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PubMed2006

The adaptive significance of sexually dimorphic scale rugosity in sea snakes.

In terrestrial snakes, rugose scales are uncommon and (if they occur) generally are found on both sexes. In contrast, rugose scales are seen in most sea snakes, especially in males. Why has marine life favored this sex-specific elaboration of scale rugosity? We pose and test alternative hypotheses about the function of rugose scales in males of the turtle-headed sea snake (Emydocephalus annulatus) and conclude that multiple selective forces have been involved. First, rugosities may aid male positioning during courtship, because histology shows that tubercles are more highly innervated than adjacent flat areas of each scale and hence are presumably more sensitive to tactile cues, and because biomechanical tests show that rugosities enhance friction between the bodies of males and females. Second, the occurrence of rugosities over the entire body of males and (albeit less well developed) in females as well suggests that rugosities also play a hydrodynamic role by modifying water flow across the snake's surface. Flow tank tests show that rugosities reduce the thickness of the boundary layer by almost 50% and create turbulent flow that should massively enhance rates of cutaneous oxygen uptake and hence prolong maximal courtship duration by males.

Adaptation, Physiological↗
PubMed2000

quick-to-court, a Drosophila mutant with elevated levels of sexual behavior, is defective in a predicted coiled-coil protein.

Remarkably little is known about the molecular mechanisms that drive sexual behavior. We have identified a new gene, quick-to-court (qtc), whose mutations cause males to show high levels of male-male courtship. qtc males also show a novel phenotype: when placed in the presence of a virgin female, they begin courtship abnormally quickly. qtc mutations are striking in their specificity, in that many aspects of male sexual behavior are normal. We have cloned the qtc gene and found that it encodes a predicted coiled-coil protein and is expressed in the olfactory organs, central nervous system, and male reproductive tract.

Amino Acid Sequence↗
PubMed2001

Molecular Dissection of the 5' Region of no-on-transientA of Drosophila melanogaster Reveals cis-Regulation by Adjacent dGpi1 Sequences.

The nonA gene of Drosophila melanogaster is important for normal vision, courtship song, and viability and lies approximately 350 bp downstream of the dGpi1 gene. Full rescue of nonA mutant phenotypes can be achieved by transformation with a genomic clone that carries approximately 2 kb of 5' regulatory material and that encodes most of the coding sequence of dGpi1. We have analyzed this 5' region by making a series of deleted fragments, fusing them to yeast GAL4 sequences, and driving UAS-nonA expression in a mutant nonA background. Regions that both silence and enhance developmental tissue-specific expression of nonA and that are necessary for generating optomotor visual responses are identified. Some of these overlap the dGpi1 sequences, revealing cis-regulation by neighboring gene sequences. The largest 5' fragment was unable to rescue the normal electroretinogram (ERG) consistently, and no rescue at all was observed for the courtship song phenotype. We suggest that sequences within the nonA introns that were missing in the UAS-nonA cDNA may carry enhancer elements for these two phenotypes. Finally, we speculate on the striking observation that some of the cis-regulatory regions of nonA appear to be embedded within the coding regions of dGpi1.

Alleles↗
PubMed2002

lingerer, a Drosophila gene involved in initiation and termination of copulation, encodes a set of novel cytoplasmic proteins.

In an effort to uncover genetic components underlying the courtship behavior of Drosophila melanogaster, we have characterized a novel gene, lingerer (lig), mutations of which result in abnormal copulation. Males carrying a hypomorphic mutation in lig fail to withdraw their genitalia upon termination of copulation, but display no overt abnormalities in their genitalia. A severe reduction in the dosage of the lig gene causes repeated attempted copulations but no successful copulations. Complete loss of lig function results in lethality during early pupal stages. lig is localized to polytene segment 44A on the second chromosome and encodes three alternatively spliced transcripts that generate two types of 150-kD proteins, Lig-A and Lig-B, differing only at the C terminus. Lig proteins show no similarity to known proteins. However, a set of homologous proteins in mammals suggest that Drosophila Lig belongs to a family of proteins that share five highly conserved domains. Lig is a cytoplasmic protein expressed in the central nervous system (CNS), imaginal discs, and gonads. Lig-A expression is selectively reduced in lig mutants and the ubiquitous supply of this protein at the beginning of metamorphosis restores the copulatory defects of the lig mutant. We propose that lig may act in the nervous system to mediate the control of copulatory organs during courtship.

Amino Acid Sequence↗
PubMed1996

Behavioral regulation of gonadotropin-releasing hormone.

GnRH controls the hypothalamic-pituitary-gonadal axis in all vertebrate species. Yet despite intense efforts, limited progress has been made toward determining how production of this neuropeptide is regulated. An alternative approach to this problem is to study species whose reproductive status is sensitive to behavioral influences and then to use behavioral interactions to probe the GnRH neuronal system. In this review, data on behaviorally induced alterations in the GnRH system will be presented. In several species of fishes, reproductive status and sex can be altered in adults by changes in the social environment. In these fishes, the numbers and size of GnRH-immunoreactive (GnRH-ir) neurons are modified by an individual's social and sexual status. In the ring dove, courtship activates ovarian follicular development and stimulates androgen production in males. During courtship, mast cells containing GnRH-like immunoreactivity enter the brain. This finding presents a new avenue for examining behavioral endocrine and immune interactions. In the musk shrew, most aspects of female reproduction are activated by contact with a male. Interactions with males trigger changes in the numbers of GnRH-ir cells and rapid production of GnRH peptide. The use of comparative animal models provides us with new insights into neuronal plasticity, neuroendoimmunology, and reproductive biology.

Animals↗
PubMed1998

Spine density changes in forebrain areas of the zebra finch by TEA-induced potentiation.

When young zebra finch males who have been reared in isolation court a female for the first time they develop a stable preference for females of this species (sexual imprinting). During this first courtship, two areas of the forebrain show a reversible enhancement of spine density, while in two other areas, spine density decreases irreversibly. Here we show that the same alterations can be induced by application of tetraethylammonium (TEA) to slices of adult, previously isolated males. TEA application induces an enhancement of spine density in two forebrain areas and leads to a decrease of spine density in two others. Although the exact mechanisms are unknown, our results indicate that potentiation phenomena are involved in the spine density changes induced by first courtship.

Animals↗
PubMed2005

Social behavior modulates songbird interpeduncular nucleus function.

Male zebra finches produce the same song while alone and during courtship of a female. However, singing-related activity in the anterior forebrain nuclei lateral magnocellular anterior nidopallium and Area X markedly depends on the social context. Thus, the anterior forebrain should receive a signal of social context from outside the song system. Here we investigated a possible source of such modulation, the midbrain interpeduncular nucleus, by monitoring immediate early genes and synaptic activity. The level of immunoreactivity for egr1 was high and calretinin was low following courtship directed singing, but the opposite pattern was seen after solo undirected singing. Further, pairs of stimulation caused depression of synaptic responses after directed singing, but facilitation after undirected singing.

Animals↗
PubMed2005

Novel male trait prolongs survival in suicidal mating.

Male redback spiders (Latrodectus hasselti) maximize paternity if they copulate twice with their cannibalistic mate. Facilitating cannibalistic attack during their first copulation yields paternity benefits. However, females have paired sperm-storage organs inseminated during two separate copulations, so males that succumb to partial cannibalism during the first copulation lose at least 50% of their paternity to rivals. In this paper, we describe a novel male trait--an abdominal constriction that appears during courtship--that allows males to survive and mate with females for a second time, despite the substantial cannibalistic damage inflicted during the first copulation. Constricted males that were wounded to simulate early cannibalism had higher endurance, greater survivorship, longer subsequent courtship and higher mating success than wounded males that were not constricted. Constriction was not found in a non-sacrificial congener that rarely survived simulated cannibalism, and the protective effect of constriction in redbacks was specific to the type of damage inflicted by females during the first copulation. Thus, the abdominal constriction allows males to overcome the potential fitness limit imposed by their own suicidal strategy-paradoxically, by prolonging survival across two cannibalistic copulations.

Animals↗
PubMed2000

Acoustic preference functions and song variability in the Hawaiian cricket Laupala cerasina.

Female preference functions for different sexual traits can differ significantly, from 'unimodal' to 'open ended'. Through the study of acoustic communication in anurans, several studies have reported an association between static (stereotyped) traits versus dynamic (variable) traits and preference function shape (unimodal versus open ended, respectively). Observing a similar pattern in a phylogenetically independent group would suggest that deterministic forces have caused a relationship between signal variability and preference function shape in acoustic signalling systems. We examined this phenomenon in crickets, another animal characterized by intersexual acoustic communication. We measured the within-male variability for three acoustic features of the male calling song in Laupala cerasina and the corresponding shape of the female preference function for each of these features. We offer support for the generalization that open-ended preference functions correspond to relatively dynamic courtship traits and unimodal preference functions correspond to relatively static courtship traits. We discuss the evolutionary significance of these findings in the context of the natural history of the Laupala species radiation.

Acoustic Stimulation↗
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↗
PubMed2004

Laboratory mating trials indicate incipient speciation by sexual selection among populations of the cichlid fish Pseudotropheus zebra from Lake Malawi.

It has been suggested that sexual selection may have played a major role in the rapid evolution of hundreds of species of cichlid fishes in Lake Malawi. We report the results of a laboratory test of assortative mating among Lake Malawi cichlid fishes from five closely related geographical populations differing in male courtship colour. Paternity of clutches was tested using microsatellite DNA typing of offspring. Out of 1955 offspring typed, 1296 (66.3%) were sired by the male from the same population as the female, which is more than three times the rate expected if females do not differentiate among males of the different populations (20%). This result indicates that mate preferences of geographical races are strongly differentiated, consistent with the races representing incipient geographical species diverging under sexual selection exerted by female preferences for different male courtship colours.

Animals↗
PubMed2004

Testosterone, cuckoldry risk and extra-pair opportunities in the Seychelles warbler.

In male birds, testosterone (T) plays an important role in aggressive and mate-attraction behaviour. In the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis, extra-group copulations (EGCs) occur frequently, but are not accompanied by sexual courtship displays as in within-pair copulations. Paternity is nearly always gained by primary males. We investigated whether T levels and sperm storage capability (cloacal protuberance (CP)) in adult primary and subordinate males were related to timing of egg laying, levels of cuckoldry and extra-group paternity (EGP) opportunities. During the sexually active period before egg laying, T levels and CP were only elevated or enlarged (respectively) in primary males, and some suggestion was found that subordinate males do not invest in elevated T levels. The peak in T occurred during the fertile period of the female partner and corresponded to the peak period of male sexual displays and mate guarding, but was independent of cuckoldry risk (density of neighbouring primary males). CP was also enhanced during this period; however, CP but not T remained elevated after egg laying by their mates, and CP but not T was positively related to EGP opportunities (density of neighbouring fertile females). We conclude that T is involved in sexual courtship displays and mate guarding, but not in gaining EGCs. These findings contrast with those in other species where EGP involves elaborate sexual displays.

Age Factors↗
PubMed2000

Sexual size dimorphism in shorebirds, gulls, and alcids: the influence of sexual and natural selection.

Charadrii (shorebirds, gulls, and alcids) have an unusual diversity in their sexual size dimorphism, ranging from monomorphism to either male-biased or female-biased dimorphism. We use comparative analyses to investigate whether this variation relates to sexual selection through competition for mates or natural selection through different use of resources by males and females. As predicted by sexual selection theory, we found that in taxa with socially polygynous mating systems, males were relatively larger than females compared with less polygynous species. Furthermore, evolution toward socially polyandrous mating systems was correlated with decreases in relative male size. These patterns depend on the kinds of courtship displays performed by males. In taxa with acrobatic flight displays, males are relatively smaller than in taxa in which courtship involves simple flights or displays from the ground. This result remains significant when the relationship with mating system is controlled statistically, thereby explaining the enigma of why males are often smaller than females in socially monogamous species. We did not find evidence that evolutionary changes in sexual dimorphism relate to niche division on the breeding grounds. In particular, biparental species did not have greater dimorphism in bill lengths than uniparental species, contrary to the hypothesis that selection for ecological divergence on the breeding grounds has been important as a general explanation for patterns of bill dimorphism. Taken together, these results strongly suggest that sexual selection has had a major influence on sexual size dimorphism in Charadrii, whereas divergence in the use of feeding resources while breeding was not supported by our analyses.

Animals↗
PubMed2002

Mutual interest between the sexes and reproductive success in Drosophila pseudoobscura.

The pre-mating behavior of female Drosophila pseudoobscura has been considered passive and "coy" relative to more active, "ardent," and indiscriminate male behavior. To test whether this long-held view-the "received wisdom" about mating behavior in Drosophila-is really true we carried out observations on how often D. pseudoobscura females approached males prior to courtship and copulation. By including only virgin females and males in the experiments, we eliminated the possibility that males are "coy" due to sperm limitation and females flexibly "coy" due to male manipulations that may affect the duration of remating inhibition. We observed the movements of females and males in vials during the first five minutes of exposure to one another. Video records revealed females went toward males as frequently as males toward females; we inferred that females were as interested in males as males in females. The total number of offspring emerging as adults correlated significantly with mutual, precourtship interest of both males and females in their vial-mates and latency to copulation. Thus, we hypothesize that females in nature approach males, perhaps actively soliciting male courtship simply by remaining close to them.

Animals↗
PubMed2002

Reproductive isolating mechanisms between two sympatric sibling species of sea snakes.

Mechanisms that maintain species isolation within sympatric congeners have attracted analysis in many kinds of organisms, but not in snakes. We studied two sibling species of amphibious sea snakes (Laticauda colubrina and L. frontalis) on the island of Efate, in the Pacific Ocean republic of Vanuatu. The two taxa are almost identical morphologically, except that L. colubrina grows much larger than L. frontalis. No natural hybrids have been reported, and geographic distributions of the two taxa suggest the possibility of sympatric speciation. Our fieldwork shows that the two taxa are often syntopic and overlap in breeding seasons. Behavioral studies in outdoor arenas show that the separation between these two taxa is maintained by species-specific cues that control male courtship. Males of both species courted conspecific females but not heterospecific females. The proximate mechanism driving this separation involves chemical cues. Adult females of both taxa possess distinctive lipids in the skin. Males directed courtship behavior (chin-pressing) to hexane-extracted samples of lipids from conspecific but not heterospecific females. Males of the dwarf species (L frontalis) were more selective courters than were those of the larger taxon (L. colubrina), perhaps because a preference for courting larger females means that L. colubrina males would be unlikely to court L. frontalis-sized (i.e., small) females even in the absence of pheromonal barriers.

Animals↗
PubMed2006

Nest ornamentation by female spotless starlings in response to a male display: an experimental study.

1. The use of behavioural traits by females in signalling condition has been practically ignored in evolutionary theory. However, females may also exhibit ornaments and behavioural displays, although less elaborated than those of males. 2. In this study we suggest that the carrying of feathers by spotless starlings Sturnus unicolor Temminck females to decorate the nest represents an elaborated and costly behaviour that is displayed in response to a courtship male behaviour: the carrying of nest green plants. 3. By experimentally increasing the amount of green plants in the nests, to give the appearance that highly attractive males defended them, we induced females to increase their feather carrying rates. 4. The amount of feathers carried to the nest was correlated to female reproductive experience and laying date, two variables correlated with female body condition. These results suggests that this behaviour may work as an honest indicator of female quality. 5. We conclude that male carrying plants and female carrying feathers can be viewed as two sex-specific functionally related signalling behaviours involved in mutual courtship or status signalling.

Animals↗
PubMed1983

Problems of medical students in India.

A sample of 505 medical students from five medical colleges with urban and regional environmental settings was selected. The subjects belonged to three groups: (1) students having covered only 3-4 months in college; (2) students exceeding 18 months in college; and (3) interns (students having graduated). A comparison was made between male and female students belonging to high and low socio-economic status groups from both urban as well as regional colleges separately. Findings suggest that in urban colleges males report significantly more problems than females in areas like: courtship, sex and marriage; morals and religion; adjustment to college work; and curriculum and teaching procedure. In regional colleges, males as compared with females reveal significantly more problems in areas like: finance, living conditions and employment; courtship, sex and marriage; home and family; the future: vocational and educational matters; and curriculum and teaching procedure.

Education, Medical, Undergraduate↗
PubMed2005

Microsatellite DNA analysis shows that greater sage grouse leks are not kin groups.

The spectacular social courtship displays of lekking birds are thought to evolve via sexual selection, but this view does not easily explain the participation of many males that apparently fail to mate. One of several proposed solutions to this 'lek skew paradox' is that kin selection favours low-ranking males joining leks to increase the fitness of closely related breeders. We investigated the potential for kin selection to operate in leks of the greater sage grouse, Centrocercus urophasianus, by estimating relatedness between lekking males using microsatellite DNA markers. We also calibrated these estimates using data from known families. Mean relatedness within leks was statistically indistinguishable from zero. We also found no evidence for local clustering of kin during lek display, although males tended to range closer to kin when off the lek. These results make kin selection an unlikely solution to the lek skew paradox in sage grouse. Together with other recent studies, they also raise the question of why kin selection apparently promotes social courtship in some lekking species, but not in others.

Animals↗