ANIMAL REPRODUCTION
QUICK AND MANY (r)The Deer Mouse (Peromyscus maniculatus) is a rodent native to North America.
The deer mouse tends to reproduce based on food availability rather than season, and are known to reproduce at various times of the year. Also, due to the vast area their species covers (from Canada to Mexico and everywhere in-between) season and ideal conditions vary. Deer mice are in profuse numbers. Gestation is between 22 and 26 days, with a female bearing a litter of between 1 and 9 (the average being 3-5). Females have on average 3 or 4 litters per year, but certain captive deer mice have birthed 14 litters in one year. Deer mice pups are born altricial (blind and naked) but have a rapid development rate, with pups reaching adult size in 6 weeks. Most deer mice travel less than 500ft from their natal range to reproduce, leaving somewhere between weaning and the next litter, indicating a significant amount of interfamilial breeding. Deer mice live a maximum of 96 months in the wild, with the average for females being 45.5 weeks and 47.5 weeks for males. The advantages of the r-selection reproduction style is that due to the low life-span, the mature mouse is able to contribute a significant number of young to the species with the aid of rapid gestation and pup development. Additionally, the ability to reproduce so quickly is extremely beneficial for when food and the environment are in good condition, at a prime time for reproduction and raising young. However, the ability for females to reproduce so readily, probably contributes to their low lifespan, with constant reproduction tolling on her health. And of course there are more young to care for more frequently, however considering development is so rapid for pups, energy devoted to development and parenting isn't overly strenuous. Information from: https://en.wikipedia.org/wiki/Peromyscus_ maniculatus |
...somewhere in between...The Moose (Alces alces) Moose reproduce only once a year and during September to October. Though moose could "rut" again in winter, they don't as it limits the calves chances of survival. Cow's (female moose) are in gestation for 8 months. Bulls are polygamous, which means they will have more than one mate per "rut". After the breeding season ends, the male doesn’t stay with the female or contribute anything to raising the calves as moose are very solitary animals and usually only find limited and short company during mating season. Moose are very independent animals. Going into labour, the cow will seclude itself and lay down until the calf is born. Once born, calves are quick to their feet, able to walk usually in a few days. At about a week old, the calf can run faster than a human. The calf will gain approximately 1/10 to 2/10 of a pound daily from consuming its mother’s milk and some vegetation. The calf stays with its mother for only normally a year, just until the cow is pregnant again and she disowns the previous season's calf. She encourages the calf to live by itself because taking care of two calves would take too much energy for the mother during the winter months. During the time in which the calf (occasionally there are two calves) stays with it's mother before her next gestation, it will learn how she survives and how likewise it will survive once it becomes independent. Similarly to the bear on the strong K-selection end of the spectrum, male moose have no involvement with raising the young and are polygamous. This contributes to the strong bond between mother and child/children of the cow/mother bear and calves/cubs and the depth of knowledge that will be passed on. However moose have a much more frequent breeding pattern than bears, however severely less than the Deer mouse. For the moose, it is definitely a K-selection animal but it shares the advantages and disadvantages of a wider spread of the spectrum. For example, though it only has young to care for for a year, it will soon rebirth and repeat the pattern. However, unlike the bear, moose do not obtain as much knowledge from their mothers as calves have only one year with their mothers where as bears have up to 3, which contributes to why moose have a lifespan of about 15-25 years while bears live 30-40 years. Information from: https://en.wikipedia.org/wiki/Moose https://bioweb.uwlax.edu/bio203/s2012/h autala_gavi/reproduction.htm |
SLOW AND FEWER (K)The grizzly bear (Ursus arctos ssp.)
Of all the species who identify as a K-selection reproducer: big cats, elephants, whales and many other large mammals, humans perhaps lye at the very end of the spectrum, being a perfect example of the reproductive style of K-selection animals. Elephants and bears though, also take K-selection reproduction very seriously. The K-selected life-style affects just about everything in a bear’s life. Because of the immense dedication mother's provide for their cubs, many of a bear's advantageous traits are attributable to this K-selection type reproduction style. Their curiosity, high problem-solving abilities, apparently near-photographic memories, extraordinary sensory apparatus, delicate manipulative ability, and their cognitive skills and integrative capacity to put it all together are results of their detailed training by their mother's, exclusive to K-selective breeders. The one-on-one, mother-and-child interaction is extremely important for the species in ensuring the generations worth of knowledge passed on by each bear's mother is once again passed on to their young. The considerable teaching process bear mother's give their young provides cubs with the knowledge of how to be a bear. Their life-span and child-bearing is strongly affected by this knowledge and upbringing. Bears live thirty to forty years, even in the wild, because short lives would waste all that learning and the gene pool cannot afford the loss. Due to the large amount of information passed down from mother to child, generations worth of bear knowledge contributes to their ability to survive, and their highly developed intellect. Bears reproduce extremely slowly because each generation must be taught as much as possible of what the previous generations have figured out, and that requires a lot more energy and time, much more than if a mother had to be nursing and caring for a large litter of children to which she would soon bear another (r-selection style). Bears are not born knowing how to be bears, the K-selection method allows for a deeper understanding of survival to take place and hence the reason for K-selective species living longer on average than r-selection. The benefits for K-selectors is an arguably easier and perhaps more guaranteed life, having being taught the ins and outs from birth. However rearing young takes an enormous level of time and energy, but then again K-selection parents will not have as many "litters" per year as r-selection parents (perhaps only one). Above information from: http://wiseaboutbears.org/about-us/bear- the-species/ |
THE BALD EAGLE
Fertilisation:
After a significant courtship process and copulation by which the male's sperm has successfully found its way to the female's ova in the infundibulum (site of fertilisation), the sperm will fertilise the yolk and then the outer egg membrane will seal off the fertile egg to prevent more sperm from entering. The egg then makes it's way through the oviduct, slowly being covered with layers (eggshell membranes, cuticle layers, and finally the outer crystallisation membranes that is the eggshell). The egg is then laid and incubated.
Female bald eagles will lay between 1 and 3 (with 2 being most common) fertilised eggs per successful mating season. The first egg is laid 5-10 days after successful copulation, with the second following a few days later, and possibly a third a few days after that. The incubation period for bald eagles is 34-35 days with both the male and female taking turns to incubate whilst the other is off finding food. Females, however, do most of the incubating in most circumstances.
After a significant courtship process and copulation by which the male's sperm has successfully found its way to the female's ova in the infundibulum (site of fertilisation), the sperm will fertilise the yolk and then the outer egg membrane will seal off the fertile egg to prevent more sperm from entering. The egg then makes it's way through the oviduct, slowly being covered with layers (eggshell membranes, cuticle layers, and finally the outer crystallisation membranes that is the eggshell). The egg is then laid and incubated.
Female bald eagles will lay between 1 and 3 (with 2 being most common) fertilised eggs per successful mating season. The first egg is laid 5-10 days after successful copulation, with the second following a few days later, and possibly a third a few days after that. The incubation period for bald eagles is 34-35 days with both the male and female taking turns to incubate whilst the other is off finding food. Females, however, do most of the incubating in most circumstances.
Number of Offspring:
Bald eagles mate for life and can reproduce every year. Each successful mating will yield 1-3 young, though only around 50% of eagles survive their first year. If there are two or three eggs, it is unlikely two will survive let alone three because the eldest sibling will often kill the other to have full attention from it's parent. This is more common only when the eldest though is a female, as females are distinctively larger than males. Parents will not do anything to stop the killing if this does occur. While three is very rare, almost half of all known bald eagles will have two fledgings. Eaglets eventually leave the nest at about 8 weeks. Bald eagle pairs will sometimes choose not to mate every year for reasons concerning weather, food and environmental stability. Due to their lifespan of and average of 20 years in the wild, of which they mate largely with only one other, there is plenty of time to reproduce.
Information from: http://www.baldeagleinfo.com/eagle/eagle4.html
and https://en.wikipedia.org/wiki/Bald_eagle
Bald eagles mate for life and can reproduce every year. Each successful mating will yield 1-3 young, though only around 50% of eagles survive their first year. If there are two or three eggs, it is unlikely two will survive let alone three because the eldest sibling will often kill the other to have full attention from it's parent. This is more common only when the eldest though is a female, as females are distinctively larger than males. Parents will not do anything to stop the killing if this does occur. While three is very rare, almost half of all known bald eagles will have two fledgings. Eaglets eventually leave the nest at about 8 weeks. Bald eagle pairs will sometimes choose not to mate every year for reasons concerning weather, food and environmental stability. Due to their lifespan of and average of 20 years in the wild, of which they mate largely with only one other, there is plenty of time to reproduce.
Information from: http://www.baldeagleinfo.com/eagle/eagle4.html
and https://en.wikipedia.org/wiki/Bald_eagle
Development and nutrition of embryo:
As the embryo develops, several membranes form: the yolk sac, amnion (the inner most membrane that encloses the animal), and chorioallantois.
The yolk sac is highly vascularized and completes formation at about half-way through incubation. It transports nutrients and aids in early respiration.
The amnion is minimally vascularized and is completed at about 1/3 of the way through incubation. It acts as a protective fluid environment and has muscle fibers that contract rhythmically to prevent early development adhesion before the embryo can move. The amnion also provides nutrients. Albumen mixes with amniotic fluid just after the mid point of incubation, and the embryo begins drinking this fluid, using it's protein for rapid growth.
The chorioallantois completes its formation after the middle of incubation. This is composed of the chorion, an ‘extension’ of the amnion, and the allantois, a highly vascularized membrane that expands to fuse with the chorion. This membrane aids in respiration, providing O2/CO2 exchange to support development. There is also passive transpiration from the chorioallantois. Urinary waste is also collected in the chorioallantois, which is released just before hatching.
The above information on embryonic development is from: http://www.iws.org/bald_eagles/Incubation%20Manual.PDF
As the embryo develops, several membranes form: the yolk sac, amnion (the inner most membrane that encloses the animal), and chorioallantois.
The yolk sac is highly vascularized and completes formation at about half-way through incubation. It transports nutrients and aids in early respiration.
The amnion is minimally vascularized and is completed at about 1/3 of the way through incubation. It acts as a protective fluid environment and has muscle fibers that contract rhythmically to prevent early development adhesion before the embryo can move. The amnion also provides nutrients. Albumen mixes with amniotic fluid just after the mid point of incubation, and the embryo begins drinking this fluid, using it's protein for rapid growth.
The chorioallantois completes its formation after the middle of incubation. This is composed of the chorion, an ‘extension’ of the amnion, and the allantois, a highly vascularized membrane that expands to fuse with the chorion. This membrane aids in respiration, providing O2/CO2 exchange to support development. There is also passive transpiration from the chorioallantois. Urinary waste is also collected in the chorioallantois, which is released just before hatching.
The above information on embryonic development is from: http://www.iws.org/bald_eagles/Incubation%20Manual.PDF
Parental Care:
Both male and female parents care for their young. One parent will always be with the nest, as it was during incubation, while the other finds food and collects nesting supplies. The female often does most of the incubating. The parent that stays with the eggs most during incubation is hard to detach from it's eggs and often needs to be pushed off of them to rest and switch roles.
For the first two to three weeks of the nestling period at least one adult is at the nest almost 100% of the time. After 5 or 6 weeks, parental nest attendance reduces significantly with parents perching on nearby trees and branches, but not necessarily occupying the nest. Eaglets develop very fast and gain up to 170gms a day. Fledging (the development of wing feathers that are large enough for flight) happens at around 8-14 weeks old, but generally stay with their parents in the nest for another 6 weeks.
Jeuvenile eagles must learn to hunt by watching their parents and practising. During this stage they more often watch how to attack rather than actually doing anything. Young eagles that stay near their nest are often still fed by their parents up until their first winter after fledging. They do not keep much contact with them other than that though. Young eagles have the instincts to hunt but do not yet have the skill, but they eventually learn how to soar and hunt prey. Winters can kill young eagles who do not yet have enough experience in hunting. Only around 50% of eagles survive their first year. From when they leave the nest until sexual maturity at about 4 or 5 years old, they have plenty of independent time to practice their skills before raising their own young.
Both male and female parents care for their young. One parent will always be with the nest, as it was during incubation, while the other finds food and collects nesting supplies. The female often does most of the incubating. The parent that stays with the eggs most during incubation is hard to detach from it's eggs and often needs to be pushed off of them to rest and switch roles.
For the first two to three weeks of the nestling period at least one adult is at the nest almost 100% of the time. After 5 or 6 weeks, parental nest attendance reduces significantly with parents perching on nearby trees and branches, but not necessarily occupying the nest. Eaglets develop very fast and gain up to 170gms a day. Fledging (the development of wing feathers that are large enough for flight) happens at around 8-14 weeks old, but generally stay with their parents in the nest for another 6 weeks.
Jeuvenile eagles must learn to hunt by watching their parents and practising. During this stage they more often watch how to attack rather than actually doing anything. Young eagles that stay near their nest are often still fed by their parents up until their first winter after fledging. They do not keep much contact with them other than that though. Young eagles have the instincts to hunt but do not yet have the skill, but they eventually learn how to soar and hunt prey. Winters can kill young eagles who do not yet have enough experience in hunting. Only around 50% of eagles survive their first year. From when they leave the nest until sexual maturity at about 4 or 5 years old, they have plenty of independent time to practice their skills before raising their own young.