Laboratory observations of aggregative behavior of garter snakes, Thamnophis sirtalis: Roles of the visual, olfactory, and vomeronasal senses.

Two experiments determined (a) whether male garter snakes require a functional vomeronasal or olfactory system to return to previously preferred shelter locations and (b) the sensory modalities used to aggregate in the absence of previously deposited chemical cues. In Exp I, 22 male garter snakes with vomeronasal nerve lesions did not return to previously preferred shelter locations when tested individually. However, when tested with a group that included 9 control Ss, they returned to previously preferred shelters. The shelter-selection behavior of Ss with olfactory nerve lesions improved postoperatively, whereas the behavior of Ss with sham lesions was unchanged. In Exp II, 32 Ss were tested for aggregation in aquaria in which the substrate and other contents were cleaned between trials. After blindfolding or olfactory nerve cuts, Ss aggregated at normal levels. When Ss' vomeronasal ducts were sutured closed, aggregation scores were significantly depressed, although 2 of the 3 groups with vomeronasal duct sutures did aggregate just above change levels. Results from both studies indicate that use of chemical signals by garter snakes in shelter selection and aggregation is mediated by the vomeronasal system and that neither the olfactory nor the visual system is critical for these behaviors. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dispensable and indispensable genes in an ameiotic fish, the Amazon molly Poecilia formosa

All-female vertebrates are excellent model systems for studying many evolutionary problems. One of these is the Amazon molly. In this review, three aspects of its biology are discussed: (1) An important question is how dispensable genes, such as all male coding genes, evolve in this species. A number of studies found that most of these genes remain remarkably stable and functional. (2) The gynogenetic Amazon mollies have to live in sympatry with males of a gonochoristic species, because sperm are needed to trigger embryogenesis. Yet, Amazon mollies cannot replace their sexual competitors, because this would lead to their own extinction. Studies on the behavior of Amazon mollies and their sperm-donor species indicate that a number of behavior patterns stabilize the mating system by providing Amazon mollies with the copulations they need to reproduce. (3) The age of Amazon mollies has been estimated to be approximately 100,000 years. This is older than predicted by some theoretical models. In Amazon mollies two ways to occasionally incorporate fresh genetic material have evolved. One way is to add one complete set of paternal chromosomes, which, in nature, leads to stable triploid lineages. The second way is the incorporation of minute, centromere-containing microchromosomes. The evolutionary impact of these phenomena, however, is not resolved so far and needs further study.     

A brief commentary on the usefulness of studying fears of snakes.

Used therapy analogue studies with Ss who feared snakes or rats to evaluate types of behavior therapy. In a small pilot study Es were able to desensitize 4 Ss to fears of snakes or laboratory rats. However, the 2 control Ss also overcame their fears of snakes. They had been instructed to hold the snake when it was presented to them and to act unafraid. They were also told that they would overcome their fears in this manner. It is suggested that any "technique" that helps a person confront the fear of snakes may "cure" him, that studying the treatment of snake fears may be irrelevant to the understanding of treating clinical neuroses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual selection, receiver biases, and the evolution of sex differences

REVIEW Recent approaches to analyzing the evolution of female mating preferences emphasize how historical influences on female receiver systems can bias the evolution of male traits that females find attractive. These studies combine animal behavior, sensory biology, phylogenetics, and artificial neural network models. They attempt to understand why specific phenotypes involved in sexual selection have evolved, rather than merely determining whether such traits and preferences are adaptive. It is now clear that traits and preferences often do not coevolve via genetic correlations, that female mating preferences for a given male trait are influenced by adaptations and constraints outside of the context of female responses to that particular trait, and that receiver biases can explain much of the diversity in male signaling phenotypes. It also appears that an understanding of historical effects will prove valuable in investigating why neural and cognitive systems respond to sensory stimuli as they do.     

Roles of the vomeronasal and olfactory systems in courtship behavior of male garter snakes.

Studied whether male garter snakes required intact vomeronasal or olfactory systems to detect the pheromone that triggers the chin-pressing behavior of courtship. Male garter snakes with testosterone propionate pellets implanted sc were tested for courtship displays with estradiol-benzoate-treated females. Three groups of 10 males were formed from snakes exhibiting strong courtship responses. Bilateral olfactory nerve cuts were attempted on 1 group, vomeronasal nerve cuts on a 2nd, and control surgeries on a 3rd. All snakes in the olfactory nerve cut and control groups courted after surgery, and 3 snakes in each group copulated. More than half of the snakes in the olfactory nerve cut group had complete nerve cuts. Nine of the 10 snakes in the vomeronasal nerve cut group exhibited no courtship responses after surgery. The 1 snake in this group that courted was the only snake in which intact vomeronasal nerve fascicles were observed. Data indicate that male garter snakes without functional olfactory systems do court and mate normally, but that male garter snakes without functional vomeronasal systems exhibit no courtship responses. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Immobility and supination in garter snakes (Thamnophis elegans) following handling by human predators.

A common response of animals to physical restraint is tonic immobility. The authors observed the behavior of garter snakes, Thamnophis elegans, in the field to determine the frequency of immobility as a response to handling. Most snakes fled after release, but the remainder remained immobile, sometimes on their backs (supination), for up to 10 min. Immobility was seen most often in pregnant snakes, which also were more likely than other snakes not to have moved before capture. Failure to move, either before or after capture, might be a consequence of the limited locomotory ability of gravid snakes. However, the lack of observations of interactions between snakes and their natural predators impedes researchers' understanding of the antipredator value, if any, of tonic immobility. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cardiotrophin-1, a cytokine present in embryonic muscle, supports long-term survival of spinal motoneurons

Activation of courtship behavior in male red-sided garter snakes is independent of androgens. Only exposure to extended periods of low temperature with subsequent warming stimulates courtship in males. The pineal gland is thought to transduce temperature as well as photoperiodic information in reptiles. Therefore, we explored the relationship of the pineal and melatonin to sexual behavior in this species. Pinealectomy of male garter snakes disrupted sexual behavior upon emergence from a 17-week period of low temperature in approximately 60% of treated individuals in each of the 3 years of study. However, 40% of the males were unaffected by the pinealectomy, engaging in vigorous courtship. Administration of exogenous, chronic melatonin did not significantly modulate the effect of pinealectomy. Upon pinealectomy in the autumn (before hibernation), plasma levels of melatonin fell. However, upon emergence from hibernation, melatonin levels in pinealectomized (PINX) and sham-treated (SHAM) animals were equivalent, indicating extrapineal source(s) of melatonin. However, PINX males did not exhibit a diel cycle in melatonin levels upon emergence. Instead, melatonin remained elevated through the subsequent 24-hr period. SHAMs did exhibit a diel cycle. Ten days after emergence, PINX animals either had a disrupted/abnormal melatonin cycle and were non-courters or had a cycle similar to SHAM males and courted. Therefore, a normal diel cycle of melatonin appeared necessary for the proper expression of courtship behavior. These results suggest that the pineal in snakes 1) is part of a complex, multi-oscillator system as it is in birds and lizards and 2) may play a role in maintaining polymorphism in timing of reproductive behavior.     

Acute alcohol exposure markedly influences male fertility and fetal outcome in the male rat

Although it is recognized that drugs ingested by pregnant females produce marked cognitive and physiological deficits in their offspring, the possibility that paternal exposure to drugs prior to mating may have adverse effects on fertility and fetal outcome has not received much attention. The purpose of the present studies was to examine whether a single, acute exposure to alcohol influences the subsequent ability of adult male rats to mate and produce healthy and viable litters. Our results showed that a relatively large dose of alcohol 24 hours prior to breeding had little effect on the mating behavior of male rats, but there were markedly fewer pregnancies in females mated with alcohol-exposed male rats than in controls. Of equal importance, we found that, even when conception occurred and live births were produced, there were striking differences in fetal outcome. Alcohol-treated males sired many fewer pups than control males and there was a markedly enhanced mortality rate in their offspring. Collectively, these data suggest that acute paternal alcohol administration 24 hours prior to breeding does not affect mating behavior, but results in a greatly diminished fertility rate and fewer and less viable offspring. These studies suggest that paternal alcohol use may be as important as maternal alcohol abuse as a negative variable in pregnancy and fetal outcome.     

Differential effects of lesions of the vomeronasal and olfactory nerves on garter snake (Thamnophis sirtalis) responses to airborne chemical stimuli.

The roles of the main (MOS) and accessory (AOS) olfactory systems of garter snakes in response to airborne chemicals were investigated. Preoperatively, all snakes responded to airborne odors with increased tongue-flick rate and duration. Postoperatively, sham-operated snakes responded to airborne odors with increased tongue-flick rates, but snakes with main olfactory nerve cuts failed to respond to the odors, and snakes with vomeronasal nerve cuts responded to nonprey odors only. Preoperatively, exposure to earthworm odor produced more frequent and shorter duration tongue-flicks during locomotion compared with exposure to water. Postoperatively, only sham-lesioned snakes exhibited differential responding to earthworm odors. This study demonstrates that the MOS is critical for the initiation of tongue-flick behavior in response to airborne odors and that discrimination of odors with biological significance requires a functional AOS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sublingual plicae (anterior processes) are not necessary for garter snake vomeronasal function.

The anterior processes of snakes may transfer odorants from the tongue to the vomeronasal (VN) organ. To test whether the anterior processes are required for a vomeronasally mediated behavior, the authors tested garter snakes (Thamnophis sirtalis) preoperatively and after cauterization of the anterior processes or control cauterization with artificial earthworms covered with earthworm wash (EWW) or distilled water. Snakes in both groups attacked EWW-covered artificial worms but not controls both pre- and postoperatively. In addition, snakes with anterior processes cauterization or control cauterization tongue flicked 3H-proline. Radioautographs of the VN organs of snakes with and without anterior processes were indistinguishable: Snakes in both groups had reduced silver grains over the VN sensory epithelium as had been reported previously with intact snakes. These findings indicate that the anterior processes are unnecessary both for a behavior known to require a functional VN system and for delivery of odorants to the VN organ. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The forked tongue and edge detection in snakes (Crotalus oreganus): An experimental test.

Many stimulus-detection systems are lateralized to allow for simultaneous comparison of paired stimuli. It has been hypothesized that the deeply forked tongue of snakes and some derived lizards functions as a chemical edge detector where cues gathered by each tine are kept separate to provide two points of lateral odor assessment by the central nervous system via vomeronasal input. While following a chemical trail, one time can be on the trail, the other off, and such differential information prompts the snake to turn back to the trail. The authors tested this hypothesis in rattlesnakes within a predatory context by unilaterally severing the vomeronasal nerves. If edge detection is used by snakes during prey trailing, then unilateral denervation should disrupt trailing ability. The authors found no change in the seven separate trailing parameters measured. Therefore, they found no support for the edge detection hypothesis as it applies to prey trailing behavior. Instead, the deeply forked tongue may represent a chemosensory specialization to increase odor-sampling area, with snakes and derived lizards detecting only the concentration of chemical trails. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Focus of attention, chronic expectancy, and responses to a feared stimulus.

Tested an attentional model of fear-based behavior with 44 undergraduates. It was predicted that among Ss with moderate fear of snakes, heightened self-attention during an approach attempt would cause increased awareness of existing anxiety, followed by 1 of 2 courses of events: Ss who believed that they could do the behavior in spite of their fear were expected to redirect their attention to the behavior–goal comparison and exhibit no behavioral deficit. Ss who doubted their ability to do the behavior were expected to divert their attention from the behavior–goal comparison and to withdraw behaviorally from the approach attempt. Results support this reasoning and discussion centers on relationships between the proposed model and previous theory. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temperature activation of courtship behavior in the male red-sided garter snake (Thamnophis sirtalis parietalis): Role of the anterior hypothalamus-preoptic area.

Adult male red-sided garter snakes (Thamnophis sirtalis parietalis) received radio-frequency lesions prior to 17 weeks of low-temperature hibernation. Animals found to have bilateral lesions of the anterior hypothalamus-preoptic area ({ah-poa}) failed to exhibit courtship behavior on emergence from hibernation. Those individuals in which the major portion of the destruction was centered in the anterior POA also exhibited deficits in thermoregulatory behavior. Animals that received unilateral lesions of the {ah-poa} initiated courtship behavior after controls and had an abbreviated period of courtship; these animals exhibited normal responses to thermal stimuli. Male snakes with lesions outside the {ah-poa} courted normally and demonstrated no differences in thermoregulatory behavior compared with the surgical controls. These results indicate that in male red-sided garter snakes, an intact {ah-poa} is critical for the integration of thermal stimuli that activate seasonal courtship behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Peacocks, Porsches, and Thorstein Veblen: Conspicuous consumption as a sexual signaling system.

Conspicuous consumption is a form of economic behavior in which self-presentational concerns override desires to obtain goods at bargain prices. Showy spending may be a social signal directed at potential mates. We investigated such signals by examining (a) which individuals send them, (b) which contexts trigger them, and (c) how observers interpret them. Three experiments demonstrated that conspicuous consumption is driven by men who are following a lower investment (vs. higher investment) mating strategy and is triggered specifically by short-term (vs. long-term) mating motives. A fourth experiment showed that observers interpret such signals accurately, with women perceiving men who conspicuously consume as being interested in short-term mating. Furthermore, conspicuous purchasing enhanced men's desirability as a short-term (but not as a long-term) mate. Overall, these findings suggest that flaunting status-linked goods to potential mates is not simply about displaying economic resources. Instead, conspicuous consumption appears to be part of a more precise signaling system focused on short-term mating. These findings contribute to an emerging literature on human life-history strategies. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Reduction of human avoidant behavior: A comparison of counterconditioning, expectancy, and cognitive information approaches.

Compared the fear-reducing efficacy of procedures based on 3 major theories that have been proposed to account for the success of systematic desensitization therapy. 33 female and 14 male undergraduates, chosen on the basis of their fear of snakes, were assigned to 1 of 5 groups, and were given 4 individual treatment sessions. Predictions were confirmed in that the outcome measures of the high-expectancy placebo group and the 2 cognitive-coping groups were significantly superior to those of the counterconditioning and no-treatment groups. Thus, the supposition is supported that changes in human avoidant behavior may be attributed to demand and expectancy variables rather than the conditioning of antagonistic responses as has been previously suggested. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The chromosomal basis of sexual isolation in two sibling species of Drosophila: D. arizonensis and D. mojavensis

The chromosomal determination of interspecific differences in mating behavior was studied in the interfertile pair, Drosophila arizonensis and Drosophila mojavensis, by means of chromosomal substitutions. Interspecific crossing over was avoided by crossing hybrid males to parental females, and identification of the origin of each chromosome in backcrossed hybrids was possibly by means of allozyme markers. It was found that male mating behavior is controlled by factors located in the PGM-marked chromosome (which, in other Drosophila species, is part of the X chromosome) and in the Y chromosome. The other chromosomes influence male sexual behavior through their interactions with each other and with the PGM-marked chromosome, but their overall effect is minor. Female mating behavior is controlled by factors located in the ODH-marked and AMY-marked chromosomes, with the other chromosomes exercising a small additive effect. Hence, the two sex-specific behaviors are under different genetic control. Cytoplasmic origin has no effect on the mating behavior of either sex. There appears to be no correlation between a chromosome's structural diversity (i.e., amounts of inversion polymorphism within a species or numbers of fixed inversions across species) and its contribution to sexual isolation. These findings are in general agreement with those from similar Drosophila studies and may not be specific to the species studied here.     

Effects of volatile and nonvolatile chemical signals on male sex behaviors mediated by the main and accessory olfactory systems.

Estrous hamster vaginal discharge (HVD) contains both volatile and nonvolatile chemical signals that collectively elicit both male attraction to females and male mating behavior. Three experiments with golden hamsters (Mesocricetus auratus) determined whether the more consummatory aspects of sexual behavior (e.g., mounting, intromission attempts) could be elicited in situations in which only volatile materials from HVD were available to the male and, if so, whether the olfactory of vomeronasal input was primarily involved in processing these signals. In these experiments, a surrogate-female test was employed, wherein females were replaced by males scented with HVD. Results show that males were attracted to female odor and engaged in significant amounts of mating behavior with surrogate females when only the volatile components of HVD were available to them. These behaviors were further enhanced when both volatile and nonvolatile components of HVD were provided. Male attraction to females and male mating behavior were differentially affected by lesions involving afferents of the main and accessory olfactory systems. Lesions of the afferents reinforced the hypothesis that the main olfactory system is preferentially involved with processing those volatile chemical signals in HVD that denote female attractiveness, whereas the accessory olfactory system is preferentially involved with processing volatile and nonvolatile chemical signals that evoke subsequent steps in male sexual behavior. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Romantic involvement often reduces men's testosterone levels--but not always: The moderating role of extrapair sexual interest.

Testosterone (T) appears to facilitate what biologists refer to as mating effort--the investment of time and energy into same-sex competition and mate-seeking behavior. Multiple studies show that men who are romantically involved (i.e., are paired) have lower T than single men, which may be due to a facultative adjustment by men of T levels in response to lower demands for mating effort. The authors proceeded on the basis of the idea that men who retain interests in sexual opportunities with women other than a primary partner continue to dedicate more time and energy to mating effort when romantically paired, and so they predicted that the association between relationship status and T depends on men's extrapair sexual interests. Study 1 used the Sociosexual Orientation Inventory to measure extrapair sexual interests, whereas Study 2 used a broader measure to examine this interaction. Both studies found support for it. These results have implications for an understanding of the biosocial regulation of men's behavior in romantic relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phylogenetic analysis of reptilian hemoglobins: trees, rates, and divergences

Phylogenetic relationships among reptiles were examined using previously published and newly determined hemoglobin sequences. Trees reconstructed from these sequences using maximum-parsimony, neighbor-joining, and maximum-likelihood algorithms were compared with a phylogenetic tree of Amniota, which was assembled on the basis of published morphological data. All analyses differentiated alpha chains into alphaA and alphaD types, which are present in all reptiles except crocodiles, where only alphaA chains are expressed. The occurrence of the alphaD chain in squamates (lizards and snakes only in this study) appears to be a general characteristic of these species. Lizards and snakes also express two types of beta chains (betaI and betaII), while only one type of beta chain is present in birds and crocodiles. Reconstructed hemoglobin trees for both alpha and beta sequences did not yield the monophyletic Archosauria (i.e., crocodilians + birds) and Lepidosauria (i.e., Sphenodon + squamates) groups defined by the morphology tree. This discrepancy, as well as some other poorly resolved nodes, might be due to substantial heterogeneity in evolutionary rates among single hemoglobin lineages. Estimation of branch lengths based on uncorrected amino acid substitutions and on distances corrected for multiple substitutions (PAM distances) revealed that relative rates for squamate alphaA and alphaD chains and crocodilian beta chains are at least twice as high as those of the rest of the chains considered. In contrast to these rate inequalities between reptilian orders, little variation was found within squamates, which allowed determination of absolute evolutionary rates for this subset of hemoglobins. Rate estimates for hemoglobins of lizards and snakes yielded 1.7 (alphaA) and 3.3 (beta) million years/PAM when calibrated with published divergence time vs. PAM distance correlates for several speciation events within snakes and for the squamate left and right arrow sphenodontid split. This suggests that hemoglobin chains of squamate reptiles evolved approximately 3.5 (alphaA) or approximately 1.7 times (beta) faster than their mammalian equivalents. These data also were used to obtain a first estimate of some intrasquamate divergence times.     

Evolutionary persistence of chemically elicited ophiophagous antipredator responses in gartersnakes (Thamnophis sirtalis).

The ability to detect and respond to potential predators is key for the survival of individuals, but this ability is sometimes lost via relaxation of antipredator behavior when prey species are separated from predators. Adult and predator-na?ve neonate gartersnakes (Thamnophis sirtalis) from mainland and insular sites where they do and do not occur with ophiophagous (snake-eating) snakes were tested to determine if responses to such predators have been lost, reduced, or retained, and what might be causing differences in such responses. Our data indicate that, overall, adult snakes from populations syntopic with ophiophagous milksnakes are more responsive to chemical stimuli from milksnakes than adults from areas where they are not syntopic with milksnakes, whereas there were few differences with neonate gartersnakes. Experiments with neonates with or without periodic ophiophagous snake chemical experience over several weeks showed that gartersnakes with such experience became more responsive to ophiophagous cues rather than habituating to them. Such evidence of both genetic and experiential factors underlying the antipredator responses to ophiophagous snakes indicates that antipredator responses have persisted despite separation of predator and prey. (PsycINFO Database Record (c) 2011 APA, all rights reserved)