Stickleback

Male Stickleback (Gasterosteus aculeatus) in breeding colors by Viridiflavus http://commons.wikimedia.org/wiki/File:PICT0246-1.JPG. GNU Free Documentation License 23/03/10
Male Stickleback (Gasterosteus aculeatus) in breeding colors - photo by Viridiflavus

Gasterosteidae is a family of fish including the sticklebacks. FishBase currently recognises sixteen species in the family, grouped in five genera. However several of the species have a number of recognised subspecies, and the taxonomy of the family is thought to be in need of revision. Although some authorities give the common name of the family as "sticklebacks and tube-snouts", the tube-snouts are currently classified in the related family Aulorhynchidae.

An unusual feature of sticklebacks is that they have no scales, although some species have bony armour plates. They are related to pipefish and seahorses.

Stickleback species are found in fresh water environments in Europe, Asia and North America. They feed on small crustaceans and fish larvae.

Sticklebacks are distinguished by the presence of strong and clearly isolated spines in the dorsal fin. All species show a similar mating behaviour, which is also unusual among fishes. The males construct a nest from vegetation held together by secretions from their kidneys. The males then attract females to the nest who lay their eggs inside where the male can fertilise them. The male then guards the eggs until they hatch.

Species

  • Genus Apeltes
    • Three-spined stickleback (Gasterosteus aculeatus)
    • Gasterosteus microcephalus
    • Blackspotted stickleback (Gasterosteus wheatlandi)
  • Genus Pungitius
    • Pungitius hellenicus
    • Pungitius kaibarae
    • Smoothtail ninespine stickleback (Pungitius laevis)
    • Southern ninespine stickleback (Pungitius platygaster)
    • Nine-spined stickleback (Pungitius pungitius)
    • Amur stickleback (Pungitius sinensis)
    • Sakhalin stickleback (Pungitius tymensis)
  • Genus Spinachia
    • Sea stickleback (Spinachia spinachia)

Three-spined stickleback (Gasterosteus aculeatus)

The three-spined stickleback, Gasterosteus aculeatus, is a fish native to much of northern Europe, northern Asia and North America. It has been introduced into parts of southern and central Europe, including Belgium, where the species was featured on a 14-franc postage stamp issued in Belgium in 1990.

Distribution and Morphological Variation

Three subspecies are currently recognised by the IUCN:

  • Gasterosteus aculeatus aculeatus is found in most of the species range, and is the subspecies most strictly termed the three-spined stickleback; its common name in England is the tiddler, although "tittlebat" is also sometimes used.
  • G. a. williamsoni, the unarmored threespine stickleback, is found only in North America; its recognised range is southern California, though there are isolated reports of it occurring in British Columbia and Mexico;
  • G. a. santaeannae, the Santa Ana stickleback, is also restricted to North America.

These subspecies actually represent three examples from the enormous range of morphological variation present within three-spined sticklebacks. These fall into two rough categories, the anadromous and the freshwater forms.


Environment Agency video showing stickleback breeding behaviours

The anadramous form spends most of its adult life eating plankton and fish in the sea, and returns to freshwater to breed. The adult fish are typically between 6 and 10 cm long, and have 30 to 40 lateral armour plates along their sides. They also have long dorsal and pelvic spines. The anadromous form is morphologically similar all around the Northern Hemisphere, such that anadromous fish from the Baltic, the Atlantic and the Pacific all resemble each other quite closely.

Three-spined stickleback populations are also found in freshwater lakes and streams. These populations were probably formed when anadromous fish started spending their entire life cycle in freshwater, and thus evolved to live there all year round. Freshwater populations are extremely morphologically diverse, to the extent that many observers (and some taxonomists) would describe a new subspecies of three-spined stickleback in almost every lake in the Northern Hemisphere. One consistent difference between freshwater populations and their anadromous ancestors is the amount of body armour, as the majority of freshwater fish only have between 0 and 12 lateral armour plates, and shorter dorsal and pelvic spines. However, there are also large morphological differences between lakes. One major axis of variation is between populations found in deep, steep sided lakes and those in small, shallow lakes. The fish in the deep lakes typically feed in the surface waters on plankton, and often have large eyes, with short, slim bodies and an upturned jaw. Some researchers refer to this as the limnetic form. Fish from shallow lakes feed mainly on the lake bed, and are often long and heavy bodied with a relatively horizontal jaw and a small eye. These populations are referred to as the benthic form.

Since each watershed was probably colonised separately by anadromous sticklebacks, it is widely believed that morphologically similar populations in different watersheds or on different continents evolved independently. There is a unique population in the meromictic Pink Lake in Gatineau Park, Quebec.

One fascinating aspect of this morphological variation is that a number of lakes contain both a limnetic and a benthic type, and these do not interbreed with each other. Evolutionary biologists often define species as populations that do not interbreed with each other (the Biological Species Concept), and thus the benthics and limnetics within each lake would constitute separate species. These species pairs are an excellent example of how adaptation to different environments (in this case feeding in the surface waters or on the lake bed) can generate new species. This process has come to be termed ecological speciation. This type of species pairs is found in British Columbia in Western Canada. The lakes themselves only contain three-spined sticklebacks and cutthroat trout, and all are on islands. Tragically, the pair in Hadley Lake on Lasqueti Island was destroyed in the mid 1980s by the introduction of a predatory catfish, and the pair in Enos Lake on Vancouver Island has started to interbreed and are no longer two distinct species. The two remaining pairs are on Texada Island, in Paxton Lake and Priest Lake, and they are listed as Endangered in the Canadian Species At Risk Act.

Other species pairs which consist of a well-armored marine form and a smaller, unarmored fresh water form are being studied in ponds and lakes in Southcentral Alaska that were once marine habitats such as those uplifted during the 1964 Alaskan Earthquake. The evolutionary dynamics of these species pairs are providing a model for the processes of speciation which has taken place in less than 20 years in at least one lake. In 1982, a chemical eradication program at Loberg Lake, Alaska, killed the resident freshwater populations of sticklebacks. Oceanic sticklebacks were introduced and colonized the lake. In just 12 years beginning in 1990, the frequency of the oceanic form dropped steadily, from 100% to 11%, while a variety with fewer plates increased to 75% of the population, with various intermediate forms making up another small fraction. This rapid evolution is thought to be possible through genetic variations that confer competitive advantages for survival in freshwater when conditions shift rapidly from salt to freshwater. However, the actual molecular basis of this evolution still remains unknown.

Although sticklebacks are found in many locations around the coasts of the Northern Hemisphere and are thus viewed by the IUCN as species of least concern, the unique evolutionary history encapsulated in many freshwater populations indicates that further legal protection may be warranted. The IUCN indicates that this evaluation may be out of date.

Head of male three-spined stickleback (Gasterosteus aculeatus) by Piet Spaans http://commons.wikimedia.org/wiki/File:GasterosteusAculeatusMaleHead.JPG. GNU Free Documentation License 24/03/10
Head of male three-spined stickleback (Gasterosteus aculeatus) photo by Piet Spaans

Life History

Many populations take 2 years to mature and experience only one breeding season before dying and some can take up to 3 years to reach maturity. However, some freshwater populations and populations at extreme latitudes can reach maturity in only 1 year. In spring, males defend territories where they build nests on the bottom of the pond or other body of water; the sequence of territorial, courtship and mating behaviours was described in detail by Niko Tinbergen in a landmark early study in ethology. Territorial males develop a red chin and belly colouration, and Tinbergen showed that the red colour acted as a simple sign stimulus, releasing aggression in other males and the first steps in the courtship sequence from gravid females. Red colouration is produced from carotenoids found in the diet of the fish. As carotenoids cannot be synthesised de novo, the degree of colouration gives an indication of male quality, with higher quality males showing more intense colouration. However, it is noteworthy that the response to red is not universal across the entire species complex, with black throated populations often found in peat-stained waters. Males also develop blue irises on maturation. Only the males care for the eggs once they are fertilised. Parental care is intense, involving nest maintenance and fanning of the eggs to ensure a fresh water supply, even at night. Males build the nests from vegetation, sand, pebbles and other debris, adhering the material together with spiggin, a proteinaceous glue-like substance secreted from the kidneys. Sticklebacks have four colour photoreceptors in their retina, making them potentially tetrachromatic. They are capable of perceiving ultraviolet wavelengths of light invisible to the human eye and use such wavelengths in their normal behavioural repertoire.

The three-spined stickleback is a known intermediate host for the hermaphroditic parasite Schistocephalus solidus, a tapeworm of fish and fish-eating birds.

Genetics

Three-spined sticklebacks have recently become a major research organism for evolutionary biologists trying to understand the genetic changes involved in adapting to new environments. The entire genome of a female fish from Bear Paw Lake in Alaska was recently sequenced by the Broad Institute and many other genetic resources are available. This population is under risk from the presence of introduced northern pike in a nearby lake.

Nine-spined stickleback (Pungitius pungitius)

Nine-spined stickleback (Pungitius pungitius) http://en.wikipedia.org/wiki/File:Pungitius_pungitius.jpg. Public domain 23/03/10
Nine-spined stickleback (Pungitius pungitius)

The nine-spined stickleback (Pungitius pungitius), also called the ten-spined stickleback, is a freshwater species of fish in the Gasterosteidae family that inhabits temperate waters. Widely but locally distributed throughout the UK and along the Atlantic coast of North America, it is also found in many northern and eastern European countries, in Greenland and in Turkey, and in the Far East. Despite its name, the number of spines can vary from 8 to 12.

The nine-spined stickleback lives in extremely weedy ditches and rivers as its small spines do not offer much protection. They have scutes or bony plates all the way down their body.

During the breeding season (April to July), the male develops a black belly and builds a nest suspended on a piece of waterweed, about an inch or so above the substrate at the bottom. The female is attracted over by the male and she lays eggs inside the nest. The male guards these eggs and the young fry when they hatch. Then when they have their spines he drives them away to look after themselves.

The colouring when not breeding is usually a dark brown, although females are a lot lighter cloured than the males. The male is normally chcolate brown with darker stripes and spots. His eyes are dark with a gold ring around his pupils, While on the three spined the eyes are silver. The female is more of a dark tan colour and has darker markings. It may have a silver belly and silver eyes. No two sticklebacks are the same; they are unique, just like human fingerprints. The body is a lot more elongated than the three spined stickleback with a thinner and longer caudal peduncal.