Rivulus Blog

Who’s Really Calling the Shots?

Although we have all heard of hormones, it’s easy to forget how important they are, not only to us, but to every organism. In high school, or maybe an introductory science class you took in college, you probably learned a little bit about hormones, most likely in relation to the physical processes that they joyfully accompany puberty. Let’s hear it for estrogen and testosterone, am I right… However, in reality, estrogen and testosterone are not even the tip of the hormonal iceberg. There are so many hormones! Don’t even get me started on what hormones do for us. They control everything…and I mean everything. When you get hungry and decide to go explore the depths of your fridge (don’t lie, we all do it), you probably think that is a decision of your own volition. Wrong. Hormones made you do it. What about that nightly ‘decision’ you make to go to sleep? Well, it’s not so much a decision as it is hormones telling you what to do. Even the trust you might feel for a significant other or your best friend is a product of hormones! While you can’t feel them or see them with the naked eye, believe me when I say that it is the hormones your body is churning out every second of every day that control everything from your mood to your appetite, heart rate, metabolism, sex drive and the list goes on and on. So now that I have made you feel like you have no free will, what exactly are hormones and why am I talking about them on a fish blog?

Well, let’s start with the basics. Hormones are special chemical messengers that are secreted by endocrine glands, often under the influence of the central nervous system (aka the brain and spinal cord), in every organism. Now don’t be intimidated by the term ‘endocrine.’ It simply refers to glands that secrete hormones directly into the blood. Why couldn’t I have just said that to begin with?! These glands can be distinguished from other bodily glands because they don’t have ducts, and they release their hormone products directly into the bloodstream where they travel, sometimes long distances, to many different target tissues in the body. It’s at these various target tissues that hormones exert their effects. Now, you might be wondering why we are studying hormones in a research lab that claims to be focused on integrative animal behavior. Well, if you think back to what I said about hormones ruling your life and a lot of your behaviors, then it makes sense we would call ourselves an animal behavior lab. Hormones dictate the lives of just about every organism, including our favorite little mangrove rivulus fish. Hormones underlie almost all of the behaviors we study. If you’re not convinced, just let me tell you a little bit about some of the behaviors that hormones control in the mangrove rivulus.

The mangrove rivulus may appear small, and definitely cute, to the naked eye, but these little guys love to fight. Have you ever seen fish fight before? It’s really just a bunch of bumping into each other. When mangrove rivulus get into a fight with another member of its species the two fish will bump into each and even hook their mouths together, which propels them into a sort of spin. It looks almost like a dance, but trust me: it’s a fight. Now, these little guys really care a lot about whether they win or lose. I mean, no one likes losing, right? Well the mangrove rivulus cares so much about the outcome of its fight that research has shown it will change its post-fight behavior based on whether it has lost or won. After a recent victory, the winners of a fight, basking in their own glory, experience a sort of ‘winner effect’ that makes them more likely to initiate and escalate other fights (see the great stuff being done in this area by our long-time collaborator Yuying Hsu) (Chang et al. 2012). Research has indicated that they have a higher chance of winning future fights as opposed to their losing counterparts. The losers of these fish fights, in addition to having to suffer obvious defeat, also become less aggressive, voluntarily retreat and suffer a higher chance of losing future fights (Chang et al. 2012). Talk about getting the short end of the stick. So what does all of this have to do with hormones? Well, it has a lot to do with hormones actually! Levels of hormones, in particular stress and sex steroid hormones, can actually predict how aggressive the mangrove rivulus will be during a fight, which, in turn, allows researchers to gauge how the fish will perform during fights. But wait, there’s more! These levels of hormones are not static. Rather, they change and fluctuate in response to a variety of things, including the fights the fish engage in. The dynamics of the fights these fish get in (that is, how nasty the fights get) influence these hormonal levels, and causes them to fluctuate. In addition, recent victories and defeats also have an affect on the individual’s behavior in future fights, as well as that individual’s tendency to win these future contests (Hsu et al. 2006). Generally, rivulus’ personal experiences with winning or losing fights actually increases, or decreases, the fish’s probability of future wins, or losses (depending on whether it won or lost, of course) (Hsu et al. 2006). Previous fighting experiences, and their outcomes, actually affect the mangrove rivulus’ perception of their fighting ability and also affects their motivation to engage in future fights (Hsu et al. 2006). Now that’s cool! If we allow ourselves to think outside of the box a little bit we can see how this research could even apply to fights between humans, or the way bullies act after they have successfully belittled someone. People often say that bullies have superiority complexes that develop from their ability to successfully make another person feel inferior. Does it seem so far-fetched to blame the increased aggression we observe on hormonal changes they might experience as a result of their previous experiences with fighting? It’s just an idea but it might merit some research. Really it illustrates an interesting point: our research, although done on fish, can have much broader applications.

Speaking of broader applications, several other studies involving the mangrove rivulus and hormones have been conducted that could speak volumes for us humans. One of these studies involved exposing the fish to environmentally relevant doses of ethinyl estradiol. Ethinyl estradiol is not a hormone that is produced endogenously (synthesized by the fish itself). Rather, it is a synthetic derivative of the major endogenous estrogen, estradiol, which is found in both our fish and in humans. Estrogen regulates a lot of developmental processes in humans. Most notably perhaps is its role in the formation of female physical features and its involvement in reproductive processes. Perhaps one of the most common misconceptions is that men do not have estrogen. Well they do, and it is absolutely essential for their health as well. So, what the heck is ethinyl estradiol then? Well, ladies, it’s the active ingredient found in almost all oral contraceptives. That’s right, its birth control! Females that take birth control pills are essentially just taking a big dose of synthetic estrogen (and often progesterone as well-another hormone involved in female reproduction). This daily dose of hormones tricks the female body into thinking it is pregnant, which leads to no more monthly ovulations and, in turn, very little chance of actually getting pregnant. Thank you ethinyl estradiol, right? Wrong. While its ability to stop pregnancy is just fine and dandy, its effects on the environment are not so great. When females taking birth control use the bathroom, the water, along with all their waste (sorry for the visuals) goes to a wastewater treatment plant. There, all the gross chemicals in the water are supposed to be filtered out before it’s released back into the waterways, like rivers. Unfortunately, one of the chemicals that is not effectively filtered by these treatment plants is ethinyl estradiol. So, this lovely synthetic estrogen is allowed to pollute our waterways, and everything that depends on these waterways. Here is where the mangrove rivulus comes in. Our lab has conducted research on the effects that exposure to environmentally relevant doses of ethinyl estradiol has on the reproductive physiology of mangrove rivulus (Johnson et al. 2016). The results were not pretty. Basically, after thirty days of exposure to a super-low dose of ethinyl estradiol, the fish experienced significant changes to their own endogenously produced hormones, which included 17β-estradiol (the most prevalent form of estrogen) and 11-ketotestosterone, which is fish-specific hormone derived from testosterone (Johnson et al. 2016). In addition, hermaphrodites and males experienced changes in the morphology of their gonads. Essentially, males had reduced sperm production and hermaphrodites experienced an increase in the number of early stage eggs (aka primary oocytes) they produced (Johnson et al. 2016). Now if these are the effects this synthetic compound is having on our fish, what do you think it is doing to people or other animals that utilize these same waterways for food or water? It’s not fun to think about but these are the real questions that we need to be asking in order to be more environmentally conscious. These are also the types of questions, and the broader applications, that our research in the Earley lab seeks to investigate.

So, now that you know a little bit about hormones, and the research that is being done with them, I challenge you to go out and explore the field of endocrinology (aka the study of hormones and their targets) a little more in depth. It’s amazing what you will discover and, I won’t lie, it will make you probably question if the decisions you make are of your own volition or of the chemicals that are constantly coursing through your body.


Chang C, Li C , Earley RL & Hsu Y (2012) Aggression and Related Behavioral Traits: The Impact of Winning and Losing and the Role of Hormones. Integrative and Comparative Biology 52 (6): 801-813.

Earley RL & Hsu Y (2008) Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus. Hormones and Behavior 53: 442–451.

Earley RL, Hanninen AF, Fuller A, Garcia MJ & Lee EA (2012) Phenotypic plasticity and integration in the mangrove rivulus (Kryptolebias marmoratus): a prospectus. Integrative and Comparative Biology 52: 814–827.

Hsu Y, Early RL & Wolf LL (2006) Modulation of aggressive behavior by fighting experience: mechanisms and contest outcomes. Biological Reviews 81: 33-74.

Johnson EL, Weinersmith KL & Earley RL (2016) Changes in reproductive physiology of mangrove rivulus Kryptolebias marmoratus following exposure to environmentally relevant doses of ethinyl oestradiol. Journal of Fish Biology 88: 774-786.


The Blueprint of Life

While most people have heard of DNA, not everyone knows how important it is. Every living thing on planet Earth has DNA, or deoxyribonucleic acid if we are being formal. DNA is the chemical compound that contains the instructions needed to make proteins that are essential to the survival of just about every organism. An organism’s entire collection of DNA is called its genome. Basically, it’s the blueprint of life and every cell in every organism contains a complete copy of its particular genome. You might be thinking “Wow, that’s a lot of blueprints for just one organism.” Yes, it is, but that’s to be expected. Life is complicated, and it requires a lot of instructions.

So, what does this have to do with the mangrove rivulus? Well, it has everything to do with the mangrove rivulus! In the Earley lab, we care about the genetic makeup, or the “blueprint,” of each of our fish. Why? Because without this information we would not be able to study them the way we do. Before we can get into the nitty gritty of this ‘genetic makeup’ stuff, and why we study it, there are a couple of things you should know. Every organism’s genome is made up of a collection of genes. Simple enough, right? Wrong. In most organisms, these genes are present in two alternative forms, or alleles, that can be identical or different. Organisms, including us, are said to be heterozygous if they have two different alleles for a given gene and homozygous if they have identical alleles for a given gene. In a previous article (see “Let’s Talk About Sex”), I mentioned that the mangrove rivulus, specifically the hermaphrodites, can fertilize themselves. This is especially cool if the hermaphrodite is completely homozygous, a situation where the animal has identical alleles for all of its genes. In this case, self-fertilization will result in offspring that also have identical alleles for all of their genes, and the exact same alleles as the parent. Thus, self-fertilization effectively produces clones! For our experiments, you can imagine why homozygous offspring would be very useful. We can expose individuals of each homozygous clonal lineage to different environmental conditions and see how it affects their behavior, physiology, morphology, or any other trait of interest. Since there is no genetic variation among siblings, the only differences we might see among them are the direct result of environmental factors. Remember, there might not be variation among siblings in one clonal lineage, but there definitely is variation among lineages. One homozygous ‘parent’ might have a different genetic composition than another homozygous ‘parent,’ leading to clonal lineages that are distinct from one another. All this talk of homozygotes might have led you to believe that heterozygotes don’t exist in mangrove rivulus populations. Well, they do. Unlike homozygotes however their offspring are not genetically identical. But, how are there both homozygotes and heterozygotes in natural populations? Instead of fertilizing themselves, hermaphrodites also can mate with male members of the population. This is known as outcrossing and it introduces new, different genetic information, and heterozygosity, to the offspring. Therefore, the kids are not all genetically identical and some might have inherited some different versions of a trait that proves to be advantageous.

Considering our research and how I mentioned that we really like to make clonal lineages from homozygotes, you might be wondering how we can tell if a fish we acquire from a natural population is a heterozygote and homozygote. Well here is where being able to actually figure out the fish’s blueprint, or at least part of it anyways, comes in handy. In order to do these types of studies, we have to decipher each fish’s blueprint before we can actually do anything with it. But how the heck can we do that? Science, duh! It’s complicated, but definitely not impossible.

So, here’s the rundown. The process of deciphering the ‘foreign language’ that makes up an organism’s genome is called “sequencing.” Technically, there are many different types of sequencing methods that can be used to determine the degree of variation between different individuals in a population, but today we will just focus on one: DNA fingerprinting. DNA fingerprinting does not require the researcher to decipher the fish’s entire genome in order to find out if it is a homozygote or a heterozygote. Instead of taking the time and resources to determine an individual fish’s genome, we can instead take only a portion of that genome, sequence it and use it to determine how heterozygous an individual is, and also levels of heterozygosity in an entire natural population. The process involves collecting a little piece of the fish’s fin, 1 millimeter by 1 millimeter in size, which is then used to determine their genotype, as well as if they are homozygous or heterozygous.

Interesting stuff, but how do we know what portion of the genome we should be comparing? Can we just take any random part of the fish’s genome and determine its heterozygosity from there? Well, no. The thing about genomes, and especially genomes from members of the same species, is that there are always parts that are the same within a species. That means that every individual mangrove rivulus, regardless of who its parent or parents are, shares part of their blueprint with other members of the species. This also applies to heterozygotes and homozygotes. Lets take a look at this from a human perspective. Part of my genome is identical to part of your genome. So how are we not exactly identical? Well, only part of our genome is conserved. Other parts of our genome might be very different from each other, and it is these differences that make me uniquely me, and you uniquely you. So with this idea in mind, lets get back to the fish. Researchers of the mangrove rivulus have identified 32 neutral loci, a fancy word for different positions in the fishes genome that do not encode a protein and that, when amplified, studied and compared, can tell us whether these fish are heterozygotes or homozygotes. These loci are called “microsatellites” and, because they do not encode proteins, they are ‘free’ to vary in their sequence without having any adverse effects on the organism. That’s exactly why these regions often have more variation than other loci; the fish can afford it! These microsatellites typically consist of tandemly repeated nucleotide bases. The genetic code is just a bunch of A’s, T’s, C’s, and G’s (nucleotides) strung together in a particular order; microsatellites can be identified because they have repeated sequences of nucleotides. For example, a microsatellite might have ATC repeated multiple times; you might have ATCATC, and I might have ATCATCATC.

Now, remember that this fingerprinting is being done on fish collected in the wild. We use these tests to find homozygotes so we can collect them and create lineages of genetically identical fish (isogenic lineages) for our experiments. The fact that homozygotes as well as heterozygotes exist in natural populations raises a very interesting question: if the homozygotes are able to successfully produce offspring in a completely self-sufficient manner, why should they ever want to deal with a male? Good question, and one that many researchers are interested in answering. One idea is that reproducing with males introduces new combinations of the blueprint into the population. If these new genotypes confer some sort of benefit to the fish in terms of survival or reproduction, then this new genotype will persist, and some combination of self-fertilization and outcrossing with males will be favored evolutionarily. It has also come to light that homozygotes collected in the field are actually more susceptible to parasites than their heterozygote counterparts (Ellison et al. 2011). This could be one possible benefit that heterozygotes have over homozygotes. Other studies have shown that male heterozygotes are often larger than homozygotes. This could be another reason we observe heterozygotes in natural populations, especially if you consider the competitive edge a larger male could have over a smaller male when looking for love or when fighting with other individuals (Molloy et al. 2011).

Wow, while this may seem like a lot of information it is really just the tip of the iceberg when it comes to what we can do with genomes, as well as genome sequencing. Being able to decipher the language of the rivulus’ genetic blueprint affords us endless opportunities for studying these little fish with a lot to offer. For more information about how examining our fish’s blueprint can provide novel insights into its biology, visit the pages of our collaborators. Dr. Andrei Tatarenkov and Dr. John Avise at the University of California, Irvine are experts in identifying microsatellites and using them (as well as an arsenal of population genetic analyses) to address fascinating questions in mangrove rivulus and loads of other organisms! Dr. Joanna Kelley at Washington State University is diving into the mangrove rivulus genome to determine how our fish’s blueprint governs many aspects of its extraordinary biology!


Ellison A, Cable J, Consuegra S (2011). Best of both worlds? association between outcrossing and parasite loads in a selfing fish. Evolution 65: 3021–3026.

Molloy PP, Nyboer EA, Côté IM. Male-male competition in a mixed-mating fish. Ethology. 2011;117:1–11.


Ana Preda-Naumescu


This week I had the pleasure of sitting down with Liz Johnson, a PhD candidate in Dr. Earley’s lab. Liz has been conducting research in Dr. Earley’s lab for some time now and has published several manuscripts. She was able to offer me some really interesting insight into what she studies as well as something that is integral to the research world: the publication process.

Liz, what initially got you interested in research? 

Honestly, I didn’t really know a lot about undergraduate research until my junior year in college. At the time, I was a chemistry major and I thought I wanted to go to medical school. Well, junior year started and I soon realized I really did not like chemistry all that much and definitely not enough to have it as my major. I had always liked biology. I had taken several biology courses along with chemistry courses during my freshman and sophomore years because they were required for the premedical program. Because I already had a solid foundation in the subject, I decided to switch my major. During the second semester of my junior year I enrolled in Dr. Philip Harris’ Vertebrate Zoology class. The class was really small so we all got to know Dr. Harris pretty well. He learned about my decision to go to medical school and asked me why I wanted to be a doctor. I didn’t really have a reason other than I wanted to help people and that I liked science. Dr. Harris asked me why I had not considered going to graduate school to study biology. Honestly, I had never thought about it! I did not know much about graduate school because my plan had always been to go to medical school. Dr. Harris asked me if I wanted to spend the following summer doing research in his lab to see if it was something I would be interested in. His lab uses molecular techniques like DNA extraction and PCR to understand the evolutionary relationships among fish species. I fell in love with research and the process of scientific inquiry. It was at this point I decided that medical school was not for me. After a summer in Dr. Harris’ lab, I found myself asking him questions about the importance of understanding evolutionary relationships and what may lead to the divergence of species. Animal behavior came up in conversation, which led to even more questions about why fish species differ in behavior. Because Dr. Harris’ lab does not deal with behavioral sciences, he suggested that I check out Dr. Earley’s animal behavior lab on campus. The following semester (now my senior year!) I met with Dr. Earley and became part of his lab where I have been ever since.

Wow, what a story! I’m glad you found the right path for yourself though. What type of research are you currently involved in and how long have you been involved in research?

 I have been studying mangrove rivulus for a long time. Technically, I have been involved in research since the senior year of my undergraduate but the focus of that research was very different from the research that I do now. As an undergraduate, I mainly helped graduate students with their own projects, but I also conducted my own senior research project establishing a photographic developmental time series of rivulus embryos from fertilization to hatching. In graduate school I became interested in endocrine disrupting compounds, which are metals, pesticides/herbicides, pollutants and pharmaceuticals that interfere with the hormone system in humans and animals. I wanted to understand how these chemicals affect the physiology, reproduction and behavior of the mangrove rivulus. Currently, I am trying to figure out whether the route of exposure to various endocrine compounds can differentially affect how the fish function. The fish can be exposed to these compounds either through bioconcentration or biomagnification. Bioconcentration simply means that the fish is exposed to the compound when water that contains it passes over their gills. In this route, the compound enters directly into their bloodstream. The second way that these fish can encounter endocrine disrupting compounds is through biomagnification, in which they eat something that is contaminated with a particular compound. These two routes distribute the compounds across the body differently, potentially resulting in different levels of exposure. I want to isolate these routes in order to determine how they result in phenotypic differences.

I think that the research I am doing is not only important for the fish I study, but also applicable to many different organisms in environments exposed to similar contaminants. We all know that factories and wastewater treatment plants are dumping hundreds of different compounds into our waterways and, although we know these compounds aren’t directly killing aquatic animals like fish, we do not know exactly how they are affecting them. The way in which these fish are exposed and how they respond is important to understand because it can provide the framework in which to make predictions about how the population as a whole might respond to exposure, and potentially inform us of issues that could lead to serious declines in both the health and abundance of the population. This is at the heart of my studies, which all have real world applications because the concentrations of compounds that I use are ecologically relevant and found in the fish’s natural environment.

 I know that some of your research has been published. Would you mind telling us a little bit about your publications? What was that research about?

 I have focused primarily on endocrine disrupting compounds during my graduate career. The first experiment that I ever did, and that was published, involved twenty fish. First, I collected samples of the fish’s hormones levels before starting the experiment. Then I exposed them to ethinylestradiol, which is a synthetic form of the female estrogen hormone estradiol, for thirty days. The reason I did this was to see if the fish had any physiological response to exposure. After thirty days I collected their hormones once again. I compared the hormones I collected before running the experiment to those that I had obtained after thirty days of exposure and I found that two major sex hormones in the fish, estradiol and 11-ketotestosterone (a fish androgen similar to human testosterone) were affected. In both the hermaphrodites and males I found that estradiol levels significantly decreased after exposure. In addition, males had a decrease in their levels of 11-ketotestosterone. These hormones are critical in regulating sexual characteristics as well as the behavior of the fish, so changes in hormones can result in changes in other phenotypic endpoints.

 For our readers that are unfamiliar with publications, could you tell us a little bit about that process? How long did it take you take have a paper published?

 Sure! When you publish a manuscript the first thing you must decide is which journal you want to submit it to. Trust me, there are a lot of options. Then you have to read all the nitty-gritty details on the exact way that they want the work formatted. For example, the journal that I submitted to required that I use British English. Once your manuscript is ready to go, the next step is sending it off. And then you wait. They usually get back to you pretty quickly saying either, “okay, we reject this,” or “we are sending it off to be reviewed.” In the second case, they reach out to relevant professors or people who have experience with your particular area of research and ask them if they would be willing to read your manuscript and provide feedback. This process can go back and forth (and back and forth) for a while.

For me, the entire process took a little over a year. We had some hurdles that we had to overcome related to the journal switching editors so, anticipate that the process might take a bit longer than expected!

 Is research your long-term goal career goal or do you have something else planned for the future?

I definitely think I would like to stay in research. However, whether I want to do research in an academic sense or a nonacademic sense has yet to be determined.

What is the most challenging aspect of research for you? 

For me, the most challenging part of research is data analysis and interpretation. Often times the data we collect is not straightforward and requires the knowledge of appropriate statistical techniques to figure out whether or not our hypotheses are supported or rejected. However, I think both null (statistically non-significant) and significant results are equally important in understanding the outcome of an experiment.

 What do you enjoy the most about research?

I really love how there is always a problem to be addressed and a question to be asked. It’s a very dynamic career, which makes it hard to get bored. It’s interesting because there is no linear goal to be reached since science is always changing. It keeps me on my toes. I have a lot to learn, and I like that. I get to be a student for a long time.

So, now we know that you love research and we know why you love research but we don’t know much else. What do you enjoy doing with your time outside of the lab?

I am a big outdoors enthusiast. Hiking, camping, kayaking, you name it. I have two dogs and my husband and I love taking them on adventures. Spending time outdoors is really important to me since I spend the majority of my time during the week inside the lab.

Let’s Talk About Sex


Well, not my sex life, or your sex life. Those two conversations would not be nearly as interesting as talking about mangrove rivulus’ sex life, or lack thereof I suppose. Rivulus’ unusual sexual behavior is one of the principal reasons that this little fish is so popular among researchers. Rivulus are the only known vertebrate that is a self-fertilizing simultaneous hermaphrodite. In other words, this fish has both male and female reproductive parts at the same time and prefers self-fertilization to doing it the traditional way. You know what they say, if you want something done right, do it yourself!

When rivulus decide that it is time to start a family, it takes matters into its own fins. No partner required. I know…how empowering! These little fish are able to fertilize themselves (here’s where having both male and female reproductive parts is particularly helpful). The babies hatch as genetic ‘clones’ of their parent. I put ‘clone’ in quotations because it’s not technically cloning. Nothing could ever be so matter-of-fact with rivulus. Although genetically identical, rivulus’ babies cannot be considered true clones because they are the result of sexual reproduction (albeit sex within the same fish, but it’s still considered sex). Clones, on the other hand, are the product of asexual reproduction. Technicalities aside, the final product is essentially the same. Being “basically clones” is an important attribute of the mangrove rivulus. When a fish reproduces, its babies are all genetically identical. You can imagine how this could be helpful during experiments. We can expose individuals of each clone to a variety of different environmental conditions and see how it affects their behavior, physiology, morphology, or any other trait of interest. Since there is no genetic variation among siblings, the only differences we might see among them are the direct result of environmental factors. Pretty cool, right? Since they are all basically clones we know that any noticeable differences are the direct result of environmental influence! We can also put many different genotypes (animals with different genotypes) into the same environment to look at how genes are associated with the traits that we study. This allows scientists to tease apart genetic and environmental factors and how they are affecting the animal! Taking things one step further, we have the ability to put many different genotypes into many different environments and look at the interaction between genes and the environment. This type of research is becoming increasingly important in many types of biology including conservation and medicine. Rivulus’ extraordinary, and entirely unique (at least among vertebrates) reproductive behavior is of great interest to researchers as it offers a lot of insight into a reproductive process that, thus far, is unparalleled in vertebrates.

As if their reproductive tendencies were not weird enough, the mangrove rivulus is also capable of changing sex. No surgery required. I know I said that rivulus are simultaneous hermaphrodites, but that is not always true. While the majority of individuals within a population are indeed hermaphrodites, there are also a smattering of males. Hermaphrodites are able to undergo a sex change in which they dismantle their female parts and begin to invest heavily in their male parts, which eventually leads to them becoming fully male.

But, why? Why would a hermaphrodite that possesses all the equipment necessary to happily procreate without the nagging of a partner, suddenly assume a fully male identity? That is the million-dollar question driving a lot of our research. While we might not know the answer to this question yet, what we do know is how these males appear in populations. Basically, it can occur in one of two ways. Baby fish can either develop directly into males when exposed to triggers in the environment (we think this is pretty uncommon in wild populations). These males are referred to as primary males. Secondary males, on the other hand, result from adult hermaphrodites transitioning into males. They stop investing energy into their ovarian tissue, and actually get rid of it altogether. They then add on more testicular tissue to create a fully functioning male testis.

Now, let’s take a moment and consider how seriously crazy this is: these guys literally morph into another sex. How do they just spontaneously turn into males though? Well, first of all it doesn’t seem to be spontaneous by any means. We know there are certain cues that can trigger the transition – keeping them in hot temperatures, for example. However, these cues, and what exactly they encompass, are not very well understood. This, among other things, makes them of particular interest to us in the Earley lab as we work to reveal secrets behind their strange sex life. If this has got you interested, keep an eye out for publications on this topic from our lab in the upcoming year! We’ve got something cooking!



Earley RL, Hanninen AF, Fuller A, Garcia MJ, Lee EA. 2012. Phenotypic plasticity and integration in the mangrove rivulus (Kryptolebias marmoratus): a prospectus. Integr Comp Biol 52:814–27.

Harrington RW Jr. 1967. Environmentally controlled induction of primary male gonochorists from eggs of the self-fertilizing hermaphroditic fish, Rivulus marmoratus. Biol Bull. 132:174–199.



Ana Preda-Naumescu



Dr. Earley’s research lab is not just focused on research; it is also a community. The faces behind the work that we do are just as important as the research itself. Every month I will be doing a “Student Feature” on The Little Fish with a Lot to Offer that will allow you to get a glimpse into the lives of the people that make this lab possible. With that being said, this week I had the opportunity to sit down with one of the lab’s graduate student researchers and my mentor, Grace Scarsella, and ask her a few questions about the work that she does and what initially drew her to research.

Grace, what initially sparked your interest in research? 

Actually, it was SCUBA diving. Both of my parents are avid divers and when I was younger we would always go on vacation to places where we could dive. As a result, I got certified early on. I love how there is an entirely different world beneath the water; it is honestly amazing. Growing up I thought that I wanted to pursue a career in medicine. I later realized that, while I found the medical profession very interesting, I did want to spend all of my time stuck in a hospital. So instead I decided to pursue an education that held at its core the things I have always loved: biology, marine sciences and the organisms I had discovered while diving.

What type of research are you currently involved in and how long have you been involved in research?

 I have been involved in research since my sophomore year as an undergraduate. Now a Master’s student, this will be my fifth year involved in research. Currently, I am studying how energy budgets might drive sex change in the mangrove rivulus fish, a really interesting little fish (Check out our blog post for more info!)

That sounds really interesting. For those of us who are unfamiliar with research terminology, would you mind explaining what you mean by energy budgets?

 Of course! When I say I am studying energy budgets I mean that I am trying to figure out how this fish distributes the energy that it gets from food.  I am really focusing on the energy needed for these fish to reproduce as well as the energy it takes to change sex! I am investigating whether it is beneficial, from an energetic standpoint, to change sex or stay hermaphrodite. Does the fish conserve energy or use it during that process? In the lab, we can quantify the fishes’ metabolic rates to measure the amount of energy they are using at a specific time.

That’s really interesting stuff. Is research your long-term goal career goal or a stepping-stone?

Well, it is definitely much more than just a stepping-stone. I would say it lays the foundation for what I hope to accomplish after I finish graduate school. My goal is to some day run a non-profit or educational program that communicates science to everyone, including children and non-scientists. The research I have been conducting has given me a solid background in designing, executing and documenting experiments, which has helped me gain a deep understanding of the research process. I think that, in order to talk about something simplistically, you need to have a really thorough understanding of the material. My background in research has helped me develop these skills. It gives me an edge that most other educators lack by allowing me to communicate complex concepts in science in a much more engaging way. I think it would be very rewarding to work for advocacy groups or for the government in order to pass conservation laws. This would also require a really solid understanding of the scientific material in order to effectively communicate it to those people responsible for making the changes.

 What is the most challenging aspect of research for you? 

 For me, it’s maintaining a balance between work and the rest of life. I have a tendency to really throw myself into my work and I overdo it sometimes. It can be easy to forget the importance of paying attention to other aspects of my life. I am very passionate about what I am studying but I know that burn-out can happen to best of us. Balance is definitely very important. The longer I’ve been in grad school the better I’ve gotten with maintaining a balanced life. It’s good to recognize that taking a day off is okay and good for maintaining sanity!

I definitely think you are right! Personal time is important. On that note, what do you enjoy doing with your time outside of the lab?

 I love to read, and also love to be on the water: kayaking, paddle boarding, you name it. I am very outdoorsy so I spend a good bit of my free time outside. When I have the time, and funds, I like to travel and experience new places. Oh, and of course, I love spending time with my two cats, Luciano and Gumbo!

What do you enjoy the most about research? 

I really love the problem solving and critical thinking that it requires. My favorite part of the whole process is designing experiments. Research is like a huge puzzle and the scientist’s job is to put all the pieces together in order to solve it. It is incredibly engaging.

Do you have any suggestions for anyone who might be thinking about getting involved with research?

I would say that if you think that research might be something that you would be interested in, try it out! It is a very fulfilling, although at times trying, career. Graduate school in research fields requires long hours, and a lot of patience. Often times, experiments do not go as planned, or the results aren’t useful. You really need to embrace the motto “try, try, and try again!” Becoming a scientist is a long process that requires many years of schooling and working your way up the academic ladder. When starting out, it’s common to be more of a ‘helper’ than an independent researcher. Don’t give up though- all of that training will be useful in the future when you’re running your own lab!

If you are currently in school, or live near a university, talk to some people in your community that have been involved in research and learn about their experiences. See what they liked and disliked. Universities are probably the best resource to tap into. More often than not, researchers are looking for volunteer help in the lab and willing to talk and offer advice to get you started!


The Little Fish with a Lot to Offer: Why the Mangrove Rivulus is Worth Talking About

Dr. Ryan Earley’s research lab investigates animal behavior and the mechanisms that underlie the vast amount of behavioral variation among individuals in a given population (check out our About the Lab tab for more info). This pretty much means that we study the factors that influence behavior and how behavioral differences affect survival and reproduction. We focus on a super cool little fish, Kryptolebias marmoratus, commonly known as the mangrove rivulus. This fish has a huge geographical range that spans Northern Central America, some Caribbean islands all the way up to Florida. For researchers and science geeks of the world, this is good news. Basically, what this means is that there is a lot of opportunity for this fish to experience different habitats and thus, to show variation in form and function that is influenced by the environment! Just like with humans, a fish’s habitat influences how it will develop. Different environments promote differences in individuals within the species and it is these differences (and what causes them) that the Earley Lab is interested in. Even though they occupy a large range, they can be really hard to catch. They choose to hang out in weird, small places known as microhabitats, like temporary pools in swamps, crab burrows and sometimes even on land!

That’s right- I said land. These little guys can live up to two months on land as long as it’s moist; for example, inside rotting logs, mud, and under leaf litter. They can switch from breathing through gills (like a normal fish) to breathing through their skin like a frog. They are the Olympic jumpers of the marine world, able to launch up and out of the water with the very precise flip of a tail, sometimes in order to catch prey on land. Watch out Tokyo, it looks like we might have some new competitors in 2020! They also are able to withstand extreme temperatures, high levels of hydrogen sulfide and very low levels of oxygen in water, all of which would kill most fish. Mangrove rivulus’ incredible ability to thrive both on land and in water is credited to its unique biology, all of which needs more study to better understand how they do all of these crazy things.

One of the mangrove rivulus’ weirdest attributes is its very strange sex life. A small fraction of each population is made up of males while the majority are hermaphrodites. They are the only known vertebrate that is a self-fertilizing, simultaneous hermaphrodite. I know, it sounds very fancy. However, what this means is that these fish have both male and female reproductive parts and they prefer to have sex with themselves. Hey, I’m not judging. In fact, I’m thankful. These guys end up producing babies that are genetically identical to themselves and all their siblings. They do this through sexual reproduction, so it’s not quite cloning (asexual reproduction), but the end picture is very similar. Hermaphrodites can also undergo sex change, where they lose their female parts and become male. Males can appear in populations in two ways. Cool temperatures drive primary male development (baby fish develops directly as a male) while warm temperatures drive adult hermaphrodites to change sex into males (sex change later in life). This unique ability makes rivulus ideal for the study of sex determination and sexual plasticity, or the degree to which an organism’s sex organs and sex drive can change as a result of environmental factors.

By now you should be convinced that the mangrove rivulus is seriously cool. But, on the off chance you aren’t, did you know that it is also an extremely interesting research model? It is a spectacular model for studying phenotypic plasticity, or an organism’s ability to alter its appearance, behavior, or physiology in response to changes in the environment! It is also a great organism to study for its adaptations to extreme environments. The species’ insane sexual habits establish it as an important laboratory model for a wide variety of studies. Since their offspring are genetically identical, researchers can eliminate genetic variation as a factor when conducting experiments, and can zero in on how the environment can shape all sorts of characteristics, from physiology and behavior to morphology. Even after extensive research, the unique nature of the mangrove rivulus continues to fascinate, and astound, the scientific community.

The mangrove rivulus can survive out of water in moist habitats!

Photo Credit


Ana Preda-Naumescu