Bite force: why islanders become giants among lizards
Jul29

Bite force: why islanders become giants among lizards

Species evolve quickly on islands. These “natural laboratories” often offer freedom from predators and competitors, isolation, and new foods and resources. Animals on islands tend to be larger or smaller than their mainland relatives. First described by Foster in 1963, this pattern is so striking that it was dubbed “the island rule” by Leigh van Valen ten years later. Many subsequent studies have investigated, debated, and refined Foster’s rule and related hypotheses explaining the evolution in body size when animals are isolated on islands. In the August 2015 issue of Ecology, Anna Runemark, Kostas Sagonas, and Erik Svensson report that diet has contributed to the development of gigantism of the Skyros wall lizard (Podarcis gaigeae) on islets around the Greek island Skyros. On the main island, Skyros lizards typically eat ants, wasps, and bees. On islets where on harder-to-chew fare like beetles and isopods were more common, and the lizards frequently dined on them, the lizards were larger, with wider heads and a correspondingly stronger bite. See more photos at...

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Forgotten beetle hunters and the foundation of evolutionary theory; Alfred Wallace remembered in puppetry
Jan15

Forgotten beetle hunters and the foundation of evolutionary theory; Alfred Wallace remembered in puppetry

The history of science is filled with famous, pivotal individuals, who were in fact surrounded by brilliant, inquisitive colleagues working on the same goals, ideas, collections, and experiments. The puppets tell the tale.

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Ecology branches into the tree of life

An August 2012 supplementary issue of Ecology explores the interface of ecology and phylogenetics. By Liza Lester, ESA communications officer Lebensbaum (Tree of Life): Detail from Gustav Klimt’s 1910/11 drawing for the immense dining room frieze at Stoclet Palace, in Brussels. Watercolor and pencil. Österreichisches Museum für angewandte Kunst, Vienna. NATURALISTS of the late 19th century tended to holistic interpretations of the natural environment and its evolutionary history.  In the decades after Darwin, the new understanding of the relatedness of organisms to each other mixed indiscriminately with the study of relationships of organisms  to their living and physical environments. Theories of natural selection and inheritance sprang from observations of communities of animals, plants and microorganisms – and, in turn, informed ideas of how communities may have been shaped by the climate and landscapes of their earthly residence. “Ecology drives evolution, evolution drives ecology, that’s how Darwin saw the world,” said University of Minnesota ecologist Jeannine Cavender-Bares. But it is possible to zoom in on one viewpoint, to focus only on the interactions of living organisms and their environment, or only on the history of life, the derivation of species from common ancestors, and their adaptations to environmental pressures. That is what biological science did for much of the 20th century. “We partitioned the processes we were looking at into more tractable components. There are benefits to doing that, but at the expense of understanding how ecological and evolutionary processes reinforce each other.” Cavender-Bares is chief editor of a supplementary issue of ESA’s journal Ecology dedicated to bridging that gap in methodology and perspective. It showcases work at the interface of ecology and phylogenetics, a field of biology that works to infer the evolutionary history of relationships among organisms. “Integrating Ecology and Phylogenetics” went online in August, and is open access. “If you start with Darwin — always a good place to start! — natural selection is fundamentally an ecological process,” said David Ackerly, one of Cavender-Bares’ co-editors for the supplementary issue. “Chapter 3 of the On the Origin of Species [1859] is really a textbook in ecology.” “As ecology became a more quantitative science, it was just more tractable not to have to consider all of evolutionary history. But it’s become tractable again,” said Cavender-Bares. She and co-editors Ackerly and Kenneth Kozak pushed forward the supplementary issue not only to showcase available technology, but to make the case for incorporating phylogenetic research questions and concepts into ecological studies. “Ecologists are thinking about history more, thinking about contingency and context, and not seeing ecological systems so much as systems in equilibrium,” said Ackerly. He trained in ecology as a graduate...

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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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Pollination from the plant’s perspective

If plants had a perspective, they would probably think of pollinators as more than just extra-friendly house guests. That is, plants would be more likely to view pollinators as the mutual friend who likes to set up blind dates. Bees might limit pollen to its use as a protein source for the hive, and birds might devour the flesh of a fruit and eliminate the seed as waste. However, many flowering plants, as Bug Girl pointed out in a post in honor of National Pollinator Week, have evolved alongside these pollinators for only one purpose: reproduction. “Sure, you can toss your pollen out on the wind and hope it lands in the right place. And for a lot of plants, evergreens in particular, this works just fine,” she wrote. “That methodology results in a lot of wasted gametes (plant sperm) though, so for nearly all flowering plants, insects or other pollinators are needed for plant nookie.” Sometimes the pollinator-plant relationship is mutualistic, and in many cases, one species or another is dependent upon the other for its survival. Take the agave plant. Probably the most well-known species is the blue agave plant (Agave tequilana), the nectar of which is used as a granular sugar substitute and to make tequila (one of the “finer” products of pollination, along with chocolate and coffee, mentioned by Bug Girl ). Leptonycteris nivalis, known as the greater long-nosed bat or Mexican long-nosed bat, and the lesser long-nosed bat (Leptonycteris curasoae), are the primary pollinators of this economically and ecologically valuable plant. This agave-bat relationship is mutually beneficial. The bats, hovering in place like a hummingbird, use their long muzzles to feed on the high-fructose nectar of the agave. At the same time, the plants’ pollen collects on the bats’ fur. The bats then travel from plant to plant, spreading pollen as they drink from the nectar-filled stalks that bloom each night across the southwestern U.S. and Mexico. The bats also migrate based on the blooming time of these plants. They arrive in Texas—particularly in Big Bend National Park, where a single colony resides in the Chisos Mountains—shortly after agave plants, such as the century plant (Agave havardiana), begin to bloom. Unfortunately, the lesser long-nosed bat and the Mexican long-nosed bat are endangered—and as their numbers decline, agave plant reproduction becomes more limited. A little farther north, however, some species of agave plants—those that are not harvested for tequila— have evolved to attract both bats and moths to serve as pollinators. Agave plants have several ways of advertising their nectar: the scent, the color of the flower and the shape, or morphology, of the structure...

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The story of the fig and its wasp

Inside the rounded fruit of a fig tree is a maze of flowers. That is, a fig is not actually a fruit; it is an inflorescence—a cluster of many flowers and seeds contained inside a bulbous stem. Because of this unusual arrangement, the seeds—technically the ovaries of the fig—require a specialized pollinator that is adapted to navigate within these confined quarters. Here begins the story of the relationship between figs and fig wasps. The queen of the fig wasp is almost the perfect size for the job—except, despite her tiny body, she often times will lose her wings and antennae as she enters through a tight opening in the fig. “The only link the fig cavity has to the outside world is through a tiny bract-lined opening at the apex of the fig, called the ostiole, and it is by means of this passage that the pollinating fig wasp gains access to the florets,” as described in Figweb, a site by Iziko Museums of Cape Town. Once inside, the queen travels within the chamber, depositing her eggs and simultaneously shedding the pollen she carried with her from another fig. This last task, while not the queen’s primary goal, is an important one: She is fertilizing the fig’s ovaries. After the queen has laid her eggs, she dies and is digested by the fig, providing nourishment. Once the queen’s eggs hatch, male and female wasps assume very different roles. They first mate with each other (yes, brothers and sisters), and then the females collect pollen—in some species, actively gathering it in a specialized pouch and in others, accumulating it inadvertently—while the wingless males begin carving a path to the fig’s exterior. This activity is not for their own escape but rather to create an opening for the females to exit. The females will pollinate another fig as queens. The males will spend their entire lifecycle within a single fruit. While this tree-wasp relationship may not be common knowledge to all fig-eaters, it is well-known to biologists as one of the most solid examples of coevolution. “One of the best activities to do with an introductory biology class is to pass around Fig Newtons, let them take a bite and then tell them the story of the fig wasp life cycle,” said tropical plant ecologist Greg Goldsmith as we recently hiked through a cloud forest in Monteverde, Costa Rica. “It’s a fascinating story.” After learning the story of the fig and its wasp, the most common question is, “Do we eat wasps when we eat figs?” The short answer is that it depends—that is, some figs are parthenocarpic, meaning they are...

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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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