Tick Tock: The Role of Circadian Clocks in Reproductive Shut Down for Northern House Mosquitoes

Date Published: February 1, 2015

Source: The Journal of Experimental Biology

Summary: A study was conducted to investigate how the effects of day length on the Culex pipiens' circadian clock components trigger their diapause.

The Northern house mosquito, Culex pipiens, faces a reproductive shut down during the winter time. This "reproductive shut down" that occurs is also known as diapause and it occurs when the amount of time the day lasts reaches a certain length – which in the case of C. pipiens occurs during the winter time. And after shutting down during the winter, C. pipiens resume their reproductive activity in the spring.

The cause of diapause has been researched in the past in numerous other species. This previous research has proved that circadian clocks, an internal clock that is in rhythm with daylight and darkness of the night, regulates body function within many organisms. In C. pipiens however, no definitive explanation to prove what particular mechanism helps these mosquitoes in measuring the day length and how that data triggers diapause is unknown. Megan Meuti from The Ohio State University and her colleagues: Mary Stone, Tomoko Ikeno, and David Denlinger studied C. pipiens to prove how their circadian clocks are affected by day length. Along with proving the role of circadian clocks, the team noted that C. pipiens are also carriers for deadly diseases. And with the discovery of what mechanisms trigger diapause, the team hopes to prevent disease transmission by controlling the mosquitoes' reproductive activity. 

To prove their hypothesis, the researchers broke down the internal clock into five parts: clock, cycle, period, timeless, and cryptochrome2. They analyzed that each of the levels fluctuate in response to daylight. In the case of the C. pipiens, researchers aimed to discover if during the time of diapause, these parts of the clock continued to still run. By using adult mosquitoes (each of which were exposed to different times and length of daylight) the team discovered that the mRNA levels, even during winter, were uninterrupted. This proved to the team of researchers that without the clock, the insects would never know when and when not to be in diapause. This proves that the clock serves as a mechanism to help measure the length of day and night. The researchers also made note of the cryptochrome, which after diapause began to hit peaks at night time. Thus proving when the mosquitoes were active the most, which was during daytime.

After attesting the influence circadian clocks have on diapause, the team decided to concentrate on the five components mentioned previously. To better understand each of their particular roles, researchers wanted to know how reduced mRNA levels would affect the adult female mosquitoes in their ability to reproduce. In order to do this, an RNA molecule designed to stop mRNA from its continuous cycle and prohibit transcription of particular parts of the circadian clock, was injected. The researchers then observed how females exposed to short daylight failed to regulate diapause when the mRNA levels of the last three regulators of the circadian clock were reduced. However, when another part of the circadian clock not mentioned previously, pigment dispersing factor, was also turned off, it initiated diapause when in fact they should have been fertile. This further substantiated that components of the circadian clock do play a vital role in diapause.

After completing their experiment, the researchers concluded how the results paint a bigger picture in the world of ecology than initially anticipated. Aside from the reproductive aspects of C. pipiens, these mosquitoes, as mentioned previously, are in fact a major carrier for diseases like: the West Nile virus, St. Louis encephalitis, and filariasis. With new knowledge on the components of the internal clock needed to be inactivated in order to initiate and halt diapause, researchers hope to prohibit the spread of these diseases in order to create a safe ecological environment. 

Citation:

Meuti, M. E., Stone, M., Ikeno, T. and Denlinger, D. L. 2015. Functional circadian clock genes are essential for the overwintering diapause of the Northern house mosquito, Culex pipiens. The Journal of Experimental Biology 218: 412-422.

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. 

Current Ecological Conservation Strategies Attempt to Save the Highest Number of Avian Species, but May Fail to Consider the More Evolutionarily Distinct Species

Date: February 5^th , 2015

Source: Yale University

Summary: Current ecological conservation tries to save as many avian species as possible, which is part of their job. However, there was not enough research done to see the effect of saving the more isolated avian species that are more evolutionarily diverse. The research shown in this research paper shows that prioritizing saving avian species based on their ecological uniqueness, rather than attempting to save as many species as possible, is the more effective strategy to preserve total evolutionary information across all avian species.

Post:

When one thinks of the words “Ecological Conservation”, one might think of security officers restraining elephant poachers, or a zoologist examining a giant panda. However, extinction and the struggle to prevent it range across a plethora of species that are not nearly as exotic. Many species of birds are heading towards extinction, and ecologists have limited resources to stem the tide of extinction. A natural debate arises when these factors are taken into consideration: which species and locations should be given conservation priority? The conventional answer to this question is to simply concentrate resources into locations that have the most endangered species, thus saving as many species as possible. A study conducted at Yale university attempts to offer an alternate solution; to concentrate resources on species with the most ecological uniqueness.

Why is every extinction a tragedy? For every species that will never again walk on this Earth, not only is their ecological niche forever lost, but also their evolutionary information. One reason for ecological conservation is that these species may survive to pass on this evolutionary information. No two species have the same evolutionary uniqueness. Some species are relatively isolated on the phylogenic tree, and it is these species that the researchers at Yale University suggest resources are used to preserve.

There are almost ten thousand species of birds on Earth, and there has not been enough time nor resources to study them all, phylogenically and ecologically. However, phylogenetic information about these bird species have been accumulating at a much faster pace than ecological information. This fact was an inspiration for the Yale research group, as this phylogenic information was then cross referenced with that of other bird species. This allowed for the ranking of birds based on their evolutionary uniqueness. They then located the most evolutionary distinct species, and found that they were generally isolated from other avian species. This means that conventional conservation strategies would not protect these species as well, despite their obvious importance to phylogenetic research.

            In conclusion, these researchers recommend that current conservation priorities be reworked, to consider the evolutionary uniqueness of the species to some capacity.

Citation:

Walter Jetz, Gavin H. Thomas, Jeffrey B. Joy, David W. Redding, Klaas Hartmann, and Arne O. Mooer. 2014. Global distribution and conservation of evolutionary distinctness in birds. Current Biology 24, 919–930

Oil Industry and Noise Pollution in the Humpback Whale

Full Title: Oil Industry and Noise Pollution in the Humpback Whale (Megaptera novaeangliae) Soundscape Ecology of the Southwestern Atlantic Breeding Ground

Date Published: January 1, 2015

Source: Journal of Coastal Research

Summary:

Marcos R. Rossi-Santos examined the effects that the noise of oil platforms in the ocean had on the whale population, specifically of the humpback whale. This study was conducted on the Brazilian coast.

Rossi states that humpback whales sing to communicate to each other and suggests that males may use it as a mating call. He hypothesizes that the oil platforms make noise at the same frequency that the whales use to communicate.

Rossi performed this study by selecting a part of the Brazilian coast and using boats equipped with special recording devices. He would record basic information of the whales including location, behavior, skin type, and recordings of the whales. He would then analyze and observe the whale’s behavior and sounds over the course of two years (2007-2009). The data collected supported Rossi’s hunch that the oil platforms were in fact adding to the noise pollution for humpback whales. This means that the oil platforms emitted noise in the same frequency as humpback whales.

For the humpback whales, this meant that they would be confused by the noise and this could affect their mating rituals. This means that this can affect the overall survivability of the whales because they may not be able to reproduce at the same rate. Rossi explains that in other marine animals, they compensate for this by changing frequencies but in whales it may cause serious complications in neurological development of the younger animals. 

This finding is not only important in understanding how whales are affected but also the effects man-made objects have on marine ecosystems. Rossi touches upon the subject of using these findings and building on it. With this information, future oil platforms can be made more efficiently. They can be made quieter and made so that they do not interfere as much with the ecosystem.

In conclusion, the noise from the oil platforms does share the same frequency as the humpback whale and affect their communication.

Citation: Rossi-Santos, R.M. January 1, 2015. Oil Industry and Noise Pollution in the Humpback Whale (Megaptera novaeangliae) Soundscape Ecology of the Southwestern Atlantic Breeding Ground. Journal of Coastal Research 31:184-195.

The Missing Link: Chimpanzee Population Density and Aggression Levels

Date Published: December 2014 

Source: Pan Africa News

Institutions Involved: Duke University; Indiana University

Summary: A study conducted by David Samson of Duke University and Kevin Hunt of Indiana University explored the relation between population density of chimpanzees and their aggression levels in an intraspecific community.

Intraspecific aggression is hostility amongst individuals of the same species and community. Previous studies relay the presence of various acts of aggression ranging from undirected to lethal pinpointed acts of violence among female and male chimpanzees. Causes of such aggression vary, from male on male competition for higher status in the hierarchy to claiming dominance over females.

In a recent report, it was found that population density was a factor that affected intercommunity aggression among 18 chimpanzees. In this study, intraspecific aggression is studied: the rates of aggression for the Semiliki chimpanzee community were recorded and compared to known rates at Gombe and Kanyawara. It was hypothesized that the Semiliki community would be the most peaceful in comparison to the Gombe and Kanyawara communities as it has the lowest population density and largest home range (area of occupancy of the chimpanzees) among the observed chimpanzee communities.  

The Toro-Semiliki Wildlife Reserve in Western Uganda served as the study area consisting of approximately a hundred and four chimpanzees of which thirty were male. Data collection occurred from August 2010 to January 2011 in forty minute periods during which visible acts of aggression were recorded. Observations that did not last forty minutes were discarded. Behavior was categorized by the standards of Goodall. In this study, chases, charging displays and contact aggression were categorized as aggression.

A total of 34.7 hours of observation were recorded. Semiliki adult males had a rate of .17 aggressive acts per observation hour which was half the rate of the Kanyawara sample. A strong correlation between population density and rates of aggression was determined as r^2 = .93 for the linear regression model (as the strength of correlation increases as r^2 approaches 1).

In context of this study, it was determined that male Semiliki chimpanzees experienced less frequent aggression than male chimpanzees of other communities perhaps due to lower population density.

The importance of this study is that it is one of, if not the only, studies to compare large home range and low population community with a small home range and more population dense community. The conclusion of the report, as in the previously conducted study of intercommunity aggression, suggested that “ecology and territory size are key predictors of violent behavior in general.”

Citation:

Samson D. R. and Hunt K. D. 2014. Is Chimpanzee Low Population Density Linked with Low Levels of Aggression? Pan Africa News 21(2): 15-17.