Generally only one ovum is released per menstrual cycle. Humans are mammals, so females give birth to young ones. Accessory reproductive glands are present in human males and females. Related questions What connects the ovaries to the uterus? What are the main parts of the male reproductive system?
What is the condition called that is failure of one or both of the testes to move from the Are there any similarities between male and female reproductive organs? Is it true that male has What are the functions of the epididymis and the seminal vesicles? Which reproductive system is more complex, a man's or a woman's? If I were a sperm, what path would I take through the female reproductive system?
Male of Leptodactylus bufonius inside the constructed terrestrial chamber where the pair will lay their eggs. Bell and co-authors found that when mating occurs away from the main body of water, the mating site is often more private and hidden from competing males. Some frog species mate in the water-containing folds of bromeliad leaves, for example, and males in other species even build volcano-shaped mud nests that they may guard while mating.
The researchers hypothesized that if sexual selection is playing a role in the evolution of these mating behaviors, then in species where competition for fertilizing eggs is fierce males should have larger sperm-producing testes, similar to what has been observed in other animals where male competition for mates is intense. Conversely, males in species with private breeding sites should have smaller testes. Indeed, Bell and colleagues determined that the mass of male testes, which is a proxy for sperm competition, is smaller and less variable in frogs that hide while breeding, indicating they are less vulnerable to other males horning in.
While adult frogs are carnivores, tadpoles can be vegetarians or omnivores. Some are filter feeders that eat algae, and others have teeth and can eat anything from rotting vegetation to other tadpoles. Either way, tadpoles tend to be voracious eaters -- it takes a lot of energy to complete their metamorphosis into frogs. Tadpoles that live in temporary rainwater ponds often become frogs in a couple of weeks.
The process can take months in species that live in permanent lakes, rivers and ponds. But most of the time, the transformation follows the same basic steps. First, the back legs begin to grow. Then, as the front legs are forming, the tadpole's internal organs began to change. It develops a pair of lungs so it will be able to breathe air, and its digestive system changes to accommodate its adult diet.
The tail gradually disappears as it's absorbed into the body. When the froglet is ready to live on land, it usually has a little bit of tail left, but that gradually disappears.
Frog eggs and tadpoles are food for fish, birds and other animals, so most eggs don't survive to adulthood. Adult frogs have several enemies as well, including those that are microscopic. Next, we'll look at some of the threats to frogs' survival and how the absence of frogs could affect human life. This process usually occurs through external fertilization, where the female releases her eggs from her body into water. Then, the male releases his sperm to fertilize them.
However, a few species of frog use internal fertilization. All mammals, including humans, use this process of fertilization. For many years now, scientists have known about a species of fanged frog, Limnonectes larvaepartus , found in the forests of Sulawesi an Indonesian island. However, little was known about how this species reproduced. Inside of the female fanged frog, the researchers found developed tadpoles rather than eggs.
Was it through the more common process of external fertilization? Or internal fertilization? Do they lay eggs on leaves or in water, like most frog species? In a recent expedition to Indonesia, scientists went out to explore streams and other bodies of water.
They searched for these fanged frogs, and caught them with their hands. After catching a number of these frogs, they discovered something unexpected. Instead of eggs, they found tadpoles inside the frogs. The scientists first noticed this while dissecting, or cutting into, the bodies of dead frogs. They did this to better understand the internal structure of the frogs. A close-up view of the tadpoles found inside a female fanged frog.
The scientists also wanted to study the body tissue and DNA from the frogs to map the frogs' genes. This would help scientists to learn the relationship between this frog species and others. In the bodies of some female frogs, scientists found fully developed tadpoles. In one instance, a pregnant female gave birth to live tadpoles on the hand of a researcher who caught her. These tiny tadpoles were mostly clear in color with spots around their bodies.
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