Ready for a fight? The physiological effects of detecting an opponent's pheromone cues prior to a contest

Abstract

Reception of pheromone cues can elicit significant physiological (e.g. steroid hormone levels) changes in the recipient. These pheromone-induced physiological changes have been well documented for male-female interactions, but scarcely in same-sex interactions (male-male and female-female). We sought to address this dearth in the current literature and examine whether mangrove rivulus fish (Kryptolebias marmoratus) could detect and, ultimately, mount a physiological response to the pheromone signature of a potential, same-sex competitor. We examined steroid hormone levels in mangrove rivulus exposed to one of three treatments: 1) isolation, 2) exposure to pheromones of a size-matched partner, and 3) pheromone exposure to a size-matched opponent followed by a physical encounter with the opponent. We found that exposure to a competitor's pheromone cues elicited a significant increase in testosterone levels. Increases in testosterone were similar across genetically distinct lineages derived from geographically distinct populations. Further, testosterone levels were similar between individuals only exposed to pheromone cues and individuals exposed to both pheromone cues and a subsequent physical encounter. Our findings led us to generate a number of testable predictions regarding how mangrove rivulus utilize pheromone signals in social interactions, the molecular mechanisms linking social stimuli and hormonal responses, and the possible adaptive benefits of hormonal responsiveness to receiving a potential competitor's pheromone cues.

What can animal research tell us about the link between androgens and social competition in humans?

“…In another example, prior to territorial patrolling in chimpanzees, which occurs every seven to nine days, there is a rise in T that is based on unknown cues, although social factors are likely involved (Sobolewski et al, 2012). Detection of an opponent's pheromones may also prime individuals through an increase in androgens in advance of an aggressive interaction, such as in mangrove rivulus fish (Kryptolebias marmoratus) (Garcia et al, 2015). These studies demonstrate that anticipatory T can be released in nonhuman animals and that as a result of some cue(s) in the environment the timing potentially can be conditioned.…”

The Genome of the Self-Fertilizing Mangrove Rivulus Fish,Kryptolebias marmoratus: A Model for Studying Phenotypic Plasticity and Adaptations to Extreme Environments

“…Indeed, virtually all studies that have employed different lineages demonstrate, under common garden conditions, significant among-lineage variation for phenotypic characteristics. These range from sensitivity of the sexual phenotype to early-life or adult temperature regimes ( Harrington 1967 , 1968, 1971 , 1975 ; Kristensen 1970 ; Turner et al 2006 ; Ellison et al 2015 ), some aspects of endocrine function (e.g., [ Earley and Hsu 2008 ; Earley et al 2013 ]), risk-taking and exploratory behavior ( Edenbrow and Croft 2011 , 2012 ), performance in aggressive contests ( Hsu et al 2008 ), the propensity to voluntarily jettison from the water ( Turko et al 2011 ), and life history traits ( Garcia et al 2015 ). These data indicate that there is considerable heritable variation among genotypes that persists for generations under laboratory conditions.…”

Chemical diplomacy in male tilapia: urinary signal increases sex hormone and decreases aggression

“…Receivers may thus be stimulated by the chemical signals present in dominant male urine and mount a physiological response in order to take advantage of the situation and try to mate, either in a neighbouring nest or attempting a parasitic fertilization 63 - a possible case of chemical eavesdropping. Similarly, mangrove rivulus Kryptolebias marmoratus males experience a rise in androgens when stimulated chemically (but not visually) with water from conspecific males 49 .…”

“…Male goldfish adaptively increase milt production in advance of an approaching ovulation by monitoring female condition both directly – by detecting the pre-ovulatory steroid pheromone – and indirectly – by detecting cues which the pre-ovulatory female has stimulated other males to release 47 . Male mangrove rivulus Kryptolebias marmoratus also increase androgen levels when smelling chemical signals from conspecific males 49 .…”