Choosy lady seeks colourful partner for short-term relationship

By Tone Kvenild
Photos: Rune Petter Ness

Trine, the guppy from Trinidad, was caught in a net, put in a bag of water and taken to Norway with 500 other little congeners. Within a short time-span Trine has become a mother, a grandmother, and even a great-grandmother, in a fish tank at NTNU.

Gunilla Rosenqvist's research on guppies helps us understand the behavioural problems of salmon when they are released into Norwegian watercourses.

Several times a day the little guppy is given a shock by the two large, light-brown eyes of a researcher peer- ing inquisitively through the glass. Trine gets frigh- tened and swims down to the bottom to make herself invisible, but this does not stop her from being regularly collected in a net to be measured and weighed.

- The large female guppies dominate the smaller females, and a large female can actually prevent a small one from producing any fry, says Gunilla Rosenqvist. She is a professor at the Department of Zoology at NTNU, and she uses the guppy to illustrate how animal behaviour and genetics are altered in controlled breeding circumstances. The results of Rosenqvist's research will help us to understand more about hatchery-produced fish, as well as the problems that threatened species have in adapting to the surroundings into which they are released.

The guppy fish quickly reaches sexual maturity, it has a short pregnancy, it is viviparous and it is a vertebrate. All this has made the guppy a popular species for research world-wide. As a result, the genetics, the DNA and the behaviour of this fish have all been carefully studied.

There are many reasons why Rosenqvist did not confine herself to sticklebacks or other local northern species, and instead took a trip to Trinidad to collect her exotic research objects. The guppy reaches sexual maturity fast, it has a short pregnancy, it is viviparous, and it is a vertebrate. All this has helped to make the guppy a popular experimental subject world-wide, which in turn means that researchers know a lot about the genes, the DNA and the behaviour of this fish.

Orange males are most highly favoured
Rosenqvist focuses a lot of her research on the guppies' choice of mates. It is the female guppy who makes the choice, and she is a very choosy lady. The male guppy thus has to become a skilled suitor and he 'dances' seductively around the female to show off.

- Colourful males are most highly favoured by the females, and the really 'hot' colour is orange. This is a colour which comes from the food the fish eats, and a strong orange colour tells the female that her suitor is able to find a sufficient amount of food, explains Rosenqvist.

As a result, a good daddy fish displays many bright colours. The colours are a sign that the male is healthy, that his immune system is in good working order, and that he is free from parasites. The problem is that these colours also make the male very visible to other fish who prefer to put a guppy on the menu. This is why the female does not choose according to colour in areas containing a lot of predatory fish. She is worried that the colours will attract such predators, who will devour her in the same mouthful, which means that she is better off with a less conspicuous suitor. That is why she also makes sure that the male does not get too close while he is wooing her.

In areas which are free from large numbers of ferocious predators, the male is allowed to get closer. Nevertheless, the male must always be a bit on the alert, says Rosenqvist. If he shows off a bit too much, he may end up getting into trouble. The larger female behaves very aggressively towards suitors who get too fresh, and many females may band together to keep the males at a distance. The female guppy must also find the right balance in order to survive and multiply. The males prefer the largest females, because they have the most fry. The problem is that the larger she gets, the more tempting she is to predators.

Fish individuals
- No single guppy is identical to another one, says Rosenqvist, and points out that each tiny individual guppy acts on the basis of learned as well as genetically inherited knowledge. This means that the males that our guppy, Trine, really falls for are not necessarily the same ones that make her friend Guri's eyes shine: each female seems, for example, to choose the male who best matches her own immune system. In this way the guppy fry will be better equipped to deal with disease.

- Each individual fish reacts to its native surroundings, which means that it is easy to go wrong if you make generalizations. You have to have a large number of fish in order to draw a general conclusion, says Rosenqvist.

Significance for Norwegian salmon production
This research may well become significant for one of Norway's most important export industries - salmon. - When you release hatchery salmon into the wild, the fish will often find it difficult to adjust, says Rosenqvist. The salmon may swim upstream either too early or too late, they may spawn at unfavourable times so that either their offspring will not mature or they mature too soon. As a result their behavioural patterns are disturbed, and a whole fishery nation is scratching its head about all the unproductive and confused salmon who lack even the faintest idea about how to behave in the wild. Many species are subject to breeding programmes to ensure a large biological variety. Rosenqvist explains that controlled mating within the programmes is determined exclusively on the basis of each animal's genes. - This means that the effect of natural pairing and behavioural patterns is not taken into account. Animals change their behavioural pattern during breeding; they adapt to conditions of captivation. This is often crucial to whether or not the animals will adapt to the wild. At worst such behavioural problems can have serious consequences for a complete eco-system, explains Rosenqvist.

* Contact at NTNU: Gunilla Rosenqvist
Tel: + 47 73 59 62 96
E-mail: Gunilla.Rosenqvist@chembio.ntnu.no