Sexual Dimorphism in Animals

Sexual dimorphism, as defined by the Merriam Webster’s dictionary, means “a condition of having the two sexes markedly dissimilar in appearance.” In other words, male individuals of a particular species have different morphological traits than the female individuals of the same species. This is displayed in many animals, some you probably recognize, like male and female mallard ducks.

Why are animals sexually dimorphic?

The main goal of any animal is to reproduce, to pass their genes on to another generation. It is what animals are biologically hard-wired to do. Sexually dimorphic traits aid in this reproductive success. These traits can make an animal appear desirable to the opposite sex. An article published in the National Library of Medicine states that there is a greater difference in the morphological traits of mammalian species that are “polygynous, diurnal and open-habitat dwellers.” Polygynous means that one male animal mates with more than one female of the same species, while females will only mate with one male.

Degrees of Sexual Dimorphism

There are varying degrees of sexual dimorphism. Song birds are an easy group of animals to identify as having high degrees of sexual dimorphism, whereas other animals like cats, have a smaller degree.

Examples of Sexually Dimorphic Species

Lions

This one is probably an obvious one. Typically, male lions have a mane, while female lions do not. This mane is a display of a male lion’s dominance, making him more attractive to females. There also tends to be an obvious size difference between the two sexes. Male lions are often larger than female lions. Turpentine Creek Wildlife Refuge (TCWR) is currently home to one male lion, and several female lions. Although none share habitats together, their sexual dimorphism is still apparent.

Tigers

Compared to lions, tigers have a much smaller degree of sexual dimorphism. Tigers do not have one super obvious indicator of sex like the presence of lack of a mane. Instead, their sexual dimorphism lies in their size. The average weight and length of each sex varies depending on the subspecies of lion, however, male tigers are often larger and longer than female lions. At TCWR, the difference in size between male and female tigers can be seen throughout the Refuge, but even in our Discovery Area. Triples Blackfire (male), Peyton (female), and Rocklyn (female) display this sexual dimorphism. And they are normally napping near each other so it tends to be fairly apparent!

Wood Ducks

A common bird found in North West Arkansas that displays significant sexual dimorphism in the wood duck. Wood ducks are a waterfowl species that live in Arkansas year round. The feather coloration of the sexes differs greatly. Male wood ducks have a more vibrant coloration that includes green, orange, yellow, reddish-purple and streaks of blue. Male wood ducks also have red eyes. Female wood ducks are much more gray. Still beautiful with a bit of blue on their bodies, the female wood ducks do not possess the red eyes like male wood ducks do. The coloration that male wood ducks have likely helps to establish themselves as a proper mate for the female wood ducks to reproduce with.

Sexual dimorphism is an interesting topic and can be seen in countless species throughout the animal kingdom. Visit TCWR to see if you can spot the sexually dimorphic traits the residents present here!