Women who like men with a different appearance, such as a special color pattern, have sons who are above average sexy. At least: that is the case with guppies, write American and Canadian biologists in Science. This attractiveness advantage does not apply to the grandsons – in their generation, their grandfather’s ‘beauty spots’ have become all too common.
Although the guppy (Poecilia reticulata) is known as a pond fish, it is originally a South American species, which lives in flowing water on the island of Trinidad, among other places. The basic color of the wild fish is silver-grey, but the males often have brightly colored or dark spots and stripes. Such appearances are passed down from father to son. Some patterns are rarer than others.
Laboratory experiments in various animal groups show that males with such a deviant phenotype are more popular with female congeners than more common males. The question is, however, whether this is beneficial in the long term: if a special male reproduces much more often, then his appearance in subsequent generations will no longer be so characteristic – and therefore less seductive.
Impress
But in the lab it is difficult to investigate such a thing thoroughly, the researchers write: there, a female is often only given the choice between two different individuals, and the experiment is not spread over many generations.
That’s why they decided to take a more thorough approach with the guppies on Trinidad: the biologists followed ten generations with a total of 7,173 individuals and captured them monthly to analyze the reproductive success. Each man was assigned a ‘rarity score’. The researchers focused on a guppy population from one pool; it was connected to some neighboring pools via a stream.
What turned out? Males with a different pattern had more than 35 percent more partners to mate with, which led to more than 35 percent more offspring. Their sons were also still rare enough to impress female guppies, and they had extra children. The same advantage did not apply to their daughters (who, due to the lack of characteristic patterns, do not look much like their father).
The attractive sons had to rely purely on their appearance: the rarity of their father did not seem to lead to any special genetic advantages. The risk of inbreeding did not decrease either.
Females that mate with the rare males do not directly benefit from the situation: they do not produce more offspring with an aberrant male. But because their sons are better marketed, this does mean that the female guppies have more grandchildren. And with that the advantage seems to be over immediately, because that large number of grandsons ensures that the unique family trait is suddenly not so unique anymore.
Fussy
Incidentally, the experiment showed that female guppies also have a preference for ‘new’ males, which come from a different habitat. Those males do not have to have a different color pattern. In other words: a ‘boring’ but new male does not provide sexy sons, and therefore no extra grandsons. Genetically, it can in theory provide an advantage, provided they are sufficiently different from each other.
Remarkably, the experiment showed that new males introduced by the researchers from neighboring pools were not necessarily less related to the females than the ‘local’ males. This may be because male guppies tend to change pools themselves quite often.
The preference for new men may be a side effect of the preference for deviant men, the researchers conclude. After all, females cannot oversee the entire population in the stream, and only know the males from their own environment. Thus, a newcomer can seem very unique and seductive. Plus, it doesn’t help if female guppies are too picky. Suppose that all females in a pool set their sights on the same male, because he looks the most different, then all their sons would start to look alike – and they would immediately cease to be sexy.