantly different from zero. 5. Elevated lactation DEE enhances ARS through a link between DEE and an unidentified measure of maternal or environmental quality, but there is limited evolutionary potential for lactation DEE to respond to our documented selection.
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Data from: Oxidative damage increases with reproductive energy expenditure and is reduced by food-supplementation
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Fletcher, Quinn E.; Selman, Colin; Boutin, Stan; McAdam, Andrew G.; Woods, Sarah B.; Seo, Arnold Y.; Leeuwenburgh, Christiaan; Speakman, John R.; Humphries, Murray M. — 2012-11-08 A central principle in life-history theory is that reproductive effort negatively affects survival. Costs of reproduction are thought to be physiologically-based, but the underlying mechanisms remain poorly understood. Using female North American red squirrels (Tamiasciurus hudsonicus), we test the hypothesis that energetic investment in reproduction overwhelms investment in antioxidant protection, leading to oxidative damage. In support of this hypothesis we found that the highest levels of plasma protein oxidative damage in squirrels occurred during the energetically-demanding period of lactation. Moreover, plasma protein oxidative damage was also elevated in squirrels that expended the most energy and had the lowest antioxidant protection. Finally, we found that squirrels that were food-supplemented during lactation and winter had increased antioxidant protection and reduced plasma protein oxidative damage providing the first experimental evidence in the wild that access to abundant resources can reduce this physiological cost.
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Data from: Very low levels of direct additive genetic variance in fitness and fitness components in a red squirrel population
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McFarlane, S. Eryn; Boutin, Stan; Humphries, Murray M.; McAdam, Andrew G.; Gorrell, Jamieson C.; Coltman, David W. — 2015-01-21 A trait must genetically correlate with fitness in order to evolve in response to natural selection, but theory suggests that strong directional selection should erode additive genetic variance in fitness and limit future evolutionary potential. Balancing selection has been proposed as a mechanism that could maintain genetic variance if fitness components trade off with one another and has been invoked to account for empirical observations of higher levels of additive genetic variance in fitness components than would be expected from mutation–selection balance. Here, we used a long-term study of an individually marked population of North American red squirrels (Tamiasciurus hudsonicus) to look for evidence of (1) additive genetic variance in lifetime reproductive success and (2) fitness trade-offs between fitness components, such as male and female fitness or fitness in high- and low-resource environments. “Animal model” analyses of a multigenerational pedigree revealed modest maternal effects on fitness, but very low levels of additive genetic variance in lifetime reproductive success overall as well as fitness measures within each sex and environment. It therefore appears that there are very low levels of direct genetic variance in fitness and fitness components in red squirrels to facilitate contemporary adaptation in this population.

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(Author: McAdam, Andrew G.)

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