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Sexual Dimorphism Facts & Worksheets

Sexual dimorphism is the difference between members of different sexes of a species. Both sexes exhibit physical differences when there is sexual dimorphism.

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Sexual dimorphism is the difference between members of different sexes of a species. Both sexes exhibit physical differences when there is sexual dimorphism. Sexual dimorphism causes variances in traits, including eye size, fur color, plumage length, and height, as well as other traits. There must be more to these variations than just the difference in sexual and reproductive organs.

See the fact file below for more information on Sexual dimorphism, or you can download our 27-page Sexual dimorphism worksheet pack to utilize within the classroom or home environment.

Key Facts & Information

ETYMOLOGY

  • The Greek roots of the term “dimorphism” are “dis,” which means “twice,” and “morphe,” which means “form” or “shape.“
  • Therefore, “sexual dimorphism” refers to the existence of two sexually different forms. The males of the same species display characteristics that distinguish them from the females.
  • In the case of sexual monomorphism, the opposite is true. The term “sexual monomorphism” (from the Greek “mono,” meaning “one”) refers to the lack of sexual differentiation between men and females of the same species other than genitalia.

WHAT CAUSES SEXUAL DIMORPHISM?

  • On Earth, there are far too many species of animals with sexual dimorphism to list them all. Invertebrates generally exhibit less sexual dimorphism than vertebrates. Birds exhibit some of the most well-known instances of sexual dimorphism.
  • Genetics, which is often exhibited through sex chromosomes, is the primary factor in sexual dimorphism. In many instances of sexual dimorphism, men and females of vertebrate animals have one X and another Y chromosome, while females have two X chromosomes. In many invertebrate species, men have two sex chromosomes, whereas females have one.
  • Hormones are another factor. Different hormone concentrations in each sex distinguish them. Additionally, a high level of testosterone in the brain during the embryonic development of some species will cause them to develop as a female.
  • Food is yet another essential component for the healthy growth of secondary sexual traits that give rise to dimorphism. Poor dimorphism and poor nutrition in an animal will make it less likely to attract the opposite sex.
  • Finally, in certain species that do not exhibit sexual dimorphism the rest of the year, the season of the year and the mating season cause dimorphism to manifest.
  • Dimorphism between sexes occurs as a result of evolution. The genetic makeup of males and females is determined by natural selection. The challenges that the sexes experience in ecosystems have caused them to evolve differently.

SEXUAL SELECTION

  • The natural selection that occurs when one sex favors particular traits in animals of the other sex is known as sexual selection. This desire boosts the reproductive success of animals who possess the preferred trait, as is the case with all forms of selection.
  • Working with Charles Darwin’s theory of sexual selection, which claimed that some evolutionary adaptations were made specifically to help people compete with one another for mates, scientists have devised a number of alternative ways to think about the evolution of desire and characteristics.
  • Intersexual selection occurs when animals of one sex prefer partners of the other sex while making mating decisions. An example is when female peacocks decide to mate with the male who has the brightest plumage. This kind of selection frequently produces characteristics in the chosen sex that do not improve survival but are those characteristics that are most desirable to the opposite sex.
  • Intrasexual selection occurs when specie members of the same sex compete for mates. An example includes intense mating rituals like rams butting heads and mating displays; the victor of these fights is the one who can mate. Numerous of these rituals require a significant amount of energy but choose the fittest, strongest, and/or most dominant individuals for mating.
  • Females can directly improve their reproductive success when picking a mate by mating with certain chosen males and reaping the rewards. By selecting healthy males, females can, for instance, increase their availability of food, get protection from obnoxious males, assist with child-rearing, and prevent contracting parasites or other diseases.

ANIMAL COURTSHIP

  • The simplest approach to comprehending the many forms of sexual dimorphism is to see how animals interact with one another and their lifestyle.
  • One of the most amazing ecological processes is courtship, or the process by which an animal chooses and competes for his or her partner to reproduce with.
  • Males work arduously to show their strength, general health, and mate-attractiveness, even if the trait varies greatly, from performing an articulate dance by flailing the bluest of feet (Blue-Footed Bobbies) to building sophisticated seduction nests (Bowery Bird).
  • According to the “good gene” model of sexual selection, females choose partners who exhibit genuine signs of the male’s capacity to transmit genes that will increase their offspring’s likelihood of future survival and reproductive success.
  • According to the Handicap Hypothesis, some sexual adornments are damaging to males but have gained appeal because they let females know that a male can handle them. For instance, a bird’s vivid colors render it exceedingly prey-vulnerable. Therefore, the vivid feathers may be a true indication of the ability to survive despite the disadvantage.
  • Another theory, known as Sensory-Bias, contends that males have evolved characteristics that draw women’s attention through the use of specific hues, tones, and shapes that appeal to their senses. For instance, male guppies with prominent orange spots tend to attract female guppies more, which may be related to an innate sensory bias of food detection.

SEXUAL SIZE DIMORPHISM

  • The difference in size between males and females of the same species is known as sexual size dimorphism, and it is frequently caused by one or more mechanisms of sexual selection. Different patterns of between-species size dimorphism can develop when these processes occur in closely related species; one of these patterns is known as “Rensch’s Rule.”
  • According to Rensch’s Rule, in species where males are the larger sex, the degree of sexual size dimorphism increases with body size, and the opposite is true in species where females are the larger sex.
  • Another example of this pattern is “adaptive canalization,” in which the larger sex is less flexible than, the smaller sex. This is because animals with sub-optimal body sizes will be less fit due to directional selection for a large body size.
  • In contrast, condition dependence may exist, where the larger sex is more strongly selected for a greater size and is more susceptible to environmental influences than the smaller sex. This suggests that sexual size dimorphism should alter as circumstances change. The patterns and processes behind sexual size dimorphism are now better-understood thanks to these theories and studies.
  • Reverse sexual dimorphism is a word used to describe situations in which females are larger. Particular birds and various types of insects are frequently some of the most notable examples of this. Sexual selection favoring small size in males and restrictions on the reduction of size in females due to some aspect of reproduction may have led to the evolution of reverse sexual dimorphism.

EXAMPLES OF SEXUAL DIMORPHISM IN MAMMALS

  • The mandrill is frequently cited as the mammal species with the greatest sexual dimorphism. One of the first things you’ll notice when comparing males and females is that males have more colorful coloration on their faces and behinds. Males within the same group can even be distinguished from one another, with the dominant adult male displaying the brightest red.
  • Studies have indicated that lionesses are more likely to choose a mate who has a black, thick mane and that the characteristic bushy manes of African lions are strongly linked to the process of sexual selection. The only cats that display sexual dimorphism are lions. Further research refuted the hypothesis that males’ manes evolved to shield their necks in confrontations with other males; instead, it was shown that when lions engage in combat, they usually aim for the back and hips. It is now believed to be just a representation of male fitness. Additionally, male lions can weigh up to twice as much as lionesses.
  • Some of the biggest animals on the planet are baleen whales. An animal’s body weight is supported by water in the ocean, giving it the possibility to grow larger than it would on land. Whales can benefit from the seasonal high food productivity because of their large size. They can consume vast quantities of food at once—more calories than they can burn—and store that energy as blubber.
  • The sexes of white-tailed deer differ in both secondary and primary sexual features, which is referred to by scientists as “sexual dimorphism.” One excellent illustration of a sex difference in whitetail deer is the fact that males typically acquire antlers while females do not.

Sexual Dimorphism Worksheets

This fantastic bundle includes everything you need to know about Sexual Dimorphism across 27 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about Sexual Dimorphism. Sexual dimorphism is the difference between members of different sexes of a species. Both sexes exhibit physical differences when there is sexual dimorphism.

Complete List of Included Worksheets

Below is a list of all the worksheets included in this document.

  1. Sexual Dimorphism Facts
  2. Hidden Word-phism
  3. Sexually True
  4. Dimorphism Twist
  5. Cuddle the Cuttle
  6. Size Matters
  7. Animal World
  8. How Romantic!
  9. Lady’s Choice
  10. Difference
  11. The World of Pets

Frequently Asked Questions

What is sexual dimorphism?

Sexual dimorphism refers to the differences in physical characteristics between males and females of the same species. These differences can include size, shape, coloration, behavior, and other traits.

Why do some animals exhibit sexual dimorphism?

Sexual dimorphism can arise due to a number of factors, including sexual selection, competition for mates, and differences in parental investment. For example, male animals may evolve larger body size or more elaborate ornamentation to attract females, while females may evolve traits that make them better caregivers.

Which animals exhibit the most extreme sexual dimorphism?

There are many examples of animals with extreme sexual dimorphism, but some of the most well-known include peafowl (where males have large, colorful tail feathers), anglerfish (where males are much smaller and attach themselves to the females), and elephant seals (where males are much larger than females and compete for access to breeding females).

Can sexual dimorphism be influenced by environmental factors?

Yes, in some cases, environmental factors such as diet, temperature, and social structure can influence the development of sexual dimorphism. For example, in some species of reptiles, the sex of an individual is determined by the temperature at which the egg is incubated.

What are the potential drawbacks of sexual dimorphism?

While sexual dimorphism can provide advantages to males or females in terms of reproduction and survival, it can also have drawbacks. For example, in species where males are much larger or more aggressive, females may face higher rates of injury or mortality during mating. Additionally, traits that make males more attractive to females may also make them more vulnerable to predation or other environmental pressures.

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