Biological Sex and Sexual Behavior
We cannot discuss sexual behavior in animals without acknowledging that
biological sex and sexual behavior are interconnected. Many species have
more than two sexes, can change sex, reproduce asexually, are
hermaphroditic, or develop secondary sex characteristics that are not
the expected phenotype of their “biological sex.”
For example, many fish species are sequential hermaphrodites and change
from male-to-female, female-to-male, or alternate between male and
female \cite{Gemmell_2019}. There are many advantages to this
lifestyle. \citet{z} writes that larger females are more fertile
than smaller females, so the largest male will change to a female. This
happens in clownfish and is also known as protandry. Larger males can
also be more dominant, which is advantageous to fish that change from
female to male. This is called protogyny, a strategy several parrotfish
species use \citep{z}. Fish that can change between male and
female have the most advantage, as they just have to find a mate and can
change to the sex needed for reproduction.
There are also numerous examples of species with more than one type of
male and female. The bluegill sunfish displays three types of males and
one type of female. \citet{1991} describes that each male sex has a
distinct size, coloration, and behavior. One of these male sexes is seen
as the “feminine male” as it schools with other females and displays
courtship behaviors with the other types of males
\citep{1991}. \citet{roughgarden2004} theorizes that the “feminine male” appears less threatening
than the larger males and can protect other males trying to mate.
Therefore, the female often chooses this type of male to mate with.
Another interesting example of a species with multiple types of males
and females is the White-throated sparrow. \citet{k2017} describes the
more aggressive and territorial males and females as having a white
stripe on their heads, while the less aggressive males and females have
a tan stripe. These four phenotypes even have distinct genetic
differences - meaning this species has four different sexes.
These are just a few examples of animals that differ from our perceived
norm of two distinct sexes - male and female. In reality, animals with
two distinct sexes that form monogamous male-female relationships are
the minority. Only 3-9% of mammals have been observed as socially
monogamous species, meaning they find life-long partners and typically
raise offspring together \cite{Lambert_2018}. Social monogamy differs
from genetic monogamy. Researchers have observed species once considered
socially monogamous to rear offspring with different genetics than the
original pair. In other words, a male and female bonded together will
still reproduce with other males and females outside their pair.
Currently, no documentation or evidence suggests that any species is
genetically monogamous \cite{Ophir_2008}.
This information is an important find as the heteronormative society we
live in today expects one male and one female to pair and mate for life.
Any sexual activity outside this pair is considered infidelity, yet it
is common amongst socially monogamous species. Based on this
information, heteronormative monogamous relationships should not be the
baseline for discussing sex and gender, as most animal relationships
observed do not fit the criteria for a heterosexual monogamous pair.