Constant Reproduction in the Tropics by Kirsten Steinke

Collecting Chthamalus spp. in my field site, Punta Culebra  

It’s a little known fact that barnacles have the largest penis to body size ratio in all of the animal kingdom, but did you know that they have an almost continuous rate of reproduction in the tropics? As an REU participant working in the Collin lab my research experiment focuses on a species of barnacle in the Chthamalus genus and aims to answer the question of whether or not there is a reproductive cycle within this continuous-brooding species. These little guys have a shell that is on average 10 mm in diameter and they like to hang out in the upper reaches of the intertidal zone so they can avoid competition with the larger Balanus species that dominate the lower intertidal zone and tide pools. This study compares the differences in reproductive cycles (i.e. percent brooding) between individuals found in the mid and high intertidal zones—at the extremes of their habitat.

At the study site in Punta Culebra I climb over the rocks to get to the four different sites where I collect my organisms. I am a slave to the tides and must do my collection during low tide when the barnacles are easily accessible! Most days during low tide the weather has been just shy of blazingly hot. However, sometimes I am afforded a nice break and get to scrape barnacles off the rocks when it’s dumping rain! When I am done collecting, I head on over to the lab to examine their broods. There are a couple things I look for: 1) Do they have a brood—notable by an orange lamella that encompasses the embryos found on the dorsal surface of the barnacle 2) their current stage of embryo development and 3) the relationship between brood size and barnacle size.

Chthamalus spp. has a shell that ranges in color 

from light grey to black.

My results thus far show a more distinct cycle from species living in the upper intertidal zone, while the individuals living in the mid-intertidal zone exhibit fluctuation in percent brooding over time with no obvious pattern. Since the start of my experiment in mid-June, the Chthamalus spp. in the upper intertidal zone have had a consistent rate of reproduction where ~80%-100% of individuals were brooding in a given day. The exception to this being on Monday, July 6 where only half of the barnacles collected in the upper intertidal had broods. There are many reasons this could have occurred, however my primary hypothesis is that it was due to the high amplitude tide that occurred over the weekend. It could have been just what the barnacles were waiting for to release their embryos in hopes of offshore settlement!

There is another high amplitude tide scheduled for the beginning of August and I’m excited to see if this drop in percent brooding occurs again! Because I am only in the Collin lab for ten weeks it is impossible to observe their long-term reproductive cycle, but it would be very interesting to repeat this experiment in the dry season to see how the cycles differ from the current wet season. Other aspects to my experiment include the effects of competition and temperature on brood size…but that’s another story!

Although my barnacles are not the most charismatic bunch, I find them fascinating. The environmental stressors that these barnacles are subject to are also impacting the reproductive success and life cycles of a multitude of animals living in the intertidal zone. A better understanding of what factors limit the reproduction and fitness of invertebrates like Chthamalus spp. is becoming exponentially important as the threats of global warming continue to grow and change the marine environment.

Using Model Species to Study Reproduction and Development in a Marine Lab

Because we study development in our lab, there is a lot of reproduction going on here! Currently, we are caring for hundreds of sea snails, carefully monitoring them for new babies.

The snail farm.  Crepidula snails hanging out while
they wait for new water to be added to their cups.

In biology, we like to use "model organisms" in our studies. Model organisms are those species that have several good qualifications for study. Naturally, our lab prefers to study animals whose reproduction can be monitored. We also like to study animals whose eggs and larvae can be maintained in the lab.

Crepidula marginalis fit my needs for my biology experiment! They are a marine snail that live in the rocky intertidal zone. And one place we can find them is a beach close to our lab, in the Veracruz area of Panama.

Crepidula are easy to collect, easy to maintain in a lab, and their reproduction can be monitored.

A female with eggs

As you can see from the photo, male snails will "climb aboard" a female snail. If the female chooses to mate, and to fertilize her eggs, then her egg "brood" will be visible through the sides of the clear cups. We use clear cups in our labs, which become the snail's new habitat, or home, while we study them.

When the eggs have developed, the brood sac will open and hundreds of veliger larvae will be released from their mama's care. For their first few days of life, they swim freely and quickly! Within a few days, their swimming slows down as their shell gets larger and heavier.

Upon hatching, we try to distribute the new larvae into new bowls with fresh, filtered sea water and algae to eat.

Of the many things I have learned under Dr. Collin's mentorship, I have learned how to choose an organism that suits your experimental needs. And for my thermal tolerance study, the Crepidula marginalis have been a good model organism for these reasons:

* They have been easy to collect in the field,
* They survive and reproduce in the lab,
* Their reproduction can be monitored, and
* Their larvae survive in the lab while we are studying them.

Nina Dropcho, Intern, Collin LabSmithsonian Tropical Research Institute

PORCELAIN CRABS

Before arriving in the CollinLab I´d never worked with porcelain crabs (porcellanids).  This is my first time with these small crabs.

They are quite different from the crabs you see on your dinner plate. Their bodies are compact and flattened; this is an adaptation for living and hiding under rocks. They are very abundant along the Pacific Coast where they congregate in tide pools under rocks because they are very sensitive to desiccation.

Another characteristic of porcelain crabs is that the antennae are inserted external to the eyes, not between the eyes like in other crab families.

Petrolisthes tridentatus

Porcelain crabs are quite fragile animals.  They often shed their limbs to escape predators (or me), hence their name. They are pretty fast and when you have to collect them, you should be very carefully because you can end up catching only the body… The good news is that they only need a few days to regenerate the legs they lost.

                                                             

P. armatus without a cheliped…yes, I tried to collect it.. 

I´m working with one species of these Porcellanids, Petrolishtes armatus.  They can be distinguished from similar species by an orange spot on the chela and blue mouthparts. Also another unique characteristic useful to differentiate them from another Petrolisthes species, P. tridentatus, is that the cheliped has 3 spines that are very clear to see.

P. armatus and P. tridentatus, very difficult to differentiate in the nature. 

But under the microscope you can see the difference in the cheliped

A few months ago I had no idea what they are.  And now…they are my workmates and I have to admit that they are amazing!