When two individuals mate, they can produce up to one hundred eggs each. Self fertilization is common in animals that have limited mobility or are not motile, such as barnacles and clams.įigure 43.5 Many snails are hermaphrodites. Hermaphrodites may self-fertilize or may mate with another of their species, fertilizing each other and both producing offspring. Invertebrates such as earthworms, slugs, tapeworms and snails, shown in Figure 43.5, are often hermaphroditic. Hermaphroditism occurs in animals where one individual has both male and female reproductive parts. However, in the animal kingdom, there are many variations on this theme. As humans, we are used to thinking of animals as having two separate sexes-male and female-determined at conception. This can be an adaptive advantage in unstable or unpredictable environments. Sexual reproduction produces offspring with novel combinations of genes. Sexual reproduction is the combination of (usually haploid) reproductive cells from two individuals to form a third (usually diploid) unique offspring. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males. Although more common in plants, parthenogenesis has been observed in animal species that were segregated by sex in terrestrial or marine zoos. Some vertebrate animals-such as certain reptiles, amphibians, and fish-also reproduce through parthenogenesis. If eggs are fertilized, diploid females develop, and if the fertilized eggs are fed a special diet (so called royal jelly), a queen is produced. Bees use parthenogenesis to produce haploid males (drones). Parthenogenesis occurs in invertebrates such as water fleas, rotifers, aphids, stick insects, some ants, wasps, and bees. The resulting offspring can be either haploid or diploid, depending on the process and the species. Parthenogenesis is a form of asexual reproduction where an egg develops into a complete individual without being fertilized. Note that in fragmentation, there is generally a noticeable difference in the size of the individuals, whereas in fission, two individuals of approximate size are formed. The large arm, a fragment from another sea star, is developing into a new individual. Some sea anemones and some coral polyps ( Figure 43.2) also reproduce through fission.įigure 43.4 Sea stars can reproduce through fragmentation. This process occurs, for example, in many asteroid echinoderms through splitting of the central disk. In other organisms, part of the individual separates and forms a second individual. Some unicellular eukaryotic organisms undergo binary fission by mitosis. After a period of growth, an organism splits into two separate organisms. Fissionįission, also called binary fission, occurs in prokaryotic microorganisms and in some invertebrate, multi-celled organisms. There are a number of ways that animals reproduce asexually. Asexual ReproductionĪsexual reproduction occurs in prokaryotic microorganisms (bacteria) and in some eukaryotic single-celled and multi-celled organisms. Species that reproduce sexually must maintain two different types of individuals, males and females, which can limit the ability to colonize new habitats as both sexes must be present. The genetic diversity of sexually produced offspring is thought to give species a better chance of surviving in an unpredictable or changing environment. An additional advantage of asexual reproduction is that colonization of new habitats may be easier when an individual does not need to find a mate to reproduce.ĭuring sexual reproduction the genetic material of two individuals is combined to produce genetically diverse offspring that differ from their parents. On the other hand, the rapid rates of asexual reproduction may allow for a speedy response to environmental changes if individuals have mutations. In an unstable or unpredictable environment asexually-reproducing species may be at a disadvantage because all the offspring are genetically identical and may not have the genetic variation to survive in new or different conditions. In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly. Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. Both methods have advantages and disadvantages. Describe advantages and disadvantages of asexual and sexual reproductionĪnimals produce offspring through asexual and/or sexual reproduction.By the end of this section, you will be able to do the following:
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