Are there sex differences in the way guppies (Poecilia reticulata) navigate their environment?

Open Access
Author:
Chaby, Lauren Evelyn
Graduate Program:
Ecology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 21, 2015
Committee Members:
  • Victoria Braithwaite, Thesis Advisor
  • Tracy Lee Langkilde, Committee Member
  • Matt Marshall, Committee Member
Keywords:
  • Spatial congition
  • guppy
  • sex differences
  • estradiol
  • fish
  • poecilia reticulata
Abstract:
Sex differences in spatial cognition have been found in mammalian, avian, and even invertebrate species. Yet, in teleost fish, one of the most diverse vertebrate groups, the consequences of sex-specific life history demands on spatial cognition remain unclear. Many evolutionary hypotheses have been proposed to explain why sex differences in spatial cognition arise, and several of these discuss the natural spatial behavior of the two sexes. Given that remarkably varied life history strategies are present in fish, determining whether sex differences in spatial cognition are present in teleosts may help identify which of the current hypotheses that address sex differences in spatial cognition have the greatest explanatory power. This thesis focuses on understanding sex differences in spatial cognition in a commonly studied teleost fish, the guppy (Poecilia reticulata). This species was selected because previous work has described the natural history of the guppy and demonstrated sex differences in mating and dispersal patterns, as well as in regions of the brain responsible for spatial cognition. I first evaluated whether adult male and female guppies show sex-specific patterns in spatial learning or preference for strategy of spatial navigation (the first set of experiments). I found that male and female guppies that were given the opportunity to solve a spatial task using either a landmark or turn-based navigation strategy solved the task in the same number of trials, indicating analogous spatial learning ability. However, when the sexes were tested for their preference of spatial navigation strategy, male guppies, similar to male polygynous mammals, exhibited a preference for a turn-based (egocentric) spatial strategy while female guppies exhibited equal preference for either a turn-based or landmark-based (allocentric) strategy. This suggests that either spatial navigation preference is highly conserved or selective forces have reprised similar sex differences in multiple taxa through convergent evolution. In order to address how these sex differences in spatial cognition might arise, I ran a further experiment in which male guppies were exposed to a sex steroid hormone that typically produces feminizing effects in male teleosts, 17B-estradiol. Unexpectedly both the estradiol and vehicle-exposed males exhibited an equal preference for both turn-based and landmark-based navigational strategies. This result is discussed in terms of the possible effects of all male housing (used in experiment 2), compared to mixed sex housing (used in experiment 1), and potential experiments that would address the relative effects of housing and exogenous estradiol exposure are proposed. Although estradiol has been demonstrated to have feminizing effects on somatic traits, it may be that the effects of estradiol on cognition are more complex and cannot be described as feminizing because of sex-specific responses to sex steroids.