Guppies do not have to compete with brothers for mates

Scientists have created a model that successfully describes the sexual behavior of male guppies depending on three parameters: attraction of females to the presence of rivals and whether rivals brothers. Animals are more actively courting large females, reduced effort if they were competitors and were even less interested, if the rivals were brothers. How exactly do guppies recognize relatives, is still not known, however, the model may be relevant for other types of animals. Article published in the journal Nature Ecology & Evolution.

Sexual selection works so that males choose to mate with the best (from a biological point of view) females. However, this inevitably leads to the fact that the most attractive females there is a high competition. So some males it may be advantageous to choose a lower-quality partner and save resources on the fight against opponents. This is especially true if competing relatives have similar genetic material and common goals in transmitting hereditary information to the next generation. It is unknown to what extent males take into account when selecting females on all three factors: quality possible reproductive partner, the presence of competitors and the relationship with them.

Mitchell Daniel (Daniel Graig) from the University of Toronto and Robert Williamson (Robert Williamson) from Technological Institute named rose Halman created a mathematical model of optimal selection of females in competition. The model assesses how the animal is beneficial to care for the female depending on her qualities and competitive environment, which determines the number of males competing for the individual and how they are related are related to the object model. The interaction of the latter two variables depend on the ecology of specific animals.

The authors have chosen the subject of their study, fish guppies (Poecilia reticulata). These animals are rarely one and the same female more than two competing males, and therefore in the model considered three scenarios: no of competitors one or more than one. The model parameters are estimated on the group of 12 adult fish. Six of them were females, two individuals of the three categories of sizes — the larger, the more attractive to the opposite sex. In two groups of males had three siblings.

Before he can impregnate female guppies for some time floating behind her: they need to find the perfect position for mating. If a male has a rival, he can overtake; the winner is the one who was behind the female. Therefore, as features of behavior that reflects courting guppies, chose a time during which the fish followed. Empirically selecting the parameters, scientists have calculated the theoretical efforts, which the male will spend on each of the females in each of the possible scenarios of competition.

The number of mating attempts per unit time decreased to 47 percent when the emergence of a competitor, this number was used as a model parameter. The behavior of guppies in the experiment coincided with the predictions of the model. Fish followed by larger females is much longer, their efforts also influenced the terms of competition: guppies actively mate with females, if they had no rivals, or if the opponent was not a brother. Exclusion from analysis of any of the three options and their combinations reduced the predictive power of the model.

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