One litter of kittens while having only one mother can have multiple fathers. This is because a female can mate several times each heat cycle, of which she wall have many a year. As we learned in class when a human gets pregnant the cervix produces a mucus that does not allow more sperm in, cats obviously don’t do this. When cats mate each time they mate, with the same or different males, they accept more sperm. Also female ovulation in cats is stimulated when the male pulls out of the female leading an egg to be released just after insemination, another reason that one litter can have multiple fathers.1 The likelihood of having multiple fathers cats in one litter has many different variables. In a study done by Say et al. they found that in urban populations cat litters had a 70-83% chance of having multiple fathers. The statistic is much lower in urban populations: only 0-22% chance of having multiple fathers.2 There are many reasons for this, one of which the authors note as cats in rural populations can monopolize a female during her heat and so the litter because they do not start mating until they are around three years old, while males in urban populations start mating as early as ten months.3 This is most likely due to the higher concentration of cats in urban areas, they are more abundant so it is more difficult for males to monopolize a female by themselves. In rural areas the cats are more spread out so the males can protect their female more easily. Also, in rural areas there are more predators so cats have to be more careful, leading males to wait until they are older to reproduce. Also since the population is lower the males have to be older or another male will steal the in heat female from the younger less experienced cat. Cat reproduction is so interesting because it is so different from humans, having multiple fathers for one litter is a strange thought for humans, but common in cats.
Works cited:
1http://en.wikipedia.org/wiki/Cats#Reproduction. 8 November 2011 at 14:36
2,3Say, L. Pontier, D. Natoli, E. High variation in multiple paternity of domestic cats (Felis catus L.) in relation to environmental conditions. Proceedings of the Royal Society of London. 266. 1433 (2071-2074). Oct. 1999. 10.1098/rspb.1999.0889
My family breeds dogs, and similarly, we find that littermates can have multiple fathers. This is because dogs are a polyovulatory species meaning they discharge several ova per ovulatory cycle, and similarly to cats, there is no cervical mucus production to prevent polyspermy for one egg. If more than one male copulates with the female while she is in heat around the same time (within 1-3 days), the litter can be a mix of dogs! This almost happened to my family actually. When we used to breed bulldogs, we had a female who went into heat, and got “accidentally” pregnant by our neighbor’s black lab stud (the puppies, called “bulladors”, are actually super cute and friendly). However, before she had the litter, we were at a loss of who the father(s) could be since we had a stud Pomeranian, and since we live in the mountains there have been incidents where coyotes and fox have bred with domesticated dogs (and have produced viable offspring). It was a relief when the puppies were born to find out that it was in fact the Labrador (bulldog + pomeranian puppies= not a pretty picture), because we knew they most likely would survive and be healthy. Sorry, went way off track. I think it is very interesting the huge age differences in reproductive maturity of male cats in rural vs. urban areas. The beginning of the study talked about how human domestication of cats could alter reproductive maturity because they are given food, shelter, and water, compared to stray cats that have to be more opportunistic given the circumstances of their environment. I think humans have a huge impact on differences in the frequencies of cat paternity in different areas, because while domesticated (urban areas), usually it is the owners selectively breeding their cats to ensure that the litters have one father, whereas stray cats (rural areas) would show more litters of multiple fathers.
ReplyDeleteI find this to be a pretty amazing topic, and also leads my family further from tracking down the other half of our family dog (One of those accidental pregnancies...with several possible fathers and our dogs litter mates vary widely in size, color, and features). I am confused though on the time frame involved in the pregnancy, the alternate times of conception would also lead to alternate developmental stages and premature offspring? Or is there a limited conception window?
ReplyDeleteWhile looking for an answer to this question I found an extremely interesting tangent. Apparently over 100 mammals are known to be capable of delaying their pregnancy. They are not delaying the actual conception, rather they are "pausing" the egg before it reaches and implants in the uterus. They can stay as free floating blastocysts anywhere from a couple of days to over a year. Although the exact cause of this pause has not been identified, there are many benefits in having the ability to pause pregnancy until physiologically prepared. Such as assuring there's abundant food to nurture a pregnancy, or not having a litter in the middle of the winter when forage for growing pups is scarce. Overall it appears to be an evolutionary advantage most closely related to the environment and ecology, food and weather availability for best survival outcomes. I would guess that having a litter from several fathers also has an advantage in allowing a wide variety so that some are more "prepared" for certain conditions/diseases, and others for an alternative environment.
http://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/1992/Mothers-in-Waiting.aspx
This article reminded me of an article I came across on MSN that talked about the a mother giving birth to twins with different fathers. As you have mentioned, the human body secretes a mucus that prevents sperm from entering the cervix upon pregnancy. If fertilization has not occurred, the cervix does not secrete a mucus, thus, sperm can still enter. We know that sperm can survive for several days in the female body. During this time period, if the female has sexual intercourse with other men, she can acquire sperm from a different man. This is what happened to Washington several years ago. Washington's ovaries released two eggs in the same month, which was fertilized by sperm from two different men.
ReplyDeletehttp://today.msnbc.msn.com/id/30864533/ns/today-parenting_and_family/t/mother-gives-birth-twins-different-dads/#.Ttw3nXP8eEw