Friday, February 27, 2009

Darwin - The Musical

Charles Darwin the musical.

Tuesday, February 24, 2009

Wetland Plant of the Week #6

Cirsium muticum

"Swamp Thistle"

Obligate biennial herb and member of the Asteraceae

Photographed in the Fakahatchee

A few thistle fans photographed the same day:

Monday, February 23, 2009

Evolution and National Security - An Analogy to Nowhere

Exploring new models for problem solving is a good thing, but I’m inclined to think that someone may be taking this analogy a bit too far…

My initial impression is that with enough creative coaxing evolution’s lessons on national security are about as meaningful as evolution’s lessons on learning to play the guitar - though admittedly I haven’t read the book.

There is a video lecture available on YouTube here.

+ + +


Take A Darwinian Approach To A Dangerous World: Ecologist Preaches 'Natural' Security For Homeland Defense

In nature, the threat level is always at least orange: Predators and plagues are an unrelenting menace to the well-being (and successful reproduction) of every living thing.
So does your body make every gulp of air take off its shoes before entering your lungs to ensure that it's not smuggling pathogens?

Of course not, says Rafe Sagarin, an assistant research professor of marine science and conservation in Duke University's Nicholas School of the Environment, and it would be ridiculous to try. If you didn't suffocate first, the microbes would simply find another way to get in. That's what natural threats do.

Sagarin, an ecologist who's normally more concerned with the urchins and starfish in tide pools, got to thinking about these things as a Congressional science fellow less than a year after the 9/11 terrorist attacks. He saw Washington building an expensive new shell, erecting large barriers around buildings and posting guards and cameras in every doorway.

"Everything was about more guards, more guns, and more gates," he said. "I was thinking, 'If I'm an adaptive organism, how would I cope with this?' "Pretty simply, as it turns out. "If they're checking every trunk, I'll put the bomb in the back seat."

Sagarin thinks this way because he's a biologist, not a cop. And, he says, it's a mode of thinking—informed by Charles Darwin's insights into life's struggle for survival and fecundity—that more security analysts would be wise to adopt.

At the annual meeting of the American Association for the Advancement of Science in Chicago, Sagarin has organized a 90-minute symposium on the subject, to be held Friday morning, Feb. 13.

Sagarin is also the editor of "Natural Security: A Darwinian Approach to a Dangerous World" (University of California Press, 2008), which convened a national committee of experts from related fields like biology, anthropology, and virology, as well as security, psychology, and math to think about ways that Homeland Security could act more like an immune system and less like a tough-talking Texas sheriff.

In nature, a threat is dealt with in several ways. There's collectivism, where one meerkat sounds the alarm about an approaching hawk, or camouflage, where the ptarmigan hides in plain sight. There's redundancy, like our wisdom teeth, or unpredictable behavior, like the puffer fish's sudden, spiky pop.

Under the unyielding pressure of 3.5 billion years of evolution, the variety of defenses is beyond counting. But they all have a few features in common. A top-down, build-a-wall, broadcast-your-status approach "is exactly the opposite of what organisms do," Sagarin says.

An immune system, for example, is not run by a central authority. It relies on a distributed network of autonomous agents that sense trouble on the local level and respond, adapting to the threat and signaling for backup without awaiting orders from HQ.

Sagarin's brand of "natural security" may take some getting used to. "Organisms do not try to get rid of risk in their environment," he says. "They learn to live with it."

The total elimination of risk is far more costly than the organism could bear, and probably futile, since the threats adapt. But by being responsive and adaptable and not putting every last bit of its budget into defense, an organism stands a far better chance of being able to handle an unforeseen risk in an escalating arms race, he says.

"Almost everything organisms do is, in some way, about security."

Saturday, February 21, 2009

Bacteria and Mass Extinctions

Peter Ward discusses mass extinctions

Another good video from TED

Harnessing the Power of Science – “Homo evolutis”

Juan Enriquez discusses the economy, advances in tissue regeneration, robotics and the merging of all three. If you’re in a hurry skip the warning of economic doom and move ahead to about 7:45 min to start the bio-science.

Good video from TED.

Defending Darwin

Just returned home from a week of fieldwork and observed the slight blogospheric bioturbation resulting from the letter sent to New Scientist by Dan Dennett, PZ Myers, Jerry Coyne, and Richard Dawkins.

Letter Posted at New Scientist – “Darwin was right"

Pharyngula – “Spanking New Scientist
Why Evolution is True – “Darwin proclaimed wrong AGAIN; we fight back!” – “Darwin was right
Sandwalk – “Blunt Talk from Four Evolutionists

Read some of the author’s arguments in defense of the original article in the comments section of – “Why’s Graham so Glum: Lawton Critiqued

Thursday, February 19, 2009

Fossils Discovered

Currently out of office - just a quick news story of interest...

Scientists are studying a huge cache of Ice Age fossil deposits recovered near the famous La Brea Tar Pits in the heart of the nation's second-largest city.

Among the finds is a near-intact mammoth skeleton, a skull of an American lion and bones of saber-toothed cats, dire wolves, bison, horses, ground sloths and other mammals.
Researchers discovered 16 fossil deposits under an old parking lot next to the tar pits in 2006 and began sifting through them last summer. The mammoth remains, including 10-foot-long tusks, were in an ancient riverbed near the fossil cache.

Officials of the Page Museum at the tar pits plan to formally announce their findings on Wednesday. The discoveries could double the museum's Ice Age collection.
Such a rich find usually takes years to excavate. But with a deadline looming to build an underground parking garage for the next-door art museum, researchers boxed up the deposits and lifted them out of the ground using a massive crane.

"It's like a paleontological Christmas," research team member Andie Thomer wrote in a blog post in July.

The research dubbed "Project 23" — because it took 23 boxes to house the deposits — uncovered fossilized mammals as well as smaller critters including turtles, snails and insects. Separately, scientists found a well-preserved Columbian mammoth that they nicknamed Zed.
An examination reveals Zed, which is 80 percent complete, had arthritic joints and several broken and re-healed ribs — an indication that he suffered a major injury during his life.

"It's looking more and more as if Zed lived a pretty rough life," Thomer blogged in December.
Some scientists not connected with the discovery said this is the first significant fossil find since the original excavations at the tar pits more than a century ago.

"Usually these things are either lost in the mixing or not recovered in the processing of the oily sand and soil they occur in," paleontologist Jere H. Lipps of the University of California, Berkeley wrote in an e-mail to The Associated Press.

The La Brea Tar Pits ranks among the world's famous fossil sites. Between 10,000 and 40,000 years ago, mammoths, mastodons, saber-tooth cats and other Ice Age beasts became trapped by sticky asphalt that oozing upward through cracks and fissures in the ground. The newly recovered fossils were also in asphalt.

Since 1906, more than a million bones have been unearthed from the sticky ponds.

Source: Here

Monday, February 16, 2009

Wetland Plant of the Week #5

Pontederia cordata


Obligate monocot plant with broad leaves (without cross-veins between the parallel veins) and purple flowers.

This one photographed in Panther National Wildlife Refuge.

Sunday, February 15, 2009

Sexual Selection, Good Genes and Condition-Dependent Handicaps

In regards to mate choice, ‘Choose, but choose wisely’ is the mantra of the discriminating female when seeking-out male suitors. By selecting the most fit, well-matched mates, females are able to reap the benefits of their own inclusive fecundity and be better positioned to obtain the dividends of more numerous, healthy offspring. Moreover, in looking to the future - beyond the perception and sight of Natural Selection - increased female-to-male genetic compatibility may contribute to the transmission of variability or adaptations that may ultimately factor into the fate of the population or the species as a whole. Mate choice matters; both in the here-and-now and in the long term.

On the average, the female gender is better positioned to choose mates because they are most commonly (but not always) the limiting gender in a population. Females take on the greater burdens of producing ova and caring for young; they also tend to be fewer in number within a given population. The power of mate choice belongs to the female; but on what grounds is her selection made, and what criteria are weighed and measured prior to committing to a costly reproductive venture? Certainly, any mate is better than no mate at all, but when the opportunity presents itself wouldn’t it be beneficial to capitalize on the availability of the most virile, successful or healthy male – how to choose?

Generally, selection of mates can be thought of as functioning along one of four lines; (1) through identifying Good Genes, (2) receiving Direct Benefit, (3) via Sensory Bias and (4) by Fisherian Runaway. These methods of mate selection may operate independently, collectively or in conjunction with other aspects of local ecology and Natural Selection – they’re not exclusive. The ability to identify “good genes” will be the focus here, with Direct Benefit, Sensory Bias and Fisherian Runaway reserved for later posts.

Identifying good genes…

Although human fertility clinics utilize modern molecular techniques to perform genetic assessments, “Good Genes” typically aren’t identified by non-human kinfolk in laboratory settings; rather evaluations are undertaken on the fly using an organism’s innate sensory capabilities.

In its simplest form, avoidance of certain physiological cues such as developmental deformities can aid a female in filtering-out unworthy genetic sets; unusual appearances, irregular gaits or abnormal vocalizations of male callers tend to stand-out to females and are almost always avoided. In other cases elaborate courtship rituals, fighting or induced ovulation tactics may be summoned into play as a means of determining the superlative mate through tests of endurance and strength. To maintain a lockstep with these challenges and to achieve female demands, males adapt to take on behaviors, morphologies and displays that maximize their chances of being selected – they sing, dance, bribe and mesmerize. The males strive to impress, because if they succeed, they’ll be selected as a mate and be provided the opportunity to pass on their genetic compliment. Of course, all of these additional behaviors and adaptations come at a price, even beyond that associated with the routine cost of maintenance, additional nutritional requirements and energy expenditures, since predators can also be attracted to flamboyant colors and patterns. As a result of this dynamic set of circumstances, male sexually selected characteristics may sometimes seem less like a benefit and more like a “handicap.”

Handicaps are those conditions that improve an animal’s chance at being selected as a reproductive mate while at the same time being detrimental to its survival. Essentially, handicaps exist as one of three types; Zahavian Handicaps, Condition-Dependent Handicaps and Revealing Handicaps.

Zahavian Handicaps (named for biologist Amotz Zahavi) describe the idea that only the strongest, most fit males could afford to take on the risk and cost associated with elaborate morphologies, colors or behaviors, and for this reason those males exhibiting such characteristics are preferred to females as reproductive partners. In short, if a peacock can lug around a massive, brilliantly colored tail and still somehow manage to survive in spite of its increased visibility to predators and cost of feather development, it must be extremely healthy! Indeed, a proponent of Zahavian Handicaps would make the argument that peahens find the boldness of the peacock to be quite sexy.

Revealing Handicaps are those sexually dimorphic characterizes which tend to be indicative of the presence of parasites or disease. The hypothesis was put forward by biologists W.D. Hamilton and Marlene Zuk in 1982 and details a scenario in which animals exhibit colorations based on the presence, or immunity against, specific parasites and diseases. These colorations can then be interpreted by mates prior to copulation as a means of determining the health of a potential partner.

[House Finch at my Feeder]
Conditional-Dependent Handicaps are those in which dimorphic characters are depicted as an overall indicator of an animal’s current health. For example, the coloration of a song bird may indicate its diet or foraging ability. Linking to current science news, research conducted by Assistant Professor Kevin McGraw of Arizona State University, indicates that dietary uptake of carotenoids by house finches (Carpodacus mexicanus) function in just such a way. McGraw explains (From ScienceDaily, here):

"We are proposing a positive fitness feedback loop for these 'self-loving molecules,' given how high carotenoid accumulation can improve one's state and one's interest in selecting carotenoid richness in mates and food. This provides a window into how major sexual selection models, such as sensory biases and assortative mating, may be explained by a common, nutritional and narcissistic currency."

In addition, the role of carotenoids in other areas of physiology is becoming apparent, including color vision, according to McGraw,

"Carotenoids play fascinating and multifaceted roles in the lives of animals. For years, we have known that, as antioxidants, they boost human health and, as colorants, make birds colorful and sexually attractive. Now, we are blending as well as expanding these paradigms and studying how consumption of carotenoids can improve or 'tune' their color vision, promote the health of offspring as they develop in the egg, and possibly improve male sperm quality."

More detail on identifying Good Genes in potential mates will be provided at a later time, and Direct Benefit, Sensory Bias and Fisherian Runaway will also be examined.

Arizona State University (2009, February 13). Carotenoids Are Cornerstone Of Bird's Vitality. ScienceDaily. Retrieved February 15, 2009, from

W. Hamilton, M Zuk (1982). Heritable true fitness and bright birds: a role for parasites? Science, 218 (4570), 384-387 DOI: 10.1126/science.7123238

Mark Kirkpatrick, Michael J. Ryan (1991). The evolution of mating preferences and the paradox of the lek Nature, 350 (6313), 33-38 DOI: 10.1038/350033a0

A. Pomiankowski (1987). Sexual Selection: The Handicap Principle Does Work -- Sometimes Proceedings of the Royal Society of London. Series B, Biological Sciences (1934-1990), 231 (1262), 123-145 DOI: 10.1098/rspb.1987.0038

Wednesday, February 11, 2009

Adaptation and Evolution in a Changing Climate

I haven't had a whole lot of time to blog the last few days, but I came across this quick write-up on Science Daily and liked the quote at the end, “We lose diversity with a rapid change, but always life finds a way. Some kind of life will fill the gap.”

Charles Darwin may have been born 200 years ago come Feb. 12, but his theory of evolution remains an everyday touchstone for modern biologists. And while the Origin of Species author might not have known the term “global warming,” he wouldn’t have been surprised that the environment is changing. He would, however, be astonished by the speed at which it’s happening today, researchers believe.

“Every species is under temporary permanence,” says Bill Saidel, an associate professor of biology at Rutgers University’s Camden Campus, where he teaches Animal Behavior and Behavioral Neurobiology. Darwin would have predicted changes in species’ habits and even changes in the environment, but the planet’s facing changes that are both drastic and unpredictable.

Saidel notes some already observed results of global warming today, like changing avian migration patterns and pH levels in oceans. But how would Darwin begin to determine how every species might respond to climate change? Most likely he’d begin by observing those habitats that are uniquely individual and well-defined.

This approach – researching one specialized habitat for insight into a larger understanding of evolution – is how Saidel conducts his own research at Rutgers–Camden. His interest in the exotic African butterfly fish is precisely because it has evolved two retinas in each eye, but only feeds from information derived from one. The fish’s highly specialized adaptations, from retina to brain, serve as a model for discerning the circuitry of feeding in all vertebrae whose visual traits aren’t as clearly segmented.

“This fish has much to teach us. It has adapted extraordinarily to a single unique environment. Yet, the consequences of a highly adapted species is that any change can be dire,” says Saidel.
Dan Shain, associate professor of biology at Rutgers–Camden, also researches highly specialized creatures: worms that thrive in the world’s most extreme climates. He studies them for insight into their adaptations and their unique cocoon production processes, which have biomaterial applications. Only the intensely frigid environs Shain once explored in destinations like Alaska aren’t as cold anymore.

This summer, the Rutgers–Camden researcher traveled to Denali National Park to observe ice worms, whose glacial habitats make them an ideal indicator species for climate change.

“Ice worms have been around at least a few million years and have been through many ice ages, but the change there now is dramatic,” Shain says. “I’ve been traveling to Alaska for 10 years studying ice worms. The mass of the glaciers is about half of what it was a decade ago.”

Disappointed, Shain didn’t find new specimens allegedly living in Eldridge Glacier. Even the glaciers he previously identified as housing a plethora of ice worms had sadly receded.

“The number of ice worms is radically down. We think ice worms are getting washed off the glaciers and they don’t have the capability to move up the glacier quickly enough,” he reports.

The issue of time is crucial to understanding the implications of global warming. Shain calls it “accelerated evolution” and predicts large-scale extinctions that even Darwin couldn’t comprehend. Species that can best adapt to this abrupt change will go on and multiply, leaving the world with less of a variety.

“We lose diversity with a rapid change, but always life finds a way. Some kind of life will fill the gap.”

Rutgers University (2009, February 10). Big Year For Darwin, But What Would He Make Of The Climate Change Ahead?. ScienceDaily. Retrieved February 11, 2009, from

Tuesday, February 10, 2009

Wetland Plant of the Week #4

Nymphaea odorata

"Fragrant Water-Lily"

Obligate plant with submerged rhizomes, floating leaves and snowy white flowers with four-sepals and multiple petals and stamens.

This one photographed in Corkscrew Swam Sanctuary.

Sunday, February 8, 2009

Sexual Siblings: Socio-Ecological Reproductive Strategy

The previous posts (Post 1, Post 2 and Post 3) in this series on reproductive strategy touched on several fundamental concepts central to the study of sexual selection. One item discussed was the idea of sex ratios as drivers for gender role assignment in organisms that exist in populations of low density or are otherwise biased towards one sex or the other. For instance, recall from Post 2 that hermaphroditic organisms can choose to take on the reproductive function of either a male or a female dependent on the relative abundance of each in the surrounding environment. The availability of mates is critical in determining an organism’s ability to procreate and pass on genetic information, to this end sex ratios can be the deciding factor in achieving ultimate success at the level of the individual and that of the population.

Considering the significance of sex ratios (the number of available males compared to that of available females in a given population) there is little wonder why organisms take into account such gender proportions in conjunction with family planning prior to establishing a nest, clutch or natal patch. Simplistically, the idea is that if there is already an abundance of males in a population, it may be best to produce mostly female offspring as a means of optimizing chances for passing on genes to future generations. Similarly, if there is a surplus of females, the best strategy may be to produce male offspring in order to maximize that offspring’s chances for finding future reproductive mates.

NOTE: For the sake of clarity, most organisms do not literally engage in family planning per se, generally the decision to reproduce, and to what extant to do so, is a product of hereditary response to physical characteristics of local ecology and sociality – evolution. Nevertheless - for the purpose of this blog - reproductive planning can metaphorically be considered as an individual choice.

Of course this is a very rudimentary view of sex ratios and doesn’t take into account the differential expenses associated with producing gametes, seeking-out mates, rearing young or competing with sexual rivals; these investment considerations would greatly impact any ratios. But, in general if one were to weigh the total costs and benefits of producing offspring of either sex - in a given environment - the ratio of males to females - on average - would be one to one (1:1). However, as hinted above, there are several exceptions to this rule; one such exclusion being “local mate competition.”

Chiefly, local mate competition (LMC) proposes that under circumstances with tightly controlled sex ratios, limited out-breeding and where sexual rivals are likely to be close relatives, it is to the benefit of the mother to produce only enough males as is necessary to inseminate available females. Although LMC can be relevant in any location with limited dispersal of organisms, it is most easily understood in situations relating to inbreeding populations.

As a hypothetical example, if a female is to produce 10 offspring in any combination of male and female - and she knows in advance that it is highly likely that the offspring will inbreed with each other – it may be best to produce one male and nine females as opposed to maintaining a 1:1 sex ratio with five males and five females. Through this strategy, mate competition between rival males will be eliminated and nine females could potentially become mothers themselves thereby maximizing the total number of second generation offspring produced – ultimately, more genes are passed on to future generations.

Contrastingly, if the female were to forego the tenants of LMC and instead choose to maintain a 1:1 sex ratio, five brothers with parallel gene compliments would waste valuable energy trying to out-compete each other for access to the five available sisters. Regardless of which of the five males eventually succeeded, in the end only a maximum of five females could go on to reproduce as mothers.

Following this rationale, numerous arthropods, as well as several other organisms, exhibit the ability to selectively determine the sex ratios of their offspring; however, more than any other organism wasps serve as the classic example of LMC.

One wasp, Trypoxylon malaisei, constructs its nest in a very unique way. The female Trypoxylon malaisei lays eggs along the interior of its tube shaped trap-nest. Starting at the inner most point of the tube, the wasp inserts its ovipositor and lays an egg that is destined to become a daughter, next to this first egg a second daughter egg is deposited and then a third, fourth and so on, arranging the eggs along a single line side-by-side until reaching the exterior portion of the tube nest. Once at the end, the mother wasp will lay one or two final eggs which will become sons (male wasps). When the eggs hatch, the male offspring mates with its numerous female siblings - the sex ratio is perfectly designed (via evolution) to maximize insemination of the female offspring and to insure second generation fecundity.
[Trypoxylon malaisei]

Another wasp, the parasitoid Goniozus nephantidis utilizes a similar strategy when laying eggs within the integument of prey caterpillars. Typically, the wasp will inject approximately 18 eggs into its paralyzed host, of these only one or two are predestined to be male. On hatching and reaching sexual maturity all will inbreed - some even prior to exiting the comfortably nutritious host.

Through even greater levels of adaptation, driven by competition, other parasitoid wasps improve on the tactics of sex ratio exploitation. Using sensitive chemo-detection, these wasps seek out prey species, such as caterpillars, that are already serving as incubators with the eggs of a rival wasp. To these already occupied hosts the newly arrived expectant mother will inject only male eggs that on hatching devour the other male competitors and breed with the remaining females.

Other exceptions to the 1:1 sex ratio will be explored in later editions of the Socio-Ecological Reproductive Strategy series.

Ian C. W. Hardy, James M. Cook (1995). Brood sex ratio variance, developmental mortality and virginity in a gregarious parasitoid wasp Oecologia, 103 (2), 162-169 DOI: 10.1007/BF00329076

Ian C. W. Hardy, Paul J. Ode, Michael R. Strand (1993). Factors influencing brood sex ratios in polyembryonic Hymenoptera Oecologia, 93 (3), 343-348 DOI: 10.1007/BF00317876

Shintarou Oku, Takayoshi Nishida (2001). Presence of Single-Sex Broods Under Local Mate Competition in(Hymenoptera: Sphecidae): Adaptation or Maladaptation?Annals of the Entomological Society of America, 94 (4), 550-554 DOI: 10.1603/0013-8746(2001)094[0550:POSSBU]2.0.CO;2

John H. Werren, Giuseppina Simbolotti (1989). Combined effects of host quality and local mate competition on sex allocation inLariophagus distinguendus Evolutionary Ecology, 3 (3), 203-213 DOI: 10.1007/BF02270721

Tuesday, February 3, 2009

Wetland Plant of the Week #3

Cephalanthus occidentalis

Wetland obligate species with ball like clusters of small white flowers.
This flower cluster photographed in the Fakahatchee Strand Preserve

Sunday, February 1, 2009

Sex with Flexible Partners #3

Wrapping-up hermaphroditism as a general topic, in this edition of Sex with Flexible Partners the relative reproductive values of male and female gametes will be reexamined in the light of dynamic social settings. For those new to this series of blogs, occasional flashbacks to broad ideas and concepts may necessitate the reading of the inaugural article found here, as well the precursor to this current writing found here. If, by chance, the title “sex with flexible partners” is the primary reason for arriving at this site – rest assured – explicit lifelike images are included below!

Moving towards the subject at hand, through several previous examples, such as with representative Chalk Bass (Serranus tortugarum), Hamlet fish (Hypoplectius), polychaete worms (Ophryotrocha puerilis) and freshwater snails (Helisoma trivolvis), the presence of heterogamy resulted in either the changing of sexes or the development of complex behaviors in hermaphroditic organisms. These dynamic strategies were adapted as a means of more efficiently managing the costly production of female gametes. The idea of relative gamete values between male and female reproductive cells pointed to the conclusion that as a rule, “eggs are expensive, sperm are cheap.” Although this rule holds true under the majority of circumstances, there are conditions wherein the comparative value of sperm increases relative to that of ova and thereby pushes functional gender roles of some hermaphrodites in novel directions.

Many sequential hermaphrodites, such as clownfish (Amphiprion), exist in complex social environments in which multiple organisms establish communal groups and engage in cooperative behaviors. Through interaction with multiple individuals, circumstances can arise that directly effect the reproductive success of not only a single mating pair, but also the fecundity of all members of the group. Often a group stake in local fecundity results in a change in the values normally associated with male and female sex cells. As exemplar of group interest in reproductive success, the common clownfish (Amphiprion ocellaris) exhibits just such a dynamic.

[Amphiprion ocellaris]

Amphiprion ocellaris, probably best known as “Nemo” from the 2003 feature animated film “Finding Nemo,” is a protandrous sequential hermaphroditic fish that combine as groups in which a single dominant male pair-bonds with a single female and then cohabits with several smaller, sexually immature males. For the sake of clarity, it is important to bear in mind here that the reproductive biology of the species Amphiprion ocellaris is being discussed, not the cartoon character Nemo’s social preferences – libel is to be avoided.

The smaller male members of the group don’t attempt to mate with the female, they’re reproductively immature, rather they stick around because of the protection offered by the dominant male who remains at guard and patrols the host anemone in which they all reside. If the female clownfish should die or be killed, rather than risk the loss of the dominant male’s protection – he would need to leave the anemone in pursuit of a new mate – the largest of the immature male anemone-mates will undergo a sex change and take up the role of reproductive female thereby insuring the dominant male's continued presence. If, instead of loosing the group’s reproductive female, the dominant male is killed or dies, then the female vacates her egg laying responsibilities and undergoes a sex change to replace the male. Her position as reproductive female will later be taken-up by one of the immature males as described previously.

In the clownfish example, social pressures linked to the protection of the group complicated the process in which hermaphroditic fish chose a functional sex role - even to the extent of abandoning the all important task of egg production - these complications also occur under circumstances in which the creation of sperm becomes more critical than does manufacture of ova. Communal groups of blue headed wrasse (Thalassoma bifasciatum) sometimes encounter just such a state of affairs.

[Thalassoma bifasciatum]

“Blueheads,” as Thalassoma bifasciatum can commonly be referred, are protogynus sequential hermaphrodites that form large, male dominated harems in which a group of females establish a female-only hierarchy. The male controls the group, provides protection and manufactures sperm; the largest female in the group is the primary egg producer and to a certain extent controls the lesser females. Because blueheads live in groups with highly biased sex ratios – many females, one male – eggs are “a dime a dozen” – they’re cheap. If the lead reproductive female should die or be killed, the next largest female in the hierarchy will hurriedly succeed her and take over as primary ova supplier with little fuss. Whereas there are an abundance of females and only a single male, the sperm he contributes is of greater importance to the group than are eggs. The eggs are expensive, sperm are cheap rule - although still valid in regards to resource allotment for an individual - in this social scenario no longer holds true. If the dominant male bluehead should be killed or die, it’s well worth the expense of undergoing a sex change to replace him, and this is precisely what the lead female does, she changes to a male and takes over the harem.

Taking over a harem is by no means an easy job, there is plenty of risk involved in defending the group against predators and out maneuvering the continuous onslaught of rivals vying for the throne; but taking the male role benefits both the individual and the group as a whole because it streamlines the passing of genetic material to the next generation. Another species of reef fish, Trimma okinawae, will even forego the hassle of finding a new harem, should his be lost to a rival; he’ll just join another one – as a female.

[Trimma okinawae]

Social dynamics can have traumatic impact on the physiological and behavioral characteristics of organisms, but it’s important to keep in mind that no single phenomenon is responsible for all biological adaptation. Evolution works along a vast continuum of gradation; the physical environment, resource availability and social constraints are but a few of the uncountable factors carefully weighed by Natural Selection.

There are exceptions to all of the examples listed in this discussion, and there are those organisms that sneak, manipulate and cheat the system to their advantage, some of these cases will be the focus of future installments, but for now it’s a safe assumption that the incredible sexual flexibility exhibited by hermaphroditic organisms has proven to be an effective strategy in assuring reproductive victory over rivals.

P MUNDAY, P BUSTON, R WARNER (2006). Diversity and flexibility of sex-change strategies in animals Trends in Ecology & Evolution, 21 (2), 89-95 DOI: 10.1016/j.tree.2005.10.020

Shohei Suzuki, Kyoko Toguchi, Yoshimi Makino, Tetsuo Kuwamura, Yasuhiro Nakashima, Kenji Karino (2008). Group spawning results from the streaking of small males into a sneaking pair: male alternative reproductive tactics in the threespot wrasse Halichoeres trimaculatus Journal of Ethology, 26 (3), 397-404 DOI: 10.1007/s10164-008-0102-3

Verena S. Brauer, Lukas Schärer, Nico K. Michiels (2007). PHENOTYPICALLY FLEXIBLE SEX ALLOCATION IN A SIMULTANEOUS HERMAPHRODITE Evolution, 61 (1), 216-222 DOI: 10.1111/j.1558-5646.2007.00018.x