The reproductive biology of Ptomascopus morio, a brood parasite of Nicrophorus

Abstract

Nicrophorine beetles (Nicrophorus and Ptomascopus spp.) use small carcasses as a food source for young, a breeding ecology distinct from other silphid beetles. While adaptations to the use of small carcasses are well known for Nicrophorus (emitting sex pheromone, burying, rounding and removing hair from carcasses, regulating brood size, regurgitating to young, and preventing predation), there is little information regarding its sister group, Ptomascopus. Like Nicrophorus, Ptomascopus morio males emit pheromone to attract females. In the absence of carrion competitors Ptomascopus morio parents were found to stay with a carcass and their brood for up to 10 days. We tested six hypotheses to examine whether young bene®t from this long period of parent±offspring contact. (1) There was no evidence that parents buried or otherwise pre-empted carcasses to reduce competitive pressure. (2) We found no evidence that parents in¯uenced the decomposition of the carcass. This was supported by experimental manipulations in which brood production (number of larvae and total brood mass) was no greater on carcasses on which parents were present than on carcasses not`prepared' by parents. In addition, the carcass was not rounded and little hair was removed by the adults. (3) The presence of parents bene®ted the brood by reducing the negative effects of competition with carrion¯y larvae. This likely resulted from predatory feeding by adult beetles. (4) Females adjusted clutch size to the size of the carcass. Parents, however, did not make a second adjustment in brood size after young reached the larval stage (®lial cannibalism), as occurs in Nicrophorus. (5) Although parents were observed to open feeding holes in the carcass, this was not necessary for normal larval growth and survival. Parents were not observed to feed young directly by regurgitation. (6) Lastly, parents did not reduce predation on their brood when a conspeci®c intruder was present. These ®ndings suggest that after the female parent adjusts clutch size to the size of the resource, the only parental bene®t is clearing the carcass of¯y larvae. Other differences with Nicrophorus include an extended period of oviposition (5 days) and less pronounced changes in ovarian mass and juvenile hormone titers in response to discovery of a carcass. In a ®eld experiment in Kyoto, Japan, 17 of 21 broods of N. concolor during August contained larvae of P. morio. Mixed Nicrophorus±Ptomascopus broods were less common at other times of the year and when N. quadripunctatus occupied carcasses. In the laboratory, P. morio was able to parasitize 19 of 20 broods of N. concolor. The pattern of oviposition, the absence of explicit parental behaviours, and the interactions with N. concolor in the ®eld suggest that Ptomascopus morio is a brood parasite of Nicrophorus.

Mating competition and parentage assessment in Ptomascopus morio (Coleoptera: Silphidae): A case for resource defense polygyny

“…In all Nicrophorus species studied, large males win contests (Bartlett & Ashworth, 1988;Otronen, 1988), as in P. morio males (Suzuki et al, 2005). Male P. morio copulate many times (Suzuki et al, 2005) and oviposition continues over 4 days (Trumbo et al, 2001). Thus, if another male usurps the carcass he can copulate with the female and sire some offspring.…”

“…Thus it can be concluded that most mating in P. morio occurs before the larvae hatch. Trumbo et al (2001) reported that P. morio males are present on or near the carcass more often than females before the larvae eclose, whereas females are more often on or near the carcass after the larvae eclose. This pattern of male presence coincides with frequency of aggression, Fig.…”

“…They use vertebrate carrion as food for their larvae (Peck, 1982) but may also use large carcasses, although this has not been documented. Males emit pheromones to attract females (Trumbo et al, 2001) and try to monopolize carcasses, but the females do not (Suzuki et al, 2005). Females often refuse to copulate with small males (Trumbo & Sikes, 2000).…”

“…The presence of parents reduces the negative effects of competition with fly larvae (Trumbo et al, 2001). However, unlike Nicrophorus they do not control carcass decomposition, regurgitate food for their larvae, or adjust clutch size (Peck, 1982;Trumbo et al, 2001). Nevertheless P. morio parents may stay with a carcass and their broods for more than 10 days.…”

“…Nevertheless P. morio parents may stay with a carcass and their broods for more than 10 days. (Trumbo et al, 2001).…”