Recently I read two publications regarding extraterritorial forays in nightingales (Naguib, M. et al., 2001) and red foxes (Iossa, G. et al., 2008).
Selectivity was discussed from the perspective of the male’s readiness to perform extraterritorial forays (also of different scope, e.g., breaching into one neighbour’s territory vs. several neighbour’s territories as well as the duration of the breaches and travel pace) as well as the male’s ability to prevent extraterritorial forays on his own territory.
Extraterritorial forays can be performed due to various reasons but one of the motivations is extrapair/extragroup mating which was explicitly studied in red foxes and implied in nightingales (nightingale males also forayed during non-mating season which suggests they had other intents).
The mating context indicates selectivity of traits that encourage/discourage extraterritorial forays (encourage embarking on foray and discourage foraying by other males on one’s territory).
The findings were quite predictable – male quality determined both the foray rate and the prevention of forays on their own range.
I began wondering, however, about a certain aspect of male quality.
Namely, the quality is usually discussed as the ability to compete (in some respects, to intimidate and to suffer lower risk of becoming attacked or severely injured).
This is, of course, correct.
I was simply considering another aspect which is that of endurance of fear.
As the individual assesses their risk, they probably essentially make fear evaluations.
If they are large (or possess other beneficial qualities), they might experience reduced anxiety because they are aware that they stand a good chance and they are used to being the intimidators rather than the intimidated.
Similarly, traits that allow to intimidate others (without physical contact, e.g., through song rates) would prevent undesirable competition.
I find it very possible that as the males make the decision on performing or not performing the foray, they conduct an analysis of their physiological response (anxiety level).
If they can overcome their anxiety (through factoring in variables such as neighbour’s size relative to theirs), they might embark on the venture.
Also, as they are already performing the foray, their movement rate as well as the duration of the foray and the distance of the foray would probably be determined by their examination of their internal state (unless an actual conflict occurred which is also relevant to anxiety thresholds).
Thus, the readiness to take chances is related to one’s ability to tolerate fear and this ability is both socially (as mentioned before – size could offer a social advantage which is experienced as a status with the corresponding confidence or lack thereof) and physiologically determined.
This leads to interesting hypotheses.
For example, if there were individuals who were highly capable of tolerating anxiety on a physiological level but who were not socially dominant due to their qualities, age or status, these individuals would also have a higher likelihood of ensuring the passing on of their genes at higher rates (in species with territorial but potentially polygamous mating systems).
The traits leading to stress endurance might not always be the same traits that are more widely recognized as traits of social dominance and therefore there might be some cryptic selectivity underlying the ‘mainstream’ population dynamics.
On the other hand, there could be additional socially-derived stress handling advantages rooted in experience or social dynamics.
For example, males who have been fathers have probably tolerated higher stress levels (during the offspring raising activities which are stressful and which might increase stress endurance due to the effects of exposure and stress management) as well as older males who have faced a greater variety of situations during their lifetime and who would not be stressed by side-factors (such as unfamiliar habitat features or the inexperience related to mating itself), might be able to perform better forays and to take risks in a more efficient manner.
If there are traits (e.g., high cognition in some males that lead to a greater reliance on their abilities of dealing with novel situations) that lead to increased stress endurance, these traits would, too, become passed on.
It is also likely that healthier males are better capable of coping with stress than less healthy males (when we experience stress, our responses are also determined on, e.g., how healthy our heart and nervous system are).
Thereby, selectivity might also act on the overall fitness (health) level where the conduct of extraterritorial forays itself served as a health-insurance on a population level (because healthier males would pass on their genes at a greater rate).
Stress can affect many processes such as reproduction, immunity etc.
If qualities were selected for higher stress tolerance, the population would benefit also through this mechanism (traits that reduce stress levels might lead to better reproduction, stronger immunity and a more sustainable, stable population).
However, some traits might become passed on that are not adaptive (e.g., risk-taking which is not founded on good health, ability to cope or social status but that is perhaps rooted in inability to make proper risk assessments which results in lower stress rates because the individual is not aware of how risky the situation is; these matings would probably become reduced in frequency due to higher mortality in such males and perhaps because the male would also be less able to manage the situation and to take advantage of his low stress rates which would render the results of his attempts to mere chance).
Interestingly, perhaps some species have evolved display signals that are ‘highly offensive’ to the sensory endurance of their competitors (for example, vocalizations in a sound frequency that is above pain threshold) thereby artificially raising stress levels while other species might attempt to evolve ‘appreciated’ traits that others admire and feel awe for.
The former strategy would only be applicable in situations where the acting party can themselves endure the signal (because this type of tolerance is species- or sex-specific) or where the ‘stress distribution’ is unequal making the competitor exposed to higher stress compared to the displaying agent so that the increase in stress due to the signal did not equally affect both the overall stress level of the actor and the reactor (e.g., while on one’s own territory or in order to prevent intrusions).
It is likely that different species can tolerate stress in different manners and to different extent (for example, some species due to their lifestyle might not have evolved morphological traits that allow to handle high stress levels while other species might have evolved in constantly high stress environment).
It would be interesting to determine whether ‘high tolerance’ species exhibit different behaviours than ‘low tolerance’ species, e.g., regarding competition, territorial behaviour, mating systems etc.
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I have frequently encountered statements in wolf ecology that prey individuals that stand their ground (bison, moose, elk but possibly also deer) are likelier to ward off wolf attacks than individuals that take flight.
This might be founded on the defense mechanism (i.e., it might work only or work better in species that have evolved actual defense such as antlers, heavy hooves, formidable size but not in species that are smaller and antlerless) of the prey species.
But sometimes I feel – and this will be a personal and philosophical claim – that the underlying ambition in the natural world is that of eliminating fear (rather than eliminating weakness itself while, certainly, reduction in disease and prolonged starvation etc. are a beneficial side-effect to this) and that fear itself is the natural enemy to the nature itself.
(Fear, in this case, should not be confused with caution or strategies that resemble fear but that are not based on fear but, for example, on agility, ability to ‘disappear’, ‘power of invisibility’ and flight capacity of the individuals.)
Notes by Ieva 