10.3 Polyandry

Many seahorse species are polyandrous, from the prefix “poly-” meaning many, and “andro” meaning male. In other words, one female mates with multiple males over her lifetime. While this mating system is relatively uncommon within the animal kingdom, it has been observed in birds, fish, insects, and even some mammals.

Polyandry often arises in species that require some parental care, but one adult is sufficient, in order to address a high offspring mortality rate. The high mortality rate necessitates a higher reproduction rate to offset high mortality. Additionally, polyandrous species tend to have more males than females, but adults are generally spread out and at low density in their environment.

Females, who require more energy to produce their large gametes, will mate with multiple males, who then, in turn, take care of the young in the early stages of their life. This provides the young with parental protection, but allows the females in the species to continue to reproduce. After copulation, females deposit fertilized eggs into the male parent’s brood pouch and leave to find more males to mate with, allowing for more fertilized eggs, and therefore offspring. This system increases the possible total number of offspring for females, which otherwise is typically much lower than males.

Under polyandry, males gain the benefit of getting to mate and raise offspring at least once in their life, allowing their genes to pass on to future generations. In other mating systems, such as polygyny, not all males get to mate. In polyandry, virtually all males produce offspring.

Polyandrous Jacanas

^[1]

Jacanas, a wading bird, are well-known for their unique mating system among avian groups. Many other birds are monogamous or polygynous, which we will discuss later in this chapter. Jacanas are one of a few polyandrous bird species, and therefore exhibit some unique behaviors. While the females spend energy on finding new mates and producing eggs, the males take over parental care. The offspring live under the careful care of the males until they are old enough to fend for themselves. By distributing themselves around a territory and carrying the young under their wings, the males are able to defend themselves and their offspring from predators. This does make for an odd scene, as seen in the video below! This mating system works well when offspring mortality rates are high; with the male keeping a watchful eye on the offspring they are protected, and the females can invest energy in producing more offspring than species in which female parental care is a stronger requirement.