Laboratory Mating Research Articles

An expanded concept of Ceratocystis manginecans and five new species in the Latin American clade of Ceratocystis

ABSTRACT The genus Ceratocystis contains a number of emerging plant pathogens, mostly members of the Latin American Clade (LAC), in which there are several unresolved taxonomic controversies. Among the most important are Brazilian pathogens in the C. fimbriata complex, C. manginecans and C. eucalypticola. Representatives of C. manginecans and C. eucalypticola from India and China, respectively, were shown to be fully interfertile in laboratory matings, and hybrids between the putative species were identified on Punica in India. An Indian tester strain was sexually compatible with representatives of what has been considered C. fimbriata on numerous hosts across Brazil. In this revision of the LAC, the name C. fimbriata is restricted to the widely dispersed Ipomoea strain, and C. manginecans is recognized as a Brazilian species that is important on Mangifera, Eucalyptus, and many other crops. C. mangivora and C. mangicola are also considered synonyms of C. manginecans. Based on phylogenetics and mating studies, two other Brazilian species are recognized: C. atlantica, sp. nov., and C. alfenasii, sp. nov., each with wide host ranges. Three new Caribbean species are recognized based on phylogenetics and earlier inoculation studies: C. costaricensis, sp. nov., on Coffea, C. cubensis, sp. nov., on Spathodea, and C. xanthosomatis, sp. nov., on the vegetatively propagated aroids Xanthosoma and Syngonium. Some of the other Ceratocystis species were based primarily on unique internal transcribed spacer (ITS) rDNA sequences, but the unreliability of rDNA sequences was demonstrated when intraspecific crossing of isolates with differing ITS sequences generated single-ascospore progeny with intragenomic variation in ITS sequences and others with new ITS sequences. Species recognition in Ceratocystis should use phenotype, including intersterility tests, to help identify which lineages are species. Although some species remain under-studied, we recognize 16 species in the LAC, all believed to be native to Latin America, the Caribbean region, or eastern USA.

Propensity for selfing varies within a population of hermaphroditic snails: coexistence of selfers, outcrossers and mixed-mating individuals.

To understand mating-system evolution in self-compatible hermaphrodites, variation in selfing rates is highly relevant. Empirical studies are rarely designed to capture variation between individuals, instead often comparing species and populations. Yet, evolution primarily occurs within populations, rendering among-individual variation essential. Observed individual selfing rates depend on the environment (e.g. differences in mate availability) and individuals' propensity for selfing. We quantified individual variation in selfing propensity in the snail Radix balthica by conducting laboratory mating trials that manipulated mate availability (low versus moderate) and estimating selfing rates from progeny arrays. We also measured female lifetime fitness. We found substantial among-individual variation in selfing propensity, including pure selfers (32%), pure outcrossers (31%) and mixed-mating individuals that selfed and outcrossed (37%). Experimental levels of mate availability did not significantly affect selfing rates. Selfers had reduced female liftetime fitness. Our results show that the propensity for selfing can differ considerably among individuals, with similar proportions of selfers, outcrossers and mixed maters. As mate availability did not affect selfing, our 'moderate' experimental level of mate availability might still have been too low to prompt selfers to outcross. This and the observed fitness differences also cautiously suggest that investigating the heritability of selfing propensities might be worthwhile in this population.

Paternity Analyses for the Planning of SIT Projects against the Red Palm Weevil

The red palm weevil Rhynchophorus ferrugineus is an invasive pest from southeastern Asia and Melanesia that has spread widely across the Middle East and the Mediterranean Basin over the last 30 years. Its endophagous larvae cause huge amounts of damage to several palm tree species from the Arecaceae family. Many of these palms are economically important for agricultural and ornamental purposes. Therefore, a lot of attention has recently been focused on studying this species with the aim of identifying sustainable and effective eradication strategies. Sterile insect techniques are biological control strategies that are currently being investigated for their potential to eradicate this pest in selected invasion areas. Mating system features (e.g., polyandry and related features) can affect the success and suitability of these approaches. The main goal of this research was to assess the performance of a previously developed microsatellite panel in terms of the paternity assignment of progeny from laboratory mating experiments. Using a simulation approach, we evaluated the reliability of the microsatellite markers in the paternity tests both in complex laboratory experiment scenarios and on the progeny of wild-caught gravid females to help future studies on the RPW mating system. As a case study of the simulation results, we performed two double-mating experiments, genotyped the progeny and estimated the P2 values to compare to the expected progeny genotypes according to the crossing scheme of each experiment. The results of our simulations on laboratory experiments showed that it was possible to carry out paternity assignments for all progeny with reliable statistical confidence using our 13 microsatellites set. On the contrary the low genetic variability measured in red palm weevil populations in invaded areas made the resolution power of our loci too low to carry out paternity analyses on natural populations. Results of laboratory crossing were completely congruent with the expectations from the Mendelian laws.

Conjugation across Bacillus cereus and kin: A review.

Horizontal gene transfer (HGT) is a major driving force in shaping bacterial communities. Key elements responsible for HGT are conjugation-like events and transmissible plasmids. Conjugative plasmids can promote their own transfer as well as that of co-resident plasmids. Bacillus cereus and relatives harbor a plethora of plasmids, including conjugative plasmids, which are at the heart of the group species differentiation and specification. Since the first report of a conjugation-like event between strains of B. cereus sensu lato (s.l.) 40 years ago, many have studied the potential of plasmid transfer across the group, especially for plasmids encoding major toxins. Over the years, more than 20 plasmids from B. cereus isolates have been reported as conjugative. However, with the increasing number of genomic data available, in silico analyses indicate that more plasmids from B. cereus s.l. genomes present self-transfer potential. B. cereus s.l. bacteria occupy diverse environmental niches, which were mimicked in laboratory conditions to study conjugation-related mechanisms. Laboratory mating conditions remain nonetheless simplistic compared to the complex interactions occurring in natural environments. Given the health, economic and ecological importance of strains of B. cereus s.l., it is of prime importance to consider the impact of conjugation within this bacterial group.

Resource partitioning is not coupled with assortative mating in sympatrically divergent ricefish in a Wallacean ancient lake.

Sympatric speciation is considered to be difficult without the coupling between ecological traits that allow resource partitioning and reproductive traits that allow assortative mating. Such "magic traits" are known to be involved in most of the compelling examples of sympatric speciation. In this study, we report a possible case of sympatric speciation without magic traits. Three species of ricefish (genus Oryzias) are suggested to have diverged sympatrically within Lake Poso, an ancient lake in Sulawesi. An analysis of genome-wide single-nucleotide polymorphisms showed that these three species are reproductively isolated from each other throughout the lake. Stable isotope analyses revealed that the three species use different food resources, which reflect differences in their feeding morphologies (gill rakers and digestive tracts) and feeding sites. Field and laboratory observations showed that O.nebulosus and O.orthognathus share a mating habitat of cobbles, where they scatter fertilized eggs, whereas this site is never used by O.nigrimas, indicating that assortative mating is partly achieved by spatial isolation. The small, less-adhesive eggs of O.nebulosus and O.orthognathus probably reflect their adaptation to spawning on cobble beaches. Laboratory mating experiments showed strong prezygotic isolation between O.nebulosus and O.orthognathus, which is achieved by strong species recognition presumably by both sexes based on species-specific mating dances and nuptial coloration. In summary, the assortative mating of O.nebulosus and O.orthognathus is probably not coupled to resource partitioning. We discussed how sympatric speciation among these species might have been achieved even without magic traits.

Comparative sexual selection in field and laboratory in a guild of sepsid dung flies

Phenomenological and behavioural studies have greatly advanced the study of natural selection. Field studies of selection well appraise the natural situation, but is this also true for laboratory studies, which are typically more mechanistic? We compared precopulatory sexual selection (mating differential based on pairing success) in field and laboratory of several closely related, ecologically similar black scavenger dung flies (Diptera: Sepsidae). Selection on fore femur (sexual trait) and wing size (nonsexual trait) and shape varied considerably among seven species and continental populations in agreement with variation in their mating system and sexual size dimorphism. Selection on trait size was mostly positive or nil, but never significantly negative, implying mating advantages of large males in most species. Strongest selection was found in species/populations with male-biased size dimorphism, associating evolutionary shifts from female- to male-biased dimorphism with intensified sexual selection for large male size by adding male –male competition to a mating system previously driven primarily by female choice. Although sexual selection on shape was closely aligned with allometric shape variation, selection on fore femur shape was more consistent than selection on wing shape, which was absent in most species. Sexual selection intensities, but not necessarily the underlying behavioural mechanisms, were overall similar in field and laboratory, suggesting that laboratory assessments well represent the natural situation. If this conclusion can be generalized, it would lend credence to the strategy of using controlled laboratory mating studies to better understand natural selection, behaviour and ecology, at least for smaller animals that can be held in captivity.

Combined effects of temperature and hypoxia shape female brooding behaviors and the early ontogeny of the Chilean kelp crab Taliepus dentatus

The ecophysiology of marine ectotherms is regulated by the interaction of temperature with environmental drivers, such as dissolved oxygen (DO). The combination of low levels of DO and temperature in the ocean affects physiological and behavioral responses, especially in early life history traits of marine species. Here, we aimed to investigate the combined effect of ecologically relevant values of temperature and DO on female brooding behavior as well as on the early ontogeny of the Chilean kelp crabTaliepus dentatus. In a laboratory experiment, after acclimation and mating of females and males in constant temperatures (11 or 14°C), we exposed brooding females to 1 of 2 temperatures (11 or 14°C) and 1 of 2 DO levels (normoxia or cycling hypoxia). We tested the effects of these 4 treatments on embryo and larval sizes, embryo developmental time, female brooding behavior (i.e. embryo ventilation), larval hatching (i.e. number of hatched larvae), Zoea 1 survival to starvation, and swimming speed. We found a negative effect of temperature on the size of early embryos, but no interactions were detected in embryo size during development. High temperature and low DO increased female brooding behavior and larval size, reduced the number of hatched larvae, and affected larval swimming speed. Embryo development time and larval survival were negatively affected by temperature. These results suggest that an increasing frequency of hypoxic events, combined with ocean warming, might have important consequences on marine invertebrate brooders, affecting female fecundity, larval performance and, potentially, their dispersal ability even well within their optimal thermal range.

Vocal divergence is concordant with genomic evidence for strong reproductive isolation in grasshopper mice (Onychomys).

Behavioral barriers to gene flow often evolve faster than intrinsic incompatibilities and can eliminate the opportunity for hybridization between interfertile species. While acoustic signal divergence is a common driver of premating isolation in birds and insects, its contribution to speciation in mammals is less studied. Here we characterize the incidence of, and potential barriers to, hybridization among three closely related species of grasshopper mice (genus Onychomys). All three species use long‐distance acoustic signals to attract and localize mates; Onychomys arenicola and Onychomys torridus are acoustically similar and morphologically cryptic whereas Onychomys leucogaster is larger and acoustically distinct. We used genotyping‐by‐sequencing (GBS) to test for evidence of introgression in 227 mice from allopatric and sympatric localities in the western United States and northern Mexico. We conducted laboratory mating trials for all species pairs to assess reproductive compatibility, and recorded vocalizations from O. arenicola and O. torridus in sympatry and allopatry to test for evidence of acoustic character displacement. Hybridization was rare in nature and, contrary to prior evidence for O. torridus/O. arenicola hybrids, only involved O. leucogaster and O. arenicola. In contrast, laboratory crosses between O. torridus and O. arenicola produced litters whereas O. leucogaster and O. arenicola crosses did not. Call fundamental frequency in O. torridus and O. arenicola was indistinguishable in allopatry but significantly differentiated in sympatry, a pattern consistent with reproductive character displacement. These results suggest that assortative mating based on a long‐distance signal is an important isolating mechanism between O. torridus and O. arenicola and highlight the importance of behavioral barriers in determining the permeability of species boundaries.

Too \u201csexy\u201d for the field? Paired measures of laboratory and semi-field performance highlight variability in the apparent mating fitness of Aedes aegypti transgenic strains

BackgroundEvaluating and improving mating success and competitive ability of laboratory-reared transgenic mosquito strains will enhance the effectiveness of proposed disease-control strategies that involve deployment of transgenic strains. Two components of the mosquito rearing process, larval diet quantity and aquatic environment - which are linked to physiological and behavioural differences in adults - are both relatively easy to manipulate. In mosquitoes, as for many other arthropod species, the quality of the juvenile habitat is strongly associated with adult fitness characteristics, such as longevity and fecundity. However, the influence of larval conditioning on mating performance is poorly understood. Here, we investigated the combined effects of larval diet amount and environmental water source on adult male mating success in a genetically modified strain of Aedes aegypti mosquitoes in competition with wild-type conspecifics. Importantly, this research was conducted in a field setting using low generation laboratory and wild-type lines.ResultsBy controlling larval diet (high and low) and rearing water source (field-collected and laboratory water), we generated four treatment lines of a genetically modified strain of Ae. aegypti tagged with fluorescent sperm. Laboratory reared mosquitoes were then competed against a low generation wild-type colony in a series of laboratory and semi-field mating experiments. While neither food quantity nor larval aquatic environment were found to affect male mating fitness, the transgenic lines consistently outperformed wild-types in laboratory competition assays, an advantage that was not conferred to semi-field tests.ConclusionsUsing a model transgenic system, our results indicate that differences in the experimental conditions of laboratory- and field-based measures of mating success can lead to variation in the perceived performance ability of modified strains if they are only tested in certain environments. While there are many potential sources of variation between laboratory and field lines, laboratory adaptation - which may occur over relatively few generations in this species - may directly impact mating ability depending on the context in which it is measured. We suggest that colony-hybridization with field material can potentially be used to mitigate these effects in a field setting. Release programs utilising mass-produced modified laboratory strains should incorporate comparative assessments of quality in candidate lines.

Quantification of Reproductive Isolating Barriers Between Two Naturally Hybridizing Killifish Species

Understanding the relative importance of various reproductive barriers to the early stages of speciation is an essential question in evolutionary biology. The closely related killifishes Fundulus heteroclitus and F. grandis occasionally hybridize in a small region in coastal Northeastern Florida showing that while barriers to reproduction exist, they are incomplete. The objective of this study was to elucidate barriers to reproduction between F. heteroclitus and F. grandis in the lab, as well as to quantify their strengths and relative contributions to reproductive isolation. Pre-zygotic (mating and fertilization) and post-zygotic (hatching) barriers were investigated by performing a variety of choice and no-choice laboratory mating experiments. Under no-choice conditions, barriers to mating had the greatest influence on hybrid production in F. grandis, whereas hatching barriers contributed to the majority of reproductive isolation in F. heteroclitus. Under choice conditions, however, pre-zygotic barriers had the greatest influence on hybrid production in both species. The total reproductive isolation that was observed in females of each species was stronger in F. heteroclitus than in F. grandis, and was nearly complete in F. heteroclitus females under choice conditions and was of moderate strength in F. grandis females. These results reveal an asymmetry in the potential gene flow between these two species, with F. grandis being more likely to hybridize than F. heteroclitus in the absence of environmental influences. No-choice backcrosses were also conducted and showed that at least some F1 hybrids are fertile. The observation that pre-zygotic barriers tend to be stronger than post-zygotic barriers in the early stages of speciation is consistent with similar studies in other organisms.

Last-male sperm precedence in Rhynchophorus ferrugineus (Olivier): observations in laboratory mating experiments with irradiated males.

The Red Palm Weevil (RPW) Rhynchophorus ferrugineus (Olivier 1790) is an invasive pest from southeastern Asia and Melanesia that in the last 30 years has spread widely in the Middle East and Mediterranean Basin. Its stem-boring larvae cause great damage to several palm species of the Arecaceae family, many of which are economically important for agricultural and ornamental purposes. Therefore, great attention has recently been focused in studying this species to identify sustainable and effective eradication strategies, such as sterile insect technique (SIT). The rapid spread of RPW is associated with its high reproductive success. To evaluate the suitability of a SIT strategy, particular physiological and behavioral aspects of RPW reproduction, such as the presence of polyandry and post-copulatory sperm selection mechanisms, were investigated. To determine paternity of progeny from multiply mated females, double-crossing experiments were carried out confining individual females with either a wild-type male or a γ-irradiated male (Co-60). Fecundity and fertility of females were scored to evaluate post-copulatory sperm selection. Results showed that progeny were almost exclusively produced by the sperm of the second male, suggesting that a last-male sperm precedence is expressed at high levels in this species, and providing interesting insights for an area-wide RPW management strategy such as the SIT.

Potential Hybridization between Two Invasive Termite Species, Coptotermes formosanus and C. gestroi (Isoptera: Rhinotermitidae), and Its Biological and Economic Implications.

The Asian subterranean termite, Coptotermes gestroi, is a tropical species but has increasingly been collected from the subtropics in recent years, making it sympatric to the Formosan subterranean termite, C. formosanus in at least three areas, Taiwan, Hawaii, and Florida. Simultaneous flights by these two species were observed since 2013 in South Florida, during which interspecies tandems were observed. Laboratory mating of C. formosanus and C. gestroi alates produced hybrid incipient colonies of larger population size. Studies are underway to examine the presence in the field of hybrid colonies in sympatric areas of Taiwan and Florida. Other biological characteristics of C. formosanus × C. gestroi hybrids being studied include temperature tolerance and preference, colony growth rate, wood-consumption rate, and reproductive fertility. This current research aims to determine the potential establishment of a hybrid termite population in south Florida and Taiwan. It investigates the risk of introgressive hybridization in field populations, with an emphasis on its potential ecological, evolutionary, and economic consequences.

Pacific Northwest Population ofLophocampa maculataHarris 1841: Evidence of a Possible Hybrid Origin

ABSTRACT. The different geographic populations of Lophocampa maculata Harris 1841 are characterized by a variety of phenotypic differences, of which larval color is the most obvious. Individuals of the Pacific Northwest (PNW) populations display significant variation in late instar coloration, arising from variation in setae pigmentation. Such variation is not found in other populations of Lophocampa maculata, including the western Interior population (WI) and California Coastal population (CAC). Analysis of the pattern of pigmentation of the PNW population suggests it represents a combination of features of the CAC and WI populations. A simple scheme that accounts for all of the color variations seen in the different geographic populations of L. maculata is presented. A laboratory mating experiment involving WI and CAC individuals resulted in viable offspring displaying the range of larval coloration seen in the wild PNW populations. The F1 hybrids were fertile and produced an F2 generation also exhibiti...

Mating type markers reveal high levels of heterothallism in Leptographium sensu lato

Species of Leptographium sensu lato are sap-stain fungi vectored by bark beetles and some species cause or are associated with tree diseases. Sexual states have been reported for more than 30 species in this group and these have been treated in the sexual genus Grosmannia. No sexual state is known for at least 59 additional species and these reside in the genus Leptographium. The discovery of sexual states for species of Leptographium relies mainly on the presence of fruiting bodies on host tissue at the time of isolation and/or intensive laboratory mating studies, which commonly have low levels of success. We developed mating-type markers to study sexual compatibility of species in Leptographium sensu lato. Using these markers, it was possible to identify mating types for 42 species and to determine thallism in many species for the first time. Surprisingly, the results showed that heterothallic and putatively heterothallic species are abundant (39 out of 42 species) in Leptographium sensu lato, and only three species were confirmed to be homothallic. The mating type markers developed in this study will be useful for future studies concerning mating type and sexual compatibility of species in this genus.

Velocity correlations in laboratory insect swarms

In contrast to animal groups such as bird flocks or migratory herds that display net, directed motion, insect swarms do not possess global order. Without such order, it is difficult to define and characterize the transition to collective behavior in swarms; nevertheless, visual observation of swarms strongly suggests that swarming insects do behave collectively. It has recently been suggested that correlation rather than order is the hallmark of emergent collective behavior. Here, we report measurements of spatial velocity correlation functions in laboratory mating swarms of the non-biting midge Chironomus riparius. Although we find some correlation at short distances, our swarms are in general only weakly correlated, in contrast to what has been observed in field studies. Our results hint at the potentially important role of environmental conditions on collective behavior, and suggest that general indicators of the collective nature of swarming are still needed.

Heterosis Increases Fertility, Fecundity, and Survival of Laboratory-Produced F1 Hybrid Males of the Malaria Mosquito Anopheles coluzzii.

The success of vector control strategies aiming to decrease disease transmission via the release of sterile or genetically-modified male mosquitoes critically depends on mating between laboratory-reared males and wild females. Unfortunately, mosquito colonization, laboratory rearing, and genetic manipulations can all negatively affect male competitiveness. Heterosis is commonly used to produce domestic animals with enhanced vigor and homogenous genetic background and could therefore potentially improve the mating performance of mass-reared male mosquitoes. Here, we produced enhanced hybrid males of the malaria mosquito Anopheles coluzzii by crossing two strains colonized >35 and 8 years ago. We compared the amount of sperm and mating plug proteins they transferred to females, as well as their insemination rate, reproductive success and longevity under various experimental conditions. Across experiments, widespread adaptations to laboratory mating were detected in the older strain. In large-group mating experiments, no overall hybrid advantage in insemination rates and the amount of sperm and accessory gland proteins transferred to females was detected. Despite higher sperm activity, hybrid males did not appear more fecund. However, individual-male mating and laboratory-swarm experiments revealed that hybrid males, while inseminating fewer females than older inbred males, were significantly more fertile, producing larger mating plugs and drastically increasing female fecundity. Heterotic males also showed increased longevity. These results validate the use of heterosis for creating hybrid males with improved fitness from long-established inbred laboratory strains. Therefore, this simple approach could facilitate disease control strategies based on male mosquito releases with important ultimate benefits to human health.

A dual function of white coloration in a nocturnal spider Dolomedes raptor (Araneae: Pisauridae)

Nocturnal animals frequently possess seemingly conspicuous colour patterns that can function in a variety of ways (e.g. prey attraction, camouflage, predator avoidance, etc.). The use of colour patterns in intraspecific signalling, especially reproductive activities, in nocturnal animals has received relatively little attention. This study tested for a dual function of colour in the nocturnal fishing spider, Dolomedes raptor (Araneae: Pisauridae), whose males develop dimorphic white stripes at sexual maturation. We tested for a role in foraging as well as mate assessment. First, quantifications of the natural variation of male stripes indicated a correlation between stripe area and male body size and weight. Subsequent diet experiments confirmed that the area of a male's white stripes are body size-dependent and thus could potentially convey information to choosey females about male quality. Field experiments used dummies resembling D. raptor in appearance to test a prey attraction function of the white stripes. We found that dummies with the white stripes present attracted significantly more prey than those without stripes. Finally, we used males with manipulated phenotypes in laboratory mating trials and found that males with intact white stripes were significantly more likely to be accepted by females than those with the white stripes eliminated. Together, our results document a nutrient-dependent trait that functions not only in strengthening foraging success, but also in a mating context, increasing male mating success. We suggest that the role of these male white stripes in reproduction has been facilitated by their function in foraging.

Time-Frequency Analysis Reveals Pairwise Interactions in Insect Swarms.

The macroscopic emergent behavior of social animal groups is a classic example of dynamical self-organization, and is thought to arise from the local interactions between individuals. Determining these interactions from empirical data sets of real animal groups, however, is challenging. Using multicamera imaging and tracking, we studied the motion of individual flying midges in laboratory mating swarms. By performing a time-frequency analysis of the midge trajectories, we show that the midge behavior can be segmented into two distinct modes: one that is independent and composed of low-frequency maneuvers, and one that consists of higher-frequency nearly harmonic oscillations conducted in synchrony with another midge. We characterize these pairwise interactions, and make a hypothesis as to their biological function.

Dense, small and male-biased cages exacerbate male–male competition and reduce female choosiness in Bicyclus anynana

Sexual selection is increasingly recognized to depend upon, and to fluctuate with, major ecological factors in natural environments. The operational sex ratio (OSR) and population density can affect the opportunity for, and strength of, sexual selection but their effects are rarely taken into account in laboratory behavioural studies. In Bicyclus anynana, a model butterfly for mate choice studies, the experimental set-up widely used in laboratories often involves very high densities compared to the field, malebiased sex ratios and small cage volumes. We hypothesized that these conditions impede the proper expression of female mating preference by promoting male competition and sexual harassment of females. Using various cage volumes, we separately manipulated OSR and density to cover the range of values used in B. anynana laboratory mating experiments and to approach field values. Male competition, quantified by the number and duration of courtships aborted by males, became stronger with increasing densities, specifically under more male-biased sex ratios, and decreasing cage volumes. Thus, male eagerness to mate was essentially due to the use of small cage volumes and very high experimental densities. Concomitantly, female choosiness, quantified by the proportion of rejections of male mating attempts, decreased with increasing densities under a male-biased sex ratio. Females also accepted more matings with decreasing cage volume, and mated more rapidly with increasing density. We conclude that the laboratory social environments frequently used to test mate choice in B. anynana, with unnaturally high densities and male-biased sex ratios, exacerbate maleemale competition and strongly hinder female choice, biasing the estimates of the strength and direction of sexual selection that were shaped under very different natural environments in the wild. We propose a set-up for B. anynana mate choice studies that allows the assessment of female choosiness in statistically robust mating experiments. © 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Understanding the processes of pair formation is a necessary, yet neglected, step to fully grasp how secondary sexual traits and mating preferences evolve under sexual selection. It requires taking into account the fact that sexual selection, like natural selection, takes place in ecologically complex environments and examining the two major selective agents of sexual selection, mate choice and within-sex competition, in an integrative way (Miller & Svensson, 2014). It is increasingly acknowledged that mating patterns depend on ecological and social constraints, which determine the

Latitudinal Variation in Male Competitiveness and Female Choosiness in a Fish: Are Sexual Selection Pressures Stronger at Lower Latitudes?

Tropical animals are characterized by their showy ornaments and conspicuous colors, and numerous studies on sexual selection have been conducted using tropical species as a model system. In this study, hypothesizing that sexual selection pressures are stronger at lower latitudes, we examined the latitudinal variation in the degree of (1) male aggressiveness in male–male competitions, (2) male eagerness in courtship, and (3) female choosiness to mates in the medaka fish (Oryzias latipes complex). Laboratory mating experiments revealed that males from lower-latitude populations fight each other and court females more frequently than males from higher-latitude populations, supporting the hypothesis that both intra- and intersexual selection pressures are stronger at lower latitudes. In addition, females from lower-latitude populations, where males are more conspicuous, did not accept males easily, especially when mated with higher-latitude males, suggesting that female choosiness has also coevolved across latitudes through Fisherian runaway process. We suggest that latitudinal cline in reproductive seasonality, which is the case not only in the medaka but also among a variety of taxa, leads to latitudinal cline in operational sex ratios of local populations, which ultimately results in latitudinal cline in sexual selection pressures.