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PubMed2006

A scan for signatures of positive selection in candidate loci for skin pigmentation in humans.

Although the combination of pale skin and intense sun exposure results in an important health risk for the individual, it is less clear if at the population level this risk has possessed an evolutionary meaning. In this sense, a number of adaptive hypotheses have been put forward to explain the evolution of human skin pigmentation, such as photoprotection against sun-induced cancer, sexual selection, vitamin D synthesis or photoprotection of photolabile compounds, among others. It is expected that if skin pigmentation is adaptive, we might be able to see the signature of positive selection on some of the genes involved. In order to detect this signature, we analyze a battery of 81 candidate loci by means of phylogenetic and population genetic tests. Our results indicate that both light and dark skin may possess adaptive value. Of the main loci presenting this signature, TP53BP1 shows clear evidence of adaptive selection in Africans, whereas TYRP1 and SLC24A5 show evidence of adaptive selection in Caucasians. Although we cannot offer a mechanism that based on these genes explains the advantage of light skin, if TP53BP1, and perhaps RAD50, have truly conferred an adaptive value to the African population analyzed, photoprotection against sun-induced skin damage/cancer might be proposed as a mechanism that has driven the evolution of human skin pigmentation.

Adaptation, Biological↗

PubMed2003

The use of multiple cues in mate choice.

An increasing number of studies find females to base their mate choice on several cues. Why this occurs is debated and many different hypotheses have been proposed. Here I review the hypotheses and the evidence in favour of them. At the same time I provide a new categorisation based on the adaptiveness of the preferences and the information content of the cues. A few comparative and empirical studies suggest that most multiple cues are Fisherian attractiveness cues or uninformative cues that occur alongside a viability indicator and facilitate detection, improve signal reception, or are remnants from past selection pressures. However, much evidence exists tor multiple cues providing additional information and serving as multiple messages that either indicate general mate quality or enable females that differ in mate preferences to choose the most suitable male. Less evidence exists for multiple cues serving as back-up signals. The importance of receiver psychology, multiple sensory environments and signal interaction in the evolution of multiple cues and preferences has received surprisingly little attention but may be of crucial importance. Similarly, sexual conflict has been proposed to result in maladaptive preferences for manipulative cues, and in neutral preferences for threshold cues, but no reliable evidence exists so far. An important factor in the evolution of multiple preferences is the cost of using additional cues. Most theoretical work assumes that the cost of choice increases with the number of cues used, which restricts the conditions under which preferences for multiple cues are expected to evolve. I suggest that in contrast to this expectation, the use of multiple cues can reduce mate choice costs by decreasing the number of mates inspected more closely or the time and energy spent inspecting a set of mates. This may be one explanation for why multiple cues are more common than usually expected. Finally I discuss the consequences that the use of multiple cues may have for the process of sexual selection, the maintenance of genetic variation, and speciation.

Animal Communication↗

PubMedDate not supplied

Evolution of male sexual characters in the oriental Drosophila melanogaster species group.

Understanding the genetic and molecular mechanisms of morphological evolution is one of the greatest challenges in evolutionary biology. Sexually dimorphic traits, which often evolve at a high rate due to their involvement in mate choice and sexual selection, present unique opportunities for investigating changes in development over short evolutionary distances. Phylogenetic analysis is essential to provide a historical framework for comparative studies of development by establishing the order and polarity of morphological changes. In this report, we apply a new molecular phylogeny to reconstruct the evolution of male sexual characters in a group of species closely related to the model species Drosophila melanogaster. These highly variable traits include wing melanin patterns, the sex comb, and the structure of external genitalia and analia. We show that sexually dimorphic characters can diverge very rapidly among closely related species. More surprisingly, we also find a pervasive pattern of independent origin and secondary loss of male sexual traits in different evolutionary lineages.

Animals↗

PubMed2002

Mammalian sperm proteins are rapidly evolving: evidence of positive selection in functionally diverse genes.

A growing number of genes involved in sex and reproduction have been demonstrated to be rapidly evolving. Here, we show that genes expressed solely in spermatozoa represent a highly diverged subset among mouse and human tissue-specific orthologs. The average rate of nonsynonymous substitutions per site (K(a)) is significantly higher in sperm proteins (mean K(a) = 0.18; N = 35) than in proteins expressed specifically in all other tissues (mean K(a) = 0.074; N = 473). No differences, however, are found in the synonymous substitution rate (K(s)) between tissues, suggesting that selective forces, and not mutation rate, explain the high rate of replacement substitutions in sperm proteins. Four out of 19 sperm-specific genes with characterized function demonstrated evidence of strong positive Darwinian selection, including a protein involved in gene regulation, Protamine-1 (PRM1), a protein involved in glycolysis, GAPDS, and two egg-binding proteins, Adam-2 precursor (ADAM2) and sperm-adhesion molecule-1 (SAM1). These results demonstrate the rapid evolution of sperm-specific genes and highlight the molecular action of sexual selection on a variety of characters involved in mammalian sperm function.

Amino Acid Substitution↗

PubMed2002

Divergence in mate choice systems: does evolution play by rules?

Understanding the genetic bases of phenotypes associated with the earliest stages of divergence will reveal a great deal about species formation. I review a number of model systems, most involving plant-insect interactions, that have already revealed genetic aspects of incipient speciation. It is suggested that progress in understanding the causal forces driving mating signal evolution and incipient speciation will be expedited in model systems where; (1) ecological and evolutionary information is available, (2) different aspects of mating behaviors that function in mate and/or species recognition are known, (3) genetic analysis of single phenotypes is undertaken, (4) analysis of sexual selection and isolation is performed under natural conditions (or in the wild), and (5) comparative data from related species are available to assess phylogenetic trends.

Animals↗

PubMed2003

Neurochemical aspects of the sexual response cycle.

What drives the human sexual response cycle? The human sexual response cycle is a highly complex phenomenon that encompasses many transmitters and transmitter systems centrally and peripherally. The endocrine system is also intricately involved in the brain and in the periphery organs. Integration of these systems is a function of the nervous system that ultimately produces a vast array of cognitive, emotional, physiological, and behavioral responses. Therefore, it is not surprising that a disturbance in even a single system will lead to dysfunction in one or more phases of the sexual response cycle. This article highlights the complex roles the aminergic system plays along with key hormones that are equally involved. The article also points out how rudimentary and fragmented our knowledge is in this field and how few controlled studies are available. The potential for development of specific agents that target selective sexual dysfunctions is exemplified in sildenafil, the first such agent ever to be brought to market.

Brain↗

PubMed2006

Assortative preferences and discrimination by females against hybrid male song in the grasshoppers Chorthippus brunneus and Chorthippus jacobsi (Orthoptera: Acrididae).

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are highly differentiated for male mating signals, and form a mosaic hybrid zone in northern Spain. At some sites within this zone, many hybrids are observed. At others, few hybrids are observed. Such bimodal sites may reflect recent contacts between parental genotypes, or local variation in levels of assortative mating or selection against hybrids. Playback of 12 parental and F1 male songs to 296 parental and hybrid females revealed positive assortative preferences in C. brunneus and C. jacobsi females, supporting a direct role of male mating signals in female choice. However, all female genotypic classes showed reduced responsiveness to F1 male songs. Such sexual selection against hybrids is consistent with the narrow cline width observed in the field for song characters relative to morphology. These results have implications for the genetic structure of the hybrid zone and for models of speciation by reinforcement.

Animal Communication↗

PubMed2006

Linkage of butterfly mate preference and wing color preference cue at the genomic location of wingless.

Sexual isolation is a critical form of reproductive isolation in the early stages of animal speciation, yet little is known about the genetic basis of divergent mate preferences and preference cues in young species. Heliconius butterflies, well known for their diversity of wing color patterns, mate assortatively as a result of divergence in male preference for wing patterns. Here we show that the specific cue used by Heliconius cydno and Heliconius pachinus males to recognize conspecific females is the color of patches on the wings. In addition, male mate preference segregates with forewing color in hybrids, indicating a genetic association between the loci responsible for preference and preference cue. Quantitative trait locus mapping places a preference locus coincident with the locus that determines forewing color, which itself is perfectly linked to the wing patterning candidate gene, wingless. Furthermore, yellow-colored males of the polymorphic race H. cydno alithea prefer to court yellow females, indicating that wing color and color preference are controlled by loci that are located in an inversion or are pleiotropic effects of a single locus. Tight genetic associations between preference and preference cue, although rare, make divergence and speciation particularly likely because the effects of natural and sexual selection on one trait are transferred to the other, leading to the coordinated evolution of mate recognition. This effect of linkage on divergence is especially important in Heliconius because differentiation of wing color patterns in the genus has been driven and maintained by natural selection for Müllerian mimicry.

Animals↗

PubMed2004

Complexity and integration in sexual ornamentation: an example with carotenoid and melanin plumage pigmentation.

Sexual ornaments often consist of several components produced by distinct developmental processes. The complexity of sexual ornaments might be favoured by mate choice of individual components in different environments which ultimately results in weak interrelationships (integration) among the developmental processes that produce these components. At the same time, sexual selection for greater exaggeration of individual components favours their stronger co-dependence on organismal resources. This should ultimately produce stronger condition-mediated integration among ornaments' components in individuals with the most exaggerated ornamentation. Here we distinguish between these two sources of integration by examining the relationship between integration and elaboration of sexual ornamentation in three bird species: two with carotenoid-based sexual ornamentation (the house finch, Carpodacus mexicanus and common redpoll, Carduelis flammea) and a species with melanin-based sexual ornamentation (house sparrow, Passer domesticus). We found that integration of components varied with elaboration of carotenoid-based ornamentation but not of melanin ornamentation. In the house finches, integration was the highest in individuals with small ornaments and decreased with ornament elaboration whereas the pattern was the opposite in common redpolls. These results suggest that in these species integration and complexity of carotenoid-based ornamental components are due to shared condition-dependence of distinct developmental pathways, whereas integration and complexity of the melanin ornamentation is due to organismal integration of developmental pathways and is largely condition- and environment-invariant. Thus, functionally, ornamentation of the house sparrows can be considered a single trait, whereas complexity of the house finch and redpoll ornamentation varies with ornament elaboration and individual condition.

Animals↗

PubMed2003

Age-related variation in mean sperm length, in the rove beetle Aleochara bilineata.

The rove beetle, Aleochara bilineata, is characterised as having monomorphic long sperm (spermatophoral mean approx. +/-2.5%), whilst simultaneously having a large variation in mean sperm length across a mixed age population. Spermatophoral means of between 627 and 996 mum were measured in this investigation. The hypothesis that sperm length increases as a function of male age is tested. In order to examine this hypothesis in a 'good genes' context, three a priori subhypotheses were tested: (1) spermatophoral mean sperm length increases as a function of male age and not as a function of the sequential order of the spermatophore from which sperm were taken, (2) the rate of this increase is dependent upon nutritional intake, and (3) sperm length is not determined by adult body size. The first prediction is supported in its entirety by the data, whereas the second is not supported at all and the third subhypothesis is supported only in older males. These findings are interesting in the field of postcopulatory sexual selection, as this is the first time that such an increase in mean sperm length has been recorded.

Age Factors↗

PubMed2005

Advertisement-call preferences in diploid-tetraploid treefrogs (Hyla chrysoscelis and Hyla versicolor): implications for mate choice and the evolution of communication systems.

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor.

Acoustic Stimulation↗

PubMed2003

Subadult experience influences adult mate choice in an arthropod: exposed female wolf spiders prefer males of a familiar phenotype.

Current sexual selection theory proposes several potential mechanisms driving the evolution of female mating preferences, few of which involve social interactions. Although vertebrate examples of socially influenced mating preferences do exist, the invertebrate examples are virtually nonexistent. Here I demonstrate that the mating preferences of female wolf spiders can be acquired through exposure as subadults to unrelated, sexually active adult males. I first conducted exposure trials during which subadult females of the wolf spider Schizocosa uetzi were allowed to interact with mature males of an experimentally manipulated phenotype (either black or brown forelegs). After maturation, these previously exposed females were paired with a male of either a familiar or unfamiliar manipulated phenotype for mate-choice trials. Subadult females that were exposed to directed courtship by mature males of a particular morphological phenotype were subsequently more likely to mate with a male of a familiar phenotype as adults. Furthermore, females that were exposed as subadults were more likely, as adults, to cannibalize a courting male with an unfamiliar phenotype. Unexposed females did not distinguish between phenotypes in either mate choice or cannibalism frequency. These results suggest a previously uncharacterized mechanism influencing the origin of female mating preferences and ultimately the evolution of male traits: subadult experience. This study also stresses the potential importance of learning and memory on adult mate choice in an arthropod.

Animals↗

PubMed2002

Sperm competition: motility and the midpiece in primates.

In animals with multiple-partner mating systems, the gametes of two or more males must compete to fertilize a given set of ova. Here we show that the volume of the midpiece in individual sperm is significantly greater in primate species in which the females mate with multiple partners, and in which males have larger testes in relation to their body weight, than in those species that mate with only one partner and have relatively small testes. Our results indicate that sexual selection by sperm competition has influenced the evolution of a specific component of male-gamete morphology, the volume of the sperm midpiece.

Animals↗

PubMed1996

Sex ratio adjustment in relation to paternal attractiveness in a wild bird population.

When the relative fitness of sons and daughters differs, sex-allocation theory predicts that it would be adaptive for individuals to adjust their investment in different sexes of offspring. Sex ratio adjustment by females in response to the sexual attractiveness of their mate would be an example of this. In vertebrates the existence of this form of sex ratio adjustment is controversial and may be confounded with sex-biased mortality, particularly in sexually size-dimorphic species. Here we use PCR amplification of a conserved W-chromosome-linked gene to show that the sex ratio within broods of a natural population of sexually size-monomorphic collared flycatchers Ficedula albicollis is related to the size of their father's forehead patch, a heritable secondary sexual character implicated in female choice. Experimental manipulations of paternal investment, which influence the size of his character in future breeding attempts, result in corresponding changes in the sex ratio of offspring born to males in those breeding attempts. In contrast, manipulations of maternal investment have no effect on future sex ratios, and there is no relationship between variables predicting the reproductive value of the brood and nestling sex ratio. Analysis of recruitment of offspring reveals similar patterns of sex ratio bias. The results suggest that female collared flycatchers be able to adjust the sex ratio of eggs ovulated in response to the phenotype of their mate. This finding is most consistent with "genetic quality" models of sexual selection.

Africa↗

PubMed2006

Peacocks, Picasso, and parental investment: The effects of romantic motives on creativity.

Four experiments explored the effects of mating motivation on creativity. Even without other incentives to be creative, romantic motives enhanced creativity on subjective and objective measures. For men, any cue designed to activate a short-term or a long-term mating goal increased creative displays; however, women displayed more creativity only when primed to attract a high-quality long-term mate. These creative boosts were unrelated to increased effort on creative tasks or to changes in mood or arousal. Furthermore, results were unaffected by the application of monetary incentives for creativity. These findings align with the view that creative displays in both sexes may be linked to sexual selection, qualified by unique exigencies of human parental investment.

Adolescent↗

PubMed2001

Drosophila bipectinata species complex.

The Drosophila bipectinata species complex belongs to the ananassae subgroup of the melanogaster species group (Genus Drosophila, Subgenus Sophophora). The members of the complex are: D. bipectinata, D. parabipectinata, D. malerkotliana, and D. pseudoananassae. Of the four species, D. bipectinata is most widely distributed. Females are indistinguishable, but males are distinguishable by their sex-comb teeth number and pattern and by abdominal colouration. Chromosomal inversions have been detected in these species. In natural populations of D. bipectinata the frequency of inversions and the level of inversion heterozygosity were found to be very low but in laboratory stocks inversions persisted for more than 20 generations due to heterotic buffering. On an average 9.3 fixed interspecific inversions separate each species pair. Non-random association between linked inversions indicated epistatic interaction in natural populations of D. bipectinata. Certain spontaneous mutations were detected and mapped for the first time in D. bipectinata. Low frequency of spontaneous male recombination has also been reported in D. bipectinata. Sexual isolation study in the complex indicated strong preference for homogamic mating. The results also indicated incomplete sexual isolation among different members of this complex. The isolation estimate among six different geographic populations of D. bipectinata ranged from 0.54 - 0.92 representing positive assortative mating which is an evidence for incipient sexual isolation. Incipient sexual isolation was also found within D. malerkotliana and D. parabipectinata . Chromosomal, hybridization and allozyme studies revealed close phylogenetic relationship among the four species of the bipectinata complex. Mitochondrial DNA study revealed net nucleotide difference (delta) between these species to be very small (0.0002 +/- 0.0008) reflecting closeness. Evidence for genetic control of sexual activity and existence of sexual selection in D. bipectinata has been shown on the basis of mating propensity tests carried out on geographic strains, their hybrids and diallel crosses. Significant variation was found among the strains tested with respect to courtship time, duration of copulation and fertility. A positive correlation between duration of copulation and fertility in D. bipectinata was found. Evidence for rare-male mating advantage was also found in D. bipectinata. A positive response to selection for high and low mating activity provided evidence for polygenic control of this phenomenon in D. bipectinata. Bilateral outgrowths on thorax, a unique phenotype, reported for the first time in D. bipectinata has been shown to affect mate recognition ability. Results of the study on pupation site preference (larval behaviour) and oviposition site preference (non-sexual behaviour) have also been included.

Animals↗

PubMed1991

"Runaway" social evolution: reinforcing selection for inbreeding and altruism.

Kin selection theory predicts that altruistic behaviors, those that decrease the fitness of the individual performing the behavior but increase the fitness of the recipient, can increase in frequency if the individuals interacting are closely related. Several studies have shown that inbreeding therefore generally increases the effectiveness of kin selection when fitnesses are linear, additive functions of the number of altruists in the family, although with extreme forms of altruism, inbreeding can actually retard the evolution of altruism. These models assume that a constant proportion of the population mates at random and a constant proportion practices some form of inbreeding. In order to investigate the effect of inbreeding on the evolution of altruistic behavior when the mating structure is allowed to evolve, we examined a two-locus model by computer simulation of a diploid case and illustrated the important qualitative features by mathematical analysis of a haploid case. One locus determines an individual's propensity to perform altruistic social behavior and the second locus determines the probability that an individual will mate within its sibship. We assumed positive selection for altruism and no direct selection at the inbreeding locus. We observed that the altruistic allele and the inbreeding allele become positively associated, even when the initial conditions of the model assume independence between these loci. This linkage disequilibrium becomes established, because the altruistic allele increases more rapidly in the inbreeding segment of the population. This association subsequently results in indirect selection on the inbreeding locus. However, the dynamics of this model go beyond a simple "hitch-hiking" effect, because high levels of altruism lead to increased inbreeding, and high degrees of inbreeding accelerate the rate of change of the altruistic allele in the entire population. Thus, the dynamics of this model are similar to those of "runaway" sexual selection, with gene frequency change at the two loci interactively causing rapid evolutionary change.

Alleles↗

PubMed2005

Factors affecting male song evolution in Drosophila montana.

D. montana (a species of the D. virilis group) has spread over the northern hemisphere, populations from different areas showing both genetic and phenotypic divergence. The males of this species produce an elaborate courtship song, which plays a major role both in species recognition and in intraspecific mate choice. The genetic architecture and physical constraints, as well as the importance of the signal for species recognition, set boundaries within which this signal can vary. Within these limits, courtship song parameters may change, depending on the males' physical condition and on the environment they inhabit. Females are likely to affect song evolution by exerting directional selection toward higher carrier frequencies. Given this complexity, only a comprehensive, multidisciplinary approach, starting with traditional field observation and combining controlled behavioral experiments, biometric measurements, and sophisticated molecular techniques, has the potential of shedding light on the past history and the evolution of this signal, and, eventually, adding to our understanding of the mechanisms, functions, and outcomes of sexual selection in acoustic communication systems.

Animals↗