Parental care is advantageous because it typically increases the survival of genetically related young. In contrast, parental care given to unrelated young incurs no benefit. A further cost of parental investment is that it reduces the future reproductive potential of the caregiver. I examined whether eastern phoebes’ Sayornis phoebe future reproductive effort was related to interspecific brood parasitism by brown-headed cowbirds Molothrus ater in prior broods. In 2000 absolute and relative measures of change in clutch sizes from first to second breeding attempts were similar in parasitized and non-parasitized broods, while the latency to renest was several days shorter for parasitized broods. In addition, the relative change in clutch size was more negative for phoebe nests with more cowbird chicks per brood. In 2001 these statistical relationships between absolute and relative measures of residual effort and prior parasite load were also confirmed in control but not in experimentally manipulated clutches. The experimental data support previous findings that parasitism per se does not seem to influence residual reproductive output of adult phoebe hosts. These data also emphasize that intragenerational residual costs of parental care should be measured by the use of a relative measure of reproductive effort or other statistical methods that take into account the biological and statistical non-independence of clutch sizes from subsequent breeding attempts.
Parental care in which females attend their offspring is recorded in over 30 species of ground beetles. Despite this, there is no quantitative data on the fate of the offspring when the mother is experimentally removed. This paper investigates parental care in Pterostichus anthracinus (Coleoptera: Carabidae). The objectives of the study were to estimate: (1) egg survival when the female is removed; (2) the ability of females to defend their eggs from attack by predators; (3) the ability of females to repair a damaged nest in which egg attendance takes place. In the laboratory, the reproductive activity of P. anthracinus lasted four months (from May till August) and peaked in late June. Mean (± SE) number of eggs in each clutch was 25.25 ± 2.19. All of the egg clutches were guarded by a female. Female attendance had no effect on egg mortality due to microbial attack. The duration of embryonic development lasted on average 5.2–5.3 days, and did not differ between the groups with and without maternal care. In P. anthracinus maternal care is important in preventing egg mortality due to predators. In the laboratory the percentage mortality of eggs without maternal care due to predators was 100%. In the group in which females attended their eggs, percentage mortality of offspring due to predation was about 51%. Female ability to repair damaged nests is important in preventing dehydration and reducing predation pressure. This laboratory study provides the fi rst quantitative data on the importance of maternal care in ground beetles in determining the survival of their offspring.
Nicrophorine beetles use small vertebrate carrion for breeding resource. While Nicrophorus spp. have highly developed biparental care, no form of parental care is recorded for Ptomascopus spp. We examined two effects of resource guarding by Ptomascopus morio. The presence of parents, especially the female, reduced the number of fly larvae on chicken carrion. Parents also enhanced the survival of brood faced with predation by the rove beetle, Ontholestes gracilis. In 6 out of 20 trials, the rove beetle predators were killed by Ptomascopus morio parents. We conclude that Ptomascopus morio has a simple, and possibly primitive form of parental care.
The benefits for offspring of attendant adult were investigated in the stag beetle Figulus binodulus. The initial growth rate of third-instar larva was significantly higher when the larvae were in a nest with adults compared to those in a nest without adults. The difference in growth rate is reflected in adult body size. Although the presence of adult beetle generally benefited the offspring, the adults did eat some of the larvae. Filial cannibalism was the primary cause of juvenile death in nests with adults. Mortality was lower in nests with adults related to the juveniles compared to nests with unrelated adults, suggesting that infanticide of nest mates may be inhibited. These results suggest that F. binodulus has a level of sociality and nest mate recognition that is very rare in stag beetles. Social behaviour may be more advantageous for small stag beetles than fighting.
The subsocial bug Elasmucha dorsalis lays egg masses on the underside of the leaves of female plants of Aruncus dioicus. Each bug straddles her eggs and shields her offspring with her body, until they moult to the 2nd instar. Females that: attended aggregations of 2nd and later instar nymphs feeding on fruit of inflorescences often settled close to the basal part of or just below the aggregation, and faced towards the base of the inflorescence. The nymphal aggregations often Seemed to be too large for females to guard effectively. The position and orientation of females attending 2nd or later instar nymphs probably enabled them to detect predators walking towards the nymphs.
Trophic eggs, which are not viable and eaten by larvae, are produced by the passalid beetle Cylindrocaulus patalis. This is the first record of trophic eggs in subsocial Coleoptera. There are differences in the morphology of trophic and fertile eggs; the former are a paler colour and softer than the latter. The surface of the chorion of trophic eggs is also smoother than that of fertile eggs. The trophic eggs are fed directly by the female parent to 3rd instar larvae following a series of specific behavioural interactions between them, including repeated stridulation by the larva. It is likely that trophic eggs supplement the protein-poor diet of the larvae and contribute to their growth and survival. The production of trophic eggs may be associated with the evolution of an extremely small clutch size in C. patalis.