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Results for “Sexual selection”

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PubMed2004

Vocal communication in frogs.

The robust nature of vocal communication in frogs has long attracted the attention of natural philosophers and their biologically inclined successors. Each frog species produces distinctive calls that facilitate pre-mating reproductive isolation and thus speciation. In many terrestrial species, a chorus of simultaneously calling males attracts females to breeding sites; reproductive females then choose and locate one male, using distinctive acoustic cues. Males compete with each other vocally and sometimes physically as well. Anuran acoustic signaling systems are thus subject to the strong pressures of sexual selection. We are beginning to understand the ways in which vocal signals are produced and decoded by the nervous system and the roles of neurally active hormones in both processes.

Animal Communication↗

PubMed2005

X-linked genes and mental functioning.

The X-chromosome has played a crucial role in the development of sexually selected characteristics for over 300 million years. During that time it has accumulated a disproportionate number of genes concerned with mental functions. Evidence is emerging, from studies of both humans and mice, for a general influence upon intelligence (as indicated by the large number of X-linked mental retardation syndromes). In addition, there is evidence for relatively specific effects of X-linked genes on social-cognition and emotional regulation. Sexually dimorphic processes could be influenced by several mechanisms. First, a small number of X-linked genes are apparently expressed differently in male and female brains in mouse models. Secondly, many human X-linked genes outside the X-Y pairing pseudoautosomal regions escape X-inactivation. Dosage differences in the expression of such genes (which might comprise at least 20% of the total) are likely to play an important role in male-female neural differentiation. To date, little is known about the process but clues can be gleaned from the study of X-monosomic females who are haploinsufficient for expression of all non-inactivated genes relative to 46,XX females. Finally, from studies of both X-monosomic humans (45,X) and mice (39,X), we are learning more about the influences of X-linked imprinted genes upon brain structure and function. Surprising specificity of effects has been described in both species, and identification of candidate genes cannot now be far off.

Animals↗

PubMed2006

Tandem repetitive D domains of the sperm ligand zonadhesin evolve faster in the paralogue than in the orthologue comparison.

Gene duplication is regarded as an important evolutionary mechanism creating genetic and phenotypic novelty. At the same time, the evolutionary mechanisms following gene duplication have been a subject of much debate. Here we analyze the sequence evolution of zonadhesin, a mammalian sperm ligand that binds to the oocyte zona pellucida in a species-specific manner. In pig, rabbit, and primates, precursor zonadhesin comprises, among others, one partial and four complete tandem repetitive D domains. The mouse precursor is distinguished by 20 additional partial D3 domains consisting of 120 amino acids each. This gene structure allows sequence comparison in both paralogues and orthologues. Detailed sequence analysis reveals that D domains evolve faster across paralogues than orthologues. Moreover, at the codon level, partial D3 paralogues of mouse show evidence of positive selection, whereas the corresponding orthologues do not. Individual posttranslational motif patterns and positive selection point to neofunctionalization of partial D3 paralogues of mouse, rather than subfunctionalization. However, as we found additional evidence for homogenization by partial gene conversion, sequence evolution of partial D3 paralogues of mouse might be better described as a combination of divergent and convergent evolution. So far, the divergence at the codon level has outbalanced the convergence at the level of smaller fragments. The probable driving force behind the evolutionary patterns observed is sexual selection. We finally discuss whether the functional determination influences the evolutionary regime acting on sperm ligands and egg receptors, respectively.

Amino Acid Motifs↗

PubMed2000

Sex-specific differences in nitrogen intake and investment by feral and laboratory-cultured cockroaches.

We compared nutrient selection in a laboratory culture of the American cockroach (Periplaneta americana: Insecta, Blattodea) and a feral population which was founded by escapees from the culture approximately 14 generations prior to the study. In a first experiment, adult male and female cockroaches were provided with two nutritionally complementary synthetic foods, and thus allowed to select the protein and carbohydrate components of their diet independently. There were no differences in the amounts of carbohydrate eaten by the two populations. However, feral males ingested more protein than cultured males. In a second experiment, the construction of nitrogen budgets showed that the additional nitrogen ingested by feral males was allocated preferentially to accessory sex glands, rather than somatic tissue or excretion via the faeces. This suggests a possible role for sexual selection in the dietary difference between the strains. By contrast with males, there was no statistically significant difference in the amount of protein eaten by females of the two populations. However, feral females were found to have a higher density of bacterial endosymbionts than cultured females. Since these symbionts are involved in the synthesis of essential amino acids, this might account for greater reproductive output observed in a previous study in the feral compared with the culture females.

Journal Article↗

PubMed2001

Speciation in rapidly diverging systems: lessons from Lake Malawi.

Rapid evolutionary radiations provide insight into the fundamental processes involved in species formation. Here we examine the diversification of one such group, the cichlid fishes of Lake Malawi, which have radiated from a single ancestor into more than 400 species over the past 700 000 years. The phylogenetic history of this group suggests: (i) that their divergence has proceeded in three major bursts of cladogenesis; and (ii) that different selective forces have dominated each cladogenic event. The first episode resulted in the divergence of two major lineages, the sand- and rock-dwellers, each adapted to a major benthic macrohabitat. Among the rock-dwellers, competition for trophic resources then drove a second burst of cladogenesis, which resulted in the differentiation of trophic morphology. The third episode of cladogenesis is associated with differentiation of male nuptial colouration, most likely in response to divergent sexual selection. We discuss models of speciation in relation to this observed pattern. We advocate a model, divergence with gene flow, which reconciles the disparate selective forces responsible for the diversification of this group and suggest that the nonadaptive nature of the tertiary episode has significantly contributed to the extraordinary species richness of this group.

Africa, Eastern↗

PubMed2000

Female control of paternity in the sexually cannibalistic spider Argiope keyserlingi.

Sexual conflict theory predicts an antagonistic coevolution, with each sex evolving adaptations and counter-adaptations to overcome a temporary dominance of the other sex over the control of paternity. Polyandry allows sexual selection to operate after mating has commenced, with male and female interests competing for control of fertilization. There are numerous examples of male control of paternity, but few studies have unambiguously revealed female control. Attributing variance in paternity to females is often difficult since male and female influences cannot be separated unambiguously. However, we show that polyandrous female orb-web spiders Argiope keserlingi (Arancidae) control the paternity of their offspring by adjusting the timing of sexual cannibalism. Our experiments reveal that females copulating with relatively smaller males delay sexual cannibalism, thereby prolonging the duration of copulation, and that these males consequently fertilize relatively more eggs.

Animals↗

PubMed2006

Postcopulatory inbreeding avoidance by female crickets only revealed by molecular markers.

Multiple mating is thought to provide an opportunity for females to avoid the costs of genetic incompatibility by postcopulatory selection of compatible sperm haplotypes. Few studies have tested the genetic incompatibility hypothesis directly. Here we experimentally manipulated the compatibility of females with their mates using the gryllid cricket Teleogryllus oceanicus. We recorded the hatching success of eggs laid by females mated with two nonsibling males, two siblings, or one nonsibling male and one sibling. In contrast with two previous studies on crickets that have adopted this approach, the hatching success of eggs did not differ between females mated with two full siblings and females mated with two unrelated males, indicating that embryo viability was not a cost of inbreeding in this species. We assigned paternity to offspring produced by females mated to both a sibling and a nonsibling male using microsatellite markers. As in previous studies of this species, we were unable to detect any difference in the proportion of offspring sired by the 1st and the 2nd male to mate with a female when females were unrelated to their mates. However, in our experimental matings the proportion of offspring sired by the nonsibling male depended on his sequence position. Paternity was biased toward the nonsibling male when he mated first. Our data show that molecular analyses of paternity are essential to detect subtle mechanisms of postcopulatory sexual selection.

Animals↗

PubMed1988

Rare male mating advantage in a natural population of Drosophila pseudoobscura.

The natural selection acting on chromosomal inversions was studied in a natural population of Drosophila pseudoobscura. Females from this population were allowed to produce offspring from their matings in nature. They were then remated to males from a laboratory strain and again allowed to produce offspring. Offspring were also produced from matings of males from nature to laboratory females. Diagnosis of salivary chromosomes in these several sets of larval offspring allowed us to deduce the karyotypes of adult females and males from nature as well as the karyotypes of the offspring of these females by their matings in nature. We reason that the males collected with the females are a reasonable sample of those that mated the females and deposited the sperm they carried on capture. Chromosome frequencies in the offspring of wild females by their matings in nature were decomposed into male and female parental contributions. Changes in chromosome frequency due to male mating success were calculated by comparing chromosomal frequencies in adult males with those in the chromosomes they contributed to their offspring. These changes were sizable and provide direct evidence that male sexual selection is an important component of selection on the inversions in this natural population. We proceeded further to classify karyotypes on the basis of their frequencies and to calculate the fraction of offspring fathered by rare or common males. Rare male karyotypes as a group had a selective value nearly twice that of the common male karyotypes.

Animals↗

PubMed1999

Long-term morbidity and quality of life in patients with localized prostate cancer undergoing definitive radiotherapy or radical prostatectomy.

PURPOSE: To assess morbidity, side effects, and quality of life (QoL) in patients treated for localized prostate cancer with curative aim. METHODS AND MATERIALS: This descriptive cross-sectional study comprises 154 patients who had undergone definitive radiotherapy (RAD) and 108 patients with radical prostatectomy (PRECT) at the Norwegian Radium Hospital during 1987-1995. At least 1 year after treatment the patients completed several questionnaires assessing quality of life (European Organization for Research and Treatment of Cancer QLQ-C30 instrument [EORTC QLQ-C30]), lower urinary tract symptoms (LUTS): International Prostate Symptom Score (IPSS), or sexuality (selected questions from the Psychosocial Adjustment to Illness Scale [PAIS]). Urinary incontinence and bowel distress were evaluated by ad hoc constructed questionnaires. A control group (OBS) consisted of 38 patients following the watch-and-wait policy. RESULTS: Twenty percent of the patients from the RAD Group had moderate (14%) or severe (6%) LUTS as compared to 12% in the PRECT group. However, 35% of men from the latter group reported moderate to severe urinary incontinence. "Overall" sexuality was moderately or severely impaired in 71% of the PRECT and 50% of the RAD patients. In the former group high age was correlated with erectile impotency (p < 0.001). In the RAD comorbidity was associated with erectile impotency (p < 0.001). Between 13-38% of the patients recorded moderate or severe bowel distress (blood per rectum: 13%; bowel cramps: 26%; flatulence: 38%), without significant differences comparing patients who had received conventional small 4-field box radiotherapy and patients who had undergone strictly conformal radiotherapy. Despite malignancy and/or treatment-related morbidity, QoL was comparable in both groups with respectively 9% and 6% RAD and PRECT patients, reporting moderately or severely impaired QoL. In the multivariate analysis physical function, emotional function and fatigue were significantly correlated with QoL, whereas sexuality, lower urinary symptoms, and urinary incontinence correlated with QoL only in the univariate analysis. CONCLUSION: In spite of considerable malignancy and/or treatment-related morbidity QoL was good or only slightly impaired in the majority of patients with localized prostate cancer who presented with stable disease > 1 year after definitive radiotherapy or radical prostatectomy with no difference as compared to the age-matched normal population. Clinicians should be aware of the fact that general QoL dimensions (physical function, emotional function, fatigue) are as a rule of greater significance for QoL than sexuality and lower urinary tract symptoms.

Aged↗

PubMed2002

Gene expression, cell localization, and evolution of rodent submandibular gland androgen-binding protein.

A small dimeric androgen-binding protein (Abp) secreted by mouse (Mus) submandibular salivary glands has been hypothesized to function in mate-selection. The alpha-subunit (Abpa) evolves rapidly under natural selection. However, cellular site(s) of synthesis, mode of function, and patterns of evolution of this biologically important protein are otherwise unknown. We used a radiolabeled riboprobe and in situ hybridization to mouse (Mus) Abpa mRNA to localize Abpa synthesis to submandibular gland acinar cells. We next used a quantitative fluorescent thermal cycler (real-time PCR) to determine relative expression levels (normalized with a constitutively expressed ribosomal gene [S15/rig; rat insulinoma gene]) in male, female, and sexually immature European striped field mice (Apodemus agrarius). We hypothesized that gender or age-related differences might occur in production of a salivary protein related to sexual selection, but found no significant differences within our sample. Finally, we also used reverse transcription-PCR of mRNAs isolated from submandibular salivary glands to determine the Abpa allele in the striped wood mouse and compare it to published information on the homologue in Mus musculus domesticus.

Amino Acid Sequence↗

PubMed2006

A time-sequence functional analysis of mating behaviour and genital coupling in Drosophila: role of cryptic female choice and male sex-drive in the evolution of male genitalia.

Male genitalia in Drosophila exemplify strikingly rapid and divergent evolution, whereas female genitalia are relatively invariable. Whereas precopulatory and post-copulatory sexual selection has been invoked to explain this trend, the functional significance of genital structures during copulation remains obscure. We used time-sequence analysis to study the functional significance of external genitalic structures during the course of copulation, between D. melanogaster and D. simulans. This functional analysis has provided new information that reveals the importance of male-driven copulatory mechanics and strategies in the rapid diversification of genitalia. The posterior process, which is a recently evolved sexual character and present only in males of the melanogaster clade, plays a crucial role in mounting as well as in genital coupling. Whereas there is ample evidence for precopulatory and/or post-copulatory female choice, we show here that during copulation there is little or no physical female choice, consequently, males determine copulation duration. We also found subtle differences in copulatory mechanics between very closely related species. We propose that variation in male usage of novel genitalic structures and shifts in copulatory behaviour have played an important role in the diversification of genitalia in species of the Drosophila subgroup.

Animals↗

PubMed2006

Embryonic origin of mate choice in a lizard with temperature-dependent sex determination.

Individual differences in the adult sexual behavior of vertebrates are rooted in the fetal environment. In the leopard gecko (Eublepharis macularius), a species with temperature-dependent sex determination (TSD), hatchling sex ratios differ between incubation temperatures, as does sexuality in same-sex animals. This variation can primarily be ascribed to the temperature having direct organizing actions on the brain. Here we demonstrate that embryonic temperature can affect adult mate choice in the leopard gecko. Given the simultaneous choice between two females from different incubation temperatures (30.0 and 34.0 degrees C), males from one incubation temperature (30.0 degrees C) preferred the female from 34.0 degrees C, while males from another incubation temperature (32.5 degrees C) preferred the female from 30.0 degrees C. We suggest that this difference in mate choice is due to an environmental influence on brain development leading to differential perception of opposite-sex individuals. This previously unrecognized modulator of adult mate choice lends further support to the view that mate choice is best understood in the context of an individual's entire life-history. Thus, sexual selection results from a combination of the female's as well as the male's life history. Female attractiveness and male choice therefore are complementary.

Animals↗

PubMed2003

A tangerine-scented social odour in a monogamous seabird.

Social odours, conspecific chemical signals, have been demonstrated in every class of vertebrate except birds. The apparent absence is surprising, as every bird examined has a functional olfactory system and many produce odours. The crested auklet (Aethia cristatella), a monogamous seabird, exhibits a distinctive tangerine-like scent closely associated with courtship. Using T-maze experiments, we tested whether auklets preferred conspecific odours and whether they distinguished between different types of scent, two prerequisites of chemical communication. Crested auklets exhibited: (i) an attraction to conspecific feather odour; (ii) a preference for two chemical components of feather scent (cis-4-decenal and octanal), which we identified as seasonally elevated; and (iii) differential responses to odours, as indicated by a preference for auklet odour, an aversion to mammalian musk, but no significant response to banana essence (amyl acetate). Our results suggest that crested auklets detect plumage odour and preferentially orientate towards this stimulus. The striking and well-described courtship display that involves the scented neck region, the 'ruff sniff', provides a conspicuous behavioural mechanism for odour transmission and the potential for scent assessment during sexual selection. Although the importance and full social function of chemical signals are just beginning to be understood in birds, including crested auklets, social odours promise to reveal a largely unexplored and possibly widespread means of avian communication.

Animal Communication↗

PubMed1995

Sexual isolation in Drosophila melanogaster: a possible case of incipient speciation.

It is generally believed that Drosophila melanogaster has no closely related species with which it can produce the viable and fertile hybrids that are essential for the genetic analysis of speciation. Following the recent report of molecular differentiation between a Zimbabwe, Africa, population and two United States populations, we provide evidence that strong sexual isolation exists between the D. melanogaster population in Zimbabwe and populations of other continents. In the presence of males of their own kind, females from most isofemale lines of Zimbabwe would not mate with males from elsewhere; the reciprocal mating is also significantly reduced, but to a lesser degree. The genes for sexual behaviors are apparently polymorphic in Zimbabwe and postmating reproductive isolation between this and other populations has not yet evolved. Whole chromosome substitutions indicate significant genetic contributions to male mating success by both major autosomes, whereas the X chromosome effect is too weak to measure. In addition, the relative mating success between hybrid and pure line males supports the interpretation of strong female choice. These observations suggest that we are seeing the early stages of speciation in this group and that it is driven by sexual selection. The genetic and molecular tractability of D. melanogaster offers great promise for the detailed analysis of this apparent case of incipient speciation.

Animals↗

PubMed2003

Functional significance of seminal receptacle length in Drosophila melanogaster.

Despite its central role in post-copulatory sexual selection, the female reproductive tract is poorly understood. Here we provide the first experimental study of the adaptive significance of variation in female sperm-storage organ morphology. Using populations of Drosophila melanogaster artificially selected for longer or shorter seminal receptacles, we identify relationships between the length of this primary sperm-storage organ and the number of sperm stored, pattern of progeny production, rate of egg fertilization, remating interval, and pattern of sperm precedence. Costs and benefits of relatively short or long organs were identified. Benefits of longer receptacles include increased sperm-storage capacity and thus progeny production from a single insemination. Results suggest that longer receptacles have not naturally evolved because of developmental time costs and a correlated reduction in longevity of mated females. This latter cost may be a consequence of sexual conflict mediated by ejaculate toxicity. Receptacle length did not alter the pattern of sperm precedence, which is consistent with data on the co-evolution of sperm and female receptacle length, and a pattern of differential male fertilization success being principally determined by the interaction between these male and female traits.

Animals↗

PubMed2006

Ecological divergence promotes the evolution of cryptic reproductive isolation.

Speciation can involve the evolution of 'cryptic' reproductive isolation that occurs after copulation but before hybrid offspring are produced. Because such cryptic barriers to gene exchange involve post-mating sexual interactions, analyses of their evolution have focused on sexual conflict or traditional sexual selection. Here, we show that ecological divergence between populations of herbivorous walking sticks is integral to the evolution of cryptic reproductive isolation. Low female fitness following between-population mating can reduce gene exchange between populations, thus acting as a form of cryptic isolation. Female walking sticks show reduced oviposition rate and lower lifetime fecundity following between-population versus within-population mating, but only for mating between populations using different host-plant species. Our results indicate that even inherently sexual forms of reproductive isolation can evolve as a by-product of ecological divergence and that post-mating sexual interactions do not necessarily evolve independently of the ecological environment.

Animals↗

PubMed1998

Female fertility and mating type distribution in a south african population of fusarium subglutinans f. sp. pini

Fusarium subglutinans f. sp. pini is the causal agent of pitch canker disease of pines. The initial occurrence of F. subglutinans f. sp. pini in South Africa was limited to a single nursery, and isolates from this population are capable of reproducing sexually. We determined the effective population number, Ne, of this population by using mating type and male/hermaphrodite polymorphisms as indicators. The effective population number for mating type, Ne(mt), is 99% of the count (total population), and that for male/hermaphrodite status, Ne(f), is 42 to 46% of the count (total population). The number of strains that can function as the female parent limits the effective population number of this population. If this population is stable, then, depending upon assumptions about mutation and selection, sexual reproduction need occur only once per 26 to 153 asexual generations to maintain this level of sexual fertility.

Journal Article↗

PubMed2001

Evidence that ultraviolet markings are associated with patterns of molecular gene flow.

Recent studies have shown UV vision and markings to be important in vertebrates, particularly birds, where behavioral experiments have demonstrated its potential importance in sexual selection. However, there has been no genetic evidence that UV markings determine patterns of evolution among natural populations. Here we report molecular evidence that UV markings are associated with the pattern of gene flow in the Tenerife lizard (Gallotia galloti). This species has vicariance-induced, approximate east--west lineages in Tenerife closely congruent with the primary lineages of the sympatric gecko species. Against expectations, these molecular phylogeographic lineages (representing geological history) and isolation-by-distance do not appear to influence gene flow. Sexually mature males from populations either side of a latitudinal ecotone have different UV markings and gene flow appears to be linked to this difference in UV markings. It may be that these groups with different UV sexual markings mate assortatively, restricting the gene flow between them. This has implications for debate on the relative importance of vicariance and biotopes in influencing biodiversity, with this evidence supporting the latter.

Animals↗