Independent Mating Preferences for Male Body Size and Coloration in Female Trinidadian Guppies

Abstract

Although females in numerous species generally prefer males with larger, brighter and more elaborate sexual traits, there is nonetheless considerable intra‐ and interpopulation variation in mating preferences amongst females that requires explanation. Such variation exists in the Trinidadian guppy, Poecilia reticulata, an important model organism for the study of sexual selection and mate choice. While female guppies tend to prefer more ornamented males as mates, particularly those with greater amounts of orange coloration, there remains variation both in male traits and female mating preferences within and between populations. Male body size is another trait that is sexually selected through female mate choice in some species, but has not been examined as extensively as body coloration in the guppy despite known intra‐ and interpopulation variation in this trait among adult males and its importance for survivorship in this species. In this study, we used a dichotomous‐choice test to quantify the mating preferences of female guppies, originating from a low‐predation population in Trinidad, for two male traits, body length and area of the body covered with orange and black pigmentation, independently of each other. We expected strong female mating preferences for both male body length and coloration in this population, given relaxation from predation and presumably relatively low cost of choice. Females indeed exhibited a strong preference for larger males as expected, but surprisingly a weaker (but nonetheless significant) preference for orange and black coloration. Interestingly, larger females demonstrated stronger preferences for larger males than did smaller females, which could potentially lead to size‐assortative mating in nature.

Female assessment of male functional fertility during mate choice in a promiscuous fish

“…For any given pair of stimulus males (both unmated) in Treatment 3 of the control trials, the male that had previously been in the right end compartment of the dichotomous-choice apparatus (at the onset of tests in Treatments 1 and 2) was denoted the Right male and the male that had been in the left end compartment was denoted the Left male. Statistical results shown were obtained using the Wilcoxon paired signed rank test (n = 20 for both experimental and control trials) when they had only visual cues originating from the males available to them (Treatment 2), presumably because the paired males were similar in phenotypic traits (namely, body length, body weight, body colouration and sexual behaviour) that are known to influence female mate choice in the guppy (Auld et al, 2016;Endler & Houde, 1995;Houde, 1997) and they had not previously observed either male sexually interact with other females, a context which can provide potential public visual information on male functional fertility (Scarponi et al, 2015). As revealed by our control trials, when both paired males were unmated and had fully intact sperm stores and were similar in measured phenotypic traits, females did not exhibit any mating preference for either male.…”

“…Using Image J software (http://imagej.nih.gov/ij/), we measured the standard body length of each fish and quantified the body colour ornamentation of each stimulus male from their digital photograph as follows. We separately quantified the areas of black (melanin) and orange-yellow pigmentation (hereafter orange colour) on the left side of each male's body, excluding the fins.Black and orange colouration in males are sexually selected through female mate choice in the Trinidadian guppy(Endler & Houde, 1995;Houde, 1997), and females from our study population prefer males with more orange and black colouration on their body as mates(Auld et al, 2016). To control for inter-individual differences in body size, we then calculated the relative area of total body colour ([Black area + Orange area]/Total body area) for each male as their individual colour ornamentation score.…”

Influences of male and female phenotypes on male mate-choice copying in the Trinidadian guppy (Poecilia reticulata)

“…In the first experiment, the stimulus females differed in body length (i.e., small vs. large females presented) and the average difference in their length was similar across treatments. I manipulated the relative sexual attractiveness and competitiveness of observer and model males by choosing males of same or different body length and body coloration, two sexually-selected traits in the guppy (Houde 1997;Auld et al 2016), in each of four treatments. I predicted that, focal observer males should be more likely to reverse their initial mate-choice (i.e., mate-choice copy) decision when social information is available, relative to when social information is not available.…”

Sexual selection, social information and male mate choice in a promiscuous fish

“…Makowicz et al 2010b;Chapter 6). Sexual rivals also vary both in their ability to attract and mate with females and the ability of their sperm to fertilize eggs (Brooks and Endler 2001;Brooks 2002;Pilastro et al 2002;Locatello et al 2006;Auld et al 2016;Chapter 3).…”

“…In my study population in Trinidad, large and(or) more colour ornamented males are expected to be more sexually attractive and competitive than smaller and(or) drabber males because females prefer larger and more ornamented males as mates (Magellan et al 2005;Auld et al 2016; Chapter 3; but see Schwartz and Hendry 2007) and more ornamented males (possessing more orange and black colour on their body) produce faster and more viable sperm than drabber males (Locatello et al 2006), suggesting that more ornamented males have a competitive advantage in sperm competition over less ornamented ones. Irrespective of body ornamentation, large male guppies might also outcompete smaller rival males for access to females through sneak copulation, because burst swimming and body rotational velocities are positively correlated with body size in this species (Ghalambor et al 2004).…”