This is a guest post by Chelsea Rochman. Chelsea is a post-doc at the University of California Davis. This is her fourth 

WARNING: Some content may not be acceptable for a younger audience. (Note from Miriam: It’s ok, Chelsea, nothing in this post is at all out of the ordinary for DSN. It’s salty in these here parts.)

Strange title you say? What can sex possibly have to do with the combination of fish and plastic debris? NO, this is not related to the recent news article regarding a strange object found in the stomach of a fish! Instead, it arises from a recent study performed in our laboratory whereby we were equally perplexed to find something very fishy (no pun intended!) in the testes of a male fish exposed to plastic marine debris.

Sex

Since the release of Rachel Carson’s Silent Spring in 1962, we have heard eerie stories about alligators with abnormal penises from exposure to DDT, amphibians with eggs in their testes from exposure to atrazine and snails turning hermaphroditic from exposure to tributyltin —all considered hard evidence for endocrine disruption.

Well, this all sounds frightening, depressing and/or a bit like a dark comedy sketch, BUT what is endocrine disruption really?? Well, put simply it is literally any disruption to the endocrine system. The endocrine system is the system in the body of an organism that controls our hormones. As such, it’s critical for functions we all know well including stress before a deadline, the infamous running high, the dreaded PMS, sexual pleasures and arguably most importantly, reproduction (critical to maintaining a population).

What does this have to do with fish??

Well, fish are often used in scientific research assessing the endocrine disrupting hazards of chemicals on wildlife. Fish are a) important for human consumption, b) arguably great ecological indicators of the health of aquatic habitats, c) sensitive to endocrine disruption and d) live in regions that ultimately receive our waste (ever read the phrase, “all drains lead to the ocean”). As such, fish are exposed to many of the chemicals produced and consumed by us and we must understand the hazards of the cocktail of contaminants entering our water bodies. This keeps researchers very busy, as the number of new chemicals synthesized and marketed has increased exponentially over the past fifty years.

OK… and plastic debris?

In the past, endocrine-disruption was not addressed when assessing the hazards associated with synthetic chemicals, and as a consequence chemicals once considered benign have become ubiquitous as environmental contaminants and threaten biodiversity. Similarly, hazards associated with plastic in marine habitats were also likely not addressed when assessing hazards associated with plastic products. Today, plastic debris is ubiquitous in the marine environment and is a contaminant of concern recognized by several countries and international organizations.

As I’ve mentioned before, plastic debris should be considered as a multiple stressor in aquatic habitats as a consequence of the physical toxicity and large mixture of chemical contaminants (i.e. ingredients and environmental contaminants that accumulate on plastic debris) associated with it. Several of these plastic-associated chemicals have been linked to endocrine disrupting effects. Bisphenol-A, now banned on baby products in several states including California and in Europe, can disrupt endocrine-system function. Furthermore, there is evidence that phthalates and nonylphenol, additives to several plastic types, are estrogenic. As such, plastic marine debris is likely associated with a mixture of endocrine-disrupting chemicals. As such, it is critical to assess if the plastic debris that thousands of animals associate with food could initiate any of these eerie hormonal effects described.

The story

Somebody has to do the dirty work, so we dove in and asked if fish experience endocrine disrupting effects when they eat our plastic waste for dinner. Some of you may remember this experiment from a previous blog post. What we did not share then, and will share here, are some troubling results sparked by hypotheses spun from one strange discovery: the very abnormal testes of a male fish fed marine plastic debris.

The image above shows the testes of a normal fish fed a control diet (left) next to the testes of a fish exposed to plastic marine debris (right). The testes of this adult male fish exposed to plastic marine debris has rather abnormal germ cell proliferation. We are unsure whether these abnormal germ cells will lead to intersex or reproductive impairment, but the abnormality of these gonads and the similarity to female germ cells is cause for concern.

Our results show early-warning signs of endocrine disruption in fish exposed to a mixture of plastic and sorbed contaminants, suggesting that plastic marine debris, reportedly ingested by multiple wildlife species, may alter the functioning of the endocrine system in aquatic animals.

Most importantly, we report evidence at the molecular and organ level, for disruption to the endocrine system caused by the “cocktail” of contaminants associated with polyethylene deployed in an urban bay. Of major concern should be the permanent effects that exposure can have during critical early- life stages of organism development, which may impair reproductive success and harm wildlife populations. Still, chronic exposure to environmentally-relevant levels of endocrine-disrupting chemicals can have an effect after maturity as reported here. Chronic exposure is typical of marine plastic debris as it accumulates in habitats and is a persistent material that can last for decades.

Current waste-management strategies for plastics remain ineffective, and in parallel global production of plastics continue to increase at an average rate of about 9% per year. Thus the current rate of infiltration of this material into aquatic habitats is likely to increase. Because there have been several reported incidents in wildlife of population declines resulting from the release of endocrine-disrupting chemicals, our results suggest the need for future studies to test hypotheses regarding endocrine disruption in wildlife as a result of exposure to the growing accumulation of plastic debris.

The published study is found here: Rochman et al., 2014, Science of the Total Environment.

The post A story about fish, plastic debris and sex first appeared on Deep Sea News.

One of the things in the title was not actually part of my latest published research, unless you count the soundtrack I played while doing analyses.  The research question was simple, how do the sexual lives and strategies for the subsequent offspring change depending on the availability of food.  In the oceans, the amount of food ranges from a single M&M to the whole damn M&M factory.  When the candy dish of single colored M&M’s is near empty, because that is what a true rocker would want, what is the most rock and roll thing a snail can do with it’s love life?  Cuz they do feel like makin’ love. Conversely, when the night is young, the world is an open book, and you can bathe in tub full of tiny chocolate candies, how does a snail rock and roll all nite?

In the oceans, when the food is low then the population of snails must also be low. There is simply not enough food to support lots of snails.  With mate choices at a minimum, better to be a hermaphrodite so any chance encounter can be a whole lotta love.

However, this is exactly the opposite of what colleagues and I found in a new study.  Collecting data for almost 200 families of snails and the amount of food available to them in the wild, we found that hermaphrodites are found in greater frequency when food is in surplus.  One of the reasons for this is that those showy nudibranchs, mainly hermaphrodites, dominate when food is great.  Those flashy sea slugs, sort of the Dee Sniders of snails, have very high metabolic demands.  They simply don’t do well where food is low.  Much like I’m sure Twisted Sister never stayed in hotel that couldn’t supply them with a whole room of frozen cheesecake bites.  Moreover, simultaneously producing eggs and sperm, i.e. always being ready to go, is also calorically expensive. In retrospect it doesn’t seem very rock and roll at all to be a hermaphrodite when food is low.

But what choices do snails make for their offspring in these two different eating scenarios? What will allow your offspring to grow up into full on rockers and ultimately throw a TV out their little snail hotel rooms?  Let’s take a step back.  A snail can produce three basic types of youth.  Planktotrophic larvae are sent up into the water column and snack to their little “hearts” are content.  Lecithotrophic larvae are sent into the water column but do not feed.  Instead, the mother gives these little larvae a yolk snack to sustain them.  Last, you can hatch maybe with a little bit of brooding little tiny adults.

What we found is that in regions of the oceans where food is low, snails that produce planktotrophic larvae dominate.

Producing offspring is costly…calorie wise.  In the three scenarios above, planktonic larvae are the least expensive.  The feed and fend for themselves.  More importantly, the larvae feed elsewhere, away from the adults.  When there are few M&M’s, you don’t have the young hanging around cramping your style.  And because they are planktonic they can drift away and maybe find a better stash of tiny candies than was ever available to you.  The other scenarios are more calorically expensive; one requires the adult to supply a yolk. The last scenario, direct development, is the most costly both to produce large young but to care for them as well.

The only thing to do now is to light a couch on fire.

Now the paper and a Spotify music list to inspire you

McClain, C., Filler, R., & Auld, J. (2014). Does energy availability predict gastropod reproductive strategies? Proceedings of the Royal Society B: Biological Sciences, 281 (1789), 20140400-20140400 DOI: 10.1098/rspb.2014.0400

The post Sex, Snails, Sustenance…and Rock & Roll first appeared on Deep Sea News.

Dear Deep Sea News,

I never thought I’d be writing to you – not least because it’s really hard to type with my radula – but I don’t know what else to do. I’m a predatory marine snail and I’ve always been FEMALE. I know that many of my molluscan cousins are hermaphrodites, but whelks like us (I’m from the illustrious Thais orbita species) don’t hold with such shenanigans. We believe that gluing a clump of egg sacs to a rock and abandoning it to its fate is a sacred act between a male and a female!

But because my family is so conservative, I don’t know who else to turn to with my very embarrassing problem. I seem to have sprouted a penis from the right side of my head. Of course, having a penis coming out of one’s head is perfectly normal – if you’re a male snail (or a hermaphrodite, if I must include them). I’ve spent the last few days hiding under a rock, afraid to show up in public with this hideous protrusion. We are dignified snails, not sex-changing perverts like those nasty slipper shells! How can I go back to normal?

Sincerely,
Penis Problem in Perth

Dear PPP,

I can understand your distress. Female whelks aren’t supposed to grow penises – but unfortunately, you’ve run afoul of an antifoulant. The culprit is tributyltin (TBT), a highly toxic compound used to prevent growth on the bottoms of boats. TBT is certainly effective, but it has the known side effect of causing staid and dignified snails such as yourself to undergo a involuntary sex change. Your ovaries and such are still there – it’s just that a penis and perhaps a sperm duct has grown over them. This is called imposex.

I don’t want to embarrass you, so I’ll show photos of a different species of snail from Brazil. Below are photos of a normal male and two imposex females. Look on the bright side, PPP – at least you haven’t grown two penises, like the unfortunate snail (e) below.

Despite the recent news coverage from Perth, sex-changing snails is nothing new. Imposex in whelks was first reported in the UK in 1970 (PDF), and linked to TBT in 1981. TBT causes gastropod females to produce way too much testosterone, leading to your current predicament. (Oddly enough, TBT only affects gastropods, not other molluscs such as bivalves.)

In some gastropod species, imposex doesn’t seem to affect reproduction much. But in others, it causes total reproductive failure – the sperm duct can block the oviduct, making it impossible for the female to release her egg sacs and leading to internal rupture and a very unpleasant death. I can only hope that your species is relatively resistant, PPP.

Today, TBT is restricted, but not banned. In Australia, where you live, TBT is banned on vessels less than 25 meters (75 feet) in length. Vessels greater than 25 meters can apply for a permit to use TBT, but are limited to a maximum leaching rate of 5 μg cm⁻² day. A 2003 study on the east coast of Australia found that imposex had decreased since the restrictions went into effect in 1989, but that hotspots remained, particularly within harbors and bays. It seems that Perth is one of those hotspots. Sorry.

Imposex is irreversible, so I’m afraid you’re stuck as you are. I hope that with time (and if you don’t die from a ruptured oviduct), you’ll come to appreciate and even enjoy your new body parts. But rest assured – if Perth has a TBT problem, there are other female snails in the same antifouling-coated boat. Have you considered forming a support group?

Tip of the tentacle to Jezebel and Dr. Bondar!

Cardoso, R., Caetano, C., & Cabrini, T. (2009). Biphallia in imposexed females of marine gastropods: new record for Nassarius vibex from Brazil Brazilian Journal of Biology, 69 (1) DOI: 10.1590/S1519-69842009000100030

Matthiessen, P., & Gibbs, P. (1998). Critical appraisal of the evidence for tributyltin-mediated endocrine disruption in mollusks Environmental Toxicology and Chemistry, 17 (1), 37-43 DOI: 10.1002/etc.5620170106

The post Female snails in Australia are just happy to see you first appeared on Deep Sea News.

Post by Matt Hoch. Dr. J. Matt Hoch is newly minted PhD from SUNY Stony Brook who is interested in the reproductive ecology and life history evolution of barnacles. We have reported on Matt’s research previously here at DSN.
“Does your mother know what you’re doing?” The question was asked from the back of the room and I responded with what I thought was a truthful answer: “Yes.  She is proud of me.”  This was one of the only questions that anyone asked me.  I had just finished presenting my first talk on my own original work at a national scientific meeting, “A preliminary study of variation in penis characteristics in barnacles.”  My mother was at least proud that I was successfully carrying out research in a good PhD program.  I don’t actually know if she was proud of my project of choice.  I imagine that when telling her co-workers about my project, she might blush or tiptoe around it, but she at least tried to explain it to my grandmother.  “Why don’t you try to figure out a way to keep barnacles off my boat?”  That’s what my dad asked when I described my dissertation topic to him; “You’ll make us rich!”

It turns out the functional morphology of the barnacle’s…ahem…naughty bit… has important implications for evolutionary theory.  Barnacles are familiar as the small rock-like crustaceans growing on almost any hard surface that spends a significant amount of time in salt water.  Probably their most famous feature is the glue that they use to anchor themselves.  Living this permanently glued lifestyle imparts a few challenges on their ability to mate.  Unlike most sessile organisms, which broadcast spawn, barnacles reproduce by copulation.  They have to physically couple.  Since they can’t get up and walk, the only way to do this is with a penis that is capable of searching for partners and then mating with them.  The penis of the barnacle can stretch to about ten times the length of its body during attempts at mating.  It’s covered with chemosensory setae, bristles that are capable of detecting chemical signals; basically a series of noses that it uses to smell out receptive mates.  Once it locates a receptive partner, it might have to compete with many other barnacles attempting to fertilize the same eggs.  Once fertilized those eggs are brooded inside their mother’s shell for several weeks until they are released as larvae.

All of the barnacles involved may act as either a male or female at any given time.  They are simultaneous hermaphrodites.  An important decision that each barnacle must make is how much effort to put into acting as a male and how much to put into acting as a female.  Theory developed by scientific superstars W.D. Hamilton (1967) and Eric Charnov (1980) suggests that competition between barnacles acting as males should drive this decision making process.  As more and more barnacles compete to fertilize eggs, they need to produce more sperm to remain competitive.  They essentially try to produce enough sperm to overflow the functional female’s mantle cavity and displace the sperm of their competitors.  Large quantities of sperm can be deposited in these competitions.  So much so that functionally female barnacles have been reported as having so much sperm stuck to their cirri that they are unable to feed.

My work, on variation in penis characteristics, aims to determine how competition between barnacles acting as males changes in different physical environments.  For example, in wavy sites, barnacles are unable to reach mates as far away as barnacles in calm bays.  When they try, their penises probably get knocked around like crazy.  They deal with this by growing thicker penises, which may be more resistant to interference by waves, but lose the ability to stretch as far as the thinner penises grown by barnacles in calm water (Hoch 2008, 2009).  Since none of the barnacles in wavy sites can stretch as far, each barnacle acting as a male will have fewer others able to compete with it.  They are freed from intense competition, and following Eric Charnov’s predictions, should have larger clutches of eggs.

I recently explained this to my parents.  They seemed to understand it, but my dad asked the follow up question that I should have expected. “Can’t you figure out how to manufacture their glue?  We could get rich off of that.”

Further Reading
Charnov, E. 1980. Sex Allocation and local mate competition in barnacles. Marine Biology Letters 1:269-272.
Hamilton, W. D. 1967. Extraordinary sex ratios. Science 156:477-488.
Hoch, J. 2008. Variation in penis morphology and mating ability in the barnacle, Semibalanus balanoides. Journal of Experimental Marine Biology and Ecology 359:126-130.
Hoch, J. 2009. Adaptive plasticity of the penis in a simultaneous hermaphrodite. Evolution in press.

The post On the study of crustaceous genitalia first appeared on Deep Sea News.

Barnacles are known as the John Holmes of the invertebrate world with penises reaching up to 10 times their body size. Not all barnacles are equally endowed though. To make the situation more complicated, barnacles are hermaphrodites. Eric Charnov proposed an extension of Sex Allocation Theory to simultaneous hermaphrodites, those individuals carrying both male and female reproductive parts at the same time. His model makes predictions for how much resources should be allocated in being male or female based upon how competitive your local environment. Thankfully for barnacles, being unable to move confines your locality to a rather small portion of rock. Or does it?

Photo from Wikimedia Commons

How much does a penis cost?
Barnacles tend to flock to one another, their larvae exhibiting what researchers call gregarious settlement. This results in dense mats of barnacles upon barnacles on rocky shores. New research from Matt Hoch, a PhD student at SUNY-Stony Brook, tests the effects of overcrowding and wave exposure on the penis morphology of the acorn barnacle, Semibalanus balanoides. But bigger is not necessarily always better as Hoch explains:

“Variation in barnacle penis traits may be important when comparing sex allocation of barnacles for several reasons. As the number of individuals in the mating group increases, mate competition intensifies, which is predicted to lead to greater relative allocation to male function. The penis itself represents a significant investment into male function, in terms of construction, maintenance and performance costs. For example, the presence of the penis, located between the feeding cirri on the terminal body segment, may reduce feeding efficiency. As penises grow larger, interference with feeding is expected to increase.”

For most of the year, the barnacle’s penis is rather languid. The vernal season for this little fellow is September to October where it rapidly grows until ready to spring into action come November. Unfortunately, the excitement of it all is short lived and the penis is cast off with the next moult upon mating. Because the growth and decay of the penis happens so quickly, Hoch hypothesizes that it is costly to maintain this one-use only appendage. If the closest neighbor is far away, it will need to invest more energy into maleness, resulting in a longer penis.

Crowding Penises
Hoch compared barnacles found in a crowd, when their shells were touching their neighbor’s (see photo above), to those in uncrowded situations. Studying barnacles in scenic Shinnecock Bay in Long Island, NY Hoch found that crowded barnacles had significantly shorter penises than its un-crowded bethren. Yet, the thickness at the base remained unchanged and there was no difference in the relationship between penis length and body volume between living arrangements. Additionally, as the distance between neighbor’s increased, there were fewer fertilized egg masses. So depending on you look at it the barnacle trades off size for action.

Barnacles take a lickin’ and keep on kickin’
The rocky intertidal is no place for a wuss. Tides and wave forces make it an intensely dynamic environment, not to mention stress from heat and drying out. One needs a “thick skin” in order to take the constant, rhythmic pressure of wave exposure. Hoch studied 2 sites at ole Shinnecock Bay. One was exposed to a higher frequency of waves, facing the Atlantic. The other site faced into the bay where it was more tranquil. As one can see from the above graph, fertilization is more successful in the protected area. The disparity of fertilization success between protected and exposed areas grows as the distance between neighbors increase. Exposure to waves appears to also hinder fertilization success. Is it because waves break off the barnacles penis? While there is no difference in penis length between areas, the basal diameter was thicker in exposed barnacles. The penis adapts to take a pounding by buffing up at the base.

What is the take home message here if you are a barnacle? If a barnacle’s goal is to be the John Holmes of sea world, live in uncrowded areas in wave-exposed environments. If the barnacle’s goal is to fertilize as many eggs as possible, live in close quarters at areas protected from wave exposure. I’m not quite sure which goal barnacle’s are seeking. They are cunning creatures with a knack for keeping their cirri to themselves.

What does this have to do with the deep sea? The deep sea is moderately protected from the wave exposure faced by intertidal organisms. Hoch provides an interesting hypothesis that, at least in barnacles, the physical environment plays a strong role in molding morphology. Such characteristics are said to be plastic. In order to understand how evolution of novel morphology arises, the degree of plasticity in the trait needs to be assessed. Reproductive morphology is typically considered to be under a high degree of selection, because it is directly associated with producing the next generation, among other reasons. Under Sex Allocation Theory, Hoch predicts that:

“… all other factors being equal, barnacles in areas protected from waves should have larger mating groups than those in exposed areas. The resulting functional mating groups will have higher levels of competition among functional males, leading to relatively greater investments into the male role. I would then predict that in areas exposed to waves, barnacles will invest relatively more energy into female function and produce larger broods of eggs. Given the higher number of males competing to mate with a single individual in areas protected from waves, individual broods are more likely to have a larger number of siring males and therefore greater genetic diversity among the offspring.”

Deep sea barnacles form similar aggregation to its intertidal cousins yet face little to no wave exposure aside from rarer events like underwater landslides. But there are local topographic highs in currents created by an outcropping. This may be as small as a lava wall (see below) or as large as a seamount. It would be interesting to see if Hoch’s predictions hold for gregarious barnacles in environments with similar conditions, but less of a physical force.

Barnacles from a hydrothermal vent community. Note orientation tends to be on the vertical surface of the lava. Species mostly composed of Eochionelasmus ohtai.

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HOCH, J. (2008). Variation in penis morphology and mating ability in the acorn barnacle, Semibalanus balanoides. Journal of Experimental Marine Biology and Ecology, 359(2), 126-130. DOI: 10.1016/j.jembe.2008.03.002

The post Environment Shapes Barnacle Penis first appeared on Deep Sea News.