Parental Care in a Nest or Burrow

Nests and burrows typically reduce the biological hazards of the external environment and reinforce social behavior (Hansell, 1993). The structures offer protection from natural enemies and act as a buffer against temperature and moisture fluctuations. In subsocial cockroaches found in nests, one or both parents also actively defend the galleries against predators and conspecific intruders. Because these cockroaches nest in or near their food source (wood, leaf litter),parents can forage without leaving or carrying their offspring. Australian soil-burrowing cockroaches nest only where their food source is ample and forage close to the entrance (Macropanesthia), and so are absent from their family for only brief periods of time (Rugg and Rose, 1991; Matsumoto, 1992). Females

Fig. 8.6 Maternal care in an unidentified apterous cockroach collected in Namibia, ventral view. The female was clinging to a rock, with the elongated edges of the tergites serving to raise her venter above the substrate and form a brood covering "cup." The presence of ants (upper-right quadrant) in this field photo suggests that the behavior functions to defend young nymphs, although it is possible the female also supplies them with nutriment. Photo and information courtesy of Edward S. Ross.

with young are quite aggressive (D. Rugg, pers. comm. to CAN).

Biparental care in a nest arose at least twice among wood-feeding cockroaches: in the ovoviviparous Panes-thiinae and in the oviparous Cryptocercidae. These insects typically nest in damp, rotted logs, utilizing the wood itself as a food source; consequently, the young are never left untended. A wood-based diet may warrant the cooperation of both parents; wood-feeding has favored paternal investment not only in cryptocercids and some panesthiines, but also in passalid and scolytid beetles (Tallamy and Wood, 1986; Tallamy, 1994).

Cryptocercus is the only known oviparous cockroach with well-developed parental care, and is discussed in Chapter 9 in the context of its sister group relationship to termites. A recent study found that adult presence has a significant effect on offspring growth in families of C. kyebangensis (Park and Choe, 2003a), but the relative influence of parental care and group effects are yet to be determined. In gregarious Periplaneta, for example, single nymphs raised with adults grow and develop as rapidly as grouped nymphs (Wharton et al., 1968). All studied species in the wood-feeding blaberid genus Salganea live in biparental families (Matsumoto, 1987; Maekawa et al., 1999b, 2005). In Sal. taiwanensis, nymphs cling to the mouthparts of their parents and take liquids via sto-modeal feeding (Fig. 8.3B). Removal of neonates from parental care results in high mortality; removed nymphs that live have a significantly longer duration of the first instar (T. Matsumoto and Y. Obata, pers. comm. to CAN).

Two different social structures have been reported for Australian wood-feeding panesthiines: both family groups and aggregations. Shaw (1925) reported that both Panesthia australis and Pane. cribrata (= laevicollis) live in family groups consisting of a pair of adults and nymphs in various stages of development. Matsumoto (1988) more recently studied Pane. australis, and found that of 29 social groups collected, the majority were families: 14 consisted of a female with nymphs, two were a male with nymphs, and two were an adult pair with nymphs. Groups never contained more than a single adult of either sex or an adult pair together with nymphs. The age of nymphs in the group ranged widely, however, so it is possible that the nymphs in these groups were aggregated individuals rather than a sibling group (T. Matsumoto, pers. comm. to CAN). The field studies of H. A. Rose (pers. comm. to CAN) indicate that neither Pane. australis nor any of the other wood-feeding Australian panesthiines are subsocial. Rugg and Rose (1984b) and O'Neill et al. (1987) found that while adult pairs with nymphs could be found in Pane. cribrata (12% of groups), the most commonly encountered groups (29%) were harems, consisting of a number of adult females, together with a single

Fig. 8.6 Maternal care in an unidentified apterous cockroach collected in Namibia, ventral view. The female was clinging to a rock, with the elongated edges of the tergites serving to raise her venter above the substrate and form a brood covering "cup." The presence of ants (upper-right quadrant) in this field photo suggests that the behavior functions to defend young nymphs, although it is possible the female also supplies them with nutriment. Photo and information courtesy of Edward S. Ross.

adult male and a number of nymphs. A possible reason for these discrepancies is that social structure in this genus may vary with habitat and population density. Harems seem to be common in areas of high population density, while family groups are generally found in marginal environments, or on the outer fringes of areas with high population density (D. Rugg, pers. comm. to CAN).

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