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Hemotrophic (blood eating) viviparity means embryos develop in the female's (or male's) oviduct and nutrients are provided directly by the parent, typically via a structure similar to, or analogous to the placenta seen in mammals. [10] Examples of hemotrophic fish include the surfperches, splitfins, lemon shark, seahorses and pipefish.
Their development is stimulated by hormones secreted by the pituitary and adrenal glands, and is induced shortly before the breeding season and discarded after. In some species, at least, there is a correlation between the level of androgens present in the endocrine system and the volume and complexity of tubercle growth. [4] [5]
In fish, waves of calcium released direct the process of cell division by coordinating the mitotic apparatus with the actin cytoskeleton, propagating cell division along the surface, assists in deepening the cleavage furrow, and finally heals the membrane after separation of blastomeres.
Evolution is the change in the heritable characteristics of biological populations over successive generations. [1] [2] It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. [3]
Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant males and females will sexually reproduce and have offspring together.
The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1.05 billion years old. [19] [20]Biologists studying evolution propose several explanations for the development of sexual reproduction and its maintenance.
The first step, which is an important prerequisite step in classical polyandry, involves the evolution of male care for eggs. [11] In the second step, females have the ability to produce more clutches than a male can handle, leading to an increase in female fecundity because these females need to find other males to mate with for the remaining ...
Fisheries-induced evolution differs from the Darwinian evolution model by virtue of the direct human factor. [2] For FIE, fishing enforces a greater selection pressure for traits, often through sheer effort and catch numbers, which can disparage natural selection pressures such as predator-prey interactions and environmental influences.