Katja Hogendoorn

Tug-of-war over reproduction in a social bee

One of the main transitions in evolution is the shift from solitary organisms to societies with reproductive division of labour. Understanding social evolution requires us to determine how ecological, social and genetic factors jointly influence group stability and partitioning of reproduction between group members. Here we test the role of the three key factors predicted to influence social evolution by experimentally manipulating them in a social allodapine bee. We show that increased relatedness between nestmates results in more even reproduction among group members and a greater productivity per individual. By contrast, the degree of reproductive skew is not influenced by the opportunity for solitary breeding or by the potential benefits of cooperation. Relatedness also has a positive effect on group stability and overall productivity. These findings are in line with predictions of the tug-of-war models, in which the degree of reproductive division of labour is determined primarily by selfish competition between group members. The alternative view, where the degree of reproductive skew is the outcome of a social contract between potential breeders, was not supported by the data.

Molecular systematics of Australian carrion-breeding blowflies (Diptera : Calliphoridae) based on mitochondrial DNA

Carrion-breeding blowflies have substantial ecological and forensic importance. Because morphological recognition of their immatures is difficult, sequencing of the mtDNA of these flies may assist with their identification. Molecular phylogenetic analysis based on DNA sequences can also clarify evolutionary relationships. In this study, the mitochondrial genes CO1, CO2, ND4 and ND4L were sequenced for 34 species of blowflies, among which are almost all species known or suspected to breed in carrion in Australia. The resulting sequences were analysed using parsimony and maximum-likelihood Bayesian techniques. The results showed that the combination of these four genes should identify most species reliably, although some very closely related taxa could still be misdiagnosed. The data also helped clarify the life histories of Calliphora centralis Malloch, 1927, C. fuscofemorata Malloch, 1927 and C. gilesi Norris, 1994, which have hitherto only been suspected carrion breeders, and revealed that the current subgeneric assignment of taxa within Calliphora Robineau-Desvoidy, based on morphology, requires revision. Unexpectedly, both Chrysomya rufifacies (Macquart, 1843) and Lucilia cuprina (Wiedemann, 1830) were paraphyletic; each probably comprises two distinct species. The application of a molecular-clock approach to the study of the evolutionary divergence of the carrion-breeding blowflies suggests that the speciation of at least the endemic Australian taxa may have been the result of increasing aridification in Australia during the last five million years.

Evolution of sociality in the allodapine bees : a review of sex allocation, ecology and evolution

Summary: Comparative studies provide one of the most powerful means of assessing the relative roles of selective agents underlying social evolution in insects. Because of the wide variation in social organisation, sex allocation and ecological traits within and between species of allodapine bees, this group provides a wealth of material for such comparative work. Recent studies on Australian allodapine bees are reviewed here and their consequences for understanding social evolution are discussed. Studies to date suggest the following trends: (i) benefits of group living appear to be linked to preventing brood failure rather than to increased brood rearing efficiency; (ii) female-biased sex allocation, when it occurs, is linked to benefits of group living and kinship among nestmates, and is probably mediated via local fitness enhancement; (iii) female-biased sex allocation patterns do not usually coincide with opportunities for sib-rearing and are therefore unlikely to facilitate eusociality; (iv) relatedness within colonies is usually high, but in some species females will nest with unrelated females if kin are not available; and (v) phylogenetic studies suggest that opportunities for sib-rearing, arising from brood development patterns and colony phenology, are plesiomorphic for the exoneurine group, but in at least one phylogenetically distal clade, Exoneura sensu stricto, the evolution of large group size and social complexity coincides with the loss or reduction of opportunities for sib-rearing. Assured fitness return models may be applicable to weakly social allodapine species, but do not predict patterns of eusociality. Instead, Australian studies suggest that the evolution of large group size and marked reproductive skew is linked with the need to defend against enemies at the nest, rather than high levels of relatedness, female biased sex allocation or opportunities to rear siblings.

Native Australian carpenter bees as a potential alternative to introducing bumble bees for tomato pollination in greenhouses

SUMMARY There is commercial pressure to permit the introduction of bumble bees to mainland Australia for pollination of tomatoes in greenhouses. Bumble bees do not occur on mainland Australia, and there are indications that the recently introduced Bombus terrestris presents a threat to native ecosystems on Tasmania. In this pilot study, it was investigated whether the native green carpenter bees (Xylocopa (Lestis)) could be used as an alternative to bumble bees for tomato pollination. It is shown that Lestis females will visit and buzz pollinate flowers in a greenhouse and that tomatoes grown from Lestis pollinated flowers are on average heavier and contain more seeds than tomatoes that were not pollinated by Lestis. Therefore, there is potential to use Lestis for tomato pollination once methods for mass rearing the bees have been developed.

The sociality of Xylocopa pubescens: does a helper really help?

SummarySolitary and social nests of the facultatively social carpenter bee Xyclopa pubescens can be found simultaneously during the major part of the breeding season. Social nests contain a reproductively dominant forager and either her adult offspring or a formerly reproductive, guarding female. The costs and benefits to the dominant animal of allowing a defeated female to remain as a guard in the nest were analysed in terms of brood loss and brood gain. The costs included the probability that the guard would regain reproductively dominant status. The most important benefits were the protection that a guard provided against pollen robbery by conspecifics and the longer foraging time available to a forager when her nest was protected. The balance between costs and benefits depended on the severity of ecological constraints. During certain periods of intense competition for pollen or nests, the benefits clearly outweighed the costs.

Increased Tomato Yield Through Pollination by Native Australian Amegilla chlorocyanea (Hymenoptera: Anthophoridae)

Amegilla spp. (Hymenoptera: Anthophoridae) have been suggested as potential native Australian alternative to overseas used bumblebees (Bombus spp.) for pollination of tomato in greenhouses. In this study, we investigate the effectiveness of Amegilla chlorocyanea Cockerell as a greenhouse pollinator of tomato, Lycopersicon esculentum Mill. We show that (1) a single buzz by a female increases tomato weight by 11% compared with pollination by using an industrial pollination wand, (2) multiple buzzes increase tomato weight compared with a single buzz, and (3) unlimited flower visits lead to an increase in fruit weight of 21% compared with wand pollination. These results are comparable with those achieved by bumblebee pollination and demonstrate that A. chlorocyanea is a valid alternative to bumblebees for greenhouse tomato pollination in Australia.

Diversity and conservation status of native Australian bees

Australia’s idiosyncratic bee fauna is characterised by a combination of numerous endemic taxa and by the complete absence of some families. Many species, and in particular several oligolectic species, remain undescribed and more than half the named taxa are in need of revision. The main threats to the native bee fauna include removal of nesting and foraging opportunities through land clearing and agriculture, the spread of exotic plant species and the consequences of climate change. Early steps to conserve the native bee fauna include commercial applications, the raising of public awareness and preservation of natural habitat. However, these actions are severely hampered by a lack of both identification keys and taxonomic expertise. Considerable investment in taxonomic research is needed to improve this state of affairs.ZusammenfassungAustralien besitzt eine einzigartige Bienenfauna, die sich durch einen hohen Anteil an Arten der Familie Colletidae und das Fehlen von Andrenidae und Mellitidae auszeichnet. Aufgrund einer geringen Anzahl an Kolonisierungsereignissen sind viele Linien endemisch. Schätzungsweise 25 % der Arten sind noch unbeschrieben und 50 % der Taxa bedürfen einer Revision. Insbesondere viele oligolektische Arten könnten übersehen worden und aufgrund fehlender Schutzmassnahmen bedroht sein. Des weiteren sind für insgesamt 57 % der Arten keine Bestimmungsschlüssel verfügbar. Dies stellt ein schwerwiegendes Hindernis für Untersuchungen der einheimischen Bienen durch Laien oder Nichtextperten dar. Informationen zum Blütenbesuch und zum Nistverhalten gibt es nur für einige wenige Arten.Die vielfachen Bedrohungen der einheimischen Bienenfauna beinhaltet die Entfernung von Nistgelegenheiten und Futtersammelstellen, die Ausbreitung eingeführter exotischer Pflanzenarten und Klimaveränderungen. Grossflächige Beseitigungen der natürlichen Vegetation für landwirtschaftliche Zwecke sind zwar im Rückgang, die Veränderungen in der Zusammensetzung der Flora sind jedoch ein Grund zur Sorge. Diese Veränderungen rühren von der Beweidung durch Vieh und andere eingeführte Säugetiere her, sowie durch den Ersatz einheimischer Pflanzen durch eingeführte Unkräuter. Letztere profitieren in ihrer Bestäbung nicht zuletzt von ausgewilderten oder beimkerten Honigbienenvölkern. Die direkte Konkurrenz zwischen einheimischen Bienen und Honigbienen ist vermutlich variabel und abhängig von den jeweils verfügbaren Pflanzen als Nahrungsquellen.Klimaveränderungen führen zu vermehrten Überschwemmungen und Buschfeuern und haben als langfristige Konsequenz unvorhersehbare Veränderungen in der floralen Abundanz und Phänologie zur Folge. All diese Faktoren beeinflussen mit grosser Wahrscheinlichkeit die Verteilung und Häufigkeit der einheimischen Bienen. Einleitende Schritte zum Schutz der einheimischen Bienenfauna könnten ihre Nutzung als Bestäuber von Nutzpflanzen sein, sowie die Anhebung des öffentlichen Bewusstseins über den Schutz natürlicher Habitate. Der allgemeine Mangel an Kenntnissen über die Taxonomie und das Fehlen von Bestimmungsschlüsseln sind hierin jedoch schwerwiegende Hinderungsgründe. Unsere Fähigkeit des Monitoring und der Beurteilung des Schutzstatus der einheimischen Bienen Australiens erfordert die Ausbildung und die Einstellung von Bienentaxonomen.

The superseded female's dilemma: ultimate and proximate factors that influence guarding behaviour of the carpenter bee Xylocopa pubescens

Both solitary and primitively social nests of the facultatively social carpenter bee Xylocopa pubescens can be found throughout most of the breeding season. In social nests there is reproductive division of labour between a dominant forager and a guarding female. Two types of guarding females can be discerned: the young pre-reproductive guards, and older, formerly reproductive guards. The latter type of guard is found when, after a take-over of reproductive dominance either by a nestmate (mostly a daughter) or an intruder, the defeated female stays in the nest instead of leaving to try and found or usurp another nest. She is then manipulated into the role of a guard. The dominant female profits from the presence of the guard since she protects the nest against pollen robbery by conspecifics (Hogendoorn and Velthuis 1993). We have studied why superseded females might “prefer” to remain as a guard, rather than try their luck somewhere else. The hypotheses investigated pertain to (1) the difficulty for the defeated female of finding a new nest and of restarting reproductive activities due to (a) ecological constraints (nest and pollen shortage) and (b) the effect of age and wear on the defeated female; (2) the effects of guarding in terms of inclusive fitness. We found that superseded females remained as guards significantly more often when a nestmate (not necessarily close kin) took over reproductive dominance than when an intruder did so. Other factors associated with the decision of the defeated female to stay or leave were her age and the number of her own young still present after the supersedure. The probability of finding or constructing a new nest was lower for old than for young females. After finding a nest, old females produced less brood than young foundresses. As a result of these two factors old superseded females gained, in terms of inclusive fitness, by staying as guards, whereas young females profited from leaving the nest. We interpret these results as an indication that guarding behaviour has evolved due to kin selection. However, kin discrimination apparently did not occur. Therefore we conclude that in this species kin selection is not, in the proximate frame of reference, based on kin recognition and preference for helping kin.

Strong constraints to independent nesting in a facultatively social bee: quantifying the effects of enemies-at-the-nest

Abstract.Constraints to independent nesting play a key role in the understanding of social evolution in insects, but the source and the magnitude of such constraints are poorly known for many key taxa. In allodapine bees it is known that solitary nesting females have low rates of successful brood rearing and that this drives selection for cooperative nesting. It has been hypothesized that these constraints are due to the presence of enemies-at-the-nest, such as ants, but no direct link has been demonstrated between such enemies and colony failure. We set up an experiment in which solitary founded nests of an Australian allodapine bee, Exoneura nigrescens, were either protected from non-flying predators or left unprotected, and compared the resulting colony survival and brood production rates. We found that protected colonies have much higher rates of survival and that the constraints to independent nesting are extreme, with a mean of less than one offspring per nest at the end of the brood rearing period. This means that cooperative nesting is essential for this species to persist in its habitat.

Socio‐economics of brood destruction during supersedure in the carpenter bee Xylocopa pubescens

In nests of the facultatively social carpenter bee Xylocopa pubescens, both intruders and nestmates destroyed brood during supersedure. However, nestmates and intruders differed with respect to the frequency and the pattern of brood destruction. Intruders destroyed more brood than did nestmates. In addition, intruders appeared to destroy all stages of brood at equal frequencies, whereas nestmates had a preference for opening and thereby destroying newly made cells. Several hypotheses concerning the ultimate reasons for these differences were tested. These differences are not due to either a lack of breeding space, or to an attempt to prevent an imminent loss of dominance. The number of brood cells destroyed by nestmates was not influenced by the degree of relatedness. This indicates that the difference between nestmates and intruders was not based on active kin recognition. The most likely reason why nestmates prefer to open young brood cells is that they can then reallocate the pollen contents of these cells to their own brood. A difference in knowledge about the location of newly made cells may explain the differences in the pattern and the frequency of brood destruction by nestmates and intruders. Furthermore, a superseding nestmate may slightly enhance her average indirect fitness by destroying the brood contents of newly made cells while leaving older brood cells intact.