Ultraviolet vision and mate choice in the guppy (Poecilia reticulata)

Ultraviolet (UV) vision is well documented for many species of vertebrates. UV cues are known to be used in foraging, navigation and in mate choice. We conducted a series of behavioral experiments to investigate the role of UV perception in mate choice in both female and male guppies (Poecilia reticulata). In our experiments the visual appearance of potential mates was manipulated using either UV transmitting (UV+) or UV blocking (UV-) filters. Female guppies significantly preferred UV+ males. Male guppies tended to prefer UV- females, but their preferences were marginally nonsignificant. Further experiments investigating the role of luminance, indicate that UV wavelengths are probably being used for color discrimination rather than for detecting differences in brightness. These experiments raise the possibility that UV is used in mate assessment in different ways by male and female guppies. This may reflect the different strategies that the two sexes have in order to maximize reproductive success. To our knowledge, these are the first data showing that UV is used by any fish species in mate selection.

Geographic variation in allometry in the guppy (Poecilia reticulata)

Variation in static allometry, the power relationship between character size and body size among individuals at similar developmental stages, remains poorly understood. We tested whether predation or other ecological factors could affect static allometry by comparing the allometry between the caudal fin length and the body length in adult male guppies (Poecilia reticulata) among populations from different geographical areas, exposed to different predation pressures. Neither the allometric slopes nor the allometric elevations (intercept at constant slope) changed with predation pressure. However, populations from the Northern Range in Trinidad showed allometry with similar slopes but lower intercepts than populations from the Caroni and the Oropouche drainages. Because most of these populations are exposed to predation by the prawn Macrobrachium crenulatum, we speculated that the specific selection pressures exerted by this predator generated this change in relative caudal fin size, although effects of other environmental factors could not be ruled out. This study further suggests that the allometric elevation is more variable than the allometric slope.

Testing the interactive effects of carotenoids and polyunsaturated fatty acids on ejaculate traits in the guppy Poecilia reticulata (Pisces: Poeciliidae)

Using the polyandrous livebearing guppy Poecilia reticulata, this study revealed no main effects of carotenoids in the diet on ejaculate traits, but significant main effects of polyunsaturated fatty acids (PUFAs) on sperm viability and weak but significant interacting effects of both nutrients on sperm length. Collectively, these findings not only add evidence that PUFAs are critical determinants of sperm quality, but also provide tentative evidence that for some traits these effects may be moderated by carotenoid intake.