Sex and sneakers

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Sex and sneakers,[link widoczny dla zalogowanych]
The plainfin midshipman fish (Porichthys notatus),[link widoczny dla zalogowanych], found in the depths of the Pacific Ocean,[link widoczny dla zalogowanych], puts a cunning twist on the battle of the sexes. Some males of this species are so similar to females that they even respond to particular chemical brain messengers in the same way,[link widoczny dla zalogowanych], announce researchers in Nature1.
This fish comes in three distinct forms: female and two 'brands' of male,[link widoczny dla zalogowanych], creatively called 'type I' and 'type II' males. Type I is the 'new man' of the fishy depths: a caring sharing Lothario who hums to attract a mate,[link widoczny dla zalogowanych], and takes on the role of nest-building and guarding the young. Small wonder that female midshipman fish flock to the nests of type Is to lay their eggs.
Unfortunately for the humming,[link widoczny dla zalogowanych], hardworking type I fish,[link widoczny dla zalogowanych], the more 'love 'em' and leave 'em'' type II males have no such scruples. Type IIs sneak into the nests of type Is and fertilize the eggs that have been laid there or wait outside and fan their sperm through the entrance.
Type II males are able to accomplish this dastardly infiltration because they are much the same size and shape as a female. They also behave,[link widoczny dla zalogowanych], and sound,[link widoczny dla zalogowanych], like females. Only the type I male can hum which is a crucial part of the courting process. Females and type II males can only grunt.
Now James L. Goodson of Cornell University,[link widoczny dla zalogowanych], New York,[link widoczny dla zalogowanych], USA,[link widoczny dla zalogowanych], and Andrew Bass of the University of California,[link widoczny dla zalogowanych], California,[link widoczny dla zalogowanych], USA,[link widoczny dla zalogowanych], have found that females and type II males have yet more common ground. The vocal circuitry in the brains of females and the type IIs responds in the same way to 'isotocin',[link widoczny dla zalogowanych], a chemical messenger molecule or 'neuropeptide'. It is isotocin that enables the type II male to copy female grunts.
And Goodson and Bass have also discovered that this particular chemical messenger does not have much of an effect on humming fish. A type I male's vocal circuitry instead responds to another neuropeptide,[link widoczny dla zalogowanych], arginine-vasotocin that is structurally very similar to isotocin.
The type I male migrates to the tidal waters along the west coast of North America in late spring. Using powerful fins he excavates gravel and rocks to build a nest,[link widoczny dla zalogowanych], where he stays for the next three months. As night falls this mackerel-sized fish 'hums' to lure females to his den. He produces the sound by contracting a pair of muscles,[link widoczny dla zalogowanych], which make his swimbladder -- a gas-filled buoyancy aid -- pulsate.
A female attracted by the song of a type I male deposits up to 200 eggs in the roof of his nest before she returns to the deeper ocean. After fertilizing the eggs,[link widoczny dla zalogowanych], he resumes his humming to attract the next female. Meanwhile type IIs lurk around awaiting their opportunity to sneak into the nest.
Clearly the male midshipman fish has evolved two distinct reproductive strategies,[link widoczny dla zalogowanych], each moderated by the action of particular neuropeptides. The researchers believe that the difference in behaviour between the two types of male is related to the different effects of isotocin and arginine-vasotocin on the brains of these fish.
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