scholarly journals Individual variation in phenotypic plasticity of the stress axis

2019 ◽  
Author(s):  
Sarah Guindre-Parker ◽  
Andrew G. Mcadam ◽  
Freya Van Kesteren ◽  
Rupert Palme ◽  
Rudy Boonstra ◽  
...  
Keyword(s):  
Phenotypic Plasticity ◽  
Individual Variation ◽  
Local Density ◽  
Reaction Norm ◽  
Tamiasciurus Hudsonicus ◽  
Stress Axis ◽  
Red Squirrels ◽  
Conspecific Density ◽  
North American Red Squirrels ◽  
Future Work

ABSTRACTPhenotypic plasticity—one individual’s capacity for phenotypic variation under different environments—is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels (Tamiasciurus hudsonicus) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant territories and overwinter survival. To help young cope with competition at high densities, mothers can increase offspring growth rates via a glucocorticoid-mediated maternal effect. However, this effect is only adaptive under high densities, and faster growth often comes at a cost to longevity. While experiments have demonstrated that red squirrels can adjust hormones in response to fluctuating density, the degree to which mothers differ in their ability to regulate glucocorticoids across changing densities remains unknown—little is known about within-individual plasticity in endocrine traits relative to among-individual variation. Findings from our reaction norm approach revealed significant individual variation not only in a female red squirrel’s mean endocrine phenotype, but also in endocrine plasticity in response to changes in local density. Future work on the proximate and ultimate drivers of variation in the plasticity of endocrine traits and maternal effects is needed, particularly in free-living animals experiencing fluctuating environments.

scholarly journals Individual variation in phenotypic plasticity of the stress axis

2019 ◽  
Vol 15 (7) ◽  
pp. 20190260 ◽  
Author(s):  
Sarah Guindre-Parker ◽  
Andrew G. Mcadam ◽  
Freya van Kesteren ◽  
Rupert Palme ◽  
Rudy Boonstra ◽  
...  
Keyword(s):  
Phenotypic Plasticity ◽  
Individual Variation ◽  
Local Density ◽  
Reaction Norm ◽  
Tamiasciurus Hudsonicus ◽  
Stress Axis ◽  
Red Squirrels ◽  
Conspecific Density ◽  
North American Red Squirrels ◽  
Future Work

Phenotypic plasticity—one individual's capacity for phenotypic variation under different environments—is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels ( Tamiasciurus hudsonicus ) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant territories and overwinter survival. To help young cope with competition at high densities, mothers can increase offspring growth rates via a glucocorticoid-mediated maternal effect. However, this effect is only adaptive under high densities, and faster growth often comes at a cost to longevity. While red squirrels can adjust hormones in response to fluctuating density, the degree to which mothers differ in glucocorticoid plasticity across changing densities remains unknown. Findings from our reaction norm approach revealed significant individual variation not only in a female red squirrel's mean endocrine phenotype but also in endocrine plasticity in response to changes in local density. Future work on proximate and ultimate drivers of variation in endocrine plasticity and maternal effects is needed, particularly in free-living animals experiencing fluctuating environments.

scholarly journals Is biasing offspring sex ratio adaptive? A test of Fisher's principle across multiple generations of a wild mammal in a fluctuating environment

2018 ◽  
Vol 285 (1891) ◽  
pp. 20181251 ◽  
Author(s):  
Andrea E. Wishart ◽  
Cory T. Williams ◽  
Andrew G. McAdam ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Adult Sex Ratio ◽  
Secondary Sex Ratio ◽  
North American Red Squirrels ◽  
Negative Frequency Dependent Selection ◽  
Fisher’S Principle

Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels ( Tamiasciurus hudsonicus ) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.

scholarly journals The effects of stress and glucocorticoids on vocalizations: a test in North American red squirrels

2019 ◽  
Vol 30 (4) ◽  
pp. 1030-1040 ◽  
Author(s):  
Matt Sehrsweeney ◽  
David R Wilson ◽  
Maggie Bain ◽  
Stan Boutin ◽  
Jeffrey E Lane ◽  
...  
Keyword(s):  
Stress State ◽  
North American ◽  
Physiological Stress ◽  
Physiological State ◽  
Public Information ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Acoustic Structure ◽  
North American Red Squirrels ◽  
Important Means

AbstractAcoustic signaling is an important means by which animals communicate both stable and labile characteristics. Although it is widely appreciated that vocalizations can convey information on labile state, such as fear and aggression, fewer studies have experimentally examined the acoustic expression of stress state. The transmission of such public information about physiological state could have broad implications, potentially influencing the behavior and life-history traits of neighbors. North American red squirrels (Tamiasciurus hudsonicus) produce vocalizations known as rattles that advertise territorial ownership. We examined the influence of changes in physiological stress state on rattle acoustic structure through the application of a stressor (trapping and handling the squirrels) and by provisioning squirrels with exogenous glucocorticoids (GCs). We characterized the acoustic structure of rattles emitted by these squirrels by measuring rattle duration, mean frequency, and entropy. We found evidence that rattles do indeed exhibit a “stress signature.” When squirrels were trapped and handled, they produced rattles that were longer in duration with a higher frequency and increased entropy. However, squirrels that were administered exogenous GCs had similar rattle duration, frequency, and entropy as squirrels that were fed control treatments and unfed squirrels. Our results indicate that short-term stress does affect the acoustic structure of vocalizations, but elevated circulating GC levels do not mediate such changes.

scholarly journals Indirect effects on fitness between individuals that have never met via an extended phenotype

2018 ◽  
Author(s):  
David N. Fisher ◽  
Jessica A. Haines ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
Jeffrey E. Lane ◽  
...  
Keyword(s):  
Population Dynamics ◽  
North American ◽  
Indirect Effects ◽  
Tamiasciurus Hudsonicus ◽  
Extended Phenotype ◽  
Red Squirrels ◽  
Lifetime Fitness ◽  
The Past ◽  
North American Red Squirrels ◽  
The Individual

AbstractInteractions between organisms are ubiquitous and have important consequences for phenotypes and fitness. Individuals can even influence those they never meet, if they have extended phenotypes which mean the environments others experience are altered. North American red squirrels (Tamiasciurus hudsonicus) guard food hoards, an extended phenotype that typically outlives the individual and is almost always inherited by non relatives. Hoarding by previous owners can therefore influence subsequent owners. We found that red squirrels bred earlier and had higher lifetime fitness if the previous owner was a male. This was driven by hoarding behaviour, as males and mid-aged squirrels had the largest hoards, and these effects persisted across owners, such that if the previous owner was male or died in mid-age subsequent occupants had larger hoards. Individuals can, therefore, influence each other’s resource dependent traits and fitness without meeting via extended phenotypes, and so the past can influence contemporary population dynamics.

scholarly journals Persistent maternal effects on juvenile survival in North American red squirrels

2007 ◽  
Vol 3 (3) ◽  
pp. 289-291 ◽  
Author(s):  
Tricia D Kerr ◽  
Stan Boutin ◽  
Jalene M LaMontagne ◽  
Andrew G McAdam ◽  
Murray M Humphries
Keyword(s):  
Maternal Effects ◽  
North American ◽  
Maternal Nutrition ◽  
Dispersal Distance ◽  
Tamiasciurus Hudsonicus ◽  
Territory Quality ◽  
Red Squirrels ◽  
Juvenile Dispersal ◽  
Supplemental Food ◽  
North American Red Squirrels

Maternal effects can have lasting fitness consequences for offspring, but these effects are often difficult to disentangle from associated responses in offspring traits. We studied persistent maternal effects on offspring survival in North American red squirrels ( Tamiasciurus hudsonicus ) by manipulating maternal nutrition without altering the post-emergent nutritional environment experienced by offspring. This was accomplished by providing supplemental food to reproductive females over winter and during reproduction, but removing the supplemental food from the system prior to juvenile emergence. We then monitored juvenile dispersal, settlement and survival from birth to 1 year of age. Juveniles from supplemented mothers experienced persistent and magnifying survival advantages over juveniles from control mothers long after supplemental food was removed. These maternal effects on survival persisted, despite no observable effect on traits normally associated with high offspring quality, such as body size, dispersal distance or territory quality. However, supplemented mothers did provide their juveniles an early start by breeding an average of 18 days earlier than control mothers, which may explain the persistent survival advantages their juveniles experienced.

Are the alarm calls of North American red squirrels (Tamiasciurus hudsonicus) functionally referential?

Behaviour ◽  
2010 ◽  
Vol 147 (9) ◽  
pp. 1201-1218
Author(s):  
Shannon Digweed ◽  
Drew Rendall
Keyword(s):  
North American ◽  
Alarm Call ◽  
Alarm Calls ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Call Production ◽  
Solitary Living ◽  
North American Red Squirrels ◽  
Functionally Referential ◽  
Necessary And Sufficient

AbstractNorth American red squirrels are a small-bodied and solitary-living species that faces a diversity of predators and produces two different variants of alarm calls in response to them. Recent studies have yielded conflicting interpretations of the predator-specific and functionally referential nature of these alarm call variants. We undertook a systematic set of playback experiments to quantify the responses of red squirrels to alarm calls produced by other squirrels during encounters with different predators. The experiment was designed to test a core requirement of functionally referential alarm calls, namely that different alarm call types induce distinct and functionally appropriate escape responses in listeners. Results indicated that squirrels registered and responded to alarm calls produced by others; however, their responses were not differentiated according to the type of alarm call they heard and, thus, did not provide evidence that the different alarm call variants hold any predator-specific, referential value. These outcomes are discussed in light of complementary work on alarm call production in red squirrels and broader aspects of this species' life history in an effort to better understand the necessary and sufficient pressures promoting the evolution of referential call systems in animals.

scholarly journals Is physiological stress state reflected in acoustic structure of vocalizations? An experimental test in wild North American red squirrels

2018 ◽  
Author(s):  
Matt Sehrsweeney ◽  
David R. Wilson ◽  
Maggie Bain ◽  
Stan Boutin ◽  
Jeffrey E. Lane ◽  
...  
Keyword(s):  
Stress State ◽  
North American ◽  
Physiological Stress ◽  
Physiological State ◽  
Public Information ◽  
Tamiasciurus Hudsonicus ◽  
Short Term ◽  
Red Squirrels ◽  
Acoustic Structure ◽  
North American Red Squirrels

AbstractAcoustic signaling is an important means by which animals communicate both stable and labile characteristics. Although it is widely appreciated that vocalizations can convey information on labile state, such as fear and aggression, very few studies have experimentally examined the acoustic expression of short-term stress state. The transmission of such information about physiological state could have broad implications, potentially allowing other individuals to modify their behavior or life history traits in response to this public information. North American red squirrels (Tamiasciurus hudsonicus) produce vocalizations known as rattles that advertise territorial ownership. We examined the influence of changes in physiological stress state on rattle acoustic structure through the application of a stressor (trapping and handling the squirrels) and by provisioning squirrels with exogenous glucocorticoids (GCs). We characterized the acoustic structure of rattles emitted by these squirrels by measuring rattle duration, mean frequency, and entropy. Our results provide mixed evidence that rattles show a “stress signature”. When squirrels were trapped and handled, they produced rattles that were longer in duration with a higher frequency and increased entropy. However, squirrels that were administered exogenous GCs had similar rattle duration, frequency, and entropy as squirrels that received control treatments and unmanipulated (unfed) squirrels. Our results indicate that short-term stress does affect the acoustic structure of vocalizations, but elevated circulating GC levels are not solely responsible for such changes.

scholarly journals Seed masting causes fluctuations in optimum litter size and lag load in a seed predator

2018 ◽  
Author(s):  
Andrew McAdam ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
Jeff Lane
Keyword(s):  
Litter Size ◽  
Picea Glauca ◽  
Life Histories ◽  
Local Density ◽  
White Spruce ◽  
Tamiasciurus Hudsonicus ◽  
Seed Predator ◽  
Red Squirrels ◽  
Seed Predators ◽  
Seed Crops

The episodic production of large seed crops by some perennial plants, is referred to as masting and is known to increase seed escape by alternately starving and swamping seed predators. These pulses of resources, however, might also act as an agent of selection on the life histories of seed predators, which could indirectly enhance seed escape by inducing an evolutionary load on seed predator populations. Lag loads in seed predators could result from mast-induced shifts in optimum phenotypes that exceed the capacity of seed predators to adaptively track optimum phenotypes through phenotypic plasticity. Alternatively, masting could generate mismatches in selection across generations, where adaptation to the parental environment leads to maladaptation in the offspring environment. Here we measured natural selection on female North American red squirrels (Tamiasciurus hudsonicus) across 28 years and five white spruce (Picea glauca) masting events. Red squirrel litter sizes were similar to optimum litter sizes during non-mast years, but were well below optimum litter sizes during resource-rich mast years. Mast events, therefore caused selection for larger litters (B = 0.25) and a lag load (L = 0.25) on red squirrels during mast years. Furthermore, we found that the annual fitness of spruce trees was negatively related to the local density of squirrels during mast years, indicating that the observed lag load on squirrels enhanced the number of spruce cones escaping squirrel predation. Although, the frequency of mast events and the demography of red squirrels were such that offspring and parents often experienced opposite environments with respect to the mast, we found no effect of environmental mismatches across generations on either offspring survival or population growth. Instead, squirrels plastically increased litter sizes in anticipation of mast events, which partially, although not completely, reduced the lag load resulting from this change in food availability. Variable selection on litter size caused by white spruce mast events, therefore, induced a lag load on the population of red squirrels that was not affected by whether individual squirrels were born during mast (matching) or non-mast (mismatching) conditions.

scholarly journals Cavity Nest Materials of Northern Flying Squirrels, Glaucomys sabrinus, and North American Red Squirrels, Tamiasciurus hudsonicus, in a Secondary Hardwood Forest of Southern Ontario

2007 ◽  
Vol 121 (3) ◽  
pp. 303 ◽  
Author(s):  
Jesse E. H. Patterson ◽  
Stephen J. Patterson ◽  
Ray J. Malcolm
Keyword(s):  
Hardwood Forest ◽  
Tamiasciurus Hudsonicus ◽  
Glaucomys Sabrinus ◽  
Red Squirrels ◽  
Southern Ontario ◽  
Flying Squirrels ◽  
Northern Flying Squirrels ◽  
Cavity Nest ◽  
North American Red Squirrels ◽  
Nest Materials

Through deployment of artificial nest boxes, we examined the composition of cavity nest materials used by Northern Flying Squirrels (Glaucomys sabrinus) and North American Red Squirrels (Tamiasciurus hudsonicus) in a secondary hardwood forest of southern Ontario, Canada. We collected 32 nests of known species association and found that 85.7% of G. sabrinus nests and 77.8% of T. hudsonicus nests were constructed almost entirely of shredded bark from Eastern White Cedar (Thuja occidentalis). Mean nest depth across all samples was 12.2 cm and showed no significant difference between species or between spring and summer nests. We review the antiparasitic properties of T. occidentalis and suggest that the use of shredded cedar bark by G. sabrinus and T. hudsonicus to line nest cavities may be a behavioural adaptation, which reduces ectoparasite loads in the nest environment.

Personality is correlated with natal dispersal in North American red squirrels (Tamiasciurus hudsonicus)

Behaviour ◽  
2017 ◽  
Vol 154 (9-10) ◽  
pp. 939-961 ◽  
Author(s):  
Eve B. Cooper ◽  
Ryan W. Taylor ◽  
Amanda D. Kelley ◽  
April Robin Martinig ◽  
Stan Boutin ◽  
...  
Keyword(s):  
Individual Differences ◽  
North American ◽  
Dispersal Distance ◽  
Natal Dispersal ◽  
Tamiasciurus Hudsonicus ◽  
Dispersal Behaviour ◽  
Red Squirrels ◽  
Intrinsic Factors ◽  
External Conditions ◽  
North American Red Squirrels

Individual natal dispersal behaviour is often difficult to predict as it can be influenced by multiple extrinsic and intrinsic factors. Individual differences in personality have been shown to be an important correlate of dispersal behaviour. However, the relationships between personality traits and dispersal are often inconsistent within and across studies and the causes of these discrepancies are often unknown. Here we sought to determine how individual differences in activity and aggression, as measured in an open-field trial, were related to natal dispersal distance in a wild population of North American red squirrels (Tamiasciurus hudsonicus). For 14 cohorts, while individual aggression consistently had no association with dispersal distance, the association between activity and dispersal fluctuated through time, mediated by population density. The environmental-dependence of the relationship between personality and dispersal in this population is indicative of the importance of considering external conditions when predicting dispersal behaviour.

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