Isopod morph α, β, ϒ

In the Gulf of California, living on intertidal sponges is a species of isopod Paracerceis sculpta, which displays another type of male polymorphism. Males have ,again, three morphs body types that each has variation in reproductive successes depending on what other type of males are present. Living on or in the sponge, three male morphs maybe present: 

ϒ                             β                                  α
The tree male morph types

Large α males that defend harems, smaller β males that mimic females in appearance and behaviour, and minuscule ϒ males that hide themselves within the sponge with large harems. To understand how male-male-male interactions functions, researches observed and alter male densities and recorded their relative reproductive success. The reproductive capability of each male morph was found to be equal, if isolated with females.  However, depending on what male morphs, as well as the number of females, were present the reproductive success changed.  The researches devised a set of rules for matting success (Table 1).

The researchers, after two years of testing and observation, using genetic marks to trace paternity, found these rules to be effective way to explain the interaction. 

Reference 

Shuster, S & Wade, M 1991, 'Equal mating success among males reproductive strategies in marine isopod', Nature, vol 350, pp.608-610.