Naturwissenschaften (2003) 90:402–405 DOI 10.1007/s00114-003-0444-1 SHORT COMMUNICATION Godfrey R. Bourne · Felix Breden · Teresa C. Allen Females prefer carotenoid colored males as mates in the pentamorphic livebearing fish, Poecilia parae Received: 15 November 2002 / Accepted: 22 June 2003 / Published online: 28 August 2003
Springer-Verlag 2003 Abstract The first results of female preference and chosen male mating success in a new model organism, the pentamorphic livebearing fish, Poecilia parae, are presented. Poecilia parae is a relative of the guppy, P. reticulata, and is assumed to have similar reproductive behavior. We tested the hypothesis that P. parae females, like female guppies, prefer caretenoid colored males as mates. Here we show that the time a female spent with males was significantly greater for carotenoid coloration in red and yellow melanzona, but time with these two morphs did not differ. The preferred red and yellow males mated significantly more often with their choosing females than did the non-preferred blue and parae males. The few blue melanzona and parae males that mated did so without performing courtship displays. Some females mated with all phenotypes including immaculata males during open group trials. Female P. parae clearly preferred males with carotenoid coloration, thereby corroborating the hypothesis. Alternative male mating tactics by blue melanzona, parae, and immaculata morphs and promiscuous mating by females also resembled features of reproductive behaviors exhibited by guppies. Introduction Theoretical constructs of sexual selection were developed to explain the evolution of highly exaggerated sexual ornaments in many organisms (Darwin 1871). Current research efforts are focused on variation among females in mate preference, and male alternative reproductive G. R. Bourne ()) · T. C. Allen Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121-4499, USA e-mail: bourne@jinx.umsl.edu Tel.: +1-314-5166674 Fax: +1-314-5166233 F. Breden Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada behaviors, because these are the determinants of the distributions of greatly elaborated male sexual ornaments across many animal taxa (Andersson 1994). Livebearing fish, especially those in the genus Poecilia, are widely used as model systems in biology because of their sexual dimorphic traits, and their marked within- and betweenspecies differences in behavior, morphology, and life histories in response to differing ecological conditions (Meffe and Snelson 1989). The reproductive behavior of many poeciliids remains a popular subject with those biologists interested in elucidating patterns of sexual selection (Meffe and Snelson 1989; Houde 1997). We wanted to know whether sexual selection operated in Poecilia parae in a manner similar to its better known relative the guppy, P. reticulata (Breden et al. 1999). While the guppy exhibits almost continuous variation in male coloration (Houde 1997), P. parae males occur in several discrete morphs (Liley 1966). Female choice for male coloration in the guppy is one of the bestdocumented cases of sexual selection (Meffe and Snelson 1989; Andersson 1994; Houde 1997). Female guppies prefer brightly colored males, especially those with carotenoid- and pteridine-based pigments (Houde 1997; Grether et al. 2001), and mate with several males (Kelly et al. 1999; Grether et. al. 2001). Thus, behavioral comparisons between guppies and P. parae should be useful for elucidating the evolution of sexually selected characters in livebearing fishes. Liley (1966) studied four species of sympatric livebearers in Guyana and reported the reproductive behaviors of guppies and P. parae to be similar. Our objective was to test the hypothesis that P. parae females, like female guppies, prefer brightly hued males with carotenoid- and pteridine-based pigments as mates. Methods Poecilia parae is a small, omnivorous livebearing fish with internal fertilization, and brightly colored males, found in coastal freshwater streams of northeastern South America east of Venezuela (Liley 1966). Within a population, males occur in five distinct morphs: a female-like immaculata, colorful melanzona (blue, red, yellow), 403 and a less colorful parae. Poecilia parae is non-territorial, associates in large mixed-sex schools, and breeds year-round (Liley 1966). Fish were collected from two connected ditches at Goed Intent (642.7350 N, 5812.4570 W), Guyana, South America, on 5 June and 21 September 2001 during the wet and dry seasons, respectively. Adult P. parae were transported to the laboratory at CEIBA Biological Center (0629.9280 N, 5813.1110 W). Two groups of three females were housed in the companion chambers of two 38-l quaternary mate-choice aquariums. Pregnant females were screened daily in order to supply appropriate parturient females for the choice tests (Liley 1966). Fish were kept on a natural daylight schedule. To determine whether recently parturient females preferred carotenoid coloration in males as mates, quaternary preference tests were conducted in the two divided aquariums (Houde 1997) in the morning and afternoon from 1828 July and 25 September7 October 2001. When placed in the middle compartment, the test female could see all four males at one end of the test aquarium, and three companion females, to provide a calming stimulus, at the other end. No immaculata males were tested because similar tests had indicated that they were never preferred (A.K. Lindholm, R. Brooks and F. Breden, unpublished data). Behaviors of the test female and males were observed 0.5 m from the glass of the companion female compartment. One digital stopwatch per male was used to record the cumulative time the test female spent orientated against the glass in front of each male compartment. Female preference for a particular male was defined as 55% of her total time within a body length of and facing that male. A parae and three melanzona males (blue, red and yellow) of equal standard length (SL; tip of snout to base of the caudal peduncle) were randomly assigned to test tank compartments. After a 10 min acclimation period, the opaque partitions were remotely removed; 2 min later the behavior of males and the female were observed for 10 min. This test was replicated to rule out spatial preferences by females; although none were found. An imprecise method (Houde 1997) was used to determine whether the preferred male had a mating advantage. The four males were given access to the test female following each replicated female preference test. The identity of the first male to mate with the female and time to mating were recorded. Mating was judged to be successful when followed by male post-copulatory jerks (Liley 1966). Females and males were used in only one replicated trial. Thirty replicated trials were conducted. Of these, ten were considered unsuccessful because the test females spent most of their time either in the central zone or in close proximity to companion females. After the afternoon replicated preference and mating success tests, an immaculata male usually not matched for size was added to the test aquarium. This open-aquarium design (Houde 1997) was used to determine which male phenotypes mated with the test female over a 14 h period. Fig. 1 Median times spent by parturient females in front of simultaneously presented male Poecilia parae morphs matched for size. Also shown are 10th, 25th, 75th, and 90th percentiles, 1 SD (top), and 1 SE (bottom) Results Females spent significantly more time with red and yellow melanzona than with blue melanzona or parae males (KW=108.15, P<0.0001; Fig. 1). Female preferences were not observed for blue melanzona or parae in any trial. There were no differences in time spent by females with red or yellow melanzona, and blue melanzona or parae (Fig. 1). Preferred red and yellow melanzona males mated significantly more often with their choosing females than the non-preferred blue melanzona and parae males (Fisher’s exact test, 2-tailed P<0.0001, n=20 pairs; Fig. 2a); however, time to mating did not differ (KW=5.49, P=0.14). No relationship was detected be- Fig. 2 a Frequencies of mating by non-preferred blue melanzona and parae males, and female-preferred carotenoid colored red and yellow melanzona males. b Frequency distribution of multiple mating by female Poecilia parae tween time spent with preferred males and time to mating (rs=–0.176, P=0.37), nor for non-preferred males (rs= 0.286, P=0.56). Open group trials indicated that six of 20 (30%) females mated with all five male morphs. Five females 404 (25%) mated with four males each—three melanzona and the parae; six (30%) mated with three males—a red, a yellow melanzona, and a parae; and three (15%) mated with two males—a red melanzona and a parae (Fig. 2b). Discussion This is the first publication of female mating choice in a new model organism, P. parae. Goed Intent females showed a clear preference for red and yellow phenotypes from four similar-sized male morphs simultaneously presented to them, and were consistent in their preferences across all trials. Why did P. parae females exhibit choice for red and yellow melanzona males, and not for blue melanzona? Female guppies and mollies, P. latipinna and P. mexicana, also prefer males with more red and yellow pigmentation (Kodric-Brown 1989; Houde 1997; Schlupp et al. 1999). These yellow and red pigments are carotenoid- and pteridine (drosopterin)-based (Fujii 1998; Grether 2000; Grether et al. 2001). Carotenoids are valuable micronutrients for vertebrates because of their immunostimulant and antioxidant activities (Britton 1995), but they must be ingested (Brush 1990). Excess carotenoids may then diffuse passively to the skin and are used as an honest indicator signal (Negro et al. 2002). Unlike carotenoids, red drosopterin pigments are synthesized by vertebrates, and tend to mask high levels of ingested carotenoids. Thus, it is posited that male poeciliids use these red pigments in a way that dilutes, but does not cancel, the indicator value of carotenoid coloration (Grether et al. 2001). Although female P. parae showed strong preferences for red and yellow melanzona males as mates, all females mated with more than one morph during open postpreference tests, some by choice and others presumably due to alternative male tactics. Whenever a female mated with more than one male it always included a parae morph. So parae males seemed to be competitive in open mixed groups, but not so during partitioned female choice tests. In any case promiscuity appears to be the rule rather than the exception in this species (Liley 1966; G.R. Bourne and T.C. Allen, personal observation), in the guppy (Kelly et al. 1999; Evans and Magurran 2000), and in the animal kingdom as a whole (Birkhead 2000). What do females gain from promiscuity? Evidence suggests benefits to the health of progeny from promiscuity (Hoogland 1998; Evans and Magurran 2000; Olsson and Madsen 2001). Some promiscuous females accrue a genetic benefit by improving their chance of finding a genetically compatible male (Newcomer et al. 1999; Blomqvist et al. 2002), and may also avoid the cost of inbreeding (Blomqvist et al. 2002; Tregenza and Wedell 2002). However, at this time we do not know what benefits accrue to individual female P. parae from promiscuous mating. It is suspected that they should be similar to the benefits documented for guppies; shorter gestation time, larger broods, progeny with better school- ing ability, and offspring with better predator escape responses (Evans and Magurran 2000). The initial measure of female preference was that of preference by association, immediately followed by mating success trials. Preferred males mated more often with their choosing females than non-preferred males. This phenomenon has already been demonstrated in binary choice tests where female guppy preferences correlated with male mating success (Bischoff et al. 1985; Dugatkin and Godin 1992; Kodric-Brown 1993), and also in other fishes (Forsgren 1992; Berglund 1993). Thus, female preference for males is equivalent to female mate choice and can be considered as such (Briggs et al. 1996). Our results suggest that female P. parae, like female guppies, prefer carotenoid pigmented males as mates, and that female preference for mates by association is equivalent to female mate choice. Preferred males mated significantly more often with their choosing females. Patterns of promiscuous mating by females, and alternative male mating tactics by blue melanzona, parae, and immaculata phenotypes resembled features of reproductive behaviors in guppies. Acknowledgements We thank the National Geographic Society, Smithsonian Institution’s Biodiversity of Guianas Program, Conservation, Food and Health Foundation, ERM Group Foundation, Norcross Wildlife Foundation, Field Museum of Natural History, and CEIBA Biological Center for support. CEIBA provided access to facilities and facilitated acquisition of research and collecting permits from the Guyana EPA. O. Clarke, M. Karl, and M. and C. Wade assisted with collecting, husbandry, and data acquisition. D.B. Tobin and R.A. Rodney assisted with the cover photograph. We also thank C. Bourne, D. Tobin, and anonymous reviewers for commenting on a previous draft of the manuscript. 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