Under selection, an endangered species runs low on evolutionary “fuel”

Atlapetes pallidiceps

A pale-headed brushfinch, Atlapetes pallidiceps. (Wikimedia Commons:Aves y Conservación/NBII Image Gallery)

The pale-headed brushfinch, Atlapetes pallidiceps, is a conservation success story, or at least the first chapter of one. The birds were thought to be extinct, until a 1998 survey [PDF] of Ecuador’s Yunguilla Valley found four nesting pairs, and observed them foraging for insects and fruit. Following that rediscovery, the Fundacion Jocotoco secured a reserve encompassing the brush finches’ known territory, and took steps to control brood-parasitic cowbirds that were threatening them. Now, the population is five times bigger, with as many as 200 of the birds living in the reserve.

Have the brush finches’ rebounded enough to secure their population for the future? Populations that decline so precipitously can lose genetic variation, and may not regain it even if their numbers increase again. With reduced genetic variation, species that have undergone such a “population bottleneck” event may be unable to respond to natural selection imposed by disease or changing environments.

Continue reading

Tracing the start of monarch butterflies’ epic journey, in their genes

Monarch butterflies (Danaus plexippus) are among the most widely recognized wild creatures in North America. Their distinctive orange-and-black wings, which warn predators that the butterflies are chock full of toxins from the milkweed they eat, make them easily spotted in backyard flower beds. They’re also known for a massive annual migration, flying thousands of miles between wintering colonies in central Mexico and summer sites across the United States and Canada. More recently, it’s been discovered that female monarchs infected by parasites respond by laying their eggs on food plants that can prevent the parasite from infecting their offspring.

Monarchs are also one of the more visible victims of the massive changes humans have made to the world around us. Increased conversion of farmland to corn production has reduced the supply of milkweed, the butterflies’ only food plant, across much of the Midwest. It’s gotten so bad the number of monarchs making the annual migration back to Mexico hit a record low last year, and while things were better in 2014, a nationwide campaign to encourage planting of milkweed in home gardens is only beginning.

For all our familiarity with monarchs, we’ve known remarkably little about their evolutionary history. That’s changing rapidly now, as evidenced by a paper published last month in the journal Nature, which uses a big new genetic dataset to trace the origins of some of the monarch’s most distinctive features.

Continue reading

Random Natural History: Valley Oaks and their Galls.

Ok, time for a short bit of natural history. I live in the Sacramento Valley in northern California. The dominant tree species (outside of urban areas) seems to be the Valley Oak (Quercus lobata). Now, there aren’t a whole lot of trees in the valley, so it’s pretty lucky that Valley Oaks are fairly spectacular.

Valley oak (Quercus lobata) on Joseph D Grant County Park Canada de Pala Trail

They are also little ecosystems unto themselves. The first thing most people notice about them are oak apple galls, so called because they bear a disturbing resemblance to (rotting) apples.

"Oak apple" galls of California Gall Wasps (Andricus quercuscalifornicus, Cynipidae, Hymenoptera) on Valley Oak (Quercus lobata, Fagaceae)

Trees can often be so laden with them that they actually look like cultivated apple trees. The galls are woody, though, not squishy like actual apples. What is a gall, you ask? Good question. A gall is essentially a plant tumor. In many cases (as here) galls are caused by insect parasites. An adult insect lays eggs in the tissue of a plant, and those eggs release hormones that induce the plant to form the gall. Galls can provide food and shelter for their hosts until they are ready to mate and lay new eggs. Galls can be quite complicated structures, the result of parasites evolving very refined control over their hosts over time. As a result, galling insects can frequently be identified by their galls alone. Oak apple galls are caused by a wasp, Andricus quercuscalifornicus, but are exploited by a constellation of at least 20 other arthropods that feed on the galls, A. quercuscalifornicus, and each other.

These aren’t the only galls associated with the Valley Oaks. There are at least two more. One of which is fairly bizarre and the original inspiration for this post: the California Jumping Gall. This gall is also caused by a wasp, Neuroterus saltatorius. In contrast to the oak apple galls, these galls are tiny, only about a millimeter across. What they lack in size, however, they make up for in quantity. These galls form on the undersides of oak leaves by the hundreds of thousands. When they mature, they drop off the leaves, wasp larva still inside. Once on the ground, they start “jumping”. The larvae violently fling themselves around inside the gall, presumably to try to move it into a sheltered spot where they can finish out their life cycle and emerge the following spring to lay new eggs.

The galls are dropping now in my neighborhood, and the result is that sidewalks and gutters under valley oaks appear to be full of jumping grains of sand. It’s a pretty weird sight:

Here’s a link to another video:

ARKive video - California jumping gall wasp - overview

Well, that’s all I’ve got for now. I’ll end on another photo of an amazing Valley Oak.

Quercus lobata VALLEY OAK/ROBLE

Scientists at work among the Joshua trees

When he’s not dismantling racist pseudoscience, Chris Smith studies the evolutionary ecology of species interactions. Willamette University sent along a videographer on Chris’s last field trip to study Joshua trees and the moths that pollinate them in central Nevada, and the result is now posted on Vimeo. It’s mainly geared toward showcasing how Willamette undergraduate students participate in the fieldwork, but I’d say it makes the desert look mighty good, too.

When a bad bird goes good … and then bad again.

cuckoos

Brood parasites are definitely the bullies of the avian world.  They lay their eggs in the nests of other birds, sometimes destroying the host’s own eggs or just waiting for their nestlings to do the dirty work after they hatch.  They then outcompete any surviving host nestlings for food, while the poor host parents are worked to the bone to feed the monstrous nest invader.

In spite of the steep costs of nest parasitism, most avian host species do not have effective mechanisms for detecting and removing brood parasites from their nests.  So, why don’t mama birds notice they have a GIANT intruder in their nest and carry out some infanticide of their own?  One hypothesis is that the cost of a mother bird making a mistake and pushing the wrong baby out (i.e. her own) outweighs the benefit of developing such a behavior.

This week in Science, Canestrari et al. published evidence for another hypothesis – that sometimes, it might actually be good to have your nest parasitized.

Continue reading

Living at the edge, range expansion is a losing battle with mutations

Environments can vary substantially in habitat quality, local population abundance, or carrying capacity. Under some climate change scenarios, new, higher quality habitats become available along the margin of a species’ range (e.g. higher latitudes or altitudes) (Thomas et al 2001). These new habitats may be able to support larger population sizes. Factors of demography, evolution, and qualities of the abiotic and biotic communities all interact to determine where a species is found and may influence the ability of a species to expand its range. New research is building genetically explicit models in order to understand how the interplay of these different factors influence evolutionary changes,

Wordle of Peischl et al 2013

The authors of a recent study focus on how the interaction of the demographic process of range expansion changes the way that natural selection favors beneficial and deleterious mutations (Peischl et al 2013). Using both computer simulations as well as mathematical approximations, the authors find that at the range margins, individuals carry a substantial load of deleterious mutations.

Continue reading

The cost of attracting pollinators is … attracting everyone else

Flowers of Dalechampia scan dens, with key measurements indicated. Figure 1 of Perez-Barrales et al. (2013).

Flowers of Dalechampia scandens, with key measurements indicated. Figure 1 of Perez-Barrales et al. (2013).

Flowers that rely on animal pollinators to remix their genetic material have evolved a tremendous diversity of strategies for attracting those pollinators—from beguiling scents to elaborate visual displays to pretending to be a lady pollinator.

But there’s a downside to making a big, showy display to attract pollinators—you might also attract visitors who have less helpful intentions than gathering up some pollen and moving on to the next flower. Showy flowers might attract animals that steal the rewards offered to pollinators—or they might attract animals that eat the flowers themselves, or the developing seeds created by pollination. So the evolution of attractive floral displays might very well be a compromise between attracting the right visitors, and attracting the wrong ones.

Continue reading