Scientists in Switzerland have discovered that the reproductive biology of the pipefish Syngnathus typhle varies according to body size, geographical location and water temperature.
Using a combination of molecular biology (microsatellite analysis), morphology and reproductive biology; V Rispoli and A Wilson at the University of Zurich studied populations of pipefish in five different locations varying in latitude and water temperature.
They demonstrated that as water temperatures decreases, body size and as a consequence numbers of eggs produced increases.
The pipefish Syngnathus typhle also known as Deep-snouted or Broad-nosed pipefish, is found throughout the Mediterranean, the Black sea and the Azov sea.
It is unusual in its breeding behaviour as males brood the eggs in a pouch made up of two ventral folds.
In addition this is a polygynandrous species; which means that males and females both breed with several mates during a breeding season and females compete more for males than vice-versa.
The study demonstrated that embryonic development was dependent on water temperature so as the water temperature decreases, the brooding time increased.
In addition, it was found that as the water became colder, body size and fecundity increased for both males and females ensuring the maximum number of eggs produced per breeding.
Where females did not produce enough eggs to fill the males pouch, multiple matings of up to five females were observed in the males.
However, as the females increased in size and the size ratio decreased, so that females produced more than enough eggs; a shift in the breeding pattern was observed so that in one population nearly 90% of the males were actually monogamous.
Apart from water temperature it was also hypothesized that other factors affecting breeding could be the frequency of mating encounters, risk of predation, mate quality and parasites.
The importance of water temperature on pipefish breeding systems means that the steadily increasing temperatures of the oceans are likely to be affecting reproduction of the pipefish already.
Studies such as these can be used to assess potential effects of global warming on fish species.
For more information see: Rispoli VF and AB Wilson (2007) - Sexual size dimorphism predicts the frequency of multiple mating in the sex-role reversed pipefish Syngnathus typhle. Journal of Evolutionary Biology, OnlineEarly Articles Published article online: 22-Nov-2007. doi: 10.1111/j.1420-9101.2007.01470.x