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PubMed2005

Correcting for regression to the mean in behavior and ecology.

If two successive trait measurements have a less-than-perfect correlation, individuals or populations will, on average, tend to be closer to the mean on the second measurement (the so-called regression effect). Thus, there is a negative correlation between an individual's state at time 1 and the change in state from time 1 to time 2. In addition, whenever groups differ in their initial mean values, the expected change in the mean value from time 1 to time 2 will differ among the groups. For example, birds feeding nestlings lose weight, but initially heavier birds lose more weight than lighter birds, a result expected from the regression effect. In sexual selection, males who remain unmated in the first year are, on average, less attractive than mated males. The regression effect predicts that these males will increase their attractiveness in the second year more than mated males. In well-designed experiments, changes in the experimental and control groups would be compared. In observational studies, however, no such comparison is available, and expected differential effects must be accounted for before they can be attributed to external causes. We describe methods to correct for the regression effect and assess alternative causal explanations.

Animals↗

PubMed1999

Male attractiveness and differential testosterone investment in zebra finch eggs.

Good-genes hypotheses of sexual selection predict that offspring fathered by preferred males should have increased viability resulting from superior genetic quality. Several studies of birds have reported findings consistent with this prediction, but maternal effects are an important confounding variable. Those studies that have attempted to control for maternal effects have only considered differential maternal investment after egg laying. However, female birds differentially deposit testosterone in the eggs, and this influences the development of the chick. This study shows that female birds deposit higher amounts of testosterone and 5alpha-dihydrotestosterone in their eggs when mated to more attractive males.

Animals↗

PubMed2005

Mate choice decisions: the role of facial beauty.

For most people, facial beauty appears to play a prominent role in choosing a mate. Evidence from research on facial attractiveness indicates that physical beauty is a sexually selected trait mediated, in part, by pubertal facial hormone markers that signal important biological information about the displayer. Such signals would be ineffective if they did not elicit appropriate cognitive and/or emotional responses in members of the opposite sex. In this article, I argue that the effectiveness of these hormonal displays varies with perceivers' brains, which have been organized by the degree of steroid hormone exposure in the uterus, and activated by varying levels of circulating steroids following puberty. I further propose that the methodology used for examining mate choice decisions has general applicability for determining how cognitive and emotional evaluations enter into decision processes.

Affect↗

PubMed2007

The unusual inheritance pattern of the courtship songs in closely related grasshopper species of the Chorthippus albomarginatus-group (Orthoptera: Gomphocerinae).

Sibling species of the Chorthippus albomarginatus-group are exceptional among all European grasshopper species because they have an extremely elaborate courtship behaviour. Here, we present a genetic analysis of the courtship song differences between two closely related grasshopper species Ch. albomarginatus and Ch. oschei. Measurements of seven courtship song characters and one parameter of courtship visual display were compared among parentals, F(1) and F(2) hybrids, and backcrosses. Variation in one morphological character, the number of stridulatory pegs, was studied as well. The distributions of song phenotypes were more consistent with a type-III genetic architecture, which involves complementary or duplicate pairs of loci. We suggest that this type of architecture may provide the novel elements of the hybrid songs, even more complex than the parental ones, which may offer a new starting point for sexual selection. One parameter of the visual display appeared to be controlled by a single locus, but differences in other characters of visual display could be explained by a more complex inheritance pattern. Inheritance of the peg number differences was consistent with a simple polygenic additive model. Sex linkage and/or maternal effects were not detected for any trait. We found a disproportionate influence of the Ch. albomarginatus parent on most hybrid song characteristics and the visual display, and this may support a previously suggested idea that Ch. albomarginatus is an ancestral form and Ch. oschei is a derived species.

Animal Communication↗

PubMed2005

Evolution of sexual isolation during secondary contact: genotypic versus phenotypic changes in laboratory populations.

We monitored the phenotypic and genotypic changes that occur when two behavioral races come into contact in laboratory populations. Drosophila melanogaster from Zimbabwe and nearby regions (Z type) show strong but asymmetric sexual isolation from their cosmopolitan counterparts (M type). Crosses of Z females and M males do not take place readily when other choices are available. At least 15 loci are known to control Z-type mating preferences and performance. By thoroughly mixing the genomes of the two types in laboratory populations, we artificially created maximum secondary contact. Despite the strength of sexual selection favoring Z-type male characters, Z-type behavior is eliminated or greatly diminished in all 12 hybrid populations after only 60 generations. This trend is consistent with the spread of the M-type behavior throughout the world as well as a detailed analysis of fitness components. Surprisingly, in contrast with the phenotypic convergence toward the M-type, genotypic samples broadly covering the genomic regions of mapped behavioral loci show no such trend. The genome appears to be "fine grained," with adjacent loci having different evolutionary dynamics and genealogical histories.

Alleles↗

PubMed1992

The potential role of custody facilities in controlling sexually transmitted diseases.

BACKGROUND: The National Commission on Correctional Health Care recommends that medical screening, including tests for syphilis and other sexually transmitted diseases, be performed by the 14th day after initial booking procedures. Because the average length of stay in detention is usually less than 14 days, most detainees are not screened or treated for asymptomatic communicable diseases. METHODS: In order to determine the incidence and prevalence of syphilis among those booked through a large county jail, a rapid screening procedure to test newly incarcerated inmates and treat those infected was implemented over a 3-week period. RESULTS: Among 6309 detainees eligible for testing during the 3-week period of the study, 129 (2%) were diagnosed with syphilis. During the preceding month when only those reporting symptoms or high-risk behaviors were screened, 20 cases were diagnosed. The sensitivity and predictive value of self-reported risk factors for syphilis infection were low. Among the first 110 diagnosed cases, 17 (15.5%) were released within 3 days and 86 (78%) were released within 6 days. CONCLUSIONS: If screening and treatment for syphilis are delayed until the 14th day after booking, the majority of infected inmates will be released prior to evaluation and treatment. Rapid screening and treatment for selected sexually transmitted diseases are likely to be an effective public health measure when implemented in custody settings.

Adolescent↗

PubMed1998

New perspectives on mate choice and the MHC.

A long series of studies on mice has shown that mate choice decisions can be made on the basis of individual genotype at the major histocompatibility complex (MHC), which accords well with the importance of immunocompetence in some theories of sexual selection. Recent work on other vertebrate species, including humans, indicates that MHC-based mate choice is not restricted to the genus Mus. However, its importance may vary among species as a result of differences in social and mating system structure, and perhaps genome structure. There appears to be a general preference expressed for MHC-dissimilar mates, and such MHC-disassortative mating may be involved in maintaining MHC and/or genome-wide diversity in natural populations. The strength and direction of MHC-based mating preference can vary, and may be modulated by factors such as genetic background, sex, and early life experience.

Animals↗

PubMed2000

The inheritance of female preference functions in a mate recognition system.

Mate recognition systems (MRSs) play a major role in sexual selection and speciation, yet few studies have analysed both male and female components in detail. Here, female preference functions have been characterized for the tettigoniid bushcricket Ephippiger ephippiger, and the inheritance of male song and female preference functions followed in crosses between subspecies. Songs are disproportionately determined by sex-linked genes. However, there is no evidence for a role of maternally derived sex-linked genes in female preference or of maternal effects. At the genetic level, there is a mismatch between peak preferences and male song, consistent with an evolutionary history of persistent directional preferences. Such a pattern of inheritance could contribute to the process of speciation via the evolution of new MRSs.

Animals↗

PubMed1991

Hypervariable minisatellite DNA sequences in the Indian peafowl Pavo cristatus.

We report here for the first time the large-scale isolation of hypervariable minisatellite DNA sequences from a non-human species, the Indian peafowl (Pavo cristatus). A size-selected genomic DNA fraction, rich in hypervariable minisatellites, was cloned into Charomid 9-36. This library was screened using two multilocus hypervariable probes, 33.6 and 33.15 and also, in a "probe-walking" approach, with five of the peafowl minisatellites initially isolated. Forty-eight positively hybridizing clones were characterized and found to originate from 30 different loci, 18 of which were polymorphic. Five of these variable minisatellite loci were studied further. They all showed Mendelian inheritance. The heterozygosities of these loci were relatively low (range 22-78%) in comparison with those of previously cloned human loci, as expected in view of inbreeding in our semicaptive study population. No new length allele mutations were observed in families and the mean mutation rate per locus is low (less than 0.004, 95% confidence maximum). These loci were also investigated by cross-species hybridization in related taxa. The ability of the probes to detect hypervariable sequences in other species within the same avian family was found to vary, from those probes that are species-specific to those that are apparently general to the family. We also illustrate the potential usefulness of these probes for paternity analysis in a study of sexual selection, and discuss the general application of specific hypervariable probes in behavioral and evolutionary studies.

Animals↗

PubMed2000

Adaptive plasticity in mate preference linked to differences in reproductive effort.

There is abundant evidence for the existence of marked mate preferences in natural populations, but the occurrence of within-population variation in mate preferences has received little attention and is often regarded as nonadaptive deviation from the optimal norm. Here we show experimentally that the preference of female collared flycatchers Ficedula albicollis for male forehead patch size, a sexually selected trait, varies with the time of breeding, an environmental factor with strong effects on reproductive success. Contrary to expectations based on time-constrained choice models, only late-breeding females prefer males with a large patch size. The variation in mate preference matches a seasonal change in female reproductive success: long-term data reveal a positive relationship between female reproductive success and male patch size exclusively in late breeders. In addition, female reproductive effort, as assessed by clutch size, appears to be adjusted relative to both timing of breeding and male phenotype. We conclude that not only can mate preferences display adaptive plasticity within populations, but this plasticity can also be linked to differences in reproductive investment.

Adaptation, Physiological↗

PubMed2001

Functional incompatibility between the fertilization systems of two allopatric populations of Callosobruchus maculatus (Coleoptera: Bruchidae).

Recent studies indicate that postcopulatory sexual selection may represent an important component of the speciation process by initiating reproductive isolation via the evolutionary divergence of fertilization systems. Using two geographically isolated populations of the polyandrous beetle Callosobruchus maculatus, we investigated divergence in fertilization systems by determining the extent of postcopulatory functional incompatibility. Through reciprocal, cross-population matings we were able to separately estimate the effects of male and female population origin and their interaction on the extent of last-male sperm precedence, female receptivity to further copulation and female oviposition. Our results indicate partial incompatibility between the fertilization systems of the two populations at all three functional levels. Males derived from the same population as females outcompete rival, allopatric males with respect to sperm preemption, sperm protection, and ability to stimulate female oviposition. This pattern is reciprocated in both populations indicating that postcopulatory, prezygotic events represent important mechanisms by which between-population gene flow is reduced. We suggest the partial gametic isolation observed is a by-product of the coevolution of male and female fertilization systems by a process of cryptic female choice. Our results are consistent with a mechanism akin to conventional mate choice models although they do not allow us to reject antagonistic sexual coevolution as the mechanism of cryptic female choice.

Animals↗

PubMed2006

Transfer and fate of seminal fluid molecules in the beetle, Diaprepes abbreviatus: implications for the reproductive biology of a pest species.

Molecules transferred from males to females via seminal fluids are important to the study of insect reproduction because they affect female physiology, reproductive behavior, and longevity. These molecules (seminal fluid molecules or SFMs) interest applied entomologists because of their potential use in insect control. SFMs are also interesting because of their relatively rapid evolution and important role in post-mating sexual selection. We studied SFMs in Diaprepes abbreviatus, a major pest of numerous plant species of economic importance. Using radiolabeled-methionine (35S), we found that D. abbreviatus males synthesized proteins de novo in their reproductive tissues after mating. Males that were fed radiolabeled methionine transferred radioactivity to females beginning within the first 10 min of mating. Male-derived substances are absorbed from the female's reproductive tract into the hemolymph and circulated throughout the body, but are found primarily in the eggs and ovaries. As a result, SFMs may be a useful means of both horizontal (to mates) and vertical transfer (to offspring) of control agents between conspecifics.

Animals↗

PubMed2003

Quantitative genetic analysis of among-population variation in sperm and female sperm-storage organ length in Drosophila mojavensis.

In Drosophila, sperm length and the length of the females' primary sperm-storage organ have rapidly coevolved through post-copulatory sexual selection. This pattern is evident even among geographic populations of Drosophila mojavensis. To understand better these traits of potential importance for speciation, we performed quantitative genetic analysis of both seminal receptacle length and sperm length in two divergent populations. Parental strains, F1, F1 reciprocal (F1r), F2, F2r, backcross and backcross reciprocal generations were used in a line-cross (generation means) analysis. Seminal receptacle length is largely an autosomal additive trait, whereas additivity, dominance and epistasis all contributed to the means of sperm length. Either an X-chromosome or a Y-chromosome effect was necessary for models of sperm length to be significant. However, the overall contributions from the X and Y chromosomes to sperm length was small.

Animals↗

PubMed2004

The evolution of female preferences for multiple indicators of quality.

In a variety of species, females exhibit preferences for multiple male ornaments. Several hypotheses have been proposed to explain this phenomenon. Which, if any, of these hypotheses is the most plausible in general remains largely unresolved based on the available empirical data. Yet theoretical studies conclude that the evolution of preferences for multiple signals of male quality is unlikely, especially when the use of an additional cue in mate choice strongly increases the overall cost of choice. This would imply that most male courtship characters do not reflect the male's genetic quality but instead evolved through Fisherian sexual selection. However, the existing models focus on ornaments that signal overall genetic quality and do not address the possibility that different ornaments provide information about different aspects of quality. Therefore, we develop a model in which the ornaments act as signals for distinct quality components. When the ornaments provide overlapping information about these quality components, we retrieve the results of earlier models. However, when the ornaments provide independent information, preferences for multiple ornaments may evolve, even when exhibiting multiple preferences is costly. We discuss our results in relation to the multiple-message and redundant-signal hypotheses for ornament diversity and identify parallels between Fisherian and good-genes mechanisms for the evolution of multiple ornaments.

Animal Communication↗

PubMed2001

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.

Animals↗

PubMed2006

Assigning sex to pre-adult stalk-eyed flies using genital disc morphology and X chromosome zygosity.

BACKGROUND: In stalk-eyed flies (Diopsidae) the eyes and antennae are laterally displaced at the ends of elongated eyestalks. Eyespan and the degree of sexual dimorphism in eyespan vary considerably between species and several sexually dimorphic species show sexual selection through female mate preference for males with exaggerated eyespan. The genes on which selection acts to regulate eyespan remain to be identified. This could be achieved by comparing gene expression during eyestalk development in males and females if the sex of pre-adult flies could be reliably assigned. Here we describe two techniques, one morphological and one microsatellite-based, that identify the sex of stalk-eyed fly larvae and pupae. RESULTS: We showed that genital discs of the stalk-eyed fly Teleopsis dalmanni have two highly distinct morphologies, compact ("C") and lobed ("L"). Segment composition (revealed by Engrailed expression) was consistent with C morphology being typical of males and L morphology of females. We confirmed the proposed association between disc morphology and sex by evaluating the combined heterozygosity of four X-linked microsatellite markers. We demonstrated that individuals with C genital discs had hemizygous (male) genotypes while those with L discs were heterozygous (female) genotypes. Similar dimorphism in genital disc morphology was observed in eight other species spanning three representative Diopsid genera. In every case the segment composition supported C morphology being male and L morphology female. We assigned larval sex by C or L morphology and compared cell division frequencies in male and female eye-antennal discs in two species (T. dalmanni and Diasemopsis meigenii) sexually dimorphic for eyespan. The number of mitotic (anti-H3-labelled) cells did not differ between the sexes in either species. CONCLUSION: We have made novel use of two complementary techniques for identifying the sex of pre-adult stalk-eyed flies. These procedures will facilitate studies of the evolution of sexually dimorphic development in a variety of other species. Morphology and En expression in male and female genital discs are highly conserved within each genus of Diopsidae. Finally, sexual dimorphism for eyespan in two Diopsid species is unlikely to be due to an increased rate of cell division at the third larval instar in males.

Animals↗

PubMed2001

Fluctuating asymmetry is nongenetically related to mating success in Drosophila buzzatii.

To date, there is still no consensus on the real significance of fluctuating asymmetry (FA) in evolutionary biology. Some studies have established links between FA and Darwinian fitness, and in a number of cases intermediate heritabilities for FA have been reported. However, many claims have been raised against the generality of these findings. I therefore tested if FA of a sexually selected trait (wing length) is indeed related to male mating success in Drosophila buzzatii from field and laboratory samples and whether FA has detectable heritability. Single, unsuccessful males had greater asymmetry for wing length than their mating counterparts both in nature and under nonoptimal rearing environments, but the higher FA in single males is most likely due to a poorer average phenotypic condition because there was no evidence of a genetic basis for this trait. Further evidence of an increase in FA under larval food stress is suggested when comparing the magnitude of the FA levels between stressful and optimal environments. On methodological grounds, a linear model is suggested that allows directional asymmetry (DA) and any genetic variation of DA that may be present to be statistically eliminated from estimates of FA.

Analysis of Variance↗

PubMed2007

Stone banging by wild capuchin monkeys: an unusual auditory display.

Primates often react to possible predators by using intimidation displays, although the occurrence of these displays is dependent on the risk of predation. Functional explanations for these kinds of displays range from sexual selection to predator deterrence. The ability to respond to different predators can be socially acquired, and social traditions could explain population differences in response to the same potential predator. Here I report wild groups of Cebus apella libidinosus banging stones to produce sound in a remarkable aggressive display. I observed this display in 6 wild groups and I suggest its primary function is a predator-deterrent behaviour. Although banging objects is an innate behaviour in capuchin monkeys, in all wild groups observed so far it has been observed only in a foraging context. Stone banging is a novel behavioural variant that is most likely learned socially. The absence of this display in other populations of capuchins, which have access to stones, suggests that stone banging could be a social tradition in the population studied.

Animals↗