Hamlets

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Spawning butter hamlets.

Anna and I arrived on the western Caribbean island of Roatan in July with hamlets on our minds. Just before the trip we read a recently published paper in the Bulletin of Marine Science entitled Speciation In The Serranid Fish Hypoplectrus. In the study, the young author marine biologist Michael L. Domeier Ph. D details research intended to resolve a long running debate among marine taxonomists concerning the species status of hamlets which make up the genus Hypoplectrus. The heart of the controversy is the essence of taxonomy -- What exactly defines a species? The intriguing dilemma centers on the hamlets' complete lack of anatomical differences and breeding tendencies. Traditionally, these distinct anatomical similarities coupled with reproductive isolation would lump all genus members together as a single species; yet, for an unexplained reason the otherwise identical fish display strikingly different color patterns. At least eleven distinct and regularly occurring color morphs have been documented. Adding even more spice to hamlet soup is the smorgasbord of hybrid color variations that occur in nature.

Even though we were interested in all facets of Domeier's ambitious project which required the difficult task of interbreeding hamlet color morphs in captivity, the author's description of what he calls "spawning bouts" immediately captured our fancy. Our first goal, while in the islands, was finding, observing, and photographing spawning hamlets in the wild.

Spawning barred hamlets.

It was apparent from our initial fish surveys that the Bay Islands are a hotbed of hamlets. Even though various color morphs of Hypoplectrus regularly inhabit the tropical waters of Florida, the Bahamas and Caribbean, we had never recorded so many color patterns, hybrids, or numbers of hamlets from a single reef system. Nearly all the solitary little hunters were sighted moving slowly about the reef's substrate in a never ending search for a quick meal of shrimp, crab or an occasional fish. We were hoping that the high number of subjects would increase our chances of observing a courting display during the narrow window of time -- beginning just before sunset and ending shortly afterwards -- when spawning was reported to occur.

Unfortunately, our first night's mooring over a shallow gorgonian plain scattered with low profile patch coral didn't bode well for finding hamlets, much less locating courting pairs. The inappropriate habitat and poor visibility, coupled with our uncertainties about what exactly to look for or even if we were diving during spawning season, didn't inspire confidence as we tumbled off the Isla Mia's platform into the darkening waters of late afternoon.

Anna and I swam a parallel course for more than ten minutes without sighting a single hamlet. Just as I was giving up the hunt a waving handlight drew my attention. When I caught up, Anna was in hot pursuit of a rapidly moving Black Hamlet. Its hell-bent swimming behavior was totally out of character for the typically sedate predator that seldom ventures far from the confines of a home range. Just as I fell into pace behind Anna and the speeding fish, I spotted two Barred Hamlets hovering head to head above an isolated patch of Lettuce Coral. By the time I put on the brakes and settled onto the sand Anna was a distant silhouette.

Shy hamlet and hybrid hamlet acting "giddy".

Since many members of the seabass family, including hamlets, are simultaneous hermaphrodites (both sexes occurring within the same individual), the fish took turns acting out sex roles during courtship; and, act out they did. One star-struck hamlet took on the female role as the aggressor. She intermittently assumed a rigid stance with snout up and fins flared while sharply snapping its head side-to-side; the acting male, whose color was distinctly blanched, nervously milled about the bottom a foot or two away. Both fish were so enthralled with one another that neither seemed disturbed by my presence. Suddenly, the female darted to within inches of the male and paused. Faster than a blink, the lovers clasped tightly together in what to the eye appeared as unbridled passion. The male's body -- head pointed directly down, mouth opened in an oval, ventral and dorsal fins spread, and ripe belly puckered -- was enveloped by the arching body of its mate. One one-thousand, two one-thousand, three one-thousand and the fish popped apart. With color renewed the male darted off to the base of a nearby coral head with its mate in chase. As darkness fell the two continued to frisk about the bottom before swimming to the top of the coral to reclasp a second, and minutes later, a third and final time. The affair ended when one of the spent partners discreetly vanished into the night.

The following evening everyone aboard attended the hamlet peep-show. This time, the Isla Mia moored over a high profile reef with a thriving hamlet population. While descending through the hundred-foot visibility, I quickly spotted three pairs cavorting below. During that single dive, the group watched six courting pairs. Throughout our two-week stay we witnessed a total of 28 spawning bouts. What we believed to be a rare occurrence delightfully turned out to be not only common, but, once you know what to look for, an easy behavior to find and observe.

As early as an hour before sunset, mature hamlets begin acting giddy. At some point they rapidly swim out of their territory in search of mates for the evening. It is speculated that because the fish are site oriented they are not only well aware of neighboring hamlets but probably spawn with the same individuals on a regular basis. During their search cruising hamlets occasionally happen upon other courting pairs. If they are the same color morph, the hamlets might try to break in but are generally rebuffed. When a solitary hamlet is found that suits their fancy a courting/feeding behavior begins, sometimes up to an hour before an actual spawn. The dramatic three-second spawning clasps generally begin ten to fifteen minutes before sunset and reoccur every few minutes until the last light fades. The number of clasps per spawning bout we observed varied from as few as three to a record ten for a robust pair of Indigos.

During our two-week stay we also surveyed the region's Hypoplectrus populations with special attention to hybrids. Of the eleven hamlet color morphs described in Reef Fish Identification, five, including the Barred, Butter, Black, Indigo, and Shy Hamlet, were sighted. What amazed and delighted us both were the many hybrids found. These hybrids, the product of crosses between color morphs, have long been used as evidence against granting separate species status to members of the genus. The argument goes that if the different color morphs are indeed individual species then there should be extremely limited spawning between color morphs. Of the 28 spawns we witnessed all but one occurred between similar hamlets. The one exception was a brownish colored hybrid (the area's most common mixed coloration) spawning with a Shy. It has been confirmed that hamlets use sight to choose a mate, and, if given a choice nearly always choose a like color pattern. During the dive, when the cross spawn was observed, I didn't see any other Shy or brown hybrids in the vicinity. Field data published in a 1980 paper by Eric A. Fisher recorded only seven of 189 pairings between unlike color morphs. Although limited, this is still a surprising amount of interbreeding between species.

In 1980 J. E. Graves and R. H. Rosenblatt performed protein gel electrophoresis on nine color morphs and discovered virtually no interspecific differences. One interesting conclusion that can be drawn from their work is that species of Hypoplectrus have differentiated recently. Domeier surmises that they may not have evolved until after the closing of the isthmus of Panama, approximately 3.8 million years ago. This date might seem ancient, but on an evolutionary time scale this makes hamlets the new kids on the block. He continues this train of thought by speculating that the different color morphs may have been later segregated into population centers by rise and fall of the sea level. Further muddling the matter is the enticing hypothesis, published in 1960 by J. E. Randall & H. A. Randall and later expanded by R. E. Thresher, that aggressive mimicry is the mechanism driving speciation in Hypoplectrus . (Morphs with color patterns resembling non-predatory reef fish have a distinct advantage procuring food [an example: the Blue Hamlets' close resemblance to the plankton-feeding Blue Chromis].)

All this pushed the hamlet question to the point where it became necessary to interbreed color morphs in captivity before re-evaluating their taxonomic status. Domeier's laboratory breeding project established that crosses between color morphs (in this case: Blue Hamlets and Butter Hamlets) produced hybrids intermediate to both parents in color and markings. He also proved that self-fertilization of a Shy Hamlet resulted in offspring that resembled the parent species. This confirmed that color pattern is genetically determinate in Hypoplectrus. These new findings, combined with field observations verifying a low frequency of hybrid hamlets in nature, have tilted the debate in the direction of granting full species rank to the regularly occurring color morphs.

Of course, everyone's opinion pivots on a preferred definition of species, and there seems to be as many as there are taxonomists. In fact, entire graduate level courses are devoted to this one perplexing question. Domeier writes, "That there is no agreement of the precise nature of the species is a reflection of the nature of the dynamic process at work and thus we should not anticipate future agreement." His thoughts share good company. After discovering astounding differences in every genus of barnacles studied, Darwin wrote, "After describing a set of forms as distinct species, tearing up my MS. and making them one species, tearing that up and making them separate, and then making them one again, I have gnashed my teeth, cursed species, and asked what sin I had committed to be so punished."

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