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. 

Purpose of Post Reproductive Whales

Source: Current Biology

Summary:

In the article titled Ecological Knowledge, Leadership and the Evolution of Menopause in Killer Whales, the major thesis of the research is that post-reproductively aged females are more likely to lead a group. Post reproductive females are those who are unable to further reproduce because they have gone through menopause. The study further describes that these same females are even more likely to lead a movement when the supply of food is low. The last aspect of this study also expresses the hypothesis that male offspring are more likely to follow a post reproductive female rather than a female offspring.

            The article essentially illustrates the correlation between female humans and their ability to reproduce and then go through menopause and killer whales same ability. In the natural habitat it is often assumed that a female organism’s ability to reproduce is what makes them attractive to the opposite sex. So naturally when a female is going through menopause there survival rates decrease because of no selection. Humans and killer whales are two of the only species known that do end up living and average of 30 years after they stop reproducing. The big question is that why do those individuals who are unable to further reproduce, usually end up leading their families and other members of the species. The article highlights a hypothesis that states how post reproductive members are known to have knowledge on how the hardships of the environment and therefore take on the role to protect the others in their group.

            All the data that was collected for this experiment was done over a long term period of time where 751 hours of footage was screened to gather the results. This footage was taken from the coastal waters of British Columbia. 102 individuals were recorded for observation all ranging in age so that the testing group was random. The classification for leaders was that the member that was at the front or head of the group was considered the leader and every other member was considered a follower.

            The results all showed that females were most often known to be the leaders and rarely ever were the men. The hypothesis was proven and post-menopausal whales were almost always the leaders of the groups. When there was fewer salmon available in an area, a post-menopausal whale often was the leader where if there was an abundance of salmon available the leader could be another female or even a male. This further proves that women who were post reproductive usually chose to be leader and in charge of a situation when a crisis was evident. However the last hypothesis of the sex of the followers was disproved simply for the reason that most of the offspring remained close to their mother and therefore there was no correlation on who followed the mother.

            The major discussion on what “use” post reproductive individuals have was answered by this study. They do play a necessary role in assisting their offspring and other members of the species. Their wisdom makes them a better protector in the end and therefore they do promote an aspect of selection.

Brent L., Franks D., Foster A. E., Balcomb K., Cant M., Croft D.,2015. Ecological Knowledge, Leadership and Evolution of Menopause in Killer Whales. Current Biology.

Free-Living Stages of Gastro-Intestinal Nematode Parasites of Ruminants

In an article written by Hannah Rose, Tong Wang, Jan van Dijk, Eric R. Morgan in February 2015, the study of gastrointestinal nematodes was practiced. The basis of this article explores the affects of gastro-intestinal nematode parasites in livestock. The researchers used simulations through historical and predicted data to illustrate how much the prevalence of infections will increase with increased temperatures. The main findings of this article conclude that regions with increased temperatures are more suitable for the growth of nematode parasites such as H. contortus and T. circumcincta. Furthermore, during winter months, the parasite is less likely to thrive due to the low temperatures of the region, decreasing the overall prevalence of the parasites in livestock. Through this, scientists can predict higher occurrences in the presence of nematodes in livestock in the summer and lower occurrences in the winter. This study is very important because it relates to the food we eat from livestock. Through this, with increased numbers of parasites in livestock, the question of how safe ingesting the infected animals for humans is raised. The fact is, our meat may be very questionable because come of it comes from infected livestock. The parasites could very easily be ingested and absorbed into our bodies. The resulting health effects of these gastro-intestinal nematode parasites need to be studied so that we are aware of possible side effects to the cause. Unfortunately, according the article, it can be very difficult to determine the similarities and differences in the behavior of these parasites in human bodies versus that of livestock. The best solution is to find an efficient way of detecting these parasites and avoiding human ingestion. Not only that, the prevention of the spreading of these parasites among livestock is vital to decreasing its prevalence. By taking careful precautions, we can minimize the dangers these gastro-intestinal parasites raise.

CITATION:

Rose, H. and T., Wong 2015 GLOWORM-FL: A simulation model of the effects of climate and climate change on the free-living stages of gastro-intestinal nematode parasites of ruminants. Ecological Modeling: Vol. 297, p232-245

A Shock from the Past: The Evolution of Electric Organs in Weakly Electric Fish

Aditya Uppuluri

Title: A Shock from the Past: The Evolution of Electric Organs in Weakly Electric Fish

Article Title: Genomic Basis for the Convergent Evolution of Electric Organs

Source: Science

Summary: A new study published in Science finds that similar transcriptional factors may explain the evolution of electric organs in different types of fish.

Researchers from Michigan State University, University of Wisconsin, Harvard Medical School, and other institutions find that similar expression of certain transcription factors explains the evolution of electric organs in certain types of fish.

One of the most interesting adaptations seen in nature is the electric organ. The electric organ is an organ that allows fish to produce an electric field that ranges in strength. Electric organs may be used for defense, communication, and perception. Current information suggests that the electric organ evolved in fish six different times. Electric organs are also known as electrocytes. Electrocytes are essentially groups of modified muscle cells. Unlike the muscle cells of other organisms, electricity generating muscle cells do not have a mechanical component; they do not exert a physical force. Electrocytes work by using ion channels to create voltage differences between the inside and outside of the specialized muscle cells. Anatomically, the arrangement of these specialized muscle cells resembles the stacking of batteries in a flashlight. The shape of the electrocyte varies with the species of fish.

The researchers looked at parts of the genomes of five species of electric fish: Electrophorous electricus, Sternopygus macrurus, Eigenmannia virescens, Brienomyrus brachyistius, and Malapterurus electricus. For experimental purposes, the researchers constructed mRNA sequences from the cells of various electric organs and other internal organs such as the kidneys, brain, and heart. Once these sequences were acquired, scientists compared the genes in these sequences to see if any were regulated in a different way. The scientists looked closely at genes that were highly up-regulated or highly down-regulated in the electric organs but not in skeletal and cardiac muscles. The researchers looked at genes responsible for muscle cell differentiation, the presence of structural proteins, voltage-dependent ion channels, and deactivation of the excitation-contraction function of muscles.

When the researchers compared these genes, they found trends in some genes across the electricity generating fish that were studies. Some genes, such as those that deposited collagen in the specialized muscle cell were highly up-regulated the electric fish species even though the species were not closely related. On the other hand, genes associated with the excitation-contraction pathway were highly down regulated in many species of electric fish.

After analyzing the sequences of these five species of electric fish, the researchers concluded that there were common regulator pathways in many types of electric fish. Scientists as far back as Charles Darwin suggested that there must be some sort of convergent evolution that explains the presence of the electric organ in different lineages. This study supports the theory that common networks of gene regulation and expression were selected for during the evolution of the electric organ in fish.

Labels: Electric Organs, Convergent Evolution, Electric Fish, Electrocytes

Citation:

Gallant J. R., L. L. Traeger, J. D. Volkening, H. Moffett, P. Chen, C. D. Novina, G. N. Phillips Jr., R. Anand, G. B. Wells, M. Pinch, R. Guth, G. A Unguez, J. S. Albert, H. H. Zakon, M. P. Samanta, and M. R. Sussman. 2014. Genomic basis for the convergent evolution of electric organs. Science 344:1522-1525.