Selective advantage of pleomorphic maleSancassania berlesei(Michael) (Acari: Acaridae)

Status-dependence and morphological trade-offs in the expression of a sexually selected character in the mite, Sancassania berlesei

“…These experiments show that direct social interaction and assessment is not necessary for individuals to judge their status for future morph determination. The treatment with higher levels of colony pheromone did have fewer fighter males, this result is consistent with previous findings showing chemical suppression of this morph (Timms et al, 1981;Radwan, 1993b). In the present study, we were able to test whether chemical suppression is a mechanism independent of that linking male morph and condition.…”

“…Individuals therefore have to have a decision rule, or algorithm, whereby they assess their status relative to other individuals in the population. In S. berlesei the morph determination is known to be influenced by chemical cues given off by the colony (Timms et al, 1980), such that fighter morphs can be completely suppressed under conditions of high density or expressed by all males under conditions of low density (Timms et al, 1981;Radwan, 1995). The adaptive significance of fighter expression in small colonies has been demonstrated in terms of a fitness advantage to fighters, in which males can kill all their rivals and dominate a number of females (Radwan, 1993a).…”

“…All these changes are relatively small. In this paper, we examine the developmental algorithm in a species in which fitness functions strongly depend on population parameters (Radwan, 1993a), resulting in radical shifts in male morph ratio between high and low density populations (Timms et al, 1980(Timms et al, , 1981Radwan, 1993bRadwan, , 1995.…”

Male morph determination in two species of acarid mites

“…Timms et al (1980) showed that, contrary to Woodring's (1969) claim, the fighter morph was not observed in stock cultures of C. berlesei and was suppressed by airborne substances from dense cultures. They also found that male morph was not heritable (Timms et a!., 1981). However, they selected as parents nonfighter males from dense colonies, whereas fighters were obtained by isolating individual larvae.…”

“…Male polymorphism occurs in several species of the mite family Acaridae (Acari: Astigmata) (Hughes, 1976;Woodring, 1969), yet only a few studies have addressed the problem of male morph determination (Foa, 1919;Woodring, 1969;Timms et a!., 1981), giving often contradictory results. In most of the polymorphic species, there are two male morphs: fighter morphs have a thickened and sharply terminated third pair of legs which are used to puncture the cuticle of other males, while nonfighter morphs have unmodified legs. However, Woodring (1969) describes four male morphs that occur in Acaridae, two of which are differentiated on the basis of the body shape.…”