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The evolution of the parthenogenetic whiptail lizard, Cnemidophorus uniparens . The all-female, parthenogenetic whiptail arose from the hybrid mating between two sexual species.
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Behaviors are adaptations to the physical, biotic, and social environments. Great diversity exists among vertebrates in reproductive behaviors and the neuroendocrine mechanisms underlying these behaviors. Study of this diversity illuminates species, population, and sex differences in hormone-brain-behavior relations. It also can provide insights in...
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Context 1
... new paradigm hinges on the fact that males evolved only after the evolution of self-replicating (=female) organisms. Thus, the female can be regarded as the ancestral sex, and the male as the derived sex. In addition to offering an alternative view of the sexual differentiation process in the brain (Figs. 7 and 8), this perspective raises the intriguing possibility that males may be more like females than females are like males. Four lines of evidence support this speculation: (i) the ease of masculinizing versus the difficulty of defeminizing mammals; (ii) maleness is imposed upon a female phenotype, not vice versa; (iii) recent findings that ...
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... mechanisms, can we put together a plausible scenario of how this may have occurred or, better yet, find any examples of evolution in action? A case in point is the all-female, parthenogenetic whiptail lizard Cnemidophorus uniparens. This species arose from the hybrid mating between two sexual species; specifically, C. inornatus and C. gularis (Fig. 8). Because representatives of both the ancestral (sexual) and descendant (parthenogenetic) species still exist, we have a snapshot of evolution in that we can compare the ancestral with the descendant species. Fig. 10. Evolution of a new neuroendocrine system. Relation among male-like and female-like pseudosexual behavior, ovarian state ...
Context 3
... sperm, resulting in a primary sex ratio, or the number of males to females in utero, being significantly male-biased. Recently it has been established that a number of factors, including the hormonal condition of the parents, the timing of insemination relative to ovulation, social rank, and even the age difference of the parents can skew the secondary sex ratio. The mechanisms underlying this manipulation are unclear, but may involve the differential mobility of X- and Y-bearing sperm or differential investment in male or female zygotes in utero leading to higher miscarriage rate of one or the other sex. But some animals lack sex chromosomes entirely. In such animals some aspect of the environment determines sex (Fig. 4). This can occur either early in embryonic life, forcing the embryo to become a male or a female, thereby adopting one of two mutually exclusive trajectories in life history, or can occur later in life when the individual changes sex after it has already reproduced. Examples of the former are many turtles in which sex is determined in the middle of embryogenesis by the temperature experienced during incubation. The latter would include sequentially hermaphroditic fish in which individuals are first male and then female (protandry) or first female and then male (protogyny). In both instances the individuals gonochoristic, existing either as males or females, but have the potential to adopt the other life history. The notable difference between these species and those with sex chromosomes is that the primary and secondary sex ratio can be extreme, with clutches being all-male, all-female, or anywhere in between. While environmental sex determination has been known for some time in plants, single-celled organisms, invertebrates, and even some fish, it was not known to occur in the higher vertebrates until about 20 years ago. As might be imagined, the mechanisms of sex determination in species exhibiting environmental sex determination are different from those found in species with sex chromosomes (Crews, 1987, 1993) (Fig. 5). Importantly, however, the process of sexual differentiation of the phenotype appears to be similar after the gonads have formed. The ‘organizational concept’ (Fig. 6, upper panel), developed from research with mammals, postulates that the female is the neutral or the default sex, and the male is the dominant or organized sex. This concept does not apply to vertebrates lacking sex chromosomes, however (Crews, 1993). An alternative paradigm (Fig. 6, lower panel) not tonly accommodates the large literature that has been gathered on sexual differentiation in animals with sex chromosomes, but also incorporates new findings on species that lack sex chromosomes. This new paradigm hinges on the fact that males evolved only after the evolution of self-replicating ( = female) organisms. Thus, the female can be regarded as the ancestral sex, and the male as the derived sex. In addition to offering an alternative view of the sexual differentiation process in the brain (Figs. 7 and 8), this perspective raises the intriguing possibility that males may be more like females than females are like males. Four lines of evidence support this speculation: (i) the ease of masculinizing versus the difficulty of defeminizing mammals; (ii) maleness is imposed upon a female phenotype, not vice versa; (iii) recent findings that female development is an active, organized process rather than a default state; and (iv) the creation of males in parthenogenetic females, indicating that the genes of maleness are present in all-female species, but normally are suppressed. Thus, George Bernard Shaw may have posed the wrong question in his play ‘Pygmalion’ ‘‘why can’t a woman be more like a man?’’ A better and more interesting question may in fact be ... why might males be more like females, than females like males? The neuroendocrine mechanisms that underlie complementary sexual behaviors must also differ in species that have different sex determining mechanisms. While all vertebrates display complementary sexual behavior patterns, they accomplish this by different means. Illustrated in Fig. 7 are the paths to the display of sexually dimorphic behaviors in the various forms of reproduction exhibited by vertebrates. Even in species lacking males altogether, such as the parthenogenetic species, complementary pseudosexual behaviors occur. This can only mean that the organization of brain process underlying these behaviors must be different from that of species with sex chromosomes. If the plasticity of the brain has facilitated this diversity of neuroendocrine mechanisms, can we put together a plausible scenario of how this may have occurred or, better yet, find any examples of evolution in action? A case in point is the all-female, parthenogenetic whiptail lizard Cnemidophorus uniparens . This species arose from the hybrid mating between two sexual species; specifically, C . inornatus and C . gularis (Fig. 8). Because representatives of both the ancestral (sexual) and descendant (parthenogenetic) species still exist, we have a snapshot of evolution in that we can compare the ancestral with the descendant species. The behavior and its controlling mechanism we have studied is the stereotyped courtship and copulatory behavior characteristic of whiptail lizards (Fig. 9). This was selected because even though males are no longer present, the parthenogen continues to exhibit pseudosexual behaviors that are remarkably similar to those seen in the sexual species (Fig. 9). This phenomenon of pseudosexual behavior in an all-female species immediately raises the question of homosexuality and whether the equivalent of same-sex love in humans is common, and therefore ‘natural’, in non-human animals. If one defines homosexuality as sexual activity between individuals of the same sex, then it is common among non-human animals. This literature has been reviewed by myself and others and I refer the reader to these sources (Crews, 1987; Dagg, 1984). However, if homosexuality is defined as a sexual preference for individuals of the same sex, then it is rare among non-human animals. Thus, homosexual behavior is biological reality, but homosexuality is a human societal issue and not an issue of biology. In C . inornatus , the maternal ancestral species, the courtship and copulatory behavior of the male is dependent upon testicular androgens, although there is a polymorphism in the sensitivity to progesterone. In progesterone-sensitive males, exogenous progesterone will reinstate sexual behavior in castrated males. In the descendant parthenogen, there is no circulating androgen to stimulate the male-like pseudosexual behavior, although the parthenogen retains a sensitivity to exogenous androgen. Since complementary behaviors are necessary for normal reproduction, the periovulatory surge in progesterone has been co-opted as the trigger for the transition from receptive to mounting behavior (Fig. 10). This relationship between male-like and female-like pseudosexual behavior, ovarian state, and circulating levels of estradiol and progesterone during different stages of the reproductive cycle is depicted in Fig. 10. Also shown are the changes in abundance of the gene transcript coding for estrogen receptor and progesterone receptor in the preoptic area and the ventromedial hypothalamus, brain areas which are involved in the regulation of male- and female-typical sexual behaviors. Finally, in the sexual ancestral species, both brain areas are sexually dimorphic in a complementary fashion, but not in the parthenogen. That is, the brain is bisexual in a functional sense, but not in a structural sense. Further, there is strong evidence that the neural activity in the brain predisposes the animal to behave in a particular manner. That is, behavior is a consequence, not a cause of brain activity. Reproduction is essentially an affiliative behavior. Affiliation is an essential property of the emotion we call in humans love. This essay has illustrated how the study of diverse organisms can identify what is fundamental ( = evolutionarily ancient) versus derived ( = recently evolved). The fact that the behavior of an individual, which emerges from its’ internal state as well as its previous experience, influences the behavior and physiology of other individual, is found in all living organisms, suggesting that it is both ancient and fundamental to reproduction. Despite this conservation of function in the consequences of behavior, the routes to achieving this end are incredibly diverse. Study of the diversity of mechanisms that underlie the basics of sex determination and sexual differentiation can reveal much about the evolution of the mechanisms that underlie the display of these behaviors. Limbic nuclei are an ancient part of the vertebrate brain and known to be sensitive to sex steroid hormones and involved in the regulation of social and sexual behaviors. However, evolutionary history has modified how these elements are regulated. Taking advantage of closely related species, systematic studies of one animal model system has shown how new hormone – brain-behavior mechanisms can ...
Citations
... Within this adaptive context, love may have evolved functionally as a temporal shortcut to bypass the slow, often tedious, and potentially unsuccessful processes of communication and social engagement to foster physical proximity and to promote intimacy and reproductive behaviors. (Porges 1998:858;see also Carter 1998;Crews 1998;Griskevicius, Haselton, and Ackerman 2015) More specifically, the argument is that "love evolved to serve several functions: Displaying reproductively relevant resources; Providing sexual access; Signaling sexual fidelity; Promoting relationship exclusivity through mate-guarding; Displaying commitment; Promoting actions that lead to successful reproductive outcomes; Providing signals of parental investment" (Buss 2006:66). The sexual functions and commitment/attachment functions may be analytically and biologically separable, they may engage distinct "systems," but their joint contribution to evolutionary fitness is evident. ...
I make a contribution to the sociology of epistemologies by examining the neuroscience literature on love from 2000 to 2016. I find that researchers make consequential assumptions concerning the production or generation of love, its temporality, its individual character, and appropriate control conditions. Next, I consider how to account for these assumptions’ being common in the literature. More generally, I’m interested in the ways in which epistemic communities construe, conceive of, and publicly represent and work with their objects of inquiry—and what’s thereby assumed about them and about the world. I argue that these implicit or explicit assumptions are a distinct type of explanandum, whose distinctiveness sociology hasn’t adequately appreciated and taken advantage of. I think it should and I hope it will.
... at University of Helsinki on January 5, 2016 pos.sagepub.com Downloaded from Neuroscience also suggests that the set of basic biological and psychological mechanisms that generate these rewards are elicited by the same modalities of sensory affiliative stimuli (i.e., touch), even if the social activities that generate the sensory stimulation are different (Crews 1998;Depue and Morrone-Strupinsky 2005;Mason and Mendoza 1998). Although activities involving shared emotional experiences certainly induce these rewards, several other activities are also capable of this effect, for example, those that are more purely coordinative, explorative, and even more competitive in character (think of how academics enjoy a verbal spar even if this activity often involves antagonistic emotions between the disputants). ...
Existing economic models of prosociality have been rather silent in terms of proximate psychological mechanisms. We nevertheless identify the psychologically most informed accounts and offer a critical discussion of their hypotheses for the proximate psychological explanations. Based on convergent evidence from several fields of research, we argue that there nevertheless is a more plausible alternative proximate account available: the social motivation hypothesis. The hypothesis represents a more basic explanation of the appeal of prosocial behavior, which is in terms of anticipated social rewards. We also argue in favor of our own social motivation hypothesis over Robert Sugden's fellow-feeling account (due originally to Adam Smith). We suggest that social motivation not only stands as a proximate account in its own right but also provides a plausible scaffold for other more sophisticated motivations (e.g., fellow-feelings). We conclude by discussing some possible implications of the social motivation hypothesis on existing modeling practice.
... Mate preference, in its simplest form, states that males compete for females and females choose between them. Although most research has focused on how females choose males, male choice of females is also important [56][57][58]. This point cannot be overemphasized. ...
Background
Mate preference behavior is an essential first step in sexual selection and is a critical determinant in evolutionary biology. Previously an environmental compound (the fungicide vinclozolin) was found to promote the epigenetic transgenerational inheritance of an altered sperm epigenome and modified mate preference characteristics for three generations after exposure of a gestating female.
Results
The current study investigated gene networks involved in various regions of the brain that correlated with the altered mate preference behavior in the male and female. Statistically significant correlations of gene clusters and modules were identified to associate with specific mate preference behaviors. This novel systems biology approach identified gene networks (bionetworks) involved in sex-specific mate preference behavior. Observations demonstrate the ability of environmental factors to promote the epigenetic transgenerational inheritance of this altered evolutionary biology determinant.
Conclusions
Combined observations elucidate the potential molecular control of mate preference behavior and suggests environmental epigenetics can have a role in evolutionary biology.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-377) contains supplementary material, which is available to authorized users.
... Moreover, the premating levels of KT, E or T also did not function as mechanism for mate choice or species discrimination as they did not differ significantly between the species. Given that studying closely related species can provide important insights into how brain-hormone-behavior mechanisms have evolved [17] we extended the research performed by Gabor and Grober [5] on sailfin mollies to the maternal parent species of Amazon mollies, the Atlantic molly, P. mexicana limantouri. Specifically, we tested the prediction that one or more of the sex steroid hormones in teleost fish (KT, T, and E) play a role in species recognition (during mate choice and/or sperm priming) for Atlantic mollies that are sympatric with the sexually parasitic Amazon mollies. ...
Much is known about the role of hormones in the regulation of vertebrate mating behavior, including receptivity, and several components of mate choice. Hormones may modulate reproductive behavior in such a way to increase or decrease the individual's motivation, and therefore hormones may be important in mediating behavior associated with reproductive isolation. The mating complex of the all female gynogenetic Amazon mollies, Poecilia formosa, and their parental species (sailfin mollies, P. latipinna, and Atlantic mollies, P. mexicana) is a model system for studying ultimate mechanisms of species recognition. However, proximate mechanisms, such as variation in hormone levels, and the effect of hormones on sperm production have not been extensively examined. We predict that one or more of the sex steroid hormones in teleost fish (11-ketotestosterone (KT), testosterone (T), and estradiol (E)) will play a role in species recognition (during mate choice and/or sperm priming) for Atlantic mollies (the maternal parental species) that are sympatric with Amazon mollies. We sequentially paired male Atlantic mollies with female conspecifics and Amazon mollies and obtained water-borne hormone samples before and after mating for all fish. We measured circulating KT, T, and E from the water samples. Although we did not find an overall KT response to mating with conspecifics as has been found previously in sailfin mollies, male Atlantic mollies that mated more with conspecific females had lower postmating T levels. Additionally, males attempted to mate more with conspecific females that had lower postmating E levels, but attempted to mate more with Amazon mollies that had higher postmating KT levels. We also examined the effect of KT on sperm priming (a mechanism of premating mate choice), and found that KT levels of male Atlantic mollies prior to mating are correlated with the sperm priming response when males were paired with conspecific females, but this correlation was not found when males were paired with Amazon mollies. Our results indicate that male mating behavior is affecting or responding to both male and female hormones, but that the hormones alone are not playing a role in species recognition. Male Atlantic mollies may not discriminate against Amazon mollies as strongly as male sailfin mollies because Amazon mollies resemble their maternal parental species more than their paternal species.
... Producing more chucks might acoustically stimulate hormone production in females, which could influence her reproductive physiology or her motivational state in ways that increase the probability of successful mating. Behaviors that facilitate reproduction in conspecific individuals of the opposite sex occur across diverse taxa (Crews 1998). A variety of male courtship behaviors facilitate ovarian development and consequently reproductive state (Wingfield 2006), and acoustic signals specifically have been shown to influence female reproductive physiology in birds (Lehrman 1965;Cheng 2008). ...
Sexual selection is responsible for the evolution of costly elaborate male traits. When male displays are dynamic, display
strategy is sensitive to contextual cues that alter the relative costs and benefits of producing each signal in a male’s repertoire.
Because females often prefer more elaborate signals, males often respond to female presence by elaborating their display.
When added elaboration increases assessment information or reproductive stimulation, females might benefit by extracting the
maximum amount of signal elaboration from males. Thus, we expect that females could exaggerate their presence and cause males
to produce even costlier and more attractive signals by exhibiting “elicitation” behaviors. We asked whether female túngara
frogs elicit increased call complexity from prospective mates. In túngara frogs, adding complexity increases both attractiveness
and predation risk. We found that females exhibit a repertoire of movements that function not in mate acquisition, per se,
but in display manipulation, by eliciting increased complexity from calling males. The probability that males add complexity
to their display increases when females produce these movements. Thus, females actively influence males to produce riskier
signals.
... Such positive stress appears to be important for the formation of social contact and attachment, since a moderate level of stress has been demonstrated to promote this kind of relationship, i.e., social bonding [3,35,54–58]. Oxytocin, as it seems, really illustrates the dynamic autoregulation involved in love and deep relationships: It is part of the ‘chill experience’ in the initial phase or the arousal of loving encounters and treatments, but simultaneously reduces stress on the psychological level (e.g., via bond formation) and on the physiological level (e.g., via stress hormone inhibition, opiate-like effects and/or NO release) [2–4,7,34,44]. Thus, love seems to be a complex phenomenon and, with regard to stress, an ambiguous experience, i.e., double-edged sword. ...
... Thus, love is an emotion often associated with consensual sexual activity, or the willing, and even eager, participation of the individuals involved [2]. Medical, or health, implications of love are still speculative and neurobiological research has only started to examine the possible mechanisms underlying this assumption and its consequences for the individual organism and associated ontogenetic health outcomes and benefits [2–6]. ...
... Love is defined in the Oxford English Dictionary as an intense feeling of deep affection or fondness for a person or a thing, a sexual passion, or sexual relations, in general. Thus, love is an emotion often associated with consensual sexual activity, or the willing, and even eager, participation of the individuals involved [2]. Medical, or health, implications of love are still speculative and neurobiological research has only started to examine the possible mechanisms underlying this assumption and its consequences for the individual organism and associated ontogenetic health outcomes and benefits [2–6]. ...
Love and compassion exert pleasant feelings and rewarding effects. Besides their emotional role and capacity to govern behavior, appetitive motivation, and a general 'positive state', even 'spiritual' at times, the behaviors shown in love and compassion clearly rely on neurobiological mechanisms and underlying molecular principles. These processes and pathways involve the brain's limbic motivation and reward circuits, that is, a finely tuned and profound autoregulation. This capacity to self-regulate emotions, approach behaviors and even pair bonding, as well as social contact in general, i.e., love, attachment and compassion, can be highly effective in stress reduction, survival and overall health. Yet, molecular biology is the basis of interpersonal neurobiology, however, there is no answer to the question of what comes first or is more important: It is a cybernetic capacity and complex circuit of autoregulation that is clearly 'amazing'.
... before or during hibernation) combined with current (spring) environmental cues influence male activity, remains the most parsimonious alternative (Crews et al., 1984; Moore et al., 2000; Krohmer et al., 2002; Creews and Moore, 2005). A complex dissociated reproductive pattern could be an adaptation to extreme environments, enabling the limitation of costly sexual behaviors to the periods when environmental conditions are favorable (Crews, 1998 ). The production of spermatozoids, under the control of testosterone, would be time-dissociated from sexual behaviors: different components of reproductive effort being distributed over time (Callard et al., 1976; Kuchling et al., 1981; Licht, 1982; McPherson et al., 1982; Kuchling, 1999). ...
... It also emphasizes the complications associated with unexpected and non-significant effects despite their scientific value (Kotze et al., 2004). Finally, the current study illustrates the interest of using complementary methods on various study models (Bonnet et al., 2002) if we wish to describe and better understand the general patterns between hormones and behaviors (Bartholomew, 1982; Crews, 1998). the implants and encouraged all the members of the research team. ...
The stimulatory effect of testosterone on male sexual activity is one of the clearest examples linking hormones and behaviors. However, this relationship is complex in Chelonians. We experimentally studied the influence of testosterone levels on the activity budget and space use in male Greek tortoises (Testudo graeca graeca) during the spring mating season. We first described the annual pattern of changes in plasma testosterone levels in free-ranging animals in Morocco. Two peaks, one in winter and one in summer, corresponded to periods of inactivity; whereas mating periods in spring and to a lesser extent in autumn were associated with low plasma testosterone levels. Second, we experimentally manipulated plasma testosterone levels in free-ranging males, and analyzed the behavioral consequences. The strong contrasts in plasma hormone levels induced by the experimental treatments did not result in changes in activity budget or space use, both in the short-term or more than one month after the beginning of the hormonal treatment. Our results suggest that testosterone levels did not influence directly behavioral activity in this species, either immediately or after a time delay of one month.
... Genel olarak, "aşk"ın diğer bir kişi için hissedilen, kuvvetli, tutkulu bir sevgi olduğu kabul edilmektedir. [1] Türk Dil Kurumu sözlüğü ise "aşk"ı "aşırı sevgi ve bağlılık duygusu, sevi, amor" olarak tanımlamaktadır. [2] Bu tanıma içkin olarak "aşk" sıklıkla bireylerin cinsel etkinliği ile ilişkilidir. ...
... [2] Bu tanıma içkin olarak "aşk" sıklıkla bireylerin cinsel etkinliği ile ilişkilidir. [1] "Aşk" kavramı, kişinin arzuladığı bir başkasına emosyonel olarak bağlanmasının yanı sıra arzuladığı duyusal uyaranları elde etmesini de kapsar. [5][6][7] "Aşk" kelimesi ise etimolojik olarak Arapça "sarmaşmak", "sıkı bir şekilde sarılmak" fiilinden gelmektedir. ...
... [7] Bu önerme ile uyumlu olarak, "aşk" fenomeninin biyolojisi, özellikle de nörobiyolojik yönleri yakın tarihte ilgi çekmeye başlamıştır. [1,3] Sevgi ilişkilerinin ve yakından ilişkili oldukları bağlanma kavramının sağlıkta ve hastalıkta önem taşıdığı bilinmektedir. [4] Bu •www.cappsy.org• ...
The biology; especially the neurobiological features of the “love” phenomenon has recently started to attract attention. Love relations and attachment, which is closely related with them, are known to be important in health and disease. Love and love relations are found to be complex neurobiological phenomena based on activation of the limbic system of the brain. Those processes involve oxytocin, vasopressin, dopamine and serotonergic functions. Additionally, endorphine and endogenous opiate systems as well as nitrous oxide play role in those processes. The stages of love and love relations may demonstrate different neurochemical and neurophysiological features and may partially overlap with m aternal, romantic and sexual love and attachments. The aim of this article is to evaluate the common neurobiological pathways underlying the “love” phenomenon as well as their importance in medicine and health.
... Romantic love is often simply associated with human sexual activity for mate choices and the willing, and even eager, participation of the individuals, and yet it is a profound emotion that prevails in human activity throughout the world.1 Romantic love is frequently described as a highly motivating and rewarding experience.2,3 ...
Previous neuroimaging studies on romantic love have focused on determining how the visual stimuli that serve as a representation of loved ones induce the neural activation patterns of romantic love. The purpose of this study was to investigate the temporal changes in romantic love over a period of 6 months and their correlated neurophysiological changes.
Five heterosexual couples (n=10, mean age 21.1+/-1.97) who started dating not less than 100 days previously were recruited to measure their blood oxygen level dependent (BOLD) signals using functional magnetic resonance imaging (fMRI) while showing them pictures of their loved ones and their previously identified, opposite-sex friends. Subsequently, the subjects were scanned under the same experimental conditions to assess possible changes in their brain activities after 180 days.
WE FOUND THAT THEIR PASSIONATE LOVE SCORE (PLS) VALUES (M: 118.6+/-9.1, F: 120.2+/-7.0) were significantly reduced after 6 months (M: 110.8+/-4.0, F: 106.2+/-3.0). Furthermore, significantly increased activations were found in the cingulate gyri, inferior frontal gyri, supramarginal gyri, etc., after 6 months, whereas the head and tail of the right caudate nucleus were deactivated, which is indicative of the inhibition of expression and sensory neglect.
These findings suggest that dynamic neural processes in the cortical-subcortical regions are involved in temporal changes in romantic love.
... Author's personal copy of the diversity seen in reptiles relates to studying variation in sexual behavior. Sexual behaviors and aggressive behaviors often show discontinuous variation between the sexes in birds and mammals, although there is typically considerable individual variation within the sexes (Crews, 1998a). In contrast, many reptiles show more continuous variation in these behaviors. ...
... Sex steroid hormones are implicated in the process of TSD, and estrogen in particular appears essential in female sex determination (Crews et al., 1994, 1996a; Lance, 1997; Pieau and Dorizzi, 2004; Sarre et al., 2004; Wibbels et al., 1998). For example, estrogens applied exogenously to red-eared slider turtle (Trachemys scripta) eggs incubating at a maleproducing temperature override the temperature effect, and female hatchlings result (Crews et al., 1991; Wibbels and Crews, 1992). ...
... Because these animals exhibit the third pattern of sex determination (discussed above), the sex ratio varies with temperature, but individuals of both sexes are produced at most incubation temperatures. By incubating eggs at these various temperatures and then following individuals as they age, we have found that incubation temperature accounts for much of the phenotypic variation seen among adults, both between (sexual dimorphisms) and within (individual differences) the sexes (Crews et al., 1998; Sakata and Crews, 2004a). ...
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