Wednesday, September 30, 2009

Demonstrating Speciation via Fisherian Runaway

The 1930 publication of Ronald A. Fisher’s eminent work The Genetical Theory of Natural Selection helped pave the way for development of the modern evolutionary synthesis.


Actually… If truth-be-told, I’d be inclined to give Fisher’s work a bit more credit for Neo-Darwinism than just “helped pave the way”. Not to shortchange the labors of Huxley, Haldane and the rest of modern biology’s forefathers, but in my assessment Fisher’s linkage of natural selection with genetics was the perhaps the greatest single contribution to the study of evolution since Charles Darwin.

Getting back to the reason for this blog post…

One of Fisher’s many contributions to biology was the idea that through a process of sexual selection, the favored phenotypic traits exhibited by individuals can – if consistently chosen during courtship – increase in frequency and become more numerous in a population, even if the traits offer no fitness advantage.

For example, if the females in a hypothetical bird species happen to find large and colorful feathers attractive, they may choose male birds who display brilliant feathers as their reproductive partners; at least more often than they choose males with dull feathers. Over multiple reproductive episodes, the hypothetical bird population may come to have more-and-more males with brilliant feathers. A greater abundance of colorful males means that competition between males for female access becomes more challenging. The reason for this increase in competition is that the colorful males are no longer competing with just dull feathered rivals, now they find themselves in contest with other brilliants! From the female’s perspective, choosing a mate becomes more tedious, now she must pick not only a male with brilliant feathers, now she must scrutinize each suitor for the brightest and boldest of feathers – the best of the best. This process of increased selection pressure for feather color continues – in a “runaway” process – that culminates with not only a population of birds in which males display brilliantly colored feathers, but even more, the end result is a population that displays larger, more ornate and more colorful feathers; the process compounds and undergoes a positive feedback. All of this due to a female’s mate preference, which she passes on to her female offspring and potentially has nothing to do with fitness (As a side note, this would be a good spot to pitch a previous post Sexual Selection, Good Genes and Condition-Dependent Handicaps).

OK, enough about birds-of-paradise, peacocks or whatever hypothetical bird population I was referring to, the point of all this was to say the following: although the tendency for preferred traits to compound through time has long been observed, it was Fisher that made the connection to genetics. He explained how secondary sexual characters and mating preferences are genotypically bound to mate choice itself. Further, because of the selection pressure levied against secondary sexual characteristics, the potential to sexually isolate a population is ever present; should a new phenotypic variation arise that falls outside the range of female preference, a new species could arise. And, new research published at BMC Biology affirms this Fisherian Runaway dynamic.

From the abstract: This study spotlighted SLa as a novel mate-choice gene in fish. In addition, these results are the first demonstration of a single gene that can pleiotropically and harmoniously change both secondary sexual characters and mating preferences. Although theoretical models have long suggested joint evolution of linked genes on a chromosome, a mutation on a gene-regulatory region (that is, switching on/off of a single gene) might be sufficient to trigger two 'runaway' processes in different directions to promote (sympatric) speciation.

Basically stated, a single gene alteration in a fish changes its color, and the preference for that color by the opposite sex. In turn, this leads to sexual isolation and ultimately a new species…

Fisherian Runaway!

Fukamachi, S., Kinoshita, M., Aizawa, K., Oda, S., Meyer, A., & Mitani, H. (2009). Dual control by a single gene of secondary sexual characters and mating preferences in medaka BMC Biology, 7 (1) DOI: 10.1186/1741-7007-7-64

Tuesday, September 29, 2009

Papilio’s Unconstrained Phenotypic Flexibility

As with most plant feeding insects, butterfly to host-plant adaptations are highly specialized towards specific plant species or plant groups. The reason for this is that plants characteristically produce chemicals that either deter or attract insects based on the defensive and mutualistic needs of the plant itself. Through natural selection, plants adapt specifically to work with (as with pollinators, like bees), or work against, the other organisms cohabitating in their ecosystem. So, if an insect is to take advantage of a plant as a food source it must first adapt tolerances or immunity to the toxic compounds that the plant produces as a defensive measure.

Sanpshot of P. glaucus taken last week in Hamilton Co, Florida. Notice the fine parallel lines of silk beneath the caterpillar; it will use these lines to slowly pull-up the edges of the leaf (Persea palustris, in this case) for protection.

Given enough time, the chemical tolerances of some herbivorous insect populations can become so specialized as to limit their ability to consume other plants; their body chemistry becomes dependent on a single, or only a few, plant species. When evolution pushes an organism’s adaptations to high levels of specialization and thus reduces its ability to be flexible and responsive in a changing environment, we can say that the organism has become “evolutionarily constrained.” This is the case with many species of butterfly, which have adapted resistance to the phytochemicals of only their favorite plants.

Side view of above larvae; the large eyes may be an adaptation to intimidate predators - possibly to look like a snake???

Called monophagy, dependence on a single plant species can leave butterflies vulnerable when environmental conditions change; when once abundant plants become rarer, food becomes harder to find, and fitness declines. Luckily, the evolutionary history of some butterflies may have imprinted sufficient genetic variability in their genome as to provide them a toolbox from which to draw ecological flexibility.

This was a newly emerged P. glaucus photographed in my backyard; it was posted with others during a discussion on ecological divergence (linked below).

Although often demonstrating monophagy, some species of swallowtail butterfly show rather substantial flexibility when it comes to the ability to physically tolerate the phytochemicals of un-preferred plants. To study the ability of Papilionidae (swallowtails) to tolerate different species of plant, researchers from Michigan State placed females of several Papilionidae species into enclosures containing the leaves of one of several plants families. After observing which leaf types the female utilized as a platform for depositing eggs, and after quantifying the larvae’s growth/mortality response relative to the specific plant species provided, the scientists determined that some butterflies exhibit greater ecological flexibility than others.

For example, the MSU study revealed that species such as Papilio troilus could not tolerate the chemicals of plants other than those of the Lauraceae Family, which it has adapted to prefer. Contrastingly, other swallowtail species, such as Papilio glaucus, demonstrated an ability to eat the leaves of several different plant families, even though it displays monophagy in the wild.

NOTE: The Papilio glaucus used in this experiment were harvested form a population found in Levy County, Florida. This particular Florida population had been previously shown to practice monophagy with preference for sweet bay trees (Magnolia virginiana); Ecographica’s prior Wetland Plant of the Week #25. Not to create conflict with my earlier post discussing Ecological Divergence in the Swallowtail, I wanted to clarify that other populations of P. glaucus are “polyphagous” – they use multiple tree species.

Scriber, J., Larsen, M., Allen, G., Walker, P., & Zalucki, M. (2008). Interactions between Papilionidae and ancient Australian Angiosperms: evolutionary specialization or ecological monophagy? Entomologia Experimentalis et Applicata, 128 (1), 230-239 DOI: 10.1111/j.1570-7458.2008.00691.x

Monday, September 28, 2009

Male Sexual Choice; an Uncommon Occurrence

During last Tuesday’s brief discussion on the sexual selection dynamic that exists between male and female barking frogs (Hyla gratiosa), I mentioned that, as a general rule, the female gender of most species are the “deciders” when it comes to choosing reproductive partners. What was meant by this was that females are more-often-than-not the limiting sex in a population and are thus behaviorally better positioned to choose between competing males during the process of sexual selection. Today, I thought that it may be a good idea to give an example of a species that exhibits a mating system typified by reversed sex-roles; one in which males , as opposed to females, are the limiting reproductive resource.

One of the many unique things about Syngnathidae, the biological Family to which pipefish, sea dragons and seahorses belong, is that its female members lay their eggs directly on the trunk or tail of the male gender. Following the ovipositioning that occurs during copulation, the eggs remain bodily attached to the male where they are subsequently fertilized by his sperm. The male then carries the eggs as they develop, providing protection and in some instances even direct nutritional support via circulatory connections to placenta-like tissues contained within his brood pouch (note: not all Syngnathidae males have true brood pouches, in some species the eggs are attached externally to the male’s body in “sockets” that lack circulatory tie).

Because males take on the responsibility of carrying and protecting the clutch, they’re ultimately accountable for the success of the offspring. Fitness measures, such as the number of viable offspring produced from a mating session, are in part determined by the resources allotted by the male to the embryonic development of the piggy-backing eggs. Of course, another significant factor in the fitness potential of offspring is the health and condition of the female whom is contributing the eggs. It is the female’s health and current condition that the male assesses during the initial stages of mate selection.

Although both mating behavior and organismal reproductive physiology differ greatly between individual species of the Subfamilies Hippocampinae (seahorses) and Syngnathinae (pipefish and sea dragons), the process of precopulatory sexual selection is characterized by a courtship dance in which the female entices the male (sometimes for a period of days) through performing elaborate maneuvers, turns, circles and tail holding. If she appears healthy and passes muster – if she’s got the right moves – the precopulatory dance may be followed by mating as mentioned above; the female deposits eggs into the brooding pouch (or, in some species places the eggs on the male’s body).

Incidentally, if you haven’t witnessed the courtship dance of seahorses or pipefish, you are truly missing out on an extraordinary display!!! Check-out this video from the Monterey Bay Aquarium:

In addition to the fitness potential read from the females’ sophisticated chorography, the Syngnathidae males also inspect the female for other visual cues that may provide indication to as to her health, condition and genetic make up.

To better understand the male’s assessment method, Adam G. Jones, Assistant Professor at Texas A & M, examined the preference of male members of the species Syngnathus typhle (a pipefish) for females displaying indicators of high parasite load. As most folks could imagine, large quantities of parasites can affect the overall health of an animal; these freeloaders tap into their host and drink with delight the vital resources acquired through the labors of their target. Even for the pipefish, large quantities of unsightly parasites observable on the exterior of a potential mate are pointers of poor current health. The parasites are literally unsightly; unsightly because that is precisely how the male Syngnathus typhle weighs the female’s appearance – by sight. Should the male perceive large or numerous dark spots on the female, he is far less likely to choose her as a reproductive partner. This is because the dark spots, the male pipefish assumes, are parasites and may adversely affect the condition of any eggs the female may be carrying; therefore black spotted females represent a risky reproductive investment for the male. However, there is one detail that the pipefish in this experiment weren’t privy to, that is that the dark spots in Jones’s study weren’t parasites at all – they were harmless tattoos.

During a recent visit to Tallahassee, Dr. Adam G. Jones explained that the tattooed pipefish experiment was originally intended as an inquiry into the post-copulatory behaviors of Syngnathus typhle. Knowing in advance that males preferentially mated with females showing low parasite loads, Jones had suspected that males of the species may engage in a cryptic choice behavior in order to reduce impregnation by parasite ridden females. Although this experiment ultimately demonstrated no support for the parasite-to-cryptic choice hypothesis, it did exhibit the possibility for cryptic choice along lines other that parasite load, AND the experiment also provided evidence to two key phenomena. Firstly, the experiment revealed that eggs from larger females had a greater statistical tendency to become viable offspring than those received from smaller females. And secondly, the study showed that the first female to mate with the male deposited a larger quantity of eggs than did those females ovipositing afterwards.

So... The natural history of the Family Syngnathidae demonstrates that male choice does exist in the natural world. Further, Jones’s work has shown that male choice extends beyond the precopulatory selection of female mates and that the behavioral ecology of the pipefish even includes post-copulatory mechanisms of sexual selection.

Partridge, C., Ahnesjö, I., Kvarnemo, C., Mobley, K., Berglund, A., & Jones, A. (2008). The effect of perceived female parasite load on post-copulatory male choice in a sex-role-reversed pipefish Behavioral Ecology and Sociobiology, 63 (3), 345-354 DOI: 10.1007/s00265-008-0668-3

Saturday, September 26, 2009

Wetland Plant of the Week #28

Rhexia mariana"Meadow beauty"

One of several meadow beauty species, Rhexia mariana displays a four sided stem, an erect posture and varying amounts of pubescence (small hairs). A perennial and rhizomonous plant, R. mariana is a Facultative Wet species in Florida and can be found residing in bogs and hydric flatwoods Statewide.

A distinctive characteristic of the genus: All of the Rhexia species have a distinctive “urn-shaped” floral tube that encloses their capsulated fruits.

This one was photographed yesterday near Stephen Foster State Park.

Wednesday, September 23, 2009

Fisheries in Peril: The Evolution of Exploitation

What happens when the commercial fishing industry and recreational fishers target certain species for size? Do these practices of selective harvest equate to active artificial selection for smaller fish? Do these practices reverberate in the fish DNA in such a way that humans can be said to be manipulating the evolutionary trajectory of marine life? Thanks to the journal of Evolutionary Applications, here’s your chance to find out!

A few weeks back Loren McClenachan of the Scripps Institution of Oceanography provided an overview of her recent work to the folks at Florida State University - where she’s currently doing some post doc stuff. The bulk of her research centers on the impact that historic human activities have on the populations of fish and marine mammal species. More specifically, using contemporary and historical records such as ship logs, archived photographs, newspaper articles, documented personal accounts, and similar sources, she examines the quantity, geographic distribution and individual sizes of harvested species.

For example, to look at the toll humans have taken on populations of the goliath grouper (Epinephelus itajara) in south Florida, McClenachan ventured to Key West and collected photographs from resident fishing charter services, and historical newspaper articles from the archives at the local county library. Through analyzing the information, she was able to statistically demonstrate (and pictorially illustrate) the change in species composition and individual size of fish harvested recreationally in the Florida Keys. More to the point, she was able to show that between the 1920s and 1970s the maximum size of harvested trophy fish decreased while at the same time the total number of caught fish plummeted.

Photo from McClenachanlen's below cited paper; Grouper Catch Dated 04/14/57

If interested, McClenachan’s grouper paper can be found here:
McClenachan, L. (2009). Historical declines of goliath grouper populations in South Florida, USA Endangered Species Research, 7, 175-181 DOI: 10.3354/esr00167

One has to wonder (i.e. worry) what impact humans are having on fisheries worldwide. Rather it is for recreational or commercial purposes, our fishing actively is reducing the abundance of many marine species, and one can argue that we’re even aggressively and proactively engaging in an artificial selection practice that seems to be in pursuit of smaller fish and reduced species diversity…

I’m reminded of McClenachan’s talk because the journal Evolutionary Applications has just published a special edition which makes available (FREE!) research presented during the 2008 American Fisheries Society Annual Meeting. Anyone with an interest in fisheries, oceanography, ecology, evolution or conservation should take a look – there’s something for everyone!

Included papers (All of which are free - HERE):

Life history change in commercially exploited fish stocks: an analysis of trends across studies (p 260-275)Diana M. T. Sharpe, Andrew P. Hendry

The role of experiments in understanding fishery-induced evolution (p 276-290)David O. Conover, Hannes Baumann

Comparison of demographic and direct methods to calculate probabilistic maturation reaction norms for Flemish Cap cod (Gadus morhua) (p 291-298)Alfonso Pérez-Rodríguez, Marie Joanne Morgan, Fran Saborido-Rey

Is fishing selective for physiological and energetic characteristics in migratory adult sockeye salmon? (p 299-311)Steven J. Cooke, Michael R. Donaldson, Scott G. Hinch, Glenn T. Crossin, David A. Patterson, Kyle C. Hanson, Karl K. English, J. Mark Shrimpton, Anthony P. Farrell

Life-history traits and energetic status in relation to vulnerability to angling in an experimentally selected teleost fish (p 312-323)Tara D. Redpath, Steven J. Cooke, Robert Arlinghaus, David H. Wahl, David P. Philipp

Avoidance of fisheries-induced evolution: management implications for catch selectivity and limit reference points (p 324-334)Jeffrey A. Hutchings

Quantifying selection differentials caused by recreational fishing: development of modeling framework and application to reproductive investment in pike (Esox lucius) (p 335-355)Robert Arlinghaus, Shuichi Matsumura, Ulf Dieckmann

Size-selective fishing gear and life history evolution in the Northeast Arctic cod (p 356-370)Christian Jørgensen, Bruno Ernande, Øyvind Fiksen

Propensity of marine reserves to reduce the evolutionary effects of fishing in a migratory species (p 371-393)Erin S. Dunlop, Marissa L. Baskett, Mikko Heino, Ulf Dieckmann

Implications of fisheries-induced evolution for stock rebuilding and recovery (p 394-414)Katja Enberg, Christian Jørgensen, Erin S. Dunlop, Mikko Heino, Ulf Dieckmann

Mitigating fisheries-induced evolution in lacustrine brook charr (Salvelinus fontinalis) in southern Quebec, Canada (p 415-437)Kenichi W. Okamoto, Rebecca Whitlock, Pierre Magnan, Ulf Dieckmann

Eco-genetic model to explore fishing-induced ecological and evolutionary effects on growth and maturation schedules (p 438-455)Hui-Yu Wang, Tomas O. Höök

Tuesday, September 22, 2009

Sexual Selection and Hyla gratiosa: Barking Fast and Barking Long

In regards to sexual reproduction, the selection of potential mates can generally be thought of as functioning along one of four lines; through identifying Good Genes, receiving Direct Benefit, via Sensory Bias and by Fisherian Runaway. However, even though most species have adapted to one of the core strategies listed above, the methods of selection themselves are far from being restrictive. In fact, these strategies of mate choice may operate independently, collectively or in conjunction with other aspects of local ecology and Natural Selection – they’re not by any means exclusive. In a word, the processes under which one chooses a mate can be rather “complex”.

In considering the complexity of this dynamic, evolution and sexual selection have, on the average, placed the female gender in a position to choose between potential male reproductive partners; when it comes to sex, the females are the deciders.


Well, this is so for a few different reasons. One of which is that females are generally the limiting gender in a population. This means that they ultimately control population numbers and take on the added burdens of producing ova and caring for young – both of which can be taxing to available resources. In addition, females also tend to be fewer in number within a given population, often outnumbered by the males.

So, if the power of mate choice belongs to the female, on what grounds is her selection to be made and what criteria are weighed and measured prior to committing to such 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?

For Hyla gratiosa, the “barking treefrog,” the female’s choice of mate seems to center on the duration and frequency of the boy’s bark.

I took this H. gratiosa snapshot two weeks ago near Wildwood, Fl

Hyla gratiosa is a rather robust looking treefrog that grows to be somewhere between five and seven centimeters as an adult. Found in the southeastern United States, these guys are easily recognized by their spots, which cover large portions of their back and legs.

Back View of above Specimen

Although generally spending the majority of their time high in the trees, they have been known to venture to the ground during the summer months in efforts to cool off in the shade of herbaceous ground plants. Mating season pushes the males to water where they call, or “bark,” for females. The male’s “bark” during mating season (March through August) is loud and explosive. Often repeated in intervals of a second or two, the duration and frequency of their call has the ability to communicate health and virility to the inquiring female.

You can Listen to a Sample “Bark” from the Smithsonian HERE (at Bottom of Page).

In testing how the female places value on the calls of the male, a couple of researchers from James Madison University recorded and played back the calls to females in order to judge the their response to the stimulus. Basically, they went out and caught females (actively engaged in amplexus), took them to a prepped area, placed them behind blinds, and then played them calls of varying structure. Once the calls had been played, the blind was lifted from the female frog and the researchers watched as she either moved to engage her would be suitor – a sound speaker, or took a non-responsive action.

Going into the experiment, the researchers developed four hypotheses to describe possible ways in which the female may assess the calls:

(1) Single-trait Hypothesis. Females may perceive multiple cues as a single trait, even though researchers may identify them as separate traits.

(2) Amplifier Hypothesis. A trait may not be directly assessed by females but may amplify another trait that is assessed directly, thereby allowing females to better discern differences between males in the assessed trait.

(3) Hierarchical Hypothesis. Females may assess traits in a hierarchical fashion, basing their choice on the higher level trait whenever this trait differs between males and using lower-level traits only when higher-level traits are difficult to discern between males.

(4) Simultaneous Hypothesis. Females may base their choice of mates on multiple traits, combining preferences for individual traits. Preferences for traits may be combined additively.

Following the experiment, the researchers concluded that the females consider both the rate and duration of the call independently, but they show an overall leaning towards high call rates over those of an extended duration. However, this preference only stands true with in certain ranges of acceptability, if the frequency of the male’s call rate falls below a certain threshold, the female will additively consider the duration as well.

Hypothesis 4, the Simultaneous Hypothesis, seems to best describe the female barking frog’s call selecting criteria.

BURKE, E., & MURPHY, C. (2007). How female barking treefrogs, Hyla gratiosa, use multiple call characteristics to select a mate Animal Behaviour, 74 (5), 1463-1472 DOI: 10.1016/j.anbehav.2007.02.017

Monday, September 21, 2009

Organic Chemistry and a Walkingstick Insect

The “two-striped” walkingstick (Anisomorpha buprestoides) is a familiar species in the southeastern United States. Here in Florida, there are a few varieties, each of which can be distinguished in field by the color of the parallel stripes that run down the length of their back. For example, the male and female pictured below (snapshots taken last week) are commonly referred to as the “brown two-striped” walkingstick. Other colormorphs include the “white two-striped” and the “orange two-striped”.

Representing one species of the more than 2500 known walkingsticks, Anisomorpha buprestoides are notorious for their ability to produce and dispense noxious and irritating chemicals. Used as a defensive mechanism, the harsh organic isomers (different compounds with the same molecular formula; i.e. they’re bonded differently) produced by the walkingstick are sprayed from the thorax into the face of would be predators - and the occasional annoying human.

Recent work published to the Journal of Chemical Ecology has shown that the isomers produced by A. buprestoides can be found as one of three diastereomers: anisomorphal, dolichodial, and peruphasmal. Furthermore, the relative proportions of the stereoisomers produced are unique to the age and geographic location of the walkingstick.

NOTE: To avoid painful besiegement by “chem-talk,” linked here is a quick refresher video on isomers; for those long removed from an organic chemistry class (Courtesy of YouTube’s “ValChemistry”).

The correlation that has been found to exist between the insect’s chemical defenses and its location and maturity seem to suggest a genetic based mechanism of development as opposed to a plant (food) or environmental based means of acquisition.

Incidentally, the photographing of a male and female together is by no means a rare occurrence. The male of the species typically attaches himself to the female when she reaches sexual maturity. He does this by locking his cerci (claspers located at the end of his abdomen) to her abdomen. There he remains – indefinitely. He’ll remain attached through her repeated molting cycles, frequently even observed being dragged behind her as dead weight…

Dossey, A., Walse, S., & Edison, A. (2008). Developmental and Geographical Variation in the Chemical Defense of the Walkingstick Insect Anisomorpha buprestoides Journal of Chemical Ecology, 34 (5), 584-590 DOI: 10.1007/s10886-008-9457-8

UPDATE: Steve (a chemist) has posted an addendum to this article at Bridgehead Carbons with additional info on walkingsticks and the chemistry described in the cited article. Check it out!

Sunday, September 20, 2009

Thinking Outside the Niche

Ecologist and evolutionary biologist Dr. Mark McPeek (Professor at Dartmouth College, and Editor-in-Chief of The American Naturalist) spoke at Florida State Thursday and Friday of last week. Unfortunately, fieldwork prevented my attendance at the first lecture, but luckily I did manage to make Friday’s session.

McPeek’s recent work has centered on community assembly in freshwater ponds, with a specific focus on the evolution and ecology of damselflies. His work as a whole (See his publications HERE) demonstrates an exceptional cross-discipline framework with representation from both the applied and theoretical aspects of population ecology, genetics, molecular systematics, comparative biology, geology and paleontology.

During Friday’s talk, McPeek discussed the biogeography, reproduction, speciation and coexistence/co-occurrence of several Enallagma species. After first describing the spatial and temporal similarities that exist between periods of past glaciation and the range expansion/speciation events recorded in the DNA of damselflies, he moved on to the neutral theory of community ecology.

The neutral theory of ecology basically maintains that a portion of the biodiversity displayed within an ecosystem is attributable to species that occupy identical, or nearly identical, niches (i. e. these species occupy comparable positions in the foodweb and utilize the same biotic and non-biotic resources). In addition, the neutral perspective states that although some phenotypic disparities may occur between different species, these disparities have no affect on the critters’ fitness or demography.

Using Enallagma as a case study, McPeek described a recent experiment in which the neutral theory was put to the test. Through directly manipulating the relative abundance (the number of one species) and absolute abundance (the total number of both species) of two like-species, McPeek placed two varieties of Enallagma in identical cages with tightly controlled environmental parameters; included as part of the tightly controlled parameters was the presence of a fish – a predator of Enallagma.

What McPeek discovered was that manipulation of one species’ relative abundance affected fitness little, whereas manipulation of the total abundance of both species showed direct effects for both.

His conclusion…

Although the two varieties of damselflies are sexually isolated, for the purposes of ecological functionality the two species are essentially one in the same.

For more on McPeek’s ideas regarding the neutral theory and niche differentiation, check out his publications list (linked above), specifically the article:

Leibold, M., & McPeek, M. (2006). COEXISTENCE OF THE NICHE AND NEUTRAL PERSPECTIVES IN COMMUNITY ECOLOGY Ecology, 87 (6), 1399-1410 DOI: 10.1890/0012-9658(2006)87[1399:COTNAN]2.0.CO;2

Wednesday, September 16, 2009

Wetland Plant of the Week #27

Sarracenia minor

"Hooded Pitcher Plant"

As with Sarracenia leucophylla and Sarracenia flava (Ecographica’s Wetland Plants of the Week numbers 24 and 25), the hooded pitcher plant is an Obligate, insectivorous member of the Sarraceniaceae Family that has evolved highly specialized leaves that are capable of capturing invertebrates. Native to Florida, this perennial plant displays yellow to yellowish-green flowers and leaves that are around 26 centimeters in length. One leaf – the hood – has adapted in such a way to overlap the cupped base of the plant, forming a "hood".

As with the above mentioned Sarraceniaceae, this plant loves wetlands, but demonstrates a greater tolerance for mesic environments than does the other two.

These were photographed in the Osceola National Forest a couple weeks back.

Tuesday, September 15, 2009

The Future of Biodiversity Research

I decided to take a short break from scratching my chigger bites to recommend a paper on ecology. The paper reviews the links between biodiversity and ecosystem function, and does an excellent job of clarifying some of the commonly held misconceptions about species diversity.

For instance one of the diversity flavored misconceptions that I encounter on a regular basis centers on the notion that species richness (the count of the different species present at a given location) is the preeminent indicator of ecological stability, quality or “value.”

Yes, richness is absolutely an important measure of a system’s health, however it is just one metric, and even if – during an assessment - one is able to identify a species list two-miles long, there are other factors that need to be considered prior to making a “value – based” determination. After all, the study of ecology should center on evaluating the processes, cycles and organismal traits that drive the actual functionality (energetics, nutrient processing, trophic interactions, etc…) of the system at hand.

It’s all about the interactions.

In other words, although having a large variety of species in an ecosystem is generally a good thing, there is always going to be some redundancy built in; some species have a higher “value” than others, some contribute less to the foodweb, some more…

So, is diversity important - yes! But not only diversity in nominal place holders, what’s important is a diversity of ecological functions. Do the traits of those present facilitate the system? Are there traits lacking in the system that, if present, would bring enhancement? What are these traits, and how can they be measured?

The recommended paper:
Reiss, J., Bridle, J., Montoya, J., & Woodward, G. (2009). Emerging horizons in biodiversity and ecosystem functioning research Trends in Ecology & Evolution, 24 (9), 505-514 DOI: 10.1016/j.tree.2009.03.018

NOTE: I don’t intend the above to deride any particular species; all have ecological “value” beyond the aesthetic. My point is simply that the concept of species diversity and its associated measure, species richness, can sometimes be mishandled.

Sort of a minor pet peeve of mine, like ecologists that think of ecological succession as a predetermined, unavoidable “potential” towards which all communities strive. This, despite the conflicting and limiting physical conditions in which the community currently resides; but that’s another rant...

Sunday, September 13, 2009

The Selfish Bee’s Genes and the Selfish Gene’s Bees

Because of the deputation of workers as caregivers, the assigned reproductive responsibilities of the Hymenopteran queen, and other observed caste-like divisions of labor, eusocial invertebrates such as bees and ants are often presented as the exemplars of group selection theory. However, recent research published in Molecular Ecology suggests that the loyalties and actions displayed by some members of these social groups hint at far more self-centered motivations.

The research, conducted using Brazilian stingless bees (Melipona scutellaris), examined the genotypes of approximately 600 bees to ascertain parentage. What the scientists discovered was that more than 20% of the male bees present in the average hive had been the offspring of worker bees - not that of the queen bee. Further, of this 20% of worker born males, 80% had been derived from worker-lineages extending from the previous queen, not the matriarch currently holding the throne! This means that not only are about a quarter of the hive’s males being propagated by workers, but they also seem to be exceeding the average lifespan of the other queen-rendered bees by about three times, and they are actively carrying on the tradition of unauthorized reproduction.

Minimally stated, the idea of group selection holds that the ebb and flow of a group’s gene pool is determined by the benefit of specific alleles rendered to the group as a whole; this as opposed to a gene pool being composed of a conglomerate of genes beneficial only to the individual members therein - or to the genes themselves. Said somewhat differently, group selection contends that the individual members of a group (species, nest, hive, etc…) may sacrifice their own individual fitness, if such sacrifice would be advantageous to the assembly of individuals viewed as a single unit.

In haplodiploid critters, such as the currently discussed bees, benefit to the hive is obtained via a caste system in which workers choose to help raise the queen’s offspring (their sisters) instead of actively reproducing themselves. Kin selection, generally thought of as the antithesis of group selection theory (though, the theories aren’t necessarily exclusive), explains the eusocial dynamic by means of a gene centered perspective. This view justifies the sacrifice of workers through demonstrating that the genes present within the workers can be amplified in the gene pool if they promote the success of their sisters over that of their own young. This because workers have a higher degree of relatedness (i.e. share more genes) to their sisters than to their own offspring.

As stated on page 7 of the paper, “…the greater reproductive rate of workers derived from a superseded queen is also consistent with kin selection theory, given that it pays workers more from exploiting the colony if costs are carried by less related individuals.”

At any rate, it also turns out that the bees from this study are not only being produced from lines other than the current queen’s, but they also contribute nothing to the hive in terms of labor or work – they get a free ride…

From page 8; “These results are the first explicit demonstration that conflict over male parentage in insect societies is not just played out between the queen and workers and between the workers of one generation, but that the conflict may also spill over from one worker generation to the next.”

ALVES, D., IMPERATRIZ-FONSECA, V., FRANCOY, T., SANTOS-FILHO, P., NOGUEIRA-NETO, P., BILLEN, J., & WENSELEERS, T. (2009). The queen is dead-long live the workers: intraspecific parasitism by workers in the stingless bee

Molecular Ecology DOI: 10.1111/j.1365-294X.2009.04323.x

Monday, September 7, 2009

Hunting Down Darwin

Probably old news for most, but new to me; funny - but sort a scary too...

Friday, September 4, 2009

Wetland Plant of the Week #26

Dichromena colorata

"White-Top Sedge"

White-top sedge, or star rush, is an herbaceous perennial plant with linear erect leaves and slender tubular stems. The flowers of Dichromena colorata are white with two stamens and no perianth; they can have three to ten bracts. A member of the Cyperaceae and a Facultative Wet species, star rush is found throughout Florida.

This one was photographed on Wednesday near Wildwood, Florida.