Wednesday, March 31, 2010

Breaking News: Footprints challenge theory of evolution

Footprints challenge theory of evolution

At least according to a paper in Arizona, which proclaims that “Research by UA assistant anthropology professor David Raichlen and his colleagues provide evidence suggesting that 3.6 billion years ago, hominins walked with the same upright gait that humans do today...”

Link: Arizona Daily Wildcat

Really, upright hominins 3.6 BILLION years ago??? Bipedal locomotion is one thing, but upright walking during the Archean that’s impressive - especially considering the lack of oxygen.

Incidentally, the mentioned research actually makes an argument for hominin bipedalism first occurring around 3.6 MILLION years ago. And the research is not a challenge to evolution; in fact, it fully endorses it.

The research is available at PloS; here’s the abstract:
Debates over the evolution of hominin bipedalism, a defining human characteristic, revolve around whether early bipeds walked more like humans, with energetically efficient extended hind limbs, or more like apes with flexed hind limbs. The 3.6 million year old hominin footprints at Laetoli, Tanzania represent the earliest direct evidence of hominin bipedalism. Determining the kinematics of Laetoli hominins will allow us to understand whether selection acted to decrease energy costs of bipedalism by 3.6 Ma.

Methodology/Principal Findings
Using an experimental design, we show that the Laetoli hominins walked with weight transfer most similar to the economical extended limb bipedalism of humans. Humans walked through a sand trackway using both extended limb bipedalism, and more flexed limb bipedalism. Footprint morphology from extended limb trials matches weight distribution patterns found in the Laetoli footprints.

These results provide us with the earliest direct evidence of kinematically human-like bipedalism currently known, and show that extended limb bipedalism evolved long before the appearance of the genus Homo. Since extended-limb bipedalism is more energetically economical than ape-like bipedalism, energy expenditure was likely an important selection pressure on hominin bipeds by 3.6 Ma.

Raichlen, D., Gordon, A., Harcourt-Smith, W., Foster, A., & Haas, W. (2010). Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics PLoS ONE, 5 (3) DOI: 10.1371/journal.pone.0009769

Tuesday, March 30, 2010

The Views of Biology Teachers towards Teaching Evolution

In discussing Marco Rubio’s anti-science perspectives during the previous post, I mentioned Florida’s miserable (though improving) track record in regards to the teaching of evolution. As it turns out, the National Association of Biology Teachers has recently published the results of a survey which focused on the attitudes held by Florida’s biology teachers towards the teaching of evolution.

The survey’s data was derived from the responses of 353 Florida biology teachers; 28% of which taught biology in kindergarten through the fifth grade, 24% instructed biology in grades six through eight and 48% taught biology at the high school level (grades 9–12).

A Few of the Findings:
20% of Florida’s biology teachers are NOT COMFORTABLE with even INCLUDING evolution as a required science standard

17% of the teachers felt that biology COULD be taught and understood WITHOUT teaching evolution

17% DISAGREED that the earth is at least 4 billion years old (34% of those that disagreed believed that the earth is only between 4,000 and 40,000 years old)

34% felt that believing in God MEANS rejecting evolution

72% of the respondents reported that they HAD NEVER BEEN criticized by other teachers or school administrators in regards to HOW they taught evolution

44% of the teachers indicated that their teaching of evolution HAS BEEN criticized by students or parents

If the above numbers seem frightening consider this: The study’s respondents were solicited from the Building a Presence in Science (BaP) program of the National Science Teachers Association. Therefore, the numbers could be biased towards the "pro" science education end of the spectrum!!!

FOWLER and MEISELS (2010). Florida Teachers’ Attitudes about
Teaching Evolution The American Biology Teacher, 72 (2), 96-99 : 10.1525/abt.2010.72.2.8

Sunday, March 21, 2010

Tadpole Tails and Predator Induced Plasticity

Last Wednesday, while doing field work near Goethe State Forest, I happened onto the paths of a couple pinewoods tree frogs (Hyla femoralis). One frog was observed practicing evasive acrobatic skills between the leaves of a saw-palmetto dominated groundcover; the second frog, taking a more leisurely approach to the day, was found lazily stretched out on mid-swamp tree branch. Because of a recent environmentally-induced neglect of this blog on my part, I thought that the two frogs would serve as a good model for a post on how tadpoles can alter their developmental physiology in response to local ecological conditions.

Like many other frogs, the pinewoods tree frog undergoes a complex life cycle which carries them from the ephemeral waters of ponds, swamps and puddles to an adulthood existence in the trees. In response to the variability of selective pressures expressed by their environments, natural selection has shaped Hyla femoralis in such away as to be flexible. One example of this flexibility is the way in which their tadpoles can alter phenotype – their morphology - in response to the presence of predators. As opposed to their developmental processes rigidly rendering tadpoles displaying uniform and unchanging morphologies, the DNA of flatwoods tree frogs has been programmed to make size, growth rate and coloration malleable characteristics. The ability of an organism to change its physical characteristics to better fit local conditions is called ‘developmental plasticity.’

In addition to normal variations encountered at the regional level, or within individual populations, the colors and shapes exhibited by tadpole tails can differ from one location to another; this is because tail characteristics can be changed in response to cues in the environment. In waters lacking abundant predators, Hyla femoralis tadpole tails are generally colorless, or are of a dull brownish-red color. In contrast to relatively safer waters, the tadpoles hosted by puddles with abundant predators (predators like dragon fly larvae, for example) are often found bearing tails with distinct red-spot markings and an enhanced, taller shape and muscular robustness. Increased tail muscle provides greater propulsion, allowing the tadpoles to employ accelerated speeds as part of their predator evasion tactics. Though, it’s still an area for inquiry, changes in the pattern and coloration of tails may provide a crypsis function by either providing improved camouflage, or by directing predatory attacks tail-ward, away from the tadpoles’ main body mass – improved survival through either concealing or revealing.

The chemical signals that switch tail enhancement into overdrive include those compounds released by other tadpoles as warning pheromones during predatory attack and those molecules discharged by the predator while digesting prey-tadpole tissues. So, in other words, a predator’s attack and digestion of a conspecific tad liberates chemicals into the water that are received by other tadpoles during development; as a result, resources are directed away from ‘normal’ growth processes and are directed to tail augmentation.

Cool stuff!

A couple quick notes:

Pinewoods tree frogs display distinct orange or yellow spots on their inner side of their thighs, while in the field these spots help distinguish Hyla femoralis from other species with similar body color patterns. Though not pictured here, the leg spots were observed during the frogs’ recent attempts at evading a certain species of primate paparazzi. Their tadpole stage lasts for about two months, and the breeding season begins in March and runs through the summer months.

Although cypress swamps and pine flatwoods are distinct natural community types, they are both occupied by the pinewoods tree frog. The first snapshot above shows one Hyla femoralis precariously perched on the stem of a saw palmetto plant just a few inches off the ground in a well-drained upland flatwoods area. The second shows another individual leisurely laying on a tree branch about five feet above the surface waters of a swamp. In Florida, these communities are often directly adjacent to each other:

LaFiandra, E., & Babbitt, K. (2004). Predator induced phenotypic plasticity in the pinewoods tree frog, Hyla femoralis : necessary cues and the cost of development Oecologia, 138 (3), 350-359 DOI: 10.1007/s00442-003-1412-3

Saturday, March 13, 2010

Evolving from Promiscuity to Monogamy

New research has revealed how the process of evolution can result in sexually promiscuous animals undergoing adaptation for monogamy.

Reproduction is an expensive endeavor. Tremendous time and resources are invested in seeking-out healthy partners, in consummating relationships, and in rearing the resultant offspring. Luckily, evolution has resulted in life being programmed to strive for resource efficiency; to work towards maximum reproductive benefit at minimum personal expense. In regards to pair-bonding between the sexes, this biological imperative for reproductive economy has made promiscuity the rule and monogamy the exception. However, despite the fact that promiscuous mating systems are the prevailing strategy in nature, environmental factors can push typically promiscuous species towards monogamy.

As a case in point, a report published in the April issue of The American Naturalist details how the ‘mimic poison dart frog’ (Ranitomeya imitator) parted ways with promiscuity to adapt a lifestyle as the first scientifically recognized genetically monogamous amphibian.

Like other frog species, poison dart frogs incur a certain amount of risk by laying their eggs in water. Although water is a biological prerequisite for frog survival, ponds, lakes and puddles also house predatory fish and other animals that prey on vulnerable eggs and tadpoles. During its evolutionary past, the menace of predation pushed the mimic poison dart frogs away from larger, riskier ponds to the considerably smaller, but safer, pools held by leaves of large bromeliad plants. Unfortunately, although the tree-top bromeliads decreased the rate of frog young predation, the movement from the big ponds raised a separate issue – nutrient limitation.

The big ponds definitely had more predators; but, they also had substantially more food. In fact, the ponds had so much food that a single frog-parent (in this case the male) was able to handle the tadpoles all by himself – a single parent family arrangement was all that was necessary to raise the next generation. In contrast, the waters held by the bromeliads averaged only about 24 milliliters in volume, far too little to hold ample provisions for a startup tadpole. In order to maintain their newly acquired safe housing, the mimic dart frogs had to adapt a new tactic.

Male mimic dart frogs had previously evolved the capacity to both transport and guard young tadpoles, but having moved to the suburbs, the females needed to help-out with feeding; rearing had become too difficult a task for the males to handle on their own. If they were to ensure the survival of their young, the days of leaving dad to care for the kids were over – monogamy was the best option. Unlike males, female mimic darts have the ability to produce eggs. To do their part, mom frogs adopted a strategy called trophic egg feeding, a practice in which they lay unfertilized eggs in the bromeliad pools for the tadpoles to eat.

An absolutely amazing video of this monogamous behavior was recorded by the BBC during the dissertation work of Jason Brown. Jason was the lead author of the cited paper, and the mimic dart footage was included in the David Attenborough narrated documentary “Life in Cold Blood.”

This is awesome footage:

Brown, J., Morales, V., & Summers, K. (2010). A Key Ecological Trait Drove the Evolution of Biparental Care and Monogamy in an Amphibian The American Naturalist, 175 (4), 436-446 DOI: 10.1086/650727

Saturday, March 6, 2010

Ecographica is a Finalist: Conservation or Geosciences

Research Blogging Awards 2010 Finalist

I just received an email from Research Blogging requesting my votes for 2010’s best blog awards…

Working through the nominees, I was surprised to discover that Ecographica was selected as a finalist in the Conservation and Geosciences category – I had no idea!

My thanks to the readers and judges for supporting this blog!!!!

Since January of 2009, Ecographica has contributed 109 research related posts to Research Blogging. Vertebrate Proxies of Climate Change has been the most popular of the research postings; it reviews/summarizes some of the ways in which vertebrates can be used to study shifting climates.

Thanks again!