SYSTEMATICS OF SEAHORSES

By:Christian Jay Rayon Nob

BS-Marine BiologyMindanao Sate University-Naawan Campus

1. HISTORY

• Seahorses belong to the Syngnathidae, a teleost family whose oldest fossils date back to the Eocene. The family also includes the pygmy pipehorses (grouped with seahorses in the subfamily Hippocampinae), pipehorses and seadragons (Solegnathinae), flag-tail pipefishes (Doryrhamphinae), and pipefishes (Syngnathinae)

• The monophyly of seahorses is supported by a number of synapomorphic morphological characters distinguishing them from most other Syngnathids

• Seahorses (genus Hippocampus) and possibly also pygmy pipehorses (genera Amphelikturus, Acentronura, and Idiotropiscis), are phylogenetically most closely associated with pipefishes of the genus Syngnathus. The worlds tropical marine faunas can be divided into those associated with an Atlantic Ocean biome (including the Caribbean and Mediterranean), and those associated with an Indo-Pacific biome. It has been suggested that this pattern arose after the closure of the Tethyan seaway, a tectonic event that resulted from the convergence of the African and Eurasian plates during the late Oligocene and Miocene

• Formal seahorse taxonomy began with an entry in Linnaeus “ SystemaNaturae” (1758), a catalogue of the natural world as it was known then. Two seahorses from his private collection are still in existence, now kept at the Linnaean Society in London, England. He recognized only a single species, and named it Sygnathus hippocampus; Sygnathusis now a pipefish genus.

Figure1. Oldest Fossil SeahorseHippocampus slovenicus• The fossils include juveniles and adults of several species, and are dated at 13 million years old, making them the oldest seahorse fossils found so far

1.1 BIODIVERSITY

Distribution

Seahorses are found world-wide, usually in shallow, coastal tropical and temperate waters. The greatest number of seahorse species is found in the IndoPacific: Australia has at least ten species around its coast, many Southeast Asian nations find at least seven species in their waters and Japan also has at least seven species. In contrast, just one species- albeit a very large one- is found off the west coast of the Americas (east Pacific) and only three species live off the east coast of the Americas (in the Western Atlantic and Caribbean). The eastern Atlantic also has few species, with only three found off Europe and Western Africa.

Most seahorses’ species are fully marine although some, such as H. capensis (the Knysna seahorse), live in estuaries where they experience fluctuating salinity and suffer mortality during freshwater flooding. Roule (1916) described seahorses from the Mekong River, 300km upstream of some waterfalls, but his account is third-hand and highly unlikely to be correct, especially given the other inaccuracies in the paper; we have found no reliable evidence of freshwater seahorses.

According to Lourie et al. (2004), there are at least 33 identified species (with H. colemani subsequently accepted as a valid species) but Kuiter (2000) argues that there may be more than 50 seahorse species. Taxonomic knowledge within the genus Hippocampus is considered incomplete and revisions are on-going.In the Philippines, scientists have found at least nine species of seahorses. These species are the following: Hippocampus barbouri, Hippocampus bargibanti, Hippocampus comes, Hippocampus denise, Hippocampus histrix, Hippocampus histrix, Hippocampus kelloggi, Hippocampus kuda, Hippocampus spinosissimus, and Hippocampus trimaculatus

Habitat

Seagrass • seagrass meadows fringe sandy and muddy tropical and temperate coasts. They form the basis of extremely productive ecosystems and serve as vital nursery grounds for many animals. Seahores species known to inhabit seagrass beds include H. borboniensis, H. erectus, H. guttulatus, H. whitie, and H. zosterae.Mangrove forests • mangrove forest fill the gap between tropical land and sea, occupying much the same, very productive, zone that salt marshes do in temperate regions. They are also important nursery grounds for many fish species. H. kuda often live in mangroves.

Coral reefs • Coral reefs are more taxonomically diverse than tropical rain forests, providing food and habitats for a wide range of organisms. Reefs perform a very important protective function, acting as break-waters to prevent the erosion of coastlines. H. comes and H. zebra are among the seahores species that live on corals reefs.Estuaries • estuaries are tidal, semi-enclosed bodies of water, open to the sea, and into which rivers run.. Estuaries are among the most biologically rich habitats in the world, supporting numerous species of invertebrates, fishes, birds, and plants. They serve as important nursery grounds where larvae and juveniles of marine fishes live and feed. A seahorse known to inhabit estuaries is H. capensis.

Taxonomy

The actual number of seahorse species is not clear, and there’s disagreement. More than 120 species names have been proposed for seahorses over the past 200 years, but many have turned out to be synonyms for the same species (list of synonyms). That’s partly because seahorses can change colour and grow skin filaments to blend in with their surroundings.Previous attempts to revise the seahorse genus sometimes added to the confusion because they were limited in scope or did not examine the specimens on which the original species description was based. Project Seahorse currently recognizes 38 species, although that number is likely to increase with further research.

Survival

Natural lifespans for seahorses are virtually unknown. Most estimates come from laboratory or aquarium observations. Known lifespans for seahorse species range from about one year in the smaller species to an average of three to five years for the larger species.Adult seahorses have few predators because of their excellent camouflage, a sedentary life style, and unappetizing bony plates and spines. They have been found in the stomachs of large pelagic fishes such as tuna and dorado. They are also eaten by skates and rays, penguins, and other water birds. A seahorse has even appeared in the stomach of a loggerhead sea turtle. Crabs may be among the most threatening predators, with damaged tails indicating a narrow escape. Young seahorses are the most vulnerable to being eaten by other fish.

Growth

• Seahorses have heads at right angles to the body and prehensile tails which wrap around seagrass stems, corals, sticks, or any other suitable natural or artificial object. These traits, along with a pouch for the young and eyes that swivel independently of each other, lend to the unique nature of these fish

• Seahorses have no stomach or teeth. They suck in prey through a tubular snout and pass it through an inefficient digestive system. Like other fish, they breathe through gills, extracting oxygen from the water.

1.2 WORKERS ON THE SYSTEMATICS

Pieter Bleeker, a Dutch medical officer stationed at various times in what was then the Dutch East Indies. Bleeker wrote about 520 ichtyological papers and described over 1100 new fish species, including eight seahorse species.

John Jacob Kaup (1856), Albert Gunther (1870) and AugusteDumeril (1870) attempted rationalise seahorse taxonomy while preparing catalogues for the European museums.

Isaac Ginsburg (1937) undertook a revision of the seahorses of the Atlantic. He created many new species and subspecies from the relatively small number of specimens at his disposal, often with very little evidence.

Ronald Fritzche (1980) published a revision of the sygnathids of the Eastern Pacific including fossils as well as recent species.

Richard Vari (1982) revised the Western Atlantic seahorses, and reduced the plethora of names. Charles Dawson (1985) published a comprehensive book on the IndoPacific pipefishes, but unfortunately did not deal with seahorse taxonomy.

Stephen Casey at the Zoological Society of London, UK and is ongoing. His preliminary results reveal broad groups of related species, including:

1. H. barbouri, H. histrix, H. subelongatus, H. whitei(all IndoPacific and Australian)2. H. erectus, H. hippocampus, and possibly H. zosterae(Western and Eastern Atlantic);3. H. ingens, H. reidi, H. algiricus, H. capensis, H.kuda(both sides of the Isthmus of Panama, Western/Southern Africa, and the IndoPacific)

His fourth group is large and still unresolved but it joins pairs of species including H. abdominaliswithH. brevicepsandH. coronatuswithH. mohnikei. Genetic data have not yet obtained for all species.

1.3 TERM IN THE SYSTEMATIC Cheek spines (CS) Spines at the bottom of the operculum on each side of theanimal’s head Cleithral ring Bony ring immediately behind the operculum Coronet Enlarged structure found on the top of the head of somespecies Dorsal fin rays Bones that support the dorsal fin Eye spines (ES) Spines directly above the eye Head length (HL) Distance from the mid-point of the cleithral ring to the tip ofthe snout. The mid-point of the cleithral ring is visible as thepoint where the ring intersects with a ridge running from thedorsal spine on the first trunk ring

Height (Ht) Distance between the tips of the coronet to the tip of theuncurled tail Keel Sharp median ridge running down the ventral side of the trunkin some species Nose spine Single spine located in front of the eyes on the upper side ofthe snout in some species Operculum Bony flap that covers the gill slits Pectoral fin rays Bones that support the pectoral fin Snout length (SnL) Distance between the bump immediately in front of the eye(not the nose spine) to the tip of the snout Tail length Distance between the lateral mid-points of the last trunk ring tothe tip of the uncurled tail

Tail rings (TaR) Raised bony ridges that encircle the tail of the seahorse Trunk length Distance from the mid-point of the cleithral ring to the lateralmid-point of the last trunk ring Trunk rings (TrR) Raised bony ridges that encircle the body of the seahorse Tubercles Raised rounded nodules located at the intersections of ringsand ridges (some species only)

1.4 TEN SPECIES

Hippocampus abdominalisBig-belly seahorse Hippocampus algiricus

West African seahorse

Hippocampus bargibantiPygmy seahorse

Hippocampus borboniensisReunion seahorse

Hippocampus camelopardalisGiraffe seahorse

Hippocampus brevicepsKnobby seahorse

Hippocampus comesTiger tail seahorse

Hippocampus fuscusSea pony

Hippocampus kudaYellow seahorse

Hippocampus zebraZebra seahorse

2. EVOLUTIONARY TREES AND ROOTS

2.1 PHYLOGENTIC TREE

Phylogeny of the circumglobal seahorse lineage.

The phylogenetic tree with the highest likelihood score reconstructed by means of likelihood ratcheting. The data matrix comprised five partitions: mitochondrial control region, cytochrome b and 16S rRNA, and nuclear S7 intron and Aldolase. Associations of lineages with biogeographic regions are indicated. Nodal support is indicated by three numbers; these represent bootstrap values from maximum likelihood searches, jackknife support from parsimony searches, and posterior probabilities from Bayesian Inference. Hyphens indicate clades that were not recovered using parsimony. White circles indicate divergence events that may have resulted from vicariance events

3.2 CHARACTERSSeahorses have a horse-like head, monkey-like tail, and kangaroo-like pouch. Their eyes are like a chameleon’s. They move independently of each other and in all directions. Instead of scales, seahorses have thin skin stretched over a series of bony plates that are visible as rings around the trunk. Some species also have spines, bony bumps, or skin filaments protruding from these bony rings. A group of spines on the top of the head is called the coronet because it looks like a crown.While seahorses appear to be very different from other fishes in the sea, they belong to the same class as all other bony fish (Actinopterygii), such as salmon or tuna.

BEHAVIOUR AND ECOLOGY

Seahorse species, while differing in some aspects of their behaviour and ecology, share many features and characteristics.

Camouflage

These squirky fishes are master of camouflage, and thus commonly very difficult to spot in the wild. Many species have blotchy skin patterns which help obscure their outline. They can change color in a matter of minutes to match their sorroundings

Mobility

Seahorses are better suited to manoeuvrability than speed. Only the dorsal fin, on their back, provides propulsion, while the “ear-like” pectoral fins, below the gill opening, are used for stability and steering; the function of the little anal fin is unknown. They lack a caudal or tail fin, which is the main power source for most fish and their bony armour makes it difficult to flex the body. Activity

Seahorses are generally more active during daylight hours or they are diurnal than at night.

Feeding

Camouflage helps seahorses in their role as ambush predators. A seahorse will remain motionless until a small animal such as mysid shrimp, passes within reach. Suddenly the seahorse will flick up its head, and suck the prey out of the water column through its long tubular snout. The entire motion occurs in a split second and is barely perceptible to the human eye. Reproduction

The male seahorse, rather than the female, becomes pregnant. This unusual mode of reproduction is the most extreme form of male parental care yet discovered. Sexual maturity in males is usually determined by the presence of a brood pouch. Male seahorses are able to become pregnant any time during the breeding season, which varies with species, and most likely depends on water temperature. Lunar and monsoon patterns may affect the timing of the breeding season.

2.3 PARTS OF SEAHORSE

3. MOLECULAR SYSTEMATICS3.1 HISTORICAL CONTEXT

• Seahorses (Hippocampus sp.) are among the many genera whose life histories might render them vulnerable to overfishing or other disruptions such as habitat damage. They are generally characterized by a sparse distribution, low mobility,small home ranges, low fecundity, lengthy parental care and mate fidelity. In addition, the male seahorse, rather than the female, becomes pregnant. Indeed,curiosity about this phenomenon explains why currently more is known about reproduction than about other life-history parameters

• Such life-history characteristics (Notwithstanding exceptions to these generalities) may help explain why 10 seahorse species are listed as ‘Vulnerable’ or ‘Endangered’ on the 2003IUCN Red List of Threatened Species (IUCN, 2003). The other 23 species are listed as ‘Data Deficient’, which reflects substantial gaps in knowledge even for heavily exploited seahorses. • Seahorses comprise one genus (Hippocampus) of the family Syngnathidae, which otherwise consists of about 55 genera of pipefishes, pipehorses and seadragons. The entire family Syngnathidae falls within the order. Seahorse species are distributed circumglobally, leading to the suggestion that the genus is pre-Tethyan in origin, and at least 20 million years old. Such ageing is supported by genetic evidence, although the origin of many species is believed to be much more recent

3.2 BASIC TECHNIQUESSample acquisition

Twenty-two of the 32 species of seahorse recognized by Lourie et al. (1999) were included in this study.Specimens were acquired from throughout the range of the genus, except for the central Pacific region, and each could be identified as being from a specific locality. The sample set comprised 93 specimens; intraspecific variation was assessed by obtaining 2–17 specimens per species from different locations in the geographic range

DNA extraction, amplification, and sequencing

Most specimens were received air-dried and the remainder were alcohol-preserved. The length of time that each specimen had been preserved varied from less than one week to several years; most had been preserved for 3–6 months. DNA extraction from alcohol-preserved specimens proved to be more successful if the tissue had been dried first. Approximately 50 mg of seahorse tail muscle tissue was macerated finely. SoftwareIndividual sequences were aligned and edited using Sequencher V.3.0 (Gene Codes Corporation). MacClade V.3.0.4 (Maddison and Maddison, 1991) was used to assign codon positions and to determine the number of haplotypes. Phylogenetic analysis was carried out using maximum parsimony (MP), maximum likelihood (ML), and the distance-based neighbour-joining methods .

Mitochondrial DNA (mtDNA) has been used extensively in animals for phylogenetic and population studies but it has been applied only occasionally to mating systems analysis, where nuclear markers are usually preferred. We used denaturing-high performance liquid chromatography (D-HPLC) to detect mitochondrial DNA polymorphisms to assess the genetic mating system in Syngnathus abaster. Our study of ten pregnant males, revealed polygyny in 30% of the males, who carried embryos originating from multiple females. In addition, 30% of the pregnant males carried embryos with the same mitochondrial haplotype. This is not sufficient to demonstrate polyandry but allows a rapid selection and a reduced sample size for further studies. In conclusion, the proposed technique is time- and cost-effective, allows the certain identification of polygyny and provides useful information to study polyandry.

Cytochrome bSpecies identification was carried out by nucleotide sequence analysis of the cytochrome b (cytb) gene. The aim of the study was to identify biological specimens from diverse vertebrate animals by extracting and amplifying DNA from 44 different animal species covering the 5 major vertebrate groups (i.e. mammals, birds, reptiles, amphibians and fishes). The sequences derived were used to identify the biological origin of the samples by aligning to cytb gene sequence entries in nucleotide databases using the program BLAST. All sequences were submitted to the GenBank including new species which were not observed in the databases. The applicability of this method to the forensic field is demonstrated by simulated casework conditions where different types of samples including problematic specimens such as hair, bone samples, bristles and feathers were investigated to identify the species.

3.3 LIMITATION ON PHYLOGENETICSMolecular systematics is an essentially cladistic approach: it assumes that classification must correspond to phylogenetic descent, and that all valid taxa must be monophyletic. The recent discovery of extensive horizontal gene transfer among organisms provides a significant complication to molecular systematics, indicating that different genes within the same organism can have different phylogenies In addition; molecular phylogenies are sensitive to the assumptions and models that go into making them. They face problems like long-branch attraction, saturation and taxon sampling problems: This means that strikingly different results can be obtained by applying different models to the same dataset

3.4 IMPACT ON PHYLOGENETICSApart from the uncertain evolutionary history, the exact species boundaries of many seahorses are obscure. Morphology-based taxonomic methods have shown to be problematic. More than 100 species of seahorses have been described (Eschmeyer, 1998), but a recent attempt by Lourie et al. (1999) at revising the genus accepts only about 32 valid species names. These controversies seem to be mainly due to convergence of morphological characteristics: since seahorses avoid predators by means of camouflage, it seems reasonable to assume that many morphological characters are under strong selection pressure. Genetic methods have great potential to both resolve disputed taxonomic issues and to infer phylogenetic relationships among different species.

Morphological Variation in the Seahorse Vertebral System

Variaciones Morfológicas en el Sistema Vertebral del Caballo de

Mar

*Emilano Bruner & **Valerio Bartolino

MORPHOLOGICAL CASE STUDY

SUMMARY: The vertebral system in Hippocampus hippocampus is highly specialized because of the vertical locomotion and tail prehensility. The vertebral elements represent a special case of morphological changes, being the metameric structures organised along a natural functional series. We investigated the shape changes along the vertebral spine in H. hippocampus through geometric morphometrics, in order to describe functional and structural patterns. Actually, the dorso-ventral tail bending ability in the genusHippocampus is one of the most impressive morphological modifications in the evolutionary history of fishes. Vertebrae were analysed using a 2D configuration from the left lateral view. The variation along the vertebral series suggests the identification of cervical, abdominal, dorsal, and caudal groups.

The first three (cervical) elements and the 10th (supra-dorsal) structure show peculiar morphologiesand local adaptations, associated with neck angulation and fin muscles, respectively. The vertebral size decreases from the anteriormost element backward, with some local variation at the dorsal area. Major changes are related to allometric variation at the neural region. The caudal elements are characterised by a marked size decrease, with consequent allometric shape changes involving the rotation of the posterior vertebral opening. This allometric trajectory leads to a natural ventral bending of the tail, promoting its prehensile function. This main functional changes in the Hippocampus biomechanics. Geometric morphometrics is rather suitable to approach metameric studiesin terms of serial variation and functional adaptations.

The origin and evolution of seahorses (genus

Hippocampus): a phylogenetic study using the cytochrome b

gene ofmitochondrial DNA

Stephen P. Casey,a,* Heather J. Hall,b Helen F. Stanley,a and Amanda C. J. Vincentc,1

MOLECULAR CASE STUDY

AbstractPhylogenetic relationships among 93 specimens of 22 species of seahorses (genus Hippocampus) from the Atlantic and Indo- Pacific Oceans were analysed using cytochrome b gene sequence data. A maximum sequence divergence of 23.2% (Kimura 2-parameter) suggests a pre-Tethyan origin for the genus. Despite a greater number of seahorse species in the Indo-Pacific than in the Atlantic Ocean, there was no compelling genetic evidence to support an Indo-Pacific origin for the genus Hippocampus. The phylogenetic data suggest that high diversity in the Indo-Pacific results from speciation events dating from the Pleistocene to the Miocene, or earlier. Both vicariance and dispersal events in structuring the current global distribution of seahorses. The results suggested that several species designations need re-evaluating, and further phylogeographic studies are required to determine patterns and processes of seahorse dispersal.

THANK YOU AND

GOD BLESS US ALL !!

PREPARED BY

MR. CHRISTIAN CASURA CAÑABS MARINE BIOLOGY II