Washington, Apr 4 (ANI): Sexual dimorphism has evolved in animals because such traits help males to obtain additional offspring.
In the bird world, male and female blue tits are hard to distinguish for the human observer.
However, in the UV-range, visible to birds, the male is much more colourful.
A closer look at the monogamous mating system of these birds again reveals that all is not what it seems - in every second nest there are chicks that are not related to the care-giving father.
An already mated male can increase the number of his offspring by siring extra-pair offspring in other nests than the one he cares for with his mate.
Emmi Schlicht and Bart Kempenaers of the Max Planck Institute for Ornithology in Seewiesen investigated whether this could be the driving force behind the evolution of sexual dimorphism.
However, their findings suggests that effects of extra-pair paternity are limited, and cuckoldry can even reduce the intensity of sexual selection.
In many species, males and females look very different. Male deer wear impressive antlers and the magnificent plumage of a male peacock is impressive not only to the hen.
In our backyard we can identify the male in chaffinches or house sparrows easily from the distinctive colouration of breast and crown.
Why do these differences exist? For deer and peacock the answer is straightforward, at least in principle: a well-endowed male can better defend the females on his territory, or attract more females in the first place.
For females sexual selection is weaker as they cannot increase their number of offspring by outcompeting other females.
However, many bird species pose a challenge for this explanation by evolutionary biologists.
Most bird species are socially monogamous, in permanent relationships with a partner of the other sex.
Both parents have to work hard to raise their offspring. So why do males in monogamous species have more colourful plumage than females, if the number of offspring for both parents is decided by the clutch size of the female?
Paternity analyses have long revealed that not all offspring are related to the male that feeds them.
Therefore, a monogamous male can have additional offspring if he succeeds in siring additional eggs in the nest of other females. (ANI)
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