Date Published: January 30, 2015

Source:                 PLOS Biology

Authors:              Timo Ernst, Suzi McCarthy, Glenys Chidlow, Dagwin Luang-Suarkia, Edward C. Holmes, David W. Smith, Allison Imrie

Summary:           A study reveals the emergence of a new lineage of DENV (Dengue Virus) from returning travelers to Australia from Indonesia.

Dengue is the most rapidly spreading viral disease among humans. It’s endemic to most tropical and sub-tropical countries and causes an estimated 390 million infections to occur every year. Most of the disease burden is borne by people of Southeast Asia and the Western Pacific region. Understanding how the dengue moves from country to country and how it changes is vital to understand how to solve the problem. However, the data required to do such an analysis was lacking, thus limiting the attempts the scientists made to understand the hyperendemicity of the virus and its severity.

The authors of the study sequenced the E gene of DENV (Dengue Virus) that was isolated from travelers travelling to West Australia from 7 countries throughout Asia. The collected these samples and sequenced the genes over a span of two years from 2010-2012. The authors found that a majority of the virus originated in Indonesia which is a popular travel destination for Australians. They identified the hyperendemic transmission of all four DENV stereotypes in Indonesia in 2010. The Dengue is caused by infection with any one of these four stereotypes. The genotypes of these stereotypes can lead to lineages that either turnover, displace or introduce new lineages that can also cause dengue. The authors explained how it is important to track these changes and novel appearances since they are associated with a severe disease.

After having done the research, the authors found that a new lineage had emerged. This variation DENV2, or the cosmopolitan genotype, had appeared among travelers returning to Australia from other southeastern Asian countries. The introduction of this new genotype to the new populations of humans was caused by transmission. The new genotype was introduce due to mutations. The authors found that this new lineage originated in Bali in Indonesia. In the end, the authors discussed how due to a dearth of information regarding DENV from countries like Indonesia regarding sequenced genotypes, they weren’t able to determine when the new lineage emerged or whether it was present in another form in other countries before 2012. However, the concluded saying that surveilling returning travelers that are ill can help determine where the illness originate from.

This study shows a prime example of evolution happening on the smallest scales which have an astounding effect on a larger scale. The emergence of a new lineage of a certain virus through mutations shows the most basic form of evolution. This new lineage of DENV shows that it is being selected for among many possible mutated forms of DENV.

Citation:              Ernst T., S. McCarthy, G. Chidlow, D. Luang-Suarkia, E. C. Holmes, D. W. Smith, and A. Imrie. 2015. Emergence of a New Lineage of Dengue Virus Type 2 Identified in Travelers Entering Western Australia from Indonesia, 2010-2012. PLOS Neglected Tropical Diseases 9: e0003442.

Call me maybe? Evolutionary purpose of false mating calls in Pavo cristatus peafowls

Date: March 5, 2014

Source: The American Naturalist  

Summary: A recent study conducted by Roslyn Dakin and Robert Montgomerie at the University of Chicago aims to understand the purpose of false mating calls by Pavo cristatus peafowls.

Evolutionary biology denotes signaling as the communication between organisms. Dishonest signaling, then, is the method by which an organism executes a false alarm to others of its species. For many reasons, dishonest signaling could threaten a species, especially if a predator is involved. In this research however, dishonest signaling has been found to be used by Pavo cristatus peacocks quite frequently: a third of all the mating hoots performed by males. Though generally, peafowl hoots are meant for mating or for attracting peahens (attempt hoot), peacocks have been using it even without the presence of the peahens (solo hoots). It is difficult to explain the purpose of a commonly used dishonest signaling, given its threat to species, which is precisely why this research is novel. The research conducted aimed to understand the purpose of the dishonest signaling executed by the peacocks. It hypothesized that the hoot calls represented male mating success, and thus the preferred males (who were able to mate) hoot more frequently than the unpreferred males.

Researchers observed a total of 39 Pavo cristatus peafowl between 2007 and 2010 at four different sites. Each of the males’ matings as well as hoot calls (attempt and solo) was recorded to determine whether or not a correlation existed between male mating success and male hoot calls. Researchers investigated other various factors such as the attractiveness of the male, the effect of the solo hoot call, the effect of only the hoot on peahen (without male behavior suggesting copulation).

The results of the study seem to bolster the hypothesis as total (attempt and solo) hoots of Pavo cristatus peacocks are representative of a male’s reproductive success as the rates of hooting by a male are linked with female visitation of the male and male copulation with the female. However, though not heavily supported, the results of the study also suggest that the benefit males may gain from false mating (solo) calls would be a slight increase in visitation of female peahens. In addition, the researchers also believe that the dishonest signaling of the males might attract female peahens who might otherwise not respond to mating rituals. Thus, the peahens are mating with lower quality males, falling victim to energetic costs. The researchers suggest a possible explanation for the presence of false mating calls despite its pitfalls: the solo hoot call may be a learned trait part of a reward based learning system where the reward is the ability to mate with females. Further research is needed to provide evidence for this theory.

Dakin R. and R. Montgomerie. 2014. Deceptive copulation calls attract female visitors to peacock
            leks.The American Naturalist 183: 558-564. 

Competing Natural and Sexual Selection: Variation in the Visual Signals of Wall Lizards

Date published: July 28, 2014

Source: Behavioral Ecology

Summary: A study suggests that coloration and conspicuousness of wall lizards evolved under conflicting demands of natural and sexual selection.

            A study suggests that coloration and conspicuousness of wall lizards evolved under conflicting demands of natural and sexual selection, according to a study published in 2014 by Kate Marshall and Martin Stevens from the University of Cambridge in the journal Behavioral Ecology.

            Three populations of Aegean wall lizards were studied from the islands of Skopelos, Syros, and Foelgandros. The authors investigated four main points: whether the lizards were more conspicuous to conspecifics (members of the same species) than to predators, if males were more conspicuous than females as a result of sexual competition, if there was variation in visual signals between different parts of the body, and whether the conspicuousness of the lizards differed among the three populations. Lizards must be noticeable enough to attract potential mates but they must also remain somewhat camouflaged to avoid detection by predators, resulting in conflicting natural and sexual selection.

            The results showed that lizards were more noticeable to conspecifics than to avian predators across all body regions in all three populations. Avian predators can only perceive relatively high wavelengths of UV light while lizards can perceive a much higher range. The increased conspicuousness to conspecifics was caused in part by the use of short UV wavelengths to remain noticeable to potential mates yet avoid detection by predators.

            In the Skopelos population, males exhibited increased conspicuousness over females, but in the Syros population, both males and females displayed higher conspicuousness of certain body regions. The Syros population has a higher population density, which can lead to increased sexual competition, even for females, resulting in the need for both males and females to attract mates. This is indicative of evolution because the conspicuousness varied among populations to best suit the needs of the lizards.

            It was also shown that there was variation in conspicuousness between body parts of the lizards. In the Skopelos and Syros populations, the flanks of the lizards were more conspicuous than the backs. Avian predators view the lizards from above, so their backs were more camouflaged, and because potential mates view the lizards from the side on the ground, the sides of the lizards were more noticeable.

             The Foelgandros population of lizards did not exhibit the significant differences in conspicuousness between body parts that was found in the other two populations. This is likely because the Foelgandros island lacks a number of the avian predators that are on the other islands, so the lizards have a lower risk of detection and therefore less of a need for camouflaged backs.

            The findings of the study indicate that the coloration of the lizards has evolved to make the lizards better suited to their environment. The competing demands of natural selection, which would make the lizards less noticeable to their predators, and sexual selection, which would result in lizards being more conspicuous to potential mates, led to different conspicuousness between certain body regions and differences between males and females. These differences are indicative of evolution.

Journal Reference:

Marshall, K.L.A, and Stevens, M. 2014. Wall lizards display conspicuous signals to conspecifics and reduce detection by avian predators. Behavioral Ecology 25: 1325-1337.

How did the SWS2 Gene Evolve?

Date Accepted: November 19,2014

Source: Wiley Online Library

Institutions Involved: Department of Ecology & Evolution, University of Chicago, Departments of Ecology & Evolutionary Biology, Cell & Systems Biology, University of Toronto, Centre for the Analysis of Genome Evolution & Function University of Toronto,

Summary: Researchers try and find out if color perception in birds had an influence on the evolution of a gene that controls feather color.

Did you ever wonder why some birds have bright feathers while others do not? The researchers from the University of Chicago and the University of Toronto had a similar question. Natasha Bloch, James Morrow, Belinda Change, and Trevor Price wondered, "Why did the Old World warblers have fewer pigmented feathers in comparison to the New World warblers?" So, they decided to conduct an experiment to find out. This particular experiment happens to be interesting because the researchers attempt to find out how the SWS2 gene (which codes for pigment) evolved.

This happens to be the cladogram from the paper. Here, you can see what is referred to as the Old World Warblers and what is referred to as the New World Warblers.

 For this experiment the researchers had three hypotheses. Their null hypothesis stated that the SWS2 gene remained unchanged during the course of evolution. The other two hypotheses each describe different ideas of how the SWS2 gene could have evolved. The first hypothesis believes that the gene is similar in both the New World and Old World Warblers, but was different in their respective anscestors; it also suggests that this difference in color is due to the environment of each of the birds. The second hypothesis states that the gene shifted as the New World Warblers diverged from Old World warblers, but they passed through another ancestor that occupied a different environment, which then lead to the different color perception and color difference in the feathers of each set of birds. This last hypothesis happened to be the researchers' most favored idea.

The researchers tested their ideas by sequencing the SWS2 gene from both of the warbler clades and also from some outgroups. For the New World warblers, the researchers collected birds that died from building collisions during migration in Chicago. For the Old World warblers, they used RNA samples. Once the researchers had  sequenced all of the SWS2 genes from various birs, they then reconstructed the SWS2 sequence evolution. They also identified all the variants with at least one substitution as candidates for shifts in color perception.They found that despite having 6 differences in the amino acid sequences, the ancestors of both

warbler clades had similar color perception.

In conclusion, they found that the color perception of the ancestors of both the New World warblers and the Old World warblers were the same, so this could not have contributed to the evolution (color variation) in the New World warbler's feathers. The researchers say that when they do figure out what the reason for behind the adaptiation is, they will then be easily able to determine if this evolved trait is due to historical  contingency or not.

Journal Reference: Bloch, N. I., Morrow, J. M., Chang, B. S. W. and Price, T. D. (2015), SWS2 visual pigment evolution as a test of historically contingent patterns of plumage color evolution in warblers. Evolution, 69: 341–356. doi: 10.1111/evo.12572

Evolution of E. coli - Beneficial, or Bearing a Growth Burden?

Date Published:  November 27, 2014

Source:  BMC Evolutionary Biology

Summary:  

Comparative studies over time have lead scientists to conclude that Escherichia coli (E. coli) cells grow larger in size, through generations of evolution. Testing this hypothesis required the collaboration of over 20 scientists. The Department of Infection Metagenomics, at Osaka University, completed the genome analysis component of this study.

The concern regarding E.coli cell growth stems from the fact that cell size is oftentimes proportionate to cell propagation. It could also indicate that there is a greater number of DNA replicating mechanisms in the cell, thus resulting in more frequent cell division. All of these aspects indicate that a larger cell size means a larger growth rate. This increased size does not come without a cost. There is a possibility, as other types of cells have demonstrated, that a segment of the DNA controlling cell division is mutated. Mutations can result in different shapes and sizes that prevent the cell from functioning normally; this is referred to as a growth burden.

Is E. coli in fact growing in size? If it is, what are the growth burdens? To answer this, researchers combined a series of tests. Using E. coli cells, the first test was done to explore whether or not an increase in cell size would hinder replication and growth. Using technology, cells that were smaller than their ancestors were carefully chosen. Scientists noted that a small number of mutations in the membrane-production genes would result in size evolution and no corresponding growth conflict. What initially seemed to be conclusive results actually contained some unforeseen bias. The technology used to select the cells did so in small samples rather than in a large population. Therefore, more tests had to be used in corroboration.

To confirm this, a similar test was done with cells that were thought to evolve towards a smaller sized cell. BSKY, a derived version of E. Coli, was used in this series of complex tests. Throughout, researchers employed a method of examining generations of cells, monitoring cell size and its relation to density. The cells thought to behave in this way did so regardless of the cell concentrations. In addition to these tests, genome sequencing was necessary to confirm mutations in genes coding for growth rates.

Results confirmed that a growth disadvantage does not directly link to cell size increase. RE Lenski, one of the key researchers in this study, conducted these experiments. In fact, we also see the significance behind the short time span needed for bacterial cell size to evolve. It is clear that cell size holds an important part in survival rates. A cell is less prone to external attack from protists if they are large and have a thick cell membrane. This is one of the results of evolutionary cell size increase. Evolution of cell size may be another form of natural selection, or survival of the fittest.

The diagram above depicts concentration versus time. ACs, T22Cs, Svr22Cs, and Mld22Cs are sample cells that behave similar to E. Coli. Thus, they were used in the empirical studies. They demonstrate a proportional growth rate despite the fact hat their concentration is increasing. As time goes on, their size has evolved as well, without any visible growth burden.

In conclusion, we can see that bacterial cell size evolution is a quick process that occurs in under 400 generations. Because of logistical limitations, scientists used “an empirical method” to test this. Cells thought to decrease in size demonstrated stringent selection, resulting in smaller subsequent generations. They shrunk without any disadvantage to the cell’s fitness. Thus, it can be pragmatically stipulated that E. coli cells are capable of evolving to become larger, without sacrificing fitness.

Citation:

Mari, Y., Saburo, T., Naoko, H., Shigeto, S., Hideo, M., Bei-Wen, Y., & Tetsuya, Y. (2014). Directed evolution of cell size in Escherichia coli. BMC Evolutionary Biology, 14(1), 104-127. doi:10.1186/s12862-014-0257-1

The bearings of genetic correlation on the independent evolution of body mass and skeletal dimensions in mammals

Date Published: December 2, 2014

Source: BMC Evolutionary Biology

Summary: Mice were selectively bred to test the hypothesis that a genetic correlation with body and mass compels evolutionary change in the tibia length of mammals. The results of the test showed that the rate of independent evolution of tibia length is hindered by its correlation with body mass (and vice versa).

Mammals typically display a scaling relationship between limb bone size and body mass.

The scaling of limb bone dimensions with body mass ensures proper musculoskeletal function, prevents bones from failing under increased strain from gravity or motion, and serve many other crucial purposes. The correlation between body mass and limb bone dimensions is so significant, in fact, that any major mismatches between the two traits in a populations can have negative impacts on the ability of a mammal to survive (thus, they should be selected against). The exact reason for how the genetic correlation between these two traits impacts a mammal’s ability to evolve independently remains unclear.

The focus of this study was to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length. Researchers at the University of Calgary in Calgary selectively bred 14 generations of laboratory mice (which came to be known as the Longshanks line) and looked for increases in tibia length independent of body mass.

The results of the experiment showed that tibia length can change quickly and independently from body mass. The quantitative genetic analyses of the test showed that phenotypic correlations were around 0.52, while genetic correlations were 0.4-0.48. In other words, roughly 20% of the genetic variation in tibia length is tied to variation in body mass (the rest of the genetic variance in tibia length evolves independently of body mass). This explains why it responded relatively rapidly to selection and why, over the 14 generations, the mean tibia length increased by 9-13%, while mean body mass remained the same.

This artificial selection experiment exhibited the impact of genetic correlations on the independent evolution of body mass and skeletal size in a mammals. It showed that the independent changes in these complex traits are possible and quick. The results further suggested that the frequent and convergent evolution of relatively longer hind limbs among rodents may also have happened at a quick pace on a geological timescale (possibly due to adaptive radiations, niche partitioning in heterogeneous environments, etc.). Moreover, the simulated evolution indicated that this independent evolution is to some extent compelled by a genetic correlation (which most likely evolved due to natural selection).

Specifically, the experiment displayed that the rate of the independent evolution of tibia length is largely impeded by its correlation with body mass (and vice versa).

Citation:

Marchini, M., Sparrow L. M., Cosman, M. N., Dowhanik, A., Krueger, C. B., Hallgrimsson B., and Rolian, C. 2014. Impacts of genetic correlation on the independent evolution of body mass and skeletal size in mammals. BMC Evolutionary Biology 2014, 14:258 doi:10.1186/s12862-014-0258-0.

Evolution of Echolocation in Bats: An Antagonistic Interplay between Natural and Sexual Selection

Date:  July 30, 2014

Source:  PLoS ONE

Institutions Involved:  Max Planck Institute for Ornithology, University College Dublin, Tabachka Bat Research Station, MTA-ELTE-MTM Ecology Research Group, Naturalia environnement, Tunis Superior Institute for Biological Applied Sciences, and Max Planck Institute for Evolutionary Biology

Summary:  Research suggests that sexual selection plays a role in the evolution of high frequency echolocation in bats, possibly against natural selection, according to a study published on July 30, 2014 in the open-access journal PLoS ONE by Sebastien J. Puechmaille and his colleagues. 

Animals generally use echolocation, or acoustic signals, as a means of communication.   Unlike bird songs or frog calls, bats are very interesting when studying the evolution of signaling systems because echolocation is used for both foraging (food detection) and communication.  While it was common belief that echolocation is influenced by ecology through natural selection alone, Puechmaille et al. investigated the role of echolocation calls with regards to sexual selection in bats. 

This study was conducted using 90 Rhinolophus mehelyi or Mehely’s horseshoe bat (75 females and 15 males) collected at two caves in North-Eastern Bulgaria.  This bat species was an ideal choice because unlike other species of the Rhinolophidae family that produce lower frequencies as they increase in body size, R. mehelyi differ greatly by producing frequencies higher than expected given their size.  Attributing this piece of information to sexual selection, researchers hypothesized that an individual’s echolocation peak frequency should be related to its body size and condition, and therefore indicate mate quality.  They predicted that females should prefer males with high frequency calls during the mating season.  As a result, males with high peak frequency should have a higher reproductive success, and therefore have higher relatedness with other members of the colony (more relatives). 

The experiments were performed in a one cubic meter box, lined with sound-absorbing foam.  The bat was placed on a listening perch (wooden basket) at an equidistant position from the two compartments, with each containing a speaker.  The set-up was also equipped with infrared light, and an infrared-sensitive camera to monitor the activity of the bat.  The assignment of low or high frequency playback to the left or right speaker was randomized before testing each individual. 

The data demonstrated that echolocation peak frequency is representative of body size and body condition, with the larger and heavier individuals have higher frequencies.  It was found that the female bats are more attracted to males with higher peak frequency during the mating season.  This result is in accordance with the theory of sexual selection that females prefer to mate with good quality males to produce fitter offspring.  Along with female mate choice, the researchers had observed a significant positive correlation between relatedness and peak frequency in male bats. 

The combination of behavioral, ecological, and genetic studies provided researchers with the first documented evidence that female bats indeed choose their mate based on echolocation frequency.  The ability of bats to precisely locate the source of acoustic signals even in complete darkness further establishes the idea that echolocation is essential for mating.  

Citation:

Puechmaille, S.J., I.M. Borissov, S. Zsebok, B. Allegrini, M. Hizem, S. Kuenzel, M. Schuchmann, E.C. Teeling, and B.M. Siemers. 2014.  Female Mate Choice Can Drive the Evolution of High Frequency Echolocation in Bats: A Case Study with Rhinolophus mehelyi. PLoS ONE 9(7): e103452. 

Eavesdropping: Can It Help Avoid Predators?

Date Published: August 1, 2014

Source: Animal Behaviour

Summary: The act of pollination is a vital action required towards maintaining the ecosystem through regulating the production of seeds from flowers and plants. Without pollinators, the ecosystem would be vastly different and potentially not function as effectively. It is essential for pollinators such as honeybees to be protected from predators. Consequently, the predation-prey relationship can play a major role in shaping an ecosystem.

Jianjun Li and his team of researchers, investigated whether a species of Giant Asian Honeybees, Apis dorsata, is able to eavesdrop and use its sense of smell to discover weaver ants, Oecophylla smaragdina, which are known to attack and kill honeybees. Numerous organisms including weaver ants are known to secrete pheromones, which are chemicals that organisms secrete to communicate with other members of the same species. The researchers hypothesized that the honeybees would be successful in detecting the ant pheromones and would be able to evade the ants. This study was conducted in Kunming, China.            

This study was conducted in two phases. The first phase involved creating two patches of five trees. One patch was used a control, while the other was treated with five colonies of weaver ants. Afterwards, over the course of 15 months, the researchers observed honeybees and took note of which of the two patches the honeybees chose to pollinate in.

The second phase of this study involved a similar method to the first phase. The researchers created two new patches of inflorescences. The researchers collected ant trail pheromones from six different weaver ant colonies, and added 20 microliters of ant pheromone to one of the patches, making it the experimental patch. The other patch was used as a control in which 20 microliters of hexane was added. Hexane was used as a control since it evaporated quickly and was commonly used for olfactory bioassays. Prior research has shown that hexane does not influence or affect honeybees, allowing the honeybees to choose between the experimental patch and the control patch using their olfactory senses.

The researchers found that 60% of the honeybees landed and pollinated on the ant-free control tree patch in the first phase. Similarly, in the second phase, 63% of the bees landed on the control inflorescent patch over the inflorescent patch treated with ant pheromone. These results are significant as it supports the researchers’ hypothesis. The results indicate that honeybees actually do eavesdrop and use their sense of smell to identify and elude ant pheromones. This is important, as the bees may have developed this ability as a result of evolution and natural selection to evade predators more effectively. It is also possible that over time, the weaver ants may evolve in which their pheromones become significantly more difficult to detect by the honeybees.

Citation: Li, J., Wang, Z., Qu, Y., Tan, K., and Nieh J.C. 2014. Giant Asian honey bees use factory eavesdropping to detect and avoid ant predators. Animal Behaviour. 97:69-76