Gulf Pipefish ( Syngnathus scovelli )
Justin Krol
Abstract
The Gulf Pipefish, Syngnathus scovelli, is a long, slender, bony fish that lives mainly in
the Gulf of Mexico and parts of South America. It is often studied for its male pregnancy
adaptions and mating systems. It displays sexual dimorphism and sex reversal with the females
being larger and showing more secondary sex characteristics. Syngnathus scovelli also employs
unique feeding tactics which will be discussed later on in the report.
Classification
The Gulf Pipefish is a bony fish in the class Actinopterygii. It is placed in the order
Gasterosteiformes, meaning bone belly. Gasterosteiformes are characterized by pelvic bones without anterior processes, the absence of the Bandelot’s ligament (a ligament that attaches the shoulder girdle to the cranial base or anterior vertebrae), and the configuration of scales that are more of a scute or plate (Grzimek's 2004). The Gulf Pipefish is then placed in the family
Syngnathidae (seahorses and pipefish). Syngnathids are characterized by male pregnancy, bony rings surrounding the body, and a fused tubular mouth.
General Characteristics
The Gulf Pipefish is a slender, tubular fish that grows to six inches in length. Its head is not at an angle to the body; it lacks pelvic or anal fins, and has a straight tail. The Gulf Pipefish exhibits sexual dimorphism with females being deeper bodied and darker in color. Females are dark olive green or brown with silvery vertical stripes, and males are lighter colored and smaller.
The male also exhibits a brood pouch on the base of the tail. Both sexes lack pelvic fins but have an elongate dorsal fin that crosses three rings of dermal armor on the body and five on the tail
(Smithsonian 2001).
(Figure. 1 A comparison of the male Gulf Pipefish on the right and the female Gulf Pipefish on the left (TPWD 2012))
One of the major morphological features of this species, as well as other syngnathids, is the elongation of the suspensorium and neurocranium that support a small mouth at the end
(Bergert 2013). This is the feature that gives them the classification Syngnathid, meaning jaw together. Two similar species are the Dusky Pipefish ( Syngnathus floridae ) and the Chain
Pipefish ( Syngnathus louisiana ). The Gulf Pipefish is distinguishable from these two species by its snout length. The Gulf Pipefish has a snout that is less than fifty percent of the head length while both the Dusky Pipefish and the Chain Pipefish have longer snouts in comparison (Figure
2) (TPWD 2013).
(Figure. 2 A comparison of the Gulf Pipefish (left) and a similar species (right) (TPWD 2013))
Habitat and Distribution
Syngnathus scovelli has a range from Brazil north to the U.S. Gulf of Mexico coastal
states. There is also a small breeding population on the northern Georgia coast line (Figure 3)
(Smithsonian 2001).
(Fig. 3 native range map of the Gulf Pipefish (Aquamaps 2010))
The Gulf Pipefish lives among sea grass beds and drift algae with the exception of the Georgia population that utilizes soft sediment bottoms instead of vegetation. It can tolerate a range of temperatures from 5-30 0 Celsius. Syngnathus scovelli is also the only species of pipefish to utilize fresh water. It is able to survive in salinity from 0-35 ppt, and has been shown to breed in freshwater as well (Smithsonian 2001).
Reproduction and Sexual Selection
Syngnathus scovelli has a polyandrous breeding structure. The potential reproductive rate
(PRR) is much higher for females since they are available to mate more often where the males are unavailable for two weeks while carrying its brood. Since the Gulf Pipefish is not monogamous the courtship is not as long as some related monogamous species. The interval of time between meeting and mating has been documented to be less than one minute under laboratory settings (Fudickar 2009). The Gulf Pipefish mate year round with males choosing their mates while females compete for selection. Both genders show a pattern of boom and bust, high reproductive abilities followed by a less successful mating and so on. The PRR is generally higher for the first breeding then declines for the second and spikes again for the third breeding.
This coincides with predicted life history strategies of how the Gulf Pipefish makes decisions of current and future investments with a limited energy supply in mate selection (Fudickar 2009).
Males will select for a larger female during the “boom” breedings. It is speculated that this is because a larger female can carry more eggs and thus increase her fitness, and since a male will breed with one female at a time usually it is better to breed with a female that can deposit more eggs. On the other hand males with bigger testes does not really increase fitness because it is thought that the Gulf Pipefish internally fertilizes the eggs once they are placed in the brood pouch and therefore does not lead to male-male competition (Fudickar 2009). Because of the lack of male-male competition male size does not have much effect and mate selection is based mainly on males choosing females. After a “boom” breeding, the male is depleted of nutrients and will usually select for a smaller and therefore unattractive female to breed with. The male will reluctantly breed with a smaller female if there is a lack of larger females. The male is also able to control how much nutrients and care goes to the developing young, even going so far as infanticide and cannibalism, if a better mate comes along. Since females are freed from the nutrient depleting role of pregnancy, they are able to produce eggs in a much quicker fashion.
There is the boom and bust cycle of the PRR in females though it is not as drastic as is it is in males. The Gulf Pipefish ovary is unique in that as one batch of eggs is moved into the lumen for reproduction the next batch can move into place and complete maturation. This would suggest a much shorter period between availability for breeding but no formal studies have been published
(Fudickar 2009). Another change due to the sex role reversal is that males, not females, employ their senses to obtain information about potential mates. The males will respond to chemical cues from the females to trace them, in the usually cluttered waters, where they reside to mate. While females do not respond to any chemical cues. However, they are not able to distinguish the size of the female from the chemical (Jones 2009).
Embryology
S. scovelli is ovoviviparous with the male carrying the large telolecithal eggs.
Telolechithal eggs are defined by those that have a large quantity of egg yolk that is unevenly distributed in the cytoplasm. The embryos are 5-10mm in length depending on maturation time and are arranged in parallel rows in the male’s brood pouch located on the tail. The embryos are bathed in an isosmotic fluid for 12-21 days before being born. The fry are able to swim, eat, and are capable of osmoregulation at birth (Smithsonian 2001).
Form and Function
One of the more important and noticeable features of the Gulf Pipefish is the brood pouch
on the males. The brood pouch has been shown to have great importance in osmoregulation for the young. Before the snout is formed on young pipefish they are unable to osmoregulate for themselves. The male Gulf Pipefish is able to regulate his brood pouch by the presence of mitochondria rich cells located on the inner surface and overlying flap of the pouch. The mitochondria provide energy for ion regulation in the relatively closed off area of the pouch. S.
scovellis pouch shows the same principles as gills in freshwater and saltwater teleost. In
freshwater, the cells of the pouch close in tightly on each other to prevent loss of ions. In
saltwater the cells are loose for Na + to be transported out. During early development, the
isosmotic fluid of the pouch is kept close to the male’s plasma ion levels. In the later stages of
development, the pouch fluid starts to line up more with environmental ion levels. This may
allow for a smooth transition of young at birth and prevent shock (Boettcher 2005).
Another important feature of the Gulf Pipefish is its head. The mouths of pipefish and
seahorses are alike and are characterized as a tiny mouth, mounted on a slender snout, followed
by a larger buccal cavity. Another structure of the head is the hyoid apparatus, which is integral
to the four bar model proposed for feeding. The four bar model tries to explain the relationship
between head movement and suction feeding exhibited by the Gulf pipefish and the other
pipefishes and seahorses. It explains that if four “bars” are linked together by common joints and
if one moves then the other bars must compensate by chain reaction and result in the passive
movement of the fourth bar. The theory tries to correlate muscle movement with the force and
velocity seen by pipefish feeding (Bergert 2013).
The way the pipefish feeds gives a clue to the curious adaption of the hyoid apparatus.
The pipefish lines up with its prey and instead of swimming at it or protruding its jaws as most teleost do it pivots its head towards its prey very quickly. The rapid head movement, low drag of the small, round mouth and expansion of the buccal cavity create a suction to ingest the prey. Pipefish have one of the fastest capture times (4-6 ms for some species) of all vertebrates because of this adaptation. Even though the Gulf Pipefish lack teeth, it is able to ingest prey larger than its mouth. Through the sucking action it is able to produce enough force to rip flesh from its victim. Snout length also plays a vital role into this pivot feeding method. A longer thinner snout is ideal for reaching prey quickly, but a shorter snout is better for larger prey (De
Lussanet 2007).
Genetics and Evolution
Due to the Gulf Pipefishes mating system, males will only have one successful mate
during a pregnancy, while females will commonly distribute their eggs to multiple males from a
single batch. This leads to the population being genetically polyandrous (Avise 1997). The
development of male pregnancy may have had other effects than just the development of the
brood pouch. In the evolution of the brood pouch two lineages came about. There are those that
brood the eggs on the tail portion of the body and those that brood the eggs on the trunk of the
body. Due to these differences different body traits are found in each type of brooder. Tail
brooders, for example, have a longer tail for a given trunk size than trunk brooders. Not only do
they have longer tails but they also have more vertebrae suggesting that vertebrae counts are a
heritable trait, capable of responding to selective pressures. In the Gulf Pipefish, there was
significant variation in trunk and tail rings to suggest heightened genetic correlation and
heritability. It was also found that there was no genetic or phenotypic correlation between trunk
and tail vertebrae counts. These findings may lead to a developmental basis for axial skeleton
evolution in vertebrates (Jones 2006).
Another adaptation in the Gulf Pipefishes evolution is the changing of a genes function in response to developing male pregnancy. Researchers at the University of Central Florida and Texas A&M have discovered that a gene used for kidney and liver function in other fish may have been conscripted for use to develop the brood pouch. Through time the gene that encodes for a protein called astacin was given the second job. Many times genes are copied and while the old gene continues with the original work, the copy will take on a new function. But this is not what happened in the Gulf Pipefish with the “patrician” gene. It is suspected that during the early days of the Gulf Pipefishe’s evolution, the patrician gene assisted with kidney and liver function solely until it was conscripted to help with the newly developed male brood pouch. Over time the gene became proficient at its second job (NSF 2006).
Status and Conservation
The Gulf Pipefish is currently stable throughout its native range (Smithsonian 2001).
Environmental estrogen may have an impact on the species with emphasis on the non-brooding male. High levels of estrogen have been dumped into the environment from xenoestrogenic sources such as pharmaceutical effluent, pesticides, surfactants, and dispersants. The effects of environmental estrogen in non-brooding males are disruption of the endocrine system, harmful to the liver, can damage the testes, and increase feminization (Boetthcher 2005).
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