Sex-ratio variation and sexual dimorphism impact ecosystems

[ This post is by Dave Fryxell, I am just putting it up.  –B. ]

The focus of most eco-evolutionary dynamics work in macro-organisms has been to describe the community and ecosystem effects of different trait variants (e.g., genotypes, phenotypes, or ecotypes) within a species. Two categorical trait variants common to most animal species are males and females. There exists a centuries-old tradition of describing dimorphism between the sexes, though little has been done to characterize sexual dimorphism in ecological effects. Take a look at even moderately dimorphic species, and, in many cases, it is difficult to imagine a scenario where males and females are completely equivalent in their resource utilization. This “extended sexual dimorphism” may become particularly relevant to our understanding of ecology when populations vary in the relative abundance of males and females – i.e., when there exists sex-ratio variation among populations – which is a surprisingly common phenomenon.

Invasive mosquitofish in a geothermal spring-fed pond in eastern California. For my dissertation, I am primarily studying how contemporary thermal adaptation in this species modifies its ecological effects. (D. Fryxell)

So, sexes might commonly differ in their ecological effects, and sex ratios can vary across space. In a new paper we sought to test the hypothesis that natural sex-ratio variation has community and ecosystem effects using mosquitofish (Gambusia affinis) – a small, livebearing fish, which currently inhabits freshwaters across the globe. Very intriguingly, this species shows sex-ratio variation across space and time from greater than 90% males to greater than 90% females. Importantly, males and females of this species are also known to differ in their ecological effects. Many differences are likely related to the relatively large size and continuous growth of females, compared with the small size and asymptotic growth of males. However, they are also a sexually coercive species, and females are known to spend relatively more time foraging when in female-biased versus male-biased groups. Observe groups of mosquitofish for just a few moments and you will readily observe how seemingly bothersome males can be to the goings-on of females.

Female mosquitofish (left) and male mosquitofish (right) in an experimental pond. Unless group sex ratios are strongly female-biased, it is rare to see a female without a male trailing close behind her. (D. Fryxell)

Because female mosquitofish have higher feeding rates, prefer larger food items, and forage more in the presence of other females, we predicted female-biased populations would induce stronger trophic cascades than male-biased populations. We used experimental ponds to test this prediction, and found our predictions supported, albeit with some interesting ecological details. You can read the specifics of our methodology and our interpretation of the experimental results in the paper (link below).

The mesocosm array at Long Marine Lab of the University of California at Santa Cruz. (D. Fryxell)

This was, to our knowledge, the first study investigating the community and ecosystem consequences of sex ratios. It was partly a proof-of-concept experiment, and we are looking forward to future investigations into other study systems. In particular, it would be interesting to combine experiments with observations of how ecological patterns in nature vary with the sex ratios of ecologically-important focal species. Our hope is that this experiment leads the way towards incorporating sexual dimorphism and sex-ratio variation into future considerations of ecological and eco-evolutionary dynamics in nature. I have also now personally learned the importance of controlling for sex ratio in experiments testing for ecological divergence among mosquitofish populations.

– Dave Fryxell

References

Fryxell, D.C., H.A. Arnett, T.M. Apgar, M.T. Kinnison, E.P. Palkovacs. 2015. Sex ratio variation shapes the ecological effects of a globally introduced freshwater fish. Proceedings of the Royal Society B. 282:20151970. doi: 10.1098/rspb.2015.1970.

Press release (UCSC): http://news.ucsc.edu/2015/10/mosquitofish.html

Press release (UMaine): https://umaine.edu/news/blog/2015/10/26/female-invaders-are-ecologically-stronger-than-males/

Evolutionary ecology of host-parasite interactions

A while back I wrote a blog post (check it here) on how host adaptation to the predation environment could influence host-parasite coevolution. This happened to be my first blog post, and also my first chapter for my thesis. I specifically explored how guppy (Poecilia reticulata) adaptation to its ectoparasite, Gyrodactylus, can be influenced by their adaptation to predation. In that study, I found that both predation and Gyrodactylus parasitism induce similar phenotypic responses in guppies (i.e. reduction in growth and higher reproductive allocation), which led me to conclude that guppy adaptations to predation could reinforce adaptations to Gyrodactylus parasites, and vice versa. Another important point, which will be evident later in this blog post, is that there were also strong and repeated variations in guppy-Gyrodactylus dynamics across the different rivers, which was independent of predation – at the end of this series of blogs, you might come to realize I have a frustration with river effects!

Given the particular experimental design of my first study (for specifics check the published paper here), I was unable to disentangle the confounding effects between highly resistant hosts and highly virulent parasites, with those from low-resistant hosts and low-virulence parasites. This restricted any potential inferences on host-parasite adaptation. Thus, I decided to build on the previous experiment to assess local adaptation of guppies and Gyrodactylus, and to determine if such adaptation is influenced by the environment (i.e., predation) or evolutionary history (i.e., river).

The mesocosms where I performed the experiments.

In the so called arms race between parasites and their hosts, parasites have generally been expected to have an evolutionary advantage over their hosts due to short generation time and potentially high host specificity, and, thus, be locally adapted to their host. Yet this has been far –really far– from a universal rule. Studies on how additional sources of mortality could influence host-parasite local adaptation, and whether they prevent or facilitate host-parasite adaptation, are still largely missing– despite that they would help to better understand the mechanisms of local adaptation. For example, in the case of predation, we could expect that under increased guppy mortality (high-predation: HP), higher Gyrodactylus’ infectivity and transmission (i.e., virulence) would evolve, and this of course would in turn select for higher resistance in HP guppies. Thus, a priori, one would expect that local adaptation is facilitated in high-predation environments.

Of course, based on the results of my previous study –more on my fixation with river effects– differences between rivers could also be important drivers of guppy-Gyrodactylus local adaptation. This is because guppy populations from different rivers are genetically diverged, in part because they originated from independent colonization events, but also because different guppy evolutionary histories (i.e., selection, genetic bottlenecks and drift) could similarly influence guppy-Gyrodactylus coevolution in the various rivers in different ways. The predatory fauna in rivers from the northern and southern slopes is also drastically distinct: visual predators of the Cichlidae family are only present in the southern drainages, whereas the main predators in the northern drainages belong to the Eleotridae, a family of generalist ichthyophagous predators. Such differences in community composition could strongly influence the relative fitness costs associated with Gyrodactylus infections in the different rivers and, hence, guppy-Gyrodactylus local adaptation. If you are still wondering what I mean by guppy-Gyrodactylus local adaptation, I refer to locally adapted Gyrodactylus when they show higher performance when infecting their sympatric than with allopatric hosts, and locally adapted guppies when guppy performance is higher when infected with sympatric than with allopatric parasites.

 I will only briefly summarize the methods for this experiment, but if you are really eager to know more details you can check the published article here.

I used fully reciprocal cross infections with two guppy populations from the Marianne (one HP and one LP), and two from the Aripo river (one HP and one LP), and their corresponding sympatric Gyrodactylus ectoparasites. This design led to four sympatric pairs (hosts and parasites from the same locations) and 12 allopatric pairs (hosts and parasites from different locations) (Fig. 1).

Experimental design with Gyrodactylus infection dynamics.

We found that Gyrodactylus performance on their sympatric host was generally similar across populations (Fig. 2), but their performance when infecting allopatric guppies was dramatically different! In particular, Gyrodactylus from the Aripo performed the best (both as mean number of parasites/fish, as parasite population growth) when infecting guppies from the Marianne, but did poorly when infecting guppies from their own river.  This could indicate a higher infectivity, virulence and/or reproductive success of the Aripo parasites. Gyrodactylus from the Marianne, on the other hand, performed similarly on all hosts, or even slightly better when infecting their sympatric guppies.

Gyrodactylus performance on sympatric vs. allopatric hosts.

We found similar differences in guppy performance (Fig. 3). Aripo guppies were able to better limit Gyrodactylus population growth than guppies from the Marianne River, indicating their strong ‘‘resistance’’ to Gyrodactylus regardless of the source of the parasite. Surprisingly, predation environment had no detectable influence on host–parasite population dynamics of sympatric or allopatric combinations. The much stronger effect of river than predation emphasizes its importance in driving local co-evolutionary dynamics. Damn you, river effects!

Guppy performance when infected with sympatric vs. allopatric Gyrodactylus

At the end of the day, I think that this study demonstrates that, contrary to a priori expectations, Gyrodactylus coevolution is not deterministic, and could be influenced by historical demographic and evolutionary processes. This is an important aspect of host-parasite interactions that has been commonly neglected in studies of local adaptation, and this study demonstrates the need to incorporate them into future research on host-parasite coevolution.

The actual paper:

Pérez-Jvostov, F., Hendry, A. P., Fussmann, G. F. and Scott, M. E. 2015. Testing for host-parasite local adaptation: an experiment with Gyrodactylus ectoparasites and guppy hosts. Int J Parasitol, 45: 409-417.

How to Get a Faculty Position II

We are now in the midst of a series of three posts on “How to Get a Faculty Position”:

1. Getting the interview.

2. Succeeding in the interview

3. Guaranteeing success

In the present post, I will deal with point 2 – succeeding in the interview. Your CV has gotten you the interview but now an entirely different set of skills comes into play. My advice here will boil down to a couple of general points, each with several supporting arguments.  Although I expect my suggestions will hold in most instances, it is important to remember that jobs/departments/committees vary just as much as do individual people, and so you might need to adjust your strategy to suit the situation.

The key starting point is to realize that the department is not hiring your CV, they are hiring you. They have already determined that your CV is sufficient for you to be a member of their faculty; now they essentially throw out the CV and judge you based on your performance during the interview. As a result, someone who just squeaked in as the last person on the short list after a bunch of folks with more impressive CVs now has an almost equal chance of actually getting hired. In fact, people in such a position sometimes have an advantage because opinions depend on expectations. Someone with a huge CV comes with huge expectations during the interview and, if they don’t blow folks away, they can seem disappointing. By contrast, someone with only a decent CV can blow folks away with a good performance during the interview. So how to succeed during the interview? Unlike my previous post where most things were rather obvious, I will hopefully now have some novel and surprising things to say.

The hiring committee wants to see a colleague

Young scientists seeking their first faculty position can sometimes interact with professors as though they are still students. That is, they can be deferential rather than assertive, shy rather than bold, intimidated rather than confident, and so on. Acting in this manner can give a strong negative impression as it really does make you seem like a graduate student, which no committee is going to hire. Instead, the people you meet, whether the committee, other faculty members, or students, really want to envision you as though you are already a professor, which is the role they are hiring you for. So, how to do this without seeming arrogant or over-confident?

Talk. If you are too quiet, it will come off as though you aren’t engaging and sometimes as though you don’t have much going on upstairs. Your CV may have all sorts of outstanding papers that show you (or your supervisor) are really smart, and it may seem clear that you will publish lots of papers once hired; but the committee is not hiring your papers – they are hiring you. Being a member of a department is so much more than the papers you produce – it is also how you interact with colleagues, how you interact with students, how you collaborate, how you hang out, and so on. In fact, some faculty members who are very successful with publications nevertheless come to be viewed by their fellow faculty as bad hires because of their arrogance or indifference or disengagement or whatever. What the hiring committee and everyone else wants to see is a nice, engaging, and challenging EQUAL (at least in North America) during the interview. Of course, you also don’t want to talk too much. That is, don’t cut folks off when they are talking (unless you can’t get a word in otherwise) and don’t talk just to make noise (say something interesting). This can be very challenging and exhausting and, as I can attest from personal experience, can lead one to say things that come out wrong – a trap that I fell into during at least one interview. 

By Kerry Soper.

Prepare well but don’t look like you over-prepared. It is frequently suggested that folks going to an interview should know a lot about everyone’s research in the department, including having read some of their papers. This advice is certainly fine at face value BUT it can’t look like you have done this specifically for the interview. Instead, it should seem like you knew something about everyone’s research just as a matter of course in your normal research activities before getting the interview. Two elements of psychology come into play here. First, it can’t look like you are desperate for the job. If you are, then it will seem like you need the department more than it needs you, which is unlikely to inspire enthusiasm for your hiring. Instead, you want to make it seem like you are very interested but that you have other (implied) options that make you relaxed about whether or not you actually get the job. If this is done well, it can lead the committee subtly to the feeling that the department needs you more than the reverse, which makes you more desirable as a hire. Second, faculty members want to think that you knew about their work outside of the desire to get the job. That is, if you read their work only in preparation for the interview, then you didn’t really know about it otherwise. However, if you knew their work independent of the interview, then it makes you seem widely read and generally knowledgeable. Perhaps the best way to walk this tightrope is to explicitly refer to the person’s work only after they first mention it. You can facilitate this sequence by asking “So, what projects are you developing now?” Then, as they talk about their projects, you can interject a comment or two that makes it clear you know earlier aspects of their work. 

By Kerry Soper.

Engage in social activities. I have also seen it suggested that, when asked in an interview if you want do something (go for a beer, have a coffee, see a local attraction), you should just say yes! I generally agree with this point but with some additional nuances. Many faculty have other departmental members as their best friends and members of their social circle. Thus, they are often consciously or unconsciously hoping that you – the interviewee – will also become a friend beyond the necessary work interactions. They want to imagine you hanging out with them and engaging in sporting activities or clubs or poker nights or garage bands, or whatever. They want to envision a causal, relaxed friend as well as an intellectual colleague - and participating in social activities really helps. Many people who have not yet had a faculty position, think that faculty spend all their time talking about and debating science. While such debates are indeed frequent, much of the time faculty talk about other stuff (music, sports, politics, etc.), even at work; so it is great if you are comfortable doing  same. These informal “fun times” during an interview can be a great way to talk about your hobbies (hopefully following naturally from other aspects of the conversation), weigh in on a political issue, or refer to the latest social media scandal. These relaxed interactions will make you seem sociable, which will help people to see the sort of value-added colleague they would love to have.

Of course, you also don’t want to project yourself as someone you aren’t. Most obviously, you shouldn’t drink if you aren't comfortable with it. In addition, you should avoid situations that encourage inappropriate comments or discussions about race, religion, sex, or other topics that can be insulting or uncomfortable. Moreover, if you receive comments of this sort during the interview, you should make sure to tell the department chair or someone higher up. Situations that make you personally uncomfortable or intimated should not be tolerated or allowed to pass. 

Found here.

The presentation is critical

In addition to the above “I am already your colleague” feel that you want to project, the most critical aspect of your interview (at least for a research-focused position) is your research presentation. If you give a bad talk, you are toast. If you give a great talk, you can rise above other candidates even with better CVs. In fact, you really must give a great talk. It not only casts your research in the best possible light in the way you want it to be viewed, but it also indirectly shows your teaching ability and how likely you are to be interactive and engaging as a colleague. So how to do it?

Follow the baby-werewolf-silver bullet approach to structuring your talk and/or elements within your talk. I have written a previous blog on this topic.

Link your work to general theory. Following from the above, the baby should be presented in a very general way. Importantly, the baby/werewolf is not your study system or your experimental approach, at least not usually. (Instead, your study system or experimental approach is the silver bullet.) The baby/werewolf is instead some general theory or question that is of interest to many people, presented independently of your study system and in explicit reference to formal theory or meta-analytic results or famous previous studies. You want everyone in the audience thinking “Yes, that is an important problem that needs to be solved if we are truly understand the way the world works.” Then you want them thinking “Yes, that is a great way to address that problem.”

Don’t oversimplify. When presenting to a general department, the temptation can be to “make it understandable to everyone.” While this is a laudable goal, you really can’t water down your research or it will simply seem trivial to anyone that actually knows something about it. You need to show your data, not just the model fits. You need to specifically mention the statistical models you used. You need to actually describe the experiments. Importantly, however, you also need to explain your work in a way that even non-specialists can grasp the key elements and their importance and suitability. Perhaps the best way is to explain things twice: once the technically appropriate way and once the simple way.

Found here

Don’t describe too many projects. Hiring committees generally want to see someone who is going to be a world expert in some particular topic, not a dilettante who jumps from one random project to another. Thus, you want to present an integrated and multi-faceted approach to a particular important question (baby/werewolf) in which your work has the potential to be world-altering, paradigm-shifting, game-changing, and all those sorts of things your letter writers have said about you but which you can't explicitly state yourself. Of course, some people really do work on several entirely different topics that are not closely related to each other. In such cases, I still generally suggest focusing on only one of the topics in your talk, unless you have a clear expectation that some of the audience is specifically interested in one aspect of your work and some other segment of the audience is specifically interested in the other aspect. In such cases, you can present both but you need to explain why you are doing so.

Talk about the work you will do next. At the end of your talk, describe some of the projects (but not too many) that you will do when you are hired. These would ideally be logical – but not trivial – extensions of what you have already been doing. You don’t want to go into too much detail about experimental design as it can leave you open to criticism about things you haven't even done yet; but you should at least make it clear that you have an idea of what you will do next and how you will achieve it. As a more specific example, many people in my fields of ecology and evolution say they are going to use Next-Gen Sequencing methods. Nearly everyone says this even if they have no experience with it and no clear reason why it is an important next step for their research. As a result, it can seem like you have methods-envy and are saying something that you think folks want to hear just because they want to hear it. If you are going to say that you are going the genomics (or equivalent) route, then you need to have a clear reason why it is necessary and important. That is, the genomics must be the silver bullet that is clearly necessary to kill the werewolf. It can’t simply be something you are doing because you think folks are expecting it or because “we need a complete picture of what is happening.”

Don’t say “that’s a great question”. By way of illustration, I will relate a personal anecdote. When I was answering questions during an interview for a faculty position in 2000, I said for the first question That is a great question. Then I paused and said out loud (as it was crossing my brain in real time) Why do we always say that before questions? If we say it for everything, then it means nothing; that, in fact, no questions are great. And, if you don’t say it for one question, does that mean the question is not great? The audience looked amused or at least bemused. Then I went on to answer the question. I was still mulling over what I had said as the next question was being asked, and so I responded histrionically That is an OUTSTANDING question. This time some folks in the audience actually laughed out loud. Then I answered the question. Then, at the start of my response to the third question, I said That is a really awful question. This time, the whole audience burst out in loud guffaws. It turned out that the third person was internally famous for asking ridiculous questions and I had timed my comment just perfectly. However, I didn’t get the job. Perhaps my flippant comments were the reason or perhaps it reflected the search committee’s chair’s first words to me I don’t even know why we are interviewing you, you are totally unsuitable for the position. In fact, knowing that I wasn’t going to get the position was perhaps one reason I felt emboldened to say what was on my mind.

As a related point, make sure to leave room for questions at the end – your talk should only be about 45 minutes but not much shorter. During questions, make sure you respond at length and with deliberation. (Don’t just say Yes, you are right and then move on to the next question.) If the question doesn’t make sense, say something like OK, I am not sure precisely what you mean – I look forward to discussing it more with you later over beers – but I will for the moment convert your question into one that I can actually answer. A response like this is often good for a chuckle, which again makes you seem fun and engaging.

One problem that I might have introduced with all of the above advice is that you will begin to overthink everything during the interview when you really should be relaxed. So here is a more general suggestion that hopefully facilitates all of the above my more organically. When you go for the interview, pretend that you are already a faculty member at University X and that you have been invited to give a seminar at University Y. This mindset will hopefully help to make all of the above flow more naturally and without conscious thought DURING the interview.

Finally, note that many website give additional more specific advice - just type "job interview academia" into Google.

Now go out there and kill that interview.