Exploring the traits that distinguish males and females within animal species can reveal fascinating adaptations. In many species where one male mates with multiple females, males often show a significant difference in body size compared to females.

However, recent research on common hippopotamuses provides new insights that challenge this common pattern. This article will guide Lykkers through the intriguing findings about how male hippos use their physical features in unique ways.

Understanding Gender Dimorphism in Animals

What is Gender Dimorphism?

Gender dimorphism refers to the physical differences between males and females of the same species. These differences are often seen in size or special features like horns, tusks, or bright colors.

Species where males compete for access to several females often display more marked dimorphism, as larger size or weaponry can provide advantages in contests or displays.

Typical Patterns in Large Mammals

In many hoofed animals with polygynous mating systems, males tend to be much larger than females. This size advantage helps in physical confrontations over mates or territory. Alongside bigger bodies, males often develop distinct structures such as antlers or tusks to assert dominance.

New Research on Hippopotamus Morphology

Study Overview

A comprehensive study analyzed morphological data from nearly 3,000 common hippopotamuses collected in the 1960s at a national park in Uganda.

Measurements included body weight, length, shoulder height, jaw mass, and canine tooth size, with details about each individual's gender and age.

Key Findings on Body Size

The results showed that adult males were only slightly heavier and larger than females—just about 5% heavier, 2% longer, and 7% taller. This is a much smaller difference compared to other large species, where males can be significantly bigger.

Jaw and Canine Differences

More striking were the differences in the jaws and teeth. Male hippos had jaws weighing 44% more and canine teeth 81% larger than females. These features stood out as the main physical distinctions rather than overall body size.

Why Large Jaws and Teeth Matter More than Size

Combat and Display Behavior

Male hippos typically engage in fights while submerged in water, where body size is less visible and a heavier frame might reduce mobility. Instead, they rely on the size of their jaws and large canine teeth to establish dominance.

These features are shown off during wide-mouth yawns, which serve as signals of strength to rivals.

Physiological Constraints

The digestive system of hippos may limit the maximum body size they can maintain efficiently. This could explain why increasing body mass is less favored, and why evolutionary energy investment is shifted toward developing large jaws and teeth.

Female Size and Role

Interestingly, young female hippos were found to be slightly larger than young males, differing from many other species. This could be linked to the need for females to protect their young and compete for limited water resources during lean periods.

To Summarize

This research sheds light on the unique way male hippopotamuses demonstrate strength and dominance. Instead of relying on a significantly larger body, males invest in developing powerful jaws and formidable canine teeth that serve as both weapons and visual signals in their watery environment. This adaptation allows for effective competition while maintaining agility underwater.

Meanwhile, female hippos may be relatively larger as an adaptation to their own ecological and social roles. These findings highlight the fascinating diversity of evolutionary strategies in the animal kingdom and remind us that visible size is not always the most important factor in nature's contests.