A few weeks ago I was given the chance to attend Genomes to / aux Biomes 2014, an evolution and ecology conference held in Montreal. My registration was courtesy of Canadian Science Publishing, to whom I am very grateful, and I wrote about my experience for their blog. You can read all about it here..
Sloths popped into the news a while ago, as one of the mysteries of their behaviour – why, once a week, they climb down from the canopy to poo on the ground – was examined in a new paper.
Sloths are known for their leisurely lifestyle in the treetops, but there is more to them than meets the eye. A complex mini-ecosystem involving moths and algae may help keep the sloth both camouflaged and fed, and be the cause of their odd weekly habits. Pieces in the New York Times and National Geographic explain it all.
“The sloth is not so much an animal as a walking ecosystem. This tightly fitting assemblage consists of a) the sloth, b) a species of moth that lives nowhere but in the sloth’s fleece and c) a dedicated species of algae that grows in special channels in the sloth’s grooved hairs. Groom a three-toed sloth and more than a hundred moths may fly out. When the sloth grooms itself, its fingers move so slowly that the moths have no difficulty keeping ahead of them.” Nicholas Wade, New York Time
Sloths popped up again yesterday. Did you know what noise a sloth makes?
Raising young lemurs in communal crèches benefits both mothers and offspring, a new study has found. Andrea Baden and colleagues, of Yale University, studied a group of black-and-white ruffed lemurs (Varecia variegata) in Ranomafana National Park, Madagascar. This is the first study to examine the consequences of different parenting strategies in the ruffed lemur. By observing how mothers split their time between different activities, they discovered that crèche use – where infant care was shared between mothers – corresponded with an increase in the amount of time a mother spent feeding. For young lemurs, being raised in communal nests actually gave them a higher chance of survival.
Black-and-white ruffed lemurs are large-bodied social primates that live in the eastern rainforests of Madagascar, and have an almost entirely fruit-based diet. Reproduction is synchronized, and in this study seven females gave birth during a two week period. Unlike many primate species, young are born undeveloped, even unable to cling to their mothers’ backs, so they must be cared for in nests until they are big enough to travel independently.
The study, published in Behavioral Ecology and Sociobiology, found that females built a number of nests during the gestation period, with some building as many as fifteen. Females gave birth to litters of 2-3 young, and for the first few weeks of life infants were cared for solely by their mothers. Communal nesting, typically involving two litters sharing a nest, began when the young lemurs were six weeks old. Six of the seven mothers nested communally at least once, although the amount of time their young spent in crèches varied. Two of the mothers only rarely or never shared nests. But females who shared nests were able to spend significantly more time feeding than those that did not participate in communal nesting, and time feeding and foraging increased with increasing crèche use. All infants survived until the start of the communal nesting period, but infant mortality was subsequently significantly higher for single nesters than communal ones.
Behavioral observations were combined with genetic data which made it possible to work out whether it was only related lemurs that were assisting each other. The study found that although relatedness and long-term social relationships were positively correlated with the extent of communal nest use, “not all cooperative dyads [two individuals] were related, and not all related dyads cooperated with each other.” The benefits of communal nesting were the same regardless of whether the lemurs were related to each other.
“Kinship may have helped the evolution of cooperative breeding in primates but the mutual benefits may outweigh the costs of helping, irrespective of any family relationships” says Baden, who believes that the current research sheds light on understanding just how communal breeding evolved. “Our results contribute to a growing body of evidence suggesting that kin selection alone cannot explain the extensive cooperation observed in many animal taxa.”
In six years of study, only one reproductive event was observed. Such rare and unpredictable reproduction makes research a challenge. The scientists point out that, despite a relatively small sample size, their study “nonetheless represents reproductive output over 48 lemur-years”. The timing of reproduction is not fully understood, but it is likely that the lemurs respond to environmental cues.
“In 2008, Cyclone Ivan hit. More than 2,000 [millimeters] of rain fell over the course of three days. It’s possible that this somehow signaled the likelihood of a highly productive fruiting year”, Baden told mongabay.com.
Black-and-white ruffed lemurs are classified as Critically Endangered by the IUCN, having suffered a decline of 80% over the last 27 years. Baden fears that their fruit-dependent diet and sporadic reproduction will make them even more at risk in the future. Ruffed lemurs are “among the first animals to disappear when habitats become disturbed or degraded, as large fruiting trees are typically targeted during selective logging” Baden explains. “My concern is that climate change and the erratic climatic variations that come with it might have severe and significant repercussions for ruffed lemur life histories.”
One of the most surprising aspects of the results for Baden was the extent to which female behavior changed during the breeding period. “It really seems like infants are driving sociality in this species. In non-reproductive years, females were almost asocial.”
“It’s fascinating” Baden added, “by having a litter of three infants and then communally rearing those babies, females can essentially make up for two lost years of reproduction. These animals have really perfected their parenting system to adapt to these reproductive lags.”
Baden feels that lemurs are frequently overlooked in discussions of primate social evolution. “Ruffed lemurs are really interesting because they actually share several traits – things like fission-fusion social dynamics and cooperative infant care – with higher primate species that many would consider to be quite socially complex” Baden said. “I think we’re starting to learn that, while lemurs perhaps differ from higher primates in several of their ‘solutions’ to evolutionary problems, they have come up with some really interesting and unusual adaptations that can still inform our broader understanding of primate evolution.”
Reference: Baden A.L., Wright, P.C., Louis E.L., Bradley B.J. (2013). Communal nesting, kinship, and maternal success in a social primate, Behavioral Ecology and Sociobiology. DOI 10.1007/s00265-013-1601-y
I’m excited to be featured on the super cool blog Dinner Table Science! Dinner Table Science has a mission: to get people talking about fascinating facts and exciting discoveries. In their own words, they “want dinner table small talk to be filled up with little amazing things someone learned on the internet that day”. Here’s my post, on the mysterious life of the Brazil nut tree, but I recommend that you also take a look at some of the many other absorbing posts on all aspects of science.
I have some very exciting news for all of my readers – this week my very first guest blogger, Claire Salisbury, comes to Dinner Table Science to talk about some 4-way mutualism in the rain forest! Claire is a biologist with a particular interest in and love of the rain forest. Her first taste of the jungle was in Belize, on an expedition she joined while she was still just in high school, and after that she couldn’t wait to find her way to the ultimate jungle: the Amazon! She’s spent many months in Peru since then, chasing leaf cutter ants and birds, and carrying out research both as an undergraduate student and as a PhD candidate. Now she is a postdoc, and she hopes to study biodiveristy in tropical rain forests, and work to conserve these amazing areas of our planet. To read or subscribe to Claire’s…
View original post 642 more words
This moth, found in the cloudforest in Ecuador (at Bellavista, which I have written more about here), blends in perfectly with its background, even down to the lichen spot mimics on the tips of its wings. The purpose of colour patterns such as these is to make the outline of the moth hard to detect, thus making it difficult for predatory birds to distinguish it against the bark of the tree. The success of the camouflage is a question of life or death for the moth. A moth that is a poor match is more likely to get eaten, and one that is a good match is more likely to live. Therefore the next generation will be dominated by descendents of moths that were successful at blending in. This is natural selection, famously stated (and often misunderstood) as ‘survival of the fittest’, with the most camouflaged moths in this example being the most fit. The predatory birds provide the ‘selection pressure’ on the moth population, which has evolved in response to this pressure to be so well camouflaged.
However, the process is dynamic: the birds are also responding to the moths. A bird who is better able to pick out a camouflaged moth against the tree will be better fed, and better able to raise a brood. So again those most successful (the fittest) will contribute more to the next generation than those less fit. Greater visual acuity will in turn select for better camouflaged moths, and so on, resulting in an ongoing coevolutionary relationship. In evolutionary biology, the ‘Red Queen hypothesis’ relates to cases such as these. The name refers to Alice in Through the Looking Glass, by Lewis Carroll, where Alice is told by the Red Queen that ‘here, you see, it takes all the running you can do, to keep in the same place’.
The main question behind my PhD research is why, and how, are there so many species in the Amazon rainforest. There really is a ridiculous number of species. Hundreds of bird and tree species can be found at single sites, dwarfing the numbers found in whole countries in Europe for example. The Amazon is not alone in being highly biodiverse, many tropical regions harbour vast numbers, but the Amazon and Andean lowlands have the greatest number found anywhere on earth.
It is mind boggling to try and grasp the magnitude of the diversity: whereas you’d be lucky to see one or two dozen bird species in your garden at home, in the rainforest hundreds of birds live in the same patch of forest. Many have had their minds boggled trying to work out why it is that diversity increases as you travel from the poles to the equator. And more still have concentrated on tropical rainforests, enthralled by the conundrum of so many species evolving in the first place, and then being able to coexist.
The particular hypothesis I am interested in is one that has roots in the earliest explorations of Amazonia. Alfred Russel Wallace, now celebrated for his insights into the theory of natural selection, set out in 1848, at 25 years old, to explore the Amazon rainforest. He noticed that some species were found on one side of a river, but never the other. The rivers themselves seemed to be the boundary, the limit of a species’ range. Since then numerous biologists have explored the extent to which rivers may limit species ranges, and more crucially, the extent to which they actually drive speciation (the evolution of two new species from one) or simply limit the distribution of species that have evolved elsewhere.
My PhD tried to unravel a tiny fraction of the story, by looking at how populations of different species are structured across rivers. I was in Peru to get blood samples from my study species, so I could work out from genetic analyses the extent to which populations on opposite riverbanks were connected with each other. If rivers are barriers between populations, meaning that birds on one side very rarely mate with birds on the other, then with a great deal of time, these populations may evolve to become distinct species. The rest of my time was spent behind a desk back home, looking at hundreds of bird range distribution maps, and how they related to the many rivers that run through the Amazon basin.
Birds may seem a daft choice for investigating the ‘river barrier hypothesis’, as they have wings. But many tropical birds are surprisingly bad at flying across open spaces such as rivers. My study species the antbirds prefer to stay in the dark dense understorey, and therefore are some of the most likely to be affected by river barriers.
Although my research questions focus on the evolution of Amazonian diversity, they are part of a much broader set of questions trying to get at the root of how and why species evolve into new species. These PhD students studying coral ecosystems are dealing with the same evolutionary questions, and do a great job of explaining their research. They also convey a little of the frustration in carrying out field and lab work:
This is quite unrelated except as another brilliant example of creative science communication, prizewinning no less, by my talented colleagues at the EGI. Original music by Stuart Noah and choreography by Cedric Tan, with a cast of PhD students…