In northern elephant seals, body size is determined by at least 8 genes. Males compete for territories on the beach and larger males are more likely to win fights. In this example, inheritance of body size is , intrasexual selection on male body size is , which results in in mean male body size in subsequent generations.

polygenic / directional / increases

Explanation:

The complete question is given below :

In northern elephant seals, body size is determined by at least 8 genes. Males compete for territories on the beach and larger males are more likely to win fights. In this example, inheritance of body size is , intrasexual selection on male body size is , which results in in mean male body size in subsequent generations.

pleiotropic / directional / increases

epistatic / disruptive / decreases

polyallelic/ stabilizing/ no change

polygenic / directional / increases

polygenic / disruptive / decreases

When several genes interact with each other in an additive manner to govern a given phenotype then such an inheritance pattern is called as polygenic inheritance.In the given case, there are at-least 8 genes which are governing the body size of the elephant seals and hence, this is a type of polygenic inheritance. When in natural selection a given type of extreme phenotype is selected over other phenotype and there is a shift away from the average to an extreme phenotype then this is known as directional selection.In the given case, larger males are more likely to win in fights and since, a larger body size is conferring an advantage for survival it will be selected for and thus, an increase in this extreme phenotype would occur. Therefore, intrasexual selection on male body size is an example of directional selection.Now as the directional selection would favour an increased body size the average weight of the elephant seals would increase and hence, in subsequent generations the mean male body size would increase.

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