Tinkering with worm sex to shed light on evolution

This post contributed by Nadine Lymn, ESA Director of Public Affairs The roundworm Caenorhabditis elegans (C. elegans) is a tiny laboratory animal that researchers have worked with for decades.  As a hermaphrodite, C. elegans makes both sperm and eggs and can reproduce by self-fertilization.  In contrast to humans, where hermaphrodites are rare, for C. elegans, this is its normal state.   However, male individuals, with only male gonads, can also occur and these individuals must mate with a hermaphrodite in order to reproduce, as shown in the video below. A central question in evolution is how variations in the genes responsible for determining gender can exist since there seems to be so little room for error; if the mutation goes awry and negatively affects reproductive ability, a species could be in serious trouble. A new paper published in the journal Evolution took a closer look.   Michigan State University researchers Christopher Chandler and Ian Dworkin and colleagues at Iowa State University used worms that had already been mutated in previous experiments.  One mutation determined that at a specific temperature, the larvae will become a hermaphrodite.  At a higher specific temperature, the larvae—while still genetically a hermaphrodite—becomes a male, and at temperatures in between, intersex individuals arise, sporting both male and hermaphrodite characteristics.   These intersex individuals are different from the normal, hermaphrodite C. elegans, in that they are truly mixed up—they have some characteristics of both the hermaphrodite and male versions of C. elegans.   Chandler, Dworkin, and colleagues exposed the worms to the intermediate temperatures, creating populations of intersex individuals. As described in a press release about the research, these characteristics made reproduction difficult, though still possible. Chandler and colleagues allowed these populations to reproduce for 50 generations, creating a strong selection for individuals still able to function sexually.  Then the researchers measured the later generations’ sex ratio and fertility.  They found that these later populations had more typical C. elegans sex ratios and higher fertility, despite the fact that they were still subjected to the intermediate temperatures that had rendered their predecessors intersex animals.  As explained in the press release, other genes were evolving to compensate for changes in the sex determination genes, in a way that allowed individual worms to develop either as a male or a hermaphrodite, instead of as an intersex animal. In other words, C. elegans was able to make up for the negative mutations brought out by the artificial conditions created by the researchers.  In their paper’s conclusion, the authors note that their experiment, funded by the National Science Foundation, demonstrates that “organisms can accommodate deleterious developmental mutations on relatively short time scales” and that the...

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Scientists dig up the history of the mole’s extra ‘thumb’

Marcelo Sánchez-Villagra from the University of Zurich and researchers have uncovered the evolutionary history of the mole’s extra “thumb.” As it turns out, this polydactyl animal evolved an elongated wrist bone to serve as a sort of extra finger, widening the paw for more effective tunneling. The researchers examined embryos of the Iberian mole (Talpa occidentalis) and the closely related—but five-fingered—North American least shrew (Cryptotis parva). They found that the “thumb” didn’t begin to grow until the embryos were 18 days old, after the other fingers had already begun to develop. The digit, which does not bend but can wiggle, suggests a relationship with the testosterone level of these animals. According to a recent Science Now article, “True to their oddness, many female moles grow not only ovaries but also some testicular tissue, hinting that they have too much of the hormone, Sánchez says. Testosterone is well known for building bones, and some evidence suggests that human polydactyly—people can occasionally develop genuine sixth fingers—coincides with high levels of maternal testosterone.” Read the original press release “How the mole got its 12...

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Panda paradox: Which came first, a taste for bamboo or a distaste for meat?

This post contributed by Monica Kanojia, Administrative Assistant/Governance for ESA While a vegetarian lifestyle is a choice made by omnivorous humans, the panda population may have been forced to convert  to a vegetarian diet between 2 and 7 million years ago to ensure survival. The preference for bamboo is unusual for pandasbecause they are classified as carnivores  even though their diet is 99% bamboo. Even more unusual is the fact that their digestive system is unable to process cellulose, the major component of plant cell walls. According to research published in Nature, the bamboo diet is both influenced by genetics, and it depends on the digestive microbes present in the panda gut. Everything from what we eat, to what we taste, to how we eat is determined by our genetics. Umami—the basic taste associated with an amino acid common in protein heavy foods like meat—is sensed through the T1R gene family in carnivores. But in pandas, the T1R gene family has experienced mutations causing the inactivation of the T1R1 gene, making it a pseudogene. Pseudogenes have either lost protein coding ability or are no longer expressed in the cell. Ruiqiang Li and the team who sequenced the genome found that the malfunction of the T1R1 gene occurred relatively recently in the panda lineage: Estimated loss was about 4.2 million years ago. The malfunction of the umami taste receptor may explain why pandas have a preference for bamboo versus meat. Gene mutations are random and can change the habits of an organism, affecting its entire existence. In the case of the pandas, it changed the way pandas perceived meat. Despite the loss of taste for meat the digestive system of the pandas remained able to process it because all the enzymes required to were still present in their system. The ability to process plant material on the other hand was not natural. According to Li et al.’s research pandas do not have the necessary enzymes to digest bamboo, hinting at the idea that their ability to do so is dependent upon their gut microbes. Luckily for the endangered pandas, according to a molecular analysis conducted by Li and his colleagues, they have a very high rate of genetic variation in spite of their low population numbers. The abundance of some genetic changes within the gene pool can be reduced by natural selection, while other “more favorable” mutations may accumulate and result in adaptive changes; this may be part of the reason why the panda population converted from meat eaters to plant eaters as well. Logically, it would go as follows: The panda population experienced a mutation affecting taste buds which...

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From the Community: space bacteria, chimeras and sea turtles

Citizen scientist notices thousands of birds trapped in the lights of this year’s 9/11 memorial in New York City, endangered turtles get a second chance in Florida, flu viruses last longer in cool, dry environments, a blogger sets up a serendipitous research collaboration and the Potomac River shows signs of improvement due to aquatic conservation efforts. Here is research in ecology from mid-September.

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From the Community: shark science, reconciliation ecology and Biodiversity 100

An analysis of Shark Week, research on reconciliation ecology from ESA’s annual meeting, flowers that are genetically predisposed to adapting to climate change, endangered, purring tit monkey species found in Colombia amidst violence and the details on the antibiotic-resistant “superbug.” Here is the latest in ecological science from the second week in August.

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Genome reveals olfactory communication in the zebra finch

In an article published earlier this week in Nature, researchers revealed the complete genome of the zebra finch and focused on the intricacies of their vocal communication. The zebra finch, the males of which are known to learn and repeat the same song generation after generation, show 800 active genes involved in vocalization. One group of researchers, however, found more hidden in the code. Doron Lancet and Tsviya Olender of the Weizmann Institute’s Molecular Genetics Department co-authored the study, but they honed in on the olfactory system of the zebra finch. They discovered that, of the approximately 500 genes encoding smell receptors, 200 of the finch’s genes can potentially produce functional smell receptors. Compared to the chicken genome, which is known to produce around 70 active proteins of the 500 genes, this shows a key role for smell, say the researchers. Given the importance of communication in the zebra finch, they suggest that smell is also playing an important part in communication. Lancet and Olender compared the finch’s sequence to other bird species and found that 95% of the receptors in the finch appeared to belong to families unique to them. That is, the gene sequence for olfaction in one finch could be distinct from another finch, suggesting the smell receptors are just as individual as the song a particular bird produces. As Lancet described in a press release, “this finding suggests that smells may be involved in the unique communications among individuals within the species, on top of the messages they send through their songs.” Read more on the implications for vocal communication in finches and humans at “From a Songbird, New Insights Into the Brain.” Warren, W., et al. (2010). The genome of a songbird Nature, 464 (7289), 757-762 DOI: 10.1038/nature08819 Photo credit: marj k on...

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From the Community: February edition

Fruit fly behavior mapped, resilience theory in an urban setting, changing the universe’s birthdate and genetic diversity in an all-female species. Here are extra news stories and studies on ecological science for the month of February.

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