The first Poeciliid Fishes Virtual Forum was held on February 26, 2021. On this site you can find the program of talks, corresponding abstracts, and links to the video recordings.
- Emily Kane: On the heritability of integrated biomechanical phenotypes in Trinidadian guppies (Poecilia reticulata)
- Samantha West: Audience effects in Girardinus metallicus
Morning: Session 1
Biomimetic robots for the study of poeciliid social behavior
David Bierbach (Humboldt Universität zu Berlin)
With Tim Landgraf and Jens Krause
Biomimetic robots are an extremely effective tool for studying animal social behavior, as they can help elucidate the important characteristics necessary to engage and interact with their live animal counterparts. I will outline how differentially controlled biomimetic robots can be used to answer questions on how animals differ in social responsiveness, what characteristics define leadership and how individual differences in movement speed affect collective behavior. Here, poeciliid fishes are very useful study organisms as they accept those robots as conspecifics and interact naturally with them. Further I will show some of the prerequisites that robots need to serve as a tool for the study of animal social behavior and how biomimetic robots help to reduce numbers of live animals used during experiments, thus promoting the 3R principle common in animal research.
Sexual selection under imminent predation risk in the Trinidad guppy
Alexandra Glavaschi (University of Padova)
With Silvia Cattelan, Alessandro Devigili, and Andrea Pilastro
Predation risk is a major factor affecting sexual selection dynamics in the Trinidad guppy through various mechanisms. We used a paired experimental design in which the same males were allowed to interact and mate with different groups of females both in the presence and the absence of predation cues to show that, by changing female behavior, predation risk may increase the opportunity for sexual selection. Building on these results, we conduct multivariate selection gradient analyses aimed at quantifying the effect of predation risk on the strength and direction of sexual selection on pre- and postcopulatory traits associated with male reproductive success in the guppy. We reveal complex patterns of disruptive and stabilizing selection both in the presence and absence of predation risk and discuss these findings in the broader context of environmental effects on total sexual selection.
Eastern mosquitofish (Gambusia holbrooki) color morphs respond differently to socially relevant cues
Tanja Zerulla (Florida International University)
With Philip Stoddard
Eastern Mosquitofish (Gambusia holbrooki) exhibit a polychromism: males are either silver or spotted. In social groups, spotted males exhibit high levels of aggression towards silver males and females, but recent work suggests that spotted males are not inherently hyper-aggressive. Instead of a difference in innate aggression, I hypothesized that the male mosquitofish morphs respond differently to socially relevant cues. I recorded aggressive and submissive behaviors for dyads of every color-combination across a range of size differences to determine social conflict outcomes. Larger relative size predicted dominance in same-color dyads, but color was more important than size in different-color dyads. Silver males exhibited increased submission or reduced aggression towards spotted opponents, making spotted males appear hyper-aggressive. Spotted males maintained their aggression levels and thus dominated silver males regardless of size. These morphs thus respond differently to socially relevant cues. My ongoing studies investigate the genetic mechanisms underlying these conflict behaviors.
Distinct effects of the social environment on life history and behavior
Liz Lange (Duke University and Florida State University)
With Margaret B. Ptacek, Joseph Travis, and Kimberly A. Hughes
Social environment has far reaching effects on phenotypes as it can affect both the development and fitness consequences of traits. We assessed the effects of variation in social environment during development on life history and sized-based male alternative mating tactics in the sailfin molly, Poecilia latipinna. We found that molly life history traits and alternative mating behaviors were affected by social environment during development. However, the most influential factors of the social environment differed between life history traits and behavior. The most influential aspect of social environment for life history traits was whether social partners were juvenile or adult. In contrast, alternative mating behaviors were most influenced by interactions between social environment, male body size, and the size of a male’s father. Our results suggest that social environment affects many phenotypes, but the pertinent aspects of the social environment differ between traits.
Morning: Session 2
Behavioral and anatomical estimations of visual acuity in the green swordtail Xiphophorus hellerii
Eleanor Caves (University of Exeter)
With Fanny de Busserolles and Laura A. Kelley
Numerous studies have demonstrated the importance of features such as sword length and body size in swordtail mate assessment, but how well swordtails can resolve spatial detail—their visual acuity—is unstudied. We quantified visual acuity in male and female Xiphophorus hellerii using anatomical and behavioral methods. First, by measuring the peak density of ganglion cells in retinal wholemounts, we estimated anatomical acuity to be approximately 3 cycles/degree (cpd) in both sexes, closely aligning with predicted acuity based on eye size. However, a behavioral optomotor assay found significantly lower acuity in males (~1 cpd) than females (~3 cpd). To further investigate potential differences in behavioral acuity between sexes, we trained individuals in a two-choice assay, from which we present preliminary findings. Overall, acuity in swordtails is low (~ 1/20th that of humans), suggesting that swordtails require close viewing distances to resolve differences in traits like sword length and body size.
Home is wherever you find food: comparative gut-content analysis of invasive mosquitofish from Italy and Spain
Sara Pirroni (Royal Holloway University of London)
With Laura de Pennafort Dezen, Francesco Santi, and Rüdiger Riesch
Eastern mosquitofish (Gambusia holbrooki) are among the most widely introduced freshwater species globally. To gain a better understanding of feeding patterns in non-native populations, and which local factors may influence them at the population level, we sampled 163 specimens from nine invasive populations in Italy and Spain. We quantified gut contents and collected local environmental and climate variables to investigate their contribution to dietary differences. Our results confirm eastern mosquitofish to be omnivores with a predilection for detritus and Cladocera, however, not a single diet item was shared amongst all populations. We also identified size- and population-specific differences in feeding patterns. Yet, while size-effects were most likely linked to sexual dimorphism, none of our environmental and climatic variables helped explain population differences. Nonetheless, the large amount of dietary flexibility uncovered in our study further helps explain the ubiquity of invasive mosquitofish across Italy and Spain (and elsewhere).
Mode of maternal provisioning in the fish genus Phalloceros
Eugenia Zandona (Universidade do Estado do Rio de Janeiro)
With Maja Kajin, David Reznick, Bruno Gorini-Pacheco, Jeferson R. Amaral, Rosana Mazzoni, and Paulo A. Buckup
Poeciliids show very diverse modes of maternal provisioning, but little is known about its evolution. Comparative studies can shed light on the placenta adaptive value. We investigated patterns of embryonic growth in 7 Phalloceros species from Brazil. We also analyzed if matrotrophy is affected by environmental factors such as predation. We found that embryo weight initially decreased and later increased rapidly, resulting in approximately 3-fold weight gain from fertilization to birth. This embryo growth function was conserved across populations and species. Phalloceros have a unique mode of maternal provisioning among poeciliids, which could be originating from mother-offspring conflict for regulating resources provisioning. Predation affected multiple life histories in Phalloceros: high predation populations were more matrotrophic, had slimmer bodies and longer gonopodium compared to low predation populations. Higher matrotrophy could allow higher fecundity and higher performance in escaping predators. Our study shed light on important selective forces acting on placenta evolution.
A large and diverse autosomal haplotype is associated with sex-linked color polymorphism in the Trinidadian guppy
Josephine Paris (University of Exeter)
James Whiting, Mitchel Daniel, Joan Ferrer Obiol, Paul Parsons, Mijke van der Zee, Helen F Rodd, Christopher Wheat, Kimberly Hughes, and Bonnie Fraser
Guppy ales are colorful to attract mates but this color increases predation risk leading to sex conflict. Since color pattern is often inherited faithfully from father to sons, it has been presumed that color genes are physically linked to the sex determining loci, as a ‘supergene’, but identifying this has been difficult. Here, we examined four ‘Iso-Y lines’ of guppies, where color was inherited along the patriline, but backcrossed into the stock population every generation for 40 generations. This breeding design should homogenize the genome, except for regions associated with color. Using a whole genome, pool-sequencing approach, we uncovered a surprising architecture for color pattern evolution. Iso-Y lines were consistently divergent at a large diverse haplotype (~4.7Mb) on an autosome, not the sex chromosome. This haplotype also showed sex-specific diversity when we examined the natural source population. We hypothesize that color polymorphism in guppies is driven by Y-autosome epistasis.
Mid-day: Session 1
Who is observing me when I eat? Audience effect on foraging guppies
Natalia Tepox-Vivar & Guadalupe López-Nava (Benemérita Universidad Autónoma de Puebla)
With Palestina Guevara-Fiore
Audience effect can influence the behavior of a forager, which has been mainly studied in primates and birds. We tested the effect of the absence and presence of an unfamiliar audience (females, males and their combination), near or far from a foraging patch, on the foraging behavior of male and female guppies (Poecilia reticulata). We quantified the latency of focal guppies to start feeding, their feeding frequency, the time they spent near the audience and their mobility. Females fed sooner and more in the presence of a female audience. While males started feeding sooner with any type of audience near the food patch and less if the audience contained males. Both sexes spent more time near the audience compartment if there were conspecifics present. Our results show for the first time how an audience affects differently the foraging behavior of females and males’ fish.
Intraspecific variation in response to chemical alarm cues in Brachyrhaphis rhabdophora
Alexandra Duffy (Brigham Young University)
With Jerald Johnson
The ability to detect and assess risk is paramount to an organism’s fitness. Chemical alarm cues emitted by injured individuals are a reliable indicator of an imminent threat and typically elicit strong, innate antipredator responses in fish. However, experience and local adaptation may shape how prey choose to respond to these cues. Using wild-caught populations of Brachyrhaphis rhabdophora from Costa Rica, we tested our hypothesis that individuals from high-predation environments are more sensitive to alarm cues. After exposure to conspecific alarm cues, B. rhabdophora decreased swimming activity. Further, individuals from low-predation environments appear to be less sensitive to alarm cues compared to individuals from high-predation environments, in addition to slight variation between males and females from both populations. This was the first test of alarm cue recognition in B. rhabdophora and contributes to our broader understanding of how chemosensory information and selective environment shape predator-prey interactions.
Sexual selection and polymorphism in Girardinus metallicus
Crystal Castillo (California Polytechnic State University)
With Hannah K. Brown, Amy P. Knudsen, Elvira Olivera-Angon, and Gita R. Kolluru
Girardinus metallicus is a poeciliid endemic to Cuba that exhibits male-specific, melanin-based polymorphism that extends to mating behavior. Melanic, “black morph” males are rare in the wild and court females, whereas common, “plain morph” males lack prominent melanin coloration and sneak copulate. We hypothesize that opposing sexual selection favoring black morph males, opposed by natural selection favoring plain morph males, maintains the rare melanic morph at low frequencies across populations. We performed dichotomous choice and direct interaction tests to assess sexual selection across morphs. We found no evidence for female choice favoring black morph males; however, black morph males were more aggressive towards males and had higher mating activity, supporting our hypothesis that intrasexual selection favors black morph males. Future studies will address whether natural selection by predators favors plain morph males, and why black morph males are rare despite their sexual selection advantage.
Male mating pursuit is thwarted by female avoidance behavior in Xenophallus umbratilis: testing a prerequisite for negative frequency-dependent selection
Mary-Elise Nielsen (Brigham Young University)
With Erik S. Johnson and Jerald B. Johnson
Among livebearers, Xenophallus umbratilis unique because it is one of few species to exhibit handedness in the male gonopodium. Males in this species are either right- or left-handed for this trait, with the terminus of the gonopodium having either a dextral or sinistral twist. Previous work demonstrated a correlation between gonopodial morph and lateralized inspection behavior, likely due to eye side-bias, in this species. Given this and the gonopodium’s critical role in reproductive fitness, we test the hypothesis that gonopodial morph is tied to side-bias in male pursuit mating behavior. Additionally, since female livebearing fishes typically actively resist forced copulation attempts, we test the hypothesis that Xenophallus females also employ side-bias behavior to counteract male mating pursuit and provide the foundation for sexual conflict in the species. Lastly, we report how results from this research point towards negative frequency dependent selection as a mechanism for maintaining polymorphism in the gonopodium.
Mid-day: Session 2
Compiling 40 years of guppy research to investigate the determinants of parallel evolution
Alexis Heckley (McGill University)
With Allegra Pearce, Kiyoko Gotanda, Andrew Hendry, and Krista Oke
Studies of parallel evolution have been essential for advancing our understanding of adaptation and natural selection, and few species have contributed as much to our understanding of parallelism as have Trinidadian guppies (Poecilia reticulata). Recent studies, however, have suggested that parallel evolution can often be weak and/or variable. Due to the vast research that has been conducted on guppy ecology and evolution, this system provides an excellent opportunity for attempting to disentangle the determinants of parallelism. Here, we conduct an analysis of papers that have measured guppy traits in each of two high and low predation environments. In doing so, we intend to break down our assessment of parallelism to consider how ecology and evolutionary history (along with sex and different trait types) impact parallelism in Trinidadian guppies.
Cascading indirect genetic effects in a clonal vertebrate
Amber Makowicz (Florida State University)
With David Bierbach, Christian Richardson, and Kimberly A. Hughes
Understanding how individual differences arise and how their effects propagate through social groups are fundamental questions in behavioral biology. Genetic variation among social partners can influence individual phenotypes, creating individual differences that might then have cascading effects in social groups. Using a clonal species, the Amazon molly, we test the hypothesis that such indirect genetic effects (IGE) propagate beyond individuals that experience them firsthand. We tested this hypothesis by exposing genetically identical females to social partners of different genotypes, and then moving these individuals to new social groups in which they were the only member to have experienced the IGE. Our data reveal that IGE can propagate beyond the individuals that directly experience them in Amazon mollies and possibly in many group-living species. Theoretical and empirical expansion of the quantitative genetic framework developed for IGE to include carry-over effects will facilitate understanding of social behavior and its evolution.
The role of plasticity in facilitating colonization of novel environments
Nick Barts (University of Pittsburgh)
With Nichole Nieves, Shawn Trojan, Lenin-Arias Rodriguez, Joanna Kelley, and Michi Tobler
Identifying the traits that allow organisms to colonize and persist in novel environments remains a key challenge in biology. There are two mechanisms that facilitate the ability of species to invade and adapt to novel stressors: 1) rapid post-colonization evolution as a result of natural selection acting on pre-existing genetic variation and 2) a trait adaptive in the original environmental context facilitates persistence in another (pre-adaptation). We conducted a comparative transcriptomics experiment to identify the potential role of gene expression plasticity in facilitating colonization of hydrogen sulfide (H2S)-rich environments by non-sulfidic freshwater species that differ in colonization success. We found evidence for adaptive plasticity in all species, with some genes being uniquely shared by successful colonizers. By far, evidence of maladaptive plasticity outnumbered evidence of adaptive plasticity in our dataset. Overall, the findings of this study suggest that pre-adaptation and post-colonization evolution play important roles in colonization of extreme habitats.
Identifying regulatory mechanisms affected by hydrogen sulfide in an extremophile fish
Kerry McGowan (Washington State University)
With Jake Landers, Caitlyn Patel, Sascha Duttke, Courtney N. Passow, Ryan Greenway, Michael Tobler, and Joanna L. Kelley
The fish Poecilia mexicana (Atlantic molly) has colonized springs in southern Mexico containing hydrogen sulfide (H2S), a toxic gas. In sulfidic populations, there are gene expression changes related to H2S detoxification and aerobic respiration compared to non-sulfidic populations. However, the regulatory mechanisms that underlie these changes are unknown. We hypothesized that the expression of transcription factor genes and their targets that affect the sulfidic phenotype would vary in P. mexicana gill tissues in the presence/absence of H2S. We used network analyses to identify genes that correlated with H2S and a literature search to classify those that affected H2S detoxification. We also hypothesized that newly transcribed RNAs captured using capped small RNA-sequencing would reveal expression differences between sulfidic and non-sulfidic populations using adult gill tissues. Finally, we will use whole genome data to identify promoter regions under selection upstream from H2S-related genes using a null model that accounts for background selection.
Afternoon: Session 1
Exploring the genetic architecture of thermal tolerance in Xiphophorus and new cell culture tools for livebearers
Cheyenne Payne (Stanford University)
With Molly Schumer
As global temperatures rise, many natural populations are facing rapid environmental change. Hybridization, and subsequent introgression, are an underexplored driver of adaptation, and may play a critical role in the transfer of advantageous genes between closely related species under thermal stress. The northern swordtail fishes Xiphophorus birchmanni and X. malinche are differentially thermotolerant and form natural hybrid zones along thermal gradients, making them an ideal system for exploring the role of introgression in driving thermal adaptations. We use a combination of QTL mapping and expression analysis to identify loci that may explain variation in thermotolerance and trace the movement of these candidates between populations along two thermal clines. In addition to uncovering part of the genetic basis of this trait, I aim to test the functional role of candidates on cellular physiology. To this effect, I will also share my progress on developing new cell culture protocols for Xiphophorus, which will open opportunities for livebearer research beyond the functional characterization of genes.
Dosage compensation and the faster-X effect: a comparative study across poeciliids
Iulia Darolti (University of British Columbia)
With Lydia Fong and Judith E. Mank
Faster rates of X chromosome coding sequence evolution relative to autosomes has been observed across a wide range of species. Theory predicts that sex chromosome dosage compensation can influence the strength of the Faster-X effect, however this relationship has not been extensively tested empirically. Recently, we uncovered an extreme variation across poeciliids in the rates of sex chromosome evolution. The common guppy (Poecilia reticulata), its sister species Endler’s guppy (P. wingei) and the swamp guppy (P. picta) share the same sex chromosome system. Remarkably, the sex chromosomes of P. reticulata and P. wingei remain homomorphic, while P. picta exhibits profound Y degeneration and complete dosage compensation. Using a combination of sequence divergence, polymorphism and expression data across these three species we estimate the Faster-X evolution and identify loci evolving under adaptive and neutral forces. Our study offers a comparative analysis of the relationship between the Faster-X effect and dosage compensation.
Five Y chromosomes facilitate the evolution of alternative male reproductive morphs in Poecilia parae
Ben Sandkam (University of British Columbia)
With Pedro Almeida, Iulia Darolti, Benjamin Furman, Wouter van der Bijl, Jake Morris, Godfrey Bourne, Felix Breden, and Judith E. Mank
There are five discrete morphs of male Poecilia parae, all morphs shoal together in natural populations and frequencies have been stable for 50+ years. Each morph utilizes a different complex reproductive strategy based on color, body size, and mating behavior. Remarkably, morph phenotype is passed perfectly from father to son. Using linked-read sequencing on females and males of all five morphs from natural populations, we found the genetic architecture underlying male morph evolved on the Y chromosome after recombination was stopped. Comparing each of the morphs revealed that there are substantial amounts of divergence between the Ys that correspond to differences in reproductive strategy, body size and mating behavior. Taken together, this shows the Y chromosome generated extreme diversity, resulting in five discrete Y chromosomes in one species that control alternative complex reproductive strategies.
Comparative epigenomics reveals conserved sex-specific DNA methylation patterns between Poecilia reticulata and P. wingei
David Metzger (University of British Columbia)
With Judith E. Mank
DNA methylation is an epigenetic mark that can modify chromatin structure and influence gene expression activity. DNA methylation patterns are modified in different environments and have been proposed to play a key role in regulating phenotypic plasticity. However, this environmental sensitivity of DNA methylation patterns makes it difficult to identify evolutionarily conserved patterns of DNA methylation variation. To overcome this challenge, we use a multi-species comparative epigenomics approach to identify conserved sexually dimorphic DNA methylation patterns between the Trinidadian guppy (Poecilia reticulata) and Endler’s guppy (Poecilia wingei). We identify conserved, testis-specific hypomethylated regions near key developmental genes including an ortholog of the imprinted mammalian gene rtl2/peg10 involved in placental development. We also find that the oldest part of the guppy sex chromosome shows a conserved pattern of male hypomethylation, consistent with signatures of Y chromosome divergence and suggests a potential role in regulating sexually dimorphic phenotypes.
Afternoon: Session 2
Modulation of kinematics and integration of Trinidadian guppies capturing functionally similar prey
Zachary Capilitan (Eckerd College)
With Emily Kane
The kinematic response of fish in integrated feeding and swimming behaviors is vital for the successful capture of prey. Many have studied modulation of suction feeding in response to prey evasiveness defined broadly, but few have tested this when capturing functionally similar prey, such as different species of evasive prey. This study used Trinidadian guppies (Poecilia reticulata) collected from low and high predation environments to examine this question. Female guppies were fed cultured daphnia, wild daphnia, and wild copepods, which differ in responsiveness to predation. Videos were digitized in MATLAB to determine modulation of kinematics and integration. If integration is a constraint, then we would expect it to be consistent across prey types, however it could vary if the underlying kinematics differ. This will give insight into functional constraints of varying evasiveness of functionally similar prey types.
Morphological trends in experimental hybrid populations of highland (Xiphophorus malinche) and sheepshead (X. birchmanni) swordtails
Max Chin (Texas A&M University)
With Stephen Bovio and Gil Rosenthal
Naturally hybridizing species represent important study systems in evolutionary biology, providing insight into the mechanisms that drive reproductive isolation and speciation. Hybrid zones occurring along ecological gradients allow us to study longstanding evolutionary questions regarding the consequences of ecological selection on hybrid populations. However, most hybrid zones are characterized by several generations of selection. Accordingly, it becomes important to monitor how selection acts on early generation hybrids to determine the evolutionary trajectory of future generations. Here, we establish 8 replicate experimental F1 hybrid populations between Xiphophorus malinche and X. birchmanni across 3 elevations. We collected morphometric and whole-genome data from each of these populations biannually over a period of 3 years to monitor and analyze changes and associations between genotypes and phenotypes. Our preliminary analysis reveals significant seasonal trends in species diagnostic morphological traits, as well as long-term decreasing trends and significant intra-site variation in several traits.
Resolving taxonomic difficulties between Poeciliopsis pleurospilus and P. gracilis
Sarah Ward (University of Oklahoma and Southeastern Louisiana University)
With Kyle R. Piller
Poeciliopsis is a genus of poeciliids that dominates the freshwater fish biomass in parts of Middle America. Two widely distributed species, Poeciliopsis pleurospilus (primarily distributed in Pacific Coast drainages) and Poeciliopsis gracilis (Atlantic Coast drainages), are morphologically similar to one another, with the species primarily being differentiated based on pigmentation patterns. Variations in pigmentation has led to uncertainty in distributional boundaries for each species. This has caused some researchers to suggest that P. pleurospilus and P. gracilis should be synonymized. However, to date, no targeted study has examined the distinctiveness of these species. Therefore, the goal of this study was to examine the monophyly of P. pleurospilus and P. gracilis using ddRADseq data from populations of these species from El Salvador, Guatemala, Honduras, and Mexico. The results from this study will provide resolution to the long-standing taxonomic issue of these two congeners.
Multi-locus phylogeny of Pseudoxiphophorus (Poeciliidae): Re-evaluation of relationships and geographic distribution
Diego Elias (Louisiana State University)
With Elyse Parker, Caleb D. McMahan, Christian Barrientos, Kimberly Foster, and Kyle R. Piller
The family Poeciliidae represents one of the dominant groups of freshwater fishes in Middle America. Despite their high diversity, species-level relationships within several Poeciliidae genera remain poorly understood. The genus Pseudoxiphophorus is represented by nine species distributed from central Mexico to northern Nicaragua. A previous molecular hypothesis suggests that the most widespread species of the genus, P. bimaculatus, is paraphyletic and harbors cryptic diversity. Our goal was to re-evaluate the phylogenetic relationships among species of Pseudoxiphophorus and their distributions using one mitochondrial and six nuclear loci. Our results recovered a novel hypothesis of relationships among species of Pseudoxiphophorus, and we provide evidence to suggest that some species within Pseudoxiphophorus are more widespread than currently recognized. Our results highlight phylogenetic relationships that need further investigation and provide a framework to better understand the evolutionary history of the genus Pseudoxiphophorus in Middle America.