I saw this ScienceDaily report earlier today and thought: "What's new?" I recall a study with similar conclusions from just a couple of months ago, and even that was not that new - I used the example in teaching about 5-6 years ago (then dropped the example as the literature got more and more contentious).
But a few minutes ago, Afarensis posted about this and cleared it up for me - the previous study was from zoos and this one is from the wild. Also, the new study incorporates ontogenetic data - the effects of age.
So, the size and color of the lion's mane is not driven by sexual selection, but by thermoregulatory needs and it seems it takes some of the lions quite a lot of time to grow a big mane:
According to the overall findings of the study, wild lions generally develop manes in accordance with local climate regimes. In Equatorial east Africa, climate is determined by elevation. Thus lions with the most profuse manes occur at the upper limit of their altitudinal range, while similar aged males in the lowest and warmest environments like Tsavo typically carry only modest or scanty manes.However, the authors also found, paradoxically, that the majority of lions in regions like the greater Tsavo ecosystem (which is famed for its "maneless" lions), did appear to acquire respectable manes, eventually, contrary to most recent popular and scientific accounts of the lions from that region.
"We knew about the climate/elevation correlation since we were the first to publish those preliminary results in GEO 2001, but this new development really threw us for a loop," says Tom Gnoske, of the Field Museum's Zoology Department and senior author of the paper. "However once we analyzed all of the statistical data we found a very strong correlation linking increased age and continued mane development, a significant variable ignored by all previous authors."
Statistical data from this study demonstrates that the onset of mane development in lions living below an altitude of 800 meters on or near the equator is delayed, and that the "rate" or speed at which a mane develops in lions from those regions is slower on average than that of the more familiar lions living in the cooler, higher altitudes of the greater Serengeti ecosystem and elevated plains extending northward, such as the Athi/Kapiti Plains and beyond. According to the researchers, in environments like Tsavo that have especially high minimum temperatures throughout the year, lions in their reproductive prime--from the approximate ages of five thru seven years old--usually possess only very marginally developed manes, while most of the more thoroughly maned lions in those same territories were already well past their breeding prime.
Furthermore, the researchers found compelling evidence indicating that manes of lions from all populations continue to develop long after a lion has achieved sexual maturity, such that the best-maned lions in any region are typically of an older age class. "Usually lions are well past their breeding prime when they carry the most extensive and often darkest manes of their lives," explains Kerbis Peterhans Adjunct curator of Mammals at The Field Museum, Professor at Roosevelt University, and co-author of the study.
Read the rest...
