Boldness and Reproductive Fitness Correlates in the Eastern Mosquitofish, Gambusia holbrooki

Animals are known to exhibit 'personality'; that is, individual differences in behaviour that are consistent across time and/or situations. One axis of personality of particular importance for behavioural ecology is boldness, which can be defined as the tendency of an individual to take risks. The relationship between individual personality and fitness correlates, particularly those involved in reproduction, remains largely unexplored. In the current study, we used female Eastern mosquitofish ( Gambusia holbrooki ) to ascertain whether certain reproductive traits (e.g. stage of pregnancy, fecundity) are correlated with individual personality in two wild populations in New South Wales, Australia. To quantitatively assess this relationship, we tested individual fish for their level of boldness, as measured by their latency to exit a refuge and tendency to shoal in a novel environment. We also quantified individual differences in general activity and tendency to swim near the water surface and substratum. For both populations taken together, bolder individuals tended to be smaller, relatively less fecund (when taking body size into account), and spent more time near the water surface than near the substratum compared with timid individuals. Individual boldness was not correlated with either general activity or stage of pregnancy. To our knowledge, our study characterizes for the first time a relationship between an individual personality trait (boldness) and a reproductive fitness correlate (fecundity) in fishes.     

Geographical and temporal variation of multiple paternity in invasive mosquitofish (Gambusia holbrooki,Gambusia affinis)

Multiple paternity (MP) increases offspring's genetic variability, which could be linked to invasive species' evolvability in novel distribution ranges. Shifts in MP can be adaptive, with greater MP in harsher/colder environments or towards the end of the reproductive season, but climate could also affect MP indirectly via its effect on reproductive life histories. We tested these hypotheses by genotyping N = 2,903 offspring from N = 306 broods of two closely related livebearing fishes, Gambusia holbrooki and Gambusia affinis. We sampled pregnant females across latitudinal gradients in their invasive ranges in Europe and China, and found more sires per brood and a greater reproductive skew towards northern sampling sites. Moreover, examining monthly sampling from two G. affinis populations, we found MP rates to vary across the reproductive season in a northern Chinese, but not in a southern Chinese population. While our results confirm an increase of MP in harsher/more unpredictable environments, path analysis indicated that, in both cases, the effects of climate are likely to be indirect, mediated by altered life histories. In both species, which rank amongst the 100 most invasive species worldwide, higher MP at the northern edge of their distribution probably increases their invasive potential and favours range expansions, especially in light of the predicted temperature increases due to global climate changes.     

Repeatability of Male Mate Choice in the Mosquitofish, Gambusia holbrooki

Male mate choice has evolved in many species in which female fecundity increases with body size. In these species, males are thought to have been selected to favour mating with large females over smaller ones, thereby potentially increasing their reproductive success. While male mate choice is known to occur, it is less well studied than female mate choice and little is known about variation in mating preference among individual males. Here, we presented individual male eastern mosquitofish ( Gambusia holbrooki ) with paired females that differed in body size, and we quantified their mate preference on two consecutive days, allowing us to assess repeatability of preferences expressed. When males were allowed to view paired stimulus females, but not to acquire chemical or tactile cues from them, they exhibited a strong preference for large females over smaller ones. However, individual males were not consistent in the strength of their preference and repeatability was not significant. When individual males were allowed to fully interact with pairs of females, the males again exhibited a preference for large females over smaller ones, as revealed by a greater number of attempted copulations with large females than with smaller ones. In the latter social context, individual male preference was significantly repeatable. These results indicate that male eastern mosquitofish from our Florida study population possess, on average, a mating preference for larger females and that this preference is repeatable when males socially interact freely with females. The significant repeatability for mating preference, based on female body size, obtained for male mosquitofish in the current study is consistent with the presence of additive genetic variation for such preferences in our study population and thus with the opportunity for the further evolution of large body size in female mosquitofish through male mate choice.     

Maternal effects on offspring size and number in mosquitofish,Gambusia holbrooki

Given a trade-off between offspring size and number, all mothers are predicted to produce the same optimal-sized offspring in a given environment. In many species, however, larger and/or older mothers produce bigger offspring. There are several hypotheses to explain this but they lack strong empirical support. In organisms with indeterminate growth, there is the additional problem that maternal size and age are positively correlated, so what are their relative roles in determining offspring size? To investigate this, we measured the natural relationship between maternal and offspring size in a wild population of Gambusia holbrooki (eastern mosquitofish), and experimentally disentangled the effects of maternal age and size on offspring size in the laboratory. In combination, our data indicate that the relationship between maternal and offspring size is nonlinear. Small mothers seem to produce larger than average offspring due to integer effects associated with very small broods. For extremely large mothers, which were only sampled in our wild data, these larger than average offspring may result from greater maternal resources or age effects. However, maternal age had no effect on offspring size or number in the laboratory experiment. Our results highlight the importance of sampling the full size–range of mothers when investigating maternal effects on offspring size. They also point to the difficulty of experimentally manipulating maternal size, because any change in size is invariably associated with a change in at least one factor affecting growth (be it temperature, food availability, or density) that might also have an indirect effect on offspring size.     

广东从化地区不同生境食蚊鱼种群的繁殖生物学特征

本文从繁殖群体的环境条件、形体特征、卵巢发育与繁殖力方面对广东从化地区溪流、池塘、农田3种不同生境的食蚊鱼(Gambusia affinis)种群展开比较研究。结果发现,无论流动水体溪流还是静水水体池塘和农田,食蚊鱼的繁殖期均在3~12月份,繁殖群体中雌鱼占比明显高于雄鱼(Chi-Square test,P0.01)。雌鱼周年平均体长及体重,池塘生境的显著大于农田和溪流生境。农田生境中雌鱼的个体怀卵量(24.1±12.1)粒,体重相对繁殖力(57.5±31.0)粒/g,二者均明显高于溪流生境[(16.6±11.6)粒,(40.8±15.5)粒/g]与池塘生境[(18.9±16.3)粒,(35.7±19.1)粒/g],但农田生境雌鱼成熟卵子的卵径显著小于溪流和池塘生境。结果表明,在环境稳定的池塘生境中,食蚊鱼的繁殖策略偏向k-对策特性;在人为干扰较大的农田生境中,食蚊鱼的繁殖策略偏向r-对策特性。不同类型生境中食蚊鱼的繁殖特性存在一定差异,主要与其栖息环境的稳定性和饵料生物的丰富度有关。     

Microsatellite assessment of multiple paternity in natural populations of a live-bearing fish,Gambusia holbrooki

Three polymorphic microsatellite loci were isolated and employed to examine paternity patterns in two natural populations of live-bearing mosquitofish, Gambusia holbrooki. Each locus displayed four to five alleles per population in samples of presumably unrelated adults. Nearly 900 embryos from a total of 50 pregnant females were assayed individually, and paternal alleles in each embryo were identified. Counts of paternal alleles, Mendelian segregation patterns, multilocus allelic associations and genetic relatedness coefficients were employed to estimate the minimum and effective numbers of fathers per brood. At least 90% of the assayed broods were shown to have been fathered by multiple males, a figure substantially higher than previous estimates based on less polymorphic genetic loci. However, the genetic data yield a face-value estimate of only about 2.2 fathers per brood, a number that seems perhaps surprisingly low based on frequencies of attempted copulations by males. Both biological and sampling factors that might bias mean sire counts downward are considered. Although higher sire counts per brood might be obtained from loci with even greater numbers of alleles, little statistical room remains for higher frequency estimates of multiple paternity in Gambusia.     

Growth characteristics of eastern mosquitofish Gambusia holbrooki in a northern habitat (Brittany,France)

The two coefficients of the von Bertalanffy growth model [maximal standard length (L_S∞) and initial growth rate (a)] were determined in eastern mosquitofish Gambusia holbrooki in the most northern area where it is established (Rennes, Brittany, France). The estimated mean L_S∞ was 57·7 and 25·0 mm in females and males, respectively. The value of a was identical for both males and females before the males diverged from the females by slowing down their growth, probably because of the onset of puberty. The sexual competition reported in males would be responsible for higher interindividual variability of L_S∞ in males than in females. a was positively correlated with water temperature and could be modulated by fish density and length at birth. Moreover, interindividual variability of a was influenced in a complex way by interactions between water temperature, length at birth and fish density. When compared to the data from studies in G. holbrooki inhabiting their native range or the southern introduced range, the present results suggest that the thermal tolerance domain for growth was altered and that males exhibited a shorter length at sexual maturity and a shorter L_S∞ in the population established in Rennes.     

Sex differences in compensatory and catch-up growth in the mosquitofish Gambusia holbrooki

In many taxa, temporary nutritional shortage early in development can favour compensatory strategies that include elevated growth (‘compensatory growth’) and/or extension of the usual period of development (‘catch-up growth’) once conditions improve. The net gains from each strategy depend on the extent to which larger body size increases fitness relative to associated costs (e.g. long-term effects on adult performance, or a greater risk of juvenile mortality). These costs and benefits are likely to differ between the sexes due to sex-specific selection. We documented the responses of male and female mosquitofish (Gambusia holbrooki) to 3 weeks of low food availability (7–28 days old) that restricted subsequent growth and morphology compared to control fish continuously reared on a high food diet (N = 635 fish total). Neither sex elevated their growth rate immediately after being returned to a normal diet compared to control fish. When measured over the entire period until maturation, however, females showed compensatory growth. Males did not. Both sexes also exhibited catch-up growth but the delay until maturation was significantly longer for males. Despite early growth restriction, both sexes eventually matured at almost the same size as control fish, although males had a significantly smaller gonopodium (a sexually selected trait) than that of control males. Reasons for these sex differences are discussed.     

Male body size and condition affects sperm number and production rates in mosquitofish,Gambusia holbrooki

Sperm number is an important predictor of paternity when there is sperm competition. Sperm number is often measured as maximum sperm reserves, but in species where mating is frequent, males will often be replenishing their reserves. Thus, variation in how quickly males can produce sperm is likely to be important in determining male success in sperm competition. Despite this, little is known about how male size, body condition or diet affects sperm production rates. We counted sperm number in large and small Gambusia holbrooki (eastern mosquitofish) after 3 weeks on either a high or low food diet. Sperm number was significantly higher in both larger males and in well‐fed males. We then stripped ejaculates again either 1, 2, 3, 4 or 5 days later to investigate subsequent sperm production. The rate of sperm replenishment was influenced by an interaction between size and diet. Large, well‐fed males had consistently high levels of sperm available over the 5 days (i.e. rapid replenishment), whereas small poorly fed males showed consistently low levels of sperm availability over the 5 days (i.e. slow replenishment). In contrast, large, poorly fed and small, well‐fed males increased their sperm numbers over the first 3 days (i.e. intermediate replenishment). Our study highlights that when mating is frequent and sperm competition is high, size and condition dependence of maximal sperm number and of sperm production rate might both contribute to variation in male reproductive success.     

Biological Characteristics of the Invasive Gambusia holbrooki in the Wetland,the Lake Van Basin,Turkey

Journal of Ichthyology - Gambusia holbrooki (Girard, 1859) is worldwide spread invasive fish species and is found in the wetland, the Lake Van basin. This study was carried out to determine the...     

GxG epistasis in growth and condition and the maintenance of genetic polymorphism in Gambusia holbrooki

Theory on indirect genetic effects (IGEs) indicates that variation in the genetic composition of social groups can generate GxG epistasis that may promote the evolution of stable polymorphisms. Using a livebearing fish with a genetic polymorphism in coloration and associated behavioral differences, we tested whether genotypes of social partners interacted with focal individual genotypes to influence growth and condition over 16 weeks of development. We found that IGEs had a significant influence on patterns of feeding, regardless of focal fish genotype. There was no influence of social environment on juvenile length, but there was significant GxG epistasis for body condition. Each focal juvenile was in better condition when its own genotype was not present in adult social partners. These data are consistent with negative frequency‐dependent selection in which each morph performs better when it is rare. Neither variation in feeding nor activity‐related behaviors explained variation in body condition, suggesting that GxG epistasis for condition was caused by physiological differences between the two genotypes. These findings indicate that GxG epistasis in a given polymorphism can generate fitness landscapes that contribute to the maintenance of that polymorphism and to maintenance of genetic variation for additional fitness‐related traits.     

Effects of water hardness and Cu and Zn on LC50 in Gambusia holbrooki

Abstract

The aim of this study was to determine by static bioassay whether water hardness affects the toxicity of Zn and Cu to a fish, Gambusia holbrooki Girard, 1859. The acute toxicity of selected heavy metals to G. holbrooki was determined in soft, hard and very hard water (25, 125 and 350 mg L^?1 as CaCO₃). Results showed that water hardness had a significant effect on Cu and on Zn toxicity on fish. Toxicity of Cu and of Zn increased with decreasing water hardness. The 96 hours LC₅₀ values for G. holbrooki were higher in the hard and very hard water compared with soft water. Water hardness had a much smaller effect upon the acute toxicity of Cu than that of Zn. It was observed that the 96 hours LC50 for Cu at the soft, hard and very hard water was found to be 0.017, 0.17 and 0.65 mg L^?1, respectively, while the 96 hours LC₅₀ for Zn at the soft, hard and very hard water was found to be 0.46, 48.1 and 121.6 mg L^?1, respectively.     

Polymorphism and pair formation in the mosquitofish Gambusia holbrooki (Pisces: Poeciliidae)

Synopsis Pair formation was studied in a polymorphic population of Gambusia holbrooki in a brackish drainage canal in Southern Florida. All females and the majority of males were gray colored and only 5% of the males were black spotted. A small fraction of the population formed pairs, composed of a female and a male that swam synchronously and close together for several minutes. During pairing the male often achieved gonopodial contact with the female. Black spotted males occurred in pairs ten fold more frequently than expected under random pairing. The major behavioral mechanism accounting for the disproportionate occurrence of spotted males in pairs is, probably, the preference of females for these males.     

Life history and parasites of the invasive mosquitofish (Gambusia holbrooki) along a latitudinal gradient

The eastern mosquitofish (Gambusia holbrooki) is among the most invasive fish worldwide and yet, while very abundant in most Mediterranean countries, it is unable to tolerate the colder winters of northern and central Europe. Understanding the effects of latitude on its life-history traits is essential to predict the potential for its invasion of central Europe in current scenarios of climate change. We studied the variation of life-history traits and parasite load in the eastern mosquitofish along a latitudinal gradient from southern France to southern Spain, sampling mosquitofish populations in eight Mediterranean river mouths ranging 5° in latitude. Southern mosquitofish populations displayed higher catch rates, allocated more energy to reproduction (gonadosomatic index and gonadal weight after accounting for fish size) and had a lower condition (total weight and eviscerated weight after accounting for fish size) than in northern populations. Despite variability among populations, size-at-maturity (L₅₀) significantly varied with latitude and northern individuals matured at smaller size (lower L₅₀). Parasite prevalence ranged from 0.0 to 26.7% but parasite richness was very low; all the parasites identified were larvae of pleurocercoid cestodes belonging to the order Pseudophyllidea. The abundance of mosquitofish parasites decreased with latitude and the presence and number of parasites infecting the mosquitofish had a significant negative effect on fish condition. The significant effects of latitude on the catch rates, life history and parasites of mosquitofish highlight the importance of latitudinal studies of invasive species to understand the interactive mechanisms of climate change and biological invasions.     

Gene Flow and Maintenance of Genetic Diversity in Invasive Mosquitofish (Gambusia holbrooki)

Genetic analyses contribute to studies of biological invasions by mapping the origin and dispersal patterns of invasive species occupying new territories. Using microsatellite loci, we assessed the genetic diversity and spatial population structure of mosquitofish (Gambusia holbrooki) that had invaded Spanish watersheds, along with the American locations close to the suspected potential source populations. Mosquitofish populations from the Spanish streams that were studied had similar levels of genetic diversity to the American samples; therefore, these populations did not appear to have undergone substantial losses of genetic diversity during the invasion process. Population structure analyses indicated that the Spanish populations fell into four main clusters, which were primarily associated with hydrography. Dispersal patterns indicated that local populations were highly connected upstream and downstream through active dispersal, with an average of 21.5% fish from other locations in each population. After initially introducing fish to one location in a given basin, such dispersal potential might contribute to the spread and colonization of suitable habitats throughout the entire river basin. The two-dimension isolation-by-distance pattern here obtained, indicated that the human-mediated translocation of mosquitofish among the three study basins is a regular occurrence. Overall, both phenomena, high natural dispersal and human translocation, favor gene flow among river basins and the retention of high genetic diversity, which might help retain the invasive potential of mosquitofish populations.     

Reproductive biology of Gambusia affinis holbrooki Baird and Girard, Xiphophorus helleri (Gunther) and X. maculatus (Heckel) (Pisces; Poeciliidae) in Queensland, Australia

The reproductive biology of three introduced Poeciliidae, Gambusia affinis holbrooki Baird and Girard, Xiphophorus helleri (Günther) and X. maculatus (Heckel) was studied over a 14-month period in Brisbane, Queensland. Photoperiod and water temperature determined the length of the breeding season in G. affinis , which produced up to nine broods between August and March, with the peak of reproductive activity in October. Fecundity was linearly related to body weight in G. affinis (mean fecundity = 22.78 ± 1.02, range = 3–108 offspring per brood).
Xiphophorus helleri bred from August to May, producing eight to nine broods, with peak reproductive activity from October to December. Fecundity was curvilinearly related to body weight (mean fecundity = 60.15 ± 3.8, range = 7–183 offspring per brood. Xiphophorus maculatus bred between September and March, producing five to six broods during the study period. Fecundity was linearly related to standard length (s.l.) (mean fecundity = 27.27 ± 2.4, range = 3–92 offspring per brood). Although the reproductive strategy of the three species differs, all have the capacity to build up large populations in south-eastern Queensland. Their present distributions and relative abundance are discussed.     

Changes in concentrations of glycolysis and Krebs cycle metabolites in mosquitofish,Gambusia holbrooki,induced by mercuric chloride and starvation

Synopsis Concentrations of glycolysis and Krebs cycle metabolites in the tail tissues of mosquitofish,Gambusia holbrooki, were measured in response to starvation and to exposure to 0.62 mg Hg l^–1 (as HgCl₂) for 48 h. In control fish, starvation caused decreased concentrations of glucose-6-phosphate (GO, –58%) and fructose-6-phosphate (F6P, –79%). Mercury exposure resulted in decreased concentrations of G6P (– 56%) and F6P (– 79%), and to increased concentrations of pyruvate (+ 75%), -ketoglutarate (+ 41%), succinate (+ 39%), and malate (+ 47%). Krebs cycle activity increased in response to mercury exposure, perhaps in response to greater energy needs associated with maintaining homeostasis under stressful conditions. We conclude that glycolytic activity is reduced in fish exposed to mercury and that this response is similar to that caused by a cessation of feeding.     

Chitosan-Nanoconjugated Hormone Nanoparticles for Sustained Surge of Gonadotropins and Enhanced Reproductive Output in Female Fish

A controlled release delivery system helps to overcome the problem of short life of the leutinizing hormone releasing hormone (LHRH) in blood and avoids use of multiple injections to enhance reproductive efficacy. Chitosan- and chitosan-gold nanoconjugates of salmon LHRH of desired size, dispersity and zeta potential were synthesized and evaluated at half the dose rate against full dose of bare LHRH for their reproductive efficacy in the female fish, Cyprinus carpio. Whereas injections of both the nanoconjugates induced controlled and sustained surge of the hormones with peak (P<0.01) at 24 hrs, surge due to bare LHRH reached its peak at 7 hrs and either remained at plateau or sharply declined thereafter. While the percentage of relative total eggs produced by fish were 130 and 67 per cent higher, that of fertilised eggs were 171 and 88 per cent higher on chitosan- and chitosan-gold nanoconjugates than bare LHRH. Chitosan nanoconjugates had a 13 per cent higher and chitosan gold preparation had a 9 per cent higher fertilization rate than bare LHRH. Histology of the ovaries also attested the pronounced effect of nanoparticles on reproductive output. This is the first report on use of chitosan-conjugated nanodelivery of gonadotropic hormone in fish.