Cooperative nest building and brood care by nestmates and non nestmates in Ropalidia marginata: implications for the evolution of eusociality

In the primitively eusocial wasp, Ropalidia marginata, low levels of intra-colony genetic relatedness, lack of intra-colony kin discrimination and acceptance of young wasps into alien colonies, prompted us to investigate whether or not there exists a cost of such high genetic variability. Freshly eclosed wasps were paired either with their nestmates or with their non nestmates and their performance in nest building and brood care were compared. There was no demonstrable difference between nestmate and non nestmate pairs in terms of success in raising adult offspring, time required for nest initiation, brood developmental period and productivity. There was also no difference in the efficiency of cooperation and division of labour between the nestmate pairs and non nestmate pairs. These results reinforce the idea that the haplodiploidy hypothesis is insufficient to explain the prevalence of worker behaviour in R. marginata and emphasize the importance of factors other than genetic relatedness in the evolution of eusociality

Corolla Morphology Facilitates Both Autogamy and Bumblebee Pollination in Mimulus guttatus

The showy corolla of Mimulus guttatus is generally considered an adaptation to attract pollinators. We use phenotypic manipulations to demonstrate that corolla morphology plays a critical mechanical role in both outcrossing and self‐fertilization. In the absence of pollinators, the lower portion of the corolla facilitates autogamy by retaining pollen released from the anthers. A substantial portion of self‐fertilization seems to occur late in the floral life span as the stigma contacts the corolla. When pollinators are present, the corolla facilitates outcrossing before, during, and after insect visitation. A large fraction of cross‐pollen is actually captured by the corolla and not by the stigma. This “indirect” pathway for pollen reception suggests that a large fraction of cross‐pollination in M. guttatus actually occurs long after a pollinator departs from a flower

Social organization in experimentally assembled colonies of Ropalidia marginata: comparison of introduced and natal wasps

In the primitively eusocial wasp, Ropalidia marginata worker behaviour cannot be explained satisfactorily by the haplodiploidy hypothesis due to the existence of polyandry, serial polygyny and movement of wasps between nests, which reduce intra-colony genetic relatedness to levels lower than the value expected between a solitary foundress and her offspring. We introduced wasps eclosing from one set of colonies into other colonies separated by a distance of 10 km or more, to examine the possibility of kin recognition and task specialization under conditions of low intracolony relatedness. Introduced wasps were readily accepted into unrelated foster colonies, where they performed most of the behaviours and tasks shown by the natal wasps. We found no evidence of kin recognition or task specialization among natal and introduced wasps. Introduced wasps sometimes became replacement queens in spite of the presence of natal wasps. Taken together with previous observations, these results lend support to the idea that factors other than genetic relatedness must play a prominent role in the evolution of worker behaviour in Ropalidia marginata

Factors affecting the acceptance of alien conspecifics on nests of the primitively eusocial wasp, Ropalidia marginata (Hymenoptera: Vespidae)

In the primitively eusocial wasp, Ropalidia marginata,individual females are known to drift from one newly founded nest to another. In the laboratory, young (< 6- to 8-day-old) alien wasps are accepted onto unrelated colonies, while older (> 6- to 8-day-old) wasps are not. Here we have investigated the factors that could influence the acceptance of foreign conspecifics onto unrelated nests. Individually marked wasps of different ages, isolated immediately after eclosion from the natal nest and from each other, were introduced onto unrelated recipient nests. Considered separately, both age and ovarian condition seemed to influence the probability of acceptance as well as the levels of aggression and tolerance received by the introduced wasps. However, partial correlation analysis and multiple regression analysis indicated that only age had a direct influence and that the ovarian condition acts only through age, a variable with which it is highly correlated. The observed acceptance of young aliens and rejection of old aliens are less likely to be due to the perception of older wasps as a reproductive threat rather than some age-related factor, other than ovarian condition, for example, the relative ease with which younger wasps can be molded into desired roles

The genetic correlation between flower size and water use efficiency in monkeyflowers

This is the publisher's version, also available electronically from http://www.evolutionary-ecology.com/.Question: Does water loss during drought stress represent an important physiological constraint on the evolution of flower size? Organism: A genetically diverse population of Mimulus guttatus (yellow monkeyflower) originally sampled from an alpine meadow in Oregon, USA. Methods: We grew plants of three different genotypic classes (small, medium, and large flowered) under both well-watered and drought-stress conditions and measured water use efficiency using stable carbon isotopes. Results: There was no difference in water use efficiency among flower size genotypes under well-watered conditions, but the water use efficiency of small-flowered plants was substantially lower than that of medium or large genotypes under drought stress. Whether this paradoxical result is a direct effect of flower size or an indirect (i.e. pleiotropic) effect, the presence of a genetic correlation between floral and physiological traits indicates that selection of one does impact the other

Seed abortion in Pongamia pinnata (Fabaceae)

In Pongamia pinnata only one of the two ovules develops into a seed in most of the pods. Since pollen was not found to be limiting and reduced fertilization could not completely explain the observed frequency of seed abortion, it implied an effect of postfertilization factors. Aqueous extracts of developing seeds and maternal tissue (placenta) did not influence abortion in vitro, suggesting that abortion may not be mediated by a chemical. Experimental uptake of 14C sucrose in vitro indicated that both the stigmatic and the peduncular seed have similar inherent capacities of drawing resources, but the peduncular seed is deprived of resources in the presence of the stigmatic seed. This deprivation of the peduncular seed could be offset by supplying an excess of hormones leading to the subsequent formation of two seeds in a pod. The prevalence of single-seeded pods in P. pinnata seems therefore to be a result of competition between the two seeds for maternal resources. The evolutionary significance of single-seeded pods in P. pinnata is discussed with respect to possible dispersal advantage enjoyed by such pods

Complex domestic conflicts in a bird family

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Factors affecting embryo abortion in Syzygium cuminii (L.) skeels (Myrtaceae)

The possible causes of low seed set in Syzygium cuminii, a woody tree bearing flowers with many ovules but fruits with single seeds, have been investigated. Pollen grain limitation and lack of fertilization do not completely explain the single seededness of fruits indicating the involvement of postfertilization factors. Developing ovules exhibited a clear pattern during the early fruit growth, and only one of the ovules eventually matured into a seed. Aqueous extracts of developing ovules significantly increased the rate of abortion of the other ovules in vitro, but the extent of abortion caused by aqueous extracts of maternal tissues from fertilized flowers did not differ from the control, implying that the developing ovules may produce a factor that causes the abortion of other ovules. Silver thiosulfate, an ethyleneaction inhibitor, significantly reduces the rate of such developing-ovule-mediated abortion in vitro as well as in vivo This study indicates that abortion in S. cuminii is mediated by chemical(s) produced by the developing embryo, a possible reflection of "sibling rivalry" among developing seeds