Male Courtship Pheromones Research Articles

Pheromones for amphibian conservation – considering new approaches in conservation breeding programmes

Pheromones for amphibian conservation – considering new approaches in conservation breeding programmes

Male Ventroposterior Brush Display Increases the Sexual Receptivity of Females in the Gregarious Beet Webworm Loxostege sticticalis (Lepidoptera: Crambidae)

Males of many moths possess scent organs, ranging from simple scales and hair-tufts to complex glands. Males of the gregarious beet webworm Loxostege sticticalis (Lepidoptera: Crambidae) display their ventroposterior brushes (VPBs), located on the eighth abdominal sternite, toward adjacent females and usually maintain this posture until sexually receptive females become available, or the arrival of photophase. The peak period of male L. sticticalis VPB display during the scotophase broadly coincides with that of mating. Our experiments revealed that females exposed to male VPB display increased their calling behavior and were more likely to mate than those exposed to males that did not display their VPBs. Volatile chemicals provide the only reliable sensory modality for intersexual communication in L. sticticalis because all behavioral assays were conducted in a sealed darkroom, thereby eliminating a role for visual signals, and no vibratory signals occurred during VPB displaying. Therefore, odors released from the VPB of male L. sticticalis may act as aphrodisiac signals to conspecific females in order to enhance female receptivity and increase his mating success. Our study indicates that chemical communication in these gregarious moths apparently involves mutually stimulating interactions between female attractant and male courtship pheromones.

Love Is Blind: Indiscriminate Female Mating Responses to Male Courtship Pheromones in Newts (Salamandridae)

Internal fertilization without copulation or prolonged physical contact is a rare reproductive mode among vertebrates. In many newts (Salamandridae), the male deposits a spermatophore on the substrate in the water, which the female subsequently takes up with her cloaca. Because such an insemination requires intense coordination of both sexes, male newts have evolved a courtship display, essentially consisting of sending pheromones under water by tail-fanning towards their potential partner. Behavioral experiments until now mostly focused on an attractant function, i.e. showing that olfactory cues are able to bring both sexes together. However, since males start their display only after an initial contact phase, courtship pheromones are expected to have an alternative function. Here we developed a series of intraspecific and interspecific two-female experiments with alpine newt (Ichthyosaura alpestris) and palmate newt (Lissotriton helveticus) females, comparing behavior in male courtship water and control water. We show that male olfactory cues emitted during tail-fanning are pheromones that can induce all typical features of natural female mating behavior. Interestingly, females exposed to male pheromones of their own species show indiscriminate mating responses to conspecific and heterospecific females, indicating that visual cues are subordinate to olfactory cues during courtship.

Male courtship pheromones as indicators of genetic quality in an arctiid moth (Utetheisa ornatrix)

One of the fundamental issues regarding sexual selection is whether females select males based on signals that represent direct phenotypic or indirect genetic benefits. In Utetheisa ornatrix (Lepidoptera: Arctiidae), females choose males based on a courtship pheromone, hydroxydanaidal (HD), derived from defensive pyrrolizidine alkaloids (PAs). At mating, virgin males transfer a spermatophore whose contents are proportional to the HD titer and body size; as a result, females receive both phenotypic benefits (more nutrients and PAs) and genotypic benefits (genes for larger body size inherited by the offspring). Previous data from field-collected individuals, however, indicated that the HD signal of nonvirgin males may not correlate with the spermatophore contents. Using chemical analyses, we determined that the HD signal does not change based on mating history, thereby supporting the importance of HD in advertising a male’s genetic quality. Thus, male HD represents original body size and PA levels, and females, by choosing males based on this pheromone, are providing their offspring with genes to sequester chemicals that confer survival and reproductive advantages. We discuss the implications regarding the relative importance of direct and indirect selection in maintaining female preferences. Key words: Arctiidae, genetic benefits, mate choice, pheromone, pyrrolizidine alkaloid, sexual selection. [Behav Ecol]

Elevated plasma corticosterone increases metabolic rate in a terrestrial salamander

Plasma glucocorticoid hormones (GCs) increase intermediary metabolism, which may be reflected in whole-animal metabolic rate. Studies in fish, birds, and reptiles have shown that GCs may alter whole-animal energy expenditure, but results are conflicting and often involve GC levels that are not physiologically relevant. A previous study in red-legged salamanders found that male courtship pheromone increased plasma corticosterone (CORT; the primary GC in amphibians) concentrations in males, which could elevate metabolic processes to sustain courtship behaviors. To understand the possible metabolic effect of elevated plasma CORT, we measured the effects of male courtship pheromone and exogenous application of CORT on oxygen consumption in male red-legged salamanders ( Plethodon shermani). Exogenous application of CORT elevated plasma CORT to physiologically relevant levels. Compared to treatment with male courtship pheromone and vehicle, treatment with CORT increased oxygen consumption rates for several hours after treatment, resulting in 12% more oxygen consumed (equivalent to 0.33 J) during our first 2 h sampling period. Contrary to our previous work, treatment with pheromone did not increase plasma CORT, perhaps because subjects used in this study were not in breeding condition. Pheromone application did not affect respiration rates. Our study is one of the few to evaluate the influence of physiologically relevant elevations in CORT on whole-animal metabolism in vertebrates, and the first to show that elevated plasma CORT increases metabolism in an amphibian.

ELEVATION OF PLASMA CORTICOSTERONE TO PHYSIOLOGICALLY RELEVANT LEVELS INCREASED METABOLIC RATE IN A TERRESTRIAL SALAMANDER

Event Abstract Back to Event ELEVATION OF PLASMA CORTICOSTERONE TO PHYSIOLOGICALLY RELEVANT LEVELS INCREASED METABOLIC RATE IN A TERRESTRIAL SALAMANDER Corina Wack1, Sarah DuRant2, William Hopkins2 and Sarah Woodley1* 1 Duquesne University, United States 2 Virginia Tech, Department of Fish and Wildlife Conservation, United States Plasma glucocorticoid hormones (GCs) become elevated when individuals are exposed to stressors. GCs alter intermediary metabolism to increase blood glucose concentrations. In the absence of compensatory mechanisms, this increase in intermediary metabolism may be reflected in whole-animal metabolic rate. Studies in fish, birds, and reptiles have shown that GCs may alter whole animal metabolic rates, but results are conflicting and often involve GCs levels that are not physiologically relevant. A previous study in red-legged salamanders (Plethodon shermani) found that male courtship pheromone increased plasma corticosterone (CORT; primary GC in amphibians) concentrations in males but not females. To understand the possible metabolic effect of elevated plasma CORT, we measured the effects of male courtship pheromone and exogenous application of CORT on oxygen consumption in male red-legged salamanders. Exogenous application of CORT elevated plasma CORT to physiologically relevant levels. Compared to treatment with male courtship pheromone and vehicle, treatment with CORT increased oxygen consumption rates within two hours after treatment resulting in 12% more oxygen consumed over a 2 hr period. Contrary to our previous work, treatment with pheromone did not increase plasma CORT, perhaps because subjects used in this study were not in breeding condition. Our study is one of the few to evaluate the influence of physiologically relevant elevations in CORT on whole animal metabolism in wildlife, and the first to show that elevated plasma CORT increases metabolism in an amphibian. Keywords: stress Conference: ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology, Ann Arbor, United States, 11 Jul - 13 Jul, 2011. Presentation Type: Poster Topic: Stress Citation: Wack C, DuRant S, Hopkins W and Woodley S (2011). ELEVATION OF PLASMA CORTICOSTERONE TO PHYSIOLOGICALLY RELEVANT LEVELS INCREASED METABOLIC RATE IN A TERRESTRIAL SALAMANDER. Front. Endocrinol. Conference Abstract: ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology. doi: 10.3389/conf.fendo.2011.03.00045 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 22 Jul 2011; Published Online: 09 Aug 2011. * Correspondence: Prof. Sarah Woodley, Duquesne University, Pittsburgh, United States, woodleys@duq.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract Supplemental Data The Authors in Frontiers Corina Wack Sarah DuRant William Hopkins Sarah Woodley Google Corina Wack Sarah DuRant William Hopkins Sarah Woodley Google Scholar Corina Wack Sarah DuRant William Hopkins Sarah Woodley PubMed Corina Wack Sarah DuRant William Hopkins Sarah Woodley Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Male courtship pheromones suppress female tendency to feed but not to flee in a plethodontid salamander

Female sexual receptivity is a behaviour at the crux of mechanistic and evolutionary perspectives of reproductive behaviour. To gain insight into the general processes by which a male persuades a female to mate with him, we tested whether the courtship pheromones of the red-legged salamander, Plethodon shermani , dampened female defensive or ingestive behaviours. Females did not sprint significantly shorter distances to evade startling stimuli when experimentally treated with pheromone solution compared to a control. However, females did consume 25% fewer fly larvae when treated with pheromone compared to a control. The female's maintenance of normal defences suggests a behavioural state that is unresponsive or resistant to pheromone stimulation, but the change in feeding activity indicates that suppression of female hunger is beneficial to male mating success. Together, these results indicate that male courtship pheromones may augment female receptivity by modulating the expression of other competing or inhibitory motivated behaviours.

Social Context Influences Chemical Communication in D. melanogaster Males

Chemical communication mediates social interactions in insects. For the fruit fly, D. melanogaster, the chemical display is a key fitness trait because it leads to mating. An exchange of cues that resembles a dialogue between males and females is enacted by pheromones, chemical signals that pass between individual flies to alter physiology and behavior. Chemical signals also affect the timing of locomotor activity and sleep. We investigated genetic and environmental determinants of chemical communication. To evaluate the role of the social environment, we extracted a chemical blend from individual males selected from groups composed of one genotype and compared these extracts to those from groups of mixed genotypes. To evaluate the role of the physical environment, these comparisons were performed under a light-dark cycle or in constant darkness. Here, we show that chemical signaling is affected by the social environment, light-dark cycle, and genotype as well as the complex interplay of these variables. Gene-by-environment interactions produce highly significant effects on chemical signaling. We also examined individual responses within the groups. Strikingly, the response of one wild-type fly to another is modulated by the genotypic composition of his neighbors. Chemical signaling in D. melanogaster may be a "fickle" trait that depends on the individual's social background.

Morphogenetic effects of alkaloidal metabolites on the development of the coremata in the salt marsh moth, Estigmene acrea (Dru.) (Lepidoptera: Arctiidae)

Pyrrolizidine alkaloids (PAs) play a fundamental role in the sexual biology of the salt marsh moth Estigmene acrea. They are precursors for the male courtship pheromone hydroxydanaidal and they stimulate the growth and development of male pheromone-disseminating organs called coremata. Yet larval Estigmene are polyphagous and feed only sporadically on PA-containing plants and those they utilize contain different classes of PAs. The various PAs ingested are hydrolyzed to the common necine metabolite retronecine and re-esterified to insect-specific alkaloids from which the male pheromone hydroxydanaidal is synthesized. Given this complex metabolic pathway, we investigated the role of retronecine and the insect-specific alkaloids that stem from it as morphogens stimulating corematal growth. Retronecine fed to terminal instar larvae in a standard caterpillar diet stimulated corematal growth. It also stimulated corematal growth when it was injected into the hemolymph of larvae. These results indicate that this common PA metabolite, and/or the insect specific alkaloids produced from it, function as corematal morphogens. The parental forms (alkaloids ingested from the plant) are not strictly necessary for corematal growth. Stimulation of the PA receptors on the galea and ingestion process are also not critical to corematal development. Since the insect-specific alkaloids are the direct precursors for the male courtship pheromone, it is argued that their level is the best indicator of the ultimate pheromone titer and would provide the most accurate developmental signal. The effects of alkaloidal metabolites as morphogens in E. acrea are compared to those for the South Asian arctiines Creatonotus gangis and C. transiens in which the developmental role of PAs was first discovered.

Courtship in the Zig‐Zag Salamander (Plethodon dorsalis): Insights into a Transition in Pheromone‐Delivery Behavior

AbstractCourtship in plethodontid salamanders includes the delivery of male courtship pheromones by two distinct modes. Within the eastern Plethodon clade of the tribe Plethodontini, members of the Plethodon cinereus species group use an ancestral ‘vaccination’ mode of delivery, while members of the P. glutinosus group use an olfactory delivery mode. In order to shed light on this transition in delivery mode, I observed courtship behavior in P. dorsalis, a species that is phylogenetically intermediate to the P. cinereus and P. glutinosus groups. My observations indicate that P. dorsalis also is intermediate to the P. cinereus and P. glutinosus species groups in terms of courtship behavior. The context of delivery of male courtship pheromones in P. dorsalis is similar to that of the P. cinereus species group; however, the mode of pheromone delivery in P. dorsalis is olfactory. Thus, a transition in the context of pheromone delivery underlies the more obvious change in pheromone delivery mode. I discuss these findings in terms of the evolution of courtship pheromone delivery across the eastern Plethodon clade. I also report the first observations of ‘premature’ spermatophore deposition by male plethodontids.

Acquisition, transformation and maintenance of plant pyrrolizidine alkaloids by the polyphagous arctiid Grammia geneura

The polyphagous arctiid Grammia geneura appears well adapted to utilize for its protection plant pyrrolizidine alkaloids of almost all known structural types. Plant-acquired alkaloids that are maintained through all life-stages include various classes of macrocyclic diesters (typically occurring in the Asteraceae tribe Senecioneae and Fabaceae), macrocyclic triesters (Apocynaceae) and open-chain esters of the lycopsamine type (Asteraceae tribe Eupatorieae, Boraginaceae and Apocynaceae). As in other arctiids, all sequestered and processed pyrrolizidine alkaloids are maintained as non-toxic N-oxides. The only type of pyrrolizidine alkaloids that is neither sequestered nor metabolized are the pro-toxic otonecine-derivatives, e.g. the senecionine analog senkirkine that cannot be detoxified by N-oxidation. In its sequestration behavior, G. geneura resembles the previously studied highly polyphagous Estigmene acrea. Both arctiids are adapted to exploit pyrrolizidine alkaloid-containing plants as “drug sources”. However, unlike E. acrea, G. geneura is not known to synthesize the pyrrolizidine-derived male courtship pheromone, hydroxydanaidal, and differs distinctly in its metabolic processing of the plant-acquired alkaloids. Necine bases obtained from plant acquired pyrrolizidine alkaloids are re-esterified yielding two distinct classes of insect-specific ester alkaloids, the creatonotines, also present in E. acrea, and the callimorphines, missing in E. acrea. The creatonotines are preferentially found in pupae; in adults they are largely replaced by the callimorphines. Before eclosion the creatonotines are apparently converted into the callimorphines by trans-esterification. Open-chain ester alkaloids such as the platynecine ester sarracine and the orchid alkaloid phalaenopsine, that do not possess the unique necic acid moiety of the lycopsamine type, are sequestered by larvae but they need to be converted into the respective creatonotines and callimorphines by trans-esterification in order to be transferred to the adult stage. In the case of the orchid alkaloids, evidence is presented that during this processing the necine base (trachelanthamidine) is converted into its 7-( R)-hydroxy derivative (turneforcidine), indicating the ability of G. geneura to introduce a hydroxyl group at C-7 of a necine base. The creatonotines and callimorphines display a striking similarity to plant necine monoesters of the lycopsamine type to which G. geneura is well adapted. The possible function of insect-specific trans-esterification in the acquisition of necine bases derived from plant acquired alkaloids, especially from those that cannot be maintained through all life-stages, is discussed.

Specific recognition, detoxification and metabolism of pyrrolizidine alkaloids by the polyphagous arctiid Estigmene acrea

Evidence is presented that the polyphagous arctiid Estigmene acrea is well adapted to sequester and specifically handle pyrrolizidine alkaloids of almost all known structural types representative of the major plant families with pyrrolizidine alkaloid-containing species, i.e. Asteraceae with the tribes Senecioneae and Eupatorieae, Boraginaceae, Fabaceae, Apocynaceae and Orchidaceae. The adaptation of E. acrea to pyrrolizidine alkaloids includes a number of specialized characters: (i) highly sensitive recognition of alkaloid sources by pyrrolizidine alkaloid-specific taste receptors; (ii) detoxification of pyrrolizidine alkaloids by N -oxidation catalyzed by a specific flavin-dependent monooxygenase; (iii) transfer and maintenance of all types of pyrrolizidine N-oxides through all developmental stages; (iv) conversion of the various structures into the male courtship pheromone hydroxydanaidal most probably through retronecine and insect specific retronecine esters (creatonotines) as common intermediates; (v) specific integration into mating behavior and defense strategies. Toxic otonecine derivatives, e.g. the senecionine analogue senkirkine, which often accompany the common retronecine derivatives and which cannot be detoxified by N -oxidation do not affect the development of E. acrea larvae. Senkirkine is not sequestered at all. Non-toxic 1,2-saturated platynecine derivatives that frequently occur together with toxic retronecine esters are sequestered and metabolized to hydroxydanaidal, indicating the ability of E. acrea to aromatize saturated pyrrolizidines. Although pyrrolizidine alkaloids, even if they are offered continuously at a high level (2%) in the larval diet, are non-toxic, E. acrea larvae are not able to develop exclusively on a pyrrolizidine alkaloid-containing plant like Crotalaria. Therefore, E. acrea appears to be specifically adapted to exploit pyrrolizidine alkaloid-containing plants as “drug source” but not as a food source.

Phenological fate of plant-acquired pyrrolizidine alkaloids in the polyphagous arctiid Estigmene acrea

The alkaloid profiles of the life history stages of the highly polyphagous arctiid Estigmene acrea were established. As larvae individuals had free choice between a plain diet (alkaloid-free) and a diet that was supplemented with Crotalaria-pumila powder with a known content and composition of pyrrolizidine alkaloids (PAs). Idiosyncratic retronecine esters (insect PAs) accounted for approximately half of the PAs recovered from the larvae. These alkaloids were synthesized by the larvae through esterification of dietary supinidine yielding the estigmines, and esterification of retronecine yielding the creatonotines. The retronecine is derived from insect-mediated degradation of the sequestered pumilines (macrocyclic PAs of the monocrotaline type). With one exception, the PA profiles established for larvae were found almost unaltered in all life-stages as well as larval exuviae and pupal cocoons. The exception is the males, which in comparison to pupae and adult females, showed a significantly decreased quantity of the creatonotines and pumilines. These data support the idea that the creatonotines are direct precursors of the PA-derived male courtship pheromone, hydroxydanaidal. Crosses of PA-free males with PA-containing females and vice versa confirmed an efficient trans-mission of PAs from males to females and then from females to eggs. In single cases a male bestowed almost his total PA load to the female, and a female her total load to the eggs. The results are discussed with respect to pheromone formation, PA transmission between life-stages, and the defensive role of PAs against predators and parasitoids

Male indifference to female traits in an arctiid moth (Utetheisa ornatrix)

Abstract. 1. Female Utetheisa ornatrix (Lepidoptera: Arctiidae) mate selectively with large males able to transmit sizeable quantities of nutrient and defensive pyrrolizidine alkaloid with the spermatophore. The female gauges male size indirectly by assessment of the male's courtship pheromone.2. Male Utetheisa invest upward of 10% of body mass in spermatophore production, and could therefore have been expected to be choosy; however, when offered females differing in alkaloid content, body mass, or mating status, males showed disregard of these parameters, both in their choice of partner and in their allocation of resources to the spermatophore.3. It is concluded that Utetheisa males do not have the option to select females by comparison shopping. Females broadcast their attractant pheromone for less than an hour per day. Given this time constraint and the potentially high cost of mate localisation, males may have no choice but to mate on an opportunistic basis.

Nutritional phagostimulants function as male courtship pheromone in the German cockroach, Blattella germanica

Males of the German cockroach, Blattella germanica, secrete a pheromonal substance from the abdominal tergal glands, which elicits a feeding response in females during the sequential courtship behavior. The nuptial secretion consists predominantly of a synergistic mixture of sugars and phospholipids. Cholesterol and a series of amino acids, which are also components of the male’s glandular secretion, significantly enhanced the phagostimulant activity of the sugar components. The nuptial feeding behavior of the female cockroach is therefore elicited by a complex assortment of nutritive components in the male tergal secretion, including sugars, phospholipids, cholesterol, and amino acids. These results indicate that a mixture of primary metabolites, and not of specific secondary metabolites, serves as a pheromonal cue that appeals to the female’s gustatory sense and effectively brings her to the precopulatory position. Although the male secretion consists of nutrients, we suggest that these compounds probably do not represent a significant nutrient investment in females and their progeny but rather function as a signal in the mating sequence of B. germanica.

Are insect-synthesized retronecine esters (creatonotines) the precursors of the male courtship pheromone in the arctiid moth Estigmene acrea?

The pyrrolizidine alkaloid (PA) profiles were determined for adults of the polyphagous arctiid Estigmene acrea, which as larvae had fed on artificial diet supplemented with Crotalaria-pumila powder with known concentrations of PAs. The larvae always had a free choice between alkaloid-containing and plain diets. The alkaloid profiles of adults revealed a striking sexual dimorphism. Both sexes contained macrocyclic PAs of the monocrotaline type sequestered from the diet and, in addition, a substantial proportion of supinidine and retronecine esters synthesized by the insects from necine bases derived from the dietary alkaloids and necic acids of insect origin. These insect alkaloids accounted for 35% and 55% of total PAs in males and females, respectively. The difference was that in females the retronecine esters (creatonotines) made up 58 microg (43% of total PAs), while males contained a fivefold lower proportion, 12 microg (13%). Four of the ten male individuals analyzed were found devoid of creatonotines. Based on the experimental data in combination with evidence from the literature, it is suggested that the creatonotines are direct pheromone precursors in E. acrea. It is hypothesized that this may represent a general mechanism of hydroxydanaidal formation from diverse macrocyclic PAs in arctiids.

The evolution of chemical defences and mating systems in tiger moths (Lepidoptera: Arctiidae)

The origin and evolution of allelochemical sequestration in tiger moths (Arctiidae) is a complex interplay of larval and adult strategies and phylogenetic history. Using a phylogeny of Arctiidae, we examine the acquisition of secondary compounds from larval host plants and the use of secondary compounds and ultrasound in male courtship displays. We note that two sets of defensive signals (secondary chemicals and ultrasound) have been incorporated independently into arctiid courtship displays. Pyrrolizidine alkaloids are used in larval defence, and transformed into male courtship pheromones in several lineages. Phylogenetic inertia best explains the presence of adult collection and use of PAs in the absence of larval sequestration. Ultrasound, an adult defensive display directed at bats and other predators, has also been incorporated into arctiid mating displays. Sensory exploitation appears to underlie this co-option of defence signals for mating purposes.

Effects of Experimental Delivery of Male Courtship Pheromones on the Timing of Courtship in a Terrestrial Salamander, Plethodon jordani (Caudata: Plethodontidae)

Male courtship pheromones are chemosignals that affect female receptivity. These pheromones are delivered by the male only after a potential mate has been located and initial courtship interactions have commenced (Arnold and Houck, 1982; Houck, 1986). Thus, these pheromones are distinct from sex attractants, which are usually produced by the female and function to bring potential mates together. Courtship pheromones typically are produced by specialized glands that develop only during the breeding season in sexually mature males. These pheromones are present in many arthropods (e.g., Birch, 1974; Boppre, 1984; Grant et al., 1989) but rarely have been reported for vertebrates (Houck, 1986). Salamanders are a notable exception. The use of courtship pheromones by male salamanders is extremely common (Arnold, 1977; Houck, 1980; Houck and Verrell, 1993). Specialized male courtship glands are widespread in salamander species representing all major lineages (Houck and Sever, 1994), indicating that courtship pheromones play an important role in male mating success. Researchers studying courtship behavior and the development of courtship (mental) glands in salamanders have speculated that courtship pheromones functioned to make the female more receptive to the courting male (e.g., Noble, 1931; Arnold, 1976). This premise was tested quantitatively by Houck and Reagan (1990) for a single species of plethodontid salamanders, Desmognathus ocoee (formerly D. ochrophaeus-, see Tilley and Mahoney, 1996). In D. ocoee, courtship pheromones are delivered by a kind of injection system: the male pulls his enlarged premaxillary teeth across the female's dorsum at the same time as his courtship gland swabs the area being scraped (see fig. 8 in Arnold and Houck, 1982). The pheromones presumably diffuse into the female's circulatory system via the capillaries that are superficially abundant in this lungless salamander. The target organ stimulated by the pheromones is unknown. Courtship pheromone effects were tested by applying disks of filter paper (saturated in either a pheromone solution or a saline control solution) to female D. ocoee prior to courtship encounters. Houck and Reagan (1990) showed that courtship time was significantly reduced for those pairs in which the female was reated with the pheromone solution. We have extended the generality of these results by addressing the effects of courtship pheromones in Plethodon jordani, a terrestrial salamander having a very different delivery mode. In P. jordani, courtship pheromones are delivered when the male rubs or slaps his mental gland directly on the female's nares (Organ, 1958; Arnold, 1976). Based on work with a related plethodontid salamander (Dawley and Bass, 1988, 1989; Dawley, 1992), we infer that this kind of direct contact results in the delivery of courtship pheromones to the vomeronasal organ and thus to the accessory olfactory system. For other vertebrates, pheromonal stimulation of the accessory olfactory system has been well documented to affect the expression of reproductive behaviors, including increased receptivity (Singer et al., 1986; Rajendren et al., 1990). We tested the hypothesis that, if a P. jordani pair engages in courtship, female receptivity will be increased following the application of male courtship pheromones. Increased receptivity is operationally defined as a reduction in courtship time relative to control values.

Integrative Studies of Amphibians: From Molecules to Mating

SYNOPSIS. Studies of reproductive behavior in amphibians have been especially successful in synthesizing data produced from molecular and physiological research with evolutionary parameters, such as measures of reproductive success. In particular, two relatively new areas of amphibian research are highly amenable to synthetic studies. One area is the nature of chemical communication by pheromone delivery in terrestrial salamanders. Male courtship pheromones, for example, are delivered to the female during mating. These pheromones typically are received by the accessory olfactory system and act (presumably via the hypothalamus) to increase female receptivity. At an evolutionary level, pheromone delivery can increase male courtship success and thus the likelihood that a given male will sire offspring. Variation in pheromone composition and effectiveness will permit us to trace the evolution of the male pheromone on a phylogeny of related populations and species. At a proximal level, salamander courtship pheromones are being chemically analyzed in order to identify specific protein components that affect female receptivity. It also will be possible to determine whether chemical variation among males is related to behavioral effectiveness. Thus, courtship pheromone delivery is a behavior that has invited scrutiny from a combination of evolutionary and mechanistic perspectives. The second research area that is gaining from a synthetic approach is the investigation of relationships between hormonal mechanisms and reproductive behavior in field populations of anurans and salamanders. Amphibians are an understudied group, and the area of hormone-behavior relationships is inspired by testable hypotheses based on studies of other terrestrial vertebrates. The ability to correlate physiological measures with estimates of reproductive success identifies areas of amphibian research that will profit from continued attention.

Courtship Behavior of the Cumberland Plateau Woodland Salamander, Plethodon kentucki (Amphibia: Plethodontidae), with a Review of Courtship in the Genus Plethodon

AbstractComplete catalogs of courtship behavior are available for only seven of the 42 currently recognized species of Plethodon. Additional detailed studies of courtship behavior in Plethodon species are needed to analyze the evolution of courtship behavior in this genus. We investigated the courtship behavior of the Cumberland Plateau woodland salamander (Plethodon kentucki) and compared it to previous accounts of courtship in other Plethodon species. In the laboratory, we videotaped the complete courtship of 30 different P. kentucki pairs, which included 46 tail‐straddling walks that resulted in spermatophore deposition. From a transition matrix of observed motor patterns, we constructed a flow diagram of significant motor‐pattern transitions during courtship. In general, the courtship behavior of this species is very similar to that of other large eastern Plethodon; however, there are some notable differences. Prior to the tail‐straddling walk, the male transfers courtship pheromone from his mental gland to the female's nasolabial grooves (via mental‐gland tapping and ‘chin‐to‐chin’ behavior patterns) more frequently than in other Plethodon. In most courtships, the female initiates contact leading to the tail‐straddling walk. Males exhibit a greater propensity to deposit multiple spermatophores per courtship (two deposited in 33% of courtships, three deposited in 10% of courtships, X = 1.53 spermatophores per courtship) than males of other plethodontids. Mean size of the spermatophore is smaller than in other large eastern Plethodon. Overall, the courtship behavior of this species is most similar to that of P. jordani.