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Dwarf Males
Sexual dimorphism occurs when one sex (gender) is typically larger than another. We are most familiar with this condition in mammals where usually males are, on average, larger than females. In our species, that size difference is approximately 10% in terms of body mass. In many other organisms, including some molluscs, the dichotomy is reversed and amplified. Females are much larger, and miniturized (dwarf) males are housed within or upon the female's body. This typically occurs when population densities are very low due to a spatially restricted and discontinuous habitat. We find this for example in some small commensal marine clams. |
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The figure on the left shows a typical male (M) and female (F) Pseudopythina rugifera.. This species of marine clam is found commensally with burrowing mudshrimp and polychaete worms off the west coast of North America. Note (left) the huge male-female size disparity. The tiny male lives within the mantle cavity of the female and is completely dependant on her for food and shelter. |
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At left is a close-up of the dwarf male Pseudopythina rugifera.Note the large suckerlike foot (f) for moving around the female host. Note also the whitish portion of the body mass (t). This is the male gonad, the testis. Although small, this animal is sexually mature. In this species the tiny male has a complete, though miniturized, anatomy. In other cases the dwarfed male may physically fuse with the female host and degenerate into a functional testis, secondarily losing all other aspects of its anatomy. |
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