Character displacement in sailfin mollies, <Emphasis Type="Italic">Poecilia latipinna</Emphasis>: allozymes and behavior

Synopsis We analyzed variation in allozymes and mating preferences in 12 populations across much of the range of the sailfin molly, Poecilia latipinna. Sailfin mollies can be sympatric with its sexual parasite Amazon mollies, P. formosa. Amazon mollies must co-exist and mate with bisexual males of closely related species (including sailfin mollies) to induce embryogenesis but inheritance is strictly maternal. Where sailfin and Amazon mollies are sympatric there is evidence of reproductive character displacement as males show a significantly stronger mating preference for sailfin molly females over Amazon mollies compared to preferences of males from allopatric populations. From the allozyme data we found a moderate amount of genetic variation across all populations but this variation did not reveal significant partitioning between sympatric and allopatric populations. Additionally, we found no evidence for isolation by distance as genetic distance was not significantly correlated with geographic distance. While allozyme variation also did not significantly correlate with male mating preferences, there was a significant correlation between male mating preferences and geographic distance. This correlation between mating preferences and geographic distance may have arisen from coevolution with Amazon mollies resulting in reproductive character displacement. Taken together, the distribution of genetic and behavioral variation among sympatric and allopatric populations suggests that behavioral evolution has outpaced evolution at the allozyme loci we examined in P. latipinna.     

Patterns of inheritance of mating signals in interspecific hybrids between sailfin and shortfin mollies (Poeciliidae: Poecilia: Mollienesia)

Differences in male morphology and mating behaviors are thought to confer species sexual isolation between sailfin and shortfin species of mollies. This study used interspecific crosses between the sailfin molly, P. latipinna, and the shortfin molly, P. mexicana, to investigate patterns of inheritance of morphological traits and behavioral rates of three mating behaviors in F1 hybrid males. The two parental species showed clear species differences with respect to the length of the dorsal fin and dorsal fin ray number. First generation hybrid males were intermediate between the two parental species for dorsal fin length and fin ray number, suggesting autosomal control of this trait with little effect of dominance by genes from either parental species. Parental species showed clear species differences in their rates of courtship displays. Unlike the pattern for dorsal fin morphology, F1 hybrid males showed a clear distinction in display rates with respect to the direction of the interspecific cross. Male hybrids whose sires were P. latipinna had courtship display rates that were up to three times higher than the rates of displays performed by hybrid males whose fathers were P. mexicana. The distribution of phenotypes between the parental species and that of hybrid males sired by that parental species was nearly identical. Such a pattern suggests the influence of Y-linked genes on the inheritance of courtship display rates in mollies.     

Within and Between Species Variation in Male Mating Behaviors in the Mexican Sailfin Mollies Poecilia velifera and P. petenensis

Polymorphism in male morphology is often correlated with the expression of alternate behavioral tactics. This relationship between behavioral and morphological polymorphisms, however, is less well understood. We characterized male mating behaviors and morphological variation within and between Poecilia velifera and P. petenensis to understand mating signal evolution in the sailfin molly lineage. In addition, we examined whether differences between these species in the size range of mature males and the strength of allometry between dorsal fin size and body length could explain the variation observed in their expression of different mating behaviors. We determined each male's mating behavior profile by observing the behavior of a single male in the presence of a receptive female. We found that P. velifera showed evidence of an alternate male mating strategy, with small males generally performing only gonopodial thrusts (forced insemination attempts) towards receptive females, while large males performed courtship displays as well as gonopodial thrusts. Males of P. petenensis performed similar rates of courtship displays and gonopodial thrusts regardless of body length. Little variation existed among populations of P. velifera in mating behaviors, while males from different populations of P. petenensis showed population‐specific average rates of each mating behavior. Population differences in P. petenensis may be driven, in part, by its occurrence in more variable habitats than those occupied by P. velifera. Variation among individuals in the mating repertoire of P. velifera, but not P. petenensis, suggests that the greater range of variation in male size at maturity, as well as considerably stronger allometry between dorsal fin size and body length, may explain why males of P. velifera show the greatest degree of expression of alternate male mating behaviors when compared to other sailfin species. These results also suggest an important role of morphological polymorphisms in predicting the expression of alternate male mating behaviors.     

Patterns of Inheritance of Mating Signals in Sailfin and Shortfin Mollies (Poeciliidae: Poecilia: Mollienesia)

Divergence in mating signals is a primary factor leading to reproductive isolation, and thus, speciation. However, the genetic changes underlying such divergence are poorly understood, especially in vertebrates. We used two species of poeciliid fishes, Poecilia velifera and P. mexicana , to explore the link between genes and mating behaviors that has resulted in pre-mating reproductive isolation between these species. Using backcross hybrids created from the F1 male offspring of reciprocal interspecific crosses between a sailfin molly ( P. velifera ) and a shortfin molly ( P. mexicana ), we examined the effects of Y-linkage and autosomal contributions on the expression of two male mating behaviors: courtship displays and gonopodial thrusts. The F1 hybrid males displayed a strong influence of sire on courtship display rates, with F1 males sired by the sailfin species showing courtship display rates that were up to three times higher than the rates of displays performed by F1 males sired by the shortfin species. These results suggest a Y-linked genetic effect on the expression of courtship display behavior. Comparisons between backcross hybrid males with sailfin Y-chromosomes or shortfin Y-chromosomes suggested that the interaction of autosomal genes also influences the inheritance of courtship display rates. Sailfin autosomal genes significantly increased the probability of performing courtship displays for hybrid males, and increased display rate for males from the sailfin Y-chromosome line. Autosomal genes had less of an impact on gonopodial thrusting behavior, however, thrust rates did significantly decrease with an increasing proportion of sailfin autosomes in males from the shortfin Y-chromosome line. These results suggest that the inheritance of species differences in mating signals between shortfin and sailfin mollies involves both genes found on the Y-chromosome and autosomal gene influences on their expression.     

Behavioural allometry and interdemic variation in sexual behaviour of the sailfin molly,Poecilia latipinna (Pisces: Poeciliidae)

Sailfin mollies, Poecilia latipinna, exhibit remarkable levels of intraspecific variation in reproductive behaviour. Larger males exhibit higher rates of courtship and lowered rates of gonoporal nibbling and gonopodial thrusting (forced copulation attempts). Larger males have relatively longer and higher dorsal fins than smaller males. The dorsal fin is a prominent component of the courtship display. Variation in fin measurements, behaviour patterns, and body size of mature males is continuous, and fin shape and behaviour patterns are allometrically related to body size. The allometric pattern is displayed by individual traits as well as by the morphological or behavioural traits in ensemble. Eight populations of mollies from markedly distinct habitats exhibited similar consistent levels of intrademic variation in the size of mature males. Detailed studies on three populations showed that dorsal fin shape could be described by the same regression relationship in all populations, and indicted that a male's shape was determined by his absolute body size. By contrast, there was some variation among populations in the relation of behaviour patterns to male body size. The pattern of this interdemic variation indicated that a male's behaviour patterns were influenced by his relative size in a population. Successful inseminations following forced copulations were rare. The average size of successful males was smaller than the average size of unsuccessful males in all three populations. These results indicated that successful insemination through forced copulation was, like behaviour patterns generally, more a function of the relative size of the male, than his absolute size.     

Lack of species discrimination based on chemical cues by male sailfin mollies, <Emphasis Type="Italic">Poecilia latipinna</Emphasis>

When making mating decisions, individuals may rely on multiple cues from either the same or multiple sensory modalities. Although the use of visual cues in sexual selection is well studied, fewer studies have examined the role of chemical cues in mate choice. In addition, few studies have examined how visual and/or chemical cues affect male mating decisions. Male mate choice is important in systems where males must avoid mating with heterospecific females, as is found in a mating complex of Poecilia. Male sailfin mollies, Poecilia latipinna, are sexually parasitized by gynogenetic Amazon mollies, P. formosa. Little is known about the mechanism by which male sailfin mollies base their mating decisions. Here we tested the hypothesis that male sailfin mollies from an allopatric and a sympatric population with Amazon mollies use multiple cues to distinguish between conspecific and heterospecific females. We found that male sailfin mollies recognized the chemical cues of conspecific females, but we found no support for the hypothesis that chemical cues are by themselves sufficient for species discrimination. Lack of discrimination based on chemical cues alone may be due to the close evolutionary history between P. latipinna and P. formosa. Males from populations sympatric with Amazon mollies did not differentially associate with females of either of the two species when given access to both visual and chemical cues of the females, yet males from the allopatric population did associate more with conspecific females than with heterospecific females in the presence of both chemical and visual cues. The lack of discrimination by males from the sympatric population between conspecific and heterospecific females based on both chemical and visual cues suggests that these males require more complex combinations of cues to distinguish species, possibly due to the close relatedness of these species.     

Female Preference for Male Lateral Projection Area in the Shortfin Molly, Poecilia mexicana: Evidence for a Pre-existing Bias in Sexual Selection

Sailfin molly (Poecilia latipinna) males possess a large dorsal fin (sailfin) and perform an elaborate courtship display. Females prefer to associate and mate with males of greater body and sailfin size. Evidence supports a single origin for the sailfin species complex from a shortfin ancestor. Unlike sailfin species, males of the shortfin species complex are sexually monomorphic in fin size and exhibit little or no courtship behavior. In this study, we tested the pre‐existing bias and lateral projection area (LPA) hypotheses for sexual selection by examining female mating preferences in the shortfin molly, P. mexicana. Specifically, we presented females with pairs of dummy males differing in: (1) dorsal fin and body size together (holding fin:body size ratio constant); (2) body size (holding dorsal fin size constant); (3) dorsal fin size (holding body size constant); and dorsal fin:body size ratio (holding total LPA constant). Females spent more time near dummies of greater body and dorsal fin size. The preference functions based on the first three sets of stimuli showed a similar pattern: the greater the LPA difference between paired dummies, the stronger the preference for the larger of the two. However, in the fourth experiment, neither fin size, body size, nor any particular dorsal fin + body size combination was preferred. These findings support the LPA hypothesis suggesting that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. Moreover, these data are consistent with results obtained in an identical series of experiments conducted on P. latipinna. The preference for increased male dorsal fin size/LPA by both female P. latipinna and P. mexicana supports the pre‐existing bias hypothesis. Thus, a bias for increased male LPA and consequent selection for enlarged dorsal fins may have preceded the appearance of the sailfin trait within the Molliensia lineage.     

Do I Know You? Species Recognition Operates Within and Between the Sexes in a Unisexual–Bisexual Species Complex of Mollies

Male sailfin mollies (Poecilia latipinna) can be sexually parasitized by closely related, unisexual, gynogenetic Amazon mollies (Poecilia formosa). This study examined possible cues used by male P. latipinna to distinguish between conspecific females and sympatric, heterospecific P. formosa. Digital photos were used to create models to test male P. latipinna preference for model female P. latipinna and P. formosa with a full suite of traits and altered models of P. latipinna and P. formosa. Male P. latipinna significantly preferred models of either species over no stimulus, demonstrating that models elicit a male response. Males also significantly preferred female P. latipinna models over P. formosa models. We also examined species recognition by female sailfin mollies using the same models, and found that female sailfin mollies significantly preferred to associate with female P. latipinna over P. formosa. These results taken together suggest that the use of fish models yield results similar to those studies using live stimuli. Male preference was then tested for unaltered vs. altered models in the following combinations: (i) P. formosa vs. P. formosa with a female P. latipinna fin; (ii) P. formosa vs. P. formosa with a female P. latipinna lateral spot pattern; (iii) P. formosa vs. P. latipinna with a P. formosa fin and their spotless lateral pattern. Males did not significantly prefer models with any isolated traits over the unaltered P. formosa models. Thus, males may be using traits other than the ones isolated for species recognition or males may be using a suite of multiple traits to recognize conspecific females.     

Female Preferences for Sailfin and Body Size in the Sailfin Molly, Poecilia latipinna

We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates.     

Male Sailfin mollies (Poecilia latipinna) copy the mate choice of other males

Female mate-copying has been shown to occur between heterospecifics:female sailfin mollies Poecilia latipinna copy the choice oftheir gynogenetic associates, Amazon mollies P. formosa. Femalemate-copying thus contributes to the maintenance of this asexual-sexualspecies complex by providing an advantage to male sailfin molliesthat mate with Amazon females; because of mate-copying thesemales increase their attractiveness to conspecific females.Here we show that male mate-copying, an unreported phenomenon,also occurs and that it can reverse male preferences for conspecificfemales. Male mate-copying should also contribute to the maintenanceof gynogens and might be advantageous in allowing males a meansto rapidly assess female receptivity although sometimes resultingin heterospedfic matings.     

Trade‐offs between salinity preference and antipredator behaviour in the euryhaline sailfin molly Poecilia latipinna

Salinity preference and responses to predatory chemical cues were examined both separately and simultaneously in freshwater (FW) and saltwater (SW)‐acclimated sailfin mollies Poecilia latipinna, a euryhaline species. It was hypothesized that P. latipinna would prefer FW over SW, move away from chemical cues from a crayfish predator, and favour predator avoidance over osmoregulation when presented with both demands. Both FW and SW‐acclimated P. latipinna preferred FW and actively avoided predator cues. When presented with FW plus predator cues v. SW with no cues, P. latipinna were more often found in FW plus predator cues. These results raise questions pertaining to the potential osmoregulatory stress of salinity transitions in euryhaline fishes relative to the potential fitness benefits and whether euryhalinity is utilized for predator avoidance. This study sheds light on the potential benefits and consequences of being salt tolerant or intolerant and complicates the understanding of the selection pressures that have favoured the different osmoregulatory mechanisms among fishes.     

Examination of boldness traits in sexual and asexual mollies (<Emphasis Type="Italic">Poecilia latipinna</Emphasis>, <Emphasis Type="Italic">P. formosa</Emphasis>)

Considering the high costs of sexual reproduction (e.g., the production of males), its maintenance and predominance throughout the Animal Kingdom remain elusive. Especially the mechanisms allowing for a stable coexistence of closely related sexual and asexual species are still subject to a lively debate. Asexuals should rapidly outnumber sexuals due to higher population growth rates, unless they face some disadvantages. Here, we investigate potential differences in feeding behavior in a system of sexual (sailfin mollies, Poecilia latipinna) and coexisting gynogenetic fishes (Amazon mollies, Poecilia formosa). In two different experiments, we tested for differences in behavioral traits associated with boldness. Bold individuals take higher risks for gains in resources, so shyer individuals should be less competitive. Our study was motivated by the recent finding that P. formosa are less likely to be preyed upon by piscine predators than P. latipinna. We asked whether this result is indicative of low boldness in P. formosa. However, no differences between the two species were detectible in our behavioral experiments measuring (a) time to emerge from shelter to explore a novel environment, (b) latency time until feeding in a novel environment, and (c) recovery time until feeding restarted after a simulated predator attack. Furthermore, different boldness measures were not correlated with each other within individuals.     

PHENOTYPIC PLASTICITY IN THE SAILFIN MOLLY,POECILIA LATIPINNA (PISCES: POECILIIDAE). II. LABORATORY EXPERIMENT

Field studies indicate that the influence of environmental factors on growth rate and size and age at maturity in sailfin mollies (Poecilia latipinna) is inconsistent over time and suggest that the marked interdemic variation in male body size in this species is the result of genetic variation. However, the role of specific environmental factors in generating phenotypic variation must be studied under controlled conditions unattainable in nature. We raised newborn sailfin mollies from four populations in laboratory aquaria under all possible combinations of two temperatures, three salinities, and two food levels to examine explicitly the influence of these environmental factors. Males were much less susceptible than females to temperature variation and were generally less plastic than females in terms of all three traits. Members of both sexes matured at larger sizes and at later ages in less saline and in cooler environments. Food levels were not sufficiently different to affect the traits we studied. The effects of temperature and salinity were not synergistic. Males from different populations exhibited different average ages and sizes at maturity, but females did not. The magnitudes of the effects we found were not substantial enough to account for the consistent interdemic differences in male and female body size that have been observed previously. Our results also indicate that no single environmental factor is solely responsible for the environmental effects observed in field experiments on growth and development. These studies, together with other work, indicate that the strongest sources of interdemic variation are genetic differences in males and differences in postmaturation growth and survivorship in females.     

Effects of temperature and salinity on the life history of the sailfin molly (Pisces: Poeciliidae): lipid storage and reproductive allocation

While the life history traits of animals usually exhibit substantial phenotypic plasticity, such plasticity might reflect either a simple alteration in the level of energy accrual and use or a genuine shift in energy allocation tactics between environmental conditions. The latter would represent genuine plasticity in the life history itself, and thus it is important to distinguish which of these two processes underlies the observed plasticity of life history traits. We investigated this issue by examining the effects of temperature and salinity variation during ontogeny on the allocation of biomass and lipid storage in male sailfin mollies, Poecilia latipinna. We raised males from four natural populations from birth to maturity in controlled laboratory conditions. Neither distinct temperatures (23 or 29°C) nor different salinity regimes (2, 12, or 20 parts per thousand) affected body mass, although males from different populations differed substantially in body mass. However, males raised at the higher temperature had a greater allocation of biomass to testis and a lower allocation to viscera mass. The amount of stored lipid was altered by temperature variation but the direction and magnitude of the effect varied substantially among males from the different populations. Salinity variation affected neither biomass allocation nor the level of lipid storage. These results indicate that male mollies possess a flexible developmental program with respect to temperature that canalizes body size and alters the allocation of biomass among competing demands for reproductive readiness and capacity for energy storage. Received: 25 November 1996 / Accepted: 1 December 1997     

Geographical variation in reproductive character displacement in mate choice by male sailfin mollies

Female Amazon mollies, Poecilia formosa, are a unisexual species that reproduce by gynogenesis. They must coexist and mate with males of other species (usually the mollies Poecilia latipinna or Poecilia mexicana) to induce embryogenesis, but inheritance is strictly maternal. We examined the mating preference of the male sailfin molly, P. latipinna, for female sailfin mollies versus Amazon mollies, P. formosa. We compared the mating preferences of sympatric and allopatric populations collected throughout the Gulf Coast of North America. Male P. latipinna from six populations sympatric with Amazon mollies showed a significantly greater strength of preference for conspecific sailfin females than males from five populations that were allopatric with Amazon mollies. These results provide strong evidence for reproductive character displacement of male mate choice in sympatry. Furthermore, the large geographical range of populations that we tested revealed variation among populations within sympatry and allopatry, indicating that it is important to evaluate a large number of populations when examining reproductive character displacement.     

Behavioural and life‐history regulation in a unisexual/bisexual mating system: does male mate choice affect female reproductive life histories?

In theory, unisexual taxa have an advantage over ecologically similar bisexual species because unisexuals produce twice as many daughters and, thus, should quickly outcompete coexisting bisexuals in any given population. For sperm‐dependent unisexual (gynogenetic) species, stable coexistence with their bisexual sperm donors can be postulated if male mate choice puts unisexual females at a disadvantage through sperm limitation, thus halving their reproductive output compared to bisexuals (‘behavioural regulation hypothesis’). We tested for a potential life‐history signature of male mate choice in a system of coexisting bisexual sailfin mollies (Poecilia latipinna) and gynogenetic Amazon mollies (Poecilia formosa). Specifically, we gave P. latipinna males an opportunity to freely interact (and mate) with both types of females and, after 25 days, quantified the proportion of (1) females with sperm in their genital tract and (2) pregnant females. A higher proportion of P. latipinna females (53.7%) had sperm in their genital tract (compared to only 25.9% in P. formosa), corroborating a previous study on wild‐caught fish. This translated into a higher frequency (42.6%) of P. latipinna females being pregnant (compared to 29.6% in P. formosa); however, among pregnant females, no significant differences between species in reproductive life‐history traits (such as offspring number or size) were uncovered. Hence, although the findings of the present study confirm that male discrimination against unisexual females leads to reduced reproductive output in unisexuals, the observed magnitude of differences in targeted life histories between the two types of females is unlikely to be the sole factor regulating stable coexistence in this system. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 598–606.     

Are you more than the sum of your parents’ genes? Phenotypic plasticity in a clonal vertebrate and F1 hybrids of its parental species

All known vertebrate clones have originated from hybridization events and some have produced distinct evolutionary lineages via hybrid speciation. Amazon mollies (Poecilia formosa) present an excellent study system to investigate how clonal species have adapted to heterogeneous environments because they are the product of a single hybridization event between male sailfin mollies (Poecilia latipinna) and female Atlantic mollies (Poecilia mexicana). Here, we ask whether the hybrid species differs from the combination of its parental species’ genes in its plastic response to different environments. Using a three-way factorial design, we exposed neonates produced by Amazon mollies and reciprocal F1 hybrid crosses to different thermal (24°C and 29°C) and salinity (0/2, 12, and 20 ppt) regimes. We measured various ontogenetic and life history characteristics across the life span of females. Our major results were as follows: (1) Reaction norms of growth and maturation to temperature and salinity are quite similar between the two hybrid crosses; (2) Amazon molly reaction norms were qualitatively different than the P. latipinna male and P. mexicana female (L×M) hybrids for the ontogenetic variables; (3) Amazon molly reaction norms in reproductive traits were also quite different from L×M hybrids; and (4) The reaction norms of net fertility were very different between Amazon mollies and L×M hybrids. We conclude that best locale for Amazon mollies is not the best locale for hybrids, which suggests that Amazon mollies are not just an unmodified mix of parental genes but instead have adapted to the variable environments in which they are found. Hybridization resulting in asexuality may represent an underappreciated mechanism of speciation because the unlikely events required to produce such hybrids rarely occur and is dependent upon the genetic distance between parental species.     

HIERARCHICAL ORGANIZATION OF GENETIC VARIATION IN THE SAILFIN MOLLY,POECILIA LATIPINNA (PISCES: POECILIIDAE)

Twenty-two percent of all allozyme variation documented in the sailfin molly (Poecilia latipinna) was attributable to regional differences, while only 3% was attributable to differences among demes within regions. Of the variation documented in a given region, 6–12% was attributable to variation among demes. Cluster analyses supported these conclusions quantitatively. Spatial-autocorrelation analyses offered more explicit support: demes separated by increasingly greater distances were increasingly dissimilar. Analyses using F statistics and rare alleles suggest “effective gene flow rates” (the product of effective population size and gene flow rate) of approximately 4, a level more than sufficient to prevent local independence of gene-frequency dynamics. These results, taken together, suggest that mollies do not have a population structure conducive to the operation of Wright's shifting-balance process and make the striking patterns of interdemic variation in body size and sexual behavior observed in this species all the more interesting.     

The effect of rearing temperature on body shape and meristic characters in zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) juveniles

Considering its immediate costs of producing dispensable males, the maintenance of sexual reproduction is a major paradox in evolutionary biology. Asexual lineages that do not face such costs theoretically should replace sexuals over time. Nonetheless, several systems are known in which closely related sexual and asexual lineages stably coexist. In the present study, we studied a sexual/asexual mating complex of a sperm-dependent parthenogenetic fish (amazon molly, Poecilia formosa) and its sexual congeners, the sailfin molly P. latipinna and the Atlantic molly P. mexicana. We asked whether differences in feeding behavior could contribute to their stable coexistence. We conducted a laboratory experiment to compare feeding efficiencies and also measured the competitive abilities between the two reproductive forms. Additionally, we measured gut fullness of fishes caught in natural habitats. Contrary to our predictions, we could not find P. formosa to be less efficient in feeding. We argue that food competition in mollies plays a minor role in mediating coexistence between closely related asexual and sexual mollies.     

Innate and Learned Shoaling Preferences Based on Body Coloration in Juvenile Mollies,Poecilia latipinna

Shoaling offers fish enhanced protection from predators through a phenomenon known as the confusion effect. This phenomenon depends on a high degree of phenotypic homogeneity within a shoal, which may confuse predators that have difficulty in targeting a single individual as prey. Accordingly, fish typically choose shoalmates with similar phenotypic characteristics to themselves. In the molly (Poecilia latipinna), dramatic differences in body coloration have been shown to affect shoalmate choice in adults. Here, we show that juvenile mollies (50 d old) were capable of shoaling and that early experience impacted shoalmate choice. When raised in isolation, mollies chose shoalmates with similar body coloration to their own. When raised with other juvenile mollies, test fish chose to associate with individuals of the same coloration as the fish with whom they had been reared. These results show that P. latipinna are capable of the behavioral plasticity that has been demonstrated in other fish species, and that early experience affects the impact of body coloration on shoaling decisions in this species.