Poeciliid Species Research Articles

Life histories of poeciliid fishes: searching for a size-dependent trade-off between number and size of offspring

A large body of knowledge about life-history traits has arisen from research on viviparous fishes of the family Poeciliidae. Still, the wide variation among species in reproductive strategies provides an excellent opportunity to further explore how life-history traits covary and the causes of covariation patterns. In this study, we provide information on brood size, offspring mass at birth, and total reproductive allotment of six poeciliid species (Gambusia sexradiata, Poeciliopsis latidens, Poeciliopsis viriosa, Priapella intermedia, Pseudoxiphophorus jonesii, and Xiphophorus hellerii). Also, we searched for a trade-off between the number of offspring that females produce and the size of each individual offspring. We tested the hypothesis that this trade-off should be stronger in small females because of the space constraints in the reproductive tract that are inherent to a small body size. If this hypothesis were correct, we expected a strong negative relationship between number and size of offspring in small females and a weaker or undetectable relationship between these two life-history traits in larger females. We found evidence of such a size-dependent trade-off in only one species. Small females of Po. latidens that produced relatively large broods experienced the cost of a reduction in the average size of each offspring. In larger females this negative relationship was weaker. Unexpectedly, we found no evidence of this trade-off in the other five poeciliid species and, in contrast, in one species (Priapella intermedia) females that produced numerous embryos were also capable of producing relatively large embryos. We discuss potential explanations for the different patterns of covariation (or lack of covariation) between number and size of offspring that we detected in these viviparous species.

Increased superfetation precedes the evolution of advanced degrees of placentotrophy in viviparous fishes of the family Poeciliidae.

The causes and consequences of the evolution of placentotrophy (post-fertilization nutrition of developing embryos of viviparous organisms by means of a maternal placenta) in non-mammalian vertebrates are still not fully understood. In particular, in the fish family Poeciliidae there is an evolutionary link between placentotrophy and superfetation (ability of females to simultaneously bear embryos at distinct developmental stages), with no conclusive evidence for which of these two traits facilitates the evolution of more advanced degrees of the other. Using a robust phylogenetic comparative method based on Ornstein-Uhlenbeck models of adaptive evolution and data from 36 poeciliid species, we detected a clear causality pattern. The evolution of extensive placentotrophy has been facilitated by the preceding evolution of more simultaneous broods. Therefore, placentas became increasingly complex as an adaptive response to evolutionary increases in the degree of superfetation. This finding represents a substantial contribution to our knowledge of the factors that have shaped placental evolution in poeciliid fishes.

Multiple paternity in superfetatious live-bearing fishes.

Superfetation, the ability to carry several overlapping broods at different developmental stages, has evolved independently multiple times within the live-bearing fish family Poeciliidae. Even though superfetation is widespread among poeciliids, its evolutionary advantages remain unclear. Theory predicts that superfetation should increase polyandry by increasing the probability that temporally overlapping broods are fertilized by different fathers. Here, we test this key prediction in two poeciliid species that each carry two temporally overlapping broods: Poeciliopsis retropinna and P. turrubarensis. We collected 25 females per species from freshwater streams in South-Eastern Costa Rica and assessed multiple paternity by genotyping all their embryos (420 embryos for P. retropinna; 788 embryos for P. turrubarensis) using existing and newly developed microsatellite markers. We observed a high frequency of unique sires in the simultaneous, temporally overlapping broods in P. retropinna (in 56% of the pregnant females) and P. turrubarensis (79%). We found that the mean number of sires within females was higher than the number of sires within the separate broods (2.92sires within mothers vs. 2.36 within separate broods in P. retropinna; and 3.40 vs 2.56 in P. turrubarensis). We further observed that there were significant differences in the proportion of offspring sired by each male in 42% of pregnant female P. retropinna and 65% of female P. turrubarensis; however, this significance applied to only 9% and 46% of the individual broods in P. retropinna and P. turrubarensis, respectively, suggesting that the unequal reproductive success of sires (i.e. reproductive skew) mostly originated from differences in paternal contribution between, rather than within broods. Together, these findings tentatively suggest that superfetation may promote polyandry and reproductive skew in live-bearing fishes.

Female reproductive mode shapes allometric scaling of male traits in live-bearing fishes (family Poeciliidae).

Reproductive mode is predicted to influence the form of sexual selection. The viviparity-driven conflict hypothesis posits that a shift from lecithotrophic (yolk-nourished) to matrotrophic (mother-nourished or placental) viviparity drives a shift from precopulatory towards post-copulatory sexual selection. In lecithotrophic species, we predict that precopulatory sexual selection will manifest as males exhibiting a broad distribution of sizes, and small and large males exhibiting contrasting phenotypes (morphology and coloration); conversely, in matrotrophic species, an emphasis on post-copulatory sexual selection will preclude these patterns. We test these predictions by gathering data on male size, morphology and coloration for five sympatric Costa Rican poeciliid species that differ in reproductive mode (i.e. lecithotrophy vs. matrotrophy). We find tentative support for these predictions of the viviparity-driven conflict hypothesis, with some interesting caveats and subtleties. In particular, we find that the three lecithotrophic species tend to show a broader distribution of male sizes than matrotrophic species. Furthermore, large males of such species tend to exhibit proportionately large dorsal and caudal fins and short gonopodia relative to small males, while these patterns are expressed to a lesser extent in the two matrotrophic species. Finally, large males in some of the lecithotrophic species exhibit darker fins relative to small males, a pattern not evident in either matrotrophic species. One unexpected finding was that even in the matrotrophic species Poeciliopsis retropinna and Poeciliopsis paucimaculata, which lack courtship and dichromatic coloration, some morphological traits exhibit significant allometric relationships, suggesting that even in these species precopulatory sexual selection may be present and shaping size-specific male phenotypes in subtle ways.

On the availability of the name Poecilia kempkesi Poeser 2013(Cyprinodontiformes: Poeciliidae).

The poeciliid species, Poecilia kempkesi Poeser, 2013, was the fourth species of the subgenus Acanthophacelus Eigenmann, 1907 to be described, based on individuals from a single urban anthropized locality close to Paramaribo, Suriname (Poeser, 2013). The description itself lacked any section clearly distinguishing the new species from the remaining species of Poecilia Bloch Schneider 1801, and in particular from the species of the subgenus Acanthophacelus, type species Poecilia reticulata Peters, 1859. According to Article 13 of the International Code of Zoological Nomenclature (ICZN, 1999) the criteria of availability for a species-group name are:.

Gambusia holbrooki Survive Shear Stress, Pressurization and Avoid Blade Strike in a Simulated Pumped Hydroelectric Scheme

Pumped hydroelectric energy storage (PHES) projects are being considered worldwide to achieve renewable energy targets and to stabilize baseload energy supply from intermittent renewable energy sources. Unlike conventional hydroelectric systems that only pass water downstream, a feature of PHES schemes is that they rely on bi-directional water flow. In some cases, this flow can be across different waterbodies or catchments, posing a risk of inadvertently expanding the range of aquatic biota such as fish. The risk of this happening depends on the likelihood of survival of individuals, which remains poorly understood for turbines that are pumping rather than generating. This study quantified the survival of a globally widespread and invasive poeciliid fish, Eastern gambusia (Gambusia holbrooki), when exposed to three hydraulic stresses characteristic of those experienced through a PHES during the pumping phase. A shear flume and hyperbaric chamber were used to expose fish to different strain rates and rapid and sustained pressurization, respectively. Blade strike models were also used to predict fish survival through a Francis dual turbine / pump. Simulated ranges were based on design and operational conditions provided for a PHES scheme proposed in south-eastern Australia. All gambusia tested survived high levels of shear stress (up to 1853 s-1), extremely high pressurization (up to 7600 kPa gauge pressure) and the majority (> 93 %) were unlikely to be struck by a turbine blade. Given their tolerance to these extreme simulated stresses, we conclude that gambusia will likely survive passage through the simulated PHES scheme if they are entrained at the intake. Therefore, where a new PHES project poses the risk of inadvertently expanding the range of gambusia or similar poeciliid species, measures to minimize their spread or mitigate their ecosystem impacts should be considered.

It's in the eye of the beholder: visual lateralisation in response to the social environment in poeciliids.

The social environment offers fish complex information about the quality, performance, personality and other cues of potential mates and competitors simultaneously. It is likely, therefore, that the environmental information regarding the context of mate choice is perceived and processed differently in species and sexes in respect to lateralisation. The present study comparatively assessed visual lateralisation behaviour in response to different social or sexual stimuli in three closely related poeciliid species (P. latipinna, P. mexicana, P. formosa) in comparison to a more distantly related species (P. reticulata). Individuals were presented with four different social or sexual stimuli that were tested against a control stimulus; (a) a conspecific male, (b) a conspecific female, (c) a heterosexual conspecific pair, (d) three conspecific females (shoal). In order to approach a target stimulus, focal fish had to perform detours to the right or left of a vertically straight-shaped barrier. The three closely related poeciliid species, P. latipinna, P. mexicana, P. formosa, appeared to have a general tendency to turn right (i.e., left-eye preference), whereas the more distantly related P. reticulata males and females showed an overall bias to the left (i.e., right-eye preference) in response to various social-sexual incitements. Moreover, body size seemed to significantly influence especially the males' detour behaviour, with smaller males acting in opposition to their larger conspecifics in response to certain social stimuli. In this case, smaller and larger Poecilia spp. males responded in the same way as smaller and larger males of the other three poeciliid species. Therefore, results possibly point to differences in the degree of general social behaviour between closely and more distantly related species and mating motivation amongst larger and smaller individuals when placed in a novel social environment. Hence, present results possibly suggest a sex-specific functional lateralisation for the analysis of visual information and seem to support the closer ancestral relationships between the Poecilia spp. tested in this study and the more distantly related guppies in terms of their left-right lateralisation. Generally, present results suggest that functional asymmetries in behaviour could be widespread among vertebrates, thus supporting the hypothesis of an early evolution of lateralisation in brain and behaviour.

Reproductive differences between three species of Brachyrhaphis livebearing fishes in Panamá

Both theory and the published literature support the importance of demographic selection for differences in life history traits between populations as well as between related species. Much attention in this area has been paid to species in the livebearing fish family Poeciliidae. I studied populations of three species of poeciliid fishes of the genus Brachyrhaphis (episcopi, roswithae, terrabensis) found from low to high elevation in western and central Panamá for reproductive life history phenotypes. To determine how reproductive life history phenotypic characters subject to both selection and environmental influence may vary between these species, field collections were made at the end of the wet and dry seasons over several years. Work with other poeciliid species suggested that these three stream species, found in different environments largely defined along an elevational gradient, may have evolved different responses in their reproductive timing and effort in response to differences in abiotic and biotic environmental factors. Differences were found between female wet and dry season reproductive output in all three species. Brachyrhaphis episcopi and B. roswithae showed similar responses to seasonal changes, with larger reproductive allotment (RA) and brood size but smaller embryo size in the wet season and a higher percentage of gravid females found in the wet season compared to the dry, 86% to 49% for B. episcopi and 71% to 45% for B. roswithae. Female B. terrabensis showed different responses to seasonal changes. RA, brood size and embryo size were all larger in the wet season than in the dry season. The percentage of gravid females among those of reproductive size was 37% in the wet season compared to 10% in the dry season. Patterns of male size varied between the three species, with more muted seasonal differences than was found with females of all three species. Brachyrhaphis terrabensis males showed a much wider size range, possibly indicative of two male reproductive strategies in the species. There is a gradient in several measures from lowland to highland species such as highland reproduction apparently stopping entirely in the dry season.

Evolving in the highlands: the case of the Neotropical Lerma live-bearing Poeciliopsis infans (Woolman, 1894) (Cyprinodontiformes: Poeciliidae) in Central Mexico

BackgroundVolcanic and tectonic activities in conjunction with Quaternary climate are the main events that shaped the geographical distribution of genetic variation of many lineages. Poeciliopsis infans is the only poeciliid species that was able to colonize the temperate highlands of central Mexico. We inferred the phylogenetic relationships, biogeographic history, and historical demography in the widespread Neotropical species P. infans and correlated this with geological events and the Quaternary glacial-interglacial climate in the highlands of central Mexico, using the mitochondrial genes Cytochrome b and Cytochrome oxidase I and two nuclear loci, Rhodopsin and ribosomal protein S7.ResultsPopulations of P. infans were recovered in two well-differentiated clades. The maximum genetic distances between the two clades were 3.3% for cytb, and 1.9% for coxI. The divergence of the two clades occurred ca. 2.83 Myr. Ancestral area reconstruction revealed a complex biogeographical history for P. infans. The Bayesian Skyline Plot showed a demographic decline, although more visible for clade A, and more recently showed a population expansion in the last 0.025 Myr. Finally, the habitat suitability modelling showed that during the LIG, clade B had more areas with high probabilities of presence in comparison to clade A, whereas for the LGM, clade A showed more areas with high probabilities of presence in comparisons to clade B.ConclusionsPoeciliopsis infans has had a complex evolutionary and biogeographic history, which, as in other co-distributed freshwater fishes, seems to be linked to the volcanic and tectonic activities during the Pliocene or early Pleistocene. Populations of P. infans distributed in lowlands showed a higher level of genetic diversity than populations distributed in highlands, which could be linked to more stable and higher temperatures in lowland areas. The fluctuations in population size through time are in agreement with the continuous fluctuations of the climate of central Mexico.

Triple trouble? Invasive poeciliid fishes carry the introduced tilapia pathogen Gyrodactylus cichlidarum in the Mexican highlands

As part of ongoing surveys of the gyrodactylid parasite fauna of freshwater fishes in Mexico, we recorded the infection of three species of poeciliids (Poecilia mexicana, Poeciliopsis gracilis, and Pseudoxiphophorus bimaculatus [syn.=Heterandria bimaculata]) with Gyrodactylus cichlidarum, a monogenean parasite of cichlid fishes, which has been co-introduced globally with its translocated, African “tilapia” hosts. This tilapia pathogen was found on poeciliid fishes both within their native distribution range in the Gulf of Mexico slope, as well as on invasive species artificially introduced to the Mexican highlands, to rivers draining into the Pacific Ocean. Identity of G. cichlidarum was confirmed by morphological and molecular analyses. Prevalence and abundance of infection were low, but this is the first record of G. cichlidarum infecting poeciliids (Cyprinodontiformes), which are distantly related to this parasite’s primary cichlid fish hosts (Perciformes). This study provides evidence that G. cichlidarum, a recognized pathogen which has been co-introduced globally with its cichlid fish hosts for aquacultural purposes, is able to infect non-related poeciliid fishes inhabiting water bodies adjacent to tilapia farms, thereby potentially increasing its ability to disperse between farms and different river basins. It is of particular concern that G. cichlidarum was found on poeciliids, as these invasive fishes have been introduced worldwide and could act as carriers for this parasite known to induce significant mortality of farmed tilapias − globally, the second most important freshwater aquaculture fish group, after the carps.

The Genome of the Trinidadian Guppy, Poecilia reticulata, and Variation in the Guanapo Population.

For over a century, the live bearing guppy, Poecilia reticulata, has been used to study sexual selection as well as local adaptation. Natural guppy populations differ in many traits that are of intuitively adaptive significance such as ornamentation, age at maturity, brood size and body shape. Water depth, light supply, food resources and predation regime shape these traits, and barrier waterfalls often separate contrasting environments in the same river. We have assembled and annotated the genome of an inbred single female from a high-predation site in the Guanapo drainage. The final assembly comprises 731.6 Mb with a scaffold N50 of 5.3 MB. Scaffolds were mapped to linkage groups, placing 95% of the genome assembly on the 22 autosomes and the X-chromosome. To investigate genetic variation in the population used for the genome assembly, we sequenced 10 wild caught male individuals. The identified 5 million SNPs correspond to an average nucleotide diversity (π) of 0.0025. The genome assembly and SNP map provide a rich resource for investigating adaptation to different predation regimes. In addition, comparisons with the genomes of other Poeciliid species, which differ greatly in mechanisms of sex determination and maternal resource allocation, as well as comparisons to other teleost genera can begin to reveal how live bearing evolved in teleost fish.

Differential sensitivity to estrogen-induced opsin expression in two poeciliid freshwater fish species

The sensory system shapes an individual’s perception of the world, including social interactions with conspecifics, habitat selection, predator detection, and foraging behavior. Sensory signaling can be modulated by steroid hormones, making these processes particularly vulnerable to environmental perturbations. Here we examine the influence of exogenous estrogen manipulation on the visual physiology of female western mosquitofish (Gambusia affinis) and sailfin mollies (Poecilia latipinna), two poeciliid species that inhabit freshwater environments across the southern United States. We conducted two experiments to address this aim. First, we exposed females from both species to a one-week dose response experiment with three treatments of waterborne β-estradiol. Next, we conducted a one-week estrogen manipulation experiment with a waterborne estrogen (β-Estradiol), a selective estrogen receptor modulator (tamoxifen), or combination estrogen and tamoxifen treatment. We used quantitative PCR (qPCR) to examine the expression of cone opsins (SWS1, SWS2b, SWS2a, Rh2, LWS), rhodopsin (Rh1), and steroid receptor genes (ARα, ARβ, ERα, ERβ2, GPER) in the eyes of individual females from each species. Results from the dose response experiment revealed estradiol-sensitivity in opsin (SWS2a, Rh2, Rh1) and androgen receptor (ARα, ARβ) gene expression in mosquitofish females, but not sailfins. Meanwhile, our estrogen receptor modulation experiments revealed estrogen sensitivity in LWS opsin expression in both species, along with sensitivity in SWS1, SWS2b, and Rh2 opsins in mosquitofish. Comparisons of control females across experiments reveal species-level differences in opsin expression, with mosquitofish retinas dominated by short-wavelength sensitive opsins (SWS2b) and sailfins retinas dominated by medium- and long-wavelength sensitive opsins (Rh2 and LWS). Our research suggests that variation in exogenous levels of sex hormones within freshwater environments can modify the visual physiology of fishes in a species-specific manner.

Persistence ofEtheostoma parvipinne(Goldstripe Darter) in a Single Tributary on the Periphery of Its Range

Abstract We report the occurrence of a single population of Etheostoma parvipinne (Goldstripe Darter) in a small, acidic, spring-fed stream within the Colorado River drainage following an extended period of below-average precipitation (January–September 2011), a wildland fire (September 2011), and subsequent debris and sediment flows (November 2011–May 2012). Goldstripe Darters were taken from Alum Creek (Bastrop County, TX) along with a cyprinid, a poeciliid, and several species of centrarchids in June 2012. Occurrence of Goldstripe Darters in Alum Creek provides a regional example of fish-community responses to wildland fires. In additio n, understanding the mechanism of long-term persistence in a single tributary on the periphery of a species range might offer insight into the origin of endemic fishes and persistence of disjunct fish populations within aquatic evolutionary refugia of central Texas.

Ecological, evolutionary and human‐mediated determinants of poeciliid species richness on Caribbean islands

AbstractAimThe theory of island biogeography provides a predictive framework relating species richness to island size and distance from the mainland. However, the theory as originally formulated does not necessarily scale to large islands and continental landmasses that are capable of generating species through in situ speciation (rather than entirely by colonization), nor does it necessarily account for how human introduction of species alters traditional biogeographical patterns. Here, we examine the ecological (colonization and extinction), evolutionary (in situ speciation) and human‐mediated (deliberate introductions) determinants of species richness in a taxonomic group that has undergone a radiation on Caribbean islands: live‐bearing fishes of the family Poeciliidae.LocationThe Caribbean.MethodsWe created a database of both native and introduced poeciliid species occurrence on Caribbean islands through literature review, and estimated the number of colonizations versus speciation events on each island using a molecular phylogeny. Linear regression and other statistical tests were used to explore species–area and species–isolation relationships.ResultsSpecies richness on small islands results entirely from colonization and does not significantly increase with island area, whereas on larger islands species richness increases dramatically as a function of area due primarily to in situ speciation. Poeciliid fishes have been introduced widely, both as a by‐product of their popularity in the aquarium hobby and as a means of mosquito control. We show that such establishments have occurred disproportionately on islands depauperate in native species, and that introduced species richness is positively correlated with economic interconnectedness (shipping traffic) and human population size.Main conclusionsOn large Caribbean islands in situ speciation has elevated the number of poeciliid species beyond that predicted from ecological processes alone. Introduced species significantly alter biogeographical patterns.

New data on the taxonomic status and distribution of Gambusia sp. in Croatia and Bosnia and Herzegovina

Background and Purpose: In the early 20th century, two native North American poeciliid species Gambusia holbrooki and Gambusia affinis were introduced to Europe as a mosquito control agent. The first introduction to Istria from Italy in 1924 was followed by several independent introductions and massive translocations. Presently, the distribution of these two species in Croatia and Bosnia and Herzegovina (Bosnia and Herzegovina) is still largely unknown and they are often confused. The purpose of this study was to determine the taxonomic status of individual Gambusia populations and to shed more light on the distribution and phylogeographic patterns of these invasive species in Croatia and Bosnia and Herzegovina. Materials and Methods: All new and literature data were plotted together to obtain the overall distribution of Gambusia sp. in Croatia and Bosnia and Herzegovina. The samples collected across this range were analysed meristically and by means of mitochondrial cytochrome b (cytb) gene sequence analysis to ascertain the true taxonomic status of the populations. For phylogeographic analysis, the cytb sequences from this study were combined with previously published data. Results and Conclusions: The methods only confirmed the presence of G. holbrooki. G. holbrooki is continuously distributed across the entire Mediterranean biogeographical region in Croatia and Bosnia and Herzegovina. Two different mitochondrial cytb haplotypes were found: the widely spread Hol1 haplotype and haplotype Hol5 that in Europe was previously found only in France and Greece. This suggests that G. holbrooki populations in the region originated from different stocks.

New data on the taxonomic status and distribution of Gambusia sp. in Croatia and Bosnia and Herzegovina

Background and Purpose: In the early 20th century, two native North American poeciliid species Gambusia holbrooki and Gambusia affinis were introduced to Europe as a mosquito control agent. The first introduction to Istria from Italy in 1924 was followed by several independent introductions and massive translocations. Presently, the distribution of these two species in Croatia and Bosnia and Herzegovina (Bosnia and Herzegovina) is still largely unknown and they are often confused. The purpose of this study was to determine the taxonomic status of individual Gambusia populations and to shed more light on the distribution and phylogeographic patterns of these invasive species in Croatia and Bosnia and Herzegovina. Materials and Methods: All new and literature data were plotted together to obtain the overall distribution of Gambusia sp. in Croatia and Bosnia and Herzegovina. The samples collected across this range were analysed meristically and by means of mitochondrial cytochrome b (cytb) gene sequence analysis to ascertain the true taxonomic status of the populations. For phylogeographic analysis, the cytb sequences from this study were combined with previously published data. Results and Conclusions: The methods only confirmed the presence of G. holbrooki. G. holbrooki is continuously distributed across the entire Mediterranean biogeographical region in Croatia and Bosnia and Herzegovina. Two different mitochondrial cytb haplotypes were found: the widely spread Hol1 haplotype and haplotype Hol5 that in Europe was previously found only in France and Greece. This suggests that G. holbrooki populations in the region originated from different stocks.

Female social response to male sexual harassment in poeciliid fish: a comparison of six species.

Sexual harassment is common among poeciliid fish. In some fishes, males show a high frequency of sneak copulation; such sexual activity is costly to the females in terms of foraging efficiency. In mosquitofish (Gambusia holbrooki), when males are present, the distance between females tends to decrease, and this behavior has been interpreted as an adaptive strategy to dilute the costs of male sexual activity. In this study, the tendency to reduce distance in the presence of a male has been investigated in females of six poeciliid species (Girardinus metallicus, Girardinus falcatus, G. holbrooki, Poecilia reticulata, Xiphophorus hellerii, and Xiphophorus mayae) that exhibit different male mating strategies and different levels of sexual activity. Results revealed large interspecific differences in the pattern of female aggregation. Females of species with a high frequency of sneak copulations tended to reduce their social distance in the presence of a male. By contrast, species that rely mainly on courtship showed little or no variation in social distance. The proportion of sneak copulations predicts the degree of variation in female social response, but the amount of total sexual activity does not, suggesting that the change in females' social distance when a male is present may indeed serve to reduce the costs of male sexual harassment.

The complete mitochondrial genome of the Monterrey platyfish (Xiphophorus couchianus)

The Monterrey platyfish (Xiphophorus couchianus) is native to the vicinity of Monterrey, Mexico and is listed as Critically Endangered by International Union for Conservation of Nature (IUCN). Here, we describe the complete mitochondrial genome (mitogenome) sequence of Monterrey platyfish. The genome is 16 638 bp in length, consisting of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, 2 ribosomal RNA genes and 1 non-coding control region. Phylogenetic tree was constructed based on the complete mitogenome of X. couchianus and closely related five Poeciliid species to estimate their phylogenic relationship. The complete mitochondrial genome of X. couchianus would provide more valuable information to assess the evolution of family Poeciliidae.

The mate choice mind: studying mate preference, aversion and social cognition in the female poeciliid brain

Male phenotypes vary across mating systems, but what about the female mind? In poeciliid fishes, we observe that female response towards males varies, both at inter- and intraspecific levels. By using the natural variation in poeciliid male reproductive phenotypes, we can probe female responses in different social contexts to isolate the neuromolecular components associated with mate choice. Female Xiphophorus nigrensis exhibit differential nonapeptide (isotocin, vasotocin) gene expression between social contexts that differ by social affiliation; while differential expression of synaptic plasticity genes (neuroserpin, neuroligin-3, NMDAR) is more strongly predictive of social contexts that differ by mate preference discrimination. Gene expression and pharmacological manipulation with X. nigrensis females suggests that the social cognition task of mate choice involves neuromolecular processes linked to learning at the cellular (synaptic plasticity genes) and regional (amygdala and hippocampus) levels. Comparative assays between two poeciliid species with different mating systems provide the first hint of a shared neuromolecular pathway underlying female mate preference response. Yet, it is still unclear how specific components of this neuromolecular pathway (nonapeptides and synaptic plasticity processes) interact to coordinate behavioural tasks associated with mate choice encounters (vigilance, affiliation, evaluation and discrimination). Nevertheless, this collection of studies, coupled with the natural diversity of poeciliid mating systems, pave the way for exciting new insights into the social cognition of mate choice.

Evidence for inbreeding depression in a species with limited opportunity for maternal effects.

It is often assumed that mating with close relatives reduces offspring fitness. In such cases, reduced offspring fitness may arise from inbreeding depression (i.e., genetic effects of elevated homozygosity) or from post-mating maternal investment. This can be due to a reduction in female investment after mating with genetically incompatible males (“differential allocation”) or compensation for incompatibility (“reproductive compensation”). Here, we looked at the effects of mating with relatives on offspring fitness in mosquitofish, Gambusia holbrooki. In this species, females are assumed to be nonplacental and to allocate resources to eggs before fertilization, limiting differential allocation. We looked at the effects of mating with a brother or with an unrelated male on brood size, offspring size, gestation period, and early offspring growth. Mating with a relative reduced the number of offspring at birth, but there was no difference in the likelihood of breeding, gestation time, nor in the size or growth of these offspring. We suggest that due to limited potential for maternal effects to influence these traits that any reduction in offspring fitness, or lack thereof, can be explained by inbreeding depression rather than by maternal effects. We highlight the importance of considering the potential role of maternal effects when studying inbreeding depression and encourage further studies in other Poeciliid species with different degrees of placentation to test whether maternal effects mask or amplify any genetic effects of mating with relatives.