
The Hermit's Call
There's always been
Someone
in these woods.
Look for what
I am
You always have.
—Bernard Quetchenbach




Mama Miti, written by Donna Jo Napoli, illustrated by Kadir Nelson (ages 4-8)
Wangari’s Trees of Peace, by Jeanette Winter (ages 4-8)
Planting the Trees of Kenya: the Story of Wangari Maathai, by Claire A Nivola (ages 4-8)
Unbowed, A Memoir, by Wangari Maathai (adult biography)
by Neil Losin (Note: Losin recently won the NESCent blogging competition for a travel grant to Science Online 2011) Imagine that you’re considering having children. Upon
visiting a genetic counselor, you discover that you and your partner both carry
the same rare, recessive genetic mutation. While neither you nor your partner
shows any symptoms, there is a 25% chance that your child will suffer from a
debilitating genetic disorder. Then imagine that the counselor tells you that
new embryo-selection technology can ensure that you’ll have a healthy baby;
with early-stage genetic testing, doctors can pick a candidate embryo with the
right genes and discard the others. This day is probably closer than you realize,
and the ethical issues surrounding such technology will no doubt be
contentious; some will argue that we shouldn’t “play God” with our
reproduction. But there is a bird in Australia that does just that. The Gouldian Finch (Erythrura gouldiae) is an almost
comically beautiful bird of open woodlands in northern Australia, but
ironically, it is perhaps better known as the bird featured in the ViewSonic
logo — a fitting emblem for a company that sells LCD displays. As if its
rainbow-colored body plumage weren’t spectacular enough, the Gouldian Finch
comes in three head-color morphs: black, red, and yellow. These morphs occur
side by side in natural populations, although the yellow-headed morph is quite
rare. Dr. Sarah Pryke, a
behavioral ecologist at Macquarie University in Sydney, studies Gouldian
Finches, focusing on how the common red- and black-headed morphs coexist in
nature. Gouldian Finches don’t mate indiscriminately with respect to
head color. Instead, red-headed females tend to pair with red-headed males, and
likewise for black-headed individuals. Biologists call this pattern assortative
mating. But what does a Gouldian Finch gain from being choosy about its mate’s
head color? As it turns out, it gains quite a lot. In a paper published
in the journal Evolution last year, Pryke showed that offspring of mixed pairs
(e.g. a red-headed female paired with a black-headed male, or vice versa) were
severely compromised compared to offspring whose parents both belonged to the
same head-color morph. Mixed-morph eggs were less likely to hatch and, once
hatched, mixed-morph chicks were more likely to die in the first 140 days of
life. Among mixed-morph offspring, female embryos and chicks were especially
likely to perish. To understand why, you need to know a little bit about bird
genetics. In humans, females possess two X chromosomes, while males
have an X and a Y. This makes males the heterogametic sex – “heterogametic”
because they have two different sex chromosomes. In birds, however, the
situation is reversed; males are ZZ and females ZW. Back in 1922, evolutionary
biologist J. B. S. Haldane showed that when a genetic incompatibility existed
between parents (e.g., the male and female belonged to different species, or to
different morphs within a species), heterogametic offspring typically suffered
the greatest viability or fertility disadvantage. This trend became known as Haldane’s
Rule, and although its genetic mechanisms are still debated, Haldane’s Rule
holds true in most animals. A female Gouldian Finch, therefore, should pair with a male
of her own color morph if she can. But if she can’t find a male with her head
color, she may be forced to pair with a less desirable male — in fact, as many
as 30% of wild Gouldian Finch pairs are mixed-morph pairs. In theory, one way a
female finch could make the best of this unfortunate situation is to produce
mostly male chicks, since male offspring of mixed-morph pairs are far more likely
to survive than female offspring. But can a female Gouldian Finch control the
sex ratio of her brood? Pryke tested this idea in an experiment published last year
in the journal Science. She paired females with red- and black-headed males,
and examined the resulting offspring. Amazingly, females paired with mates of a
different head-color morph produced significantly male-biased broods — 82%
male, on average! Does this prove that females can manipulate the sex ratio of
their offspring? Not quite… Male-biased broods could result from female embryos
dying early in development, and this wouldn’t constitute sex ratio manipulation
on the female’s part. To resolve this uncertainty, Pryke painted the heads of
red-headed males black, and paired these phony black-headed males with red- and
black-headed females. In this situation, black-headed females produced broods
with an unbiased sex ratio, despite their genetic incompatibility with their
mates. And red-headed females, mating with compatible males painted to look
like incompatible males, produced more sons than daughters. Sure enough, in an
effort to maximize their reproductive success, females were actively
manipulating the sex ratio of their brood. And they were doing so based on
nothing but the appearance of their mates! The physiological mechanism by which females accomplish this
feat is not yet known; this is one of many unanswered questions about these
remarkable birds. But our opportunities to answer these questions are
dwindling. Gouldian Finches once occurred throughout northern Australia, but
they have declined dramatically in the last half-century, mostly because of
large-scale habitat alteration by humans. Now only about 2,500 Gouldian finches
remain in the wild. Dr. Pryke’s experiments often involve captive birds,
minimizing impacts on remaining wild populations. Studying the reproductive biology of an Australian finch
might seem an esoteric pursuit. But in evolutionary biology, lessons learned
from one species can be applied to others. And if the Gouldian Finch is any
indication… Well, maybe “playing God” isn’t so unnatural after all. References:
Pryke, S. R. and S. C. Griffith. 2009.
Postzygotic genetic incompatibility between sympatric color morphs. Evolution
63(3):793-798. Pryke, S. R. and S. C. Griffith. 2009. Genetic
incompatibility drives sex allocation and maternal investment in a polymorphic
finch. Science 323(5921):1605-1607. N.B. Please do not interpret this post as an endorsement of
eugenics. It is not. To view the colorful images of these beautiful birds go to: http://www.daysedgeproductions.com/neil.blog/?p=562



The practitioner looked the part of a Buddhist monk, with shaven head and maroon robe. Rather than sandals he wore an ordinary pair of street shoes. The wingtips seemed to clash with the rest of his outfit, but I suppose this footware made more sense in the climate of Ulan Ude. His dark eyes had a piercing quality, giving the impression he could use his vision to penetrate skin and bone to root out sickness. He was introduced and we shook hands. He bowed slightly and I awkwardly bowed to him. With a sweep of his hand he asked me to be seated. I sat in a straight-backed chair and he seated himself opposite me on a sofa.
