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PubMed2002

Sandpipers (Scolopacidae) switch from monoester to diester preen waxes during courtship and incubation, but why?

Recently, a shift in preen wax composition, from lower molecular weight monoesters to higher molecular weight diesters, was described for individuals of a sandpiper species (red knot, Calidris canutus) that were about to leave for the tundra breeding grounds. The timing of the shift indicated that diester waxes served as a quality signal during mate choice. Here, this hypothesis is evaluated on the basis of a survey of preen wax composition in 19 sandpiper species. All of these species showed the same shift observed in the high-Arctic breeding red knots. As the shift also occurred in temperate breeding species, it is not specific to tundra-breeding sandpipers. Both sexes produced the diester waxes during the incubation period until hatching, in addition to the short period of courtship, indicating that diesters' functions extend beyond that of a sexually selected 'make-up'. The few non-incubating birds examined (males of curlew sandpipers (C. ferruginea) and ruffs (Philomachus pugnax)) had the lowest likelihood of secreting diesters, indicating a functional role for diester preen waxes during incubation. We propose that diester preen waxes enhance olfactory crypticism at the nest.

Animals↗

PubMed2001

Ring species as bridges between microevolution and speciation.

A demonstration of how small changes can lead to species-level differences is provided by ring species, in which two reproductively isolated forms are connected by a chain of intermediate populations. We review proposed cases of ring species and the insights they provide into speciation. Ring species have been viewed both as illustrations of the history of divergence of two species from their common ancestor and as demonstrations that speciation can occur in spite of gene flow between the diverging forms. Theoretical models predict that speciation with gene flow can occur when there is divergent ecological selection, and geographical differentiation increases the likelihood of speciation. Thus ring species are ideal systems for research into the role of both ecological and geographical differentiation in speciation, but few examples have been studied in detail. The Greenish warbler is a ring species in which two northward expansions around the Tibetan plateau have been accompanied by parallel evolution in morphology, ecology, and song length and complexity. However, songs have diverged in structure, resulting in a lack of recognition where the reproductively isolated forms come into contact in Siberia. Our analysis suggests that these differences could have arisen even with gene flow, and that parallel rather than divergent ecological changes have led to divergence in sexually selected traits and subsequent speciation.

Animals↗

PubMed2006

Mating systems of blood-feeding flies.

The mating system of each species is a unique, dynamic suite of interactions between the sexes. In this review I describe these interactions in the families of flies that contain blood-feeding species. A transition from the aerial swarm, with rapid copulae and no direct female choice, to substrate-based systems with lengthy copulae and opportunities for female choice is evident at both a phylogenetic scale and within nematoceran families under specific ecological conditions. Female monogamy is associated with the former, polyandry with the latter. I suggest that the intensity of sexual selection operating on males in systems where the probability of mating is low has favored male ability to control female receptivity. Reproductive success of males is universally correlated to successful foraging for sugar or blood and (in some species and ecological conditions) to body size. Understanding the ecological basis of the mating systems of these flies will help formulate integrative, sustainable, and biologically lucid approaches for their control.

Animals↗

PubMed1997

Choreography of the squid's "nuptial dance".

A mass spawning of squid resembles, at first glance, a chaotic "nuptial dance" (1). But for the first time, we have applied 3-D, radio-linked acoustic positioning (RAP) to this confusing process, and our early results now reveal a choreography that is, in fact, well organized in time and space. Remote tracking with RAP of individual Loligo vulgaris reynaudii off South Africa has provided insights into the daily sequence of behaviours that lead these animals to aggregate for sexual selection. Each dawn, the squid navigate for several kilometers, towards the shore, to small, well-defined zones near egg beds on the substrate. After several hours of circling above the egg beds, a pelagic, 3-D lek-like aggregation of large males forms: females are drawn in, and the aggregation condenses as the females and males pair, mate, and lay eggs. Smaller "sneaker males" remain on the periphery of the mating arena and, from this station, attempt extra-pair copulations (EPCs). The mating system of squids is thus unexpectedly complex, rivaling those of mammals and birds (2, 3). Commercial squid-jigging fishermen in South Africa have recently been attracted to the spawning grounds, and they have been successful. Moreover, their activities may be selective for large males. Thus, attention should be devoted to ensuring that such targeted fishing does not alter the characteristics of squid population genetics. Remote tracking and video observations, in combination with genetic analyses, may offer a new opportunity to monitor mating effort and reproductive success, and thus to manage the fishery.

Animals↗

PubMed1997

Genetics and the origin of bird species.

External (environmental) factors affecting the speciation of birds are better known than the internal (genetic) factors. The opposite is true for several groups of invertebrates, Drosophila being the outstanding example. Ideas about the genetics of speciation in general trace back to Dobzhansky who worked with Drosophila. These ideas are an insufficient guide for reconstructing speciation in birds for two main reasons. First, speciation in birds proceeds with the evolution of behavioral barriers to interbreeding; postmating isolation usually evolves much later, perhaps after gene exchange has all but ceased. As a consequence of the slow evolution of postmating isolating factors the scope for reinforcement of premating isolation is small, whereas the opportunity for introgressive hybridization to influence the evolution of diverging species is large. Second, premating isolation may arise from nongenetic, cultural causes; isolation may be affected partly by song, a trait that is culturally inherited through an imprinting-like process in many, but not all, groups of birds. Thus the genetic basis to the origin of bird species is to be sought in the inheritance of adult traits that are subject to natural and sexual selection. Some of the factors involved in premating isolation (plumage, morphology, and behavior) are under single-gene control, most are under polygenic control. The genetic basis of the origin of postmating isolating factors affecting the early development of embryos (viability) and reproductive physiology (sterility) is almost completely unknown. Bird speciation is facilitated by small population size, involves few genetic changes, and occurs relatively rapidly.

Animals↗

PubMed2006

Suicide triggers as sex-specific threats in domains of evolutionary import: negative correlation between global male-to-female suicide ratios and average per capita gross national income.

From an evolutionary perspective, suicide is a paradoxical phenomenon given its fatal consequences on one's reproductive fitness. That fact notwithstanding, evolutionists have typically used kin and group selection arguments in proposing that suicide might indeed be viewed as an adaptive behavioral response. The current paper posits that in some instances, suicide might be construed as the ultimate maladaptive response to "crushing defeats" in domains of great evolutionary import (e.g., mating). Specifically, it is hypothesized that numerous sex-specific triggers of suicide are universally consistent because they correspond to dire sex-specific attacks on one's reproductive fitness (e.g., loss of occupational status is much more strongly linked to male suicides). More generally, it is proposed that many epidemiological aspects of suicide are congruent with Darwinian-based frameworks. These include the near-universal finding that men are much more likely to commit suicide (sexual selection theory), the differential motives that drive men and women to commit suicide (evolutionary psychology), and the shifting patterns of suicide across the life span (life-history theory). Using data from the World Health Organization and the World Bank, several evolutionary-informed hypotheses, regarding the correlation between male-to-female suicide ratios and average per capita Gross National Income, are empirically tested. Overall, the findings are congruent with Darwinian-based expectations namely as economic conditions worsen the male-to-female suicide ratio is exacerbated, with the negative correlation being the strongest for the "working age" brackets. The hypothesized evolutionary outlook provides a consilient framework in comprehending universal sex-specific triggers of suicide. Furthermore, it allows suicidologists to explore new research avenues that might remain otherwise untapped if one were to restrict their research interests on the identification of proximate causes of suicide. Global clinical and epidemiological data emphasizing other universally robust triggers of suicide would afford additional support for the postulated framework.

Biological Evolution↗

PubMed2005

Snake mating systems, behavior, and evolution: the revisionary implications of recent findings.

Sexual selection and mating systems profoundly influence the behavior and psychology of animals. Using their own studies of green anacondas (Eunectes murinus) and reviewing other recent studies, the authors conclude that incomplete data derived from a few well-studied snake species have led to general acceptance of polygyny as the dominant mating system in snakes. New data on behavior, paternity, and life history in a diverse taxonomic array of snakes support the view that polyandry is not only common in snakes but may have been the ancestral mating system. This interpretation helps to explain many seemingly paradoxical behavioral differences between lizards and snakes, such as the lack of territorial systems in most snakes and their frequent female-biased sexual size dimorphism.

Animals↗

PubMed1988

Sexually dimorphic behaviors.

Sex differences in behavior are the result of natural and sexual selection. The dimorphic classes of behavior described here, courtship, copulatory, and parental behaviors, reflect both kinds of evolutionary selective pressures. We can further distinguish two kinds of mechanisms that produce differences in male and female behaviors. In one, both sexes can perform a behavior but one does not because of sex differences in the external stimuli or the endocrine milieu. Maternal behavior in rodents falls into this category, as do certain other reproductive behaviors. In the other, the sensory, CNS, or motor components that produce behaviors are different in males and females. Many courtship and copulatory behaviors are in this category. I have considered some cellular mechanisms that generate sex differences in behavioral effector neurons, including sensitivity to hormones, cell number, and synaptic connectivity. A common feature of many such systems is a degree of developmental arrest: sexually dimorphic, hormone-sensitive neurons or muscles are immature at stages when other cells have completed differentiation. The cellular and molecular processes whereby hormones harness the developmental programs of behavioral effector cells remain largely unknown and are the focus of active investigation.

Animals↗

PubMed2006

Insights into the mating habits of the tiger salamander (Ambystoma tigrinum tigrinum) as revealed by genetic parentage analyses.

Among urodeles, ambystomatid salamanders are particularly amenable to genetic parentage analyses because they are explosive aggregate breeders that typically have large progeny arrays. Such analyses can lead to direct inferences about otherwise cryptic aspects of salamander natural history, including the rate of multiple mating, individual reproductive success, and the spatial distribution of clutches. In 2002, we collected eastern tiger salamander (Ambystoma tigrinum tigrinum) egg masses (> 1000 embryos) from a approximately 80 m linear transect in Indiana, USA. Embryos were genotyped at four variable microsatellite loci and the resulting progeny array data were used to reconstruct multilocus genotypes of the parental dams and sires for each egg mass. UPGMA analysis of genetic distances among embryos resolved four instances of egg mass admixture, where two or more females had oviposited at exactly the same site resulting in the mixing of independent cohorts. In total, 41 discrete egg masses were available for parentage analyses. Twenty-three egg masses (56%) consisted exclusively of full-siblings (i.e. were singly sired) and 18 (44%) were multiply sired (mean 2.6 males/clutch). Parentage could be genetically assigned to one of 17 distinct parent pairs involving at least 15 females and 14 different males. Reproductive skew was evident among males who sired multiply sired clutches. Additional evidence of the effects of sexual selection on male reproductive success was apparent via significant positive correlations between male mating and reproductive success. Females frequently partitioned their clutches into multiple discrete egg masses that were separated from one another by as many as 43 m. Collectively, these data provide the first direct evidence for polygynandry in a wild population of tiger salamanders.

Ambystoma↗

PubMed2006

All4You! A randomized trial of an HIV, other STDs, and pregnancy prevention intervention for alternative school students.

This study evaluated All4You!, a theoretically based curriculum designed to reduce sexual risk behaviors associated with HIV, other STDs, and unintended pregnancy among students in alternative schools. The study featured a randomized controlled trial involving 24 community day schools in northern California. A cohort of 988 students was assessed four times during an 18-month period using a self report questionnaire. At the 6-month follow-up, the intervention reduced the frequency of intercourse without a condom during the previous 3 months, the frequency of intercourse without a condom with steady partners, and the number of times students reported having intercourse in the previous 3 months. It also increased condom use at last intercourse. These behavioral effects were no longer statistically significant at the 12- and 18-month follow-ups. The All4You! intervention was effective in reducing selected sexual risk behaviors among students in alternative school settings; however, the effects were modest and short term.

Adolescent↗

PubMed2002

Why do some traits show higher fluctuating asymmetry than others? A test of hypotheses with tail feathers of birds.

Certain characters are more susceptible to increased fluctuating asymmetry (FA) than others. This trait-specific susceptibility has normally been attributed to different degrees of developmental stability, which could be caused by different modes of selection, functionality, or the stress experienced during the development process. Recently, it has also been suggested that the expression of FA not only depends on developmental stability, but also on the cost of growth of the trait, defined as the amount of structural components necessary to form a unit of length of a given character. In accordance with this argument, a trait with more structural components per unit of length should show lower asymmetry than a simpler one. To test this hypothesis, we examine the structure (number of barbs, barb length, and rachis width) and asymmetry of the longest tail feathers in 26 bird species. Regression analyses using phylogenetically independent contrasts show that FA is negatively correlated with the number of barbs and feather rachis width in males (including species with elongated tails subjected to sexual selection), and with rachis width in females, whose tails supposedly evolve by natural selection. Moreover, the negative correlation between FA and rachis width persisted when taking only the males of non-dimorphic species. These results confirm the hypothesis, suggesting that a trait's susceptibility to express developmental instability by fluctuating asymmetry depends on its structural composition.

Animals↗

PubMed2005

Inheritance of female mating preference in a sympatric sibling species pair of Lake Victoria cichlids: implications for speciation.

Female mate choice has often been proposed to play an important role in cases of rapid speciation, in particular in the explosively evolved haplochromine cichlid species flocks of the Great Lakes of East Africa. Little, if anything, is known in cichlid radiations about the heritability of female mating preferences. Entirely sympatric distribution, large ecological overlap and conspicuous differences in male nuptial coloration, and female preferences for these, make the sister species Pundamilia pundamilia and P. nyererei from Lake Victoria an ideally suited species pair to test assumptions on the genetics of mating preferences made in models of sympatric speciation. Female mate choice is necessary and sufficient to maintain reproductive isolation between these species, and it is perhaps not unlikely therefore, that female mate choice has been important during speciation. A prerequisite for this, which had remained untested in African cichlid fish, is that variation in female mating preferences is heritable. We investigated mating preferences of females of these sister species and their hybrids to test this assumption of most sympatric speciation models, and to further test the assumption of some models of sympatric speciation by sexual selection that female preference is a single-gene trait. We find that the differences in female mating preferences between the sister species are heritable, possibly with quite high heritabilities, and that few but probably more than one genetic loci contribute to this behavioural speciation trait with no apparent dominance. We discuss these results in the light of speciation models and the debate about the explosive radiation of cichlid fishes in Lake Victoria.

Animals↗

PubMed1998

Rapping, a female receptive call, initiates male-female duets in the South African clawed frog.

Finding a sexually receptive partner of the opposite sex is a challenge; one solution is to advertise. That advertising is usually the province of males has shaped scenarios for sexual selection, especially the ardent active male courting the passive but choosy female. Herein we consider an unusual case in which constraints on reproduction may have led to fertility advertisement by female frogs. When oviposition is imminent, female South African clawed frogs swim to an advertising male and produce an aphrodisiac call, rapping, that stimulates both male vocalization and approach. Males respond to rapping with a distinctive answer call. The rapping-answer interaction thus forms a duet between partners of a receptive pair.

Animals↗

PubMed1998

The evolution of multiple male traits in the yellow-browed leaf warbler

I examined how male competition and female choice influence the evolution of multiple male traits in the yellow-browed leaf warbler, Phylloscopus inornatus, by investigating the roles of colour patches, territory size, body weight and song rate in sexual selection. Comparison of 3 years of observational studies and 3 years of experimental studies, in which the colour patches on the wings of males were experimentally altered, suggest several mechanisms that may explain the evolution of multiple characters in males. First, females based their choice of mates on several male characters, not a single character. Second, the male characters preferred by females were different in observational and experimental studies. Females apparently preferred high-quality males as mates, and were able to vary the characters used in mate choice to distinguish these individuals under both experimental and observational conditions. Third, the characters important in male competition differed from those that formed the basis of female choice: the manipulation of colour patch size directly affected male territory size but was not associated with female choice. These results may provide an explanation for the diversity of sexual ornaments shown by males of many species.Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1994

Sex differences, sex ratios and sex roles.

Sexual selection theory predicts that sex roles will be determined by the operational sex ratio (OSR), the sex ratio among individuals searching for mates at any given time. There are two predictions: (i) the sex which is in 'excess' will be the more competitive sex with respect to access to mates; and (ii) the sex of which there is a 'shortage' will be the more choosy with respect to potential partners. We examine the second prediction and find that current OSR theory does not consider an important factor which affects mate choice. This factor is sex differences in variation in mate quality. Hence, we develop a new model of mate choice which shows that the parameter which should be optimized during mate choice is the trade-off between reproductive rate and mate quality. If mate choice is too lax, reproductive rate may be high but partners will be of low quality. If mate choice is too stringent, partners will be of high quality but reproductive rate will be low because such partners will be rare. Stringency of mate choice is, therefore, a facet of OSR theory. Indeed, our model shows that OSR theory can be used to integrate the effect of sex differences in both mating rate and variation in mate quality to predict the direction of mate choice. Our model suggests that: (i) mate choice is only selected when individuals of the opposite sex vary in their quality as mates; (ii) if the extent of variation in mate quality is equal within each sex, the sex with the lower potential mating rate will be the more choosy sex; but (iii) if there is sufficiently greater variation in mate quality among the sex with the lower potential reproductive rate, the sex with the higher potential mating rate will be the more choosy sex.(ABSTRACT TRUNCATED AT 250 WORDS)

Game Theory↗

PubMed2000

Do extraterrestrials have sex (and intelligence)?

This thought experiment addresses the range of possible evolved psychologies likely to be associated with extraterrestrial (ET) intelligence. The analysis rests on: (1) a number of assumptions shared by the SETI project; (2) recent arguments concerning convergent evolution; and (3) current theories of how intelligence evolved in our own species. It concludes that, regardless of how and which cognitive abilities arise initially, extraterrestrially they can develop into intelligence only if an amplification process involving a form of predation and/or sexual selection occurs. Depending on the amplification process, ETs may be xenophobic; however, it is more probable that they will be ethnocentric. Their ideas of reciprocity and fairness are likely to at least overlap with our own. They will definitely be culture-bearing and probably have two sexes, both of which are intelligent. Regardless of the degree of physical similarity of ETs to ourselves, convergence makes it likely that we will at least find their evolved psychology similar enough to our own for comprehension.

Adaptation, Physiological↗

PubMed2006

The evolution of host preference in allopatric vs. parapatric populations of Timema cristinae walking-sticks.

Divergent habitat preferences can contribute to speciation, as has been observed for host-plant preferences in phytophagous insects. Geographic variation in host preference can provide insight into the causes of preference evolution. For example, selection against maladaptive host-switching occurs only when multiple hosts are available in the local environment and can result in greater divergence in regions with multiple vs. a single host. Conversely, costs of finding a suitable host can select for preference even in populations using a single host. Some populations of Timema cristinae occur in regions with only one host-plant species present (in allopatry, surrounded by unsuitable hosts) whereas others occur in regions with two host-plant species adjacent to one another (in parapatry). Here, we use host choice and reciprocal-rearing experiments to document genetic divergence in host preference among 33 populations of T. cristinae. Populations feeding on Ceanothus exhibited a stronger preference for Ceanothus than did populations feeding on Adenostoma. Both allopatric and parapatric pairs of populations using the different hosts exhibited divergent host preferences, but the degree of divergence tended to be greater between allopatric pairs. Thus, gene flow between parapatric populations apparently constrains divergence. Host preferences led to levels of premating isolation between populations using alternate hosts that were comparable in magnitude to previously documented premating isolation caused by natural and sexual selection against migrants between hosts. Our findings demonstrate how gene flow and different forms of selection interact to determine the magnitude of reproductive isolation observed in nature.

Animals↗

PubMed2003

Characteristic odor of Osmoderma eremita identified as a male-released pheromone.

Osmoderma eremita (Scopoli) is an endangered scarab beetle living in hollow trees. It has mainly been known for its characteristic odor, typically described as a fruity, peachlike or plumlike aroma. The odor emanating from a single beetle can sometimes be perceived from a distance of several meters. In this paper, we show that the characteristic odor from O. eremita is caused by the compound (R)-(+)-gamma-decalactone, released in large quantities mainly or exclusively by male beetles. Antennae from male and female beetles responded in a similar way to (R)-(+)-gamma-decalactone in electroantennographic recordings. Field trapping experiments showed that (R)-(+)-gamma-decalactone is a pheromone attracting female beetles. Lactones similar to (R)-(+)-gamma-decalactone are frequently used as female-released sex pheromones by phytophagous scarabs. This is, however, the first evidence of a lactone used as a male-produced pheromone in scarab beetles. We propose that the strong signal from males is a sexually selected trait used to compete for females and matings. The signal could work within trees but also act as a guide to tree hollows, which are an essential resource for O. eremita. Males may, thus, attract females dispersing from their natal tree by advertising a suitable habitat. This signal could also be exploited by other males searching for tree hollows or for females, which would explain the catch of several males in our traps.

Animals↗