Sexual Dimorphism
Definition: Sexual dimorphism is the biological term for the differences in physical appearance, size, structure, or behavior between the males and females of the same species, other than sexual organs. Sexual dimorphism can develop from evolutionary factors like sexual selection, ecological adaptations, and reproductive roles.
These differences draw attention and often signify something more than the mere differences in sex organs between the sexes. Sexual dimorphism may influence survival, reproduction, and fitness and may manifest in a number of ways (e.g., by size, color, behavior, or physical form such as antlers or tusks). Red, conspicuous male finches and blue jays employ color in the attraction of females, whereas females tend to be dull-colored or to blend in with their environment in order to protect their offspring. There are numerous drivers for the disparities occurring in sexual dimorphism, such as sexual selection, ecological functions, and parental investment. These are the major factors showing how the species evolved to fit into the environment through generation cycles and their reproductive approaches at that point.
Types of Sexual Dimorphism
Sexual dimorphism can be broadly categorized into three main types:
1. Size Differences (Sexual Size Dimorphism)
Different species show different definitions and requirements for Sexual size dimorphism. As concerning spending reproduction time and mating, one of the two genders in most animals is always bigger or smaller than the other. As an example, in most mammals like the lion and the gorilla, the male is bigger, which helps him in winning mates or defending his territory. However, in the case of most spiders and insects, the female is bigger so that she can store eggs and ensure reproduction. Evolutionary changes and the size differences based on ecology, natural selection, and sexual selection are sheer evolutionary pressure on the two genders.
2. Color and Ornamentation
Differences in color and ornamentation in animals are often seen in sexual dimorphism of highly differentiated attributes in males and females of the same species, and have been identified and described in bowers and many other taxa dominated by procedures and patterns of mate attraction, sexual signaling, fitness signaling, and even camouflage. For instance, there are pronounced color differences between the males and females in species of the family Phasianidae: male peacocks are ornamented with exquisite, feathered plumes that are shed and replaced once yearly, while peahens are camouflaged during nesting and brooding, lacking in bright colors. Also, in many examples of birds, fish, and insects, males are often more colorfully attired and gaudily marked than the more cryptically colored females. Predominantly attributed to sexual selection, such differences are characteristics that improve the chances of mating success and are therefore more pronounced in one sex.
3. Structural Differences
That part of sexual dimorphism which deals with the morphological characteristics of the two sexes other than size and color is referred to as structural differences. These differences may include fighting, display, or mating organs, and specialized appendages, which might include horns, antlers, tusks, or other fighting and display organs. Thus, male deer have large antlers to compete with rivals and attract females, which the females lack. Elephant seals exhibit sexual dimorphism in which the males have large, pronounced noses, while the females have smaller and less conspicuous noses. These structural variations are most often the result of sexual selection, where one sex is favored to have greater competing, defending, and reproducing capabilities.
Behavioral Dimorphism
The term behavioral dimorphism encompasses the behavioral differences exhibited by male and female members of the same species, usually in the context of mating, territoriality, or parental care. Behavioral dimorphism is influenced by evolutionary pressures (natural selection) and by the strategies of reproduction. Examples would be songs and dances by male birds to attract females, while females choose a nesting area, caring for young birds. In many mammals, males may show aggression towards one another or defend prospective breeding territory to gain access to mates, while females emphasize nurturing and protect young from harm. Behavioral differences will typically characterize sexual dimorphism, or given how males and females evolve in nature to maximize reproductive success, differential behaviors may be called a behavioral adaptation.
Why Does Sexual Dimorphism Exist?
Sexual dimorphism exists because males and females of a species are frequently exposed to alternative evolutionary pressures in regard to survival and reproduction. When species mate sexually, sexual selection will be one pressure on potential mates. Sexual selection can cause differences in a trait, since traits that facilitate mating success or success in competition (an alternative) appeal more greatly to sexual selection. Male lions, for example, will have more pronounced traits than female lions, such as low-frequency roars and large manes that demarcate their strength in a lion pride, making the male with the most pronounced characteristics better suited to obtain mates. Ecological adaptation is another pressure that can contribute to sexual dimorphism. Males and females may evolve alternative traits to reduce competition over food (or other resources), as seen in some species of birds, where males and females develop different shapes of beaks when competing for different dietary niches. Parental investment has additional evidence for sexual dimorphism considerations – species with high female parental investment evolve traits to protect their offspring from predators and traits that support energy efficiency, whereas male parental investment focuses on traits that would facilitate competition for females or courtship displays. Overall, although males and females will evolve different strategies for reproductive success and survival, sexual dimorphism in shape will evolve because of increased reproductive success and survival for females and males.
Examples.
- Lions- The males have large, thick manes, which make them seem much larger and intimidating, and also protect them in fights. Females do not have manes and are designed for hunting.
- Peacocks- Males have extravagant, colorful tail feathers to attract females. Peahens are drab brown and therefore camouflaged so that they can remain hidden while nesting.
- Elephant Seals- Males can be three times larger than females, and they have an enlarged, inflatable nose used in displays of dominance and fights.
- Mallard Ducks- Males are characterized by bright green heads and colorful plumage, whereas females are dull brown in color, a camouflage for when they are incubating eggs.
- Deer- Males grow antlers, used in fights for mates, but females generally do not.
These are some examples of sexual dimorphism, which offer each sex an adaptation for the reproductive roles and tactics for survival.
