Sex Differences in Discrimination of Shoal Size in the Guppy (Poecilia reticulata)

For a diversity of species, differences in sexual and parental roles, along with differences in body morphology, often result in males and females having different diets, distinct predators and even different patterns of habitat use. As a consequence, the two sexes often face different environmental challenges and selection may favour the evolution of sex differences in cognition. We tested this prediction in the guppy (Poecilia reticulata). Under perceived hazard, individual guppies join the larger available social group, a behaviour that is thought to minimise predation risk. In this species, females are more frequently exposed to predation and more averse to predation risk; we therefore expected greater accuracy in shoal size discrimination in females. We compared the accuracy of male and female guppies in discriminating shoals of 4 and 6 conspecifics, which represents the upper limit of discrimination for this species. Overall, we found no sex differences in the accuracy of discriminating the two shoals. However, while females showed this ability at the beginning of the test, males began to select the larger group only after several minutes. In three control experiments, we found indications that this sex difference cannot be accounted for by differences in motivation or antipredator strategies between the two sexes, suggesting female guppies are more efficient at rapidly estimating shoal size.     

Aerial Jumping in the Trinidadian Guppy (Poecilia reticulata)

Many fishes are able to jump out of the water and launch themselves into the air. Such behavior has been connected with prey capture, migration and predator avoidance. We found that jumping behavior of the guppy Poecilia reticulata is not associated with any of the above. The fish jump spontaneously, without being triggered by overt sensory cues, is not migratory and does not attempt to capture aerial food items. Here, we use high speed video imaging to analyze the kinematics of the jumping behavior P. reticulata. Fish jump from a still position by slowly backing up while using its pectoral fins, followed by strong body trusts which lead to launching into the air several body lengths. The liftoff phase of the jump is fast and fish will continue with whole body thrusts and tail beats, even when out of the water. This behavior occurs when fish are in a group or in isolation. Geography has had substantial effects on guppy evolution, with waterfalls reducing gene flow and constraining dispersal. We suggest that jumping has evolved in guppies as a behavioral phenotype for dispersal.     

Genetic Linkage Maps of the Guppy (Poecilia reticulata): Assignment of RAPD Markers to Multipoint Linkage Groups

Genetic linkage maps of the guppy (Poecilia reticulata) were constructed from independent crosses between the Tuxedo strain and a feral line (Wildtype). Segregation patterns of random amplified polymorphic DNA (RAPD) markers and phenotypic markers were investigated in F₂ offspring of Tuxedo × Wildtype and Wildtype × Tuxedo crosses. Among the 300 and 276 RAPD markers scored for the respective crosses, linkages were identified for 230 and 212, respectively. The Tuxedo × Wildtype and Wildtype × Tuxedo maps spanned 2100 Kosambi centiMorgans (cM_K) and 1900 cM_K, respectively, in 28 linkage groups. Average marker resolution was 10 cM_K. Genome length was estimated at 4410 cM_K and 4060 cM_K for the respective crosses, with an average physical distance of 166 kbp/cM_K. Several RAPD markers were closely linked to or mapped onto the loci for the sex-determining region (SdR), and the sex-linked black caudal-peduncle (Bcp) and red tail (Rdt) genes. These primary linkage maps are the initial step toward the construction of a composite high-density map to facilitate map-based cloning and marker-assisted selection of quantitative trait loci that are essential for the development of comprehensive breeding programs for the guppy.     

Validation of a Method for Quantifying Male Mating Preferences in the Guppy (Poecilia reticulata)

Male and female mating preferences are commonly inferred from association times spent with potential mates in a dichotomous‐choice test. However, this assessment method is rarely validated, particularly so for male mating preferences. Using the Trinidadian guppy (Poecilia reticulata), an important model species in the study of sexual selection, we tested whether a male’s mating preference for either of two stimulus females in a dichotomous‐choice test predicted his mating behaviours directed at the preferred female when he was allowed to swim freely with both females. First, we presented individual males with two females that differed in body length in a dichotomous‐choice apparatus in which the male could only use visual cues to assess the paired females. We quantified male mating preference as the duration of time a focal male spent associating with each female. Immediately following this test, the focal male was allowed to swim freely with both females, and we quantified the time he spent sexually pursuing each female and the number of courtship sigmoid displays and copulation attempts he directed at each female. On average, males did not significantly prefer either of the two stimulus females in either of the two tests; however, the magnitude of male preference for the larger female tended to increase as the size difference between the paired females increased. More importantly, there was a significant positive relationship between male association time in the dichotomous‐choice test and both the time spent sexually pursuing and the number of courtship sigmoid displays directed at the same female initially preferred in the dichotomous‐choice test. Collectively, these results confirm that association time measured in a dichotomous‐choice test is a reliable predictor of male mating preferences in the Trinidadian guppy.     

Molecular and Biological Characterization of a Cryptosporidium molnari-Like Isolate from a Guppy (Poecilia reticulata)

Histological, morphological, genetic, and phylogenetic analyses of a Cryptosporidium molnari-like isolate from a guppy (Poecilia reticulata) identified stages consistent with those of C. molnari and revealed that C. molnari is genetically very distinct from all other species of Cryptosporidium. This study represents the first genetic characterization of C. molnari.     

Evidence for Strategic Sex Allocation in the Guppy (Poecilia reticulata): Brood Sex Ratio and Size Predict Subsequent Adult Male Mating Success

Sex allocation theory predicts that females should produce more sons when the reproductive success of sons is expected to be high, whereas they should produce more daughters, not daughters when the reproductive success of sons is expected to be low. The guppy (Poecilia reticulata) is a live‐bearing fish, and female guppies are known to produce broods with biased sex ratios. In this study, we examined the relationship between brood sex ratio and reproductive success of sons and daughters, to determine whether female guppies benefit from producing broods with biased sex ratios. We found that sons in male‐biased broods had greater mating success at maturity than sons in female‐biased broods when brood sizes were larger. On the other hand, the reproductive output of daughters was not significantly affected by brood sizes and sex ratios. Our results suggest that female guppies benefit from producing large, male‐biased brood when the reproductive success of sons is expected to be high.     

Orange Spots as a Visual Cue for Female Mate Choice in the Guppy (Poecilia reticulata)

Previous studies have suggested that orange pigment in the color patterns of male guppies is a cue for female choice. This paper describes a manipulative experiment designed to test this hypothesis. The color patterns perceived by females were manipulated by varying the color of light used to illuminate the experimental aquaria. Orange light dramatically reduces the conspicuousness of orange spots to human observers, and probably also to female guppies. As in previous experiments, female guppies discriminated among males based on differences in the extent of orange pigment, under white, blue, and green light conditions. Under orange light, however, females no longer appeared to discriminate on the basis of orange spots. These results support the hypothesis that orange spots, rather than other correlated characteristics, are a basis for female choice under normal lighting conditions.     

Male Mating History Influences Female Mate Choice in the Trinidadian Guppy (Poecilia reticulata)

Based on the phenotype‐linked fertility hypothesis, sexual selection should favour females that can accurately assess the recent mating history of available sexual partners and preferentially avoid mating with recently‐mated males [who may be sperm depleted (SD)] so as to minimize the risk of their eggs not being fertilized. This hypothesis has received to date only limited attention and empirical support. Therefore, in the current study, we investigated experimentally whether females of a vertebrate species, the Trinidadian guppy (Poecilia reticulata), are able to assess the recent mating history of males, and thus potentially their functional fertility, and choose to avoid mating with males that appear to have recently mated and who may be sperm limited. Individual virgin females were first given a dichotomous choice between a male that had not been recently observed to interact sexually with another female (i.e. not sperm‐depleted) and another male that had been observed to interact sexually with a female (i.e. potentially sperm‐depleted) as sexual partners. Paired males were matched for body length and coloration. Immediately following this test, the focal females were subjected to a free‐swimming mate‐choice test using the same paired stimulus males. As predicted, on average, female guppies avoided the apparently recently‐mated (and potentially sperm‐depleted) male and exhibited a significant preference for the other male not recently observed mating (and thus not likely sperm limited) during both tests. We do not yet fully understand the underlying mechanisms of this preference. Therefore, further research on the particular cues that females use to assess the recent mating history and fertility status of males is required.     

Low Predictability of Colour Polymorphism in Introduced Guppy (Poecilia reticulata) Populations in Panama

Colour polymorphism is a recurrent feature of natural populations, and its maintenance has been studied in a range of taxa in their native ranges. However, less is known about whether (and how) colour polymorphism is maintained when populations are removed from their native environments, as in the case of introduced species. We here address this issue by analyzing variation in colour patterns in recently-discovered introduced populations of the guppy (Poecilia reticulata) in Panama. Specifically, we use classic colour analysis to estimate variation in the number and the relative area of different colour spots across low predation sites in the introduced Panamanian range of the species. We then compare this variation to that found in the native range of the species under low- and high predation regimes. We found aspects of the colour pattern that were both consistent and inconsistent with the classical paradigm of colour evolution in guppies. On one hand, the same colours that dominated in native populations (orange, iridescent and black) were also the most dominant in the introduced populations in Panama. On the other, there were no clear differences between either introduced-low and native low- and high predation populations. Our results are therefore only partially consistent with the traditional role of female preference in the absence of predators, and suggest that additional factors could influence colour patterns when populations are removed from their native environments. Future research on the interaction between female preference and environmental variability (e.g. multifarious selection), could help understand adaptive variation in this widely-introduced species, and the contexts under which variation in adaptive traits parallels (or not) variation in the native range.     

Effects of the Nematode Parasite Camallanus cotti on Sexual and Non-Sexual Behaviors in the Guppy (Poecilia reticulata)

Since the publication of Hamilton and Zuk's model of sexualselection there have been many studies on the effects of parasiteinfection on host mate choice and sexual behavior. In this paperI discuss the effects of nematode parasites on sexual behaviorin the guppy and the parallel effectson non-sexual behavior.This more general approach allows a test of the hypothesis thatsexual displays are particularly selected to reveal parasiteinfection in the host.     

Size‐Assortative Shoaling in the Guppy (Poecilia reticulata): The Role of Active Choice

Many fish species exhibit size‐assortative shoaling, which is often thought to be driven by predation risk. Recent fieldwork has revealed that guppies (Poecilia reticulata) are more size assorted in high‐predation populations than in low‐predation ones. However, size assortment does nonetheless occur in some low‐predation populations, suggesting that predation is unlikely the sole driving force behind size‐assortment. Here, we investigated in the laboratory the potential role of active choice in size‐assortative shoaling in wild‐caught female guppies originating from two populations of the same river system in Trinidad. Small or large focal females from each population were offered a binary choice of shoaling with either four small female conspecifics or four large ones. Observed shoaling preferences depended on the body size of the focal fish, suggesting phenotype‐mediated conflict over group composition. Large focal fish preferred to shoal with the size‐matched stimulus shoal of large fish. In contrast, small focal fish did not shoal assortatively but also preferred to shoal with larger females. Our results suggest that size‐assortative shoaling in female guppies is likely to be due to factors other than active choice, such as habitat segregation and sexual harassment.     

Genetic Diversity Within and Among Feral Populations and Domesticated Strains of the Guppy (Poecilia reticulata) in Singapore

Genetic variability within and among feral populations and cultured strains of the guppy (Poecilia reticulata) was investigated by random amplification of polymorphic DNA (RAPD) fingerprinting. Feral guppies were collected from 6 isolated populations (BT, Bukit Timah; NS, Nee Soon; TS, Tuas; MF, Mount Faber; KR, Kranji; LI, laboratory-inbred feral line), while the Tuxedo and Green Variegated strains were sampled from 2 guppy farms in Singapore. Pairwise genetic distances analyzed by unweighted pair-group method with arithmetic means revealed distinct clustering of guppy individuals into their respective populations and strains. Percentage polymorphic loci ranged from 54.96% (TS) to 68.70% (KR), while average heterozygosity ranged from 0.220 (GV) to 0.271 (KR). In contrast, TS guppies had the highest (0.850) intrapopulation genetic similarity (S), whereas KR had the lowest (0.781). Among populations and strains, S ranged from 0.703 (between GV and LI) to 0.809 (between NS and MB). The GV strain S was closer to TX (0.784) than to the feral guppies. Bootstrapped genetic distance trees depicted 3 major nodes comprising BT-TS, NS-MF, and TX-GV. Principal coordinate analysis also differentiated the 6 feral populations from the 2 cultured strains.     

The Disruption Hypothesis Does Not Explain Mate‐Choice Copying in the Guppy (Poecilia reticulata)

In some species, female mate choice is non‐independent as, under certain circumstances, females may copy the mate choice of other nearby females. One standard experimental protocol used to test for mate‐choice copying is the mate‐choice ‘reversal’ protocol. In this protocol, a focal female is allowed to choose between two males as potential mates and then is presented with an opportunity to see another female (i.e. the model female) choose the male that she did not initially choose. The focal is subsequently allowed to again choose between the same set of males. An observed reversal of her initial choice in this second preference test has been previously interpreted as evidence for mate‐choice copying. Alternatively, it has recently been proposed that environmental events, such as seeing the mate choice of nearby females that occur within the visual field of a female actively engaged in mate assessment, may ‘disrupt’ her decision‐making behavior and consequently alter the consistency of her mating preference, and may thus cause mate‐choice reversals. The disruption hypothesis predicts that if a model female is placed near the male that the focal female initially chose, the latter's mate preference would be disrupted and she would subsequently and consistently prefer the male that she initially rejected. Here we examined whether the disruption hypothesis explains mate‐choice copying in the guppy (Poecilia reticulata). Our results do not support this hypothesis, but rather provide further support for mate‐choice copying in the guppy.     

Gene Duplication and Divergence of Long Wavelength-Sensitive Opsin Genes in the Guppy, Poecilia reticulata

Female preference for male orange coloration in the genus Poecilia suggests a role for duplicated long wavelength-sensitive (LWS) opsin genes in facilitating behaviors related to mate choice in these species. Previous work has shown that LWS gene duplication in this genus has resulted in expansion of long wavelength visual capacity as determined by microspectrophotometry (MSP). However, the relationship between LWS genomic repertoires and expression of LWS retinal cone classes within a given species is unclear. Our previous study in the related species, Xiphophorus helleri, was the first characterization of the complete LWS opsin genomic repertoire in conjunction with MSP expression data in the family Poeciliidae, and revealed the presence of four LWS loci and two distinct LWS cone classes. In this study we characterized the genomic organization of LWS opsin genes by BAC clone sequencing, and described the full range of cone cell types in the retina of the colorful Cumaná guppy, Poecilia reticulata. In contrast to X. helleri, MSP data from the Cumaná guppy revealed three LWS cone classes. Comparisons of LWS genomic organization described here for Cumaná to that of X. helleri indicate that gene divergence and not duplication was responsible for the evolution of a novel LWS haplotype in the Cumaná guppy. This lineage-specific divergence is likely responsible for a third additional retinal cone class not present in X. helleri, and may have facilitated the strong sexual selection driven by female preference for orange color patterns associated with the genus Poecilia.     

Contrasting Population and Diet Influences on Gut Length of an Omnivorous Tropical Fish,the Trinidadian Guppy (Poecilia reticulata)

Phenotypic plasticity is advantageous for organisms that live in variable environments. The digestive system is particularly plastic, responding to changes in diet. Gut length is the result of a trade-off between maximum nutrient absorption and minimum cost for its maintenance and it can be influenced by diet and by evolutionary history. We assessed variation in gut length of Trinidadian guppies (Poecilia reticulata) as a function of diet, season, ontogeny, and local adaptation. Populations of guppies adapted to different predation levels have evolved different life history traits and have different diets. We sampled guppies from sites with low (LP) and high predation (HP) pressure in the Aripo and Guanapo Rivers in Trinidad. We collected fish during both the dry and wet season and assessed their diet and gut length. During the dry season, guppies from HP sites fed mostly on invertebrates, while guppies in the LP sites fed mainly on detritus. During the wet season, the diet of LP and HP populations became very similar. We did not find strong evidence of an ontogenetic diet shift. Gut length was negatively correlated with the proportion of invertebrates in diet across fish from all sites, supporting the hypothesis that guppy digestive systems adapt in length to changes in diet. Population of origin also had an effect on gut length, as HP and LP fish maintained different gut lengths even in the wet season, when their diets were very similar and individuals in both types of populations fed mostly on detritus. Thus, both environment and population of origin influenced guppies gut length, but population of origin seemed to have a stronger effect. Our study also showed that, even in omnivorous fish, gut length adapted to different diets, being more evident when the magnitude of difference between animal and plant material in the diet was very large.     

Inheritance of the snakeskin color pattern in the guppy, Poecilia reticulata

We made single-pair reciprocal crosses between the Green Snakeskin and Yellow Snakeskin domesticated strains of the guppy, Poecilia reticulata. The two snakeskin strains differ by a single autosomal gene, with the Green Snakeskin strain having the wild-type background coloration caused by the dominant gene (B), whereas the Yellow Snakeskin is homozygous for the recessive blond allele (bb). The snakeskin body and tail patterns characterizing males of these two strains are determined by two genes--Ssb and Sst--that are closely linked on the Y chromosome. The greenish-yellow tail color of the Green Snakeskin strain is mediated by an X-linked dominant gene, Grt. The recessive wild-type allele, Grt+, gives the hyaline tail color. In the Yellow Snakeskin strain, the Grt gene is expressed as a golden-yellow color as a result of the presence of the bb homozygous condition. The putative genotypes of the males and females of the Green Snakeskin strain are BB XGrt YSsb,Sst and BB XGrt XGrt, respectively. Males and females of the Yellow Snakeskin strain have the putative genotypes bb XGrt YSsb,Sst and bb XGrtXGrt, respectively. As a result of crossing over between the X and Y chromosomes, a few males and females of these two snakeskin strains may carry one or both snakeskin pattern genes (Ssb and Sst) on the X chromosome.     

The Use of Digitally-modified Videos to Study the Function of Ornamentation and Courtship in the Guppy, Poecilia reticulata

The use of video playback, digitally-modified video images, and animations is a potentially powerful tool for exploring the interactions between morphological and behavioral components of complex sexually selected traits. The utility of digitally-modified video was evaluated by the responses of females to male images in which either the behavioral components of display or the colors of ornamentation were manipulated. Females were presented with paired male images that varied only in the size of the orange or blue spot on the body (19.1% vs. 8.6%), courtship duration (7sec vs. 2.3sec), or courtship rate (3 displays min^-1 vs. 1 display min^-1). Females preferred male images with more vigorous courtship displays (both duration and rate) but did not discriminate between images differing in spot size. The results of the present study suggest that females discriminate more strongly between variation in male behavior than in their morphological attributes. The results of morphological manipulations should be interpreted with caution, however, because several factors could have contributed to the lack of female responses to color spot variation. Among them are lowered resolution of the computer image, which fails to capture the precision and complexity of the color pattern. Despite these potential difficulties, digitally-modified video promises to be a powerful method to study complex visual communication systems, where the function of and interaction between the various morphological and behavioral components is as yet poorly understood.     

Size-Dependent Female Mate Copying in the Guppy (Poecilia reticulata): Large Females are Role Models but Small Ones are not

Previous work on guppies has shown that small females copy the mate‐choice decisions of larger females, but not vice versa. We extended this work to ask, when put in a situation where they have little information available to distinguish between males, whether large females will also copy large females, and small females will copy small ones. Using Dugatkin's criteria, our study suggests that large females copy the mate‐choice decisions of large females, that small females might copy the decisions of large females, but that neither small nor large females copy small females. Our results provide support for the notion that females are more likely to copy when they perceive that there is an imbalance between their ability to assess a male's quality and the ability of another female to assess that male. However, we did not find evidence of mate copying using criteria used by other researchers.     

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

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

Geographical 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.