Understanding the evolution of nocturnal mammals by studying their extinct relatives

Humans are diurnal. We sleep at night and are active during the day. (That isn’t to say that I feel particularly diurnal most mornings, given that my alarm has to make it through a few snooze cycles to wake me up and coffee is the only thing keeping me from napping under my desk at work.) Most mammals, though, don’t share our ostensible predilection for daylight; only 20% of mammal species are diurnal like us. Of our mammalian relatives, nearly 70% are nocturnal. The rest are crepuscular (active at dawn and dusk) or cathemeral (active during both day and night).

A tarsier (Flickr: )

A tarsier from Borneo. (Flickr: Erwin Bolwidt)

Mammalogists like myself often think nocturnality is a particularly mammalian thing because—let’s be honest here—nearly all of the coolest nocturnal vertebrates are mammals. How can you compete with the likes of tarsiers, vampire bats, leopards, and—strangest of them all—the aye-aye? I’ll throw the ornithologists a bone and acknowledge the enduring awesomeness of owls, but they are the odd birds out in a group that’s mostly diurnal.

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Friday coffee break: Potato blight, phylogenetics 101, and venemous FAQs

2010.03.24 - Breakfast

From Amy: Analysis of DNA from museum specimens has identified the pathogen responsible for the Irish Potato Famine of 1845.

…the strain that changed history is different from modern day epidemics, and is probably now extinct.

From Sarah: Digital visualizations may be making it easier to teach students how to understand evolutionary trees. As in, for instance, this visualization of the phylogeny of birds.

Taxa appear as dots whose relative spatial distances are determined by phylogenetic relatedness. When reading a cladogram, the intuitive impulse to infer relatedness from spatial distance between branch tips inevitably leads to error. The DEM works with this intuition, rather than against it.

From Jeremy: Hard as it may be to believe, this FAQ about dealing with the bites of venemous snakes just keeps getting better as you go down.

On Molecular Genetics and the Origin of the Polar Bear.

Polar bear

Understanding the history of species is critical to understanding evolutionary processes and for making predictions about how biodiversity will fare in a rapidly changing climate. Information about how species are related (phylogeny) and how their populations have responded to past climate change (historical demography) can inform us about the conditions under which they have evolved and adapted, and how they might respond to changes currently under way.

Modern scientists get at these questions by examining two types of data: the fossil record and patterns of DNA sequence variation. The fossil record is relatively straightforward. You find a fossil in location X. You identify it as species Y and you use some method to (e.g. radiocarbon dating) to infer it was there at time Z. Making inferences from DNA sequence variation, by contrast, involves complex, computer-intensive statistical analyses, and the field is in a state of tumultuous, rapid advance.

A fascinating case study that involves the integration of fossils and DNA sequence data, and illustrates the ways in which rapid statistical advances are changing our understanding of species’ evolutionary histories is that of the origin of the polar bear (Ursus maritimus).

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Timing is everything: In which an intimate relationship turns out to be rather one-sided

Euglossine bee collecting scent

A euglossine bee collects scent from an orchid

Orchids have some of the most remarkable pollination relationships of all the flowering plants. Their flowers are adapted into wild shapes for placing packets of pollen on precisely the right part of a pollinator’s body, and many species attract pollinators with lures that are somewhat kinkier than simply offering nectar—such as mimicking a female pollinator’s scent and appearance, to dupe males of the species into, er, making intimate contact.

ResearchBlogging.orgA somewhat less exploitative orchid-pollinator interaction involves offering scent compounds to euglossine bees. Male euglossines collect scents from their environment—things that smell pleasant to humans, as well as things that really don’t—in special structures on their legs. It’s thought that they use the collected scents to attract females. Three large, diverse groups of orchids transport pollen by generating bee-attractive scent compounds, then saddling any bee who comes to collect the scent with a packet of pollen.

From the outside, this looks like a mutually beneficial relationship. The bees get their perfume, the orchids a pollen transporter. Over millions of years, such an interaction should lead bees and orchids to diversify together—when one orchid species splits into two, the bees that collect scent from them might very well speciate with the orchids. A recent paper in Science provides pretty good evidence that, over the long history of euglossines and the orchids that perfume them, the interaction hasn’t worked like that at all.

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