I’m afraid I probably won’t be writing any long or especially informative posts today. Earlier I visited to zoo where I had a chance to feed the giraffes and see a number of other animals (pictures will be up as soon as I get transfer them to the computer), and I’ve spent my time since trying to finish off A Primate’s Memoir. This evening looks booked up as well, but hopefully tomorrow I’ll get to share a bit of what I learned (or at least transcribe some thoughts about Sapolsky’s excellent book).
Good news everyone! I got the wireless connection to work at the house I’ll be staying in for the next week (+), so you can expect plenty of new material as I try and dig myself out of the avalanche of books I’ve brought upon myself. Tonight, however, I’m going out to see Ratatouille; I can never say no to a Pixar feature.
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Categories : Birds, Housekeeping, Movies
Just in case you didn’t get your extinct bird fix from my giant-penguin post, there’s plenty more news to go around. Greg Laden tipped me off to a gorgeous photo of the Recurve-billed Bushbird (Clytoctantes alixii), a bird that was once thought to have gone extinct. According to the National Geographic article, this bird was thought to have died out in 1965, but reappeared in 2004, although it has been seen seldom since. I’ll have to consult my copy of Errol Fuller’s Extinct Birds for more when I get home.
Perhaps even more momentous is the recovery of Dodo (Raphus cucullatus) remains from a cave on Mauritius, perhaps good enough to yield some DNA for study. The skeleton was in relatively good condition, although it doesn’t appear that it will be mounted or put on display (the only known soft tissue remains were saved from destruction in one of the most famous tales of academic heroism, and now reside in the Oxford University Museum of Natural History). Unfortunately Yahoo!News is not well-known for its excellent reporters, so details are scant at best. It’s definitely be something to keep an eye on, though.
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Categories : Birds, Extinction
For the next 9 days I’ll be petsitting and may or may not have access to the internet during that time, so whether or not I’ll be able to post anything new this weekend is anyone’s guess. You’ve got plenty to digest between giant penguins and deer sexual selection, and I know I usually don’t come up with anything that great on weekends, but I figured I would just let any readers know. It’s really funny how stat counters follow trends, especially in relation to ScienceBlogs (and especially Pharyngula). When SciBlings is having a slow day, I almost always have a slow day as well, and every weekend my stats do a bit of a nosedive only to resurface Monday, keep moving up through Thursday, only to taper off again. I’ve been getting many more visitors over the past few weeks so the counter shows less of a pattern, but previously my stat counter featured a few peaks and troughs of nearly the same amplitude and frequency.
Anyhow, yesterday Feduccia’s The Origin and Evolution of Birds, Romer’s Vertebrate Paleontology, and Quammen’s Song of the Dodo all arrived so I have no reason not to dig into at least one of them (more books probably coming today, and I’m about halfway through A Primate’s Memoir). So much to learn, so little time…
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Categories : Books, Housekeeping
I always get a little bit antsy when I see morning news reports about a new study appearing in Nature, Science, or some other journal, not having access to the actual paper until sometime later in the day. This past week, however, the mass-media slipped up a bit in this regard; they announced a new paper in the Proceedings of the National Academy of Sciences about two huge, extinct penguins on Tuesday, but the paper itself has only just now become available.
Art by Kristin Lamm. From right to left; Icadyptes salasi, Spheniscus humbolti (extant Humbolt Penguin), and Perudyptes devriesi
The reason this particular paper is so significant (other than 5-foot-tall penguins being utterly cool in and of itself) is that the prevailing hypothesis for penguin evolution was that they originated in cooler, southern latitudes and eventually made their way up to warmer areas like Peru, the Galapagos, etc. after temperatures during the Cenozoic began to cool. In fact, the Eocene (the time period in which the two new penguin species pictured above lived) experienced a temperature spike that threw various systems out of whack and contributed to the extinction of many groups of animals, including mammals. At the onset of the Eocene, there was a sharp thermal spike known as the Paleocene-Eocene Thermal Maximum, following by an overall rise in temperature before cooling down, and looking at the overall trend the world was much warmer during the time of the giant penguins than it is now, reversing the notion that penguins could only advance as far north towards the equator as cold temperatures would allow.
Analysis of the two penguins (there are also species yet to be identified from the same site, so expect more from Peru in the future) shows that they are not the ancestors of living penguins, belonging to the Order Sphenisciformes but outside the Family Spheniscidae, the authors citing the radiation that produced living groups taking places approximately eight million years ago during the Miocene. While much of the mass-media has focused on the “giant” size of Icadyptes, it should be noted that Icadyptes is only one of many known large, extinct penguin varieties, the largest yet known being Anthropornis nordenskjoeldi from Seymour Island and New Zealand, other examples being Pachydyptes ponderosus and Palaeeudyptes klekowskii.
Icadyptes is notable amongst its nearly equally-sized relatives for another reason; we wouldn’t expect to find such a large penguin in such a warm climate. While a foraminiferan indicative of warm-water has been found in association with the giant Pachydyptes, it was generally assumed that penguins followed “Bergmann’s Rule.” Bergmann’s Rule essentially states that among warm-blooded animals, we should expect body mass to increase with increasing latitude (hence, colder climates). This rule seems to work not only across species, but within species as well, working on the inherent plasticity of the animals to vary their size (i.e. wide-ranging animals are usually larger in the far north or south than close to the equator). Icadyptes gives “the flipper” to Bergmann’s Rule, being a warm-blooded bird in a hot environment of equal size to contemporaries from cooler latitudes, but there are exceptions to every rule.
The general reason why we observe Bergmann’s Rule is because of body heat; if you live in the cold you want to retain it, which large body size allows you to do, and in hot climates you don’t want to overheat, so it behooves you to be small and thus give off plenty of heat. Bob Bakker provides perhaps the best illustration of this in The Dinosaur Heresies; if you have to spend the night in a zoo and want to stay warm, should you snuggled up to one elephant (and remember, elephants are large and do live in hot climates, also “in violation” of the Bergmann’s Rule) or cover yourself with 100 bunny rabbits? The rabbits, although not even coming close to the mass of the elephant, radiate more heat, and while I think 100 is a bit excessive (I don’t want to toast in my sleep), you’ll be far warmer under their mass of fur than up against the wrinkly skin of an elephant. It is therefore apparent that something else is at work with Icadyptes; either there were patterns of upwelling that kept things cool enough for them (as in the case with Galapagos penguins today), or they were somehow otherwise adapted to keep their large body size without overheating in the equatorial region.
Overall, I am probably more excited about this find than I was about Gigantoraptor, and I actually enjoyed reading the PNAS paper (you need to be up on your anatomy to get the most out of the species descriptions, but otherwise it was easily accessible), and it seems to be a rare joy to find a paper that is both important and able to keep me engaged. I can’t wait to see what else has come out of the strata in Peru, and hopefully there can be a greater collaboration between paleoclimatologists, paleontologists, ecologists, and others to find out why there were giant penguins in the very last place we would expect to find them.
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Categories : Birds, Climate Change, Ecology, Evolution, Paleontology
Female White-Tailed Deer (Odocoileus virginianus), taken in Hopewell, NJ
July 18th Update: LiveScience has caught onto the Nature paper and has a short article here.
A new Nature paper entitled “Sexually antagonistic genetic variation for fitness
in red deer” (Foerster, et al., 2007) has some very interesting implications for fitness selection; the most fit males may not produce especially fit female offspring, and the most fit females may not produce especially fit male offspring. While it seems to be “common sense” that the most powerful, impressive male will father the strongest offspring, male and female Red Deer (Cervus elaphus) behave differently, and what makes a fit male does not make a fit female. The authors put it this way in their introduction;
Males compete intensely for matings during the short annual rut but do not invest in offspring care, whereas female maternal investment extends over a long period during each reproductive event. Consequently, male and female life histories are likely to be under divergent selective pressures, and a particular genotype may have very different effects on fitness in males than in females.
Males have to carry around a good deal of weight on their heads and be physically strong (thus the most “masculine” males being favored when it comes to breeding), while females have to raise the young all by themselves, better mothers leaving more offspring. This is not a revelation, but I have to admit that I never really considered the differing selective pressures between males and females in a population.
The primary trend pointed out in the paper is that females who mate with robust males typically produce daughters who do not leave as many offspring; we can’t simply say that the father has “good genes” offspring of both sexes will benefit equally from them. Likewise, it is not apparent if robust fathers leave especially productive sons; the deer are polyandrous, a few males mating with most of the females, and so many (if not most) of the males never successfully mate or leave any offspring.
An itchy Elk (Cervus canadensis) at New Jersey’s Turtle Back Zoo
Of further interest to us in this topic is another new paper by Jakob Bro-Jørgensen in the journal Evolution, “The Intensity of Sexual Selection Predicts Weapon Size In Male Bovids.” While Bovids are distinct from Cervids (deer) at the Family level, I think it’s important to compare the armaments of deer with those of bovids such as antelope, gazelle, buffalo, etc. The important distinction to make here (at least for our purposes) has to deal with the weapons the males conspicuously carry about; in deer, the males grow a new set of antlers every year, the antlers being made of bone and growing from an attachment to the skull called a pedicle. Horns, on the other hand, are typically hollow, have a covering of keratin, and do not fall off annually. All male deer have antlers, and many male bovids have horns, whether females have horns/antlers or not varying from species to species (i.e. female reindeer and caribou have antlers, but not as impressive at those of males. Even among species where antlers are not a typical female characteristic, some are commonly found to have antlers). All these details, of course, make generalization difficult, but there do seem to be some larger trends at work.
A Mhorr Gazelle (subspecies of Gazella damaAntler Size in Red Deer: Heritability and Selection but No Evolution” appeared in the journal Evolution, and the authors (Kruuk, et. al) found that directional selection for more impressive antlers is not happening because the success of the competing males depends on more than just antler size. Horns and antlers are dangerous things, and at least some weapon-wielding mammalian herbivores make at least some attempt at avoiding violent conflict. A male antelope that is obviously larger and has obviously bigger/longer horns than a rival will likely be able to drive off or otherwise force into submission a rival just because the rival knows he can’t possibly compete with such an impressive specimen, fights occurring more frequently when males are close to be equally matched (although things do not always proceed as orderly as this, some inadequate combatants giving it a go despite their less-impressive characteristics).
If a fight does occur, it’s not all about the antlers or horns; the weapons do not hold any sort of magic power that make their owner necessarily any more adept at fighting or stronger than any given opponent. Imagine, if you will, two men facing off with nearly equal length swords; how well they do while fighting does not so much depend on the blade but how they use it, strength, agility, health, and experience being more important than the weapon itself. Such appears to be the case with the antlers of red deer. While Kruuk’s study found that horns were heritable and did play an important role in sexual selection, how the competing males were doing in terms of health and nutrition mattered just as much (if not more) than antler size, a male will smaller/shorter/less impressive antlers able to beat a male with more robust antlers if he was physically stronger and it better health. Thus, nutrition and health mitigates runaway sexual selection for a dimorphic trait, essentially halting evolution. I especially liked the following quote from the conclusion;
Associations between phenotype and fitness, however appealing, will give a misleading impression of the potential for evolution in a trait if the true target of selection is unmeasured or immeasurable.
Indeed, sexual selection may have played the major role in the development of impressive antlers, but such evolution is not ongoing; there eventually comes a point where the antlers (and even horns or tusks) do not get bigger because the strength of competing individuals makes more of a difference than differences in antler size or shape. This study brought to mind the famous Irish Elk (Megaloceros giganteus), an extinct deer with perhaps the most impressive set of antlers known. There are hefty prices to pay when you have to not only carry such a huge rack about, but also to grow it. While their antlers were the size one would expect for their body size, they were still huge growths of bone, and these features may very well have contributed to its demise. While there does not appear to be any conclusive finding as yet, the size of the antlers may have prohibited the elk from moving through thick vegetation as climate and local ecology changed, or even suffered from various disorders/diseases as the nutrients in the soil needed to grow so much bone began to disappear. For now all we can do is look for more evidence to confirm or refute these hypotheses, but if either were true then natural selection would push against body form generated by sexual selection, showing us that we should be careful not to be become so enthralled with just one feature of an animal that we overlook all else.
If nothing else, the studies I’ve mentioned show us that there is certainly more to consider when it comes to sexual selection, reproduction, and evolution than the “most fit” males getting together with the “most fit” females and continuing the species; a more integrated approach is needed if we’re going to truly understand what’s going on and why the evolution of certain structures (especially those influenced by sexual selection) can come to a halt.
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Categories : Ecology, Evolution, Mammals, Sex
Regarding “Lucy” going on tour, PZ writes the following;
Just a thought, but the creationists have got it all wrong. They think we worship Charles Darwin, but actually, if there are any objects of reverence among evolutionary biologists, it would be the evidence — the bones of Lucy, of Archaeopteryx, of Tiktaalik, the little trilobite in shale that I keep by my hand at my office desk.
Some days I swear that if I hear the word “Darwinism” or “Darwinist” one more time I’m going to scream; Charles Darwin was an exceptionally smart and unusual man, but I do not keep a little shrine next to my bed with a copy of On the Origin of Species that I read passages from every night before going to bed or anything of that sort. If there is anything that I truly have come to love and cherish in terms of evolution, it has been seeing the various forms of life that attest to it. The Berlin Archaeopteryx specimen is finer than any work of art, an Amur tiger roaring on a cold February morning more impressive than any poem… there is simply no way for me to look at the various life on earth, past and present, and think that they are not united by ancient ancestry and divided by processes that continually provide new reasons for excitement.
Even if certain fossils or organisms lose their privileged status as ancestors to other forms (and especially to us), they are no less amazing or beautiful. They are all complete in their own time, never quite finished in geologic time, “endless forms most beautiful” without question. I hate to make the religious analogy, but if I had my own place of worship it would be the fourth floor of the American Museum of Natural History. While many of the original fossils have been replaced with sturdy fiberglass replicas, a number of the real skeletons are still on display, the bones of creatures long-gone towering over the heads of all. Walking amongst the monstrous and terrible forms, I can’t help but sport a smile; I am among giants otherwise separated from me by a gulf of over 65 million years. Their bones correspond to my bones; we may have missed each other by a long shot, but we share a relative that provided us both with a wonderful body plan that has been carried through the rise and fall of many an evolutionary dynasty.
While it was remodeled in the mid-1990’s and will likely undergo future changes and renovations, I will never forget my first visit to the great Dinosaur Halls, awkwardly craning my head back to get a full view of animals that my imagination could not have conceived on its own. Without this love, this amazement when confronted so forcefully with what evolution has produced, I would make a rather poor scientist indeed. Writing papers in the passive voice, making tentative qualifications about hypotheses, and spending hours pouring through technical articles may be important to the academic advancement and standardization of science, but without the inner desire to discover more about nature, what good is all that? Without at least some amount of childlike enthusiasm, how can we ever hope to continue our enterprise or even interest others in it? While paleontology is the most famous discipline in which adults are supposedly paid to act like children, I think the sometimes near-inexhaustible inquisitiveness is an important part of what makes any good scientists; without it, it’s all just another job.
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Categories : Community, Dinosaurs, Evolution, Harmless (Mostly) Fun