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2017年06月28日 23:34:14来源:69热点

A new study could now help shed light on the matter. Stefan Lüpold, a new member of the Depart-ment of Evolutionary Biology and Environmental Studies, University of Zurich, and his colleague John Fitzpatrick, University of Stockholm, compared the influence of sperm competition on the evolution of sperm in 100 mammalian species. Unlike previous studies, however, they didn't just consider sperm length, but also the number of sperm per ejaculate, which is important as the resources available for sperm production need to be shared between sperm size and number. In other words, the longer every individual sperm, the fewer of them a testicle of a certain size can produce. Earlier studies sug-gested that the number of sperm might be just as important as sperm length, if not even more so. After all, the more sperm a male fields against his competitors, the greater the likelihood that one of them will win.。

  • The study, ;Assessing the Risk of Persistent Drought Using Climate Model Simulations and Paleoclimate Data,; was also co-authored by Julia E. Cole, David M. Meko and Jonathan T. Overpeck of University of Arizona; and Gregory T. Pederson of the U.S. Geological Survey.。
  • The opposition has praised the swift transition to Mr Mahama, saying it showed Ghana was a mature democracy.。
  • In the current issue of the journal PLOS ONE, researchers at Michigan State University reveal that these color-coded communiqués evolve over time through gradual steps. Equally interesting, the scientists show how drab-colored, oft-eaten prey adopt garish(过分鲜艳的) colors to live long and prosper, even though they aren't poisonous, said Kenna Lehmann, MSU doctoral student of zoology.。
  • Bats are not as stereotyped when they hunt as previously believed. New research shows that these flying mammals are capable of making ultra-fast decisions about how to attack their prey -- or maybe even call off the attack. It takes only milliseconds. Bats use echolocation for orientation. They emit ultrasonic sounds, which hit potential prey nearby, sending an echo back to the bat. From this echo the bat can define where the prey is and attack it. A new study has examined how hunting bats react when approaching their prey. The study concludes that bats are capable of gathering information from the environment and process it surprisingly fast in order to determine how to carry out the attack or maybe call it off.。
  • ;When we placed the sponges in our lab, they continued to breathe and grow even when the oxygen levels reached 0.5 per cent of present day atmospheric levels,; says Daniel Mills.。
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