 |
|
 | |||||||
 |
|||||||
|
HEADLINE SCIENCE: A Toxic Tale Poisonous frogs from two different continents acquire their = toxins=20 the same way =96 by eating poisonous ants. The toxic frogs of Panama and Madagascar may look different = from one=20 another ( Panama=92s Dendrobates pumilio sports stunning = red robes=20 while Madagascar=92s Mantella frogs flaunt flashy oranges = and=20 greens), but their brightly colored bodies send the same message = to=20 potential predators: Stay away =96 I=92m poisonous. Frogs from = both countries=20 secrete toxic chemicals called alkaloids from their skin, which = often=20 prove deadly and distasteful to predators. Research over the past = several=20 decades has shown that Panama=92s poisonous hoppers acquire their = alkaloids=20 by eating ants, but the poison source for Madagascar frogs = remained=20 unknown. Now, Academy entomologist Brian Fisher and Cornell = chemist=20 Valerie Clark, together with colleagues from the United States and = Madagascar, have found that Madagascar=92s Mantella frogs = also=20 acquire their toxins from ants. Like their counterparts in Panama, = they=20 have evolved a way to ingest the poisonous ants without harming=20 themselves. The ants that supply the poison to the frogs in Panama and = Madagascar=20 are not closely related to one another, but they contain many of = the same=20 poisonous alkaloids. Thus, even though the frogs in Madagascar and = Panama=20 live nearly half a world apart from one another, they share 13 = identical=20 poisonous compounds. This, Fisher notes, is a beautiful example of = convergent evolution =96 similar evolutionary pressures in two = different=20 parts of the world have led unrelated frogs to find and sequester = the same=20 poisonous alkaloids in the same way.
|
| ||
|
\n'+
' '
if (menu.bgImageUp) dTag =3D '
\n\n';
}
i=3Dx;
}
if (document.layers) { =09
container.clip.width =3D window.innerWidth;
container.clip.height =3D window.innerHeight;
container.onmouseout =3D mouseoutMenu;
container.menuContainerBgColor =3D this.menuContainerBgColor;
for (var i=3D0; i';
var left =3D 0, top =3D 0, right =3D 0, bottom =3D 0;
left =3D 1 + menu.menuItemPadding + menu.menuItemIndent;
right =3D left + menu.menuWidth - 2*menu.menuItemPadding - =
menu.menuItemIndent;
if( menu.menuItemVAlign =3D=3D 'top' ) top =3D menu.menuItemPadding;
if( menu.menuItemVAlign =3D=3D 'bottom' ) top =3D =
menu.menuItemHeight-menu.fontSize-1-menu.menuItemPadding;
if( menu.menuItemVAlign =3D=3D 'middle' ) top =3D =
((menu.menuItemHeight/2)-(menu.fontSize/2)-1);
bottom =3D menu.menuItemHeight - 2*menu.menuItemPadding;
var textProps =3D 'position:absolute;left:' + left + 'px;top:' + top =
+ 'px;';
if (lrs) {
textProps +=3DitemProps + 'right:' + right + ';bottom:' + bottom + =
';';
dTag =3D "";
dClose =3D "";
}
=09
if(document.all && !window.mmIsOpera) {
item =3D '
\n' + dClose);
else content +=3D ( dTag + dText + dClose);
if (lrs) {
l.document.open("text/html");
l.document.writeln(content);
l.document.close();=09
content =3D '';
theStat +=3D "-";
tsc++;
if (tsc > 50) {
tsc =3D 0;
theStat =3D "";
}
status =3D theStat;
}
countItems++; =20
}
if (lrs) {
var focusItem =3D new Layer(100, body);
focusItem.visiblity=3D"hidden";
focusItem.document.open("text/html");
focusItem.document.writeln(" ");
focusItem.document.close();=09
} else {
content +=3D ' \n';
content +=3D '
\n ' + item + =
'
';
} else if (lrs) {
item =3D '' + =
item + '
';
} else {
var hitem =3D null;
if( menu.menuItemHAlign !=3D 'left' ) {
if(window.mmIsOpera) {
var operaWidth =3D menu.menuItemHAlign =3D=3D 'center' ? =
-(menu.menuWidth-2*menu.menuItemPadding) : =
(menu.menuWidth-6*menu.menuItemPadding);
hitem =3D '';
item =3D '';
} else {
hitem =3D '';
item =3D '';
}
} else hitem =3D null;
}
if(document.all && !window.mmIsOpera) item =3D '';
var dText =3D '\n'
+ '';
if (childMenu) content +=3D ( dTag + dText + '