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The decline in amphibian and reptile populations has led to an awareness of the effects of pesticides on reptiles and amphibians. [177] In the past, the argument that amphibians or reptiles were more susceptible to any chemical contamination than any land aquatic vertebrate was not supported by research until recently. [ 177 ]
Fertilization is the fusion of gametes to produce a new organism. In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization.
Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, and reptiles. This type of reproduction has been induced ...
Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization of the ovum by a sperm results in the formation of a diploid zygote that develops by repeated mitotic divisions into a diploid adult. Plants have two multicellular life-cycle phases, resulting in an alternation of generations. Plant zygotes ...
During their life cycle, all anamniote classes pass through a completely aquatic egg stage, as well as an aquatic larval stage during which all hatchlings are gill-dependent and morphologically resemble tiny finless fish (known as a fry or a tadpole for fish and amphibians, respectively), before metamorphosizing into juvenile and adult forms ...
Gastrulation in frogs commences in the marginal zone— the region encircling the blastula's equator where the animal and vegetal hemispheres meet—differing from sea urchins where it begins in the most vegetal part. In contrast to the vegetal blastomeres, the endodermal cells in the marginal zone of frogs are smaller and contain less yolk. [2]
The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother. Modes of reproduction include [3] based on relations between zygote and parents: Ovuliparity: external fertilisation, as in arthropods, many bony fishes, and most amphibians
[citation needed] Internal fertilization with many vertebrates (such as all reptiles, some fish, and most birds) occurs via cloacal copulation, known as cloacal kiss (see also hemipenis), while most mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization. [3] [4]