{"id":45912,"date":"2012-07-07T09:05:06","date_gmt":"2012-07-07T12:05:06","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=45912"},"modified":"2017-03-01T18:20:45","modified_gmt":"2017-03-01T21:20:45","slug":"the-sexual-flexibility-of-females","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/the-sexual-flexibility-of-females\/","title":{"rendered":"The sexual flexibility of females"},"content":{"rendered":"
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MIGUEL TREFAUT RODRIGUES<\/span>The whiptail lizard: one of the few Brazilian lizard species comprised entirely of femalesMIGUEL TREFAUT RODRIGUES<\/span><\/p><\/div>\n

If God exists and has a gender she\u2019s definitely a woman,\u201d says biologist Rodrigo Marques Lima dos Santos, excited when he see what lizards \u2013 or rather female lizards \u2013 manage to do.<\/p>\n

Several species of lizards exhibit surprising ways of reproducing. Females generate their young asexually, without the participation of any male. They are independent, but not radical: in some species, if a male passes close by they allow copulation and may be fertilized. Reproductive autonomy reaches such a point that in some species there are only females, which reproduce in an asexual manner known as parthenogenesis, which, it now seems, is more flexible than was previouly thought.<\/p>\n

Biologists from the University of S\u00e3o Paulo (USP), from the Federal University of S\u00e3o Paulo (Unifesp) and from the National Laboratory of Biosciences (LNBio), when studying different aspects of parthenogenesis, concluded that alterations in a gene known as c-mos might enable the transformation of female reproductive cells (ova) into an embryo, even without spermatozoa.<\/p>\n

Rodrigo Santos followed the trail after this mechanism in his PhD, while he was studying the teiidae<\/em> lizards, a group that includes species that range from 10 cm long to the tejus, which grows up to 1.5 meters in length. Without expecting it, he began to see mutations in the c-mos gene in parthenogenetic species. In 2008 he began to work with Andr\u00e9a Balan, from LNBio, to model the forms of the protein produced by c-mos in lizards and snakes. Together they identified mutations in one of the four active sites (interaction points) of the protein, thus reinforcing the initial hypotheses.<\/p>\n

The c-mos gene produces a protein that blocks the end of cell division of the ovum until the spermatozoon arrives. When the male sexual cell fertilizes the ovum it deactivates the protein, cell division ends and an embryo is formed. The hypothesis of the researchers is that when the c-mos undergoes alterations it does not function correctly and may make the ovum continue dividing, even without a spermatozoon. They believe that defects in this gene could attenuate the blocking of the division of the ovum and allow other stimuli, like hormones, to reactivate cell division.<\/p>\n

If this work progresses it might throw light on one of the mechanisms of parthenogenesis. Today, little is known about how species of lizard that are capable of reproducing asexually came about, and even less about how they acquired and maintain this skill. According to the most widely accepted hypothesis, parthenogenetic snakes and lizards may be the result of crossing between close species.<\/p>\n

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MIGUEL TREFAUT RODRIGUES<\/span>Equal on the outside, but genetically different: Leposoma percarinatum may be diploids…MIGUEL TREFAUT RODRIGUES<\/span><\/p><\/div>\n

Leposoma percarinatum<\/em>, one of the species found in Brazil, is showing the reach of this genetic maze. The lizards of this species, recognized as parthenogenetic in 1952, are at most 5 centimeter long and live among leaves in the forests of an extensive region that stretches from Venezuela to the north of Mato Grosso State and from the Andes to the east of Par\u00e1. One hypothesis, presented in the 1970s, suggests that L. percarinatum<\/em> is the result of the crossing of two different species, Leposoma guianense<\/em> and L. parietale<\/em>, which are found in the humid forests of South America.<\/p>\n

Katia Pellegrino, from Unifesp, and Miguel Rodrigues, from USP, came across an unusual situation: the females of Leposoma percarinatum<\/em> were practically the same appearance-wise but had an astonishing difference from the genetic point of view. Some females, the diploids, had 44 chromosomes (two equal pairs of 22 chromosomes) in each cell, while the triploids had 66 chromosomes (three pairs of 22).<\/p>\n

\u201cWithin what had been supposed to be the same species there are two different strains, which will allow us to reconstruct their history and the mechanisms of their origin,\u201d Katia concluded. She believes that the triploid variety must have arisen from another hybridization event between the diploid form of L. percarinatum<\/em> and L. osvaldoi<\/em>, since L. guianense<\/em> does not occur so far to the south of Brazil.<\/p>\n

Sometimes creatures turn up that do away with all explanations. From a trip to the archipelago of Anavilhanas on the Negro River, Rodrigues brought back specimens of Leposoma guianense, <\/em>some individuals which were revealed to belong to a new clone of Leposoma percarinatum<\/em> and others that were different to the point of representing a new species, which was named Leposoma ferrerai. <\/em>They were all diploids living in the same area.<\/p>\n

The whiptail lizard, or Cnemidophorus nativo<\/em>, one of the few species of Brazilian lizard that is exclusively parthenogenetic (and that is also threatened with extinction) is merely diploid, according to the analyses of Santos. Found in the forests in the north of Esp\u00edrito Santo and the south of Bahia, these animals belong to a sister family of the Leposoma<\/em>, but can grow to 30 cm long. According to Santos, other parthenogenetic species that live in the Amazon, such as the Cnemidophorus lemniscatus<\/em> and Gymnophthalmus underwoodi, <\/em>seem to have mixed diploid and triploid populations.<\/p>\n

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MIGUEL TREFAUT RODRIGUES<\/span>… or triploidsMIGUEL TREFAUT RODRIGUES<\/span><\/p><\/div>\n

The biologists are working with the possibility that parthenogenesis does not just form clones of the mother, but also allows some genetic variation, although smaller than with sexual reproduction, through recombination in chromosomes of the ovum. \u201cA recent study showed that a snake generated an albino offspring by parthenogenesis, indicating that there is, indeed, genetic recombination even in asexual reproduction,\u201d argues Santos. \u201cThe spontaneous origin of parthenogenesis, an alternative hypothesis to the hybrid theory, cannot be discounted in Leposoma<\/em> and Cnemidophorus<\/em>, since this mechanism has already been suggested for specimens of Gymnophthalmus underwoodi<\/em> from Roraima,\u201d adds Katia.<\/p>\n

An indispensable embrace<\/strong>
\nSantos believes that Cnemidophorus nativo <\/em>may behave similarly to lizards of the genus Aspidoscelis<\/em>. Found in desert regions in Asia and North America, Aspidoscelis<\/em> only begins to form embryos after being embraced, which biologists call pseudo-copulation. When one of them detects the touch or grating from another it should activate the release of hormones that unblock the c-mos, the biologists from USP believe.<\/p>\n

\u201cFor some parthenogenetic species of the genus Aspidosceles<\/em> to reproduce,\u201d Santos comments, \u201ccopulation between females is obligatory.\u201d David Crews and Jon Sakata, from the University of Texas, showed in 2000 that embracing females had a reverse hormonal cycle, one with high levels of estrogen, the most abundant hormone in females, and the other with high levels of testosterone, produced more intensely by males.<\/p>\n

In 2011, researchers from the University of Kansas managed to induce hybridization and confirm that sexual reproduction may form a parthenogenetic species by crossing two species of Aspidosceles<\/em>. Making a parthenogenetic female reproduce in the laboratory, alone or through being \u2018cuddled\u2019 by another female, however, remains one of the dreams of the biologists.<\/p>\n

Of the 5,634 species of lizard already identified, some 40 are parthenogenetic and they generally live in tropical forest regions or the desert climates of Asia or Oceania. \u201cReproduction by parthenogenesis results in less genetic variability than with sexual reproduction, but may be an adaptive survival response to extreme environments,\u201d comments Yatiyo Yassuda, a geneticist specializing in lizard genetics who is monitoring the study on the possible origins of parthenogenesis.<\/p>\n

In the 1980s, Yatiyo faced a similar problem and at great cost managed to convince other geneticists that lizards of the genus Tropidurus<\/em> had a sexual differentiation; the males had a different chromosome from the females, but it was so small that it was almost imperceptible. Many species of lizard have the same set of chromosomes and are differentiated sexually by unknown genes or temperature variations while they are developing; if the temperature is higher it may favor the development of male embryos in some species, or females in others.<\/p>\n

Yatiyo\u2019s room, where Santos talks about his work, has some paintings of flowers, some figurative, others abstract. \u201cThis was the beginning. I\u2019ve already painted more than 300 pictures since I retired,\u201d she says, imagining the sun she intended to paint on the following day, a Saturday. \u201cBut I still come here every day.\u201d<\/p>\n

Induced cloning<\/strong>
\n\u201cMeiotic parthenogenesis is a form of natural cloning similar in part to induced cloning for the reproduction of animals that are of commercial interest,\u201d he observes. In 2004, researchers from the Paulista State University (Unesp) in Jaboticabal indicated that ethanol and the chemical strontium can induce cell division in the ova of cows, functioning like an external stimulus, analogous to the male sexual cell.<\/p>\n

Similarly, the eggs of experimental animals, like Dolly the sheep, only developed after they had received an electric shock, which must deactivate the c-mos. Santos believes that if parthenogenesis could be regulated it could help in livestock farming or in the conservation of wild species at risk of extinction. \u201cMammals have mechanisms that avoid parthenogenesis, like imprinting,\u201d he observes. Another application would be medical, since mutations in this gene might make the eggs divide uncontrollably, giving rise to tumors.<\/p>\n

If they make progress, maybe the biologists will find new answers to two basic questions of biology. The first: what is sex for? The other: what is the advantage of sexual reproduction? According to Santos, sexual reproduction requires the meeting of two organisms to form offspring, while in parthenogenesis just one organism is sufficient to generate another. Genetic variability resulting from sexual reproduction is not always beneficial to species, argue the biologists.<\/p>\n

\u201cSexual reproduction is better for environments in transformation, with a high risk of predation and disease, but it is bad in stable environments and healthy populations, because a well-adapted individual can produce offspring which do not adapt well ,\u201d he says. \u201cIn stable environments, clonal reproduction, as carried out with the breeding of animals and plants, result in offspring with high yields, is the most frequently indicated.\u201d<\/p>\n

The Projects<\/strong>
\n1.<\/strong> The systematics and evolution of neotropical herpetofauna (n\u00ba\u00a02003\/10335-8<\/a>);\u00a0Modality\u00a0<\/strong>Thematic Project;\u00a0Coordinator\u00a0<\/strong>Miguel Trefaut Rodrigues \u2013 USP;\u00a0Investment\u00a0<\/strong>R$ 975,589.35.
\n2.<\/strong> Genetic diversity in unisexual and bisexual species of Cnemidophorus<\/em> of the Ocellifer (Teiinae<\/em>) group and structural characterization of the Mos protein in the Squamata (n\u00ba 2008\/56444-6<\/a>);\u00a0Modality<\/strong>\u00a0Post-doctoral Studies Grant;\u00a0Coordinator<\/strong>\u00a0Rodrigo Marques Lima dos Santos \u2013 USP;\u00a0Investment\u00a0<\/strong>R$ 277,872.66.
\n3.<\/strong> Cytogenetic and molecular studies in micro-teiidae lizards (Squamata, Gymnophthalmidae<\/em>), with an emphasis on species of the genus Leposoma from the Amazon and Atlantic rainforests (n\u00ba\u00a01998\/05289-7<\/a>); Modality\u00a0<\/strong>Post-doctoral Studies Grant;\u00a0Coordinator\u00a0<\/strong>Katia Cristina Machado Pellegrino \u2013 Unifesp;\u00a0Investment<\/strong>\u00a0R$ 37,720.00.<\/p>\n","protected":false},"excerpt":{"rendered":"Males not always necessary for lizard reproduction","protected":false},"author":17,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[231,237],"coauthors":[5968],"class_list":["post-45912","post","type-post","status-publish","format-standard","hentry","category-science","tag-evolution","tag-genetics"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/45912","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/17"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=45912"}],"version-history":[{"count":0,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/45912\/revisions"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=45912"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=45912"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=45912"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=45912"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}