The Syngnathidae is a family of
fish
A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
which includes
seahorse
A seahorse (also written ''sea-horse'' and ''sea horse'') is any of 46 species of small marine Osteichthyes, bony fish in the genus ''Hippocampus''. The genus name comes from the Ancient Greek (), itself from () meaning "horse" and () meanin ...
s,
pipefishes, and seadragons (''
Phycodurus'' and ''
Phyllopteryx''). The name is derived from (), meaning "together", and (), meaning "jaw".
The fused jaw is one of the traits that the entire family have in common.
Description and biology
Syngnathids are found in temperate and tropical seas across the world. Most species inhabit shallow, coastal waters, but a few are known from the open ocean, especially in association with
sargassum
''Sargassum'' is a genus of brown macroalgae ( seaweed) in the order Fucales of the Phaeophyceae class. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and ...
mats. They are characterised by their elongated snouts, fused jaws, the absence of
pelvic fin
Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...
s, and by thick plates of bony armour covering their bodies. The armour gives them a rigid body, so they swim by rapidly fanning their fins. As a result, they are relatively slow compared with other fish but are able to control their movements with great precision, including hovering in place for extended periods.
Uniquely, after syngnathid females lay their
eggs, the male then fertilizes and
carries the eggs during incubation, using one of several methods. Male seahorses have a specialized ventral
brood pouch to carry the embryos, male sea dragons attach the eggs to their tails, and male pipefish may do either, depending on their species. The most fundamental difference between the different lineages of the family Syngnathidae is the location of male brood pouch.
The two locations are on the tail (Urophori) and on the abdomen (Gastrophori).
There is also variation in Syngnathid pouch complexity with brood pouches ranging from simple ventral gluing areas to fully enclosed pouches. In species with more developed, enclosed pouches it has been demonstrated that males directly provide their brood with not only nutrients but also immunity to pathogens.
Syngnathids with more developed brood pouches are also known to be able to partially or completely abort a brood from a female with low fitness.
A wide variety of
mate choice
Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choi ...
and mating competition has been observed in Syngnathidae.
For example,
''Hippocampus fuscus'' exhibits conventional sex roles of males competing for female access while
''Corythoichthys haematopterus'' is completely sex role reversed.
Most conventional sex role syngnathids are monogamous whereas sex role reversed species mostly exhibit polygamous behavior.
Seahorses and pipefish also have a unique feeding mechanism, known as
elastic recoil feeding. Although the mechanism is not well understood, seahorses and pipefish appear to have the ability to store energy from contraction of their
epaxial muscles (used in upward head rotation), which they then release, resulting in extremely fast head rotation to accelerate their mouths towards unsuspecting prey.
Evolution
Phylogenetic analysis implies that the most recent common ancestor of all syngnathids was likely pouchless. The family ''
Solenostomidae'' (ghost pipefish) is a family in the order Syngnathiformes. Female ghost pipefish incubate their developing embryos inside fused pelvic fins. Evolutionary transitions from female to male care are practically nonexistent in
teleosts, so brood pouches were likely not ancestral.
Genome sequencing supports this, revealing multiple different origins across and within different brood pouch types.
Oviparity was the ancestral trait, and the evolution of viviparity must have relied on the evolution and integration of multiple complex traits such as morphology, physiology, and behavior.
Syngnathidae was historically divided into two major lineages based on brood pouch location: ''Neophinae'' (located on the trunk) and ''Syngnathinae'' (located on the tail).
[ Genome sequencing shows a parallel increase in brood pouch complexity in both ''Neophinae'' and ''Syngnathinae''.][ Some species may have also independently evolved to have trunk brooding phenotypes, separate from the ''Neophinae''. One example of this convergent evolution arises in pygmy seahorses ('' Hippocampus bargibanti, Hippocampus denise, Hippocampus pontohi''). Pygmy seahorses are very small (about 1–2 cm tall) trunk brooders, phylogenetically surrounded by tail brooders. It's likely that the pygmy seahorse once had their brood pouch on their tail. The brood pouch may have moved locations when there was strong a correlated selection for a ]prehensile tail
A prehensile tail is the tail of an animal that has Adaptation (biology), adapted to grasp or hold objects. Fully Prehensility, prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and ...
and diminutive size, resulting in a very small, trunk brooding organism.[
Viviparity and male-pregnancy in Syngnathidae have a complex evolutionary history with many independent origins of similar traits. Early members of the family developed traits to limit the presence of deleterious mutations, allowing for more rapid evolution. The advantage of a more controlled and protected embryonic development seemed to be enough to enact evolutionary development throughout Syngnathidae to varying degrees.
In species with the most complex brood pouch systems, many traits (behavioral, physiological, morphological, and immunological) must have co‑evolved to allow for male pregnancy, driven by the increase of the fitness of those individuals’ offspring. The evolution of these traits resulted in a sex-role reversal in which females may exhibit competitive behavior for a mate.][ has allowed for greatly improved understanding of the evolutionary history of Syngnathidae, but there is still a need for further development in the field. Further investigations into the genetic mechanisms and selective motivation for the evolution of these traits in Syngnathidae may provide insight into the evolution of pregnancy separate from the female reproductive system.
The earliest syngnathids are known from the ]Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
of Monte Bolca, Italy.
Classification
As it is currently classified, the family Syngnathidae includes about 252 species in 62 genera.
* Family Syngnathidae
** Species † "''Syngnathus''" ''heckeli'' (fossil)
** Species † "''Syngnathus''" ''bolcensis'' (fossil)
** Genus †'' Prosolenostomus'' (fossil)
** Subfamily † Eogastrophinae (fossil)Hippocampus
The hippocampus (: hippocampi; via Latin from Ancient Greek, Greek , 'seahorse'), also hippocampus proper, is a major component of the brain of humans and many other vertebrates. In the human brain the hippocampus, the dentate gyrus, and the ...
'' (seahorses)
**Subfamily † Pshekhagnathinae (fossil)Syngnathus
''Syngnathus'' is a genus of fish in the family Syngnathidae found in marine, brackish and sometimes fresh waters of the Atlantic, Indian and Pacific Ocean. Fossils of these species are found from the Oligocene to the Pleistocene. They are kno ...
''
*** Genus '' Trachyrhamphus''
*** Genus '' Urocampus''
*** Genus '' Vanacampus''
Images
File:Hippocampus.jpg, Seahorse
A seahorse (also written ''sea-horse'' and ''sea horse'') is any of 46 species of small marine Osteichthyes, bony fish in the genus ''Hippocampus''. The genus name comes from the Ancient Greek (), itself from () meaning "horse" and () meanin ...
File:Leafydragon.jpg, Leafy seadragon
The leafy seadragon (''Phycodurus eques'') or Glauert's seadragon, is a marine fish. It is the only member of the genus ''Phycodurus'' in the family Syngnathidae, which includes seadragons, pipefish, and seahorses.
It is found along the s ...
File:Phyllopteryx taeniolatus1.jpg, Weedy seadragon
File:Ruby seadragon.jpg, Ruby seadragon
File:Alligator Pipefish 2.jpg, Pipefish
File:Banded Pipefish skeleton.jpg, Skeleton of a banded pipefish ('' Dunckerocampus dactyliophorus)'' on display at the Museum of Osteology
The Museum of Osteology, located in Oklahoma City, U.S., is a private museum devoted to the study of bones and skeletons (osteology). The museum displays over 450 skeletons of animal species from all over the world. With another 7,000 specimens a ...
.
References
External links
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{{Authority control
Marine fish families
Taxa named by Constantine Samuel Rafinesque
Extant Ypresian first appearances