Predation Risk Reduces a Female Preference for Heterospecific Males in the Green Swordtail

The presence of a predator can result in the alteration, loss or reversal of a mating preference. Under predation risk, females often change their initial preference for conspicuous males, favouring less flashy males to reduce the risk of being detected by predators. Previous studies on predator‐induced plasticity in mate preferences have given females a choice between more and less conspicuous conspecific males. However, in species that naturally hybridize, it is also possible that females might choose an inconspicuous heterospecific male over a conspicuous conspecific male under predation risk. Our study addresses this question using the green swordtail (Xiphophorus helleri) and the southern platyfish (Xiphophorus maculatus), which are sympatric in the wild. We hypothesized that X. helleri females would prefer the sworded conspecific males in the absence of a predator but favour the less conspicuous, swordless, heterospecific males in the presence of a predator. Contrary to our expectation, females associated more with the heterospecific male than the conspecific male in the control (no predator) treatment, and they were non‐choosy in the predator treatment. This might reflect that females were attracted to the novel male phenotype when there was no risk of predation but became more neophobic after predator exposure. Regardless of the underlying mechanism, our results suggest that predation pressure may affect female preferences for conspecific versus heterospecific males. We also found striking within‐population, between‐individual variation in behavioural plasticity: females differed in the strength and direction of their preferences, as well as in the extent to which they altered their preferences in response to changes in perceived predation risk. Such variation in female preferences for heterospecific males could potentially lead to temporal and spatial variation in hybridization rates in the wild.     

Experience Plays a Role in Female Preference for Symmetry in the Swordtail Fish Xiphophorus malinche

Variation in female mating preferences was previously detected in wild-caught Xiphophorus cortezi and Xiphophorus malinche females: smaller (presumed younger) females preferred symmetrical males, while larger (presumed older) females preferred asymmetrical males. We examined the influence of experience on this variation in female preference by determining if X. malinche females would express a preference for symmetry as virgins, shift their preferences for bar symmetry as they got larger (older) and if experience with males of different bar number symmetry could explain the variation in female preference previously detected. Virgin females exhibited no preference for vertical bar number symmetry when tested in the young- or old-age classes. However, young virgins spent more time with the opposite treatment in the second when compared with first test, indicating an ability to detect the difference between symmetry and asymmetry, and potentially a preference to mate with multiple males. When females were reared in one of three treatments, housed with symmetrical, barless or both symmetrical and asymmetrical males, we detected both a treatment and tank effect on strength of preference for symmetry, suggesting that barring pattern and some other aspect of the social environment influenced the development of this mating preference. Finally, we detected no effect of age class on mean strength of preference for symmetry; however, there was a statistically different relationship between female size and strength of preference for symmetry across the two age classes, suggesting that the preference function for symmetry may not be linear in relation to female size.     

Defining Vertical Bars in Relation to Female Preference in the Swordtail Fish Xiphophorus cortezi (Cyprinodontiformes, Poeciliidae)

Defining a male trait in relation to female preference is an important step towards determining the role that female preference has played in the evolution of a male trait. The pigment pattern 'vertical bars' is a complex male trait that functions as a sexual signal in swordtail fishes. A previous study suggested that X. cortezi females had a preference for males with more vertical bars. In that study, however, bar number had been reduced on the stimulus males by removing the most posterior bars, which changed the distance over which the bars spanned, in addition to changing bar number. To determine whether X. cortezi females have a preference for greater bar span and/or number of bars, we tested for female preference in two experiments. First, we gave females a choice between males with a greater bar span or a smaller bar span, holding bar number and total pigmented area constant. Females spent significantly more time with the males with the smaller bar span. This result, together with results from the previous study, suggest that females do not assess bar span alone, but possibly a composite component of the bars, such as bar frequency (number of bars/bar span). Secondly, we gave females a choice between six thinner bars or one wider bar of equal pigmented area. The six-bar treatment had a greater bar span in addition to more bars. We detected no preference for either treatment. These results suggest that the previously detected preference for more bars may actually reflect a preference for greater pigmented area. Finally, we present data on natural variation in the bars for X. cortezi and use principal components analysis to provide a composite definition of this trait.     

Conspicuous Female Ornamentation and Tests of Male Mate Preference in Threespine Sticklebacks (Gasterosteus aculeatus)

Sexual selection drives the evolution of exaggerated male ornaments in many animal species. Female ornamentation is now acknowledged also to be common but is generally less well understood. One example is the recently documented red female throat coloration in some threespine stickleback (Gasterosteus aculeatus) populations. Although female sticklebacks often exhibit a preference for red male throat coloration, the possibility of sexual selection on female coloration has been little studied. Using sequential and simultaneous mate choice trials, we examined male mate preferences for female throat color, as well as pelvic spine color and standard length, using wild-captured threespine sticklebacks from the Little Campbell River, British Columbia. In a multivariate analysis, we found no evidence for a population-level mate preference in males, suggesting the absence of directional sexual selection on these traits arising from male mate choice. Significant variation was detected among males in their preference functions, but this appeared to arise from differences in their mean responsiveness across mating trials and not from variation in the strength (i.e., slope) of their preference, suggesting the absence of individual-level preferences as well. When presented with conspecific intruder males, male response decreased as intruder red throat coloration increased, suggesting that males can discriminate color and other aspects of phenotype in our experiment and that males may use these traits in intrasexual interactions. The results presented here are the first to explicitly address male preference for female throat color in threespine sticklebacks.     

Female Mate Preference for Males Having Long and Symmetric Fins in the Bower-holding Cichlid Cyathopharynx furcifer

Female mate preference in a bower-holding cichlid, Cyathopharynx furcifer, was studied in Lake Tanganyika. Most males held territories with crater-shaped bowers in sand, but some males held territories without bowers. Territories were distributed adjacently and females visited them to spawn. After engaging in circling behaviour with the male, a female deposited eggs in the bower. Soon after spawning, the female picked the eggs up into her mouth and brooded them in places away from male territories. Female mate choice appeared to follow three steps: 1) females visited only bower-holding male territories, and more frequently visited territories of males that performed courtship displays at a higher frequency and had longer pelvic fins; 2) females preferred to start circling with males having longer and more symmetrical pelvic fins; 3) females chose males with more symmetrical pelvic fins as their mates. Less than 7% of females that visited male territories spawned eggs in the bowers. In contrast to other bower-holding species, bower size did not correlate with male reproductive success in C. furcifer. Bowers may therefore be essential as spawning sites or may function as a species recognition character for females. Female choice may be dependent instead on males having long and symmetrical pelvic fins apparent during the circling behaviour carried out in the bowers.     

Achromatic Plumage Reflectance, Social Dominance and Female Mate Preference in Black-Capped Chickadees (Poecile atricapillus)

Individual variation in achromatic plumage reflectance of male Black‐capped Chickadees (Poecile atricapillus) is correlated with social rank and reproductive success, suggesting it may play an important role in sexual signaling. We asked whether female chickadees could assess male quality based on plumage, in the absence of information about relative social dominance. Sexually mature but inexperienced females captured during the pair formation period in late fall and early winter were presented with a choice of two unfamiliar, sexually experienced males in separate compartments of an outdoor mate choice arena. Following each preference trial, we released the males into a single compartment and scored their pairwise dominance interactions. In 10 of 11 trials, females spent significantly more time with the male subsequently identified as dominant, despite not witnessing the males interact. Spectral analysis of male plumage reflectance revealed that UV‐chroma of dark body regions (bib, cap and mantle) was significantly greater in dominant, preferred males and that dominant, preferred males had significantly brighter white cheek patches. There were no differences in vocalization rates of preferred and non‐preferred males. These results show that female chickadees can rapidly assess unfamiliar males based on visual cues, and suggest that variation in achromatic plumage functions in sexual signaling.     

Co-Occurrence of Preference Functions and Acceptance Thresholds in Female Choice: Mate Discrimination in the Lesser Wax Moth

Basic economic models adapted from foraging theory predict that decisions in mate choice may be determined either by ‘best‐of‐n’ preference functions or by sequential rules incorporating acceptance thresholds. However, in some species, more complex determinations that incorporate versions of both protocols are found. To understand the functions of co‐occurring protocols, we studied mating decisions in the lesser wax moth, Achroia grisella (Lepidoptera: Pyralidae), an acoustic species in which females prefer males, the advertisement songs of which are delivered at relatively high ‘pulse‐pair’ rates. In addition to this preference, A. grisella females avoid mating with a male, the song of which does not exceed a minimum pulse‐pair rate, and they hold to this criterion even when no other singing males are present and regardless of song amplitude. Thus, mating decisions are not simply based on acoustic power (pulse‐pair rate × amplitude). We recorded male songs and female responses in an A. grisella population and found that male pulse‐pair rates showed a median of 87/s and ranged from 50 to 115/s, while female acceptance thresholds for male song showed a median of 60/s and ranged from 30 to 105/s. The distributions of thresholds were approximately normal and were not significantly skewed toward the right. Male song rates declined slightly with age, but female thresholds remained stable over the adult lifespan. Both the male and female traits showed significant repeatability within individuals. Whereas phylogenetic inference indicates that hearing in pyralid moths originated as a means of avoiding predation by insectivorous bats, the specific distribution of female acceptance thresholds suggests that currently this protocol does not primarily function to preclude inappropriate, and potentially lethal, responses to bat echolocations: pulse rates in the searching‐phase echolocations used by either aerial‐hawking or substrate‐gleaning bats mostly range from 10 to 20/s, and the lack of positive skew in the distribution of thresholds indicates an absence of directional selection from the left. Rather, we infer that thresholds augment preference functions in A. grisella by precluding mating with males which are markedly inferior in a critical song character. In general, co‐occurring protocols may be important where population density fluctuates markedly, as preference functions may be ineffective in preventing mating with inferior males when density is low.     

Experimental Evidence for Male Sequential Mate Preference in a Lekking Species

In lekking species females visit male aggregations solely to copulate or have their eggs fertilized. Because lekking males do not contribute to parental care, evolutionary theory does not expect them to be choosy. However, we show here that in the cichlid fish Astatotilapia flaviijosephi the lekking males exhibit sequential mate preference that strongly suggests a trade‐off between present and future reproductive effort. We tested mate preferences of A. flaviijosephi males by sequentially presenting them with two images of a gravid female, differing only in size. Previously, males were shown to prefer larger, more fecund females in simultaneous preference tests. The sequential presentation experiment reported here indicates that even in the absence of simultaneous presentation, males spent more time courting larger female images, and stayed longer in their vicinity. Thus, our study suggests that lekking males may be much choosier than previously appreciated. Furthermore, considering the intense competition among lekking males we also suggest that male choosiness, combined with other factors, may help to solve the ‘paradox of the lek’. It can make less attractive females more available to subordinate males, thereby increasing the contribution of the latter to the population gene pool and keeping genetic variability among males at a level that justifies female choice.     

Female Mate Preference and Male Mating Success of Ayu Fish,Plecoglossus altivelis (Osmeridae) under a Promiscuous Mating System

The ayu, Plecoglossus altivelis, is known to show wide variation in adult body size. We examined the spawning behavior in experimental spawning groups of fish in which male body size varied. Males never competed with each other for females or spawning site, while females spawned repeatedly, 17–97 times depending on body size, with previous or novel males. Males exhausted their sperm after a single mating episode, on average, regardless of body size. Moreover, repeated sperm production apparently reduced the residual lifespan. Females preferred mating simultaneously with more than one male and allowed males of body size similar to their own to mate more frequently. Thus the largest male within a spawning group was not always the most successful at mating, but mating success of any given male appears to depend upon body size distribution of females within the population. Female mate preference has apparently evolved to ensure complete fertilization under circumstances where males have been selected to economize sperm output during any one mating episode.     

Brain Regions Associated to a Kinesthetic Illusion Evoked by Watching a Video of One's Own Moving Hand

It is well known that kinesthetic illusions can be induced by stimulation of several sensory systems (proprioception, touch, vision…). In this study we investigated the cerebral network underlying a kinesthetic illusion induced by visual stimulation by using functional magnetic resonance imaging (fMRI) in humans. Participants were instructed to keep their hand still while watching the video of their own moving hand (Self Hand) or that of someone else''s moving hand (Other Hand). In the Self Hand condition they experienced an illusory sensation that their hand was moving whereas the Other Hand condition did not induce any kinesthetic illusion. The contrast between the Self Hand and Other Hand conditions showed significant activation in the left dorsal and ventral premotor cortices, in the left Superior and Inferior Parietal lobules, at the right Occipito-Temporal junction as well as in bilateral Insula and Putamen. Most strikingly, there was no activation in the primary motor and somatosensory cortices, whilst previous studies have reported significant activation in these regions for vibration-induced kinesthetic illusions. To our knowledge, this is the first study that indicates that humans can experience kinesthetic perception without activation in the primary motor and somatosensory areas. We conclude that under some conditions watching a video of one''s own moving hand could lead to activation of a network that is usually involved in processing copies of efference, thus leading to the illusory perception that the real hand is indeed moving.     

Male Courtship Pheromones Affect Female Behaviour in the Swordtail Characin (Corynopoma riisei)

Pheromones constitute an important cue used by both males and females during courtship. Here, we investigate the effect of male pheromones on female behaviour in the swordtail characin (Corynopoma riisei), a species of fish where males have a caudal pheromone gland which has been suggested to affect female behaviour during courtship. We subjected female C. riisei to male courtship pheromones and investigated the effect on both female behaviour and brain serotonergic activity levels compared to a control group. While no difference in serotonergic activity was found, the pheromone‐treated females showed lower stress levels compared to the control group. Furthermore, pheromone‐treated females increased locomotor activity over time, while a decrease in locomotor activity was observed in the control group. These results suggest that the male courtship pheromones may serve to reduce female stress and increase female activity, possibly to aid males in gaining access to females and facilitating sperm transfer.     

Sex Differences in Mate Preference Between Two Hybridizing Species of Poeciliid Fish

When hybridization between two species in secondary contact is costly, natural selection should favor pre‐mating isolation barriers. The invasive Gambusia affinis has been introduced to habitats of a closely related species, the endangered Gambusia nobilis. Although other Gambusia species readily hybridize in secondary contact, previous studies in this system found low abundance of hybrids in sympatry. To examine whether hybridization is limited by behavioral pre‐mating isolation that may have evolved in allopatry, I examined each species’ mating preferences using individuals from allopatric populations in male and female visual/olfactory association preference tests as well as open mating tests with and without male–male competition. Gambusia affinis and G. nobilis males had significant association preference for conspecific females in visual/olfactory tests. Only G. nobilis females had statistically significant preference for conspecific males. In open mating tests, males of both species had lower chase times overall when in competition, but there was no difference in number of copulation attempts. Males of both species had higher copulatory success rates with conspecific females when in competition, suggesting females may exert some control over copulation success of males. These results suggest that there are differences in mating preferences between these species. This mate choice may act as a pre‐mating isolating barrier to reduce hybridization in sympatry, a proposed threat to the endangered G. nobilis.     

Effect of Early Sucrose Diet on Ethanol Preference and Behavior in Male and Female Wistar Rats

The effect of adolescent sucrose diet on ethanol preference was studied in female and male Wistar rats. Our data show less pronounced ethanol preference in females. In males, pubertal exposure to sucrose was crucial for further ethanol preference, suggesting that cross-sensitization is more inherent to males than females, for whom the increased anxiety factor proved to be more significant. Finally, it was shown that in rats of both sexes habitual alcohol intake determins ethanol preference in the two-bottle test. Overall, our study demonstrates sex differences in ethanol preference as well as its anxiolytic properties.     

Influence of Female Age on Variation of Mate Choice Behavior in Mediterranean Fruit Fly (Diptera: Tephritidae)

In spite of the fact that studies concerning the mate choice by females have largely been based on the idea of the unanimity of the preference for certain male characteristics, variations in this behavior have been reported. Considering this aspect, we studied the influence of female age on mate choice and on the acceptance of courting by males of different ages in lab-reared medflies. The effects of the age of both sexes on the total courtship duration and on the behavioral units performed by males were also examined. Our results demonstrated that: (1) 4 to 12 day-old females prefer younger males; (2) 20 day-old females were less selective; (3) the acceptance of courting was not influenced by male age neither by the duration of behavioral units of courtship; (4) only the duration of continuous wing vibration was affected by the age of both sexes.     

Female Remating Behavior in a Lekking Moth

In polyandrous species, male reproductive success will at least partly be determined by males' success in sperm competition. To understand the potential for post‐mating sexual selection, it is therefore important to assess the extent of female remating. In the lekking moth Achroia grisella, male mating success is strongly determined by female choice based on the attractiveness of male ultrasonic songs. Although observations have indicated that some females will remate, only little is known about the level of sperm competition. In many species, females are more likely to remate if their first mating involved an already mated male than if the first male was virgin. Potentially, this is because mated males are less well able to provide an adequate sperm supply, nutrients, or substances inhibiting female remating. This phenomenon will effectively reduce the strength of pre‐copulatory sexual selection because attractive males with high mating success will be more susceptible to sperm competition. We therefore performed an experiment designed both to provide a more precise estimate of female remating probability and simultaneously to test the hypothesis that female remating is influenced by male mating history. Overall, approximately one of five females remated with a second male. Yet, although females mated to non‐virgin males were somewhat more prone to remate, the effect of male mating history was not significant. The results revealed, however, that heavier females were more likely to remate. Furthermore, we found that females' second copulations were longer, suggesting that, in accordance with theory, males may invest more sperm in situations with an elevated risk of sperm competition.     

Seismic Signaling is Crucial for Female Mate Choice in a Multimodal Signaling Wolf Spider

Complex courtship signals can be dissected into distinct components that can either function independently or via interactions with one another. Male Rabidosa rabida wolf spiders use courtship displays that couple a seismic signal with the waving of an ornamented foreleg. While previous studies suggest that female R. rabida exhibit mate choice and that both the seismic and visual modalities are important in mating interactions, it remains unclear how variation in each component influences female mating decisions. To investigate this, we ran two separate experiments in which we manipulated (1) male diets, to induce variation in the seismic courtship signal, and (2) male foreleg color, to artificially induce variation in visual foreleg ornamentation. To determine the influence of variation in each component independently, females were paired with males in environments that allowed the detection of only the manipulated signal component (e.g. seismic signal only and visual signal only). Variability in the seismic signal alone influenced female mate choice, but variability in visual ornamentation alone did not. In a third experiment, we manipulated foreleg color and allowed it to interact with the seismic signal to determine whether inter‐signal interactions influence female mating decisions. When females were able to detect both signal components, variation in visual ornamentation did influence mate choice – females preferred ornamented males. Together, these results suggest that the seismic signal of male R. rabida is integral for female mate choice and that the components of the courtship display interact to influence female mating decisions.     

Genomic Regions Associated with Amino Acid Composition in Soybean

Soybean [Glycine max (L.) Merr.] is the single largest source of protein in animal feed. However, few studies have been conducted to evaluate genomic regions controlling amino acid composition in soybean. It is important to study the genetics of amino acid composition to achieve improvements through breeding. The objectives of this study were to determine the ratios between essential to non-essential (E:NE) and essential to total (E:T) amino acids, and to identify genomic regions controlling essential and non-essential amino acid composition in soybean seed. To achieve these objectives, 101 F₆-derived recombinant inbred lines (RIL) developed from a cross of N87-984-16 × TN93-99 were used. Ground soybean seed samples were analyzed for amino acids using a near infrared spectroscopy (NIRS) instrument. A significant (p < 0.01) difference among the RIL was found for amino acid composition. Heritability estimates on an entry mean basis ranged from 0.13 for His to 0.67 for Tyr. A total of 94 polymorphic simple sequence repeat (SSR) molecular genetic markers were screened in DNA from progenies. Single factor ANOVA was used to identify candidate quantitative trait loci (QTL), which were then confirmed by QTL Cartographer. At least one QTL for each amino acid was detected in this population. QTL linked to molecular markers Satt143, Satt168, Satt203, Satt274 and Satt495 were associated with most of the amino acids. Phenotypic variation explained by an individual QTL ranged from 9.4 to 45.3%. QTL detected for amino acids in soybean in this experiment are expected to be useful for future breeding programs targeting development of improved soybean amino acid composition for human and animal nutrition.     

Female Medflies Mate Selectively with Young Males but Gain No Apparent Fitness Benefits

Species in which female choice is not strongly shaped by male-controlled resources present a challenge to sexual selection research, because it is typically difficult to identify the male phenotypic cues used in female mate selection or the fitness benefits accruing from such selection. In such species, mate selection is presumably based on direct benefits associated with sperm quantity or quality and/or indirect benefits relating to the viability or mating probability of the progeny. Across animal taxa in general, male age has received considerable attention as a potential indicator of these fitness benefits, and the importance of male age in affecting female choice and fitness has been investigated in various insect species with highly variable results. The present study examined whether females of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wied.), a lek-forming species, discriminate among potential mates on the basis of male age and whether this selectivity results in fitness benefits to the females. Both young (10 days old) and old (40 days old) females were offered males from two groups differing in age by 10, 20, or 30 days. Young females mated randomly when the age difference between the younger and older males was 10 days but mated preferentially with the younger males when the age difference was 20 or 30 days. Old females did not discriminate among males of different ages. Although young females showed mate selectivity, we found no differences in fecundity, fertility, or larval viability between young females mated to 10 versus 40 day old males.