Larval development of Diploptera punctata reared alone and in groups

Journal of Experimental Biology

2012

SUMMARYIn many animal species, social interactions can influence the morphology, physiology and behavior of individuals, including their rate of development and reproduction. Reproduction in cockroaches is regulated by juvenile hormone III (JH), and social interactions have been shown to accelerate female reproduction in the German cockroach, Blattella germanica (L.), by stimulating JH production. However, it is not clear in this or any other insect species whether social facilitation of the reproductive rate occurs throughout the ovarian cycle or only at certain stages. We compared the effects of social interactions during the preoviposition period (when JH production is high) and during gestation (when little JH is produced), as well as during the first ovarian cycle (when females are virgin) and the second ovarian cycle (after females had mated). Social interaction with one conspecific female was sufficient to accelerate JH production and oocyte maturation, but this effect was reversed by crowding. Social interactions also accelerated the onset of sexual receptivity in virgin females. However, social interactions failed to shorten gestation, suggesting that social cues stimulate JH production only when the corpora allata (CA) are active and not when CA activity is suppressed by the central nervous system. Females were most responsive to transient social isolation and transient social interactions when 2-3days old, suggesting that they are particularly sensitive to social interactions when their CA become active. Overall, these results show that all JH-dependent events in the reproductive cycle of B. germanica females are under the strong influence of social interactions.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Differential physiological responses of the German cockroach to social interactions during the ovarian cycle

Uzsák

Journal of Experimental Biology

2012

“…For example, a desert locust (Schistocerca gregaria) nymph reared at high density grows significantly faster than one reared alone (4) and such ''group effects'' (5) have now been characterized in dozens of insect species. In some insect species, the nymphs of several cockroach species (e.g., Diploptera punctata) for instance, interaction between just two individuals is sufficient for expression of a group effect (6,7). Beyond affecting its immediate physiology and development, the social condition of a nymph can influence its adult traits.…”

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confidence: 99%

“…Embryos increase 50-fold in dry mass during gestation (17), as the embryos ingest the nutritive secretion of the uterine lining (18), and at parturition, a brood can exceed its mother's weight by 50% (19). Paired male nymphs of D. punctata usually reach adulthood after just three molts, but they reach adulthood in four molts when isolated (6,7). Therefore, the potential seemed great for a beetle cockroach mother to contribute substantially to phenotypic variation in neonates and possibly influence postnatal development of offspring.…”

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confidence: 99%

“…Beyond affecting its immediate physiology and development, the social condition of a nymph can influence its adult traits. Cricket larvae, for instance, reared in groups of 10 grow faster and become larger adults than those reared alone (8,9), whereas grouped cockroach larvae also grow more quickly than isolated ones but become smaller adults (6,10). Because adult size is often related to fecundity (11) and reproductive success (12), it is expected that group effects would influence individual fitness and, therefore, play a major role in population dynamics, as in locusts, for example (13,14).…”

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confidence: 99%

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Maternal investment affects offspring phenotypic plasticity in a viviparous cockroach

Holbrook

Proc. Natl. Acad. Sci. U.S.A.

2004

Maternal effects, crossgenerational influences of the mother's phenotype on phenotypic variation in offspring, can profoundly influence the fitness of offspring. In insects especially, social interactions during larval development also can alter life-history traits. To date, however, no experimental design, to our knowledge, has manipulated the prenatal and postnatal environments independently to investigate their interaction. We report here that the degree of maternal nutrient investment in developing embryos of the viviparous cockroach Diploptera punctata influences how quickly neonate males become adults and how large they are at adulthood. An offspring's probability of reaching adulthood in fewer than four molts increased with birth weight: the heavier neonates were, consequently, more likely to become smaller adults. Social interaction also affected nymphal development and adult size. Nymphs reared in pairs molted fewer times than solitary nymphs and, thus, became smaller adults. The social effect on developmental trajectory was, however, eliminated by experimentally increasing the level of maternal nutrient investment per offspring, which was accomplished by removing one of the female's paired ovaries (allometric engineering). We conclude that a particular prenatal environment can result in different offspring phenotypes under different postnatal social conditions. By investing more in each offspring, however, D. punctata mothers, because they are viviparous, are able to produce broods with environmentally (socially) independent phenotypes.

Juvenile hormone biosynthesis and oocyte development in adult female Blattella germanica: Effects of grouping and mating

Gadot

Burns

Arch Insect Biochem Physiol

1989

The roles of grouping and mating in modulating the activity of the corpora allata (CA) in adult female cockroaches were investigated using the in vitro radiochemical assay of juvenile hormone (JH) biosynthesis. Isolated virgin females have longer, asynchronous cycles of CA activity and oocyte maturation than do isolated females mated on day8. Three factors were identified as the major contributors to this difference: I) an experimental artifact of selection for sexually receptive females, 2) a positive effect of grouping on J H synthesis and oocyte maturation, and 3) a positive effect of copulation on oviposition and retention of the ootheca. Mated females constitute a subpopulation of receptive females that differ significantly from other females by having higher rates of JH synthesis prior to mating. The relative importance of such selection is substantial when the rate of mating i s low, as in experiments with isolated females that are exposed to males for a short period of time. Long-term exposure of females to males introduces a grouping effect, which obscures any additional effect of mating on CA activity and oocyte development. However, mating influences ootheca formation and its retention. The effect of grouping can be mimicked in isolated females by transection of the nerves connecting the CA-corpora cardiaca complex to the brain, suggesting that in this insect isolation causes brain inhibition of the CA, and grouping provides disinhibitory stimuli that release the CA from brain inhibition.