Many Like It Hot 



Warmth and water do more than just make 

 plants grow quickly. In the tropics, it 

 seems, evolution itself proceeds at a faster 

 pace than it does in temperate zones. 

 Shane Wright, a biogeographer at the Uni- 

 versity of Auckland in New Zealand, and 

 two colleagues studied forty-five pairs of 

 closely related plant species. One member 

 of each pair is from the tropics; the other 

 hails from a temperate clime. To determine 

 the rate of evolutionary change, the team 



Hawaiian Islands record the track of the 

 Pacific plate over a geologic "hotspot." 



souri in Columbia, have confirmed mounting 

 evidence that at least one of those assump- 

 tions must be wrong. The hotspot traces, 

 they discovered, aren't where they should 

 be if both assumptions are correct. 



The geologists' analysis indicates that 

 though there has been no major reorgani- 

 zation of the plates in the past 40 million 

 years, the hotspots have been moving. 

 The good news is that they seem to be 

 moving in the direction opposite to that 

 of the plates that overlie them. Thus 

 geologists need not abandon hotspot 

 traces to make inferences about the 

 movements of the Earth's crust. (Geology 

 34:465-8, 2006) —N.W.A. 



compared a section of genetic code in the 

 members of each pair with the correspon- 

 ding section in a third species, the pair's 

 closest relative. The tropical plants, Wright 

 and his colleagues discovered, have 

 evolved twice as fast, on average, as their 

 temperate cousins. 



Compared to cool, dry ecosystems, 

 warm, wet ecosystems grow enormous 

 numbers of organisms, which tend to have 

 high metabolic rates. Wright thinks the 

 higher productivity and faster metabolisms 

 raise the likelihood of genetic mutations. 

 More frequent mutations should lead to 

 more rapid evolutionary change. Faster 

 evolution, in turn, may cause species to 

 proliferate. If so, Wright's discovery may 

 explain the tremendous diversity of the 

 tropical forests. {PNAS 103:7718-22, 2006) 

 — Krystin N. Mementowski 



Who Needs Sex? 



Sex is an evolutionary conundrum. If the point 

 of sex, as most biologists believe, is to propa- 

 gate your genes, parthenogenesis, in which 

 females' eggs develop into young without fer- 

 tilization by males, would seem to beat sexual 

 reproduction hands down. Why split your ge- 

 netic legacy with a second parent? 



Yet the cost of sex doesn't stop 99.9 

 percent of known animal species from 

 reproducing sexually. To understand why, 

 biologists study the evolutionary history of 

 the other 0.1 percent. Four evolutionary 

 biologists, led by Michael Kearney of the 

 University of Melbourne in Australia, studied 

 two parthenogens in the deserts of 

 Australia: a grasshopper (Warramaba virgo) 

 and a gecko (Heteronotia binoei). In both, 

 parthenogenesis evolved as a result of 

 hybridization between sexual ancestors. And 

 in both, parthenogenesis probably arose not 

 once but twice. 



Kearney's team sequenced 

 DNA from the parthenogenetic 

 grasshoppers and geckos, then 

 compared it to that of their sexual 

 ancestors, which are still alive to- 

 day. The team discovered that the 

 first parthenogenetic populations of 

 both grasshoppers and geckos had 

 historically expanded their ranges 

 at the same time and in a similar 

 pattern. So had the second. Dur- 

 ing the same period — late in the 

 Pleistocene epoch, which lasted 

 from 1.8 million until 10,000 years 

 ago — the Australian desert under- 



Walkabout 



m 



About 5,000 years ago, after nearly thirty 

 millennia in Australia, Aborigines began 

 traveling a great deal throughout the conti- 

 nent and sharpening their tool-making 

 skills. Was it a baby boom that prompted 

 their cultural transformation, as some inves- 

 tigators contend, or something else? A new 

 study indicates that a turn in the weather 

 may have been part of the story. 



Chris S.M. Turney and Douglas Hobbs, 

 both archaeologists at the University of 

 Wollongong in Australia, tracked the 

 Aborigines' activity of the past 12,000 

 years from the dates of 710 archaeological 

 samples — charcoal from fires and discarded 

 shells — that were discovered throughout 

 the northeastern state of Queensland. They 

 then compared the pattern of activity to 

 published geological records of the El Nino 

 phenomenon, in which warming of the cen- 

 tral and eastern equatorial Pacific Ocean 

 alters weather patterns around the globe. 



Five thousand years ago El Nino began 

 to act as it does today: its frequency and 

 severity increased and it brought periods 

 of intense drought to northeastern 

 Australia. Turney and Hobbs discovered 

 that the start of the new El Nino pattern 

 coincided with a boost in Aboriginal activi- 

 ty across Queensland's inland countryside. 

 Subsequent spikes in activity were also in 

 sync with periods of intense weather 

 caused by El Nino. 



The archaeologists think drought may 

 have forced Aborigines to develop better 

 tools, roam farther to hunt, and explore 

 new areas in search of scarce necessities 

 for survival. {Journal of Archaeological 

 Science, in press) 



— Edyta Zielinska 



went a series of expansions and contrac- 

 tions. Kearney thinks the shifting desert 

 habitat probably brought isolated popula- 

 tions of the animals' sexual ancestors into 

 contact long enough for their asexual hy- 

 brid offspring to become established. 

 Parthenogenetic reproduction might be ad- 

 vantageous in harsh climates where mates 

 are hard to find. In more comfortable envi- 

 ronments, however, the genetic diversity 

 that sex bestows may outweigh the costs 

 of sharing your genes. {Molecular Ecology 

 15:1743-8,2006) —N.W.A. 



Warramaba virgo, a grasshopper that 

 reproduces without sex 



September 2006 natural history 13 



