Boy Or Girl? In Lizards, Egg Size Matters

SOURCE

ScienceDaily (June 22, 2009) — Whether baby lizards will turn out to be male or female is a more complicated question than scientists would have ever guessed, according to a new report published online on June 4th in Current Biology. The study shows that for at least one lizard species, egg size matters.

"We were astonished," said Richard Shine of the University of Sydney. "Our studies on small alpine lizards have revealed another influence on lizard sex: the size of the egg. Big eggs tend to give girls, and small eggs tend to give boys. And if you remove some of the yolk just after the egg is laid, it's likely to switch to being a boy, even if it has female sex chromosomes; and if you inject a bit of extra yolk, the egg will produce a girl, even if it has male sex chromosomes."
In many animals, the sex of offspring depends on specialized sex chromosomes. In mammals and many reptiles, for instance, males carry one X and one Y chromosome, while females have a pair of X chromosomes. In contrast, animals such as alligators depend on environmental cues like temperature to set the sex of future generations.
The new findings add to evidence that when it comes to genetic versus environmental factors influencing sex determination, it doesn't have to be an either/or proposition. In fact, Shine and his colleagues earlier found in hatchlings of the alpine-dwelling Bassiana duperreyi that extreme nest temperatures can override the genetically determined sex, in some cases producing XX boys and XY girls. His group had also noticed something else: large lizard eggs were more likely to produce daughters and small eggs to produce sons.
Despite the correlation, Shine said he had assumed that the association was indirect. In fact, his colleague Rajkumar Radder conducted studies in which he removed some yolk from larger eggs, more likely to produce daughters, to confirm that assumption.
"We were confident that there would be no effect on hatchling sex whatsoever," Shine said. "When those baby boy lizards started hatching out, we were gob-smacked."
Shine thinks there will be much more to discover when it comes to lizard sex determination.
"I suspect that the ecology of a species will determine how it makes boys versus girls, and that our yolk-allocation effect is just the tip of a very large iceberg," he said.
The authors include Rajkumar S. Radder, University of Sydney, Australia; David A. Pike, University of Sydney, Australia; Alexander E. Quinn, University of Canberra, Australia; and Richard Shine, University of Sydney, Australia.
Journal reference:
Rajkumar S. Radder, David A. Pike, Alexander E. Quinn, and Richard Shine. Offspring Sex in a Lizard Depends on Egg Size. Current Biology, 2009; DOI: 10.1016/j.cub.2009.05.027
Adapted from materials provided by Cell Press, via EurekAlert!, a service of AAAS.

Close Social Ties Make Baboons Better Mothers, Study Finds

SOURCE

ScienceDaily (June 11, 2009) — Baboons whose mothers have strong relationships with other females are much more likely to survive to adulthood than baboons reared by less social mothers, according to a new study by researchers at UCLA, the University of Pennsylvania and other institutions.

"If you're a baboon, the strength of your mother's relationship with other females is the best predictor of whether you'll live to have children yourself," said Joan Silk, the study's lead author and a UCLA professor of anthropology. "The study adds to mounting evidence of the biological benefits of close relationships among females."
The findings are significant because "survivorship to reproduction is the gold standard in evolutionary biology," said co-author Dorothy Cheney, a professor of biology at the University of Pennsylvania. "Females who raise offspring to a reproductive age are more likely see their genes pass along, so these findings demonstrate an evolutionary advantage to strong relationships with other females. In evolutionary terms, social moms are the fittest moms — at least when it comes to baboons."
The study appears online in the Proceedings of the Royal Society B, a peer-reviewed journal published by the national academy of science of the United Kingdom and the Commonwealth.
Silk, Cheney and seven other researchers from the University of Pennsylvania, the University of Michigan and the University of St. Andrews in Kenya analyzed 17 years worth of records on more than 66 adult female baboons in the Moremi Game Reserve, a 2,000-square-mile national park in Botswana that teems with wildlife.
Collected on the ground by primatologists who tracked the baboons six days a week, 12 months a year, the records reflected the sex and survival rates of baboon offspring, as well as telling details of the mothers' social lives, including their ranking within the group, as measured by the direction of approach/retreat interactions, and the amount of social interactions they had with each of the group's other females.
In addition to showing how often one animal approached another, the records of social interactions included details of grooming, which is known to be the primary form of social interaction in Old World monkeys. The researchers noted how much time — frequency and duration — the females spent grooming each other and how often they solicited grooming from other females.
Of all the factors studied, the strength of a mother's social bonds with another female had the most significant effect on the survival rates of offspring. A mother's dominance rank proved to have no affect on the survival rate of her offspring.
"We really expected dominance status to be more influential than it proved to be," Silk said.
Offspring from the most social mothers turned out to be about one-and-a-half times more likely to survive to adulthood than offspring from the least social mothers.
The strongest social bonds were measured between mothers and adult daughters, followed by sisters and all other potential relationships, including aunts, nieces, cousins and baboons with no familial ties. Bonds between mothers and adult daughters proved to be three times stronger than those between sisters and 10 times stronger than relationships with other females.
"What really matter to these girls are mother-daughter bonds," Silk said. "They're really strong, and they last forever. If your mom is alive, she's one of your top partners, always. But more importantly, it's the strength of these bonds, because females whose bonds with their mothers and daughters were strong had higher offspring survival than females whose bonds with these relatives were weak."
Silk's past research with Jeanne Altmann, the Eugene Higgins Professor of Ecology and Evolutionary Biology at Princeton University, and Susan C. Alberts, a professor of biology at Duke University, on baboons in the Amboseli Basin of Kenya had found a higher survival rate for baboons with social mothers, but the research only tracked offspring through the first year of life.
For the new study, researchers followed offspring from 1 year of age through sexual maturity — roughly 5 years of age. The new study also differs from past baboon research by focusing on the strength and duration of relationships between pairs of females rather than on the amount of social interactions in general.
"The benefit comes not from being wildly social — it's about having close social bonds," said Cheney, who runs the Moremi baboon-tracking project with University of Pennsylvania psychology professor Robert M. Seyfarth.
"These females form strong relationships with particular partners," Silk said. "They don't treat everyone the same. They spend a lot more time with — and a lot more time grooming — some females than others, and these relationships tend to be very long-lasting."
Additional research is needed to determine how the female bonds improve infant survival, but it may have to do with such stress hormones as cortisol, Silk said. Research has shown that prolonged elevations of stress hormones in primates can lead to cardiovascular disease and other serious health problems. Research has also shown that grooming tends to lower these stress hormones in baboons.
"Our research suggests that somehow there is a link between the kind of social relationships you form and the natural, normal stresses that occur in everyday life, and that seems to have — at least in baboons — a long-term effect on reproductive success," Silk said.
Said to share 92 percent of their DNA with humans, baboons are close relatives of humans. Baboons and humans last shared a common ancestor about 18 million years ago. The new findings on social interactions among mothers parallel recent research that has shown health benefits for humans who enjoy particularly close social networks.
"Our findings suggest benefits from forming close relationships are built into us from a long way back," Silk said.
The research received funding from the National Geographic Foundation, the Research Foundation of the University of Pennsylvania, the Institute for Research in Cognitive Science at the University of Pennsylvania, the National Institute of Health and the National Science Foundation.
Adapted from materials provided by University of California - Los Angeles.

Communal Stomach Of An Ant Colony

SOURCE

ScienceDaily (May 11, 2009) — How do ant colonies manage the nutrients in their food? Audrey Dussutour from the Centre de recherche sur la cognition animale (CNRS/Université Paul Sabatier) and Steve Simpson from Sydney University have shown that an ant colony functions like a “collective mouth and gut”. The members of a colony are capable of dealing with the nutritional needs of their social structure by sharing tasks (foraging, digestion and excretion).

In an ants' nest, food is brought home by only 10% of the colony members - the foragers. This food is then regurgitated and shared among all the ants in the colony. Nutritional needs differ, however, between the young (larvae) and adults of the colony.
Audrey Dussutour and Steve Simpson have recently shown that the larvae, which cannot move or leave the nest, are capable of communicating their nutritional needs to forager ants, who adapt their gathering strategy accordingly. These researchers provided sugar- or protein-rich foods for ant colonies with and without larvae, and observed that ant behaviour differed. When a colony had larvae, high protein foods were preferentially gathered that could sustain larval growth. Inversely, when there were no larvae, the ants preferentially gathered sugar-rich foods.
In a second experiment, the researchers showed that sugar is the key nutrient regulating gathering in ants. Provided with a range of food containing varying proportions of protein and sugar, foragers are capable of harvesting the same quantity of sugar. These researchers also observed that when the food was rich in protein and poor in sugar, the excess of proteins was ejected from the nest. Ants are therefore capable of extracting sugar from food and regurgitating protein in the form of waste pellets.
However, despite this food manipulation, the colonies reared with protein-rich food had extremely high mortality due to protein toxicity and suffered losses of up to 75%. In comparison, the ant colonies reared on food of lower protein content lost less than 5% of their numbers.
The scientists noticed that the mortality was lower in colonies with larvae. They demonstrated that the ants in these colonies managed to partially escape the toxic effects of proteins by giving the work of nutrient processing to the larvae, which are better equipped for protein digestion. The researchers also confirmed the highly toxic effect of protein-rich food on ants, as they had previously demonstrated in fruit flies.
Journal reference:
Dussutour et al. Communal Nutrition in Ants. Current Biology, May 12, 2009; DOI: 10.1016/j.cub.2009.03.015
Adapted from materials provided by CNRS.

Gender And Handedness Influences On Monkeys' Brains Similar To Humans

Source:

http://www.sciencedaily.com/releases/2007/08/070829143613.htm

Science Daily — Capuchin monkeys are playful, inquisitive primates known for their manual dexterity, complex social behavior, and cognitive abilities. New research now shows that just like humans, they display a fundamental sex difference in the organization of the brain, specifically in the corpus callosum, the region that connects the two cerebral lobes.

A recently published paper by Associate Professor of Psychology and Biology Kimberley A. Phillips (Hiram College), Chet C. Sherwood (George Washington University) and Alayna L. Lilak (Hiram College), reports finding both sex and handedness influences on the relative size of the corpus callosum.
In the study, thirteen adult capuchins underwent magnetic resonance imaging of the brain to determine the size of their corpus callosum, which is the major white matter tract connecting the left and right cerebral hemispheres. The monkeys were later given a task to determine hand preference. The authors' results led them to conclude that, as in humans, male capuchins have a smaller relative size of the corpus callosum than females, and right-handed individuals have a smaller relative size of the corpus callosum than left-handed individuals.
As the two hemispheres show greater independence of function, the relative size of the corpus callosum is expected to be smaller. This has been documented in humans, and same pattern was found in capuchins. Phillips and her co-authors hypothesize their results are related to hemispheric specialization for complex foraging tasks that require the integration of motor actions and visuospatial information. In the wild, capuchin monkeys utilize both arboreal and terrestrial substrates and are also noted for being very adept at capturing small rapid prey, such as birds, lizards, and squirrels.
Citation: Phillips KA, Sherwood CC, Lilak AL (2007) Corpus Callosum Morphology in Capuchin Monkeys Is Influenced by Sex and Handedness. PLoS One 2(8): e792.doi:10.1371/journal.pone.0000792
Note: This story has been adapted from a news release issued by Hiram College.

Fausto Intilla

www.oloscience.com