Avoiding a compromise between sexual selection and species recognition: female swordtail fish assess multiple species-specific cues

Females increase their risk of mating with heterospecifics whenthey prefer the traits of conspecifics that overlap with traitsfound in heterospecifics. Xiphophorus pygmaeus females havea strong preference for larger males, which could lead to femalespreferring to mate with heterospecific males; almost all sympatricX. cortezi males are larger than X. pygmaeus males. In thisstudy, we show that X. pygmaeus females preferred the chemicalcues from conspecifics over those of X. cortezi males. However,preference for the chemical cues of conspecifics could not reversethe preference for larger heterospecific males. Only when femaleswere presented with two species-specific cues (vertical barsand chemical cues) did more females spend more time on averagewith the smaller conspecific males. These results support the"backup signal" hypothesis for the evolution of multiple preferences;together, the two species-specific cues increased the accuracywith which females were able to avoid heterospecific males.In addition, the results suggest that in those situations inwhich the traits of conspecifics overlap with traits found inheterospecifics, females can use the assessment of multiplecues to avoid mating with heterospecifics without compromisingtheir preference for the highest-quality conspecific.     

Sexes of a monomorphic species differ in preference for mates with a novel trait

We investigated the different roles of the sexes in the originationof novel traits in the sexually monomorphic Javanese mannikinLonchura leucogastroides. We introduced a red feather as anevolutionarily novel trait in both sexes and tested their preferencesfor prospective mates with this trait. Males rejected femalesbearing the red feather and preferred to court unadorned females.In contrast, females partly preferred adorned males. Specifically,previously unattractive males gained in attractiveness and could increasetheir reproductive success when bearing the ornament, whereas previouslyattractive males lost in attractiveness, but this did not affect theirreproductive success. We introduced two other novel traits inmales and investigated the females' response to these in matechoice tests. Each of the three new traits interacted with thenatural attractiveness of males. The more attractive a malewas before ornamentation, the more it lost in attractiveness afterornamentation and vice versa. Thus, the position of the traitdid not affect the interaction. Because males rejected adornedfemales and females partly preferred adorned males, novel traitsmight evolve by intersexual selection in males rather than infemales. This can lead to a sexual dimorphism with conspicuoustraits in males. Our study reveals a new insight into the mechanismof the evolution from monomorphism to dimorphism with ornamentaltraits in males.     

Carotenoids, oxidative stress and female mating preference for longer lived males

Some of the most spectacular exaggerated sexual ornaments are carotenoid dependent. It has been suggested that such ornaments have evolved because carotenoid pigments are limiting for both signal expression and in their role as antioxidants and immunostimulants. An implicit assumption of this hypothesis is that males which can afford to produce more elaborate carotenoid-dependent displays are signalling their enhanced ability to resist parasites, disease or oxidative stress and hence would be predicted to live longer. Therefore, in species with carotenoid-dependent ornaments where a parent's future longevity is crucial for determining offspring survival, there should be a mating preference for partners that present the lowest risk of mortality during the breeding attempt, as signalled by the ability to allocate carotenoids to sexual displays. In an experimental study using three-spined sticklebacks (Gasterosteus aculeatus), we show that when dietary carotenoid intake is limited, males attempt to maintain their sexual ornament at the expense of body carotenoids and hence suffer from reduced reproductive investment and a shorter lifespan. These males also suffer from an increased susceptibility to oxidative stress, suggesting that this may constitute the mechanism underlying the increased rate of ageing. Furthermore, in pairwise mate-choice trials, females preferred males that had a greater access to carotenoids and chance of surviving the breeding season, suggesting that females can make adaptive mate choice decisions based on a male's carotenoid status and potential future longevity.     

Male and female genitalia in some Libyan species of Acrididae (Orthoptera: Acridoidea)

A comparative study of male and female genitalia was carried out in thirty‐seven Libyan species representing twenty genera of the family Acrididae. An attempt has been made to describe and illustrate the different structures, namely, epiphallus, aedeagus, subgenital plate, supra‐anal plate and cerci of the male, and spermatheca, ovipositor, subgenital plate, supra‐anal plate and cerci of the female, in Acridids, with an aim to discover their significance in order to make the identification of genera and species, together with other generic characters, more perfect and convenient. Distinct family characters are shield or bridge‐shaped condition of epiphallus; presence or absence of dorso‐lateral appendices, oval sclerites and lophi on epiphallus; divided, undivided or flexured condition of aedeagus; presence or absence of gonopore process on aedeagus; condition of apical and pre‐apical diverticula of spermatheca; presence or absence of glandular pouches of Cornstock and Kellog on female subgenital plate; and rudimentary or well developed condition of egg‐guide. Stable characters for separating the subfamilies are taken to be presence or absence of ancorae on epiphallus, long or short condition of aedeagal sclerites; elongate, slender or short and broad condition of ovipositor valves: presence or absence of Jannone's organs and setae on posterior margin of female subgenital plate; and shape of diverticula of spermatheca. Useful generic characters are shape of male subgenital plate, supra‐anal plate and cerci, broad or narrow condition of bridge, presence or absence of branch of bridge connecting lophi with bridge of epiphallus; mono‐, bi‐ or tri‐lobate condition of lophi of epiphallus, length and upcurved or downcurved condition of apical valve of aedeagus, shape of posterior margin of female subgenital plate, presence of setae on the whole posterior margin or confined to lateral margins only; and toothed, tuberculate or smooth condition of ovipositor valves, length of the lateral apodeme in relation to the dorsal valves. Specific characters are shape of egg‐guide of female subgenital plate, shape of ovipositor valves and apical tips, shape of male supra‐anal plate and cerci, size of anterior and posterior lobes of lophi of epiphallus, size and shape of ancorae, shape of apical valves of aedeagus; and size of apical and pre‐apical diverticula and presence of protuberance on pre‐apical diverticulum.     

Male versus female mate choice: sexual selection and the evolution of species recognition via reinforcement

Male mate choice, expressed through courtship preferences, sometime occurs even under the mating system of polygyny, when the operational sex ratio is skewed toward males. The conditions under which male mate choice may be expected during polygyny are not well established. Servedio and Lande (2006, Evolution 60:674-685), assuming strict polygyny where all females have equal mating success, show that when having a preference does not increase the amount of energy that a male can put into courtship, male preferences for "arbitrary" female ornaments should not be expected to evolve; direct selection acts against them because they place males that carry them into situations in which there is high competition for mates. Here I explore in detail two situations under which logic dictates that this effect may be overcome or reversed. First I determine the contributions that direct and indirect selection place on male versus female preferences for traits that increase viability, using notation that allows the exact expression of these measures of selection. I find that direct selection against male preferences still predominates in the male mate choice model, causing less evolution by male than female preferences under these conditions. Second I address whether male mate choice is likely to evolve as a mechanism of premating isolation leading to species recognition, driven by the process of reinforcement. Reinforcement is compared under male and female mate choice, using a variety of models analyzed by both analytical techniques assuming weak selection and numerical techniques under broader selective conditions. I demonstrate that although under many conditions stronger premating isolation evolves under female mate choice, reinforcement may indeed occur via male mate choice alone.     

Testing synaptic plasticity in dynamic mate choice decisions: N-methyl d-aspartate receptor blockade disrupts female preference

Social behaviours such as mate choice require context-specific responses, often with evolutionary consequences. Increasing evidence indicates that the behavioural plasticity associated with mate choice involves learning. For example, poeciliids show age-dependent changes in female preference functions and express synaptic-plasticity-associated molecular markers during mate choice. Here, we test whether social cognition is necessary for female preference behaviour by blocking the central player in synaptic plasticity, NMDAR (N-methyl d-aspartate receptor), in a poeciliid fish, Xiphophorus nigrensis. After subchronic exposure to NMDAR antagonist MK-801, female preference behaviours towards males were dramatically reduced. Overall activity levels were unaffected, but there was a directional shift from ‘social’ behaviours towards neutral activity. Multivariate gene expression patterns significantly discriminated between females with normal versus disrupted plasticity processes and correlated with preference behaviours—not general activity. Furthermore, molecular patterns support a distinction between ‘preference’ (e.g. neuroserpin, neuroligin-3, NMDAR) and ‘sociality’ (isotocin and vasotocin) gene clusters, highlighting a possible conservation between NMDAR disruption and nonapeptides in modulating behaviour. Our results suggest that mate preference may involve greater social memory processing than overall sociality, and that poeciliid preference functions integrate synaptic-plasticity-oriented ‘preference’ pathways with overall sociality to invoke dynamic, context-specific responses towards favoured males and away from unfavoured males.     

Characterization of female preference functions for Drosophila montana courtship song and a test of the temperature coupling hypothesis

Female mate preferences are a major cause of diversity and elaboration in male sexual traits. Here we characterize the shape of female preference functions for pulse length and carrier frequency of the courtship song of Drosophila montana by fitting both parametric and nonparametric functions to the incidence of female receptive gestures to synthetic song. Preference functions for both traits are strongly directional. That for pulse length is linear and favors short pulses, whereas that for carrier frequency is stabilizing in shape, but would exert directional preferences favoring males with high carrier frequency. The preference for carrier frequency has probably evolved under sexual selection, but reasons for the preference for short pulses are less apparent. We also examine the effect of ambient temperature on the carrier frequency of male song and on the preference function for carrier frequency. For many similar acoustic communication systems, temperature coupling, a compensatory effect of temperature on preference functions, is thought to maintain coordination between preferences and signals. However, although the carrier frequency of D. montana song is highly dependent on environmental temperature, there is no temperature coupling of the female preference function. We suggest that temperature coupling may often arise due to a common effect of temperature on song and preference, rather than be an advantageous characteristic whose function is to maintain coordination in temperature-affected communication systems.     

Differences in preference for species-specific female calls between acoustically experienced and acoustically naive maleRibautodelphax planthoppers (Homoptera: Delphacidae)

Males of the planthopper Ribautodelphax imitanswere exposed to playbacks of either conspecific or heterospecific (R. imitantoides)female calls during their development from egg to adult, and thereafter these, as well as naive males,were offered a two- way choice between these calls. Males of all treatments approached the conspecific call significantly more often. However, males primed by the conspecific call chose the heterospecific call almost four times less often than did males primed by heterospecific calls or naive males, thus showing that the preference for conspecific calls can be partly learned. Males primed by heterospecific calls performed very similarly to completely naive males, suggesting that the signal recognition mechanism is much less sensitive to heterospecific calls than to conspecific calls. Males with experience of the conspecific female call tended to take more time to reach the call source in the trials than both other types of males. The evolutionary implications of these findings are discussed.     

A test for preference of association in a color polymorphic poeciliid fish: laboratory study

Synopsis The ecological and evolutionary forces maintaining genetic polymorphism within populations is of continuing interest to evolutionary biologists. Male pygmy swordtails,Xiphophorus pygmaeus, are polymorphic at a Y-linked locus controlling body color. Fish with the + and cp alleles have blue bodies; those with the con allele have bright gold bodies. Male and female fish were tested in the laboratory to determine if there were any preferences for association with groups of male fish based on color. Single test fish were presented with two groups of males of different phenotypes, and times in which the test fish spent in proximity to each group were recorded. Males of different phenotypes showed no differences in preference, nor did phenotype of the males in the groups affect the behavior of the test fish. Females also showed no preference for males of a particular phenotype. Finally, female test fish showed no preference for groups containing a male with the rare phenotype compared to a group containing all males of the same phenotype.     

Genetic and behavioral components of the cryptic species boundary between Laupala cerasina and L. kohalensis (Orthoptera: Gryllidae)

Cryptic species are often hypothesized on the basis of differences in courtship signals. These signal differences suggest that mate recognition systems, which include both courtship signals and responses to those signals, have diverged between genetically isolated populations. Cryptic species are therefore thought to represent distinct genetic units, the boundaries of which are maintained by premating incompatibilities, specifically by receiver preferences for conspecific signals. Laupala cerasina and L. kohalensis are sympatric species of swordtail crickets endemic to the big island of Hawaii, that are distinguishable by differences in male courtship song. We first tested whether groupings hypothesized by acoustic similarity reflect genetic groupings, using AFLP data to estimate genetic relationships. Second, we tested whether genetic boundaries are maintained by female preferences for conspecific song characteristics. Phonotaxis trials were used to determine the extent of female preferences for conspecific male song. Results generally support both hypotheses, but suggest the presence of porous species boundaries.     

Geographic variation in male ornamentation and female mate preference in the house finch: a comparative test of models of sexual selection

I compared the mate preferences of female house finches (Carpodacusmexicanus) from populations in which males differ in both plumagecoloration and the extent of ventral pigmentation (patch size).Phylogenetic analysis indicated that the small patch of ventralcoloration displayed by males in some populations is derivedfrom a larger-patched ancestral state. Regardless of the appearanceof males in their own populations, however, females from allpopulations showed a preference for the most brightly coloredmales and males with the largest patches. A reduction in patchsize independent of a change in female mate preference is notconsistent with sensory-bias or reproductive isolation modelsof sexual selection or with general predictions of runaway modelsof sexual selection. In contrast, a lack of congruence betweenfemale mate preference and male trait expression is predictedby the honest advertisement model, with house finches respondingto variation in regional and local access to carotenoid plumagepigments.     

Male mate preference for large size overrides species recognition in allopatric flat lizards (<Emphasis Type="Italic"> Platysaurus broadleyi</Emphasis>)

Species recognition and mate preference both influence mate choice but can be in conflict with each other. In such cases the relative importance of the two functions depends on the costs of mating with heterospecifics and the frequency of such interactions. We tested whether male flat lizards (Platysaurus broadleyi) are able to discriminate between conspecific females and females of its allopatric sister species P. capensis. Given a simultaneous choice between equally sized females of both species, males courted conspecific females in 85% of trials. We then tested whether mate preference for large female body size can override species recognition. When offered a choice between a larger heterospecific female and a smaller conspecific, males showed no preference for conspecifics and courted larger heterospecific females in 58% of trials. Comparison of the two sets of trials showed a significant effect of female body size on male mate preference, supporting the hypothesis that mate quality can override species recognition.Communicated by K. Kotrschal     

Comparison of blood brain barrier permeability in normal and ovariectomized female rats that demonstrate right or left paw preference

We explored the relations among paw preference, cerebral asymmetry and asymmetrical disruption of blood-brain barrier (BBB) permeability in normal and ovariectomized female rats with known paw preference. A high dose of pentylenetetrazol was used to disrupt the BBB and induce acute hypertension. To determine the areas of macroscopic infarct, samples were stained with 2,3,5-triphenyltetrazolium chloride. Histological staining techniques were used to show the areas of infarct microscopically on paraffin sections. Sixty-two percent of the rats demonstrated right paw preference, 24% demonstrated left paw preference and 14% were ambidextrous. Areas of infarct, which indicated destruction of the BBB, were determined microscopically and macroscopically in rats that demonstrated right and left paw preference. We found a relation between permeability of the BBB and paw preference. There may be a relation between paw preference, cerebral asymmetry and asymmetrical destruction of the BBB in rats. Asymmetrical destruction of the BBB in experimental rats was similar to the control group, which had asymmetrically disrupted BBB with respect to paw preference. Like the control rats, asymmetrical areas of infarct consistent with cerebral asymmetry were observed in ovariectomized rats.