BEYOND MONOGAMY - TERRITORY QUALITY INFLUENCES SEXUAL ADVERTISEMENT IN MALE BURYING BEETLES

Burying beetles, Nicrophorus defodiens, reproduce on vertebrate carcas ses, and the number of beetles of either sex on a carcass is known to be highly variable. Field and laboratory studies were conducted to exa mine how sexual advertisement by males is affected by resource quality and number of mates, and to determine the reproductive output of male s in different breeding associations. Carcass size had a strong influe nce on the reproductive benefits of polygyny to males, and on male sex ual advertisement. In the field, polygynous groups produced more young and a greater brood mass than monogamous or polyandrous groups when u sing a large carcass (40-60 g). On a small carcass (15-18 g), however, no differences in reproductive output between the three breeding asso ciations were found. In light of these findings, advertisement for mat es was monitored when males were provided: (1) a small carcass and one female; (2) a large carcass and one female; and (3) a large carcass a nd four females. Most males that were paired with a female on a large carcass released pheromone even after copulating with the resident fem ale. Pheromone emission was rare, however, in males that were paired w ith a single female on a small carcass, or in males that were given ac cess to four females. Male N. defodiens thus assess both resource qual ity and number of mates when deciding whether to emit pheromone, and t his decision appears to agree with the reproductive interests of males but not necessarily that of resident females.