All entries for Monday 27 March 2006

March 27, 2006

The Sex Life of the Ladybirds: Pick it, Choose it

Follow-up to The Sex Life of The Ladybirds: Meeting, Courting, Mating from Reverie

Pick it, Choose it
Adalias are polymorphic. This means that different breeds of ladybirds can inhabit one the same area, living in perfect peace and harmony with each other. One could say they are true diversifiers: they choose partners paying little attention to the colour of the partner. However, the choice is always conscious and based on a number of principles.

Studies have revealed that the ‘ethnic minorities’ among the ladybirds are most popular sex partners. The red-winged female ladybirds are inclined to choose black-winged males as their sex partners. And such preference grows stronger with generations. Scientists interpret such behaviour as caused by laws of natural selection.

How many boys do we need?
If one male individual can impregnate dozens of females, then the question begs: how many males a populace needs? With beetles, like with humans, the sex of the offspring is defined by the X and Y chromosomes; this ensures the 1:1 proportion of males and females produced. If the populace of Adalias is inhabiting a resourceful area with ample amounts of food for everyone, the plentiful of male individuals won’t compete with the females for food and thus won’t threaten the survival of the populace. However when conditions of living aren’t so great, the males present a major hindrance to females’ existence on every stage of life. It is the number and productivity of the females that essentially defines the number of offspring of the next generation. Taking into account the high sexual verve of the males, in times of hardship, the number of males necessary to retain a populace of ladybirds can be reduced to as little as 10% of the total Adalia population. Yet, in practice such proportions can be harmful: due to the deficit in male the incest rate is likely to go up considerably and result in potentially defective ladybird-babies born.

Hence, the optimal proportion of male individuals in a populace is defined by the availability of resources, their sexual zest and the destructiveness of incest. The proportion of males in a populace of ladybirds can serve as an indicator of the overall environmental condition of the area: in France the ratio of male and female ladybirds is 50%:50%, in St. Petersburg (Russia) 30%:70%, in Stockholm – 18%:82%.

Some female ladybirds have acquired an ability to produce mono-sexual offspring: even copulating with normal males they only give birth to female offspring. This is the way the sex ratio is regulated in a populace. This miraculous yet discriminative ability still remains largely unexplained, although it has been discovered that there is a certain bacteria inhabiting the cytoplasm of the Adalia, which is harmless to the females, yet lethal to the males.

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