Bonin Islands Fiddler Crab, Uca boninensis (Fiddler Crab of the Week)

The Bonin Islands Fiddler Crab, Uca boninensis is fairly unique in that it is both endemic to the Ogasawara Islands of Japan (“Bonin Islands” is a historical name) and is not sympatric with any other species, being the only fiddler crab found on these islands. The only other fiddler crab with no sympatric fiddler associates is Uca tangeri, which has an immense range across most of the west coat of Africa and even the southern edge of Europe. There are a few other species endemic to small islands, but each of these overlaps with one or more other fiddler crabs.

Figure from Shih et. al (2013)

Until its recent description, this species was thought to be Uca crassipes. Shih et al. (2013) identified the new species through clear genetic differentiation between it and other populations of U. crassipes; they also found some minor morphological differences between these two very similar species, although nothing so striking as to allow easy identification. Little is known about the ecology of Uca boninensis since almost all previous work simply noted its presence on these islands. It is a medium sized fiddler crab, found in the upper intertidal zone of the estuaries of small rivers, in fragmented rock and muddy-sand substrates.

Because this species is known from only a few remote islands in the Pacific Ocean, its existence is likely threatened by climate change and is a candidate for conservation evaluation and protection. The Ogasawara Islands contain many endemic, unique, and endangered species across all forms of life and were added to the UNESCO World Heritage List in 2011.

Bowed Fiddler Crab, Uca arcuata (Fiddler Crab of the Week)

The Bowed Fiddler Crab, Uca arcuata, is one of the more widespread and better known species from eastern Asia, found along the coasts of China, South Korea, Taiwan, and Japan.  It is a large species, with a dark brown or maroon carapace (often with cream edges and highlights), cream eyestalks, black-to-red legs, and a robust major claw with a red hand and cream fingers.

In parts of its range, both males and females of this species build chimneys around the mouths of their burrows, extending the entrance upward from the muddy surface. They are often found on open mud flats and banks near the mouths of rivers. This species has been the focus of many studies by marine ecologists in both China and Japan.

Jocelyn Crane reported that this species could sometimes be found canned in local seafood markets in Japan, making it one of only two species eaten by humans.

Word Cloud of Names

I recently happened to stumble across the lab page of a faculty member who used a word cloud based on his research papers to display the key words that come up most often in his own research. I thought this was a rather interesting way to get an objective view of ones research so started playing with the idea for my own work. Unfortunately, this turned out to be more difficult than I expected, not because building a word cloud was hard (there are plenty of available tools for that), but because extracting the text from the PDFs of all of my publications led to a lot of weird biases and errors (this is a PDF issue) and it’ll take a lot more effort to dig up the original raw text documents than I’m willing to go through right now.

It occurred to me secondarily, however, that we could use the same approach on the fiddler name data to get a visualization of how often each name appears in the literature.

First we have the occurrences of binomial/compound names in the literature. The frequencies are based on the number of publications each name appears in if used as a valid name (thus, a paper which states that name A is a junior synonym of name B would only count the senior synonym B and not the junior synonym A). No matter how many times the name is used within the paper, it counts as only one occurrence with respect to this exercise.

The results are pretty much what one would expect, but it does provide a somewhat interesting (if not particularly statistical) rendering of the relative name uses.

As with other parts of the site, we can do the same thing with the specific names only (ignoring both genera and lumping alternate/misspellings). Again, the major names are what one would expect.

I may need to play with the visualization a bit (color schemes, shape, etc.), but these images will be added to the name summary part of the website on the next monthly release.


Beebe’s Fiddler Crab, Uca beebei (Fiddler Crab of the Week)

Note: the fiddler crab of the week series was temporarily derailed due to some unexpected health issues, but will hopefully be back on track going forward.

This week we find another species from the Pacific coast of the Americas, Uca beebei, named after the famous naturalist, explorer and author William Beebe. This small species is found from El Salvador through Peru on open mudflats. In the Pacific entrance of the Panama canal it tends to be one of the more numerous species, often found mixed with larger species such as Uca stylifera or Uca heteropleura or more similarly sized species such as Uca deichmanni. Relative to many other species, it is also more of a generalist when it comes to substrate preference, ranging across both sandier and muddier mudflats. Not the most colorful species, it tends to be a grayish-brown with some teal on the back of the carapace; the long, slender fingers of the large claw are white, while the rest of the major limb often has dark purple highlights. The eyestalks are thick and yellow.

Photo provided by Pat Backwell.

Unlike many of the other species in the series so far, Uca beebei is actually fairly well studied. John Christy and colleagues spent many years studying the behavior of this species in Panama. It has a fairly classic, basic wave, quickly moving laterally its claw to the side, then forward in an overhead circle back to the rest position. The small claw often goes up and down as well. The waving can be done either standing in place or sometimes shuffling toward or away from another crab.

Beebe’s Fiddler Crab is one of a number of species which build structures around the mouth of their burrow. As seen in the photo below, the males build a sort of wall or pillar or partial hood on one side of the burrow opening. The exact purpose of these structures is unknown, but in part it seems to be used as a beacon to allow themselves to find their burrow more quickly if they’ve wandered away from it.

Photo provided by Pat Backwell.


The Slender-legged Fiddler Crab, Uca tenuipedis (Fiddler Crab of the Week)

The Slender-legged Fiddler Crab (Uca tenuipedis), is a very small species from the eastern Pacific Ocean, ranging from about El Salvador to northern Peru. It is similar in size to some of its sympatric associates, such as Uca batuenta, Uca intermedia, and Uca saltitanta, but is readily distinguishable from the first of these by the somewhat triangular shape of the pollex and manus, and the latter two by its color: a fairly cryptic-colored brown and gray body, with a white pollex and pinkish-salmon dactyl and top part of the major claw.

Photos by M. Rosenberg, Panama, 1997.

The waving display of this species involves bringing both the large and small claws straight out to the side, pausing for a moment, then bringing them up and forward in a circle back to the starting open-wide position. The whole body rocks backwards slightly with this motion and sometimes the first few legs may come off the ground as well.

Unlike some of the other local species, this one seems to stay closer to the shoreline, found among the muddy stream banks or the fringes of mangroves rather than out on the open mudflat.

Introducing the Fiddler Crab Paper of the Month

This endeavor will be similar to my Fiddler Crab of the Week series, except less often and without the random component. The goal will be to try to highlight one fiddler crab research study every month. Around the start of each month I will look at all of the papers about fiddlers published in the previous month (more or less…I’ll also include older papers I happened to only discover in the previous month) and choose one to discuss. The basic rules about choosing a paper will be:

  1. One or more fiddler crab species have to play a prominent role in the paper, preferably as the focus, but optionally as a major component of the study.
  2. Any sort of publication is eligible: journal articles, books, book chapters, dissertations, theses, etc.
  3. I need to be able to get a hold of a copy of the publication to discuss it.
  4. My own publications are ineligible (since I’ll likely discuss and/or highlight them on the blog anyway).

If nothing meets the criteria from those published and/or discovered in the previous month, I may just choose an older publication that I find interesting. I will also tentatively try to avoid repeating papers by the same author(s) if they happen to be particularly productive (over a reasonable time span), and will also try to choose papers on a wide variety of topics rather than sticking to one particular subarea of research.

Nothing precludes me from highlighting multiple papers in a single month if the mood (and time) strikes me, but the goal will be to get to at least one. The precise publication schedule is not fixed, but my aim will be to post within the first week of the month. Keep an eye out for the first of these in the next week or so.

The Pygmy Fiddler Crab, Uca pygmaea (Fiddler Crab of the Week)

The Pygmy Fiddler Crab (Uca pygmaea) is an obscure, very small fiddler found on the Pacific coast of the Americas, from southern Costa Rica through northwestern Colombia. It’s name refers to it’s tiny size. Almost nothing is known about this species; there appear to be no observational studies of it in nature beyond its original collection along the muddy bank of a stream in Costa Rica.

The large claw of this species is interesting in that the hand is very thick and the fingers are relatively short and stubby. Many species have juveniles with claws that are thick and stubby; as they get older the proportions shift into those that we tend to associate with most fiddler crab claws today. This change in shape with size is known as allometry. It has been proposed that the Pygmy fiddlers’ claws stop developing at a more “juvenile” shape, a pattern known by the technical term paedomorphosis. It is certainly not a requirement that a species this size have a claw of this shape; while thicker, stubbier claws are not uncommon among some of the other very small species (e.g., U. saltitanta and U. inaequalis), one of the very smallest, Uca batuenta, has a perfectly “normally” proportioned claw.

The Styled Fiddler Crab, Uca stylifera (Fiddler Crab of the Week)

This week we move to the Americas for the first time and to one of my favorite species, the Styled Fiddler Crab, Uca stylifera. The Styled Fiddler is arguably the most striking species found in the western hemisphere and one of the easiest to identify. It is a medium (trending toward large) species where males have a white body (sometimes more dull yellow if inactive); white and purple legs; a robust large claw which is reddish-purple at the base, with an orange pollex (the immovable finger) and white dactyl (the movable finger); and yellow eyestalks. A single long style (as long or longer than the eyestalk) projects from the top of the eye found on the same size as the large claw.

Photo provided by Pat Backwell.

If it looks familiar, that might be because it is the species featured in the logo of this site.

Because they tend to be found on open, dark sandy mud flats, males of this species are among the most conspicuous fiddlers you can find. In contrast, except for the yellow eyestalks, females are a more-or-less solid muddy brown which allows them to readily blend into the background.

Photo by M. Rosenberg, Panama, 1997. Note the brown female to the left and behind the male.

The Styled Fiddler is found on the Pacific coast of Central America and northern South America, from El Salvador to northern Peru. It’s found on open mudflats (rather than in mangroves) in what might be considered the mid-intertidal zone. It seems to prefer a muddy substrate which is a bit firmer, with somewhat higher sand content than many other species; it’s not found on sandy beaches or pure sand bars, but neither is it found in the thicker, stickier, softer mud. More than a dozen other fiddler crab species can be found at the same locations as this species, but since they tend to stick to different parts of the intertidal region, only a few are actually likely to directly intermix with Uca stylifera, with Uca beebei and Uca heteropleura being fairly common.

The waving display consists primarily of the male holding his claw out to the side and then making moderately slow, fairly tight back-and-forth motions with it while simultaneously taking a “stride” (if that’s what you call the combination of all eight legs taking one step) to one side or the other. The small claw is often also held up in the air during the wave as well. The video below is old and low quality, but shows a fairly typical display. The smaller crabs seen in the background are Uca beebei.

The obvious question about this species (or at least, the one I get most often) is “What’s up with the style?” To a large extent, we really don’t know.

This is not the only species which can have a style; they are sometimes found in adults of the closely relates species Uca heteropleura, as well as in juveniles of other similar species. However, Uca stylifera is the only species in which (a) every male has a style, and (b) the style is as long as the entire eyestalk. In the other species which have them, the style tends to be very short (less than half, or even a third of the length of the stalk) and is only found in a small proportion of males. Some non-fiddler crab relatives also have styles (e.g., some species of ghost crab), so the character is not entirely unique to fiddlers.

Very little is known about the function or purpose of the style; it plays no role in vision and serves no obvious function in courtship or display. Superficially it seems like a character that could be driven by sexual selection and female choice, although there is no evidence females choose males on the basis of the style (to be fair, experiments on this are lacking). The only study that has ever looked into elongated eyes (and secondarily, the styles) in Ocypodid crabs in any serious way (von Hagen 1970) suggested styles were likely a developmental artifact and likely served no primary function. More work may be necessary if we really want to understand this odd feature.

One aspect of the style actually highlights an interesting, often missed feature of fiddler crabs. The most striking characteristic of male fiddlers is the asymmetry of the claws: this is the character best known and recognized by most people. What is underappreciated is that the asymmetry is not restricted to the claw; it just happens to be the structure in which it is most obvious. In Uca stylifera, the presence of the style is asymmetric: it is only found on one eye and always on the eye on the same side as the large claw. In fact, in most male fiddler crabs, the entire side of the body with the large claw is slightly larger than the side with the small claw. The legs tend to be slightly longer and heavier, the carapace can be a little asymmetric and heavier, the internal muscles on that side of the body tend to be larger (likely necessary to support the asymmetric weight), etc. Even the eyes are different lengths. It’s not always obvious in smaller species, but look at the photos at the top of this post: even ignoring the style, you’ll see that the eye on the side of the large claw is longer than the eye on the side of the small claw.

Whole body asymmetry is pretty much true for males of all species, it is just that beyond the claws themselves, the other asymmetries tend to be substantially more subtle and pale in comparison to the differences in claw size. But whatever the developmental mechanism is that controls the asymmetry, it applies to the whole body, not just the claw. This is more obvious in Uca stylifera that most other species because the asymmetric presence of the style draws attention to a non-claw asymmetry.

Constructing Fiddler Range Maps, part 3: A Better Way?

This is the third of four planned posts about how I construct the range maps for fiddler crabs. The first part gave the history and background of how these maps were drawn in the first place. The second part discussed where the maps become problematic when we want to use them as input data for analysis. This part will present a possible solution to the problem detailed in the second part. The fourth and final part will step back and ask if we’re actually thinking about range maps the wrong way entirely.

As highlighted in part two, even beyond general questions of their accuracy there are some potential problems with using the range maps as data, particularly if we are thinking about estimating the sizes of their ranges. Three parts of the solution are completely obvious. First, for any question involving coastline length (whether to measure available space or estimate a fiddler range), one must be very specific about the map scale and background map used to make such measures since changing these could change the results. Second, when comparing species and/or regions, one must use the same base maps (optimally) or maps constructed from identical scales (suboptimal, but tolerable if necessary) to calculated values for each species or region. Third, species ranges and coastline lengths have to be determined from the identical maps if they are to be at all compared.

This last part is where the most work suddenly looms. As detailed in the previous post, currently our species ranges are generated from one map set while our coastlines are generated from a different one. To make them match, we would likely need to recreate the range data…again…on our new coastlines. Doing so highlights the fragility of the current process…but also leads to the realization that there is likely a better way to store the base information about fiddler crab ranges.

I’ve mentioned a few times that fiddler crab ranges should likely be viewed as one-dimensional lines rather than two-dimensional areas. But we can take advantage of areas and polygons to define a fiddler crab range in an easy and flexible manner. The idea here (which one can view as theoretical since I have not implemented it yet) is that for a given species we only need to define the general boundaries of the range—define a loose polygon which includes all of the within-range coastline and none of the outside-range coastline. Whenever we need to draw the actual range or estimate a distance, we then just need an algorithm which compares that polygon to a coastline map and extracts just the coastline inside the polygon.

There are a number of clear advantages to this approach.

  1. The range data is not fixed to a specific background coastline map, allowing any coastline map to be used to generate the actual mapped or measured range. Changing maps would not require redoing the range data.
  2. Updating the range data for a species simply requires updating the enclosing polygon, likely a vaster simpler operation in most cases than the current system.
  3. The polygon that describes the range data does not require tremendous precision over most of its boundaries. A simple rectangle might be adequate for many species (some will require more complicated shapes, unfortunately).

In theory, for some species with extreme simple ranges (a single contiguous coastline without any outlying islands), one could define the entire range by just noting the end points. In reality, we’ll likely define these by a simple shape that intersects the coast at those two points.

For example, below is a range map for Uca maracoani which I used in the first post of this series, with the addition of a blue rectangle to serve as the polygon denoting its “range.”

This rectangle adequately represents the range of the species, as long as we recognize that the range is the coastline within the rectangle and not the area of the rectangle itself. We need not concern ourselves with how far into the Atlantic the rectangle extends (as long as it isn’t so wide as to clip Africa), nor that it includes two landlocked countries without any shoreline. This rectangle would serve as the masking template for the species, to be applied to any coastline map. An algorithm would simply need to extract the coastline in the rectangle (marked in red) as needed for display or analytical purposes. If we need to change the range of the species we make the rectangle bigger or smaller or use a more complicated polygon as necessary (for example, we could not extend the rectangle west to encompass the Atlantic coast of Colombia and Panama without it intersecting the Pacific coast of Peru…in that case we’d have to use a slightly more complicated polygon that avoided intersecting the Pacific coast).

The biggest question mark about this approach is how complicated the computation will need to be to extract the correct coastline from a complex polygon of an arbitrary shape (simple polygons would be pretty easy), but my presumption is not too complicated. If nothing else, this problem is not unique and  has been solved in many other applications (e.g., masking or clipping figures using complex shapes in vector drawing programs such as Illustrator or Inkscape) so likely a workable solution already exists.

While not solving every problem, using this simpler bounding concept with algorithmic coastline extraction seems like a much more flexible manner of storing the range data. Of course, maybe the way we are thinking about range maps is completely wrong to begin with. Stay tuned for final thoughts…

The Flame-backed Fiddler Crab, Uca flammula (Fiddler Crab of the Week)

The Flame-backed Fiddler Crab, Uca flammula, is a particularly striking species whose name derives from its color. In adults, the carapace is usually more-or-less solid black, except for a pair of whitish-red parallel back-to-front markings toward the center (most fiddler crabs have what appear to be creases in the carapace that roughly form the letter H…it is the vertical arms of the H that are red in this species) and a solid red band at the front of the carapace. Most of the rest of the crab is usually a bold and bright scarlet-orange, with the tips of the large claw (particularly on the movable finger) trending toward white. Somewhat unusually, females are colored more-or-less identically to males (in many species where the males have bold and bright colors, the females are more dull and cryptic), although sometimes with the red extending even further onto the carapace.

Photo provided by Pat Backwell.

A slightly unusual aspect of this species is that the juveniles are a very different color, usually almost a uniform gray-blue with darker-blue eyestalks and a pale yellow large claw in males. The complete lack of red and the fact that young males will sometimes wave could mistakenly lead one to think they might be a separate species (von Hagen and Jones, 1989).

The Flame-backed fiddler is found in northern and northwestern Australia, as well as on the western half of New Guinea. It is a large species, with a narrow front (eyes close together), and a robust looking major claw, usually with very obvious bumps (tubercles) and grooves when examined closely.

Photo provided by Pat Backwell.

It’s waving display is fairly vertical (mostly up and down without much movement of the large claw out to the side), usually starting with an initial strong wave, followed by a series of diminishing smaller ones (Crane 1975). In what I am now realizing is going to be a very common statement, the biology of Uca flammula is relatively unstudied, although some recent papers by Madeleine Nobbs has examined how its distribution on shorelines is related to vegetation patterns, so perhaps more information about this species is on the near horizon.