The evolution of hyperactivity, impulsivity and cognitive diversity

Posted on December 7, 2011 by Kathryn Sparks

This paper focuses on the past and current effects of the impulsivity trait associated with ADHD, specifically the hyperactive/impulse subtype of ADHD, also referred to as ADHD-HI. One of the main questions in the class discussion was what is the difference between ADHD and ADHD-HI…according to various medical websites, I discovered that ADHD, or attention deficit hyperactivity disorder, has three basic forms: primarily inattentive, primarily hyperactive-impulsive, and a combination of the inattentive and hyperactive-impulsive. The combination ADHD is the most common, the primarily inattentive kind is often seen, especially in girls and adults, but is less common than the combination type, and the hyperactive-impulsive type, as discussed in this paper, is rare.

The paper looks at the possible influences of the persistence of ADHD in the population. Since ADHD is associated with an allele that has been shown to be positively selected for since the appearance of the anatomically modern human, the seven-repeat allele of dopamine receptor type D4 (DRD4-7R), perhaps ADHD is also selected for. The authors suggest that ADHD’s most characteristic feature is behavioral variability, which manifests itself as impulsivity, the willingness to take risks, and novelty-seeking. Since novelty-seeking has also been associated with DRD4-7R, the authors propose that perhaps this trait has been selected for and is beneficial to certain types of society, including female-dominated farming and migratory societies. This might explain why the DRD4-7R allele is prevalent in South America. Those who migrated to South America as an empty ecological niche would be more likely to explore if prone to novelty-seeking.

The authors seem to be examining the possibility of whether ADHD-HI have been selected for as a benefit to individual fitness. Besides being adaptive in the sense of behavioral variability, the authors suggest several other ways it might be adaptive to the individual: having the ability to gain maternal attention, to be more creative, to fight in an unpredictable manner, and to be more aggressive. However, with each possible adaptive behavior, they list a negative drawback, leading the reader to believe that perhaps they don’t believe in the idea of ADHD-HI as an benefit to individual fitness.

The authors hypothesize that the individual with ADHD-HI may use their novelty-seeking and risk-taking behaviors to gain exploratory knowledge, which can be advantageous for other members of his social group (ADHD-HI, as rare as it is, is most often seen in boys). The few individuals with ADHD-HI in the social group test social limits, perform risky experiments, and explore physical space, while the reliable and predictable non-ADHD members of the social group learn from this information risk-free.

The authors demonstrate this hypothesis with a computer simulation that loosely uses the optimal diet model of foraging in hunter-gatherers. A food-changing task is used to represent a changing environment and the accuracy with which each group obtains knowledge of food quality. Four groups with 40 members each are used in the simulation: 2 homogenous groups entirely composed of either “predictable” or “unpredictable” individuals and 2 mixed groups composed of either 5% or 25% unpredictable members. The “undpredictable” members simulate the risk-taking individuals with ADHD-HI. Of the 4 groups, the one containing the 5% “unpredictable” members, or 2 members out of the 40, gained the most accurate knowledge of food quality the fastest, thus the group members died more slowly over time. In the group with all predictable individuals, members were more likely to stick to only the foods that they knew were of good quality, so members died relatively quickly over time of malnutrition. In the group with all unpredictable individuals, the members were more likely to take risks and try foods of unknown quality but did not learn from the mistakes of others, thus dying relatively quickly over time from food poisoning.

Therefore, the authors conclude that perhaps ADHD-HI was selected for via group selection, rather than individual selection, early on in hominid evolution in certain types of societies like the hunter-gatherer society, where members had to forage for foods of both known and unknown quality. This disorder perhaps persists in humans today since the cost of including an unpredictable minority in society is small compared to the cost of lacking such individuals in a rapidly changing environment.

In class we discussed how the authors didn’t really go into a detailed account of how this group selection specifically occurred, in a genetic sense. They didn’t deal with the possible problems with their group selection theory, such as how group selection would even happen when individual selection will always occur at a faster rate when conflicting selection pressures are at work. In my opinion, even though the authors did ambitiously attempt to hypothesize about a disorder of relatively unknown cause, their group selection theory was not supported with facts and was unconvincing at best.

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Predator-Driven Trait Diversification in a Dragonfly Genus: Covariation in Behavioral and Morphological Antipredator Defense

Posted on December 5, 2011 by nfurlan

The impact of predation on phenotypic diversity is a topic that has only been studied recently. Prey use predator-specific correlated sets of morphological and behavioral traits to deter predators, and depending on the selection regime, these traits can be differently correlated with one another. For instance, trait compensation occurs when only one of the traits is beneficial to the organism and as a result, the traits are negatively correlated with one another. Conversely, trait cospecialization refers to the simultaneous application of two traits that are each helpful to the organism; these traits will be positively correlated with one another.

Ancestral Leucorrhinia dragonfly species are hypothesized to have inhabited lakes with fish as top predators (fish lakes) and possessed large abdominal spines to deter predation; fish often spit out spined dragonfly nymphs. However, with a shift into ponds with dragonflies as the apex predator (dragonfly lakes), these spines have undergone a reduction in length. Mikolajewski et al. (2010) sought to study the antipredator defenses of Leucorrhinia against the backdrop of these different habitats and predation regimes. More specifically, the researchers studied the covariance of abdominal spine length, burst escape swimming speed, and arginine kinase (Ak) activity, the mechanism responsible for providing energy for short-lasting, highly consumptive muscle activity (as occurs in burst escape swimming). The researchers hypothesized that burst escape speed is under weaker selection pressure in dragonfly lakes and may in fact be costly to maintain. As such, they anticipated higher burst escape swimming speeds and Ak activity in Leucorrhinia species inhabiting fish lakes than those species inhabiting dragonfly lakes.

Five Leucorrhinia species were considered: L. albifrons, L. caudalis, L. dubia, L. pectoralis, and L. rubicunda. L. dubia and L. rubicunda are traditionally considered dragonfly-lake specialists, although L. dubia’s phenotypic plasticity allows it to survive in both habitats. Nymphs’ abdominal spines were measured, and those lacking spines were subjected to a sham measurement. Burst escape speed was then measured for each nymph; a predator attack was simulated and burst escape swimming was videotaped. Three trials were completed, and the mean burst escape swimming speed was calculated. Directly after the swimming trials, nymphs were individually frozen, weighed, ground and assayed for Ak activity, which was expressed at absorbance per mg wet mass.

As expected, fish-lake specialists L. pectoralis, L. caudalis and L. albifrons had higher burst escape swimming speeds than dragonfly-lake specialists L. dubia and L. rubicunda. Although fish-lake L. dubia had lower burst escape speeds than true fish-lake specialists, they had higher burst escape speeds than that of dragonfly-lake L. dubia. Evolutionary contrast analysis regressions reported positive correlations between spine length and burst escape speed (R^2 = 0.84), spine length and Ak activity (R^2 = 0.76), and Ak activity and burst escape speed (R^2 = 0.98).

This work broaches a number of questions that could be addressed with follow-up studies. First and foremost, common garden experiments would be invaluable in determining the basis of population differences in L. dubia; are these differences the result of genetic differentiation or phenotypic plasticity? Furthermore, are these traits influenced by independent selection, or are they controlled by pleiotropy?

Citation: Mikolajewski et al. 2010. Predator-driven trait diversification in a dragonfly genus: covariation in behavioral and morphological antipredator defense. Evolution 64: 3327–3335.

Figure: Mikolajewski and Johansson (2004)

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Ecological and Evolutionary Consequences of Coastal Invasions: A review

Posted on December 5, 2011 by kturek

The paper “Ecological and Evolutionary consequences of Coastal Invasions,” by Edwin Grosholz presented a review of the literature regarding invasive species in estuarine and marine environments. He begins with an introduction of how these environments are among the most invaded habitats  and yet had not been as well studied with regards to the consequences of invasions as terrestrial or freshwater ecosystems. However, research in this area is beginning to increase (especially since the time of publication) since the effects like hybridization, impacts on species and ecosystems, cryptic species invasions and extensive geographical spread of the invaders suggests that the consequences might be worse than realized.

Grosholz begins by examining the ecological consequences of invasions looking at different levels. First he looks at species-level consequences between the invader and a single species. He uses studies of invasive snails and their impact on native snails to illustrate this point. Next he looks at community-level consequences by the Asian mussel introduced into mudflat communities in San Diego. The study found that the mussels provided byssal thread habitats and therefore a novel community structure. However the cascading effects on higher trophic levels were not addressed because they were not yet known for the discussed environments. Next were ecosystem-level consequences and how a species of  Asian clam changed the food web in  San Francisco Bay by inhibiting the spring phytoplankton blooms.

In order to provide a well-rounded view of invasive species Grosholz provided information about the effects on the invaders themselves as well. These include suffering higher predation, as in the case of the Asian mussel, native species resisting exotic species, and the debated theory that more diverse communities are less easily invaded. Native communities can affect the geographical spread of invaders as well.  Coastal invasions showed greater variation in the rate of spread  and a more extensive range expansive over a short amount of time. Finally Grosholz also mentioned the more frequent transportation of pathogens and parasites in harbors which could have profound effects.

There are also many evolutionary consequences to the introduction of invasive species which are outlined with examples from literature. First is the tracing of invasion pathways using microsatellite DNA (which is NOT abbreviated: mtDNA). But this technology will hopefully aid in predicting impacts of invasions, preventing future invasions and seeing the invasion pathways. Cryptic invasions are also a problem with misidentification of native and invasive species. Native genotypes can be lost through hybridization and introgression and invasive species can also affect phenotypic plasticity and population structure. The thickening of snail shells as a result of crab invasions depicts changes in phenotypic plasticity and variation among subpopulations of clams was used to demonstrate changes in population structure.  The final evolutionary consequence was physiological adaptation or the selection and physiological evolution influencing success in invading populations. The example for this was the multiple invasions by genetically distinct copepods in different areas of the world.

Grosholz ended his review with some final conclusions about the gaps in the knowledge we have as well as future directions of study to fill in these gaps. Overall it was a good review of the literature and applicable to any environment that has invasive species. The paper brought up several points of discussion however. First it raised the question of what constitutes a “naturalized” species. It seems that there isn’t a clearly defined answer at this time, although these species seem to be ones that do not have harmful effects on the environment they have invaded and over some period of time have become “normal.” We all seemed to agree that for science to move forward it is important to integrate ecology and evolution but it was also important that we distinguish the two. Despite the interconnectedness, the two areas do have their differences; the largest component seems to be time. Ecology is the study of relationships in an environment at the present time  while evolution is change over time. Both are necessary to understanding biology and, while it is not always possible, integrating the two provides  a more complete understanding for the future.

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Coral reefs promote the evolution of morphological diversity and ecological novelty in labrid fishes.

Posted on December 5, 2011 by mmalone7

S.A. Price, R. Holzman, T.J. Near, and P.C. Wainwright.

Ecology Letters 2011 14: 462-469

Those of us studying biology are familiar with the concept that coral reefs support biodiversity.  The authors of this paper nicely demonstrate this concept and give evolutionary importance to many of the conservation efforts occurring on reefs across the world.  Estimates of species richness on coral reefs have shown about 50% of all habitat restricted, marine species to occur on reefs.  Paleontological work has also shown that throughout the Paleozoic many marine genera originated on reefs and those reefs have supplied diversity to many other marine regions.  Finally, work on other fish groups, such as the Tetradontiformes (puffer fish), has shown that higher rates of evolution have occurred on reefs than non reef habitats. 

These prior examples give the authors a strong basis to the morphological and ecological evolution they want to address.  The authors chose to look at morphological diversity and ecological niches rather than pure taxonomy because they are looking to address the evolution of functional diversity.  Functional morphology is expected to have profound implications for ecological diversity, as morphology can constrain an organism’s ability to perform or have reproductive success.  Labrids (wrasses) are the study family of species to address morphology and ecology constraints on evolution on coral reefs.   They are a very diverse group with 60 families and over 500 species.  They are highly studied reef species and much is known on their evolutionary history as well as feeding morphology and ecology on reefs.

The authors use tropical reef and non reef fishes, excluding any temperate species.  Utilizing a systematic tree developed by Kazancioglu et al. 2009, the authors imposed reef and non-reef origins, trophic niches, and head morphology, thus demonstrating the diversity seen within Labridae.  The methods the authors used in particular were morphological data dealing with feeding, dietary data from literature surveys, trophic novelty developed from morphological principal component analyses, and finally evolutionary rates. 

Evolutionary rates were developed using the Brownian motion (BM) model of phenotypic evolution.  BM models generate evolution via randomization.  Rates were developed utilizing one rate for both reef and non reef species, as well as a faster rate for reef species and a slower rate for non reef species.  These were then corrected with an Akaike Information Criterion that takes into account smaller sample sizes.  Finally, rates were averaged and compared between reef and non reef groups. 

The authors found 75%  of the variance in their data attributed to the first 4 priciple component analyses run.  69% of morphological data was unique to reef fishes, while only 4% unique to non reef fishes.  Novel feeders (such as cleaner fish or coralivorous fish) were removed to eliminate any bias, and similar results were found.  Finally, evolutionary rates were found to be significantly higher for PC1, PC4, and PC7 for reef inhabiting fishes than non reef inhabiting fishes, thus confirming the authors’ hypothesis that higher rates occur for reef fishes than non reef fishes. 

The authors discuss differences that could occur utilizing different evolutionary models, the importance of prey abundance on reef systems and the functional difference size could have on morphological data.  Coral reefs are biodiversity hotspots, and important habitats for evolutionary and ecological mechanisms that may maintain or generate this biodiversity.  Preservation of reefs is necessary not only for maintaining current diversity, but for the conservation of future adaptability of organisms. 

In class we discussed the use of principal component analyses and phyologenetic trees.  Personally, I felt this paper nicely tested the authors’ hypotheses and I also liked the two simple graphs that demonstrated their results from PCA and evolutionary rates.  Dr. Reddy discussed systematic and agreed to give a seminar prior to the start of spring semester.  I will let everyone know when something is set up!

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Reproductive performance of alternative male phenotypes of growth hormone transgenic Atlantic salmon (Salmo salar)

Posted on December 4, 2011 by mhassett

The ever-increasing human population places increasing stress on global food resources. In response to this, an idea to improve fish farming has come about to create transgenic salmon that would have an increased growth rate. Researchers have been able to take growth hormones from Chinook salmon and an antifreeze protein gene promoter from ocean pout, then injected them both into Atlantic salmon that have since been raised in labs. The genetic manipulation has been proven to work, but no studies have addressed the ecological concern of the potential for these transgenic salmon to escape into the ocean and alter the gene pool of the wild Atlantic salmon fishery. Another concern is that the transgene itself could have a Trojan horse-like effect on the wild Atlantic salmon population, where the initial impact may seem beneficial, but would have negative effects in future generations of salmon.

In the paper I brought to class this week by Moreau et al. (2011), the researchers wanted to test the potential breeding performance of the transgenic Atlantic salmon. Atlantic salmon are anadromous fish, which means they are born in freshwater, migrate to the ocean, return to freshwater to spawn. Two of the life stages, parr and adults, have the potential to contribute to spawning. Adult Atlantic salmon develop secondary sexual characteristics and fight for access to females, while the precocial parr use their immature appearance to use sneak fertilize with females. In order to take account for both mating strategies, the researchers created separate sets of breeding trials for transgenic captive-reared adult male vs. anadromous wild type adult male, and transgenic parr male vs. wild type parr male. For identification purposes, individuals were injected with either Peterson disc tags, passive integrated transponder (PIT) tags, or implant elastomer six weeks before the breeding trials. The researchers used underwater and overhead cameras to observe spawning behaviors. A genetic parentage analysis was conducted only on the fry from the parr trials because the behavioral analysis of the adult trial was easily able to determine breeding success.

As predicted, the anadromous transgenic males were significantly larger than anadromous nontransgenic males in mass and length, but this did not significantly affect the frequency of aggressive behavior between anadromous transgenic and nontransgenic males. Nontransgenic anadromous males had significantly higher nest fidelity both with and in the absence of competition. Nontransgenic also had higher quivering frequency (a courting behavior) and participated in more spawning events with and without competition.

Transgenic precocial parr were significantly larger than wild type parr of the same age in both mass and length. However, when transgenic parr of age 0+ were compared to nontransgenic age 1+ parr, there was no significant difference in mass or length. Nontransgenic parr had a higher nesting fidelity in most of the breeding trials. Fertilization for both transgenic and nontransgenic parr was low, but nontransgenic parr were significantly more successful.

The most important data that comes out of this paper is that it shows that although transgenic fish were out-competed in both set of breeding trials, the transgenic fish still had the ability to spawn and alter the gene pool of the next generation. A previous study by Bessey et al. (2004) showed that when transgenic and nontransgenic males were both cultured in a laboratory setting, both groups experience poor spawning success. The spawning differences in Moreau et al.’s study could be a result of comparing wild caught nontransgenic fish and lab cultured transgenic fish. However, the different rearing environments for the two sets of fish correctly mimic a possible invasion scenario if transgenic Atlantic salmon were to escape into the wild. The authors note that in a real invasion scenario, multiple breeding partners would exist as opposed to just one female per each of these breeding trials. There is a lot of uncertainty about what would happen in a real invasion and the authors recommend future studies compare breeding performance in a variety of ecologically relevant scenarios.

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Serotonin and aggressive behavior in rodents and nonhuman primates: Predisposition and plasticity

Posted on December 4, 2011 by Kathryn Sparks

The authors in this review analyze research involving aggressive behavior in rodents (mice and rats), nonhuman primates (Old World Monkeys and Chimpanzees) and humans and attempt to categorize the aggression as either adaptive to evolution or pathological. They divide adaptive aggression into two broad categories: competitive aggression, involving competition for resources, and protective aggression, involving the protection of the animal or its offspring from predators or potentially dangerous conspecifics. They question whether extreme cases of aggression, such as the deadly Chimpanzee “killing parties” and the “sexually selected infanticide” in primates and rodents would be considered pathological; while they remain inconclusive in regards to the Chimp killing parties, they believe the killing of infants to gain access to mates and/or resources is an adaptive form of aggression that selectively began as a form of competitive aggression. Through further reading in the article, “Lethal intergroup aggression leads to territorial expansion in wild chimpanzees” (Current Biology, Vol. 20 No. 12), I discovered that other researchers recently found that the killing parties are adaptive in the form of competitive aggression, as they lead to territorial and resource expansion and, therefore, greater reproductive success.

The authors are assuming, of course, that aggression, as a species-specific behavior, must have inherited characteristics in order to be shared by all members of the species. In their analysis of the aggression found in the social organization of rodents, the authors find that the dominant rat or mouse displays aggressive behavior that is highly adaptive since the territorial male has the access to reproduction. In both rats and mice, the dominant, more aggressive rodent dominates a group of breeding females, therefore having greater reproductive success compared to subordinate or non-territorial males. While, in mice, the subordinate males are kicked out of their territory by the aggressive, dominant mouse, at the age of puberty, rats form more complex dominant/subordinate hierarchical relationships that are maintained by aggressive behavior. The authors suggest that, based on studies measuring aggressive behavior and cerebrospinal fluid levels of the serotonin neurotransmitter metabolite 5-HIAA, that perhaps low levels of 5-HIAA correspond to an aggressive trait in rodents that is adaptive to evolution.

The social organization and use of aggression in Old World monkeys are much different than those of rodents; rhesus monkeys, for example, live in large social groups called “troops” which are headed by three or more generations of females with immigrant adult males. Aggression is a small portion of a monkey’s total daily activity (2-5%) and is usually at its highest levels when monkeys attempt to attain a higher social status: male monkeys emigrate from their natal group at the time of puberty, and both males and females aggressively attempt to prevent the emigrating monkey from entering their group (30 to 50% of emigrating monkeys are killed off or disappear). Competitive aggression can also become quite intense between groups when territory and resources need to be defended. The authors view the aggression that is correlated with low levels of 5-HIAA as maladaptive to evolution since it is related to those forms that are at excessive levels and are injurious and persistent. Similarly, in human studies, low CSF 5-HIAA levels are seen to be correlated to forms of aggression involving impaired impulse control, which are also excessive and lead to negative social consequences. Therefore, based on these studies, the authors suggest that in humans and nonhuman primates, low levels of 5-HIAA in the CSF may correlate to an impulsivity trait that is maladaptive to evolution. The impulsivity and excessive, injurious aggression are predicted to be maladaptive since they will lead to social isolation from the other group members and few opportunities to reproduce successfully.

The authors also discuss how genetic polymorphisms can be influenced by environmental factors, such as early life experiences, resulting in various aggression phenotypes. For instance, the polymorphism that results in low monoamine oxidase A activity is influenced by early life experiences, or “rearing” experiences, of the rhesus macaque. (Monoamine oxidase A degrades and inactivates serotonin and other neurotransmitters, so in MAO-A knockout mice, in which the MAO-A gene is not expressed, serotonin levels are increased. Despite this serotonin level increase in MAO-A mice, they exhibit increased aggression. In other words: low MAO-A activity equals increased aggression.) Rhesus monkeys who were normally reared by the mother showed higher levels of aggression when in competition for food only when they carried the low-activity MAO-A allele. Rhesus monkeys with the high-activity MAO-A allele and impoverished infancy showed species-typical levels of competitive aggression. Therefore, even when negative environmental factors come into play, high MAO-A activity results in a species-typical phenotype, showing the complex environment between genes and the environment.

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Metabolic evolution of energy-conserving pathways for succinate production in Escherichia coli

Posted on November 22, 2011 by Alexandra Ozaki

This biochemistry paper was definitely a grueling one, but I am glad we worked our way through it and brought up some interesting questions.  One of the questions that was brought up was, how do we gauge the level of what is “more evolved”?

In this paper the KJ073 and KJ060 were determined to be more evolutionarily advanced because it developed the alternative carboxykinase pathway with a higher succinate yield.  However, if this pathway was truly more advantageous for E. Coli, then why haven’t E. Coli developed this pathway over time?  We know that the evolution of bacteria and yeast is fairly rapid; if reversing the gluconeogenesis pathway was a “better” use of the carboxykinase enzymes, E.Coli strains had billions of years to acquire this process as its primary carboxylation pathway.

So are rumen bacteria “more evolved” than E. Coli?  Especially with microorganisms, its difficult to know exactly, and on what scale do we base this on? The engineered strains of E. Coli may be more useful biocatalysts for industrial or bioenergy purposes, but we cannot deem them more evolved simply because they are more useful to mankind.

Also, sequencing the genes for each of the carboxylation enzymes as well as the glucose phosphotransferase systems in both engineered and natural bacteria provided important information to understanding mutation and expression changes.  It was interesting to learn that the PEP carboxykinase genes were not even influenced in the “evolved” strains, but a single point mutation upstream (G->A).  Adding a loss of glucose inhibition, and the PEP carboxykinase becomes the primary metabolite pathway.  From the study’s set of experiments, we were able to see how minute and specific changes in base expression can influence the life-sustaining pathways of an organism.

In microorganisms, metabolism studies are especially valuable to research because these pathways are usually one of the few indicators of its adaptations for survival.  Research can investigate respiration and fermentation processes and how they are changing over time; while these evolutionary results are not dramatic, microorganism response to a changing environment can be the first bioindicators to how larger organisms will be affected over time.

Zhang, X., Kaemwich, J., Moore, J., & Jarboe, L. (2009). Metabolic evolution of energy-conserving pathways for succinate production in escherichia coli. PNAS, 106(48).

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Breakdown of the brown trout evolutionary history due to hybridization between native and cultivated fish

Posted on November 21, 2011 by ccaldwell3

As previously discussed, fishing tends to exploit certain size and age classes in populations, leaving managers with the problem of maintaining healthy populations. Last week we discussed how somatic growth rate and population levels of harvest will evolve in directions opposite to the size bias harvest, a common problem with fisheries. One solution not discussed was releasing hatchery raised fish in native populations. This allows the population to stay at healthy levels and sizes but inputs new genetics and evolutionary history.

Released hatchery fish will spawn with native fish, causing a loss of local population genetic diversity. Araguas and colleagues performed a study in Girona, Spain where a complex evolutionary history of brown trout once occurred. There were multiple colonization events by distinct populations in the region, but the evolutionary history has been compromised by the release of hatchery fish. Consequences of hatchery releases include loss of diversity within populations, introgression and possibly extinction of local populations. Policies were enforced in Girona to attempt to save native populations by balancing exploitation and conservation genetics. They created “genetic reservoirs” in 1997, in headwaters that had little to no impact of hatchery release. Release of captive fish was forbidden in these areas, conserving native genetics of brown trout.

The goal of this paper is to assess local and regional impact of hatchery releases on the genetic population structure of brown trout. They sampled 13 headwaters in 1993 and 1999, headwaters varied from fishing to unfished areas and 4 became genetic reservoirs in 1997. The effects of hatchery fish on native populations was estimated by the LDH-C*90 allele, which is fixed in hatchery fish and absent in the native populations.

Results show significant temporal changes on the genetic composition of brown trout populations. In 5 sites, 3 of which are genetic reservoirs, changes in genetic composition were mainly due to changes in the frequencies of native alleles. Fishing did occur at most of these sites, so by pulling adults from an already depleted population it could be promoting genetic drift. A significant increase in the hatchery allele, over the 2 sampling periods, was recorded at 2 sites. Both of these locations were stocked for more than 3 years.

One site, that became a genetic reservoir in 1997, was stocked in 1994 with 800 catchable fish. This site did not show significant changes in the genetic composition. The paper fails to go into detail about the stocking that took place in 1994; they only state that selective hatchery fishing took place. I feel it is important to study this site further. What allowed this site, which was exposed to hatchery fish, to not show changes in the genetic composition? I think by expanding on environmental parameters and the management techniques used at this site, questions of what allows hatchery introgression may be answered. On the other hand, a site which had never been stocked showed introgression of hatchery fish. They predict that hatchery fish are migrating from other sites. This could cause problems because over time the protected areas could then serve as a reservoir for hatchery genes. Management in the area proposed a massive kill, but by destroying the hatchery genes you also destroy the native genes (kind of defeats the purpose of preserving them…). What could be some solutions to keeping the “genetic reservoirs” for native trout only?

This paper concludes that hatchery genes are diluting native genetic populations, which can lead to distortion of population genetic structure and possibly break down evolutionary divergence. They predict that at this rate (not counting any other environmental impacts) hatchery ancestry will be present in native populations within a few years. So, this brings me back to last weeks discussion. Are other management solutions (slot and inverse slot) a better way of keeping populations at healthy levels? Are there ways to combine or change these management plans to improve the outcome? And finally should we care about conserving natural genetics?

To address the last question, personally, I think yes. Adaptations have been formed over thousands of years in order to properly exist in the environment. They have adapted to physicochemical properties along with predator and prey availability of the system. By placing new genetics and alleles you could be diluting genotypes selected for a certain environment; therefore kicking the species back a thousand years or so. But, as brought up in class, with rapidly changing environments could hatchery fish be raised or engineered to better adapt?

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Life-History Evolution When Lestes Damselflies Invaded Vernal Ponds

Posted on November 21, 2011 by nfurlan

While copious research has been conducted on the evolution of morphological characters, the macroevolution of life-history traits along environmental gradients is a relatively unknown field of study.  Life-History Theory posits that the timing and duration of important events in an organism’s life, such as age at sexual maturity and first reproductive event, are shaped by natural selection.  As such, life history strategies respond to biotic and abiotic factors and organisms will segregate into the habitats that they are best suited for.  The environmental gradient selected for this study was pond permanence driven by hydroperiod.  At one end, permanent ponds are large, stable water bodies that hold water continuously for centuries to millennia.  At the other end of the spectrum are vernal ponds, which are small, ephemeral water bodies that reliably dry up every year.  Temporary ponds fall between the two extremes, as they can either hold water continuously or dry up depending on pond structure and drought conditions.  Pond drying imposes severe time constraints on the obligate aquatic life-history stages of some species, with vernal pond species expected to have the most rapid growth and development rates.  These researchers sought to illuminate the evolution of life histories to pond permanence in three species of Lestes damselfly: L. dryas, a vernal pond specialist, L. forcipatus, a phylogenetically close relative of L. dryas and temporary-pond specialist, and L. congener, a basal temporary-pond specialist.

The researchers conducted a 3x2x2 factorial experiment, subjecting the three Lestes species to two photoperiod treatments (Early vs. Late) and two transient starvation periods during the final instar (Fed vs. Starved).  Starvation treatments were performed in order to evaluate whether either fixed growth or plastic responses to photoperiod hinder larvae’s ability to deal with stressors, and photoperiod treatments approximated the Light:Dark hour ratios that nymphs would experience if they’d hatched either early or late in the season.  Body mass and growth rates were calculated for each nymph.  Innate immune function was quantified by scoring phenoloxidase activity after emergence in an effort to determine whether the responses to treatments impeded larval ability to deal with pathogens.

As expected, the researchers found that the vernal-pond specialist L. dryas reached each developmental stage before the other two species, emerging on average seventeen days earlier.  L. dryas also had the lowest mass at emergence of the three species, corresponding with its shorter development time.  L. dryas also experienced the highest growth rate of the three species.  These results are consistent with the hypothesis that temporary ponds are the ancestral habitat of Lestes damselflies, that L. dryas adapted after invading the vernal pond habitat, and that regular pond drying was the definitive selective pressure driving these life history traits.  All three species in the late photoperiod treatment accelerated growth and development by approximately three days, indicating that they were growing at less than their maximum physiological capacity in the early photoperiod, and starvation delayed emergence in all species and treatments.  There was no clear evidence than an accelerated life history had detrimental effects on immune function at emergence, although the class agreed that this portion of the study could have used more attention and perhaps its own study in the future.

While a well-thought-out and elegant experimental design, the class spent the majority of the class discussion debating the merits and drawbacks of lab studies compared with field studies.  Lab work may benefit from the removal of potentially confounding variables, but those same variables are often important pieces of the puzzle.  Research performed in the lab allows the observation of a select few variables and facilitates otherwise impossible experiments; however one must be careful not to impose lab findings onto the natural environment simply because the organisms studied are the same.  To be sure, each form of research has its place and the two are often complementary to one another.

Citation: De Block, M., M.A. McPeek, and R. Stoks. 2007. Life-history evolution when Lestes damselflies invaded vernal ponds. Evolution 62:485-493.

Photo Credit: Carl P. Lutz, 2009

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Sustaining Fisheries Yields Over Evolutionary Time Scales

Posted on November 21, 2011 by ccaldwell3

Fisheries want to exploit the largest fish, usually enforcing minimum size limits, which creates a truncated size and age distributing that lack larger and older fish. This form of management tends to ignore the potential for evolutionary change in harvestable mass. Conover and Munch designed an experiment to show evolutionary effects of size-selected mortality on somatic growth yield and population biomass. With the use of the Atlantic Silverside, which has similar characteristics to many harvested fish, they set up 6 harvested populations. Populations (n=1000) were harvested on 3 size-specific rules (i) all fish larger than the 10th percentile in length (large-harvested); (ii) all fish smaller than the 90th percentile in length (small-harvested); (iii) 90% harvest was random in respect to size (random). Two replicate populations for each size-specific rule were harvested on day 190. Survivors (n=100) were induced to spawn and embryos reared under identical conditions for 4 generations.

Results of this study supported the hypothesis, somatic growth rate and population levels of harvest will evolve in directions opposite to the size bias harvest. By the 4th generation the mean weight of the small-harvested population was twice that of the large-harvested population. This is due to increased juvenile growth rates in populations that the smallest 90% are harvested. Selection for fast growing genotypes increases somatic growth in these populations, bringing the fish to a “safe size” where mortality rates are decreased. The opposite, decreased larval and juvenile growth rates, is seen in the large-harvest. This means that the large-harvest is becoming reproductively viable at smaller sizes and remaining in larval stage for longer periods. This leads to smaller egg size (affecting embryo quality) and increased predation or other larval mortalities.

This experiment creates important questions for management. If anglers continue to take the larger fish (minimum restrictions) are we stunting the population? If the population reacts to this size-biased mortality, will the results be reversible?

We discussed some positive aspects of the small-harvested population in class. By removing the smallest 90% of the population, fast growing genotypes are selected for. Fast growing genotypes allow the fish to speed through the vulnerable larval stage and the larger adults play an important role in the food web (large predators). Although, would keeping the smaller fish satisfy anglers? Also, are there downfalls to this method as well?

Finally, we discussed newer management techniques the slot and inverse slot limit. Slot limit protects the intermediate size while inverse slot exploits the intermediate size. With the slot limit you could see the affects of the small harvest, speeding up larval growth; while creating more resources in the ecosystem by removing the larger fish. Although, this means anglers need to do their part and take the smaller fish, or else we are back to stunting the population. The inverse slot also has benefits, by protecting the smaller fish you allow proper larval growth and you preserve the sexually mature adults.

This paper shows that selection will occur in the opposite direction of size-specific harvests, which can have many impacts on the population (not all bad). From a management point of view, you want to keep the population at a healthy level and size distribution, but you also want to entice anglers with the possibility of a large catch. What would be your method to solve this dilemma?

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